ELI5: Why do small animals move in quick twitchy movements?
Couple of different answers to this. This is a bit long, but it should help. It mostly has to do with avoiding predators and not being eaten. Consider the Rabbit - their movements are either big and strong, fast hops and leaps. Or when are still, only their faces, where their sense organs are, tend to move around quickly, to scan the area and make sure that nothing of danger is around them.
As to why some motions are larger and stronger than others, you have to go into a bit of muscle biology, a bit advanced for a 5 year old...
Animal muscle fibers are catagorized in two types - Red and White Muscle Fibers. These types are based off of the amount of Glycogen (White) and Myoglobin (Red) that is found in the individual muscle cells. These fibers coexist in all musculature, in humans and animals.
Red Fibers, those higher in Myo, can carry more O2 to the cells, and are built for long, steady action. Thighs, Legs, Glutes - weight supporting muscles White fibers are higher in Glycogen, a sugar molecule, which gives quick bursts of energy when used, but doesn't have the same overall energy carrying potential that HgB heavy cells would. Muscles more responsible for quick movements than supporting weight
This is why Chickens have White and Dark meat. The dark is the Thigh, carrying the whole weight of the bird. Take a biopsy of it and you would expect to see a higher concentration of Red fibers. the white is the Wing; doesn't really do too much except the occasional flap, it will have a lower % of Red fibers, and more White fibers. But no tissue is 100% of either.
So, now that we have addressed these 2 fibers, we can actually answer the question.
"Small Animals" say, a Rabbit is going to have greater concentrations of those White Fibers in some muscles, and Red's in others. The hind legs of a rabbit are going to have more Red fiber, while its facial and frontal muscles would be more of the White type - fast reacting, short spastic movements
So, these animals move by launching with these strong Red Fibers, giving off massive shots of energy to move as far as possible in one motion.
Other movements, like twitching, sniffing, anything else cute that little bunny rabbits do - those are all based off of the White Fibers. They move in quick little twitchy - in fact, their other name is Fast Twitch fibers (the Red fibers are Slow Twitch). They can move around without expending too much energy. But if a rabbit has to escape a wolf or a hawk? it just has to get from point A to point B as fast as possible, in one single motion, to avoid being eaten. But do it for 20+ minutes and it'd be exhausted. Different types of movement
Have you ever shivered in the cold? Your body is putting itself into a Fast-twitch Overdrive to burn as much energy as possible and keep its temperature elevated. Little furry animals do the same. Quick movements to heat up the body, based off the rapid firing of White Fibers. Now, throw in things like Sight and Smell to avoid predators, instinctively being afraid of larger animals, you can see put together the puzzle of why these animals would move around the way they do.
SO! And finally, here's the answer to the question. Small animals are twitchy, because;
It takes more energy for them to move (a rabbit hopping vs a large dog casually walking), so they tend to save
The way rodents and other small mammals twitch their noses around, or seem to focus from point to point with ninja-like concentration but ADHD-like speed, is because those movements are controlled by muscles that are predominantly White fibers. Or in some cases, to conserve or produce heat, the way we shiver, or how we blink to produce tears. While the larger motions, such as moving legs, would be done by muscles with a higher concentration of Red fibers.
They just don't have the dexterity for fine movements, so to us, they seem twitchy and spastic, like a dog scratching itself
I understand that this is ELI'ing a little more than 5 years old, tried to put it as simple as possible, if you have any more questions feel free to ask
Here are a couple of sources that will give you some more info on Red v White Fibers
Edit: Obligatory "Thanks for the gold"
other users have been mentioning Mass / Force, and they are correct; the muscles of some small animals don't have to be as strong and delicate as those of larger animals -> consider a cow's legs vs those of a gerbil. One is going to be a lot more Red than the other, simply because it needs 1000's of times more energy (O2) than the smaller animal's related muscles would.
And, a very common question; Humans have both of these fibers in all of our muscles as well. Your glutes would have a different composition of red and white than your pecs would, as would your triceps from your palmar muscles. Lebron's calves would have a different makeup of the two fibers than Messi's, or Bolt's. The exact makeups are not exact and are subject to change in every individual
as for the user who asked why I Capitalize every Other word? Because I can't gesticulate over the internet and that's how I add emphasis in my text. Eat it :)
I get the feeling you're referring to the full-body movement of something like a mouse or squirrel, but my first thought was the twitchy movement that birds make when examining their environment. This is done to aid in their depth perception.
Because their eyes are on the sides of the head, they're unable to use the fact that one eye sees the same scene slightly different from the other as we do, something known as parallax. In order to compensate for this, they examine a scene, then move their head quickly to get another perspective. Their brain is able to use the two images to give a rough estimate of depth.
To copy unashamedly from here, there appear to be three main reasons:Increased detection rate for predators (can listen out) Increased evasion by prey (less noise from movement) Increased endurance (taking breaks)
Planet Earth II has a great example of this in its episode on grasslands (UK only).
*Edited for Clarity.
Late to the party, but the muscle fiber answer is not all that relevant. I don't study this specifically, but have done some work on animal locomotion and sensing.
So... if small things don't move in quick, twitchy movements because for some random reason small things have white muscle fibers (this isn't true in all cases, and even if it were it wouldn't be the reason they have that)... why do small things move fast and then stop?
There are a lot of parts that go into it, but I think they mostly boil down to three basic reasons: 1) It's easier for them to move fast 2) Moving fast is still hard 3) They need to know what's going on around them
Small things have much less mass relative to the amount of force they can generate, and can do things much faster because of it. This is the same reason that ants can lift big things. Muscles generate force based on the cross-section of the muscle (area, r2 ), while inertia changes with the volume (r3 ). That means bigger is, all else being equal, slower. If you are interested in how scaling affects living things, I highly recommend Haldane's essay "On Being the Right Size". It's a great read, and still basically accurate even though it was written in 1928. We've known about some of this stuff for a long time.
It costs more energy to run at a high step frequency (how many steps you take per second) than to run at a low step frequency, even after you take size into account! This sucks for small things that have to take many steps to cover distance quickly. Mouse muscle, for example, uses 6 times as much energy per gram as horse muscle when they are both running. Here is a paper about it! So you can take steps fast, but they cost energy.
Okay, but how do you control your movement while you do this? Small things see at about the same speed as fast things: it takes ~1/10th of a second to perceive a change, or about 100 milliseconds, almost no matter your size (a few animals are a little faster, like 70-80ms if I'm remembering right, but same ballpark). This means, among other things, that when you're jouncing around taking many steps every second, it is much harder to compensate for the movement of your eye. A mouse takes nearly 10 strides per second at full speed (same paper I linked earlier); that means that each stride takes barely over 100 milliseconds! It is very difficult to figure out what you need to do on the next stride before you take it at this scale, especially with your eyeballs bouncing around very fast. You are mostly relying on faster senses for this, but vision gives you much better long-distance information. So, if you want to move effectively, you want to know where you're going. What's the best way to do this with the slow visual system? Stop running around and take a look! (Weirdly, because hearing is faster but sound takes time to travel, it looks like bat echolocation works on about the same time scale.)
Basically, if you are small, there are several things you want. One, you want to get where you're going, and you can move very quickly for your size! Two, you want to not use up all your energy at once, and that's hard when you take a lot of steps fast! Three, you want to stop and figure out what's going on around you occasionally!
So what's the solution? You can take a lot of steps very quickly, then stop and breathe and look, then take a lot of steps very quickly. This also is probably good for avoiding predators, as some other posters have mentioned. It also probably means you're going to want to use a little more fast-twitch muscle, as the current top post mentioned. And seriously, every person who has worked with small animals will be able to tell you that they actually do this, even on treadmills! That paper I mentioned above looks at running at difference sizes, and has this to say about small animals:
It proved very difficult to obtain data from small animals walking at a constant average speed on the treadmill. The mice, chipmunks and white rats normally maintained slow average speeds by running to the front of the treadmill, stopping, and riding to the back. The animals sustained these oscillations for long periods without utilizing a steady speed walk.
This really is inherent to how small animals move; they love to go fast then stop, then go fast then stop, and even when you really, REALLY try to get them to do something else, they won't do it! It's not just fear, either: people have tried a lot of ways to get them to run at a constant speed. They are built for this!
ELI5:Why are some pale skinned people able to tan easily but others just burn and peel?
The color in skin is from a pigment called melanin. Melanin protects the skin from UV rays in sunlight. Too much UV causes a sunburn. Depending on your genes, you make a mix of eumelanin (brown color) and pheomelanin (red color). The brown blocks UV best. The red can actually make the UV do more damage. Fair skinned people all look pale, but those with more pheomelanin will burn more.
To everyone in this thread so far: yes we know it's genes. If you don't know more stop guessing and get out
Wait, you're not on the internet every waking moment? Is this what a normal person is like?
B.S in Biology but I'll try my best anyways.
Assuming you've read everyone's explanation of how genes play a role, I'd like to explain why these genes are present in certain individuals and answer your question as to why certain individuals burn while others don't.
Evolutionarily, it all comes down to how certain shades helped individuals based on their location. It's beneficial for someone who is closer to the equator to be darker and absorb less sunlight since it's almost always readily available. In comparison to places further away from that center point where sunlight isn't as abundant throughout the day. A more pale complexion would allow you to maximize the amount of sun you take in.
So if your genes originated from a place where absorbing the maximum amount of sun is best and you're out in the sun for extended periods of time, you'll eventually end up burning simply because that's what the sun does when you have little protection. While others who's genes may have originated from a place with varying degrees of the sun, will be able to tan. That may be why we lose tans in the winter. Evolutionarily, tanning would be to increase your protection against the sun to not burn. The best catalyst for this reaction would of course be prolonged exposure to the sun which would be signaling extra protection needed. You would then lose this tan in the winter, or when you stop being in the sun as much, since you would need to absorb more.
Extra information: Since Humans as a species have been fairly good at adapting as needed, this may explain why we have lighter people in places where it'd make sense for everyone to be darker toned. Things such as umbrellas, sun block and houses would allow those with little natural protection to the sun to easily live in places where it is over abundant.
ELI5: I heard that recycling plants use magnets to sort aluminium from the rest of the rubbish. How, when aluminium isn't magnetic, does this work?
They use alternating current to magnetize the sorting magnet. If you use permanent magnet then aluminium will not be attracted to it, but if you put aluminium in magnetic field that constantly changes direction this magnetic field will generate electric curent inside the aluminium. When electric curent flows trough metal it generates magnetic field and the aluminium becomes small magnet with opposite poles as the magnetic field that generated the current in the aluminium. But the current inside the aluminium is not permanent, it's only short spike of current so if the outside field stayed the same the aluminium would stob being magnetic after a split second. But the outside field keeps changing back and forth that means the spike of current in aluminium keeps occuring and the aluminium is attracted to the magnet.
Edit 1: It was pointed out to me that I got the directions wrong. The aluminium would be pushed away from the magnet. Writing it here so I won't confuse people.
u/intjengineer linked a video of this in action. Linking it here in case it gets burried in the replies. If you can find his comment uvote it so it can be visible for others.
Edit 2: OMG I am internet famous now! What will I do with all this sweet karma?
Oh, that's cool. I didn't connect the fact you could make non-ferrous metals into magnets. Thanks!
What he said; eddy currents.
You've got to move the conductor (aluminium in this context) relative to a fixed magnetic field (permanent magnet, DC electro-magnet) to induce a current in the conductor,
you have to use an AC electro-magnet (magnetic field constantly increasing or decaying).
The latter method is what allows transformers to work.
I just woke up, read that title and was Hella confused what a 'recycling plant' is. Thought of something like carnivorous plants...
ELI5: Why are galaxies relatively flat as opposed to being spherical?
I took a look at and noticed every galaxy I see are always generally flat and not spherical, why is that? Please remember I'm 5.
Edit : front page? ok
From Previous thread - Here is a great ELI5 explanation.
Have you ever seen pizza made from scratch? The dough begins as a ball. It is then thrown in the air and spun. As it spins, the dough flattens and moves outwards into a disc shape. Solar systems and galaxies form like that.
Because they spin. When you have loosely connected matter, like the dust from which galaxies are formed--or, say, pizza dough--as it rotates, it tends to push material away from the axis of rotation. Thus, gravity can compress the matter into a disc-like shape, but the faster it rotates, the harder it is for it to compress into a spherical shape.
This applies to the formation of many objects in astrophysics--it's why solar systems tend to have a 'plane' much like galaxies, and even stars are originally formed from a collapsing disk.
It's also worth noting that there are more spherical galaxies, as well as a large central bulge in otherwise 'flat' galaxies. There's quite a lot of variance.
As kind of an addendum to this question, is it possible for a disc shaped planet or star to exist? Or is it not possible for one to spin fast enough to achieve the effect? Is a pulsar the closest you can get to this?
If you have a large clump of particles swirling around randomly, there is generally a direction of rotation that the whole clump is spinning in. As for why its flat; generally, while the whole is spinning, the up and down motion tends to cancel out as particles crash into each other with the spin persisting. The result is a spinning flat disk that many galaxies this video describes it better than i ever could
So the main thing at work here is conservation of angular momentum, which is a fancy way of saying that the total amount of rotation in a closed (isolated, not connected to some other source or sink of energy) system has to stay the same.
So say you have a huge cloud of dust that will one day be a galaxy. At the moment it's a huge blob with particles flying in all directions and bumping into each other. If you add up the trajectories of all of the particles in that cloud, you will end up with a net amount of rotation on one axis (in 3D space), which means that the whole cloud is rotating in some direction on some 2D plane.
Since the total amount of angular momentum in an isolated system has to stay the same, that means that the cloud must rotate no matter how the forces inside it end up balancing out. Particles that aren't rotating in that direction continue to bump into each other, as well as rotating particles, and over time, all of those opposing directional forces cancel out, leaving the cloud more or less all rotating in the same direction, on that same flat plane.
The reason the disc doesn't collapse into a sphere is because the particles are individually too light relative to their distance between each other to overcome the centripetal forces keeping them locked in their orbits. Planets form spheres rather than discs because the particles that make them up, while starting as a cloud and collapsing into a disc, are able to pull together into clumps gravitationally. They still keep rotating in the same direction, but they all become larger chunks with enough mass to maintain a 3D shape against the speed of their rotation.
This is also why all of the planets in most solar systems orbit in the same direction, because all of the particles that made them did so as well, and had nowhere to dump that rotation.
ELI5:Why do some people 'forget' to breathe when immersed in an activity or under extreme stress?
There's different ways that our brains control what we do, very roughly we could break them up as:Instincts - stuff we're born knowing how to do Learning - stuff we figure out through repeated exposure Conscious control - we can choose to override some actions
So for example pulling your hand back from a hot stove is instinct, walking is learned, and you can choose to walk backwards (which requires thinking about to happen).
Breathing is something that can and does fall in to any of the categories:Everyone's born knowing how to breath If we practice breathing (say for swimming or yoga) we can learn to do it differently sometimes We can choose to stop breathing, for example if we smell something bad
In stressful situations, especially ones we haven't practiced alot, we're paying a lot of attention to everything we do and consciously trying to avoid doing anything incorrectly. We can go overboard trying to control everything and control our breathing by just holding it during tense moments. If it's a situation we've practiced then our breathing will probably be fine, and even if we hold our breath a long time our instincts will eventually kick in.
TL;DR: our brains aren't a single unified system always working in a rational way, a lot of behavior is a bunch of different systems trying to figure out what's best.
This intrigues me. I've been married for 18 years. My husband has a CPAP (EDIT: a C-flex CPAP) machine to sleep, and has had one for about 17 of those years. He's done sleep studies and been to doctors, and apparently it's his brain. When he sleeps, it just forgets to breathe. As a result, he would stop breathing for up to a minute at night and semi-wake up (not fully, as he wasn't aware he was doing it) with a gasp, breathe a few times, rinse and repeat. When he got his CPAP, he woke the next morning absolutely amazed, as he had no idea how badly he'd been sleeping.
Recently, I noticed he does this during the day too. It's always been there, but I'd become so used to it, I stopped noticing. When he's semi or fully reclined AND distracted (playing on the computer, reading, watching tv) his breathing gets really weird, just like before he had his machine. He'll stop breathing a few seconds; inhale....hold breath.... exhale long. It's almost maddening when I start noticing it. I asked him why that happens and he said, "I don't know. It's just hard to breath in that position."
I only just now realized, writing this, that it's the distraction in common. If he's laying in bed and we're talking, I don't seem to notice the weird breathing. HOWEVER, at the same time, I don't seem to recall the weird breathing when he's sitting upright at the table and reading either.
I'm not sure how this helps OP, but it does seem to go along with the idea that when distracted (or asleep), it's possible the brain just forgets in some people.
I do this. It's called central apnea.
I've ADD and growing up in the 80s, there was a lot of concern among parents at the time about the drugs used to treat ADD. My parents refused to treat me and I was a very early adopter of computers (I got my first at the age of 5) and we lived in the country away from anyone to play with. So I was likely one of the pioneers when it comes to reinforcing my ADD with technology.
According to my shrink it's common to learn coping mechanisms for ADD that are a bit counter intuitive. Because I have trouble focusing and I'm easily distracted, I learned to be able to "hyper focus" on tasks. Meaning, I kind of go into a zen-like state where I literally ignore all outside stimuli. This results in situations where I'll be doing something (like typing this message) and if my wife is asking me what I want for dinner I'll not hear her. She'll eventually come up to me, tap me on the shoulder and the shock of getting yanked back to reality is so jarring I'll jump "WHAT?!?!" etc... Now that I'm older I can decide to take my own medication, learn to deal with my focus issues but 40 years of coping mechanisms are hard to unlearn.
But, getting back to your question, this focus issue includes breathing. When I hyper focus like this, I often start breathing very shallowly, sometimes stopping all together. I'm doing it somewhat unconsciously. For example, while I'm typing this I have to remember to breath when I get to a period. (breath) I recently had some fairly major surgery and they had me hooked up to all the monitoring equipment... every time they brought in some paperwork for me to sign, while reading it I'd set off all their alarms because it wouldn't register me breathing anymore. If I did not slow down like that, I would have had trouble reading the document. The ADD just wont let me concentrate that long on something.
TL;DR: It's like a meditation I do when concentrating.
You stop breathing in order to increase thoracic pressure when performing stressful physical tasks. Stabilizes your body wall.
ELI5: Why do you need a Master's Degree to become a librarian, especially when the median salary is barely above $50,000?
On Jeopardy tonight, one of the contestants stated that he obtained a Masters Degree online just to become a librarian.
It depends on what type of Librarian you are talking about.
Librarians assistants are generally just the people who learn about librarian functions and are the people who put the books away, do general checkout functions, so on and so forth.
Librarians, are generally like supervisors. They oversee the librarian's assistants and do daily work such as general supervision, overseeing a libraries general functions in addition to just checking out books, and organizing the Libraries overall day to day affairs. Ordering new books, processing new releases, so on and so forth...
Librarian Managers are usually overseeing multiple installations, or even non-traditional library resources. Sometimes Museums will have libraries or specialty function libraries such as University libraries. Also, this is where you will start to get into special functions such as document maintenance, archival and care. Larger institutions such as University libraries have VERY LARGE collections, spanning 100s of thousands of pieces, in multiple different departments, more than 1 single Librarian and their assistants can adequately manage.
Then you have Librarian Directors. When Libraries get so large that they have multiple departments, you need a Director level, who typically will be overseeing the business side of opening and maintaining either large University Libraries, or entire systems of local libraries. Take a single City... You could have 20 or more libraries within a system that serves that city, as well as manages several school library's contents and local municipal libraries. You'll have 1 Director, Several Managers, and at least 2-5 Librarians per library itself.
That level of staffing, needs proper management. So when you are getting your Masters in Library Science, some of the courses are also business management skills as well as advanced Librarians systems classes. Document restoration, special documents care, archival systems... these are not simple procedures that can just be taught on the fly, several years of education is needed to make sure that not only does the library stay properly stocked, but also that you can handle the challenges of maintaining books, relics, artifacts and everything else that may walk in your door.
edit: In addition to my normal post, like I said there are many other positions inside libraries that require specialized training and having someone that has been properly trained is a necessity, regardless of how much you make.
Handles copyright, contracts, resources used in courses, assists professors and course designers, has spoken on learning topics and libraries as a part of legislation for the state, has co-authored books, and participates in research.
I took management, legal issues for librarians, and digital preservation course in addition to the traditional reference, information organization, and collection development. I also took classes in archival description and arrangement, archival appraisal, and metadata which are very applicable to my job. I also help my patrons navigate copyright issues that are quite complex when you work in an archive.
edit 2: Woot! FP of ELI5 w/ top comment. First time ever!
edit 3: WOW! Actual FP! amazing! I've never been here before... I feel everyone deserves
edit 4: This comment went gold! thank you anonymous redditor!
Edit: Thank you for the gold and the many kind comments. It's been a wild 16 hours.
I'm halfway through my master's right now. Classes center around three topics. (1) The philosophy of librarianship (2) The business side and management aspects of running a library (3) The nitty gritty of turning raw information into a searchable form and organizing it into something relatively intuitive for the layman.
Compared to most degree programs, it's not difficult. But there is a lot more to it than people realize.
I'm willing to get the degree and spend the rest of my life making a five-figure salary because I'm passionate about reading, history, knowledge, democracy, sticking it to the man, helping people realize their full intellectual potential, and - yes - getting a pension and medical for life. I used to work for the most hated bank in America and I didn't like myself or what I was doing to the poor people in my community. Now I like waking up on Mondays. Do you know how good it feels to talk Harry Potter with a seven-year-old? Or help a woman covered in bruises find legal aid to escape her abusive husband? It feels amazing. It's worth it to me.
Edit: I appreciate the gold, but if anyone else feels compelled to gild my comment, please consider donating that money to your local library or to EveryLibrary. Libraries are going to need all the support we can get in the coming years!
I am the youth services librarian at a small city library. Well, technically my position is listed as library assistant so the city can pay me less, yes I make less than 50k, but that's a whole different issue. The point is I have the duties of a librarian and have the degree to go with it regardless of what my position is actually called. I don't currently have it with me at home, but tomorrow when I am at work I can pull up my job description from when I applied for the position. It is four pages long.
As a youth services librarian I need to plan programs for youth from newborns to high school. I run storytimes two to three times a week that require extensive knowledge of early literacy practices. In spite of popular belief, storytimes are not just reading books to kids. In addition to weekly storytime programming, I also develop and run other programs aimed at youth of various age groups. This includes things like STEAM programs for elementary aged students and community outreach programs at the local schools.
I am responsible for developing the collection of books and media for all youth, newborn through high school, and making sure that the collection meets the needs of my community. Collection development is not just buying new books, but also weeding old materials and cultivating the collection to reflect the community it serves.
Summer reading is a huge thing at nearly all public libraries. Guess who is responsible for planning and organizing that? Yep, me.
In addition to all that, I need to do things like write grants to ensure that we get extra funding for special programming and events that we might not be able to fit into the budget otherwise.
I also provide reference assistance to all library patrons. People underestimate the value of reference librarians in the age of google, but we can be a huge asset in finding the information you need and making sure that it is from an accurate and reliable source.
Since I knew I wanted to go into youth services, many of the classes I took gave me that early literacy training that is essential to making sure I am successful at my job. I also took courses in collection development, cataloging, copyright, and research methods. We learn how to not only find information, but also figure out what that person is actually looking for even when their questions aren't clear.
There is so much to being a librarian that people don't really see. They think all we do is shelve books and check them out and in, but a lot goes on at your library to make sure that it is actually the valuable asset to the community that it should be.
I am a librarian/archivist (my title is librarian but I'm actually an archivist in a public library) who got my MSLS last year. While I honestly wish librarianship was more of an apprenticeship, I do apply things I learned in grad school in my job. I also worked in libraries before attending library school and I found I was nowhere near prepared to be a professional. Library school isn't just shushing and cat petting. I took management, legal issues for librarians, and digital preservation course in addition to the traditional reference, information organization, and collection development. I also took classes in archival description and arrangement, archival appraisal, and metadata which are very applicable to my job. I also help my patrons navigate copyright issues that are quite complex when you work in an archive. These are skills I probably wouldn't learn in an apprenticeship situation unless I had a librarian dedicated to teaching me those skills. My professors were those dedicated librarians basically. I despised library school but as a professional, I see how it's useful.
Edit: This blew up overnight and I have a lot of interesting questions in my inbox that I am happy to answer when I get home from work today. Also, thanks to whoever gave me gold but I would prefer you spent your money on causes that help libraries out. With slashes to the National Endowment for the Humanities and the Institute of Museum and Library Services, libraries are at risk of losing all of their federal funding in the next budget. Organizations such as Every Library and the American Library Association are working hard to advocate for themselves in this time of crisis for libraries. Please consider supporting them in their fight. And please call your representatives and fight for the issues you care about. Consider adding the NEH and IMLS to those issues you don't want to see slashed.
ELI5: Why is it important not to fall unconscious after you suffer a concussion?
It has nothing to do with consciousness affecting your recovery. It's all about them being able to ask you questions and observe your responses. If you're awake with your eyes open they can tell if your pupils dilate properly or if your speech is slurred or if you're even aware of your surroundings. These are all important tests to see how severe your concussion is. Without that, the only option is a brainscan.
Wow that reply was almost immediate. Thanks for the speedy response.
Emergency doctor here (work in ED / A&E / ER depending on your locality). Just to add on a little to the previous answers which are mostly correct that, in short, it's not actually important to keep someone awake after a head injury.
Everyone, especially children, can become quite sleepy after a good enough blow to the head. That, in itself, isn't a cause for concern. But we are looking at how rousable you are from that sleepiness amongst a list of other "red flag" symptoms and signs (such as vomiting or the more obviously neurological signs such as weakness or seizures).
If, after a couple of hours, your natural state is still to drift off to sleep shortly after being roused - you've just earned yourself a CT head to look for signs of a significant head injury (e.g., bleeds). But if you were so sleepy that it took a reasonable amount of painful stimulus to wake you up then there would be no waiting and you'd be getting scanned straight away.
So, again in summary, there's no benefit to remaining awake after a head injury - you won't suddenly drift in a coma because you wanted to rest your eyes for a moment... Instead, it's how easily you're woken or how long that sleepiness lasts for after the head injury that matters.
Edit: I need to address one of my bugbears (... where on earth does that phrase come from?) which is in the current top answer: Pupil reflexes. If you have uneven pupils due to the effects of a head injury you will not be conscious! The cause of unilateral dilated pupils, in the context of head injury, is due to there being a significant enough rise in intracranial pressure - due to the presence of blood within the head - that it causes a 3rd nerve palsy. The other softer signs of significant head injury will already be present long before you blow a pupil.
See, it's a good thing he was conscious to answer.
ELI5: what mechanism allows seed to "hibernate" for long periods (the record is 32,000 years) and simply wake up to the first sign of water?
Seeds generally require three things to "decide" to germinate: warmth, oxygen, and water.
Water affects seeds by causing them to swell enormously and break through their coating, allowing the seed to begin to grow. At the same time, the water activates hydrolytic enzymes (chemicals which cause water to react with other chemicals, producing hydroxides and hydrides), and these enzymes break down stored food and other nutrients in the seed into useful things which the plant can use to grow - an example being the breakdown of stored starch into sugar (glucose) molecules, which can be used by the germinating seed to respire aerobically and produce energy for all sorts of things, as well as the production of cellulose for cell walls.
Oxygen is required for the seed to germinate because it is used in many processes, but most importantly, aerobic respiration which provides energy to the plant (as mentioned above). The seed simply cannot germinate without oxygen.
Temperature affects many chemical reactions in the plant, and usually lower temperature means slower/no reaction, which again means that the seed cannot grow and germinate. A sudden rise in temperature allows reactions to occur, which in turn allows the seed to germinate.
How do the seeds hibernate? Well, a seed is robust, and requires a very tiny amount of energy to remain living. Similar to how a chicken egg can remain dormant and rely on minuscule nutrition for 10 days while the mother chicken decides whether or not to sit on it, the living part of a seed (called the embryo - here's a diagram) can also consume tiny quantities of food and remain living for a long time, waiting for the right conditions to begin growing. The embryo has evolved to survive on a small amount of nutrients in a number of ways. A huge proportion of the energy intake of a human is spent on heating the body; plants do not heat themselves, and so don't need to spend energy on this. This is also the main reason that a snake can eat a deer and not eat again for weeks or months. The embryo doesn't grow or repair itself either, another large expense of energy for most life. It is incredibly efficient.
In the case of the Siberian seeds which were germinated after 32,000 years, the freezing, oxygen-starved and dry conditions in which the seeds were kept would have slowed down the processes of the embryo significantly, allowing for more longevity, as the embryo would consume its stores at a much slower rate. In carefully controlled lab conditions, with the right care, the seeds are able to germinate - although they probably wouldn't have been able to do so if they had just been planted in some field.
ELI5: How can we estimate that the golden record on Voyager will last a billion years?
Also what would even cause it to be destroyed over time?
How can we estimate that the golden record on Voyager will last a billion years?
We can't, really.
As the pre-poster wrote in space you have a barrage of "small particles" that might wear anything away.
We have radiation that also wears material away, it is little, but it is there.
We do not know what exactly is out there at the fringe of the solar system, there's theories/observations that there's an area (large!) with solar winds, we have no idea what the effects/long-term effects of this are.
Finally, at the end of the solar system, is the Oort cloud. It is icy particles and... stuff? We don't know.
We really do not know about our solar system and much, much less in specific about what is beyond.
A billion years is a very long time. A very long time.
Now, we do assume that because the record is from gold there are not many chemical reactions happening. As we assume that there is not that much radiation out there and gold is pretty robust (the gold atoms are pretty heavy) we assume it cannot really wear it down. As it is pretty cold out there we assume there is not much happening inside the material ("heat" is basically just movement of atoms and as it gets cold, they move less). As we assume that, while it is "stuff" out there it is not "dense" in any way we use the term here on earth, there is not much physical interaction (note that even gas clouds and asteroid fields still constist of "basically nothing" if we use our earth-bound terms for "a lot" and "basically nothing"). Couple 1.-5. with 6. and... we can assume it will survive a very long time - but we really don't know.
ELI5 the concept of bankruptcy
I read the wiki page, but I still don't get it. So it's about paying back debt or not being able to do so? What are the different "chapters"? What exactly happens when you file bankruptcy? Isn't every homeless person bankrupt?
From the previous thread - this is a great ELI5 version
Like you're Five: On the day you get your allowance, you buy a bag of candy. The next day, you want more candy, but you spent your allowance, so you ask your brother if you can borrow his allowance, and pay him back with your next allowance. You buy another bag of candy. The next day you ask your sister if you can borrow her allowance, and promise to pay her back when you get your allowance. You buy another bag of candy.
When you finally get your allowance, you realise you're in trouble - you can't pay your brother and your sister. You get so worried about it that you go buy a bag of candy instead. When you get home, you get in a big fight with your brother and sister about it.
When your Mom asks what you're fighting about, your brother and sister tell her that you borrowed money and you won't give it back. She asks you why not, and you say that you spent all of the money on candy, and you don't have any money left. She sighs, and makes you give all the candy you have left to your brother and sister. They want to know when they get their money back, and she tells them the money is gone, and they need to stop fighting with you and forgive you. They say that that isn't fair, and she says that it really isn't, and that they should remember this the next time you ask them for money.