字幕列表 影片播放 列印英文字幕 Hey, Vsauce. Michael here. And our faces have a lot of holes. We have two ears and two eyes. It makes sense, because the difference in time it takes for a sound to reach one ear and the other, allows us to localize where the sound is coming from. And having two eyes gives us two slightly different perspectives that we can put together in order to perceive depth. But why do we have two nostrils? I mean, our sense of smell isn't good enough to localize one nostril over the other, why not just have a big hole in our nose, like we have a mouth. Well, Stanford University's olfactory research project investigated this and they found that throughout the day one nostril inhales air better and faster than the other. Now, which one is dominant changes throughout the day, but having a good air sucking nostril and a not so good air sucking nostril is important. We need both, because you see, odorants and molecules are absorbed by our skin and snot at different rates. Some things are absorbed so quickly they need to be rushed on the olfactory receptors before they're absorbed earlier on in the nose. Other molecules, other odorants, are slowly absorbed and they need to be given time to get to the receptors and not just rushed right to the lungs. And so having two nostrils allows us to smell more things. Alright, so let's smell some weird stuff, like outer space. What would space smell like? Okay, right, it's a tough question, it actually doesn't make much sense because space is a mere vacuum. If you went into space and took your helmet off to smell it, well, all of the air in your lungs and throat, nose would be violently sucked right out. In fact, even if you really tried to get some sort of olfactory sensation, about all you would feel is the quick evaporation of water coming out of your mucous membranes and you might smell, for the few seconds that you were conscious, nasal fluid and blood. That doesn't sound fun at all. But here's the thing. Objects that have been taken out into space and then returned to a habitable atmosphere, like inside a space station, smell differently than they did before they went into space. Astronauts report that their suits, after being in space, have a strange metallic burn meat arc welder fumes smell. It's believed that the odor is caused by high energy particles that cling to the suit and then, once brought inside, react with the air, creating a burning smell. One particular type of high energy molecule found all over interstellar space are polycyclic aromatic hydrocarbons. These guys are the result of combustion. And in 2004, the University of Toledo, Ohio found evidence that those very molecules may exist in old nebula. The result of convection currents cooling carbon and hydrogen allowing them to bond into giant shapes. Polycyclic aromatic hydrocarbons are also formed, when cooking meat at high temperatures. So, in order to train astronauts even more realistically here on earth, NASA actually reached out to Steven Pearce of Omega Ingredients to replicate the smell of things that have been to space as a perfume. If we know the chemical makeup of something, even something light years away from us, we can assemble those ingredients here on earth and get an idea of what it would smell like. Recently, researchers have discovered Ethyl Formate in the dust cloud Sagittarius B2. Now, again, if you were to go there and lift up your space suits visor and take a whiff, you would die. You wouldn't be able to take a whiff, all of the air in your nose and lungs and throat would be immediately expelled. But if you were able to take a bucket of Sagittarius B2 home with you to earth and then give it a smell, because of the ethyl formate Sagittarius B2's stuff would smell like raspberries and rum. Pretty neat, right? But let's get closer to home. What does the inside of your nose smell like? Well, it's kind of hard to know because we are smelling it all the time and our bodies become desensitized to constant stimuli to keep us from being overloaded and to keep us prepared to sense any out of the ordinary smells that we might need to know about. This happens to us all the time. When you first step into a restaurant, you can smell all the food, but halfway through the meal you're no longer aware of the smell. It's called neural adaptation. I guess the point I'm trying to make is that in order to figure out what the inside of a nose smells like you'll need to smell a novel one, like, for instance, smell the inside of your friend's nose. It might seem weird at first, but it could be a great way to form new memories. Our sense of smell may not be as acute as our other senses, but it seems to be tied to memories very very closely. A single whiff of an odor can instantly remind you of where you used to smell that smell and maybe even who you were with. This may be because of the olfactories' connection to the limbic system in the brain. Olfactory information is sent through the limbic system, which is known to be involved with emotions and memories. No other traditional sense is connected to the limbic system in this way. We've also found that patients who have memory loss caused by brain damage tend to also have an impaired ability to smell. So treasure your sense of smell, because it not only keeps us safe from gross odors or rotten food, it can also keep us safe from incest. Individuals who are raised together in the same home for the first few years of their life, whether they are genetically related or not, will tend to be less physically attracted to each other later in life than they are to strangers. This is known as the Westermarck effect and one of the main mechanisms it works via is the olfactory system. Us humans have an interesting ability to distinguish the smell of a stranger from someone that we are genetically related to or grew up in very close proximity with. This entire phenomenon may be a natural way for us to avoid inbreeding. But what about someone who can't smell? What do we call them? Someone who can't see is blind, someone who can't hear is deaf and someone who can't speak is mute, but what do you call someone who can't smell? Well, there's a word for the inability to smell - anosmia. Now, even though the adjective form is very very rare, it exists. A person who can't smell is anosmic. There's another word we should have investigated a long time ago. Olfactory. What does is it come from? Well, the "ol" part comes from odor and from smell, but "factory?" Well, factories make things, but the nose doesn't makes smells, it smells smells. Right? Well, here's the thing. We smell objects because molecules from those objects react in certain ways with our olfactory receptors. And molecules have specific shapes and vibrations and ways of behaving, but the smell is not actually intrinsic to the molecule. The smell is merely a consequence of how that molecule reacts with us. No us, no smell. So, olfactory is a fantastic word. Every sight and feeling and sound and smell we get from our universe is actually just the universe reacting with us. Everything we know about the universe we know because it has already been processed and changed and analyzed and filtered inside the factory of our sense. And as always, thanks for watching.