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ELI5: How does light have momentum if photons have no mass? Momentum is mass times the acceleration (p=mv), so something with no mass should have zero momentum.

Good question! Let's think of momentum as the idea a moving object has energy it can transfer to another moving object through a collision. For things with mass, one object speeds up and the other slows down after a collision (or their velocities change, to be more accurate). With light, we see that light can hit an object with mass, change its velocity, and the deflected light will be red-shifted (indicating it lost energy). If we look at the system as a whole, the change in the momentum of the deflected object will match the energy lost by the photon. By our momentum definition, that means the photon had momentum and then transferred it to the object! More generally, we can describe momentum due to an objects mass (p = mv) and momentum (energy) due to its wave-character (p = h/lambda or hf/c [since lambda = c/f]). All matter has wave character (as described by its de Broglie wavelength), but for massive objects, the wavelength tends to be so large it's unobservable and the contribution to momentum basically rounds to zero (especially next to the large momentum of an object with mass). Usually we worry about this "dual character" with electrons, which have both mass and wave-like characteristics and we need this relativistic explanation of momentum to better understand their behavior. This idea that light has momentum is how solar sails work. Even if individual photons have very, very small momentum compared to a massive object, the sun makes a lot of them and overtime it can push around small objects like probes!

Can this concept be used to power a spacecraft by shooting light out the back?

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ELI5: How should I recognize what time signatures are used in songs?

Firstly time signatures can be ambiguous. A lot of songs can be written in different time signatures and still be played the same. So guessing a time signature that is different from what the sheet music say does not necessarily mean you are wrong. When identifying the bars you should be listening for the first downbeat of the bar which is often emphasized. So you would count 4/4 as **1**\-2-3-4-**1**\-2-3-4-**1**. And this is usually audible in the music. It does not always sound as obvious as in for example waltz but after some practice you should hear this in most songs. And when you listen for this and also for any rhythmic repetitions you should be able to identify a bar and then just count how many beats there is in that bar. So if you hear something like **1**\-and-2-and-3-and-4-and-5-and-6-**1**\-and-2- ... you are dealing with a song in 11/8.

How is 1-and-2-and-3-and-4-and-5-and-6 an 11/8?

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ELI5: Why is eating humans not healthy?

Tiny things (like germs) that eat one animal may have trouble eating a different kind of animal. If you eat a human, the tiny things that eat a human have a higher chance of being able to eat you, and thus make you sick. In a related notes, the most famous disease assocaited with humans eating humans is a prion disease. It's a misshapened human brain protein, that when it hits a normal human brain protein, turns it into the exact same misshapened brain protein. You can get that misshapened protein in your brain by eating it.

Basically, don't eat brains?

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ELI5: Why do image and video quality worsen the more they are saved and uploaded? What contributes to this?

Every time you put content into editing software and make any changes, the saved file will be re-compressed and that will reduce the quality. RAW photo files, RAW format video, and so on do not suffer degrading if that is your saved format. The problem is that the file sizes for those are huge, so no one shares RAW format.

This is a misconception: compression does not mean lossy. Do your zip files lost some content? Some compression algorithms lose data but preserve general quality like jpeg or mp3. Some does not like png, or bmp. Also tiff if both a file format and a series of compression algorithms. Single tiff file can contain multiple pages where every page can be in different sizes and can use different compression algorithm including zip.

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ELI5: If light takes hundreds of thousands of years to travel from other galaxies, but we can observe those galaxies today, does that give us incontrovertible proof the universe has been around for, at the very least, hundreds of thousands of years? Or is there some other factor I'm missing?

Many modern creationists theorize that God created the universe with an appearance of age. Basically, if God created Adam as a full grown adult, then He could have also created the universe as fully established, including all the photons already in transit.

The problem I’ve always had with that argument is if God made the universe to look like it’s old, how is that different from it actually being old? It’s not as if God is on a deadline. If he is going to make the universe look billions of years old, why not just take billions of years to make it?

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ELI5: why are ponds (closed ecosystems) not as genetically atypical as isolated regions, like the Galápagos Islands?

I accidentally did a little experiment. I dug a hole in unfertile clay. It filled with water the next time it rained and so I had the pond full of dirty water. A year later it was full of rushes, other plants, and frogs and turtles and all sorts of life and had a visiting heron. There's no way that a pond is genetically isolated.

That's interesting. Was it for an experiment, or just coincidence?

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ELI5: How did the US has debt?

All governments have debt of some sort. Governments make money from taxes. But tax revenue only comes in spurts at certain times. Also, you've heard about budget surpluses and deficits? Well, when a government wants (or needs) to spend more than they earn, that's a deficit. Just like you and me they go and borrow money. Except unlike a really big Platinum credit card, they have to issue government bonds instead. That's the debt we're talking about. Run a budget deficit to pay for covid relief? That's debt the government has to borrow. Invade another country? More debt. Cut taxes for the wealthy but maintain spending? More debt. Government debt isn't necessarily bad. i.e. sometimes even in a balanced budget, there are cash flow issues. Government has to pay employees year round, but only gets paid during tax season. And sometimes you want to spend more NOW and pay it back LATER. Its when a government has so much debt it can't make its _interest_ payments - that's what happened to Greece in the banking crisis bunch of years back. Greece had borrowed from Germany, France, UK etc. and could not pay them back. So they were forced to not only balance their budget, but reduce it further ("austerity") to be able to pay back their debts. Who owns it? You and I own it. Banks own it. Other countries own it, corporations own it. If you want a nice safe, if somewhat low growth investment, government bonds are pretty safe.

So yesterday they had voted to default on its debt. Does it mean they're just gonna declare bankruptcy? If so then what's gonna happen?

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ELI5: How did the US has debt?

If you buy a Treasury bill you are lending money to the US. As the T-bill matures they owe you an increasing return. A lot of US debt is owned by banks, investors, and foreign gov'ts, too. This is why it's a big deal if the US gov't credit rating slips from AAA - future loans would then cost a lot more to service and pay back. So if the US decided "eh, we ain't paying anyone back, our debt no longer exists" your investment would become worthless. Also people wouldn't be keen to lend the US money anymore. Also, it isn't just rich, connected people who would suffer. There are plenty of investment funds managing mom and pop retirement savings that would lose their asses. It would blossom into a global economic catastrophe.

Man it's really hard to wrap my head around the idea of THE US just stick up their finger and say "screw you, we're not paying crap back". Did any country default on their debt before ?

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ELI5: How does a calculator perform calculation?

You are not memorizing the full multiplication table and the additions table. You only memorize the calculations for one digit and then use techniques to do the calculation for multiple digits. The calculator does the same. Except that instead of using the decimal system where each digit is one of ten number it uses binary where each digit is one of two numbers. That makes the calculations very simple as each digit is just a one or a zero. So it uses logic gates to work as a kind of lookup table. For example 1+1 it will find the least significant digit by doing True XOR True which is False meaning that the number ends in 0. Then it finds the carry bit by doing True AND True which is True. Since there is only one digit in the input numbers the carry is put last and you get a result of 10. But that is in binary and when it display this it looks it up in a table to check which lights to turn on in the display it makes sure to show it to you as a 2.

Wow, so every single math problem can be expressed as a series of True or false statements? That sound so cool, I really want to see some sort of compilation of math operations and their true/false representation.

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ELI5:Why do people seem to have invariably negative opinions of ghost kitchens?

It’s also the case where an unpopular restaurant will create ghost kitchens solely to trick Ubereats and postmates customers into ordering from them.

Are they really tricking them? They’re just forgoing the sit down portion of the restaurant, which absolutely makes sense in a post COVID world.

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ELI5 What is Data Retention and should I be worried about it?

Data retention is the storage of information about people. It can be by the government or by companies. This goes from name and/or address all the way to recording phone calls. Plenty of phone calls to companies/governmental agencies are actually recorded. And all of that is rarely removed. Which mean that in 35 years, if someone get access to these record, could use them to cause you trouble. I'm not even gonna talk about the fact some people just like privacy and that plenty of companies hoard data like Jeff hoard money. For government they usually record but can't access it unless very specific circumstances (terrorism for example) but nonetheless, someone could one day get access to all that. As for being worried, it depends if you care about your privacy. I believe we should, but many people think that they don't have anything to hide and thus we shouldn't mind. I disagree with them, but that's another debate entirely.

Why should I care about my privacy?

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ELI5: How does an Apple Watch or Fitbit “know” when you’re asleep (vs. awake but relaxed) or what stage of sleep you’re in?

It has whole host of sensors, heartrate, accelerometer and gyroscope for example to detect movement and position and it even has a clock to tell time. There are algorithms running that take all this data and give a probability score of what the wearer is doing. For example, high heartrate, arm position moving in certain angles, with a certain cadence, outside of the average person sleeping hours, wearer is probably running. And for sleeping, arm horizontal, low heart rate, no movement, normally sleeping hours, wearer is probably sleeping. Moving a bit more, still lying down, heartrate a bit elevated, still sleeping time, probably rem sleep. You can reinforce these algorithms by telling if the prediction was right, by for example adding the workout manually or telling the app/watch your normal sleeping hours.

Leads me to wonder... can my Fitbit tell when I'm having, or have had sex? Seems to me if the algorithm can figure out waking vs. sleeping, it shouldn't be difficult to pick out the specifics of sex.

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ELI5: How can an area code run out of numbers?

It isn't particularly difficult math 7 digits in a local phone number is just under 10 million possible phone numbers Factor in that reserved numbers like 311, 411, 511, 911, 555, etc remove 10,000 possible numbers each. Which leaves us with roughly 7,909,900 phone numbers for an area code If your region has a larger population than that then you're likely to exceed the capacity of your area code with that alone. Now also keep in mind that today lots of people have multiple phone numbers between their house, internet, cellphones, and work numbers. Then you have businesses that have things like cellular activated services. Coke for example might have a cellular modem attached to each vending machine, each of those in turn has a phone number. 5000 ish vending machines in a city translates to 5000 phone numbers. With all that factored in it doesn't take long before you end up using all the phone numbers in a given area.

But can’t unused numbers be reused?

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ELI5: When interest rates are raised or lowered does something physical happen?

It just means that the next time someone wants to borrow, the bank will charge a higher interest rate. There doesn't need to be anything physical. Sure, it'll be recorded in a bunch of different systems and circulated to banks, but it's really the same thing as a business raising the price of an item. Might edit your inventory management system with a new price and make a new price tag, but nothing changes beyond that.

This is a very hypothetical and outlandish scenario, but: Let's say the chairman of the central bank is about to announce that interest rates are being raised. But he is stuck on a cruise ship in the middle of the ocean, without any kind of reception or internet or means of communicating with the world. Could the central bank just then do everything "behind the scenes" so to speak, and the interest rates would be raised? Is it more like a clerical function of the banks, or more of a declaration?

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ELI5: is there a medical/physiological reason why male birth control doesn’t exist yet?

When pregnant, females produce a hormone to stop egg production. "The Pill" is this hormone in an easy to swallow tablet. Males do NOT have a similar hormone. No drug currently exists that can stop sperm production and reliably let it start up again. Furthermore, messing with testicles can risk halting testosterone production, having serious consequences to muscle mass and bone density. Methods to stop sperm from reaching the penis has been devised (surgical vesectomy and a gel that requires professional injections every couple of weeks). Simply put, a male birth control pill may never exist because the male anatomy was never meant to stop sperm production.

>Simply put, a male birth control pill may never exist because the male anatomy was never meant to stop sperm production. Isn't there a stage 3 trials for male birth control?

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ELI5: Why does spoiled meat make you sick even after fully cooking it? If heat make bacteria go bye bye, then why get sick?

from my health inspector dad: it doesn’t. it just tastes bad. “spoiled” food is fine, it just won’t be edible and could upset your stomach, but you won’t get food poisoning from it.

Then why is spoiled meat considered so dangerous as opposed to something like spoiled milk? And why are there stories of people getting super sick from bad meat?

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ELI5 - Why does water increase the friction between my foot and the sock I'm trying to put on, but decreases friction between my foot and the bathroom floor?

because the water in the sock pushes out the air. The air is what acts as a spring between threads keeping only a minimum of threads touching the foot. Add on the water, now every thread is madly in love with your skin.

Interesting. So the lack of air is the primary problem? The air is replaced by water?

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ELI5 how did horse & carts go downhill without the carts picking up speed and crashing into the horses?

The saddle was equipped with a wood seating connection. Not chains or rope. Cart never moved faster or slower than the horse.

And brakes too, no?

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ELI5: What is "Ray Tracing" in a video game, and how does it differ from previously made reflections?

Yes, that's precisely it, in a sense. Games run at very fast speeds, often times more than 60 frames per second. That means, the GPU has less than 16.66ms to render one frame at 1920x1080 resolution, or the game will start to dip below 60 FPS. Now, have you heard the commonly circulated internet fact that a single frame of Frozen took a week to render? So how do we do that, but in 16ms? The answer is that engineers created "hacky" ways to render your game that are in no way physically accurate, but will produce okay-ish results really quickly. One of the most difficult things to simulate with these "fake" methods are reflections. Because well, reflections are inherently a byproduct of realism. Light bouncing around multiple times makes things reflect off each other. We certainly cannot afford to do that kind of processing, otherwise it would take longer to render the frame, and we don't want to play games with the FPS of a slide show. But the engineers are smart, so they created special methods to once again "fake" the reflections. For example, [cube maps](https://learnopengl.com/img/advanced/cubemaps_skybox.png)! These work by pre-rendering beforehand the reflection of the world around the object, and then drawing a texture based on that rendering. So, when you play the game, it's simply just drawing a texture, not rendering multiple bouncing light rays. The downside of this method is that it does not allow dynamic reflections, because the textures are already pre-rendered beforehand and cannot change. With ray tracing, like the name implies, games are able to draw light rays (simulating light bouncing) more realistically, and hence draw real time reflections and such, but without much more effort. This can be done with the help of the novel RT cores that Nvidia developed in their 2xxx and 3xxx cards.

Oh, okay! So the biggest example I've seen of Ray Tracing is Spider-Man PS4. For the original edition, does that mean you couldn't see Spider-Man in the reflections, because the reflections were just pre-rendered images stuck on the surfaces, whereas you CAN see him in the remaster because it's copying the light source onto the surface, and he is a light source?

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ELI5: Why are long haul trips like airplane rides and bus rides so exhausting, even though all we do is sit?

One important consideration is the constant body position. Sitting around the house when you're relaxing, you'll be shifting positions periodically, leaning forward, leaning back, bearing more weight on your hipbones or your thighs, lifting or crossing or uncrossing your legs, etc. A long car or plane ride doesn't give you nearly as much freedom to do that. The sitting position is pretty rigid, and you might be able to lean the seat further back or more upright, but that's typically about all the freedom you get. Add to this the fact that you're actively balancing even as you sit, if there is any wobbling, bumpiness or G-forces on the ride. You can't fully relax in a car because muscles in your back and abdomen are constantly responding to the little lateral forces produced by handling the car. Depending on the size of the plane and the air conditions, the same might be true on a flight. Finally, the sensory input can be mentally exhausting. Highway driving is noisy, and can expose you to pretty fast-moving visual scenery which, even if you're not really paying attention to it, your brain might be noticing and spending some energy on. Planes in flight are also very loud places to be. That can wear you down and push you toward mental fatigue.

That's a good answer, I'd also like to add the following: Travelling is uncomfortable, on a psychological basis atleast. Here in the comfort of your home you can just doze off for half an hour in your underpants and it's all okay. When you're travelling you need to process and react to much more sensory inputs than sitting around the house. Go through TSA, Keep the passport and tickets ready, sit on the correct seat, get off on the correct bus stop if you're on one, make sure your luggage doesn't get left behind, make sure your children don't get left behind. All that requires you being more alert than usual, and it may seem trivial, but over 8 or 10 hours it really does add up. Similarly, people are quite amazed what a professional Chess player goes through in a 6 hour game of Chess. Just sit and think, and move tiny pieces back and forth a feet or so? It's a massive effort to do that though. Atleast, if you're planning to win.

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ELI5: What is spaghetti code ?

The original meaning of Spaghetti code isn't just any bad code - it's the specific kind of bad code created by misuse of GOTO instructions where following the code flow feels like reading a choose-your-own-adventure book - or like looking at a plate of spaghetti where you look at the end of one noodle and have no idea where the other end is gonna be.

I really like the choose your own adventure analogy. To elaborate on why this is bad, imagine if one of your readers tells you there's a spelling error in the chapter where you meet the goblin. Okay, so what chapter? You can't read the book front to back because that's insane, the best you can do is take a path and hope you meet the goblin. Worse yet, maybe multiple paths lead to the goblin. Maybe each of those paths introduces the goblin in a different way, only one of which has a spelling error. Maybe multiple paths don't ever reach the goblin. Oh, have I mentioned there's 5 goblins in this book? By the way, you're not even the original author, he's moved on writing many more great and fun books and has left you to maintain this one. Good code reads more like a wikipedia article. There's a clear structure. Titles, subtitles, references. I can understand the general contents of the article just from reading the index. Better yet, if a subtopic is too broad, it probably has its own article, readily available for you.

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ELI5: Air weighs 14 pounds per square inch, yet we don't feel it crushing us. The notion that internal pressure somehow acts as a counterbalance just seems to mean that we're being crushed in both directions. Shouldn't we feel this massive weight on us?

Haven't seen a simple answer yet so I'll give it a shot: Close your mouth and breathe in, sucking in your cheeks. The thing pushing on your cheeks is the 14 pounds per square inch. If your cheeks were strong enough to lift those 30-40 or so pounds, then you could suck all the air our of your mouth until it was a perfect vaccum and be perfectly fine :)

Thanks....that actually helps. But here's the thing. If I pinch my cheek (one finger in my mouth, one on the outside) I definitely feel the pressure from the "balanced" forces of my fingers. But with air pushing on both sides (in place of my fingers), I don't feel a thing. I'm still working through that oddity. What's the key difference between the pressure exerted by air and fingers??

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ELI5:What are "wrapped coins" (wEth, wBTC, ...) ?

Back in the 2017 crypto bull run, bitcoin was really expensive to send around because of the network congestion but sending eth around was super cheap. Since eth allows you to do smart contracts, you can make an eth token called “bitcoin” (or “wrapped bitcoin” so it doesn’t confuse people), and essentially lock up an actual bitcoin in a ethereum smart contract and send around that eth token (called eth wrapped bitcoin) instead. The real bitcoin is still there, gaining or losing value, but you can send around your eth token and pay minimal eth fees instead of sending around that actual bitcoin. Fast forward to this bull run and people made jokes how it should be bitocin wrapped eth now (since eth fees got pretty ridiculous). This can’t happen quite yet because bitcoin can’t do smart contracts. It’s basically a bridge between chains. So you can use any coin on any network. Edit: I’m going to add to this because I’m obsessed with crypto and want everyone else to be as well. You may see tokens like cETH, aUSDC, or CAKE-LP (as opposed to the actual assets: ETH, USDC, or CAKE). These are called proof of ownership tokens. You can look at them like receipts. For example, let’s say I have some USDC (US dollar coin), and I want to get interest on my USDC. To do this, I deposit them into a lending pool (let’s say I use the Aave protocol). Once they leave my wallet, I get aUSDC (Aave USDC) in return. This is an absolutely amazing and overlooked feature of crypto. This aUSDC I have is just as valuable as the asset itself + any interest it’s generating. If I sent you my aUSDC tokens, you can withdraw all my usdc (and any accrued interest) out of Aave. This allows the usdc holder to not only gain interest in the Aave lending pool but now take that “receipt” and use that value somewhere else to generate even more passive income. Uhhhg I could go on but then I’ll for sure be treading on waters that are too difficult for 5 year olds if I haven’t already >.< Dm me if you have any questions! Always happy to explain more :D

Since you're a crypto enthusiast, could you explain the reasoning behind it? From an economics point of view crypto is at best a store of value (assuming it's relatively predictable). I think my econ prof explained it best with the gold coins vs silver coins example. When there were gold coins and silver coins, people would hoard the gold, and spend the silver. This was because silver was relatively abundant and more was entering the supply each day. As a result of the influx, silver devalued while gold didn't. Applying this to crypto, we have fiat currency and crypto, even assuming that crypto tames volatility, it's still just another gold, except you can argue that gold has intrinsic value from being useful, whereas crypto is just a thing that exists. I don't see what crypto is supposed to do, it's advertised strengths are, security of value, and freedom of capital. However, store of value only works when there is relative stability, which there isn't. And even if there were, it still holds no advantages over gold. Additionally, transitioning to a crypto based currency system would mean national governments lose the ability to pursue expansionary fiscal (and monrtary) policy, resulting in every economic downturn hitting like it was 1929. The freedom of capital is also dubious since, the blockchain is made up mainly of large operations as opposed to the grassroots vision of people with their GPUs. If crypto were a mainstream commerce tool beyond a speculative thing, it would once again be dominated by institutional players like banks, and with a digital medium they can probably pull as yet unthought of schemes.

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ELI5: Air weighs 14 pounds per square inch, yet we don't feel it crushing us. The notion that internal pressure somehow acts as a counterbalance just seems to mean that we're being crushed in both directions. Shouldn't we feel this massive weight on us?

It's pressure, not weight. It's not a directed force, it's force on every surface. The air pushing in from above has the same force as the one pushing from below, same for left and right, etc. And yes, we *are* being constantly squished together by air pressure. That pressure is even necessary for life. Water is only liquid at room temperature because the pressure squishes it together, preventing it from boiling.

So water would boil in space?

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ELI5 why does unusually high concentration of salt in water makes you float. Just like dead sea?

The word of the day is *density.* Density is a property of matter obtained by dividing mass by volume -- that is, if an object with a mass of one gram occupies a volume of one cubic centimeter, its density is one gram per cubic centimeter. The more mass you have in a given volume, therefore -- the more stuff you have in a given space -- the denser it is. Salt water has more stuff in it than fresh water -- the salt takes up space between the water molecules. Dense objects sink, and less-dense objects float; so, if you have a body of water with *so much salt* in it that its density is greater than a human's, that human will float.

Can I then put salt in my swimming pool and float?

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ELI5: what differences does lossless audio have on the sound of music, specifically on Apple music?

The media itself is only half the equation. If you have your phone plugged into a cassette adapter in the shitty 2-channel 10-watt tinny radio of an 80s Dodge truck, you will reap zero benefit. Imagine it like hooking up a 4K BluRay player to one of those old CRT TVs that came in a big wooden cabinet. Lossless audio is for audiophiles/enthusiasts who have invested in equipment for a fuller listening experience, whether it's high-end headphones or a full-on proper home stereo system or a car with a nice Harman Kardon stereo in it. That's the places where you'll see some difference with lossless audio. If you don't have high-end equipment or have an obsession with audio quality you'll probably do just fine with the non-lossless that takes up less storage and less bandwidth.

How about on AirPods? Do you know how they're affected?

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ELI5: Why aren’t there insects the size of man or larger?

In the simplest terms, millions of years ago there were insects that were larger and over 7-8 feet long. It had to do with the higher percentage of Oxygen in the atmosphere back then. But as the levels of gases in the atmosphere stabilised and Oxygen decreased, so did the size of these insects. Check out the fossils found in Madagascar of Large insects.

May i ask, why was there a higher percentage of oxygen? Was it because there were more plants and no human pollution? And why did it go down?

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ELI5: Why aren’t there insects the size of man or larger?

Two main reasons. The first being that the physical structure of their legs couldn’t support their body weight if they were much bigger than they are, they’d simply collapse like if you tried to walk on your fingers. The second is that there isn’t enough oxygen in our atmosphere, they don’t have lungs but a system of tubes that deliver oxygen and their efficiency is directly correlated to the oxygen percentage in the air. Some insects were larger millions of years ago when oxygen concentrations were higher.

Why would their legs not be able to support them?

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ELI5: What happens to the brain after a tumor is removed? Does the brain regenerate the lost space/damaged functions?

The brain does not regenerate, as the neuron cells that make it up do not multiply after a certain age. The remaining cells may create new connections to the surrounding cells, but those connections (called dentrites, who look like tree branches) do not go far. But function depends on the area that the tumor was located, besides the age of the person. The younger the brain, the easier it makes new connections to repurpose the functions of the lost area, as there are cases of young children having an entire half of the brain removed, with no significant problems to their mental development.

Wait. Do brain cells not get replaced like other cells?

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ELI5: Why are PS4 and PS5 unable to read PS1 or PS2 discs?

PS1 and some PS2 disks are based on the CD standard. The drive in a PS4 (and I assume PS5) doesn't read CDs. Among other things it's only equipped with lasers for DVD (650nm) and Blu-ray (450nm).

A lot of PS2 games were on DVD though. Why can't the console read those?

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ELI5: What is a chromosome? Why do humans have 26 XY chromosomes why do ferns have 64 chromosomes?

Chromosomes hold dna. As organisms replicate they can mutate and give their children more or less dna. If the mutations help the organism it will probably spread through the population. Ferns have more because they randomly mutated more in beneficial ways.

Are there things with say 37, 41, 43, 47, 53, 59 (prime numbers) of DNA? Does having 64 chromosomes confer some sort of evolutionary ~~answer~~ advantage? What would that be? Edited to fix autocorrect

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ELI5: How does large scale desalination work?

So essentially, in the ocean and seas, water is constantly evaporating. When it evaporates, it's mostly salt free, as the salt doesn't go with water vapor. It turns into clouds as it gathers together, then goes inland and rains. Man made desalination works similar. Except accelerated and in a much smaller surface area. We heat up the water. That causes it to evaporate quickly, and we collect the water vapor, and get fresh water. The residue of the man made desalination process is very salty water. Which gets pumped back into the ocean, and can cause issues with the area it gets pumped into getting too salty and killing off everything. The limitation is cost. It takes a huge amount of energy to heat up water to produce enough fresh water to be usable. That huge amount of energy is very expensive.

Thank you for the reply. Okay, so what I am getting from this, essentially it is just an issue that ”electricity costs too much money”. If we could build a solar farm big enough to produce the electricity, we would eventually get to a point where, after all expenses paid, the farm would generate the electricity needed for the desalination plant, at break-even or at profit. Also on the residue brime, how high salt concentration are we talking about? If reintroducing it back into the ocean it disturbs the flora and fauna, could we not just make a huge inland sea into a desert without an outflow point, similarly to the Dead Sea?

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ELI5: Why do words stop sounding like words when thought about too much?

When you say or think of a word (for example, “pink”), it creates a sensation in your brain. That sensation is electric impulses traveling from neuron to neuron in a specific, complex network that your brain accepts and registers as “pink”. However, during the travel of the electric impulse, your neurons release certain chemicals, and those chemicals need to be restored. This is known as “reuptake.” Thus, when you first think “pink,” all the neurons used to create that thought are all strong and ready to give you a nice, strong, comprehensive, and clear idea of pink. However, after immediately triggering those neurons over and over and over, while your neurons are still in the reuptake process, they get, “tired out” in a way, and aren’t all able to perform as expected. Duly note; neurons firing is like a gun firing; they either do or don’t. They can’t half fire and create a weak image. Instead, the idea of pink gets less and less clear as less and less neurons are working to create the image until they all “pass out” and you’re left thinking “...what IS pink?”

Side question: why would repeating the same phrase over and over lead to memorizing it if the neurons respond less and less to the stimulation? I know it's better to memorize a little bit over a long period if you really want it memorized. But in short-term, like a week, it seems like just wearing your brain out on it is better?

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ELI5: What is it that causes that 'old-timey' quality to voices in old recordings?

I made a saltshaker microphone out of an old telephone speaker. Gives that old time sound without using studio effects. http://imgur.com/gallery/EuBeqOP

Do you have an audio clip using it?

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ELI5: How is electricity physically measured (like at the meter on my house)?

Maybe not ELI5, but here you go. Electricity is the flow of electrons. Electrons flow because they are pushed by a *voltage*. The voltage is like the pressure causes water to flow in a pipe. The amount of electrons that flow is termed the *current*. The current is like the flowrate of water in the pipe. More voltage (pressure) = more current (flow). So if you want to talk about flow, you might say there are 10 electrons travelling past a point every second (electrons per second), just like how you might talk about water flow in litres or gallons per second. If you want to find the total volume of water, you take the flow and multiply it by time. So if you had 10 litres per second, after 100 seconds you used 10×100=1000 litres. Same for electricity. You take the amperage, and multiply it by time. We could do electrons per second, but we use Amperes to measure current. We also use hours instead of seconds. So what do you get when you multiply Amperes and Hours? Ampere-hour (Ah), which is what you see on your electricity bill. The ampere-hour is the amount of electricity you used. Now we know how you measure time, but what about current? Inside your meter is a *current transformer*. This consists of a metal donut that surrounds the main conductor going into your house. A copper wire is coiled around the donut. The electricity going through the main conductor is AC (*alternating current*). Now when electricity flows, it creates a magnetic field. When that current *alternates*, so does the magnetic field. So you have an *alternating magnetic field* surrounding the main conductor. This fluctuating magnetic field causes magnetic field lines to pass through that copper coil in your little current transformer, and that *induces* a small current in the copper coil. This copper coil is connected to a smarter device which includes an ammeter which measures the current. This is then used to calculate the current in the main conductor. The current × time calculation is done at small intervals and added together to account for varying loads.

Are ampere hours the same as kWH?

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ELI5: Why are high impedance headphones hard to drive yet low impedance hifi speakers require a more powerful amplifier to get them to perform optimally?

High impedance headphones are a result of the much thinner wires that make up the voice coils which drive the membrane in order to keep them as light as possible. These extremely thin wires are of much higher resistance because resistance is a function of the cross sectional area of a conductor. Because power is voltage squared divided by resistance you need more voltage to increase the effective output power which is what makes them "harder" to drive. If the output circuit isn't compensating the sound will just be much quieter. Speakers on the other hand are about massive displacement of air. The lower the resistance, the more current, the more power at the same voltage, the more powerful an amplifier you need. So if you go down from 8ohms to 3ohms you've nearly tripled the amount of current those coils can handle so you need almost triple the power so you need a much higher wattage amp to drive the speaker. In short, high end headphones require more voltage to drive them to compensate for the resistance of smaller wires while high end speakers allow more current due to the lower resistance of the wire.

Aren't headphones also about the displacement of air though just on a much smaller scale compared to speakers? I understand the principle of greater resistance needing more voltage to get the same level output for headphones. I still don't understand why lowering the resistance means more input is needed for speakers though as this seems to be the exact opposite way to how headphones work? Surely 1 volt into headphones with a resistance of 30ohms is going to give a much louder output than headphones with a resistance of 300ohms, so why is it the other way around for speakers and a more powerful amplifier required? Edit: just to add that I've played around with the calculator linked below to see if I can understand this. My amp is rated at 60w at 8ohms or 120w at 4ohms. At 8ohms fed by 60 watts we get 2.73A and 21.9V. At 4ohms and 120w we get the same volts, but current has increased to 5.47A, so effectively doubled. A few questions on this then: Is the increase in current the reason why a better quality amp that can handle the higher current is needed at lower resistances even though it should be easier to push the current through and if so, why? Is the power going to the speakers determined by the number of volts being fed into them and in order to keep the voltage up as resistance decreases more current is needed? If I'm correct with both of these then why isn't current an issue with higher resistance headphones, or is it? https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html

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Eli5-How do sounds retain their individuality even when there are a lot of them? (like identifying specific sounds in public)

Because our brains have been using sound for a long time. By using the delay time between a sound reaching our ears in conjunction with the shape of our ears we can establish a direction and distance from the source without ever having to consciously decide to do so. We can do this for a huge number of simultaneous sounds because we can tell where each sound started. As a neat aside, we can also hear the difference between hot and cold running water, and how full a vessel is. Loops back to the same point however, we've evolved a very strong skillset revolving around our ears because we've had them much longer than we've been human.

I think I phrased my question poorly. I meant, sound is transmitted via vibration of air, right? So the same air is vibrating for different types of sounds at the same time, so why don't different sound waves distort each other? Like if there are 5 people are speaking at the same time, it doesn't turn into a jumble of noise

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eli5 How do countries exchange their currency to purchase foreign goods? Suppose India buys an Airbus plane from Germany, and India pays in Rupees, why would Germans accept Rupees if their currency is Euros? How does the Indian rupee get changed into Euros?

That's the whole purpose of foreign exchange trading, why currencies fluctuate in value. Trillions of dollars in currency gets traded every day to facilitate international trade. India would need to convert Rupees into Euros to pay for the planes, and if the overall trend is more demand to convert Rupees into Euros then the Rupee would weaken against the Euro -- those willing to accept them would demand more for same number of Euros. But maybe Europeans are buying lots of textiles made in India that need to get paid for in Rupees, so the value of the airplanes and textiles evens out and the currencies stay relatively stable.

No, my question was how are rupees converted to euros? I am aware of currency fluctiation, though your reply gave me more information about that so thanks to you for it.

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ELI5: Air weighs 14 pounds per square inch, yet we don't feel it crushing us. The notion that internal pressure somehow acts as a counterbalance just seems to mean that we're being crushed in both directions. Shouldn't we feel this massive weight on us?

No, because it’s normal. When you feel pressure, it’s *abnormal* pressure, like someone sitting on your leg or something. If we evolved with more or less pressure, we would notice the difference on earth. Think of it like diving deep in a pool or lake; the deeper you go, the more it hurts because of the pressure. On the contrary, look at the blobfish. They’re so “blobby” because we see them in lower pressure environments than they’re used to. Their bodies can’t hold their shape because the pressure normally holds them together. As a result, they just sag everywhere.

Bonus question: a naked man on the moon would appear fatter because of the lack of air pressure?

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ELI5 How can camflouges in moths/insects imitate nature? Like, how does the camouflage of a leaf insect looks exactly like a leaf or dried leaf? Are they born with camouflages? If so, how does the genetics work?

It's just that those who resembled those leaves the most had more chance of surviving. So they will reproduce and their offspring would look more like the leaves. From the offspring, those who resembled the leaves the most would survive, etc. After a while you get insects that almost look the same.

Yeah but, how do they know how to imitate nature? Do they so it voluntarily? Like, do they think ," yeah I must start to look like this leaf right here inorder to survive " ?

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ELI5 : How do stocks work ?

You'd almost definitely need more money than you have to make a stock move in any sustained manner. Sure, if a stock trades $1m worth of shares on an average day and you buy $10m in a day it'll cause price to rise, but if demand isn't sustained then it'll fall right back down. Also, if you did that specifically to pump up price and then sell, that's fraud.

thanks, also would it be fraud in crypto ? i can see in stocks the government has rules and regulations, but I assume the crypto world is like the wild west

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Eli5, Why do people buy nfts? I dont get it.

I am very much just as puzzled at this whole hype as you are. However, the fact that there are copies of the video all over the net isn't a good argument, imho. You can get prints (copies) of the Mona Lisa all day long, it's still a different matter to actually *own* the painting. I know that this is not a perfect analogy because if you own the Mona Lisa, you have an actual physical thing you can touch. Still, this is about owning the original.

It's like if you bought the Mona Lisa but it is stated in the contract that it must stay at the Louvre and you have no say in any decision concerning the painting and you make no revenue from museum tickets or merch and copies ... But you own a receit saying it's technically "yours" so... I guess you just bought bragging rights? And eventually you could sell them.

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ELI5: What is it that you see when you press your finger between your eye socket and eyeball, on the eyelid?

The light sensing cells in your retina fire off not only from light but also from pressure. When you press on your eyeball you increase the pressure inside of your eye which then causes cells in your retina to fire off. Your brain then interprets this as light.

So the black spot and light circle around it, is a reaction of the pressure, on the opposite side of the eye?

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ELI5: How does transfer proof/"kiss proof"/budge proof lipstick work? The kind that is very difficult to remove, and won't leave a mark on glass wear.

Your lippie is probably half assorted silicones, half dyes. Isododecane is also used in hair spray. It goes on clean and minimizes transfer. Trimethylsiloxysilicate is a soft skin adhesive (kind of like other silicones used for healthcare applications). Dimethicone is a moisturizer (all three of these have moisturizing properties apparently). Cyclopentasiloxane, or D5, repels water. It's basically a soft, smooth sealant. Cyclotetrasiloxane, or D4, is a kissing cousin of D5. Trihydroxystearin is a castor oil derivative that basically thickens the mix and moisturizes your lips. Disteardimonium hectorite is a modified clay compound. I think it's being used as a dispersing agent to make sure everything in the mixture stays, well, mixed? Propylene carbonate is a solvent. You dissolve stuff in it. Tocopheryl acetate is just vitamin E. Phenoxyethanol is a preservative. Ethylhexylglycerin helps preservatives work and also helps protect your skin and keep everything mixed. The rest is dyes and minerals. A lot of these are emollients (moisturizers) and solvents (things you dissolve other things in) as well as these properties. Because many of the top ingredients act as sort of sealants, whatever proprietary mixture they have will therefore end up working in conjunction together to... Well. Do what you want lipstick to do. Stay mixed, not go bad, go on smooth, keep your lips moisturized, and not come back off. It's all chemistry. And it's a billion dollar industry. Fascinating stuff.

Its interesting to me, because when I say it's budge proof, I really mean it. I can rub my mouth with makeup Wipes, the back of my hand, water, and literally nothing happens except the smallest bit of dye transfer. Apart from the moisturising end emollient ingredients, what on that list would contribute to this? Would it be the isododecane? The only thing that takes it off are oils/creams.

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ELI5 Prior to modern timekeeping technology, how did they determine winners of extremely tight competitive races (e.g., swimming, track &amp; field)?

How did you judge a race when you were a kid? Basically a judge watching the race. It was tough to compare people in separate races though. I feel like intense training has brought modern elite athletes to where fractions if a second make a difference and video makes a difference. It hasn't been so consistently close in the past

I’m aware that they obviously had judges watch the race but I asked about extremely tight races. How could they depend on a judge or judges to accurately make a call when sometimes, to the naked eye, it looks like a tie? I agree that intense training makes modern athletes stronger and faster but in olden days, there still could have been athletes that had some extremely close finishes with each other (maybe not the fastest as compared to today).

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ELI5: How do phones listen for the voice command ‘hey Siri/Google’ constantly and not run out of battery?

On an iPhone at least inside the A series CPUs is a coprocessor that is always running, ultra low power and basically runs a deep neural net looking for the "Hey, Siri" phrase along with a few other things (motion data is the other big one). This coprocessor is extremely specialized, extremely simple, and uses next to no power because of that. Once it thinks it has heard "Hey, Siri" it sends a message to fire up the main CPU and process the rest of the message. There's [a really good paper](https://machinelearning.apple.com/research/hey-siri) that Apple wrote about how the deep neural net distinguishes the sounds if you want to go deeper.

It just occurred to me that this is one of those cases where the neural network basically matches almost exactly how our unconscious picks out our name, even when we're half asleep. Is anyone able to confirm that's what happens with humans too?

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ELI5: Why can't you just cut off cancer cells?

Cutting out a tumor is something doctors can try to do but in only works in specific circumstances. Many types of tumors can communicate with the body and request blood vessels be built to them and consume resources meant for other organs. In addition, they grow virulently and can grow around critical blood vessels and organs making it essentially impossible to cut out the entire tumor without risking killing the patient. Sometimes the tumors can grow and kill off the cells that form the walls of organs complicating the removal process. If even a single cancerous cell is left behind and not destroyed by the body - it can grow back into another tumor, so it can carry many risks. Lastly, the most dangerous types of cancer are tumors that actively spread freely throughout the body. Cells can break off and float throughout the body and embed themselves elsewhere growing new masses simultaneously everywhere in the body. At this stage the tumors are likely inoperable - the only way to fight them is chemically or via other means.

That is…not what malignant means. Did you mean metastatic?

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ELI5: How can we keep taking water from inground wells? There's not an infinite supply of water, so how doesn't the water run out?

It's actually a big problem in a lot of places right now. Underground water aquifers seem to come in two types, recharging and non recharging. As the names imply, recharging aquifers have sources of groundwater which replenish them over time. Non recharging ones are more like underground tanks that you just empty out over time, and you have to keep digging deeper and deeper wells and pumping water farther and farther upwards to use them. Many non-recharging aquifers in places like the central US and China (and many other places) have been pumped heavily over the last century, and are getting very difficult to use. This is a big threat to agriculture in these regions, which has grown to depend on artificial irrigation from these sources.

How might you suggest we combat this problem?

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ELI5: Why will water start to taste bad when you leave it in a glass for too long, but will taste fine when you dispense it out of a tap where it's been sitting for months?

As others said, mostly loss of dissolved gases. Our water company aerates the water as part of the treatment from open reservoir to pipe. Basically a open tank/pond with water forced up, like a decorative fountain.

Mind if I ask which water district? I've been in water treatment a while and never heard of that. Aerating water is a step in wastewater treatment, but as others have said air in distribution water tends to mess with your chlorine levels. Also when they aerate water, they typically use pipes that bubble up ~~water~~ air out of open holes and it's super scary because if you fall in you can almost instantly die.

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ELI5: What real use are real estate agents if we can sell our home ourselves?

What use are chefs when we can cook for ourselves? :-) Selling a home is a process, which means depending on the law where you live, there might be serious consequences for missing out a step in that process. You absolutely can do it yourself but then you are liable for any mistakes in the process. And the fact you do this very infrequently means you’re more likely to make a mistake. An estate agent should be doing the process frequently enough that they do it efficiently. And if they make a mistake they are accountable (and probably have professional liability insurance to cover the cost of the mistake). So in the same way a professional chef probably will turn out a better meal than you or I would (and is covered by insurance if they do give you food poisoning) a professional estate agent should provide an easier process for you selling your house than you would do on your own. In both cases, expect to pay for this.

> What use are chefs when we can cook for ourselves? :-) Most people cook the majority of their meals at home.

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ELI5: What real use are real estate agents if we can sell our home ourselves?

I bought a house within the past two years and used a real estate agent. At first I was getting kind of mad because she wasn't doing anything I couldn't do. In fact, I was looking up the listings and found the house I ended up buying. However, on the day of signing, she spotted an error in the paperwork that would have cost me more than 10x her fee. We had to close a day later because a new contract had to be drawn up, but it was something I never would have caught. Sure, I could have done most of the work myself had everything gone right, but I was happy to have someone with experience when I was clueless that something went wrong.

What was your lawyer doing? That's why they go to law school. 10X her fee??? so they error was 50% of the house price?

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ELI5 what the difference between a murder, homicide, manslaughter and the 2nd and 3rd degree versions of these charges are?

The main difference between homicide and murder is that homicide is the general act of killing a human where murder is the willful, planned act of killing a specific person. Like, did you take your gun and intentionally shoot someone, or did you fire the gun in the air and tbe bullet accidentally land on someone? The degrees can mean different things in different places but they’re basically the level at which you intended to kill something. They describe intent.

But what about manslaughter then?

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eli5: why do men seem so disproportionately lonely?

You're looking at r4r. That's not a very evenly split sample. Women get PLENTY lonely, they just handle it differently than men. Men feel confident reaching out to strangers on the internet for companionship. For women, that's a pretty sure way to get SUPER harassed by a lot of unwanted attention. (and no, not all attention is good).

so how do women respond when they're lonely? do they just bottle it up like some sort of toxic masculinity for chicks? is there a chicks only outlet that i dont know about?

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ELI5: Why does veto power exist at the United Nations?

After WWII it was decided that we needed some type of organization that could try to keep another world war from happening. The main force was the allies who had won the war. So the allies all agreed they'd have permanent membership to the un and also veto power.

But why was Russia provided veto power? They're not an ally to most of the UN countries except maybe PRC.

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ELI5 Is there a good reason why we don't just drop all of our unrecyclable waste into a volcano?

This has been asked many times before, do a search Logistics. There are extremely few volcanoes in mainland North America so you are talking about MASSIVE amounts of shipping of garbage. Why would we do that instead of piling everything nearby? Risk. How are you going to dump it there? You can't build a facility there. Roads can't be kept stable. Are you gonna fly over it and drop stuff in? Even if you did that nonstop with the biggest cargo transport you could, you wouldn't be able to keep up, and if you use many at once then airspace is going to be a concern. https://www.youtube.com/watch?v=lDxOhfiFsuc Here's someone throwing a single container with some water in it into lava. You think it's going to be a good idea to throw a bunch of other trash in there? You're going to have fire plumes, explosions, trigger a lava flow, etc.

Also what capacity to receive waste would each volcano have?

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ELI5: Why is male circumcision much less controversial and more widely accepted than female circumcision?

My mom works at a nursing home, she has to clean places and give meds. One man hasn't cleaned in the foreskin for years so when he has morning wood it hurts bad. So make sure to clean everywhere, (this is kinda off topic but that is my 2 bits)

does she see more cleanliness issues with male genitalia or female genitaltia?

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ELI5: Why is male circumcision much less controversial and more widely accepted than female circumcision?

Medically speaking a vasectomy is a lot less complex and invasive than a tubal ligation. A man can have a vasectomy and leave the hospital in the same day potentially.

Done under a local anaesthetic, you can leave the hospital pretty well straight away. But why are we talking about vasectomies and tubal ligation?

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ELI5: How does the U.S. debt work? Don’t they need to pay it off like Andrew Jackson did?

It is constantly being paid off while at the same time new debt is being issued. Government debt is in the form of bonds. Investors buy bonds, then after a pre-determined amount of time, the bonds mature and can be redeemed for the borrowed amount plus interest. Historically, the US has never defaulted on these, making them a low-risk, low-return investment. There really is no reason to pay it all off. As long as the US is able to put the borrowed funds to use in a way that stimulates the economy, the increased tax revenue from that stimulus can make up for the interest, creating a positive incentive for the government to continue issuing new bonds.

So… National debt is kind of like a pyramid scheme?

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ELI5: Why do different screws have different heads, like flat head or phillips?

Different needs. Flat heads are easily operated by machines, Phillips heads are very common yet are designed to limit the maximum torque applied. Hex heads and especially Torx-style heads are useful when a fastener needs a large torque in a small head, and you don't want the head damaged if a large torque is applied. And then there's odd varieties used when the manufacturer deliberately doesn't want end users removing the fastener.

Forgive me if this is a dumb question, but what makes say, a phillips head harder for a machine to operate than a flathead? In my head I'd have thought a philips would be easier because it has four orders of rotational symmetry rather than two; it's less 'fussy' about positioning for the bit to engage with the screw.

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ELI5: Is it more likely that I would live or die after being run over by a car?

As a person who has been run over by a car (a Chevy Tahoe going about 20mph, stopped and started up again halfway, both passenger-side wheels drove over me, in a hit-and-run), the friction removed some patches of skin and I broke or compacted a few bones. And also I'm finding the phrasing of this scenario a bit ghastly.

Did they catch whoever hit you? And do you have any lasting damage? Glad you made it!!!

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ELI5 what is the keto diet and what can I eat?

The keto diet is all about reducing your carb (sugar, bread, pasta, etc.) intake to next to zero and replacing those calories with calories from meats/fats. The idea is that if you don't have carb intake, your body will start burning fats for fuel, which will promote weight loss. There are hundreds of resources out on the web that will give you detailed dietary advice, but the gist of them all is don't eat carbs (including most fruit) and replace it with meat.

Thank you, which foods are ”fat”? And how is fat good for weight loss like cheese or what is fat?

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ELI5 “Hot Hands” or other hand warmers - how do they work/ how are they safe?

There are different types, but one uses sodium acetate dissolved in water. It's a super-saturated solution, meaning that really there is more stuff dissolved in the water than the water would "like". So the sodium acetates "wants" to start come out of solution and form solid crystals. To start growing a crystal, though, you need a *nucleation site*, some little bit of something that the first sodium acetate molecules can latch onto and then gather into a crystal from there. Without a nucleation site, the sodium acetate stays in its super-saturated solution. The hand warmer packet contains this solution along with a little strip of metal. If you bend this strip, little bits of metal come off and these provide nucleation sites for the crystals to start growing. This crystallization process is an *exothermic*, i.e. heat-releasing, reaction. How did the heat get there? Well, to create a super-saturated solution, you need to dissolve the sodium acetate in hot water (which can hold more stuff in solution) and then let it cool. Some of the heat you put in gets stored in the solution - the heat that was necessary to get it super-saturated (in other words, the solution reaction was *endothermic*). When the excess sodium acetate crystallizes, the heat energy stored in the solution is released. As to why it is safe, you can calculate how much heat energy will be released and thus how hot the hand warmer will get. So you can ensure that the temperature will be in a safe range. There's no danger of a "runaway" reaction since you know exactly how much sodium acetate you dissolved and how much solution you put in the packet.

To your last point shouldn’t it be the freezing point on the phase diagram (60 C, 140 F) where the maximum temperature can reach regardless of amount of solute?

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ELI5: Why are so many photos of celestial bodies ‘enhanced’ to the point where they explain that ‘it would not look like this to the human eye’? Why show me this unreal image in the first place?

Lots of images show colors that human eyes are not sensitive to. You might see photos of galaxies that include infrared, ultraviolet, etc but since your eyes are not able to see these colors, they have to me manipulated to represent those as visible colors.

How did we figure out that stuff was there if it can’t be viewed by human eyes? Unless they were discovered after standard telescopes?

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ELI5 Why did things like dinosaurs grow much bigger in the past than current day animals do?

The blue whale is the biggest animal that's ever lived and it's alive today, so there's a flawed premise in your question. There was more big dinosaurs, but those were spread across tens of millions of years. Tyrannosaurs lived 70 million years ago. Stegosaurs existed **150 million years ago**. That's a 70-80 million year period of us documenting large creatures. We tend to mash all those creatures together at once in our heads, and that's just not the reality.

how do we know there was never a bigger one?

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ELI5: How do they decide on which direction to point the James Webb telescope?

By committee of course! Research proposals are submitted to a review board which then will rank them based on things like potential research value, etc. The end goal is to book as much of the telescope's time as possible and to work out a schedule where it can move the most easily between points of observation. The telescope can't point just anywhere at any given time as some areas of the sky are only visible during certain times of the year, meaning scheduling certain windows of observation is important.

Good point. I recall reading that one of its missions was to explore some of the oldest stars in the universe, so it made me wonder where do they believe those are?

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eli5 Why are housing prices so high across North America and Europe?

Supply and demand. The US has an estimated shortage of 4-6 million houses. Coupled with low interest rates for loans over the past few years it’s been cheaper to borrow money. These two causes (cheaper money and fewer houses) have raised prices substantially.

Thank you! Is this a recent phenomenon? It seems like prices exploded 10-15 years ago

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ELI5: What does the concept of entropy mean?

The most intuitive way to think of entropy is to consider it as a measure of how disordered a system is. For example, consider a fresh pack of cards. It's in one order and one order only, and it's very easy to tell when the deck is no longer in that order. The fresh pack has very low entropy, because there's only the one arrangement it can be in. Now, if you shuffle the deck, so that the cards are completely randomized, you've raised the entropy of the deck. You can rearrange the individual cards very freely without damaging your ability to say "Yes, that's a shuffled pack of cards." Another way to think of entropy is the ability to pull useful work out of a system. For example, you need a temperature difference to do any work with a heat engine; if there's no gradient, nothing's going to want to move from point A to point B. You need *low entropy*, a condition of order and being able to say "This is different than that," in order to perform work.

Thank you for this explanation! I think it mostly makes sense. One thing that I am still confused about is whether it is an absolute or a relative term. So, in the example of the card deck, if Jack shuffled it and it didn’t have any pattern, I get that it would be called entropy (or having high entropy?). But what if Jack later discovered a pattern to his shuffling that allowed him to predict where each card was. Would the deck no longer have entropy? Or did it not have entropy to begin with because there was a pattern (one that Jack didn’t know about). Or is it that after shuffling the deck, it no longer had the pattern that he was looking for (that he cared about), so it had entropy regardless of other patterns?

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ELI5: What does the concept of entropy mean?

Entropy. Such a simple word, but so complex in what it is. Okay. Let's say I have a perfectly nice stack of blocks, stacked vertically, ordered by A, B, C, D, E, and so on. This is a state of low entropy. Then I smashed the stack. Now we see blocks scattered all over the floor, randomly. This is a state of higher entropy. How do we get the stack back in order? We spend work to put it back, or we can reset the universe (or open up the menu and press Load). Entropy is the same. You can spend work and try to reduce entropy, or simply go back in time. Entropy as laymen can understand is a representation of disorderliness of a state of things in a particular space. It naturally goes up (unless you're rewinding time). You have to put some work in so it comes back down. (And whoever playing jumbo jengas at 2AM in a fucking loud party next to my apartment, you can go fuck yourself. The noise of jenga entropy is too damn loud.)

Can entropy increase to infinity or does it reach 100% or a value of 1 (full entropy)?

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ELI5: Given the many layers of checks and balances in the court system, how can 1-5% of innocent people end up in prison for crimes they didn’t commit?

Human error has a lot to do with this, really. Even after taking out all the biases people have in general, such as accusing someone based off their physical appearance, and a lot of circumstantial evidence making a case, you'd still get those wrongful convictions (probably a lot less, but you'd still get them.) There are two major causes of these. The first one is the fact that human memory is complete and utter garbage, and can be modified by repetition of alternate facts. This has been proven time and time again, where a police officer repeatedly smashing you with facts about a crime you didn't commit, may lead you to believe you actually did. This further extends to dubious and faulty memory of events. Many wrongful convictions depend on witnesses misidentifying the culprit, as their brain sees the accused, and if they look close enough to the actual culprit, they will identify them as if they were, because minute differences do not register unless you put the two side by side. Likewise, other details may be super vague, and mis-remembered or misquoted. Often, all you remember is "the man robbed a bank, and he looked a bit like this", because your brain needs to remember this for survival reasons, but the rest of the details won't even be remotely in there. This explains the reason why if you are in a similar situation to a crime, you will be also suddenly a bit more anxious, as if the crime was about to happen again. Survival instinct is a fickle thing that hurts all this stuff. And then, we get to the second major cause: Plea deals. This one is probably the biggest culprit, and it basically goes like this. You get arrested for (let's say) drug trafficking charges. You know you didn't do it, but somehow, they found a pound of cocaine in your car. While you're struggling with the confusion of "how the hell did that get there", and "who the hell do you know might have left it there for you to be screwed over", an officer comes in for interrogation, and tries to coax a confession out of you. They say they found the cocaine, they say that through a few contacts, they have witnesses to say you're guilty, and to boot, they found your fingerprints on the cocaine's bag. After a few hours of back and forth and forth and back of you telling them you wouldn't even know where to get cocaine, and them saying that they have all this evidence, the confession is only a formality at this point, but they still want it, because "confessing goes a long way in reducing your sentence", since it means you admit and know that what you did was wrong... Well, they drop in the bomb: If you admit that it is your cocaine, they can drop the charge from drug trafficking, to drug possession, whose sentence is much lighter, so that's sort of meeting halfway. Tired, annoyed, and honestly just wanting to be done with this, you accept the deal, write and sign a confession, and they send you either to the station's cell, or home (often with bail), awaiting the formality that is the trial. At this point, they have everything they need: They have heavily circumstantial evidence, that is corroborated by you confessing. Suddenly, you get a year in jail for a crime you don't even know how to commit, because honestly, it's better than the alternative of being in jail for drug trafficking... And that's how you got wrongfully convicted. That kind of scenario happens a lot more often than you probably think, with more and more police officers being caught planting evidence they "find" in a car they are ssearching (often illegally) thanks to their body cams. This can also land the same way with murder, but the steps that have to be taken are very different, since there isn't really a step down they usually get you to in order to get there. Those are the main two culprits of wrongful convictions.

Extremely good response. Wish I had an award to give. The police interview of witnesses is not to be discounted at all. Many cops lack the training to ask questions that aren’t leading. The approach taints the evidence. For example, a cop interviews a potential witnesses and asks “when you saw John James shoot at the neighbor’s house, what did you do?” gets a different response than asking, “describe the scenario from the moment you became aware of it.” Memory is indeed easily influenced and you did a great job of detailing that. Love love love this response. Bravo!

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ELI5:Why do we yawn when we watch someone else yawn too?

It's a tribal thing. we all sat around the camp fire, and needed to signal to the others in the group that we want to sleep but before speech, that was hard.

Is this a guess or do you have sources? You state this rather factually - as if you may be a time traveling scientist who has personally researched this topic extensively using the scientific method and have definitive proof corroborated by time traveling scientist peer review boards. ELI5 should not be BS me like I am 5... (Rules 5 and 8)

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Eli5 What is the difference between regular aa batteries and the rechargeable ones? Why can't the disposable ones also be charged

Regular ones are alkaline batteries, cheaper but difficult to charge. Rechargeable are lithium, more expensive but easier to charge.

I see... But what is happening on a molecular level? Why can't alkaline be recharged

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ELI5 What is the least number of notes &amp; coins I would need to carry in order to pay for anything up to $100 in exact change? (AUD)

50$ + 20$ + 10$ + 10$ + 5$ +1$ +1$ +1$ +1$ +1$. For cents there is no 1c coin so it's impossible to get a perfect amount. Edit: for cents you would do the same thing: replace the last 1$ with 50c+20c+10c+ 10c + 5c+5c (if there were a 1c coin you would have the same like the one for dollars.). Also fixed the dollars with another 10$ note

Does that also mean it's impossible to give change correctly?

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ELI5: What is bandwidth? (literally)

> And then you can modulate the wave so it carries data. For digital modulation, that means you vary the amplitude or power level of the transmission. And/or you can vary the frequency or phase. In FM transmission, you would change your 2400MHz signal up or down by up to 10MHz, and your 'bandwidth' would be just that - your band width, the difference between the lowest and highest frequency you're sending. Other modulation schemes which use phase and amplitude together are in use too. One example is [QAM](https://en.wikipedia.org/wiki/Quadrature_amplitude_modulation). If you're transmitting a digital AM signal by pulsing a single carrier frequency on and off, then your bandwidth is the result of a tradeoff based on how fast you're pulsing on and off relative to the frequency of the carrier wave. If you're pulsing a carrier wave on and off very fast, approaching the frequency of the carrier itself, then the spectrum of what you're sending gets quite wide. If you transmit a pure 2400MHz signal at constant level forever, never stopping or starting, then that would be a 0 bandwidth signal, a pure frequency. But when the signal is stopping and starting, the band gets wider than 0. This is just a mathematical consequence of how frequencies work. A great video to get intuitions about this is here: https://www.youtube.com/watch?v=MBnnXbOM5S4

Thanks, I think I am a little less confused now. Phase modulation is something I hadn't thought about. So... in simplest terms, the more the frequency of the carrier wave is allowed to fluctuate, the higher the bandwidth? Yet that's \*not\* frequency modulation, but... something else?

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ELI5: If humans can have plastic electronics inserted to regulated their hearts, steel to replace bone, why can't we simply have wigs surgically attached to us when balding?

We do, it is called hair transplant surgery. Why go through a more intense procedure for a wig that will wear out over time, when you can get real growing hair?

What about those who have 0 head hair left?? Can they transplant hair from other areas, say... The balls?

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ELI5: Why does heat make us sleepy when we are tired? We naturally cool down when it's bed time and we sleep better when our bodies are cool.

I would guess because your body needs to do a lot of work to cool down, so a lot of energy is missing, therefore there's not enough energy to keep you awake.

ELI5 why would the body need energy to cool down? Heat is a byproduct of energy conversion. Wouldn't cooling down imply the body rests, stops working so much and thusly stops producing so much heat?

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ELI5: how does your body develop real physical symptoms from your brains manifestations?

Setting aside /u/GroundPoint8's explanation for a sec, your brain absolutely can cause physical symptoms. Think about something scary or arousing and your heart rate will go up. Think about something that angers you and your muscles will tense. Or, more easily, you can will your arm to move. Your mind isn't some ethereal thing separate from the physical structures in which it exists. Your thoughts "are", in a physical sense, your experience of the electrical impulses and chemical states of the neurons in your brain. And those neurons are connected to neurons in others areas of your body that control things like the release of certain hormones or the contraction of muscles.

Your brain can also make up unrelated symptoms as a way of alerting you to a different problem. I read about someone who had persistent, debilitating cramps every month, but learned to ignore them and continue functioning most days. Then one day, her vision faded and she was completely blind. Her eyes were fine, it was a psychosomatic symptom. Since she was no longer responding to the pain signal alerting her to a problem in her body, the brain started flicking other switches to try and get her attention. Once the pain was treated, her vision returned. To answer the original question a bit better, when you're anxious, the brain starts trying to figure out what's wrong with you, be it a physical issue or a dangerous situation. Usually when it can't come up with anything, it gives you a stomachache (those organs are so densely packed and busy, it's impossible to tell which one is causing a problem, so if theres a problem the brain can't find, it blames it on the abdomen). But if you're anxious about a specific disease or ailment, then you're giving your brain a new thing to blame. "Worried we might have lice?? We must have lice! Go itch!!"

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ELI5 What is a "waifu" and do people have real crushes on fictional characters?

To answer the second question first, yes. Parasocial relationships with fictional characters or celebrities are quite common. You've probably had such a relationship. A waifu is a female anime character who is, to the person using the term, attractive enough, both in personality and aesthetics, that they wish she was real. The term typically applies to certain cutesy-sexy teenage or adult characters(the more socially acceptable version is to imagine a grown-up version of the minor characters, or one who has aged alongside the speaker) with certain stock personalities. The term is common to the western version of Otaku culture, where (for good or ill) one embraces social ineptitude and awkwardness, generally as a defense mechanism. They can't insult you for it if you're proud of it.

Yes I thought something like that and you are right that I had a crush on cartoon characters when I was a kid. What I dont get is, how it is possible for an adult or even young adult to have a relationship with a fictional character. Do they really think about it as a relationship and how exactly does it work? Do they talk to their waifu? Watch TV with her? Is it 100% fantasy or are there real world components to it?

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ELI5 What is a "waifu" and do people have real crushes on fictional characters?

"Waifu" is some form of anime bastardization of the word "wife" if I'm understanding correctly. People do have real crushes on fictional characters. It's pretty fucking sad.

>What I dont get is, how it is possible for an adult or even young adult to have a relationship with a fictional character. Do they really think about it as a relationship and how exactly does it work? > >Do they talk to their waifu? Watch TV with her? Is it 100% fantasy or are there real world components to it?

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ELI5: What does the sun do to pigment that makes it fade over time?

UV radiation is EMR that has a little more power than the visible light spectrum so we're talking some photons packing a decent punch of energy, and an aaaaabsolute *shitload* of photons coming here from the Sun to begin with. These photons hit the dyes and pigments and impart some of their energy by being absorbed, over time breaking the molecules down.

Does the pigment lose mass? Is the sun "sand blasting" at a molecular level?

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Eli5 If someone wants to escape the death penalty, can they just go commit crimes in countries that don’t have that and get away with it?

What are you even asking here? Are you asking if a person can't be sentenced to death in a country with no death penalty? Yes, obviously. How is this a real question?

Well maybe they could send you back so you have to serve in the state you’re from? I don’t know, it’s a question. No need to be so rude

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ELI5: Why does heat and humidity make things less sticky?

Like a lot of things, Command Strips have a melting point. Or, more accurately, the adhesive used on Command Strips does. Adhesive of that kind is meant to never 'set' or harden, so it's already soft to begin with (in a semi-solid state), and that means it's melting point is likely not much higher than room temperature. As the temp in the room rises, the adhesive starts to undergo a transition from semi-solid to full on liquid which loosens the protein chains that are holding everything together, which causes the weight on the Command Hook to be enough to release the bond. The way to combat this is to either get better air conditioning (or set your AC to kick on at a lower temp), or use permanently anchored hooks to hang things.

That's what I ended up doing. Thank you. You seem knowledgeable in this area so I'm going to ask another question. What makes a suction cup stick to a surface? More specifically, what's the equation to figure our how much force is being applied by the cup? I'd like to make a free body diagram of this

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ELI5: How does a motor produce movement from electricity/ fuel?

motors are generally speaking energy converters. Electrical motors convert from electric to magnetic to kinetic energy. Combustion engines from chemical energy to expansion (technically already kinetic) to kinetic energy.

Ok, but how does the motor convert the Electric energy to kinetic energy?

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[ELI5]: Why does friction make our car turn?

Friction opposed the tires not the car and points inside the circumference. &#x200B; The resulting frictional force is perpendicular to the rolling direction of the tire and opposite direction. (Negligible friction when rolling, maximum friction when moving a car laterally.) The direction of the car is the direction of the tires as that is 100% of the friction. If tires were flat square bricks that didn't roll turning would be difficult as turning wouldn't change the direction of friction. If Tires were round balls turning would be difficult because no direction provides "sliding friciton"

What I don't get though is why it points inside the circumference. If the tires are pointing to the left to turn left, isnt the friction pointing the back of the tire? So, if we have that, shouldn't the friction be like [this](http://imgur.com/a/il77K12)? Edit: if the image isn't clear I can make a better one

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eli5- Private ambulance system in the US?

So I don’t have all the details here. I took my EMT class, but then changed my mind and it was over a decade ago. 1-private ambulance companies hire employees that have gone through their EMT basic, EMT, intermediate, or EMT advanced class (can’t remember the name). So all employees must be certified. These are the same classes that the county paramedics train. Patient handoffs are going to be the same for either. They retrieve the patient and apply EMT to the patient, then handoff to the hospital as needed. 2- I did not know if any incentive to bring a patient to a specific hospital. When I did clinicals, we brought the patient to the closest one. 3- As for the choice of private versus county ambulances and who gets the patient, I’m pretty sure that they get the same pages that go out but private is normally going to get there first. I was also told that if it’s a tie, normally the private ambulance will take the patient.

For point 3 - So its a race? how inefficient, two competing resources are trying to get to the same patient?

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ELI5: Why do we follow conventional current if we know electrons flow the other way?

Just think of it like protons flowing the correct way. &#x200B; With that you can't be more fundamentally wrong while correct in every single real life situation.

That is a bad way of looking at it. If you change proton number you change the elements., So if you change up a capacitor with the same metal plates I would the elemental composition of both sides. That or one side contains a lot of hydrogen ions that are just protons, the question now is where to the hydrogen come from? The better way to look at that is [Electron\_hole](https://en.wikipedia.org/wiki/Electron_hole) that flows or just holes. That is what is used in science. If you look at semiconductors you describe them with negative electrons and positive holes that both can move around. In reality, only electrons move positive protons sty in place in the atoms., and holes are just a location that electrons have to move away from but it is simple to look at is as if they are both positive and negative charged particle that exists and moves around. There is a good reason that the positive particle that moves in conductors are called holes and not protons. Calling them protons would induce new problems like too the mistake of the direction electricity moves, I think the problem is worse. So quite reasonable they are called holes, not protons.

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ELI5: How does "moisturizing" soap moisturize if the point of soap is to strip oil and dirt from you body?

It's a trap... No literally, moisturizing soaps generally use glycerine (also called glycerol) as the moisturizing agent and it leaves a film on your skin which both traps moisture evaporating from your skin and attracts moisture from the air being an hygroscopic chemical. &#x200B; Further simplifying, in the soap formulation there is a chemical that both keeps moisture in and pulls moisture from air so your skin remains moist. &#x200B; (It's the same reason why sanitizing gel has it, if you used only 70% alcohol your skin would dry really fast but the glycerine that remains on your skin combats that effect and protects your skin)

Is that why my hands always feel disgusting after using hand sanitizer?

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ELI5: How does "moisturizing" soap moisturize if the point of soap is to strip oil and dirt from you body?

When they market it as "moisturizing" it means it doesn't degrease as much as a regular, clarifying or volumizing soap would do.

Does that mean it is not cleaning as well?

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ELI5: What is the difference between Liberalism and Libertarianism?

Liberals; government should exist to help people and businesses do their thing rather than do it for them. Generally government should not get in their way and should let things be. Libertarians; governments shouldn't do anything but the absolute essentials. It shouldn't be the government's job to help people. ----------- The term "liberal" has a slightly different meaning in the US due to the US purging a lot of its leftists and left-wing groups during the 20th century (although some are coming back now). So in the US "liberal" tends to also refer to leftists, despite liberalism and leftism traditionally disagreeing on most things. Also, in practice (and being a bit unkind), libertarians tend to have a view that the "absolute essentials" a government should do are whatever helps them as individuals (rather than helping other people). So often a libertarian will say that the government services they rely on are essential and should be carried out, while the services their neighbour relies on aren't.

McCarthyism was wrong, but it wasn't a "purge." Political opponents weren't exterminated. > Also, in practice (and being a bit unkind), libertarians tend to have a view that the "absolute essentials" a government should do are whatever helps them as individuals (rather than helping other people). So often a libertarian will say that the government services they rely on are essential and should be carried out, while the services their neighbour relies on aren't. In practice, liberals only consider their own freedoms in lifestyle and actively try to oppress other lifestyles, such as religious freedoms. Gay rights? Awesome. Religious rights? No, they're the enemy.

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ELI5: What is the difference between Liberalism and Libertarianism?

Liberals want common sense rules like not poisoning water supplies. Libertarians want no rules: if you poison a water supply, the local town might think about maybe not buying your product, possibly.

Ehhh I wouldn't say that. More that I pay taxes to take care of things I don't have the time or skill to do. Like make sure my water is safe or fixing holes in the road. I don't like being taxed for oil wars, militarizing the police, building a useless wall. I especially don't like my paycheck going to a bunch of congress members (who many of which are earning tons through lobbying already). Why would I want my paycheck going towards people who want to suppress women's autonomy, black rights, weed. Why would I pay for a bunch of people arguing about no-duh topics just because it was the other party's idea? Too big of a government, plus lobbying and religion, causes corruption imo. In that sense, I am mostly libertarian

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ELI5: Why it's WAY more windy when going down a street that lead to the open sea?

In the illustration, you show "weak wind" that hits the building side that faces the water. That wind doesn't just end at the building. It keeps going *around* the building. So the wind on the street is not only the wind that was heading towards it, but the wind that was heading towards the buildings and was deflected into the street. It's kind of like how if you squeeze a hose, the water comes out at a higher pressure, because you still have the same amount of water coming through a smaller space.

If I understood correctly..., the strength of the wind on the straight road is stronger thanks to the wind (the "weak wind") that is joining from both side of the road, from buildings etc?

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ELI5: Can you break a phone by charging it with a voltage too high? (e.g. 65V laptop adapter)

Your laptop charger ain't 65 volts I can tell you that much now. Probably 18 to 20 volts actually. What you were reading was probably 65 watts.

You are correct, I meant Watts. It has a USB-c output so it would fit a smartphone. But the question is would doing that damage the phone?

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ELI5: Why is japanese culture as a whole, so popular in the west? When compared to other foreign cultures?

You mean like Mexican Food, Chinese Food, of Italian Food? Or perhaps French Fashion or German Machinery? The main part of Japanese culture that's popular is Toys, and the anime that feeds their toy industry. You don't see Americans building Shinto Shrines everywhere or attending Japanese theater, which is a shame because the noh, kyogen, kabuki, and bunraku traditional performing arts are really exceptional.

Are you japanese??? I'm not talking just about the gastronomic side of things....

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ELI5: Why do animals love us petting them? If someone constantly rubbed my belly or head I will be very annoyed.

Somebody may be rubbing the wrong thing.... People’s relationships with animals are interesting. You get a cat or dog and start feeding it, and you’re their best friend. Show them some affection, and it’s love. They show affection by coming to you and jumping on your lap or rubbing against your leg. One of my cats sometimes licks the back of my head. When you reciprocate, you’re showing them, in their language, that you care about them. All animals crave affection and crave contact.

Wait....you lick your cat's head?

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ELI5: All the ancient civilizations remains are deeply buried under ground. Where does this earth come from?

The Colosseum wasn't buried. Neither were the Carnac Stones, or Machu Picchu. Some old things were buried gradually by dirt and sand being blown over them, like the Sphinx. Actually the head stayed visible, which must have been confusing during excavation. You've digging up a big statue of a dude and then there's paws. Some things were buried on purpose, like Newgrange. It was always a partially underground structure. Other things were buried very suddenly, like Pompeii. We know exactly where the stone came from because Vesuvius is right there. Remains that weren't buried were usually either maintained, so we can't find them because they're not lost, or they were worn away and carried off so we can't find them because they're not there.

>Machu Picchu [Do YOU want to be the one to try to tell him that you're going to bury him?](https://youtu.be/Uu7NkAS6jZ8)

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ELI5: What part of a firearm is the 'gun'? - Since there's custom trigger, slide, grip, barrel, etc... What makes a certain firearm a Sig Pxxx vs a Glock xx for example.

I feel like collectively all parts combined make it a functional “gun”. Although if a part is missing authority’s will still consider majority of the parts together a “gun”, if that makes sense. If you have 90% of the parts together and it looks complete, you can bet it will be treated as such.

An analogy is a car, what part makes it a car? Is it the frame, the engine, the wheels, or the body panels? You can’t point at any part and say “that is a car”. Take anything away from it and it’s a nonfunctional car, but still a car. though if you completely disassemble it it suddenly is either a pile of parts or a pile of junk

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ELI5: Why do TV stations still broadcast in 1080i when all TVs now use progressive scan/deinterlacing?

It all boils down to that every time you change broadcasting standard, you need some new equipment. There is always some shit in the tech racks that needs replacement. Something that needs a more expensive software license. Some cable that is not good enough. And, and this is really more important than you think, you cut out every single one of your customers who still own fully functional, a bit older, equipment. It's the kind of thing that you are going to loose customers over. And with them, income. The incentive to offer a better quality service eventually outweighs the incentive to keep customers with old equipment happy. But the harsh reality is that most people buy a new TV once every ten-fifteen years or so and expect to keep it until it doesn't turn on any more. Us tech geeks who buy new stuff all the time, we are not a majority on that market, and that's a fact.

I see, good explanation, thank you. Do you happen to know if most content today is produced using 1080p equipment and then artificially interlaced for broadcast? (in which case deinterlacing would produce a perfect result). Or if they are still mostly using 1080i cameras?

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Eli5: What causes epilepsy?

No real cure just managed care for most people. I was diagnosed later in life(41, 49 now) and have had only grand mal seizure in my life. This is how I got the official diagnosis. Since then, I have noticed several small seizures. Looking back, I have had those smaller seizures that cause me to space out throughout my childhood (absence and/or petit mal). Docs have told me there is a genetic component to it. My great grandmother had violent seizures on and off in her life. My second cousin also was diagnosed later in life(53). The DNA is also shared with autism. That doesn't mean that I might have autism. It means I got luckier and the genetic mutation for it is not in my DNA. My nephew is on the autism spectrum and he also has the genetic mutation for both. I can mange them with meds and I have gone almost a year without a trackable seizure.

I just recently got the diagnosis after a series of petit mal seizures. I’m 38. I’m on meds and mostly just have what I call spasms now (do those count as a type of seizure?). I suppose I’m also just struggling with the diagnosis. I had thought diagnosis happens earlier in life.

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ELI5: How are people in physical professions (eg construction worker) able to grow large muscles but many people recommend to have rest days if you're going to the gym if you're trying to build muscle?

They're strong in certain ways, like tough as heck, but really beat up and don't walk normally and are in constant pain once they hit a certain (youngish) age. Big muscles, probably not, unless they lift outside of work. And they have to eat reasonably well just like everyone else. I just think you're wrong about construction worker physiques. They're usually fucked.

“Dad, why did you bring me to a gay steel mill?”

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ELI5: What does it mean to be “massless”?

Oh boy, all aboard the brain hurt train, next stop - Quantum mechanics! Mass is a property that particles can have, its a way for energy to be stored but not the only way and not all particles have mass. Most things you deal with are large and are made up of massive quantities of particles which all have mass so most stuff you think of has mass, but the light from the sun doesn't have mass but it can still push things because a photon's energy is in its momentum (not mass*velocity but a more intrinsic momentum). You'll often see E=mc^2 (energy = mass * speed of light^2) but the full equation is E^2 = p^(2)c^(2)+m^(2)c^(4) where p is momentum. Photons have momentum but not rest mass which forces them to travel at the speed of light, nothing with mass can reach the speed of light without infinite energy and nothing without mass can travel at any other speed. Basically the universe has a set of fields that things interact with. The electromagnetic field interacts with charge and magnetism, its force is carried by photons. The Higgs field is what gives things mass, its force is carried by the Higgs boson. Photons happen to not interact with the Higgs field and therefore don't have mass, while quarks and electrons and neutrinos all do interact with the Higgs field and therefore have mass. Why don't photons interact with the Higgs field? Just the way the rules happened to be set up.

ELI5: what is a field? It occurs to me that I’d have no idea how to explain that to a child.

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ELI5: Why does Chronic Wasting Disease cause that wasting?

CWD is a prion disease that affects the brain, similar to Mad Cow Disease. It basically melts your brain, so a deer infected with CWD slowly loses its ability to control its own actions, forgets to eat, and eventually starves to death, if it doesn't do something stupid like stumble directly over a cliff first.

I've heard some sources saying that even when the deer continues to eat it still will lose weight; was this misinformation, or is there a reason behind this?

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