We get asked a lot of questions here at SciShow. Sometime we get a question that has maybe
never been asked before in the history of questions, and sometimes we get questions
that are so universally wondered, that they get asked over and over again. So, we’ve compiled some of those frequent
asks into one place, here, so hopefully, if you’ve ever wondered these curious questions,
you can get a whole bunch of answers right now. Recently, Patreon patron, Rob Margolis, reminded
us of two of these questions that come up a lot. The first, I hope you’re not wondering right
now, but if you are, I hope you recover quickly and can watch this video about what causes
migraines. If you’ve never had a migraine, you might
think it’s just a really bad headache. But if you’ve ever had them, or you know
someone who does, you know that they’re much worse -- and much more complicated -- than
that. A true migraine is a multi-symptom disorder
of the central nervous system that affects the brain. But, yes, really bad headaches are a major
component of it -- probably the single most significant and identifiable component. But it usually lasts longer than a normal
headache -- anywhere from 4 hours to several days// -- and brings a whole array of other
symptoms with it. Most migraine sufferers experience extreme
sensitivity to light and sound, and sometimes smells. They also commonly experience nausea, vomiting,
even fainting. What little relief they can find is generally
only achieved by being very still in a dark, silent room until the symptoms pass. And believe it or not, it gets worse. Migraines also cause problems both before
and after the headache. It’s different for everyone, but the ordeal
can start with symptoms as seemingly minor as constipation, weird food cravings, neck
stiffness, or excessive yawning. As the symptoms worsen, people generally enter
a phase called aura, in which they may experience things like vision disturbances -- like seeing
shapes or lights, blurred or doubled vision, or even loss of vision -- “pins and needles”
sensations in the extremities, weakness, and sometimes even slurred speech. Now, you might notice that these sound a lot
like the symptoms of a stroke, and in fact migraines have so many things in common with
strokes that doctors sometimes have to do tests to determine which disorder they’re
dealing with. After the headache has passed, most migraine
sufferers experience a period of weakness and fatigue that can last from a few hours
to a few days. Obviously this isn’t the sort of thing that
anyone wants to experience. So what causes it? Can it be controlled? Or at least treated? Doctors think migraines are probably caused
by a sharp drop in your brain’s levels of serotonin -- a neurotransmitter that plays
a key role in regulating things like sleep and mood. And once that imbalance strikes, it causes
a whole cascade of effects. But what triggers this imbalance is complicated
and uncertain. We do know that one of the most important
factors is genetics. If one or both of your parents has experienced
a migraine, odds are that you will too. For reasons that we don’t understand, women
are far more likely to have migraines than men, and they’re even more likely to experience
one during times of hormonal changes, like puberty, menstruation, ovulation, pregnancy,
when using hormonal contraceptives or hormone replacements, and menopause. Beyond that, everyone’s triggers are different. For many people, it may depend on stress,
their activity level or their sleep schedule -- all things in which serotonin plays a role. And still others may be triggered by things
as seemingly random as bright lights, loud sounds, unusual or strong smells, or even
weather changes. The //treatment// of migraines is further
evidence that it’s not just a headache. It’s true that the headache itself can sometimes
be treated with pain relievers, although they’re often less effective. In addition to pain relief, migraine sufferers
may take medications that try to treat the source of attacks, like by controlling the
constriction of blood vessels in the brain, blood pressure, serotonin levels, and inflammation. So clearly a migraine is more than just a
bad headache, remember that when you hang out with people who get them. If they’re in a bad way, the biggest favor
you can give them is just to let them be by themselves in a dark room. You can just keep watching SciShow //quietly//. Rob’s second question is another that comes
up a lot, but is less painful...for humans anyway. Welcome to I Don’t Think It Means What You
Think It Means, where we look at bits of scientific theory that’ve wiggled their way into popular
culture and taken on a life of their own. Today we’re talking about Schrodinger’s
Cat, a famous thought experiment devised by Austrian physicist Erwin Schrodinger, who
helped piece physics back together after Einstein and his crew blew a giant honkin’ hole in
it back in the early 20th century. It can’t really be overstated how much of
a giant crap circus the 1920’s were for physicists. Until then, everything had pretty much just
been good old-fashioned Newtonian physics -- where you could observe objects moving,
and predict how they’d react to various forces. But then along came new research into subatomic
particles that showed they didn’t act predictably at all. In fact, sometimes stuff seemed to be two
things at once. Like, an electron in a beam might act like
a particle sometimes and like a wave at other times. And to make things even more -- [heaves tense
sigh, sort of like hyperventilating]-- the more you try to observe and measure these
particles, the less naturally they seem to behave. Sphincter-say-what, now? [js: Um, it’s from Wayne’s World and I
think I’m trying to bring it back.] My friends, welcome to one of the biggest
mind-flogs of quantum mechanics; it’s called superposition -- the idea that a particle
can exist in all of its theoretically possible states at the same time. So Schrodinger came up with this thought experiment
to help folks understand it: Say you have a cat and you put it in a steel chamber for
an hour with a vial of deadly gas, a Geiger counter, a hammer, and a tiny bit of something
radioactive. OK just bear with me. Now say there’s a 50/50 chance that one
of the radioactive atoms is going to decay within that hour. If one of the atoms decays, the Geiger counter
is going to trigger the hammer, shattering the vial of poisonous gas. Really, Schrodinger? This is not the best way to get people behind
the idea of funding the sciences. So, there’s a 50% chance at the end of the
hour that the vial has been broken and the cat is dead, and an equally good chance that
the vial hasn’t broken and the cat’s just kickin’ it, wondering what’s for supper. But, what’s actually happening in the box? According to quantum mechanics, any one of
those radioactive atoms would be in a superposition of being both decayed and not decayed at the
same time. Because that’s how quantum objects act. So then that decayed atom will have both killed
and not killed the cat, right? Well that’s the logical conclusion but the
cat isn’t a quantum object. The cat is a big normal thing that obeys old-fashioned
Newtonian laws. So it, just like ever other cat in history
is either alive or dead. Schrodingers point, at least one of them is
that the object is subject to two separate sets of laws that can’t be reconciled. In order to know whether the atom is decayed
or not is to open the box as see if the cat is dead. But in quantum mechanics, the state of superposition
can’t be observed. So when the evil mad scientist finally opens
the chamber, to observe, the superposition collapses once the outcome is ensured. Today, Schrodinger’s Cat is talked about
as some undead zombie cat or discussed at being dead and not dead, alive in the box. But Schrodingers point wasn’t to prove you
can make a cat both alive and dead but instead prove that the quantum world doesn’t mesh
well with the normal world. Alternatively the point the universe is pretty
freakin’ weird. There are other interpretations of quantum
mechanics that resolve the paradox but none of them are easy to test. My favorite is of course the “Many Worlds”
interpretation that states at the end of the experiment and at the end of the superposition,
alternate universes are created. But in this case, one in which the cat is
alive and one in which the cat is dead. And to be clear I don’t like this interpretation
because it’s the most likely one, I like it because it’s such a excellent plot device
for science fiction novels. Dreaming is one of the weirdest thing we do. I mean, I don’t want to diminish all the
other strange crap our bodies are capable of, ‘cause a lot of it is cracked out on
so many levels. But dreams are a special kind of crazy. No matter how many dreams you have in your
life, every once in a while you wake up like, “WHAT THE HELL WAS THAT?” But as with everything else, science is helping
us understand why we dream, what our brains are up to when they do it, and why dreaming
may be critically important to the functioning of our awake brains. Try to stay awake for this, ‘cause it’s
really cool. People have been trying to understand dreams
since--well, since there’ve been people. But the person we associate most with the
science of dreaming is probably Sigmund Freud. In 1899 he wrote The Interpretation of Dreams,
where he suggested that dreams were largely symbolic and allowed us to sort through the
repressed wishes that piled up in our unconscious minds. And most of those wishes involve weird sex
stuff. Freud was kinduva perv, if you must know. It wasn’t until the 1950s, when scientists
became able to read the electrical activity of the brain, that we began to understand
what a dreaming brain was actually up to. Two researchers at the University of Chicago
-- Eugene Aserinsky and Nathaniel Kleitman -- pioneered this research by hooking people
up to the newly-invented EEG machine and monitoring their brain activity while they slept. What they thought they’d find was that a
sleeping brain was a resting brain, but they discovered exactly the opposite. They found that brain activity fluctuates
in a predictable pattern over a period of about 90 minutes. This cycle takes sleepers from an initial
period of drifting off, gradually into a really deep sleep with slower brain activity, back
into almost-waking. And this stage of sleep where the sleepers
were aaaaalmost awake again was the most interesting: brain activity in this phase was almost identical
to when people were awake. But even more weird, during this stage, the
subjects became functionally paralyzed--the only parts of their bodies that moved were
their eyes, which darted back and forth under their eyelids. So Aserinsky and Kleitman called this period
R.E.M. sleep, after the rapid eye movement that characterized
it. They also called it “paradoxical sleep,”
because the subjects seemed to be awake, according to their brain activity, even though they
were basically dead to the world. I guess they figured these names were better
than “Sexually Aroused Sleep,” which is another rather common feature of this stage. But another thing the scientists found was
that if REM sleepers were awakened, they reported having really vivid dreams that were often
emotionally intense. It wasn’t the only stage of sleep in which
the subjects dreamed, but it was the time they reported having the most lifelike dreams. It turns out that every 90 minutes or so,
during the final stage of the sleep cycle, the brain phases into the R.E.M. sleep and our brains start creating crazy
narratives that last maybe 20 or 30 minutes. This is when you have those really vibrant
dreams that can easily be confused with reality. So WHYYYYY so busy, Sleeping Brain? And what’s so important about dreaming that
you have to paralyze your entire body in order to have really realistic dreams? Well, there are probably several answers,
but one of them is that during all periods of dreaming, our brains are making important
connections between real-life experiences that will help us in our waking lives. These days, researchers are finding that Freud
was wrong about dreams in one important way: We don’t dream much about our hidden desires. We mostly dream about what we did today. While we sleep, our brains are sorting through
what happened while we were awake, deciding which new experiences were important enough
to remember and which should get tossed, searching for links between seemingly unrelated events
that might be able to help us be a more successful human tomorrow. And it’s actually really important that
we do this while we’re asleep, because our conscious, waking brains are generally too
controlling to allow this kind of creative problem-solving. And this dream-time activity helps our waking
brains be better at things that require making connections and thinking outside the box. Dreams have actually been responsible for
some really important inventions and discoveries in history. For instance, Dimitri Mendeleev came up with
a system for the structure of the periodic table of elements in a dream after months
of grueling conscious thought was getting him nowhere. And research shows that our brains are much
better at solving puzzles if they’re allowed to take a nap in the middle of doing one. In a study in 2004, for instance, subjects
were asked to search for links between two sets of numbers. The subjects who napped solved the puzzle
about 60% of the time, whereas only 25% non-nappers were able to do it. In another study, where people were asked
to find connections between seemingly unrelated words, those who lapsed into R.E.M. sleep between sessions solved 40% more puzzles
than those who didn’t. So dreams are all about making associations
and finding patterns that our waking brains have a hard time detecting. But it seems to work in slightly different
ways in non-REM sleep than in REM sleep. During non-R.E.M. sleep, you dream, but the
dreams aren’t necessarily vivid, and they’re often about something you’ve been doing
or thinking about a lot. During these stages, people often report dreaming
about kind of boring stuff -- like if you spent a lot of time in the car during the
day, that night you might dream about driving down a long street, stopping at a series of
stop lights. This might seem lame, but it’s actually
useful to the brain in its own way: it’s telling itself things it already knows--like
“when you’re driving a car, you’re supposed to stop at the stop lights.” So in non-REM sleep, it’s basically reinforcing
existing connections. But in REM sleep, we get to test out that
reinforced knowledge in a context that is virtually indistinguishable from real life. It’s like our brain running simulations. So if you’ve been driving to your grandparents’
house in Boca Raton all day, and in non-REM sleep you spend a good 20 minutes practicing
stopping at traffic lights, during REM sleep your brain might have you trying to steer
a steamroller through Manhattan from the backseat. REM dreams can be very lifelike and very stressful,
but that’s part of it: A vivid REM dream is an opportunity to safely let us try something
difficult. Because our brains aren’t here to make friends. Our brains are here to win. The evolutionary purpose of dreaming--like
the evolutionary purpose of virtually everything else we do--is to make us more successful
animals tomorrow than we were yesterday. So if during non-REM sleep, the brain is taking
data from past experience and fiddling with it to figure out how that might relate to
the future, in REM sleep, the brain’s actually trying to experience the future in order to
test possibilities. So, maybe you’re making out with your algebra
teacher on Jay-Z’s yacht while wearing a banana suit. What of it? Does it mean you subconsciously want to make
out with your teacher? Maybe, but not necessarily. Does the banana suit have something to do
with penises? I dunno - -who am I, Freud? The thing is, during REM sleep you can try
that experience out with no consequences whatsoever. Another benefit of REM sleep is that it helps
us process emotions that our dunderheaded waking brains aren’t really equipped to
handle. Although the content of our dreams might be
wacky, the emotions attached to them are absolutely real. Remember, your dreaming brain is charged with
working on real-life problems, so if you feel really angry at your boyfriend in your dream,
chances are you’re probably pretty pissed at him--or maybe someone else you’re close
to--in real life. The stories our dreams create are essentially
attempts to give our emotions a narrative that can kind of suck the poison out of them
and give them a form our brain can deal with better. In fact, people who can’t experience REM
sleep often experience other psychiatric disorders. So, dreams help regulate traffic between our
experiences, our emotions and our memories, so we can dial down the crazy. And hey--if the outcome makes your rational
brain uncomfortable, well.... That’s just how sausage is made, folks. Since I’m on the topic of weird dreams and
REM sleep, a lot of you have said you’d like to know more about what’s called lucid
dreaming. This is when you become aware of the fact
that you’re dreaming and can actually direct the narrative of the dream. Since REM sleep is simulation time in the
brain, lucid dreaming is basically a simulation that lets a portion of your conscious brain
in on the action. Most of us can probably recall at least one
lucid dream, and about 1 in 10 of us have them regularly. Some lucid dreamers can even communicate with
researchers studying them through gestures like eye movements and hand-squeezes. What ultimately separates lucid dreams from
regular old REM sleep may lie in the physiology of the brain. During non-REM sleep, the cerebral cortex
-- that’s your gray matter -- loses its ability to associate with other parts of the
brain. This is probably why those dreams are more
boring and less complex. But once a dreamer reaches REM sleep, the
cortex becomes active again and begins talking to other areas of the brain -- except for
this one little part of the cortex--called the dorsolateral prefrontal cortex -- that
doesn’t reactivate. This is the region right about at your left
temple that’s responsible for, among other things, applying memories to other situations,
like planning stuff and predicting outcomes. This helps explain why REM sleep dreams are
so weird -- your brain literally can’t tell what’s going to happen next. But during lucid dreaming, the dorsolateral
prefrontal cortex actually does wake up, which is probably why we regain a sense of self-awareness
and can plot out stories for ourselves. Some people claim lucid dreaming can help
cure reccurring nightmares or even help cure depression and anxiety. The jury’s still out on that, but dreaming
itself--all kinds of dreaming--is definitely useful, and even imperative, to the function
of the brain. So, why are you still awake? Go take a nap or something! First thing you should know if you’re having
a hard time getting some shuteye, is that you’re wired to sleep regular hours...going
to bed the same time each night and waking up at the same time each morning. Having a regular wake-up time seems to correlate
pretty highly with the ability to fall asleep consistently. This is because it keeps you aligned with
what’s known as your circadian rhythm, your body’s natural tendency to stay in sync
with the cycles of day and night. And you know what controls your body’s circadian
rhythm more than anything? Light. A lot of the help you get falling asleep comes
from hormones -- they lower your heart rate and reduce your blood pressure and basically
let you relax. The key player here is the hormone melatonin,
and it’s regulated by your exposure to light. In darkness, it flows freely. But when you’re exposed to light -- whether
natural or artificial -- the release of melatonin stops. So you know what that means? No phones or laptops in bed! The light emitted by electronics simulates
sunlight, and confuses your body into not knowing that it’s time to sleep. So scientists suggest at least an hour of
screen-free time before bed...though I am completely incapable of that myself. Another obvious enemy of sleep: caffeine [pic]. Even though you might think that cup of coffee
after dinner might only affect you for an hour or so, studies have shown that caffeine
consumption as much as TWELVE HOURS before bedtime is linked with insomnia. And even the way you //think// about sleep
can affect your sleep patterns. Worrying about not getting enough sleep is
a common enough cause of insomnia that it has its own name, Sleep Onset Insomnia. But you know what’s weird? A lot of the time, when we feel like we can’t
sleep -- we actually ARE sleeping. When scientists rouse patients in the first
or second stages of sleep, more than 60% of them say that they weren’t sleeping, even
though they were. Now, of course, there’s a whole class of
medications that will help you sleep, from antihistamines to the pharmaceuticals known
as hypnotics, which include Ambien and Lunesta. However, research has shown that while patients
[pic] //can// fall asleep faster on hypnotics, the effect is small, adding only about 15
minutes to their sleep times. Other studies indicate that //our minds//
are significantly more powerful than any medications. In double-blind studies, patients who were
simply //told// that they were taking a sleep drug ended up sleeping far better than patients
who were told they weren’t. So, if you want to know how to sleep, the
answer is right there in your head. As part of our work answering the world’s
most asked questions, we asked you, our scishow viewers, some questions...and one was how
many hours per night you sleep. Bad news: Only 10% of you are sleeping more
than eight hours per night, and eight and a half is the doctor-recommended amount. And OVER HALF of you report having trouble
getting to sleep at least once per week. Oh but wait...we haven’t gotten to the fun
part...MEANINGLESS CORRELATIONS!!! The best sleepers for countries where we had
enough data to make a judgement were Saudi Arabians, with 76 percent reporting that they
experience insomnia infrequently or never. Most of Europe scored better than average,
with The Netherlands, Russia, and Spain all sleeping relatively soundly. The English speakers in the US, UK, and Australia
all had some of the worst scores. And, finally, unsurprisingly, our staggeringly
unscientific survey reports that people who commonly drink coffee, soda, energy drinks
or tea are all more likely to suffer from insomnia. Though maybe they’re just drinking those
things because they’re so tired! So now that you know all about migraines,
hypothetical cats, and sleep, on to the serious questions! Why? WHY do we have baby teeth? Missing teeth… not so cute on the lead singer
of the Pogues, but pretty dang cute on a smiling toddler. But why do humans have baby teeth, and why
do we lose them? Humans, like most mammals, are diphyodonts
[dye-FYE-oh-donts], meaning we grow two sets of teeth in our lifetimes -- a permanent set
of adult teeth, and a deciduous set of baby teeth. Deciduous teeth are smaller and fewer in number,
because a toddler’s jaws are tiny and could never fit a full set of 32 adult teeth. Poor kids would look like something out of
a horror movie. So, instead, we begin life with 20 smaller
teeth, which start erupting out of our gums when we’re about six months old and are
fully in by the time we’re two and a half. Just like our permanent teeth, deciduous teeth
grow in pairs. Meaning that when two incisors erupt from
the lower jaw, you can bet that two incisors will soon erupt from the upper jaw. This allows our mouths to bite down and chew
evenly, and helps ensure that our jaws grow and wear down evenly, too. Now, as we get bigger, we need more teeth. But instead of wedging these new teeth in
between the old ones, we lose the old teeth and grow a whole new set. That’s why baby teeth are called deciduous
-- just like the leaves on deciduous trees, they’ll shed at a specific stage of development. Four new molars erupt in the back of our mouths
when we’re around five or six years old. Then our deciduous incisors -- which are right
here [points to teeth in front of mouth] fall out and are replaced with permanent incisors. By the time we reach puberty, we have an almost-full
set of 28 permanent teeth. The last four emerge later in life. These are the so-called “wisdom teeth,”
molars in the back of our mouths. They were a good idea some 100 million years
ago when our jaws were bigger. But evolution has made our mouths smaller,
and now these molars crowd out other teeth and can cause pain, which is why a lot of
us get them pulled. And being a diphyodont is actually kind of
a disadvantage in other ways, too. While it sounds nice to have an extra set
of something, we only get two sets of teeth in our lives. Polyphyodonts [pol-ee-fye-o-donts], on the
other hand, can grow and regenerate teeth multiple times. These include alligators, fish and even some
mammals, like elephants, who can regenerate their teeth up to six times, to help them
enjoy long lives of grinding up plants. But /our/ second set of teeth will just keep
wearing and breaking over time, so take care of them while you can, because they’re the
only ones you’ll get! Our final FAQ that we’ll share with you
today is one I’m pretty sure everyone has wondered about whenever you’ve really stopped
and thought about your eyebrows. Or arm hair. Or any hair. You’re probably quite happy that your armpit
hair isn’t dragging on the floor. So it’s good that there’s a system to
prevent that. But what is that system? Us humans grow hair all over our bodies -- except
on our palms and the soles of our feet. But some of it, like leg hair, stops growing,
while the hair on our heads just seems to grow out forever. That’s because every hair on your body goes
through the same cycle -- growing for a while and then falling out -- but each /type/ of
hair spends a different amount of time growing, and grows at a different speed. Every hair begins the same way, in a phase
of the cycle called anagen. During anagen, blood flow starts to ramp up
at the base of the follicle, feeding oxygen to specialized stem cells. These cells begin rapidly dividing and producing
keratinocytes [ker-AT-in-oh-sites], which form the root of the hair. As the expanding mass of keratinocytes is
pushed toward the surface of the skin, the cells die, releasing a protein called keratin
[CARE-a-tin], which holds the strand of hair together. Eventually that strand pops out of your skin. So the visible part of the hair is entirely
dead, which is why, thankfully, it doesn’t hurt to get your hair cut -- though try explaining
that to a three-year-old. During anagen, hair can grow up to 1 and a
quarter centimeters every month, depending on where it’s located on your body. The second phase is called catagen [CAT-a-jen],
and lasts about two weeks. Here, the blood supply is cut off at the bottom
of the follicle, which stops the production of new keratinocytes. So for that particular hair, the party is
over. The follicle then shrinks to about a sixth
of its original size, and the existing hair strand is pushed closer the surface. The third phase is called telogen [TELL-o-jen],
otherwise known as the resting phase, where the follicle remains dormant for one to four
months. Finally, the hair is released, or shed, when
the follicle dilates, and starts the anagen phase again. So, how long a hair on your body gets, depends
on how long it’s in the anagen phase, and how /fast/ it grows during that time. The hair on your scalp, for example, stays
in anagen for two to six years, which is why it can grow so long. Other hair types, like eyebrows and eyelashes
and body hair have a short anagen phase -- only 30 to 45 days. But they also grow much more slowly, with
eyebrows, for instance, growing only 4.2 millimeters every month. This is my eyebrow closeup. Hey... As for how your hairs know when to grow and
when to stop, that’s something scientists are still trying to figure out. It’s known that genetics can lead to longer
or shorter anagen phases in certain hair types. But the current thinking is that your hairs
get their instructions -- by way of chemical growth signals -- from stem cells in the skin. And considering how extremely inconvenient
it would be for all of the hairs on your body and all mammals’ bodies to just continue
growing forever, it makes sense that there’s a system for making sure they don’t grow
too long. Thanks for watching this Frequently Asked
Compilation video. Please keep asking us questions! You can ask in the comments, on Patreon, Tumblr,
Facebook, Snapchat, email, via pigeon--if you can figure that out, we’ll have questions
for you too! And in the meantime, keep getting smarter
with us by going to youtube.com/scishow to subscribe.
