ELI5: The difference between a router, switch, hub, a bridge and a modem

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Edit: Network traffic broken into packets, which you can think of like a letter in an envelope. The letter is your data (like a Google query) and the envelope has a ‘to’ and ‘from’ line to help know how to forward it on. All those devices have different techniques for knowing how and where to forward an envelope onto, once they get it.

**Hub:** Make a copy of a letter and give it to every one of your neighbors with a t-shirt cannon, whether you meant to give it to them or not

**Switch:** Make a copy of your letter and use a map to drive it to a specific neighbor

**Bridge:** When you want to give a letter to Billy the next neighborhood over, so you give it to his brother who lives right in-between the two neighborhoods

**Router:** Send your letter to the post office, and they’ll send it to your grandma by forwarding it to her post office and then driving it to her house using a map

**Gateway:** The post office in your neighborhood

**Modem:** Send your letter to the post office by saying it over the phone to a postal worker, where they type and print it off and forward it on


**Router:** Directs network traffic based on destination addresses and preset rules. These are usually situated between gateways/modems and switches.

**Switch:** These devices simply connect multiple devices together, sort of like a splitter. Although managed switches can do quite a bit more, such as create VLAN’s, which can help organize and protect network traffic.

**Gateway:** These are often times mistakenly referred to as modems or routers. They are devices that connect a private network to the internet. However they can also just be a device that connects one private network to a larger private network. A residential gateway is likely the device you have at home that connects you to the internet.

**Hub:** These are essentially the dumb versions of switches. They function like repeaters, so when a computer talks on the network, the hub will broadcast that message to every port on the hub. If the message reaches the target PC, then that PC will do the same. This is a very inefficient method, which is why hubs are obsolete. Switches contain memory, so they remember which PC is on which port, and will direct messages to the correct port without having to constantly broadcast to all ports.

**Bridge:** A network bridge joins two networks together. Such as one PC sharing the network connection with other PC’s. Things like transparent bridges create a seamless link, these are often times used by security devices such as firewalls. They will inspect network traffic and block anything that violates the rules.

**Modem:** A device that converts network traffic into a format that can be used on the media that connects you to the internet; Whether that be fiber, coaxial cable, 3G/4G wireless signals, or a copper phone line.


Edit: What you have at home, which is often times referred to as a ‘Wireless router’, or just a ‘router’, is actually a combination of a lot of these devices. They are indeed routers, but also switches, wireless access points, and sometimes modems/gateways. If it contains a modem, it can be referred to as a residential gateway, if it doesn’t, then it’s a wireless router. Small businesses will often use these same devices, but larger businesses will use enterprise class hardware, where these devices are separate and usually mounted in an equipment rack.


Hub: Everybody yells in your house whenever they want something, it sucks, plus now everyone knows everyone else’s business. Nobody yells anymore, hubs are bad.

Switch: If you want to yell at someone in your house, you go to them and yell at them, nobody else hears it. To yell back at you, they come to you. This is awesome but still local and indoors.

Router: You want to yell at your neighbor but don’t care where he is, these take the noise and pass it around all the way to his ears.

Bridge: It’s like that door that connects two rooms in a hotel so the family can yell at each other.

Modem: It converts the yelling into electricity so your yelling can travel far and reach your neighbor (you don’t know/care where he is, see router above)


Your ELI5 answer:

Modem = where internet comes from

Router = routes internet to devices from modem, usually creates wi-fi

Switch/hub = same as router just more dumb/less features

Bridge = Used to cross a body of water, or to connect two connections into one.


edit: a lot of people don’t understand what ELI5 means


Router = A call center phone system where everyone can only be reached through an extension from the main line.

Hub= a friggin mega phone. Literally.. Imagine every phone call received by a call center just get blasted out on the entire floor.

Switches=Everyone gets his own direct phone line in a call center.

Bridge=Two completely different physical call center locations using the same main phone line.

Modem=Modem is more like a translator. It’s a magical translation machine that can turn all the calls from Japanese speakers into English.

That’s the best ELI5 I can think of.


ELI5 Why does your metabolism get worse as you grow older? When is your metabolism at its best and when does it usually slow down?

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People already hit on the main reasons which are decreased activity and increased food consumption, but I have a feeling that’s not really what you were asking for.

The main reason many teenagers are notorious for being able to eat a ton of food without gaining weight is that their body is rapidly growing. All the processes required to fuse growth plates, increase bone density, and develop the brain use a lot of energy. At around age 25-30, this development mostly stops and our body reverses to break-down processes rather than build-up processes. (Muscle is an exception to this if you do strength training)

Another thing to take into account is that as we do things, our bodies acclimate to it. For example, someone who begins running 1 mile a day will burn many more calories the first time they run it than the 100th time they run it because their body will naturally find the path of greatest efficiency. Someone who’s young will likely be doing many different tasks and exercises for the first time, so they tend to burn more calories until they reach that acclimation.

Edit: This in no way is me saying that exercise is bad just because you acclimate to it. It’s just an observation on a common issue that leads to a plateau, which almost every person who works out will experience at one point. The general solution to this, for anyone of any age, is to try to have a varied exercise routine. Instead of doing the same workouts every week change your pace, the day you’re working different muscle groups, how much of your max weight you lift with, the type of cardio you do (running vs jump rope vs HIIT all make your body do different things).

Source: Biochemistry degree and my own experiences with exercise


Edit: Not a doctor, shhhshhh…

Your metabolism does not slow down with age, or at least not like you probably think. The main culprit is changing exercise and nutrition habits. Of course there are the additional costs of growing for kids, which is why a 16 year old will have a greater BMR (base metabolic rate) than a 30 year old of the same height and weight. BMR is the energy you burn by basically just existing, e.g. lying in bed all day.

While most of us were probably more active when we were younger – think of playing outside, PE class and so on – adults are mostly sedentary. We drive to work, sit in an office the whole day and sit at home afterwards. This is why younger people seem to have a larger TDEE (total daily energy expenditure). TDEE is your BMR plus energy burned from moving about and exercise.

Humans are really bad at noticing subtle changes over time, which is why most of us don’t see that we are moving less and often eat more as we get older. Therefore the resulting weight gain is attributed to the mysterious slowing metabolism. While there are specific health problems or other factors that lead to weight gain, they mostly work by increasing appetite or making you lethargic and therefore use less energy. But these are often minor contributors compared to nutrition and exercise habits.


“Metabolism” is treated as this mysterious force that controls our weight gain. In reality, it’s essentially just the sum total of all the energy (calories) that your body burns in a day in order to keep operating/living.

The reason your ‘metabolism’ slows down as you age is simple: You get lazier, slower and more immobile, so you burn less energy (calories). The reduced activity also tends to lead to less muscle mass (for men, a decrease in testosterone as you age will lead to a reduction in muscle mass), which again leads to less energy use.

That’s it. There’s some subtle nuance to it that’s not discussed here (the reduction is not *all* explained by less activity, but that’s the lion’s share of it), but that’s the the broad strokes of it. You do less as you get older, which means your body is using less energy – ergo, your ‘metabolism’ (or ‘total energy/calories burned’) is reduced. It’s better to think of metabolism as simply a unit of measurement – that’ll help dispel most of the false notions surrounding metabolism.


BMR will reduce linearly with age, but that’s almost solely due to a reduction in muscle mass. As for “metabolism” decrease with age, the contributing factors to an increased weight gain given the same nutritional patterns are:

1. Less muscle mass
2. Lowered activity levels

For older individuals that hold onto a decent amount of muscle mass and stay fit to a similar degree, the changes will not be nearly as noticeable. For an individual that undergoes TRT and is able to hold onto the same amount of muscle mass and activity levels, the changes would be insignificant at best.


Short answer: it doesn’t. People tend to get less active as they grow older, but still eat the same amount of food and they get fatter.

Longer answer: we eat stuff every day to fuel our bodies. The total amount of food we need to eat to exist (exluding moving/exercise) is called the Base Metabollic Rate or BMR. Muscle requires more energy to maintain than fat. A 70kg man with a lot of muscle will have a higher BMR than a 70kg man with mostly fat.

Young people tend to move more, play more sports and are more active in general. As a result, they tend to have more muscle mass than older people of a similar weight and height. Also, because they move more, they use more energy, so they need to eat more to gain weight.

The result is that older people with little muscle need less energy to exist, plus move less, so need less energy to do all their activities outside of just existing. Often they still eat the same amount of food or more as when they were young, so they get fat.

Not so ELI5 addendum: the difference in BMR between two individuals that are equal in body composition (height, weight, bf%), but vary largely by age is indistinguishable from the statistical difference in BMR between equally aged individuals.


ELI5: How do spiders create brilliant webs through the night but by mid morning they disappear with no trace? Have they fallen prey to larger animals?

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Spiders eat their own webs, digest them and re-spin them later.
They do this because their webs become less sticky over time.
They contain/take a lot of protein, so just leaving them would likely result in the spider starving to death.
So they eat it, and squirt it out all sticky again.


I have two Orb Weavers that live in my front yard. Both make huge webs that go from the ground to the branches of my trees. Then they sit in the middle and wait for insects. Every morning they will take their webs down and go fuck off for the day. Then come night they remake the web. I have a timelapse i made of one. Shows him creating the web and then taking it down. I will post link in a while.

EDIT: I have to get my old laptop guys! I will try my best to get it done today. I just woke up to a full inbox, and a message from reddit saying they noticed suspicious activity on my account. I will probably just post it on a subreddit instead of linking it here.


Spiders are true master builders. They are little engineering geniuses with the webs they build. This is hard to explain but I once lived at a house with one of those tall lamp posts on the lawn next to my drive way. A spider had constructed a web below the lamp. It was a brilliant place to put it because the light would attract god only knows how many insects to it. The fact that the spider had somehow figured this out was the first brilliant thing it did. The second was how this web was constructed. The lamp was at the edge of the lawn so there was nothing near it. There was a hedge of arborvitaes across on the other side of the driveway. This spider knew that he had to find something to attach one side of the web to otherwise it would not work. The web would have been really small and effectively useless. What this spider did truly astonished me. It somehow spun a single spool of web from the lamp clear across the driveway to the other side where it was attached to a branch of one of the arborvitaes. It was a distance of about 10 feet. This created a kind of “top beam” from which he was able to construct a triangle shaped web. One side was mounted against the lamp while the other was strewn across this “top beam” created from stringing it to the arborvitae. Unbelievable. I really hope I’m explaining this right and that someone can appreciate the skill this spider showed. I know they’re creepy and all but you have to admire their skills. I know I do.


If you’re referring to the *spider* disappearing, as opposed to the web, most of the time they haven’t disappeared at all. They’re just hiding where you can’t see them, waiting for their next meal to get caught in the web.


I think OP is asking about why you’ll often find empty webs.

Often the spider is just hiding up in a corner of the web, but yes, they do sometimes get eaten by other animals. Birds, fish, bats, lizards, wasps, and many other things like to eat spiders. Some spiders also eat other spiders.

The spider may also have just died or have fallen from its web.


ELI5: why do most DVD’s and Blu Rays have the action and background noise much louder than the actor’s voices?

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Dvd’s and Blu-rays have the audio mastered in surround sound. Voices are typically sent through the center channel, while background noises and action come through all of the other speakers (typically, 4).

When played through a stereo, headphones, or a TV, all of those channels of audio are played through only 2 speakers.

Depending on how the engineers master the audio, and how your device decodes the signal, you sometimes wind up with those 4 channels of other noise overpowering the one channel of voice.


Dear OP what you’re experiencing is dynamic range, or the difference between the loudest sounds, and the softest sounds, in a recording. Modern pop music tends to have a low dynamic range, where the volume of the music doesn’t change very much, and the difference between the loudest part of a song, and the quietest part, is not that high.

Movies on the other hand need to have dynamic headroom (room to get LOUD) so that explosions and sound effects retain their impact. Movie soundtracks have a very high dynamic range, and so you have to turn the volume up much higher, to make dialogue sound loud enough, but then when the explosions come, your drink vibrates off the table.

Most stereos and DVD/Bluray players have a setting to change the dynamic compression from off, low, medium, or high. The higher you set this, the less the difference between loud and quiet is, which makes it useful for listening to a movie more quietly, and makes the audio more intelligible without having to turn the volume up higher.


Movies tend to be mastered for cinemas, with a good speaker setup, a quiet viewing experience and the expectation to get deafeningly loud occasionally. This is not the typical TV-watching experience, but often, movie releases will not give you a more TV-friendly master.


I will watch films with subtitles on sometimes for this reason – I also have auditory processing difficulties that are a factor.


Are you using 5.1? Maybe your middle channel is set too low. When i watch movies I have to crank up the center speaker to compensate for the big left and rights i have. Sometimes I disable it entirely.


ELI5: How can Gorillas sustain all that muscle mass with most of their diet coming from Vegetation? Do they really get enough protein and fiber from just that?

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There are a couple things at play here.

First, gorillas can fully digest cellulose, and humans cannot. That’s all their fiber right there. On top of this, they have a really long digestive tract that can turn cellulose into omega-3 fatty acids, which isn’t so important for muscle growth as it is for brain health, but it’s an important thing to note anyway.

Second, the way gorilla society tends to work is that the biggest, strongest gorilla is the alpha (meaning the one who mates). This has led to a very long history of genetic predisposition to being big and strong. So what very little exercise they do get is very useful, and this is a very important characteristic that determines their mass. Anthropologists call this “robusticity”. You’ll find this characteristic in some herbivores like horses, buffalo, oxen, and elephants, to name a few. They’re big because that’s how they evolved.

Last, gorillas aren’t vegetarians. They eat meat whenever they can, and a whole lot of fruit as well. Recent studies of wild gorilla scat have shown they like to eat monkeys, antelopes, and slow lorises.


They have to eat insane amounts of food to keep that up. The big strong adult males eat 16-18kg of veggies (and some east some tiny bits of ants/termites) a day. To put that in perspective, in human scale that would mean an adult human male eating 8-9kg of food per day, every day (1.5-2kg is normal per day). So short answer, they do it by eating ridiculous amounts and spend most of their day sourcing food with naps in between.


Gorillas are mostly vegetarian, but not completely. They also eat insects regularly and will occasionally eat meat, though they eat meat less than the other apes.

Having evolved to eat mostly plants they have enzyme production and gut bacteria that are capable of breaking down plant matter to extract or synthesize what they need, this includes proteins. Humans do not have this ability which is why we are omnivores.

Also, fiber is the dietary term for indigestible plant matter. It is passed through the system as waste and is a bulking agent that helps move other waste product through the digestive system. Gorillas get plenty of fiber, I am not sure why they would not get enough.


Plants can be similar to meat in terms of the amount of food energy coming from protein. 100 calories worth of lettuce (which is like 2 heads of lettuce) has 10 grams of protein. 100 calories of steak has 9 grams of protein. 100 calories of chicken breast has 19 grams of protein. Gorillas also eat a lot.


Something others haven’t noted, though not directly related to gorillas, is that typical first world diets, particularly in the US, contain far more protein than even a body builder needs. The average adult needs around 50-60 grams of protein per day, but in the US the average adult eats something like 90 grams (as of a few years ago. It’s probably even higher now with the recent trend of adding protein to everything). Fruits and vegetables do contain protein too, and items like beans, peas, and nuts contain considerable amounts.


ELI5: Microplastics are present in 94% of tap water in the United States. How and at what threshold do they cause harm?

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We do not yet know the effects of microplastics on living organisms. This is still a very new discovery and the research is still in its early stages. There are several people claiming they cause things like obesity, diabetes or reproductive harm, but no definitive link has been determined. Microplastics are small enough that they can pass through most barriers in our body and go directly into the blood stream. They’ve also been found to pass through the placenta into fetuses.

The only way to remove microplastics from water is through carbon filters or reverse osmosis purification. You can still be exposed to them through food though, but they’re most prevalent in drinking water.


There is no study that I know of that shows microplastics is harmful to large animals – certainly not in the quantities present in tap water. You have much more pressing environmental problems to worry about.


Note large plastic refuse can certainly harm animals e.g by choking them or blocking intestinal tracks – and I could see microplastic doing something similar to very small animals but I have yet to see such a study -if anyone has found one I would be interested to see it.


Do we know how to clean them out of water is there a filter available? Are we talking PPB in water ?


One of the problems is that those particles absorb environmental toxics, such as POP pollutants. This subject is not very studied yet but these toxins build up in us until there’s more and more inside out bodies. They are stored for example in fat tissues, liver etc. Many toxins cause fertility issues and many kinds of sicknesses in animals, but usually those toxins come from different sources than microplastics. This could mean that if we continue to gain more and more plastic inside us that have absorbed toxic stuff, we could have fertility issues, lung diseases etc because of them.


I’m reminded of Ren (of Ren and Stimpy game) saying “THAT’S JUST IT! We don’t. Know. MAYBE something bad? MAYBE something good?”


ELI5: How do actors/actress do sex scenes in tv/film?

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Question has been answered and the comments are mostly anecdotes about that one scene in that one movie and this thing I heard. Sorry guys, topic is getting locked.


I’ve posted this before:

I work in film, so I can shed some light on this actually happens. When a script calls for nudity or simulated sex, there is an additional contractual discussion about what can and cannot be shown, the way in which the scene will be filmed, and many other aspects (they basically go through everything line by line, shot by shot, which is why you want a good agent and lawyer). Unlike the stories you may hear about the seventies, or some indie films, Hollywood is very strict about these scenes, and there are no surprises. A lot of the guidelines are regulated by the guilds, such as having bathrobes standing by, etc.

Keep in mind that you are not going to be filming anything real, because you couldn’t show it anyway if you wanted to get an R rating or below. Everything you can get away with at the R level or below can be faked. NC-17 (formerly X rating) is the kiss of death, because most theaters refuse to screen NC-17 films. That is why some films will choose to be unrated, or get into a fight with the MPAA like Blue Valentine or more recently Charlie Countryman.

If the scene is showing a lot, like Game of Thrones, the actors are probably naked, and the man will wear a small skin colored sock. The set is designated a closed set while filming, which restricts the set to only essential personnel. That would include the actors, director, cinematographer, assistant director, assistant cameras (possibly only the 1st AC), hair/make-up, and wardrobe. A few other people may be on set, and then others may be watching from the monitor depending on the scene, like the production designer.

The Assistant Director (AD) team would lock the set up, despite the grips trying to get a peek. In between every take, the wardrobe team rushes onto the set with bathrobes for the actors. Then for the actual act they are touching naked on screen, and it is very awkward but most actors will tell you it is not romantic in the slightest. I seriously doubt many people would enjoy being naked in front of a dozen people, starting and stopping every few minutes for a few hours while people run out periodically to adjust a light. Every situation is different and I am sure some actors are comfortable crossing the lines of professionalism, but this is how the vast majority of major films handle these scenes.

A few funny anecdotes:

I cannot remember which actor it was, but a male actor was quoted telling the actress before a sex scene the following, “I’m sorry if I do, and I’m sorry if I don’t.”

My mentor also told me about the day she was walking across a backlot and a grip came running out of a sound stage in his boxer shorts. Apparently, the actress said, if I have to take my pants off then everyone watching does too. So the entire crew removed their pants to make her more comfortable while filming.


Intimacy coordinators are becoming much more popular on sets! HBO has them for any of their shows that have sex scenes.

The coordinators job is a mix between a counselor and a stunt coordinator – they chat with the actors and directors and set firm boundaries of what each person is comfortable filming. Then they plan out the scene very much like you would plan a fight scene – where the hands are going, what movements will happen etc.

Once filming, the coordinator stays to make sure that no boundaries get crossed, that the actors are happy and thus reducing the chance of an accusation of sexual assault.

Basically they look after everyone working on a sex scene and keep them happy and safe! Most of them come from dance and stunt coordinating backgrounds.


They let prospective actors know about the nude scene up front, so the actor can refuse the part if they’re not comfortable.

They clear the room of everyone who doesn’t absolutely need to be there. It may be only the director and the camera operator, once they’ve got the lights and so on set up.

Careful placement of bedclothes (sheets).

Instead of showing you long single takes, they edit to show lots of short cuts that look suggestive but aren’t. Sort of like they do for fight scenes.

They focus on things other than crotches and butts… hands, arms, necks, legs, feet. Again, making it look suggestive without being X-rated.

They can add sound later, if needed.

They can use flesh-shaded thongs and CGI to make you think you’re seeing something that you’re not.

If it’s a foreign film (not a U.S. film) the actors and the audience may accept fully-nude scenes. In the U.S. we can kill dozens of people with guns or let zombies rip them apart and splatter blood and guts everywhere, but crotch shots give people the vapors.


Genital guards — cloth or plastic, sometimes even menstrual pads — are attached to the woman with latex glue so she can be seen from different angles without showing off more than she wants to. Men wear modesty bags — a sack with a drawstring, basically. And there is rarely any chance of accidental sex because when someone’s acting under the lights in front of 20 people for seven hours, arousal is rarely an option.


ELI5: How do ”350 millions trees planted each year” actually work?

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Hey, Canadian tree planter here. Canada actually has similar rules with planting 2 trees for every 1 cut down. Reforestation companies hire large amount of people to work in remote areas to plant trees. An average camp size is about 45 planters not including staff and cooks. An average planter can plant about 2000 trees a day but really good ones can do more. In just one summer/ spring season Canada plants millions of trees. It takes a lot of work to get these camps up and running but once everyone knows how to plant and is serious about making money then trees really start to get planted quickly. Not sure how Sweden does their reforestation but I would imagine similar to Canada.

Now that I think about it I want to plant some trees in Sweden.


I planted over 100k trees during my summer of tree planting. You can plant a tree every 2 seconds if you are good. Some people can do it while pretty much running.


I wish someone would ever take into account that you can’t just stick a tree sapling in the ground and walk away, and expect it to live. “Ethopia planted 350 million trees in one day!” isn’t as impressive when 90% of them die within the year due to to not being managed.

It gives people a false and dangerous sense of accomplishment.


I know Georgia Pacific used to brag in commercials of planting an insane number of seedlings.


To also follow up on this, why are pine trees (or other softwood) chosen to replant vs leafy trees (hardwood) and is there an advantage to one over the other?


ELI5: If a prediction of a recession causes the market to crash, can it be said that the prediction itself is part of the cause of the recession? Like a self-fulfilling prophecy?

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The prediction is a sort of self fulfilling prophecy. However a prediction of a recession will not do much unless all the analysts in the market also make the same prediction. In addition people will be looking for some sort of trigger in addition to having predicted the recession. So if there is some sort of trigger and nobody predicts a recession then there will not be one yet. However if at some later point you get the same trigger but the majority of the market does predict that the recession is close it will trigger it and cause a recession.


There is a theory that when it comes to large scale human behavior as soon as you start to measure something, the measurement loses some of its value. You want to measure how well your business is doing? Measure quarterly profit and instantly the company will start to do weird shit to boost quarterly figures in the short term.

However just because measurements corrupt things doesn’t mean that they are useless. Everyone has been eyeing the market thinking that it is behaving oddly. Valuations on assets are sky high, unemployment is low, yet inflation is low and wages are not rising. People have been watching these bond yield numbers for a year now seeing them flashing danger signs and this is just the straw that broke the camel’s back in terms of convincing people there is a real challenge here.

The fundamentals of the market are fucked up right now.


The man who sold very good hot dogs

There was once a man who lived by the side of the road and sold hot dogs. He was hard of hearing so he had no radio – he had trouble with his eyes, so he read no newspapers and of course he didn’t look at television. But he sold very good hot dogs. He put up signs on the highway telling everyone how good they were, he stood on the side of the road and cried out to all that past ‘buy a hot dog, they are the best in town’.

And people bought his hot dogs and he increased his meat and bun orders. He bought a bigger stove to take care of all the extra business. He finally got his son to come and help him out with his business.

But then something happened, his son who had been well educated said . . . ‘ Father, haven’t you been listening to the radio or reading the newspapers or watching television? There’s a big recession happening right now. The current business situation is terrible in this country – we have problems with unemployment, high living costs, strikes, pollution, the influence of minorities and majorities, the rich, the poor, drugs, alcohol, capitalism and communism ‘.

Where upon his father thought, ‘ well my son’s been well educated, he reads the papers, listens to the radio and watches television, so he ought to know ‘.

So his father cut down on his meat and bun orders, took down all his advertising signs and no longer bothered to stand by the side of the road to promote and sell his hot dogs, . . . . and his hot dog sales fell almost overnight.


If it were that shallow, yes. But there is a ton of real data, visible to all investors, that goes into that prediction. So in reality it is the actual data about economic performance that leads to the recession.


The way you phrased the question, “if prediction *causes* a market recession, is the prediction part of the cause?” Yes. Yes it is. By definition.

Instead, “do predictions cause market crashes?” No, probably not. People make predictions every day. It probably balances-out on average.


ELI5: Why do people shudder/twitch occasionally when falling asleep?

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These shudders and twitches are called “hypnic jerks.”

Science doesn’t really know precisely why they happen, but a couple competing ideas exist.

* One holds that our brains misinterpret a drop in blood pressure and relaxation of the muscles as a sign that we’re in trouble, that we’re dying, so it makes our muscles jump and wakes us up so that we can correct whatever the problem might be.
* The other popular idea relies on the same misinterpretation, but attributes it to a period in history when early humans slept in trees, saying that these signals meant we were about to fall out of our tree, and woke us up so we could catch ourselves.


Ooh! I know the answer to this! I saw a sleep researcher give a talk and this was a question asked at the end of the event. His answer: When you are falling asleep, the part of your brain that does the thinking starts to log off. At the same time, the part of your brain that controls voluntary muscles switches to “off.” The reason your brain switches off your muscle control is so you don’t act out when dreaming.

The “jump” you feel happens when the two parts of the brain aren’t in sync with each other. The thinking part of the brain hasn’t quite logged off yet, but the muscle control has been shut down. Because the thinking part can’t register any sensations that tell it where the body is in space, it freaks out. The thinking part of the brain quickly “wakes up” the motor part by making a big movement in order to find something – anything – to give it some bearing.

As I understand it, sleepwalking is the condition of the thinking brain being turned off but the motor control is not paralyzed and so is fully functional. Sleep paralysis is the opposite – the thinking brain is wide awake but the muscles aren’t operational yet.

Fun fact, when you sleep, the “thinking” part of your brain “turns off” your ability to think logically. That’s why weird things can happen in dreams and you just go with it.


Beside the scientific explanation, I’ve realized I often twitch when I have my lucid dreams which mostly involve falling down random places, like a stair, waterfall, a tree etc, and my left leg would twitch lol