00:00:00
There is this famous Google interview
question that everyone gets wrong.
00:00:04
You're shrunk down to the size of a nickel
and put into a blender.
00:00:08
The blades will start spinning in 60 seconds,
so what do you do?
00:00:13
I would like to think I could duck down
and miss the blades
00:00:16
Break the thing at the bottom maybe?
00:00:18
Push the blades?
00:00:20
Ask nicely for the blender
not to be turned on.
00:00:23
Tie my clothes together, and then like
use it as a rope I guess?
00:00:27
If I was lighter I could maybe catch a draft up?
00:00:29
- Just accept defeat.
- I mean, I'm the size of a nickel
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what quality of life is that?
00:00:34
Okay, resonance.
00:00:35
I'm going to run to one wall,
push on it, run to the other wall. Push on it.
00:00:39
Run to the other wall, so
I'm going to tip the container over.
00:00:41
Honestly, the thing I would think about
00:00:43
is trying to get to the very center
of the blades.
00:00:46
It's spinning around me, but
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the actual RPM is probably not that high,
if I'm standing in the middle.
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I tie my clothes to one of the tips
of the blades as it’s starting up.
00:00:56
Yeah, I get it to swing
me around and then I woooo!
00:00:59
But these answers don't cut it.
00:01:03
Now, I first heard about this problem
in this book.
00:01:06
It describes how each year Google received
00:01:09
about 3 million applications,
but they would only hire 7000 people.
00:01:14
That's a 0.2% acceptance rate.
00:01:16
So one way to screen out
millions of applicants was to use brainteasers,
00:01:21
and the interviewers
would make these up for fun.
00:01:25
We didn't get a list, at that time of
what questions to ask.
00:01:29
We would share questions among each other.
00:01:31
Some of them gained traction,
questions like:
00:01:33
How many golf balls can fit in a 747?
00:01:37
Or, how much should you charge
to wash all the windows in Seattle?
00:01:42
But the blender question
really stuck with me, and I'm not alone.
00:01:47
- Just lay back and enjoy that breeze.
The best model in the world is only going to
run maybe 10 or 11 hours,
00:01:54
so we're getting out and when we do, we're better off for it because whatever doesn't kill you makes you stronger.
00:01:58
- The question has been hotly debated
in Reddit comment sections.
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There are so many different answers,
but which one is the best?
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I try to hide underneath the blades,
I guess.
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Hide under the blade, probably
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Great first reaction,
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but maybe that doesn't solve your problem
entirely.
00:02:20
Now you're just stuck inside of a spinning
blender, so maybe you want to escape.
00:02:23
Can I climb the walls?
00:02:24
Are there defects in the walls that are
sufficiently large for me to grip on to?
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Do I have Van der Waals forces that are
strong enough to connect me to the wall?
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Am I, like, essentially a tiny gecko?
00:02:36
A gecko can stick
to the wall of a blender,
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even though neither its foot, nor
the glass are charged.
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The gecko's foot has to be pressed
firmly against the glass,
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so its atoms are within a few nanometers
of the glass atoms.
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Then, at any moment one atoms electrons
aren't uniformly spread about the nucleus,
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they might be slightly more on one
side than the other.
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This makes the atom momentarily
slightly positively charged
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on one side and slightly
negatively charged on the other.
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The glass atom next to it experiences
the pull of this charge imbalance,
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and so a similar charge
imbalance is induced on the glass atom,
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and therefore the electrons in the glass
atom are drawn
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to the nucleus of the gecko
atom, and vice versa.
00:03:20
So there is a very weak attractive force
between neutral atoms.
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This is known as a Van der Waals force,
and it's what makes geckos stick to walls.
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It's the same force
that holds graphite together.
00:03:32
There's no actual bonding between
the layers of graphene in a pencil.
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It's like a stack of paper.
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The layers only stick because of Van
der Waals forces.
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Now these forces are pretty weak.
00:03:44
But since we're so small, maybe
they'd be enough to help us climb out.
00:03:49
This I can almost certainly say,
we wouldn't be sticking at that scale,
00:03:52
and that's because the Van der Waals
type interactions are still small.
00:03:57
And I studied climbing, so that of these types of
scale, cockroach and gecko, you know,
00:04:02
it turns out that you have to get
very special to do that.
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Geckos have millions of tiny
branches on their feet that increase
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their surface area
and allow them to mold to surfaces.
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Our hands aren't like that,
but ants and cockroaches
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don't rely on Van der Waals forces,
and they can still climb up walls.
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So maybe a miniature human could too?
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The mechanism of a cockroach foot,
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and I used to know all that
cockroach feet, is absolutely gorgeous,
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Same with an ant, by the way.
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There's two little claws, the tarsal claws
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those are things
that slap down on a surface and really do slap
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when climbing meters a second... slap and
engage, despite having no adhesion,
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they have very sophisticated,
frictional attachment.
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Those claws can grip almost anything,
even glass.
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While glass feels smooth to us,
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It's actually covered in tiny surface
imperfections.
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At insect scale,
these features are significant.
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- Ants basically have climbing gear.
- Oh yeah.
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They're like, using these little
like axes basically to pick their way in.
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We don't have the attachment disks
or whatever that would be,
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or like the special claws
or the Van der Waals forces.
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Well, we have claws, if you're that scale,
our fingers are claws.
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We have only really got... we have
two claws, really.
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And then our feet
aren't great at climbing, I don't know.
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Well, again, at that scale though,
I don't know, right?
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Imagine putting a little sharp, spike into your foot
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and sharpen your
shoes, wear high heel shoes.
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You'll be good to go.
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So now I'm climbing in heels.
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But there's still a problem.
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I mean, I'll have to be pretty careful
placing each hand and foot slowly.
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It's going to take longer
than 60 seconds to get out.
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And in that time,
the blades will have started spinning.
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One mistake and I'm a smoothie.
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So Google was looking
for a different answer.
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Now we’re going to the physics building.
Maybe they know?
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Yeah. I really got nothing. I’m stumped.
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This is so embarrassing.
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We’re in our last year of our degree, we should
definitely know this!
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I feel like I could probably swing running
around the sides and yeeting myself out.
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Okay, if we're just talking about the entropy,
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it should increase at some point.
So some sort of chaos should be...
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None of the system will stay un-disrupted...
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Take that as a limit to infinity
and I'll be chilling...
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Like using that logic
if I just like extrapolate...
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Now that's still too big for me
to Quantum Tunnel or anything like that.
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- Whoa whoa whoa whoa.
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I mean, that is really overthinking it.
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It's actually not that complicated.
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- Do you want to hear the best answer I've heard yet?
- Sure.
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Just jump.
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Just jump?
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How would that work?
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- Just jump!
- How?
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-Does that work like that?
- Jump where?
- Out of the blender, just go up.
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- So whoever told you that is...
- ...crazy, right?
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Yeah, does that makes sense to you?
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No, it doesn't, but...
do you want to hear why that works?
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Yeah, tell me how it works.
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Jumping out of a blender seems impossible
because at nickel size,
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the wall of a blender is 15x
your height.
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It'd be like leaping over an eight story building.
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But watch these clips...
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Did you notice it?
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A horse, a dog and a squirrel.
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They all jump to about the same height.
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This is exactly what Alfonso Borrelli,
the father of biomechanics,
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looked at in the 17th century.
As he put it, in the same conditions,
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smaller and lighter animals
make bigger jumps relative to their body.
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if the other conditions are equal,
and indeed the limbs and the other organs
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are in the same proportion,
the dog will jump as far as the horse.
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Now, sure, there is variation.
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A species whose survival depends on
jumping will be optimized for it,
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while others, like turtles and elephants,
they don't jump at all.
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But when you consider the huge variations
in size,
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I mean a horse is 1500 times
heavier than a squirrel.
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It's incredible that they jump to
around the same height.
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And it's not because squirrels
are super muscly or something.
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Horses and squirrels have similar muscle
to weight percentages,
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and insects have even less muscle
relative to their weight.
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Why do you think an ant can lift
50 times its own body weight?
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Like, is it any more muscular? No
you guys hit the gym.
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Come on. Like
you're more muscular than an ant.
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So how are small things so strong?
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Well if you look closely at a muscle. It’s made up of tiny units called sarcomeres.
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They act like miniature springs.
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How far a muscle compresses depends on
how many of these springs are in series.
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But the strength of a muscle depends
only on how many are working in parallel.
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The thicker the muscle, the more springs
in parallel, and the greater the strength.
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Therefore strength depends
on the cross-sectional area of a muscle.
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And as animals shrink,
this cross-sectional area
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scales down
with the square of their height.
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But an animal's weight
is proportional to its volume,
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so that scales
with the cube of their height.
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So as you scale down, weight decreases
faster than strength,
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and as a result, smaller animals have much
higher strength to weight ratios.
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I mean, you could probably lift,
your own weight,
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like if you were to put your own body
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weight on your back and squat that, you could now lift...
100 hundred times.
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Yeah. Let's go!
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And for us, stuck in that blender,
that extra strength
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relative to our weight
means we could jump right out.
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Your surface area
decreases with the square.
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You'd be like a little superman.
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- I see, okay!
- That's really cool.
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So I could jump, like,
literally out of a blender.
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You could jump out of a blender.
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But in movies and games
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where people are shrunk,
they almost never show it like that.
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Honey, I Shrunk the Kids It was one of my favorite movies
when I was a kid.
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I loved that.
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Tiny people struggle picking up scissors.
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They almost get crushed by raindrops.
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If it was scientifically accurate, they’d actually be overpowered.
00:10:10
Most people don't think of this
when they first hear the question.
00:10:14
The answer almost seems too simple.
00:10:17
When you ask the right questions,
you define the problem.
00:10:20
There's some really obvious solutions
that work, and that's
00:10:24
actually true for a lot of problems
in the real world too.
00:10:27
Now I'm all for obvious solutions,
but from the start,
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the answer of jumping out
didn't sit right with me.
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Even this idea of like, I'm
going to jump out of the blender like that
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doesn't make sense to me,
because jumping is not just like,
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okay, how strong
you are relative to your weight.
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It's also timing
and your kinetics and all that.
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So like, how long can you be in
touch with the ground?
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How much can you apply that force in
one burst like over a really short period?
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Would it be
fair to say you're overthinking things?
00:10:55
You got to suspend your disbelief
somewhere.
00:10:58
I think if you like, factor in all the
potential challenges a human would have.
00:11:02
Just like if they just all of a sudden
that size, they don't have
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like time to practice using their legs
and stuff in that new environment.
00:11:09
Like, I don't give them very good
chances of jumping out.
00:11:11
Sometimes there are people
who make everything more complex
00:11:14
than it needs to be,
and that can be problematic.
00:11:17
I would like to see like,
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you know, realistic modeling of,
we scale me down 100 times.
00:11:23
Like, can I jump higher?
00:11:25
I want to see someone do
those physics equations, yeah,
00:11:28
you could jump higher, but you couldn’t jump
100x higher, you know?
00:11:32
So that's why we got the researchers
at Georgia Tech's biomechanics lab to investigate.
00:11:37
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00:12:49
Now let's see how that
simulation is coming along.
00:12:52
Okay, so we have our simulated blender.
00:12:55
We’re 2 centimeters tall and we have to jump at least 30 centimeters to get out.
00:13:00
I was like, well, what about me?
00:13:02
Like, I'm pretty,
you know, embarrassingly non-athletic.
00:13:06
What if I do this? So I did it right here
next to my desk.
00:13:09
My partner sort of measured my jump height,
00:13:11
and I know how much I weigh
and all that stuff.
00:13:13
So what would it look like for me?
00:13:15
If we have a person
that weighs 84kg, is squatting
00:13:19
15cm and has a jump height of 27cm.
00:13:24
That person, if they were scaled down
00:13:27
to 1% of their original size,
00:13:30
they would jump 42cm high.
00:13:33
The simple simulation
shows a jump height of 42cm.
00:13:38
So you would make it out.
00:13:40
But we need to add in air resistance.
00:13:43
Since our cross-sectional area is now
100 times larger relative to our weight,
00:13:48
drag should have a greater effect
at nickel size.
00:13:51
If it was 42cm jump height
before for the jumper, with drag...
00:13:56
considering drag, then it's about 39cm.
00:14:01
So we do decrease in jump height a little bit.
00:14:04
But that drag calculation
is assuming you jump perfectly vertically.
00:14:08
But what if you're a bit uncoordinated
and you flip onto your side mid jump?
00:14:13
Well, then you're exposing
ten times the surface area
00:14:16
and that increases
the amount of air resistance.
00:14:20
Like if somehow you flipped,
and you're still moving up like this.
00:14:23
Like what is the air resistance then?
00:14:25
So doing that,
00:14:28
that means 22 centimeter jump height.
00:14:30
Oh. So we don't we don't.
00:14:32
Oh. Darn.
00:14:34
If you start getting overconfident
and you wanted to do,
00:14:37
like, a backflip while you're at it,
then you're going to mess it up. Yeah.
00:14:42
Don't backflip out of the blender
is a good piece of advice.
00:14:46
Don't try and show off.
00:14:47
You're trying to not get chopped up.
00:14:49
Just like, just go headfirst.
00:14:51
It's not so much getting out
of the blender.
00:14:54
It's what happens next.
00:14:56
You've got two nickel sized men free
in the world. Think of the posibilities.
00:15:01
The simulation came back,
00:15:02
You can jump out of the freaking blender.
00:15:05
Alright, okay.
00:15:07
I'm glad we went through this,
this exercise.
00:15:11
Do you want me to do another month
of research on this?
00:15:13
No. You know, like you've done it.
00:15:15
You've done enough.
You've done enough. I'm convinced.
00:15:21
I feel like jumping is
an unsatisfactory answer.
00:15:24
It was unsatisfactory
when you mentioned it in the first place.
00:15:27
And you went through
and you got the simulation,
00:15:29
you got the model, and you're like, look,
you know, our little guy can jump 40cm.
00:15:33
Are you convinced now?
00:15:34
And I'm like, I guess.
00:15:37
But like, my spidey sense was tingling.
00:15:41
- Oh was it now!
- There is something going on...
00:15:44
You're telling me
that I have to apply a force
00:15:49
in 1/1000 of a second,
and I have to undergo
00:15:52
278 G's?
00:15:56
I'm not going to survive that.
00:15:58
So what I'm getting now is that, like,
my intuition was good.
00:16:03
I think everyone's intuition was like,
you can't jump out of a blender.
00:16:07
I think they're right.
00:16:09
And you may say,
00:16:10
well, that's overthinking it,
but that's the whole point of the brain
00:16:13
teaser is to overthink it is to get to
that point where you're thinking about it
00:16:18
in the detail of like,
what would actually be feasible.
00:16:22
A whole lot of things would go wrong.
00:16:24
Our hearts have to generate
a certain amount of pressure
00:16:27
to get the blood, you know, going up
to our head and going all the way down.
00:16:31
If you take the human heart
and shrink it down,
00:16:33
it's not going to be able
to generate the same kinds of forces.
00:16:36
I think it would be a catastrophe,
in a smaller size. Controlling
00:16:39
air pressure inside these countless sacks
inside of our lungs.
00:16:43
There's an exquisite balance there.
00:16:45
Now, you try to take that same design
and squeeze it down.
00:16:50
I would be skeptical that you'd be able
to keep the passageways open.
00:16:54
You wouldn't even be able
to think this through, because you just
00:16:57
wouldn't have the brain structures that we have.
00:17:00
You can't fit 86 billion neurons in a nickel sized volume.
00:17:04
You can't scale cells down either.
00:17:06
That's the thing. Like cells are cells.
00:17:09
I mean, jumping out would be, to me,
seems like your only option, but I don't
00:17:12
think you're going to be able to jump
00:17:14
because you can't breathe
and your heart can't pump blood,
00:17:18
so you just keel over and die
before you can make your jump.
00:17:23
Okay, so if you're a biologist,
you think we die.
00:17:26
If you're a physicist, you can decide
whether we'd be little supermen or,
00:17:30
as I believe, incapable
of fully harnessing our extra strength.
00:17:34
What did Borelli know?
00:17:35
He didn't even have blenders.
00:17:38
He doesn't know the stress.
00:17:39
But if you're an interviewer at Google,
you might not even care what the answer is.
00:17:45
I think one of the misconceptions
that candidates have is
00:17:49
when I'm asked this question, it's
because they want to see
00:17:53
if I can solve this problem.
00:17:55
That's actually not quite right.
00:17:56
There are five attributes
people are looking for.
00:17:58
There's addressing ambiguity,
00:18:01
There's breaking down the problem,
being creative, being smart,
00:18:05
and then communication.
00:18:06
- So I guess like none of those five are
whether it's correct.
- Right.
00:18:12
We’re the idiots who went
and tried to figure out what's the best
00:18:15
of those answers.
Um, yes!
00:18:20
Google realized that asking these types of questions
didn't make much sense.
00:18:25
Laszlo Bock, the senior vice president
of people operations at Google, said this:
00:18:30
On the hiring side, we found that brain
teasers are a complete waste of time.
00:18:34
How many golf balls
can you fit into an airplane?
00:18:37
How many gas stations are in Manhattan?
00:18:39
A complete waste of time.
They don't predict anything.
00:18:42
They serve primarily
to make the interviewer feel smart.
00:18:45
But I just feel like there's that moment
00:18:47
where you're like,
so are you going to admit you're wrong?
00:18:49
And I'm like, nyah, you know, I think
this is further to like, I'm not wrong.
00:18:54
This is crazy.
00:18:55
This question is crazy.
00:18:57
And I think it goes to your very point.
00:18:59
Your very point,
which is that like brain teasers like this
00:19:02
are not good ways to assess whether people
know what they're talking about.
00:19:07
So although brain teasers aren't useful
to assess
00:19:10
job applicants,
they are useful for something.
00:19:13
I mean, every time we ask this question
to people on the street,
00:19:17
to physics students and to scientists,
they lit up.
00:19:21
They had to try to see the world
from a new perspective.
00:19:24
And it's exactly this way of thinking
that has led to
00:19:27
some of the biggest scientific
discoveries.
00:19:29
Einstein used thought experiments
to come up with his theory of relativity.
00:19:34
Euler's solution
to the bridges of Königsberg puzzle
00:19:37
is what inspired graph theory.
00:19:39
And when Schrödinger wanted to illustrate
his problems with quantum mechanics,
00:19:43
he imagined a cat in a torture box.
00:19:47
The blender question is admittedly silly,
but silly
00:19:50
questions can yield profound answers
and show us new things.
00:19:55
I think in order to learn something new,
you have to be willing
00:19:58
to embrace the ridiculous
and just go with it.
