Neil deGrasse Tyson Explains the Physics of Size and Life

[Music] chuck i got a new topic for you uh oh excellent what do you mean uh oh what's that supposed to mean that means i'm ready i always that makes you like you're a little scared no no for me uh oh doesn't mean scared i'm like uh oh like all right you know so i don't use uh oh properly okay clearly clearly i'm not using uh oh in its proper form if someone says oh something bad is about to happen yeah you know what i i supply and you know what i'm gonna have to stop doing that so uh now i know what the problem is every time i say uh-oh and people were like what and i'm like nothing all right so consider a few things i want to talk about life and well okay yeah it's relevant and uh on size and life well um listen the way i see it is this okay uh you know size is a preference thing okay and not all of us can actually you know be what some people might have as a preference and you know why are you looking at me like that because why perhaps you've been told something about you know uh my ethnicity and maybe i'm supposed to be a certain way well it doesn't necessarily happen that way for every every person in my in my position and someone who looks like me we are witness to chuck digging himself out of a box that's what that is so here we go so yeah you you're in a room there right all right it looks like a hotel room all right you can walk around on the floor okay okay um if there were an aunt walking around on the floor it would be doing just what you're doing absolutely however an aunt can go to the wall and then just walk up the wall right how come you're not walking up the wall because i'm not spider-man okay that's all if i were spider-man i'd be walking up the wall okay because spider-man is imitating a spider yes he is okay but there are no spiders the size of humans this is true that can just walk up the wall correct all right there's a reason for that there's a very good reason for it and has to do with the physics of life nobody ever talks about it that way because the biology this you can talk any biology you want at the end of the day physics sets the rules take that biologist there's a little smackdown for you you physics sets the rules even in your world physics all right so it all comes down to this go ahead chuck okay so um how strong are your limbs well the strength of your limbs is measured by the cross-sectional area oh all right so that tells you how big your muscles are well you're just embarrassing me on every level today first we're talking about size now we're talking about skinny wrist shanks all right so just take any part of your body your legs and your arms take the cross section and that tells you how big your muscles are and when you say have big muscles you're measuring sort of a circumference okay right and that's that's related to the that's always the way you measure the circumference of the air okay right so as you get bigger your strength will grow as your the area of your muscles right cross-sectional area of your muscles okay however your weight goes up as the cube of those dimension dimensions oh my goodness i now of course i know your your weight goes up but i didn't realize hey wow that's a lot that's okay so that's why okay a 300 pound person does not look all that much bigger than a 200 pound person right okay they're chubbier and they're big if they could be taller whatever but if you start increasing depth height and width right your volume as your volume increases so does your mass but your strength necessary to sustain that volume and that weight does not go up in proportion right so your limbs if you're gonna hold up a heavy animal your limbs have to be much fatter than they would otherwise be if you were smaller and what are your heaviest animals on earth uh your elephant your whale yeah on earth's surface the way the the elephant the elephant how its legs are huge yes okay they don't have spindly legs no their legs are huge to compensate for the fact that strength only goes up as the area of their muscles while the weight is going up as the volume and volume rapidly outstrips area okay now you can go the opposite direction as you get smaller and smaller and smaller your the weight with your volume gets lower and lower and lower and the strength of your limbs becomes better relative to your body weight that's why ant can lift what is it what not only is it why they can lift things relative to their body weight relative to the body weight okay all right that's not only can they do that it's why they can get around with really skinny legs right okay yes they have six of them but they're really skinny compared to the size of the thickness of their body because the legs aren't holding up much weight relative to their own strength right so and they intermittent fast they do intermittent fasting too so is that how that works thank you thank you go wow so you know what you just you just gave me a really um stark thought which is i watched this documentary about this uh guy who climbed uh uh the only cliff face that these people die all the time climbing without any belly and um this guy was super skinny yep yep not not strong like with big giant muscles but i mean his muscles when you look at his musculature this dude was ripped he's ripped but he doesn't wear very much but he doesn't weigh much at all correct correct and that's why in the movie cliffhanger which involved rock climbers and mountain climbers it starred sylvester stallone who's got all these muscles is like now every mountain climber on earth knew that that is not the body type because he's got muscles where he does not need them he's got body mass that is counter to his ability to support himself right so so the point is generally and there's certain exceptions depending on environments the smaller you are the the less you weigh the thinner your legs can be and still hold up your weight and the bigger you are in mass the thicker your legs are so rhinoceros is and hippopotamuses right hippopotami and and elephants all have really thick legs because as they got bigger uh if they kept their thin legs they break their legs and that'd be that's the end of you you get eaten and that you leave the gene pool very quickly when that happens okay all the lions are missing you okay remember what we used to none of those elephants with the skinny legs man we used to just find them lying around oh they made such a delicious meal remember remember those days we were just on crutches because they kept breaking their legs right so and anyhow so snap so that's why you don't find very tiny creatures with really thick legs that's that so because they don't need it that's the point okay so so now that so that's a important fact number one whales are different because they don't weigh anything right you got to go back to our weight density and whatever you're about to say we talk about i think we talked about no we didn't but they're buoyant because they're at a certain depth in that right so they don't they so they don't have to hold up their own weight that's why they can get so big right okay so it doesn't it's not fair to say how much does that well weight 400 tons no it doesn't it weighs zero because it is neutrally buoyant in the water and if you bring it onto the land it will die because it cannot hold up its own weight it cannot do anything in its own way so you cannot say it weighs that much because that's not where it lives it makes so much sense because you've never seen a beach whale all right i'm out of here i'm good i'm good with the land thing i said i tried the beach i tried to breach that i'm gonna roll myself back on in here i'm good i'm yeah you never saw that you never saw that so that's so they don't weigh anything they don't have to hold up their own weight so they're really not so everything i'm describing is sort of in the air on earth's surface okay all right so but i'm not done oh cool not only that the laws of physics don't all manifest equally at all size scales interesting okay so um if you're going to drink water you'll put it in a glass and then you'll drink it like this right why do you put it in a glass why don't you just sort of pour it in front of you well because it'll flatten out on the table and you'll make a mess right okay but suppose i am an insect again i suppose i'm an ant does an ant need a vessel in which to put the water in order for it to drink no because water beads up there's a bead of water that does not continue to spread it could just walk up and suck the juice right out of the out of the bead of water until it's gone okay now the producers and writers of the movie bug's life knew this so when the mosquito went to the bar and ordered a drink and what drink did the mosquito order a bloody mary of course okay so bloody mary i just i just turned it to my mother i can't believe you you turn into your parents that's right turned into my parents then oh my god okay sorry bloody mary o positive okay and so the bartender which is another insect i don't remember what kind has a spigot pours out a blob of bloody mary and plunks it down in front of the mosquito and it's just a ball okay held up by surface tension surface tension is this sort of this imaginary film that exists on the surfaces of liquids that you have to sort of puncture that in order to fall through but that's that sort of film actually contains it in small enough amounts surface tension is not strong enough to contain a big blob of water like this because gravity wins but when you're small enough gravity loses against surface tension super attention wins they plop this drop of bloody mary in front of the mosquito mosquito put in its nose sucked it out and then that's that was the end of that scene this was brilliant and it's in that movie it's a pixar movie that phys people who knew physics and chemistry writing the script for that movie so different forces operate when you're small than when you are large and so that's why they have there's something called is it a jesus spider a water strider sometimes called there's a yeah there's one something that's that walks on the water swiftly and in some regions they call it a jesus spider i think um anyway because jesus in the bible walked on water well except jesus weighs more than the surface tension would have held them up so jesus would have just sunk without some kind of magic or spirit or miracle okay right whereas if you're small enough well maybe he had just giant foam sandals we didn't check it was right he was the first person to wear the giant foam sandals and they're just like oh my god jesus it's the mirror people misinterpreted it right they were like hey but go ahead so so with the so all i'm saying is that if you're small enough that surface tension you don't weigh enough to break the surface tension so then you can just sort of walk on the water as some insects do so my point is size is everything in this world and you might say well could you have something really big like a life form the size of a galaxy probably not here's why because suppose you're that big by the way the galaxy's 100 000 light years across suppose you you have your head itches and then you send the signal to the brain and then it goes to your finger and you got to bring your finger up to scratch your head well that that took uh that took about 30 million years it took it's going to take at least 100 000 years to get your arm to your head moving at the speed of light and you're probably not moving at the speed of light so so you just you're not going to be able to respond to stimulus the way life needs to in order to thrive in an environment so there's certain sizes above which are not realistic so physics contains the largest and the small and by the way you can't be so small that quantum physics prevents your molecules from from binding you can't be smaller than the sizes of molecules right because what are you at that point okay if m if molecules comprise life you can't be life that's smaller than a molecule it's just not there's no so so the chemistry and physics contain all the realms in which you will find biology and that's just the beginning of it i'm giving you the basics of it where where that's the entry level sort of size and life 101. uh so so there you have it so so so spider-man he's got the powers of a spider no not if he's that size no doesn't no he doesn't no he doesn't right no he doesn't he can't no he basically just has the powers of a really uh really good rock climber rocklin yes that's about it that's about it all right we got we got to go there good to have you always a pleasure neil degrasse tyson signing off [Music] you

Channel: StarTalk

Views: 200,770

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Keywords: startalk, star talk, startalk radio, neil degrasse tyson, neil tyson, science, space, astrophysics, astronomy, podcast, space podcast, science podcast, astronomy podcast, niel degrasse tyson, physics, Chuck Nice, A Bug’s Life, surface tension explained, Sylvester Stallone, Cliffhanger, physics of life

Id: pqa2dC5Tmb8

Length: 15min 45sec (945 seconds)

Published: Tue Dec 08 2020