ELI5: Why is that cars don’t get significantly more fuel efficient year by year?

Read the Story

Show Top Comments

Law of diminishing returns. You can only squeeze so much efficiency out of a combustible engine. For the design of a specific car, it has its weight and aerodynamics to contend with. Those values are mostly static.

sgrams04

There are some serious limits imposed on fuel efficiency by the way engines work. Diesels tend to be better and there is potential for improved gas mileage with new technologies, but it is not leaps and bounds.

Gas mileage is fundamentally limited in cities by the speed limit, mean free path, and mass of the car. On the highway, it is aerodynamics.

Aerodynamics haven’t changed much in the last 40 years, especially in the subsonic domain, so that’s that.

Lighter cars aren’t really an option – they’re already pretty light. Changing the mean free path and speed limits of cars is a city planning issue and not an engineering issue.

The only real solution is to find a different way to power our cars. Regenerative braking in electric or hybrid vehicles seeks to do this by getting power back from the brakes, making a significant difference in city driving.

TheJeeronian

Something else to highlight – cars have gotten significantly more fuel efficient. But we’ve used that efficiency to add power, not increase economy.

The average new car….
1980
MPG – 16 mpg
Horsepower – 118hp
Weight – 3,221 lbs (actually from 1987)

2020
MPG – 25 mpg
Horsepower – 247hp
Weight – 4,156lbs

So we’ve doubled power while still increasing fuel economy by 56%.

If we look to match performance with the average 1980 car, we’re 422% as efficient now.

But like the other answers have stated, safety, consumer preference, etc has soaked up a lot of those gains.

No-Corgi

In 1969 the average fuel efficiency was 12.9 mpg

In 1990 it was 19.5 mpg

in 2018 it was 21.8

It seems like fuel efficiency pretty steadily climbs over time. It’s not like there is some magic technology that makes it double every year or anything but it’s risen almost every year for half a century a bit at a time.

zeiandren

In addition to fuel efficiency they also have to reduce emissions every year. Most emissions systems reduce fuel mileage. The fact they manage to continually improve both is pretty impressive.

Proper_Barracuda_495

ELI5: How can scammers call you from a line that is no longer in service the moment you try to call it back?

Read the Story

Show Top Comments

Caller ID doesn’t have to be the same phone number you are calling from, and many spammers/scammers deliberately use a forged caller ID to appear more legitimate

TehWildMan_

Scammers can fake the number they are calling from because the telephone system is designed in such a way that there is no verification of such information.

Now the telecom companies *could* redesign their systems so it isn’t this way, so that faking the originating number isn’t possible, but they don’t.

Phage0070

I always ask the caller “what city are you calling from?”. It never matches the I.D. When I call them out on it, it’s fun to argue with them.

cjheaford

As someone pointed out, the scammers can spoof their number quite easily and the telecom companies could prevent this if they wanted to. But there has been a longstanding utility of presenting different numbers to the network. As a former call center engineer we would create various groups of call center agents (both inbound and outbound calls) that would need the calling line identification modified for each customer or campaign. I could literally type any number I wanted into the field on the phone system (12345678, or 000000000) even the number of another company. Interstingly if I entered the number of another company or institution, the public network would automatically insert the name of the company in addition to the number I presented. That means a lot to call centers. I used it a lot when routing calls to other call centers for load sharing. So shutting down the capability to spoof your numbers would impact a lot of legitimate business.

BaconReceptacle

They use VOIP (voice over internet protocol) that allows them to call people. Since it doesn’t have a real number, they can spoof any number they choose. Many use numbers similar to your own to pretend to be locals. Like if your number is 555-123-4567, they will call from numbers that are 555-123-****.

I send all calls that are not from people in my contact list straight to voicemail. My phone won’t even ring. If they leave a VM and it’s someone I need to call, I’ll call them back. If not I just delete the VM.

SpacemanSpiff6962

Eli5: If youtube disappeared would the videos be saved somewhere or just gone nowhere? How does youtube store its data exactly?

Read the Story

Show Top Comments

Google has data centers, their data, including YouTube videos, is stored there. If YouTube disappears as a platform, the videos would still be in the data centers. If someone attacks and destroys one or many data centers, some or most of the videos would be gone. At least some of the videos would still be stored locally by their authors.

nmxt

Depends on what “YouTube disappeared” means. If just the website disappeared from the internet, but nothing happened to Google’s big ol’ data centers, the videos would be safe, if inaccessible.

LuckyEmoKid

Although Youtube has huge data centers where the video content is stored, they also use 3rd party data centers called “Content Delivery Networks”. This is because it’s much more efficient to have a CDN provide the content to you in your geographical region rather than have everything stream from a handful of Youtube data centers.

BaconReceptacle

Google operates millions of computers, and has tens of millions of hard disks. They write software that lets them work together as if they were one big computer, except if one computer goes down another just takes over. If one hard disk dies, there’s always a backup ready and the dead disk can just be unplugged and a new one popped in its place.

The way they store the data is very complicated (more so than ELI5 permits), but in simple terms they have many locations with many disks and data is copied and spread between locations, and thee disks themselves are grouped in sets where if one fails it can be removed and replaced with no loss of data (because other disks in the set have copies). The entire thing is designed to be tolerant of big chunks of the service failing or going offline and still be operational.

What would happen if “YouTube disappeared” would depend on what you man by “YouTube disappeared. If you mean “Google loses interests and shuts down the service”, then they can do that in seconds without disturbing any of the videos by just “closing the program” to turn it off. If they knew that they didn’t want any of the videos, they could just set some of those millions of computers to deleting files from those millions of hard disks, then use them for something else later (anything else).

If you mean that someone hacked YouTube to bring it down — it depends on what they did. They could turn off the service, delete files and all their copies, etc. How far they got would depend on how quickly Google responded and how they address the problem. YouTube could be turned back on eventually, but some videos, comments, and things could be lost despite having multiple copies of everything.

If you mean destroyed by catastrophe (bomb, volcano, hurricane, etc)… Well, these computers and hard disks are spread out over many locations around the globe. If one location was suddenly wiped off the map, some processing power and some videos may be lost, but mostly YouTube would pretty much just keep going.

FellowConspirator

The videos are stored on their servers. If YouTube disappeared, they would shutdown the servers, or repurpose them and delete the videos.

palomdude

ELI5 How come bananas are harvested in Ecuador, taken to the port, loaded on a ship to the USA, go through customs, make it to a distribution center and then your local supermarket in perfect shape… only to get brown on the short trip from the store to your house (or the couple of days after that)

Read the Story

Show Top Comments

There are some questionable answers here. You dont chill or refrigerate bananas. It can cause an irreparable stop to the ripening process and the banana will just darken and then rot without ever softening. Banana’s are never refrigerated. In fact, greengrocers will often temp the bananas as they arrive to ensure they are not too cold.

Instead, like many have said, they are picked and shipped quite green. Ripening of a banana can take about 1 1/2 to 2 weeks. A lot of that time is spent in shipping. The starting to yellow to starting to brown is only a matter of a few days. We never sprayed them with ethylene to initiate the ripening once in country, it is all a mater of timing. If you have ever seen a banana box, you will note how open they are compared to other fruit boxes. This is all to slow the build up of ethylene, for which bananas create a lot of. Triggering that process intentionally before you sell them is just silly (see edit for correction).

So why do they start to yellow and brown just as you bring them home? Well, good timing on the part of the grocers, but there are a couple other factors you might be in more control over. Storing bananas near other fruit can increase their exposure to ethylene and speed up ripening, so dont keep them in a fruit bowl. Likewise storing in a plastic bag like a produce or shopping bag traps in that gas. Take them out and leave them exposed to air as much as possible.

Edit: u/theinfamousloner has corrected me that gassing is in fact a thing. I knew they went to ripening centers, but was under the impression that was a storage step. Thank you for your insight, and I stand corrected on this.

I will not give in on the refrigeration. They are temperature controlled to 13C, but storage coolers and refrigerators are normally 4-5C. AC != Refrigeration. In Northern Canada, temperature control keeps them warmer than the ambient temperature but we dont say we are cooking them.

Sabetheli

They’re picked and shipped unripe. The stores then expose them to ethylene gas, which quick ripens them and allows them to ripen at your house.

Jgordos

I buy and sell used office furniture and find all sorts of interesting stuff inside old filing cabinets. I once found a thin long brown coloured, looked like a runner bean, really dry but supple thing that had a lovely liquorice smell when I snapped it in half. It took a while to realise that it was a banana.
It had dehydrated inside the cabinet because of the air conditioning in the building and was not the slightest bit mouldy, just kinda shrivelled.
I still have it 5 years later and it still has a nice aroma when bent a little.

MonkNo5

As some have already mentioned, they pick them quite unripe.
Usually they ship them in a big plastic transparent bag in a box. (As i’ve been told) when shipping to europe, they will fill that bag with nitrogen. Doing so slows the ripening process even more, easily giving them over a month time for travel.
When you open the box and the bag in the store, a more natural environment will be there for the banana’s to quickly (relatively) ripe.. and get brown in the end.

regen100

If something has a lifespan of one month, and it takes three weeks to ship, distribute, etc, it only has a week of it’s life left by the time it gets on the store shelves for you to purchase it…

Cuteandhonest

ELI5 How come bananas are harvested in Ecuador, taken to the port, loaded on a ship to the USA, go through customs, make it to a distribution center and then your local supermarket in perfect shape… only to get brown on the short trip from the store to your house (or the couple of days after that)

Read the Story

Show Top Comments

There are some questionable answers here. You dont chill or refrigerate bananas. It can cause an irreparable stop to the ripening process and the banana will just darken and then rot without ever softening. Banana’s are never refrigerated. In fact, greengrocers will often temp the bananas as they arrive to ensure they are not too cold.

Instead, like many have said, they are picked and shipped quite green. Ripening of a banana can take about 1 1/2 to 2 weeks. A lot of that time is spent in shipping. The starting to yellow to starting to brown is only a matter of a few days. We never sprayed them with ethylene to initiate the ripening once in country, it is all a mater of timing. If you have ever seen a banana box, you will note how open they are compared to other fruit boxes. This is all to slow the build up of ethylene, for which bananas create a lot of. Triggering that process intentionally before you sell them is just silly (see edit for correction).

So why do they start to yellow and brown just as you bring them home? Well, good timing on the part of the grocers, but there are a couple other factors you might be in more control over. Storing bananas near other fruit can increase their exposure to ethylene and speed up ripening, so dont keep them in a fruit bowl. Likewise storing in a plastic bag like a produce or shopping bag traps in that gas. Take them out and leave them exposed to air as much as possible.

Edit: u/theinfamousloner has corrected me that gassing is in fact a thing. I knew they went to ripening centers, but was under the impression that was a storage step. Thank you for your insight, and I stand corrected on this.

I will not give in on the refrigeration. They are temperature controlled to 13C, but storage coolers and refrigerators are normally 4-5C. AC != Refrigeration. In Northern Canada, temperature control keeps them warmer than the ambient temperature but we dont say we are cooking them.

Sabetheli

They’re picked and shipped unripe. The stores then expose them to ethylene gas, which quick ripens them and allows them to ripen at your house.

Jgordos

I buy and sell used office furniture and find all sorts of interesting stuff inside old filing cabinets. I once found a thin long brown coloured, looked like a runner bean, really dry but supple thing that had a lovely liquorice smell when I snapped it in half. It took a while to realise that it was a banana.
It had dehydrated inside the cabinet because of the air conditioning in the building and was not the slightest bit mouldy, just kinda shrivelled.
I still have it 5 years later and it still has a nice aroma when bent a little.

MonkNo5

As some have already mentioned, they pick them quite unripe.
Usually they ship them in a big plastic transparent bag in a box. (As i’ve been told) when shipping to europe, they will fill that bag with nitrogen. Doing so slows the ripening process even more, easily giving them over a month time for travel.
When you open the box and the bag in the store, a more natural environment will be there for the banana’s to quickly (relatively) ripe.. and get brown in the end.

regen100

If something has a lifespan of one month, and it takes three weeks to ship, distribute, etc, it only has a week of it’s life left by the time it gets on the store shelves for you to purchase it…

Cuteandhonest

ELI5: different species can’t breed, apart from some exceptions like lions and tigers, or donkeys and horses. What stops species from producing offspring and what’s the biggest species separation that can produce offspring?

Read the Story

Show Top Comments

Picture the information that is given from the mommy tiger and the daddy donkeys like zippers.
Tiger zippers have really big teeth like a snowsuit.
Donkey zippers have really small teeth like those on a delicate piece of clothing.

If you try to zipp the one side of the snowsuit to the other side of the delicate clothes it just won’t go.
If the two zippers were similar enough though – like a horse /donkey or lion / tiger… they may just fit. Not perfectly but they might fit..

gruesome_drewsam

First things first: Species doesn’t exist. It’s an extremely vague term with millions of exceptions. We just use it because it’s *good enough* that we generally know what people mean when they say it. The cases where “species” doesn’t mean anything are sufficiently rare that the only people likely to talk about them regularly already know enough to know the limitations of the word.

The idea that two organisms belong to different species if they can’t reproduce to create fertile offspring was something someone came up with *after* people already started using “species” to mean stuff. It was some dude’s attempt to give “species” a better definition than “Y’know, it’s how cats and dogs are clearly different, don’t think about it too hard”. There are many, many things we class as species that can in fact reproduce. For example, bacteria can exchange DNA in a process called horizontal gene transfer, meaning bacteria can essentially change their species. There are also things called ring species, where you have lots of different populations arranged in a line, and organisms from each population can breed with adjacent populations, but the populations on each end can’t breed with each other cos they’re too distantly related.

There are many things that could prevent two organisms from breeding. The most common incompatibility is reproductive organs. A fish that fertilises eggs by ejecting sperm into the water over a nursery lacks the anatomy necessary to impregnate a mammal, which gestates internally. Plants don’t even produce sperm, so we’re not going to be seeing any chrysanthemum-chicken hybrids any time soon. You also have many cases where organisms can’t recognise the mating dances of other species. This is common in birds. Then you have basic fertilisation incompatibility. For sperms and eggs to fuse, they need to recognise particular features of each other (very similar features to the spike proteins of viruses, in fact, which you may have heard of in the context of Coronavirus). If these molecules don’t match, the cells won’t recognise each other, and the fusion process won’t start. The more distantly related the two organisms, the more likely they will have incompatible recognition systems.

If you have compatible mating rituals, genitals and gametes, you then have to contend with chromosomal differences. Gametes are produced by a process called meiosis. Meiosis can only happen if the cell has an even number of chromosomes, because the chromosomes need to pair up, but it might not do if it’s a hybrid. Eg, if a tiger egg provides 23 chromosomes and a lion sperm only provides 22, when they try to pair up for meiosis, there’s going to be one chromosome from the tiger that has no pair from the lion. This means the liger will be unable to produce gametes. This is where the “fertile offspring” part of that outdated species definition comes in: Ligers aren’t fertile.

The next problem to deal with is missing vital genes. There are many cases where a missing gene is simply lethal. The cell will fertilise correctly, but will die instead of growing into a baby. Since different species have different vital genes, hybrid cells are relatively likely to be missing a vital gene, if the sperm doesn’t provide the ones the egg is looking for. You can also get gene incompatibilities, where genes from the mother and father work in ways that put them into conflict. This again tends to be lethal. Perhaps the most prominent of this case is in body plan genes. If you took tiger genes and put them into a giraffe cell, the cell is now being told to make a tiger and make a giraffe simultaneously. It can’t do both, so it’s likely to just die instead. You only get functional body plans out of very, very closely related species. Lions and tigers are extremely similar in terms of the basic body plan, differing only in places where the cells are capable of creating a blended shape.

Nephisimian

Speciation is when two organisms have diverse enough genetic differences that they can no longer produce viable offspring. (Usually the difference in DNA prevents the spermazoa from reaching or penetrating the egg, or it will not develop past a certain stage from lethal mutations) In cases like mules or ligers, these are not considered viable offspring because they cannot reproduce (most are sterile). Sometimes scientists got a little too biased in competition for taxonomy, and we ended up with separate species names for creatures that do produce viable offspring like wolves and dogs. Part of the problem too is that we keep hauling species around that normally wouldn’t interact and mate in the wild (like inbreeding the f out of lions and tigers and sticking all the derpy tigers and lions together in one cage to make ligers for roadside zoos). Most crossbreeds do not come from some natural interaction but human meddling. In the wilds, these animals typically would avoid each other and not choose to mate (the only exception I can think of are some wild herds of horses and donkeys escaped from domestic herds have stuck together and occasionally make mules, but that’s still on us humans I think)

drkpnthr

We consider two animals separate species, if they cannot produce fertile offspring.

Therefore a lion and a tiger are different species, because while they can produce offspring, ligers are infertile. Same with zonkeys, mules and so on.

A lion and an eagle cannot produce offspring, and so they are also separate species.

If two groups of the same animals stop interbreeding, they are gonna evolve separately, and if that goes on long enough, eventually they are going to lose the ability to interbreed as it is no longer an evolutionary advantage.

Dogs are pretty unique in the separation with the species. A chihuahua can produce fertile offspring with a Grand Danoise,( though it will require some sort of stepladder) even though they look like they might be different species.

Felix4200

There are good answers, but everyone seems to be forgetting about prezygotic mechanisms. These include things like temporal (time) separation, such as if salmon spawn in September but trout spawn in January. They might be able to reproduce, but they are never together at the right time. Another big one is behavioral isolation, like mating rituals that are often complex. If bird A does mating dance A and bird B does mating dance B, they may not be able to understand that the other is trying to breed.

Together, all of these make up more reproduction barriers than postzygotic isolation mechanisms, which are what everyone else is talking about.

Lil_Bits

ELI5: Why does the moon appear bigger when closer to the horizon, when surely it’s closer to us when directly above us?

Read the Story

Show Top Comments

At the horizon, you have something to compare the size of the moon to and it looks larger, high in the sky you have nothing to compare to and it looks smaller.

A simple way to have something constant to compare to is to extend your arm and hold your thumb below the moon. If you do that when it is close to the horizon and high in the sky it will look the same size compared to your thumb

You are correct that the moon will be large when it is high in the sky compared to at the horizon but the difference is not noticeable with just your eyes.

The moon is on average 384,400km from earth. The radius of the earth is 6,371km so on the square the distance will increase to sqrt((384400+6371)^2+6371^2)=390822km

The angular size of the moon is it’s diameter divided by the distance so we can calculate the change by just looking at the distance.

390822/384400 =1.0167 that is an increase in diameter of 1.6%, you will not notice that difference with just your eyes

Target880

Teacher here. For lots of people, if you extend your arm all the way, your smallest finger nail will just cover the moon. No matter where the moon is on the horizon.

CapeAnnimal

It looks bigger close to the horizon mainly because there are usually other objects in the backdrop which the eye can compare it with. I.e., it looks larger than that mountain, or that building etc. whereas up in the sky it looks smaller because it’s there alone on its own. In other words, this is an optical illusion. You can check this easily – the Moon is always about as wide as a thumb on your outstretched arm, regardless of where it is on the sky.

nmxt

Moon doesnt get bigger or smaller, our brains perceive geometry in relation to object surrounding it or relative to it, there is nothing in the sky so it looks smaller when compared to near horizon when it is in reference to other object which our brains are adapted to.

GrandmaGotGuns

Because human vision did not develop with moon gazing or accuracy in mind. Our eyes and brains are consistently bamboozled by reality.

RIP_Sinners

ELI5: If the body raises its temperature to kill bacteria, why is it bad to take a hot shower when you have a fever?

Read the Story

Show Top Comments

It’s not bad to take a hot shower during a fever, it’s just uncomfortable. At the same time, taking a cold shower is not recommended because as your skin (periphery) cools down due to cold water, the body tries to compensate by increasing your core (inside) temperature which we don’t want in a patient already suffering from fever. Hence lukewarm water is the best for this situation.

Now there are chemical compounds called pyrogens (molecules that cause fever). Usually the process goes like this : bacteria/virus/microorganisms enter our body, body/immune system detects certain proteins and chemical structures on them (like the cell wall,etc), sends a signal to the brain, brain is like oops need to kill that, need more ammo, so they release some other substances/chemical compounds which further activates the immune system.
Now both the microorganisms and the brain/immune system’s compounds are what we call pyrogens.

So exogenous ( from outside) pyrogens like bacteria give rise to endogenous (from inside the body) pyrogens like the immune system cells which increases the body temperature level just the way you adjust the thermostat to a higher setting.

Hope this helps. Feel free to ask any questions 🙂

Edit : Thanks for all the upvotes and awards, science is great, I love it

awkguy13

It depends what you mean by raises its temperature to kill bacteria.

If you mean a raised body temp is high enough to kill the bacteria then no, that’s not what it is doing.

The raise in body temperature is to give a boost to the immune system which works better at a higher than normal body temp. and it is this which then kills the bacteria. So the killing of bacteria with a raised body temp. is a more indirect method of killing bacteria.

However, I can’t remember ever being told by a doctor to not take a hot shower when I have been sick. In fact, the opposite is true. The old remedy of cold baths or showers to treat a fever is not recommended.

The_Thunder_Child

For the last 20+ years when I have had a bad fever I always have a hot shower. I sit either on a plastic stool or on the floor resting my head on the cold tiles. This has helped me sleep and break the fever much faster. It almost always gets rid of the muscle aches, allowing me to sleep. Resting my head on the tiles is like a cold pack keeping my head cool while my body warms.

It works for me and I haven’t had any negative side effects that I’m aware of except a guilty conscious for using so much water.

Vastant

Your immune system works better at higher temperatures, but nothing else in your body does. It’s why when you overheat you feel terrible.

I don’t know how much showers effect your body temp, I just feel like my skin is extra sensitive during a fever so I don’t like to be in showers for long.

jt_totheflipping_o

You can get too hot and pass out.

A former colleague of a friend died because he was drunk, got a super hot shower and passed out. He was found dead and half cooked the next day…

Ok now back to the topic, when you have a fever that thing will kill bacteria effectively up to 38C, at 39C it kills more bacteria but your brain start malfunctioning, at 40C your brain may get permanent damage.
Because having a fever puts the body on the border line, you must be careful not shift your temperature out of limit. Reducing fever too much will help the infection and increasing it may kill you. Sudden temperature change up or down may shock your circulatory system and make you pass out.

druppolo

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?

Read the Story

Show Top Comments

There is a lot of interesting stuff that the human eye can’t see. A billowing nebula of hydrogen and helium gas slowly collapsing to form a new star is really cool!

But, it would be too dim for the human eye to see so it would just be black. So we up the brightness. But also the human eye can’t see sparse gas against vacuum, and it can’t see the frequencies of light required to distinguish between hydrogen and helium. So we shift the frequency into something in visible light, effectively picking a color to represent each gas.

At the end you have an image that doesn’t really represent what the naked eye could view. But it would also be pretty silly to say “Check out this image from my infrared camera!” and hand you a blank sheet of paper because you can’t see infrared light.

Phage0070

Imagine I am playing a beautiful song, but the notes are so high that you cannot hear a thing.

So… I lower the music by a few octaves. Now you can hear and appreciate it. It is the same beauty but in a range you can experience.

We essentially change the octaves of light, allowing you to see what would otherwise be invisible, but maintaining all the original beauty.

Knave7575

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.

ReallyQuiteConfused

Kinda like why an X-ray of your bone is informative to look at, even though no human eyes can see them naturally. Not all “lights” are visible to human eyes, yet they reveal a great deal of structures that are interesting to a human.

evanthebouncy

Because it’s actually there, you just can’t see it. They are trying to show what it would look like if you could see it lol

narwaffles

ELI5: What does the concept of entropy mean?

Read the Story

Show Top Comments

You can set off a stick of dynamite. But you can’t put it back together again. The amount of disorder in the universe always increases.

Well, technically you could take all of the gasses etc produced in the explosion, refine them, process them, and after a lot of work end up with a stick of dynamite again. But by introducing a lot of order to that random swirl of gasses, you will introduce even more disorder in the rest of the universe – e.g. you’re burning stuff to generate electricity to power the machines, you likely have used pure chemicals as part of your reactions and now you have a load of mixed chemical waste, etc. The amount of disorder in the universe always increases.

The “disorder” in this example is technically called “entropy”.

someone76543

Entropy is NOT disorder, it’s often called that because entropy LEADS to disorder but they are not the same thing. Entropy is simply a statistic that arises because energy is more likely to spread out than to concentrate into a specific state.

For example, imagine you have 100 cups and a pitcher full of water. Now imagine you put drops of that water into the cups at random. What are the chances that *all* of the water ends up in 1 or 2 cups? It’s very slim, definitely possible, but very unlikely, what is more likely is that the water gets spread out between the cups evenly (relatively speaking of course, some cups will have more water than others). Each different way of filling the cups, for example, all the water in 1 cup, the water spread perfectly evenly between the cups, and anything in between, is called a microstate. Some microstates are more likely to occur than others (such as the water spread out evenly is more likely than the water in one cup).

Entropy is essentially just a way to measure which state is more likely. If a state is more likely its said to have high entropy. And that’s why entropy is said to always increase in a closed system, because the system will always evolve to a state that’s more likely.

Now in physics usually when people talk about enteopy they’re talking about energy. So instead of the water used in the previous analogy, it’s energy that gets distributed across the system, and instead of cups, it’s atoms and molecules and other particles and waves where the energy gets distributed in. Now one thing to remember is that there’s nothing in physics that says entropy HAS to increase, it’s just that entropy is extremely (and I can’t stress the extremely enough) likely to increase.

Edit: One example my professor gave that really resonated with me during the talk of entropy is that there is absolutely nothing in physics that is stopping all the air in the room you’re in from suddenly moving to one side and suffocating everyone in the other side. The only thing that keeps the air from doing that is probability. Its just incredibly unlikely that all the trillions of air molecules which have velocities that are more or less random would all randomly start to move in the same direction to the other side of the room, it’s much more likely that they all spread out relatively evenly in the room. That is entropy.

Wickedsymphony1717

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.

ToxiClay

One way to think about entropy is from statistical point of view. This basically says that if there are more ways of arranging things which result in the same outcome, the entropy is higher. So for example you have 10 balls, 5 identical black and 5 identical white. You arrange them in a row. There are exactly 2 ways to arrange them in an alternating way. Also only 2 ways of having 5 of the same color touching. But let’s say I want 5 black balls always grouped and the white balls wherever. There are exactly 5 ways to arrange that, therefore the state of “5 black balls touching” has higher entropy than “balls alternating”. And so on.

Another example is 2 die system. When you roll them, you can achieve combined result of 7 in many ways, while for results of 2 and 12 there is only one way for each of them.

In a physical world, imagine a perfect crystal. So the atoms are ideally arranged where they should be. There is only 1 way of doing that therefore the lowest entropy. Nature does not like low entropy, so in real world this is hard or impossible to achieve, depending on the scale. Therefore, there are always some defects to that structure which introduce some entropy, which in turn lowers the overall energy of the system. What I am trying to describe here is more or less thermodynamic potential, called Gibbs free energy if you want more reading.

plandeka

All information in the universe becoming less orderly over time, carbon reacts, atoms decay etc , in early universe was all the same type of matter and now… Complex. Very difficult if not impossible to put it back together the way it was

Possible_Border_4111