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(intense orchestral music)
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Everything in the universe has its size.
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Planets are big.
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Insects are small.
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People are somewhere in between.
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Everything has its place in the grand order.
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Things are as they should be.
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But does it have to be that way?
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Does size really matter or could things be different?
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After all, short people live longer than tall people.
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Small things are stronger than big things.
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And really tiny creatures can do things
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we can only dream of.
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So why are things the size they are
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and what if we could change that?
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Using the latest science,
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we are going to do the ultimate thought experiment.
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We are going to shrink everything in our world
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including us
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to see whether a smaller world really is more beautiful.
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Along the way, we're going to discover
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just how much size matters,
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how it defines everything.
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You'll never look at yourself or your world
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the same way again.
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(explosion blasting)
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You might think this looks like an ordinary house
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on an ordinary sunny morning.
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If you watched the last program,
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then you'll know that this is a parallel universe,
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one just like our own, but with one important difference.
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In this universe, we can change the size of things
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just to see what happens.
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(alarm beeping)
(man sighing)
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We're going to change the size of stars,
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planets, and living things,
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and see the surprising effect it has
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on a normal guy going about his normal day.
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We'll find out if the way things are
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is the only way they can be or if size is just an accident.
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In our last grand thought experiment,
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we made everything big, but it all went wrong, badly wrong.
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So now, we're going to go the other way
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to see if small really could be beautiful.
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(intense orchestral music)
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So where do we start?
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Since this is a thought experiment,
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we can start anywhere we like.
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So how about here?
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Home, our planet.
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Earth is the fifth largest planet in the solar system
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or the fourth smallest.
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Maybe we could move it down the scale
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towards Venus, Mars, or Mercury.
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This is the Earth you're used to,
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12,756 kilometers across
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with a circumference of 40,000 kilometers
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which takes an airliner about two days to fly around.
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There's an atmosphere
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100 kilometers deep all the way around,
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then a thin layer of solid rock,
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five thousand kilometers of rock and molten metal,
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and finally, a 2,600 kilometer ball
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of solid iron at the core.
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But these are just numbers.
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The question is do they matter?
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Is it important that our world
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is exactly the size it is now?
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Surely, it's simple enough to imagine our Earth
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but say half the size across.
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All made of the same stuff, same proportions,
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just a bit smaller.
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Problem is changing Earth's size
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changes things you don't want to be changing
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and one of those is gravity.
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Gravity, basically a very,
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very important force in the universe.
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Whenever you have an object,
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it will attract everything that you have around you.
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So this works for planets,
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but it also works for everything in the universe.
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For instance, galaxies or stars.
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Everything attracts everything.
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A half-sized planet
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means half the normal gravity at the surface,
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enough of a change to put a spring in your step.
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And if you're athletic,
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who knows what you would be capable of.
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Half gravity means you can jump higher
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and fall slower.
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So far, so good, but then the fun would stop.
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The universe is a system basically,
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so size is important in the sense
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that if you change the size of one single element
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with respect to the others, then the whole thing breaks.
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For starters, half gravity
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means air pressure is half what it was
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as the planet pulls the atmosphere less strongly towards it.
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Pressure at sea level is now
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the same as it used to be 5,500 meters up a mountain.
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There is less oxygen in every breath.
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Within a few hours, humanity would have oxygen deficiency,
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otherwise known as altitude sickness.
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Humans can adapt to thinner air.
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After a few days, red blood cell counts
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would begin to increase
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to compensate for the reduced oxygen.
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Just in time to notice the next strange change.
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The aurora is an amazing display of light
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sometimes visible near the North and South Poles,
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but why does the aurora exist
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and what has made it turn up
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far from where it's supposed to be?
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It's a puzzle, and to solve it,
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we need to look not to outer space,
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but to the University of Maryland.
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Daniel Lathrop has spent 20 years
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building models of the inside of planet Earth
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to help him understand just how our planet
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generates a magnetic field,
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work that is vital for understanding the aurora.
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Dan's model has a solid metal ball at its center
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surrounded by a thick layer of molten metal
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just like planet Earth.
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As the Earth rotates, the currents of molten metal
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generate a magnetic field.
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Dan built his model to study how this happens.
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You may wonder why he bothered.
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The fact is the Earth's magnetic field
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is very important indeed.
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So the Earth's magnetic field serves as a shield
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against the worst parts of bad solar weather.
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So the sun has storms
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that occasionally give large amounts of radiation
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aimed at the Earth.
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And the Earth's magnetic field
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inflates something like a bubble around the Earth.
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The magnetosphere that acts as a primary barrier
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to the worst of the radiation.
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It's this solar radiation
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that causes the aurora.
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The shape of the planet's protective magnetic field
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tunnels the sun's radiation towards the poles
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where it hits the upper atmosphere.
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This makes the gases glow, giving us a beautiful light show.
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But Dan's machine can also help us find out
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why a smaller Earth has auroras in unexpected places
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because over the years,
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he's built several smaller versions of his model Earth.
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So these actually are the first three sodium experiments
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we built to try to understand the Earth's magnetic field.
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So the first one,
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20 centimeter diameter model rapidly rotating.
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Next came a 30 centimeter experiment.
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There's an inner sphere deep inside there
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that you can't see.
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And the third experiment at 60 centimeters.
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Here's the bottom half of the outer sphere
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and then a solid copper model of the inner core
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that independently rotates.
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And then the whole thing
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would be filled with liquid sodium in the experiments.
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Thinking about what it would be like
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if the Earth were half sized,
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we could then examine data
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between the different size experiments
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to see how the magnetic fields are different.
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Dan's model is filled with the metal sodium
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because of its low melting point,
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but it still takes three days
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before it's fully melted and ready to spin.
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(intense orchestral music)
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So here, we see magnetic field data
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from the 30 centimeter smaller experiment
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and comparing it then to more recent data from three meter,
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it's very evident
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that as our experiments have gotten larger,
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we have much more magnetic induction,
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much stronger magnetic fields overall.
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So smaller Earth
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would have a weaker magnetosphere.
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But that's not all the experiments reveal.
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When we go from larger to a smaller experiment,
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the magnetic field strengths have both become weaker
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and have changed pattern.
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If you look at the data in the larger model,
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there's a kind of well-defined north, south magnetic poles,
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where in the smaller experiment at these parameters,
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we have like a ring of south poles around the equator
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and then two magnetic norths at either end.
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So it is possible
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for the shape of the magnetic fields to change
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when you change its size.
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A smaller Earth would be likely
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to have many magnetic poles spread around its surface
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meaning auroras could show up where you least expect them
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and they'd be stronger than ever,
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but that's a bad thing, a very bad thing.
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It's a sign that our magnetic field is being overwhelmed.
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If you have a smaller planet
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with a weaker magnetic field,
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there would be more problems with telecommunications.
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The sun still has these big angry things
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that could (mumbling) mass ejections
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where it really sends a burst of radiation in space.
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We have systems on Earth which are so big
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depending on electricity that when the sun is angry,
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potentially, you have (mumbling) and it causes problems.
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The sun's outbursts
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would cause a weaker magnetic field to wobble violently
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inducing surges in electrical systems.
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The result is havoc to power supplies,
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communications, and in fact, just about all electronics.
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Then things go from bad to worse.
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If we had no magnetic field
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around the Earth at all,
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then we would be directly hit
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by the radiation from the sun
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and the Earth would become a very, very toxic environment.
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Without the protective effect
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of a strong magnetic field, Earth is in real trouble.
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Lower gravity means gases can escape into space.
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Cosmic radiation supercharges the process.
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Eventually, there would be no air left to breathe,
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its precious atmosphere stripped and blasted away.
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(dramatic orchestral music)
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The Earth would end up like Mars.
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It's the curse of small planets.
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Small planets are not really up to supporting human life,
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so it's time to put things back to how they were.
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A planet 12,756 kilometers across
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with an atmosphere 100 kilometers deep all the way around
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and a circumference of 40,000 kilometers.
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Planet Earth just as it should be.
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Not too big, not too small.
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(alarm beeping)
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So far, so not so good.
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In pursuit of a smaller, more beautiful world,
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we turned it into an inhabitable desert.
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Maybe it's time to try something a little less risky
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like human beings.
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So how big are people anyway?
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There are about 4,000 mammal species in the world
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and they come in all different shapes and sizes.
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The largest, of course, are the whales.
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The blue whale is absolutely enormous,
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the size of several school buses put together.
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And the smallest mammal is very small.
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Two grams.
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It's essentially the size of your thumb.
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And the typical size of a mammal however,
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it not sort of in the middle.
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Instead, it's much closer to the smallest size,
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about 40 grams which is the size of a rat.
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Humans are about 65 kilos on average, give or take,
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and so that makes us enormous.
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When we look at an elephant,
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we may feel small, but in fact,
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human beings are around 1,600 times heavier
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than the average mammal,
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but that's not necessarily good news.
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Aaron Clauset is a data scientist
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who studies the relationship between size and extinction.
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What we've found is that the larger an animal is,
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the more likely that species is
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to go extinct in the long run,
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and there are various reasons for this.
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Typically, species that are larger have smaller populations
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and so if there happen to be a few bad years
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in terms of reproduction or food,
271
00:14:46,399 --> 00:14:48,300
then their population could crash,
272
00:14:48,300 --> 00:14:50,230
and as a result, they can become extinct.
273
00:14:50,230 --> 00:14:52,070
Whereas much smaller animals
274
00:14:52,070 --> 00:14:54,080
typically have much larger populations
275
00:14:54,080 --> 00:14:57,793
and so they are robust to these kinds of events.
276
00:15:01,511 --> 00:15:04,030
In the extinction that wiped out the dinosaurs,
277
00:15:04,030 --> 00:15:07,763
every land creature that weighed over 25 kilograms died
278
00:15:07,763 --> 00:15:11,493
which is why the only dinosaurs we have today are the birds.
279
00:15:13,220 --> 00:15:15,040
So in general, the larger the animal is,
280
00:15:15,040 --> 00:15:16,713
the faster it goes extinct.
281
00:15:17,837 --> 00:15:18,670
Bye-bye.
282
00:15:20,560 --> 00:15:21,810
For living things,
283
00:15:21,810 --> 00:15:24,500
size is a matter of life or death,
284
00:15:24,500 --> 00:15:27,160
but human size is not fixed.
285
00:15:27,160 --> 00:15:29,903
It has changed a lot over the course of history.
286
00:15:31,549 --> 00:15:35,330
Back in the Stone Age when humans lived as hunter-gatherers,
287
00:15:35,330 --> 00:15:37,480
the average male height was similar to now.
288
00:15:39,000 --> 00:15:42,456
During the Neolithic Revolution when we started farming,
289
00:15:42,456 --> 00:15:46,136
we shrunk hugely as our new grain-based diet
290
00:15:46,136 --> 00:15:48,203
had a lower nutritional value.
291
00:15:49,500 --> 00:15:52,521
Humans stayed short for several thousand years.
292
00:15:52,521 --> 00:15:54,820
It's only in the last 200 years
293
00:15:54,820 --> 00:15:57,570
that we finally got back to hunter-gatherer size
294
00:15:57,570 --> 00:15:59,910
and beyond thanks to modern improvements
295
00:15:59,910 --> 00:16:01,660
in food and medicine.
296
00:16:01,660 --> 00:16:06,010
But paradoxically, getting taller isn't always a good thing.
297
00:16:06,010 --> 00:16:07,100
Although big animals
298
00:16:07,100 --> 00:16:09,435
have longer lifespans than smaller ones,
299
00:16:09,435 --> 00:16:12,900
within each species, the story is different.
300
00:16:12,900 --> 00:16:14,870
It's been observed that in many species,
301
00:16:14,870 --> 00:16:17,840
it's the shorter individuals that actually live longer
302
00:16:17,840 --> 00:16:19,450
like in dogs.
303
00:16:19,450 --> 00:16:22,283
Could the same also be true for humans?
304
00:16:29,434 --> 00:16:31,120
I guess in a lot of species
305
00:16:31,120 --> 00:16:34,520
and if we look at dogs, horses, elephants,
306
00:16:34,520 --> 00:16:37,167
it's actually the smaller variants of that species
307
00:16:37,167 --> 00:16:39,170
that seem to live longer.
308
00:16:39,170 --> 00:16:41,100
And of course, then the real question is
309
00:16:41,100 --> 00:16:43,340
does it also apply to humans?
310
00:16:43,340 --> 00:16:45,620
But that's not so easy to answer.
311
00:16:45,620 --> 00:16:48,120
There are so many influences on our lives.
312
00:16:48,120 --> 00:16:50,120
How can you tell what's due to size
313
00:16:50,120 --> 00:16:52,563
and what's due to, say, diet or exercise?
314
00:16:53,645 --> 00:16:57,250
Geneticist Diana van Heemst has been reexamining
315
00:16:57,250 --> 00:17:01,280
a remarkable 1970's study that found a solution.
316
00:17:01,280 --> 00:17:03,081
It honed in on a group of people
317
00:17:03,081 --> 00:17:06,880
with very similar lifestyles, but varying heights.
318
00:17:06,880 --> 00:17:08,183
Professional athletes.
319
00:17:09,310 --> 00:17:11,083
For example, American baseball players,
320
00:17:11,083 --> 00:17:13,566
there's a nice encyclopedia
321
00:17:13,566 --> 00:17:16,450
which is actually a rich source of information
322
00:17:16,450 --> 00:17:18,607
not only for the baseball fans
323
00:17:18,607 --> 00:17:22,820
about all the details of batting performances and nicknames,
324
00:17:22,820 --> 00:17:25,510
but also actually, it contains date of birth,
325
00:17:25,510 --> 00:17:30,200
date of death, their adult height, and their weight.
326
00:17:30,200 --> 00:17:31,870
The study took this information
327
00:17:31,870 --> 00:17:35,660
on height and age of death and looked for a pattern.
328
00:17:35,660 --> 00:17:38,033
Wally Burnette, one meter 83.
329
00:17:42,120 --> 00:17:45,053
Murry Dickson, one meter 78.
330
00:17:46,904 --> 00:17:48,980
The original study used data
331
00:17:48,980 --> 00:17:50,940
from thousands of players,
332
00:17:50,940 --> 00:17:52,390
but we can see what they discovered
333
00:17:52,390 --> 00:17:53,753
by looking at just a few.
334
00:17:56,739 --> 00:17:59,740
I took from the encyclopedia of baseball
335
00:17:59,740 --> 00:18:02,891
nine representative examples of baseball players,
336
00:18:02,891 --> 00:18:06,970
and we have, you know, attached them to the wall
337
00:18:06,970 --> 00:18:10,020
based on the height and the age at death.
338
00:18:10,020 --> 00:18:13,160
And this kindly mimics the original study
339
00:18:13,160 --> 00:18:16,618
which made use of the full sample of the encyclopedia
340
00:18:16,618 --> 00:18:19,550
which found there's negative correlation
341
00:18:19,550 --> 00:18:22,417
between height and the age at death.
342
00:18:22,417 --> 00:18:26,830
The 1970s study found that size did matter.
343
00:18:26,830 --> 00:18:30,070
Being five centimeters shorter meant on average
344
00:18:30,070 --> 00:18:32,650
you would live two years longer.
345
00:18:32,650 --> 00:18:35,070
The big question is why.
346
00:18:35,070 --> 00:18:38,246
Although the original work was conducted in the 1970s,
347
00:18:38,246 --> 00:18:40,870
it's only now researchers like Diana
348
00:18:40,870 --> 00:18:43,490
have come up with a possible explanation.
349
00:18:43,490 --> 00:18:46,610
In order to grow, our body makes growth hormone
350
00:18:46,610 --> 00:18:48,670
which stimulates growth,
351
00:18:48,670 --> 00:18:51,240
but at the same time, it also influences
352
00:18:51,240 --> 00:18:54,071
lots of other processes in our body.
353
00:18:54,071 --> 00:18:56,133
And if you look at the data
354
00:18:56,133 --> 00:18:59,618
that have been derived from work on other animals,
355
00:18:59,618 --> 00:19:03,370
we can see that those growth hormones,
356
00:19:03,370 --> 00:19:05,590
they stimulate the body to grow
357
00:19:05,590 --> 00:19:07,330
and this is kind of a signal
358
00:19:07,330 --> 00:19:08,770
that there's enough food,
359
00:19:08,770 --> 00:19:10,817
that there's favorable conditions
360
00:19:10,817 --> 00:19:14,834
that it would be wise to invest as much as possible energy
361
00:19:14,834 --> 00:19:16,700
in growth and reproduction.
362
00:19:16,700 --> 00:19:18,510
And this may come at a cost
363
00:19:18,510 --> 00:19:20,700
because it means there's less energy available
364
00:19:20,700 --> 00:19:24,250
to invest simply in maintaining our bodies in good shape.
365
00:19:24,250 --> 00:19:27,600
And actually, when conditions get adverse
366
00:19:27,600 --> 00:19:31,120
or become less favorable like when there is a food shortage
367
00:19:31,120 --> 00:19:32,550
or lots of toxins,
368
00:19:32,550 --> 00:19:36,776
then as a consequence, as a response to that, we don't grow.
369
00:19:36,776 --> 00:19:38,300
We kind of stop growth
370
00:19:38,300 --> 00:19:40,260
and we really invest the available energy
371
00:19:40,260 --> 00:19:41,620
in maintaining our body
372
00:19:41,620 --> 00:19:46,438
and trying to kind of survive this period of hardship
373
00:19:46,438 --> 00:19:48,343
until things get better.
374
00:19:49,280 --> 00:19:52,622
It seems being big comes at a price.
375
00:19:52,622 --> 00:19:54,150
But for tall people,
376
00:19:54,150 --> 00:19:56,550
there is some light at the end of the tunnel.
377
00:19:56,550 --> 00:19:59,000
However, height is not the only thing that matters.
378
00:19:59,000 --> 00:20:01,130
There's lots of things that people can do themselves
379
00:20:01,130 --> 00:20:02,609
to adopt a healthy lifestyle
380
00:20:02,609 --> 00:20:06,650
like not smoking, healthy food, lots of exercise.
381
00:20:06,650 --> 00:20:11,417
So it matters, but it's not the only thing that matters.
382
00:20:19,640 --> 00:20:21,690
So just how small can we go?
383
00:20:22,980 --> 00:20:25,567
Well, let's start with what we know.
384
00:20:25,567 --> 00:20:28,346
The smallest adult humans known to science
385
00:20:28,346 --> 00:20:31,370
are just over 50 centimeters tall
386
00:20:31,370 --> 00:20:34,563
like Jyoti Amge, the world's smallest woman.
387
00:20:48,580 --> 00:20:50,650
24 year old student Jyoti
388
00:20:50,650 --> 00:20:53,040
is on a sight seeing trip to London.
389
00:20:53,040 --> 00:20:55,470
Wherever she goes, she gets as much attention
390
00:20:55,470 --> 00:20:56,933
as the biggest attractions.
391
00:21:02,230 --> 00:21:03,880
When I go outside,
392
00:21:05,270 --> 00:21:07,833
then everyone gathers together and stares at me.
393
00:21:09,900 --> 00:21:13,743
Then I feel a bit strange, but at the same time,
394
00:21:15,340 --> 00:21:17,290
it feels good that they all look at me.
395
00:21:20,210 --> 00:21:21,600
In our last episode,
396
00:21:21,600 --> 00:21:25,290
we met Sultan Kosen, the world's tallest man.
397
00:21:25,290 --> 00:21:27,100
Sultan is so tall because his body
398
00:21:27,100 --> 00:21:29,063
produces too much growth hormone.
399
00:21:30,100 --> 00:21:32,663
For Jyoti, the opposite is true.
400
00:21:33,964 --> 00:21:38,524
While Sultan has various health issues caused by being tall,
401
00:21:38,524 --> 00:21:40,693
for Jyoti, the story is different.
402
00:21:42,097 --> 00:21:43,680
The doctors told me
403
00:21:43,680 --> 00:21:45,433
I have hormone deficiency.
404
00:21:46,880 --> 00:21:48,993
This is the reason I can't grow taller.
405
00:21:50,040 --> 00:21:52,033
I don't have any other health problems.
406
00:21:53,070 --> 00:21:55,400
Jyoti's main complaint is simple.
407
00:21:55,400 --> 00:21:57,100
The world is just too big for her.
408
00:21:59,530 --> 00:22:00,940
One thing which I can't do
409
00:22:00,940 --> 00:22:03,283
because of my height is drive cars,
410
00:22:04,290 --> 00:22:08,013
and when I want to go out, I can't go out alone.
411
00:22:10,130 --> 00:22:12,220
I always have to have help from my family
412
00:22:13,830 --> 00:22:15,500
like my sisters and brothers.
413
00:22:15,500 --> 00:22:17,220
I always need help.
414
00:22:17,220 --> 00:22:19,660
These are the problems I face.
415
00:22:19,660 --> 00:22:22,110
But in a specially adapted environment,
416
00:22:22,110 --> 00:22:23,293
it's a different story.
417
00:22:26,080 --> 00:22:26,970
In my house,
418
00:22:26,970 --> 00:22:29,123
everything is specially made for me.
419
00:22:30,860 --> 00:22:35,860
In my bedroom, I have a small bed, cupboard, chair, table,
420
00:22:39,410 --> 00:22:42,533
and everything made in my size, all my furniture.
421
00:22:45,090 --> 00:22:47,423
I don't have any problems in my house.
422
00:22:52,637 --> 00:22:55,693
So what if we were all the size of Jyoti?
423
00:22:57,530 --> 00:23:00,630
We could adapt our environment to suit our smaller size.
424
00:23:09,540 --> 00:23:11,800
We would need less food and energy,
425
00:23:11,800 --> 00:23:13,250
which has to be a good thing.
426
00:23:16,254 --> 00:23:18,593
But surely, we can go further than this.
427
00:23:21,490 --> 00:23:23,573
Could a mammal this small survive?
428
00:23:25,220 --> 00:23:26,920
The answer is yes.
429
00:23:26,920 --> 00:23:30,880
In the wild, Etruscan shrews weigh just two grams
430
00:23:32,920 --> 00:23:35,820
which makes them one of the smallest mammals in the world.
431
00:23:37,060 --> 00:23:40,480
So it's a good role model for a miniature human being.
432
00:23:40,480 --> 00:23:42,430
Each one has a heart, lungs,
433
00:23:42,430 --> 00:23:44,434
and all the organs you would expect,
434
00:23:44,434 --> 00:23:47,473
but the similarities with human beings stop there.
435
00:23:48,370 --> 00:23:50,600
This tiny mammal lives its life
436
00:23:50,600 --> 00:23:52,733
right at the edge of what is possible.
437
00:23:53,730 --> 00:23:56,873
Professor Michael Brecht has studied them for years.
438
00:23:58,160 --> 00:23:59,153
Here they are.
439
00:24:00,353 --> 00:24:03,330
And I want to chase them into this.
440
00:24:03,330 --> 00:24:05,610
So now, here we have him.
441
00:24:05,610 --> 00:24:09,480
Let me show you what we do for gender determination.
442
00:24:09,480 --> 00:24:12,460
So the sexes, they look quite similar.
443
00:24:12,460 --> 00:24:16,330
The really foolproof sex testing
444
00:24:16,330 --> 00:24:17,800
is what I'm gonna do now.
445
00:24:17,800 --> 00:24:20,853
So we actually use this box here
446
00:24:20,853 --> 00:24:24,304
and what you do is you carefully,
447
00:24:24,304 --> 00:24:27,440
you put the shrew into the little box
448
00:24:27,440 --> 00:24:29,320
and you carefully sniff on it.
449
00:24:29,320 --> 00:24:34,320
Now, if it's very, very stinky, it turns out it's a female.
450
00:24:34,786 --> 00:24:38,763
If you sniff on it and you pass out, it's a male.
451
00:24:40,160 --> 00:24:41,793
So let me do this here.
452
00:24:43,180 --> 00:24:44,740
Female.
453
00:24:44,740 --> 00:24:47,233
Okay, now let's figure out how much she weighs.
454
00:24:49,040 --> 00:24:52,110
This is on the higher side for these animals.
455
00:24:52,110 --> 00:24:54,950
Many of the adults are just two grams.
456
00:24:54,950 --> 00:24:59,630
They have perfectly the same mammalian equipment.
457
00:24:59,630 --> 00:25:01,250
It's all there.
458
00:25:01,250 --> 00:25:03,154
It's just very tiny.
459
00:25:03,154 --> 00:25:06,840
It's very difficult to circulate blood
460
00:25:06,840 --> 00:25:08,370
through such a small body.
461
00:25:08,370 --> 00:25:10,300
The circulation system of mammals,
462
00:25:10,300 --> 00:25:13,679
it's much more suitable for bigger bodies.
463
00:25:13,679 --> 00:25:17,216
And both the respiration and the blood supply
464
00:25:17,216 --> 00:25:20,700
are a huge challenge for such a small body.
465
00:25:20,700 --> 00:25:24,430
So what we would see is they have a (mumbling) heart
466
00:25:24,430 --> 00:25:28,860
of 5% of the body weight or so, a really big heart.
467
00:25:28,860 --> 00:25:30,960
What we also see
468
00:25:30,960 --> 00:25:34,460
is that they have unheard of respiration rates.
469
00:25:34,460 --> 00:25:37,490
So when they are very excited, very nervous,
470
00:25:37,490 --> 00:25:39,910
one would see breaths per minute
471
00:25:39,910 --> 00:25:43,440
go up to about 1,000 breaths per minute,
472
00:25:43,440 --> 00:25:46,610
an absolutely unheard of rate in mammals.
473
00:25:46,610 --> 00:25:48,500
Really, also difficult to understand
474
00:25:48,500 --> 00:25:53,143
how a mammalian brain and lung could do that.
475
00:25:54,070 --> 00:25:57,628
Almost a thousand breaths a minute is certainly fast,
476
00:25:57,628 --> 00:26:00,780
but their hearts push things even further,
477
00:26:00,780 --> 00:26:03,430
beating up to 1,500 times a minute.
478
00:26:03,430 --> 00:26:06,303
That's 20 beat for every beat of a human heart.
479
00:26:07,210 --> 00:26:10,630
It's clearly hard work for a mammal to be so small.
480
00:26:10,630 --> 00:26:12,850
The question is why bother?
481
00:26:12,850 --> 00:26:17,468
The idea that ecologists have about these animals
482
00:26:17,468 --> 00:26:21,339
is that they are specialists for small spaces, yeah?
483
00:26:21,339 --> 00:26:26,339
For tunnels, and that they go into small spaces
484
00:26:26,368 --> 00:26:28,590
where no other predator can go
485
00:26:28,590 --> 00:26:30,360
and where they're then paradoxically,
486
00:26:30,360 --> 00:26:32,880
are again big predators.
487
00:26:32,880 --> 00:26:34,800
Matching your size to your environment
488
00:26:34,800 --> 00:26:37,060
is an important part of evolution,
489
00:26:37,060 --> 00:26:40,975
but filling this niche comes at an incredible cost.
490
00:26:40,975 --> 00:26:43,943
The biggest problem they face is heat loss.
491
00:26:45,158 --> 00:26:47,640
You see him in a thermal camera
492
00:26:47,640 --> 00:26:51,599
and you see how much heat he gives off,
493
00:26:51,599 --> 00:26:53,550
how much he lights up.
494
00:26:53,550 --> 00:26:57,365
And this is actually a central problem of their life.
495
00:26:57,365 --> 00:27:02,322
Their immense heat loss they have or energy loss they have
496
00:27:02,322 --> 00:27:06,863
as a result of their unfavorable surface to volume ratio.
497
00:27:07,910 --> 00:27:09,460
For every gram of body mass,
498
00:27:09,460 --> 00:27:11,010
small creatures like the shrew
499
00:27:11,010 --> 00:27:13,890
have more skin than bigger creatures like us.
500
00:27:13,890 --> 00:27:15,963
A human has a quarter of a square centimeter
501
00:27:15,963 --> 00:27:20,930
of skin for every gram, but a shrew has much more,
502
00:27:20,930 --> 00:27:23,536
almost 20 times more, in fact.
503
00:27:23,536 --> 00:27:26,620
So a shrew loses heat much more easily,
504
00:27:26,620 --> 00:27:29,670
which is particularly bad news for a mammal.
505
00:27:29,670 --> 00:27:31,560
Unlike insects and reptiles,
506
00:27:31,560 --> 00:27:33,770
mammals have to keep their bodies at a temperature
507
00:27:33,770 --> 00:27:36,603
of around 37 degrees centigrade to survive.
508
00:27:38,070 --> 00:27:40,440
Only one mammal has the heat loss problem
509
00:27:40,440 --> 00:27:43,573
worse than Etruscan shrews, their babies.
510
00:27:45,720 --> 00:27:50,160
But somehow, with the help of their parents, they survive.
511
00:27:50,160 --> 00:27:52,500
The newborn shrews are incredibly small,
512
00:27:52,500 --> 00:27:55,210
inconceivably small, 0.2 grams.
513
00:27:55,210 --> 00:27:57,640
It's just absolutely incredible.
514
00:27:57,640 --> 00:27:59,780
And they look kind of unreal.
515
00:27:59,780 --> 00:28:02,370
I mean, the whole body is totally transparent.
516
00:28:02,370 --> 00:28:04,611
They huddle together very heavenly.
517
00:28:04,611 --> 00:28:07,160
The mother is very protective
518
00:28:07,160 --> 00:28:12,160
and obviously also supplies a lot of energy.
519
00:28:15,740 --> 00:28:17,730
If mammals can get this small,
520
00:28:17,730 --> 00:28:19,033
then why not a human?
521
00:28:22,880 --> 00:28:24,630
It's feasible that the human body
522
00:28:24,630 --> 00:28:27,650
could work at just five centimeters tall,
523
00:28:27,650 --> 00:28:30,970
but of course, we'd face all the same problems as the shrew.
524
00:28:30,970 --> 00:28:34,353
An insane heart rate and a constant battle to keep warm.
525
00:28:37,700 --> 00:28:41,653
Life at this size requires a totally different lifestyle.
526
00:28:44,500 --> 00:28:48,250
It's not just about huddling together for warmth,
527
00:28:48,250 --> 00:28:50,260
if you're losing energy fast,
528
00:28:50,260 --> 00:28:52,750
you need to be very good at replacing it.
529
00:28:52,750 --> 00:28:54,540
In fact, scientists have discovered
530
00:28:54,540 --> 00:28:56,490
that small animals have to have
531
00:28:56,490 --> 00:28:58,643
a completely different relationship to food
532
00:28:58,643 --> 00:29:00,700
than big animals.
533
00:29:00,700 --> 00:29:01,920
More than 100 years ago,
534
00:29:01,920 --> 00:29:04,800
a scientist named Kleiber observed empirically
535
00:29:04,800 --> 00:29:07,414
that the amount of food that an animal requires
536
00:29:07,414 --> 00:29:10,780
increases, of course, with how big the animal is.
537
00:29:10,780 --> 00:29:13,411
So an elephant eats more than a deer does.
538
00:29:13,411 --> 00:29:16,700
But the relationship doesn't go up proportionately.
539
00:29:16,700 --> 00:29:19,642
So an elephant eats a little bit less than you'd expect
540
00:29:19,642 --> 00:29:22,583
than an equal number of deers would.
541
00:29:25,860 --> 00:29:28,942
An Asian elephant weighs about 5,000 kilograms,
542
00:29:28,942 --> 00:29:30,593
but how much does it eat?
543
00:29:31,776 --> 00:29:33,633
Just ask a zookeeper.
544
00:29:37,154 --> 00:29:38,460
This is the amount of hay
545
00:29:38,460 --> 00:29:40,710
one of our male elephants get every day.
546
00:29:40,710 --> 00:29:43,530
43 kilos to 45 kilos.
547
00:29:43,530 --> 00:29:46,440
Which is about 1% of its body weight.
548
00:29:46,440 --> 00:29:49,780
For the dik-dik, their mass is about seven kilos.
549
00:29:49,780 --> 00:29:51,240
This is amount of alfalfa
550
00:29:51,240 --> 00:29:53,317
our dik-dik get on a daily basis.
551
00:29:53,317 --> 00:29:55,440
0.5 kilos.
552
00:29:55,440 --> 00:29:57,933
Around 7% of its body mass.
553
00:29:59,852 --> 00:30:02,540
Repeat this for all kinds of different animals
554
00:30:02,540 --> 00:30:04,070
and a clear pattern emerges.
555
00:30:04,070 --> 00:30:05,870
The smaller the animal,
556
00:30:05,870 --> 00:30:08,917
the more food energy they need per kilo of body mass.
557
00:30:08,917 --> 00:30:10,499
And for the smallest animals,
558
00:30:10,499 --> 00:30:13,633
the amount of food they need goes through the roof.
559
00:30:17,000 --> 00:30:19,300
Applied to our five centimeter human,
560
00:30:19,300 --> 00:30:20,680
Kleiber's Law reveals
561
00:30:20,680 --> 00:30:23,343
we'd have to eat our own body weight every day.
562
00:30:26,923 --> 00:30:29,830
Most of our life would be spent looking for food
563
00:30:31,070 --> 00:30:32,623
just like the Etruscan shrew.
564
00:30:38,631 --> 00:30:41,403
But what if we went smaller still?
565
00:30:42,240 --> 00:30:43,841
So if you were to take a mammal
566
00:30:43,841 --> 00:30:47,660
and to make it smaller than the smallest current mammal,
567
00:30:47,660 --> 00:30:49,709
then it would cease to be a mammal as we know it
568
00:30:49,709 --> 00:30:53,220
because the rate at which it would lose heat
569
00:30:53,220 --> 00:30:54,500
into the environment would be so great,
570
00:30:54,500 --> 00:30:57,225
it couldn't maintain its internal temperature
571
00:30:57,225 --> 00:30:58,850
to be warm blooded.
572
00:30:58,850 --> 00:31:00,990
And so it would have to change its physiology.
573
00:31:00,990 --> 00:31:02,240
It would have to become cold blooded
574
00:31:02,240 --> 00:31:03,830
and use different strategies
575
00:31:03,830 --> 00:31:05,680
in order to regulate its temperature.
576
00:31:07,660 --> 00:31:08,760
So going smaller
577
00:31:08,760 --> 00:31:11,620
means saying goodbye to being a mammal.
578
00:31:11,620 --> 00:31:13,319
From here on, we'll need to be cold blooded
579
00:31:13,319 --> 00:31:15,403
with organs more like an insect.
580
00:31:17,220 --> 00:31:19,954
But it's worth it because incredible things start happening
581
00:31:19,954 --> 00:31:22,403
once you get down to the size of a wasp.
582
00:31:25,590 --> 00:31:28,000
At Cambridge University, they're finding
583
00:31:28,000 --> 00:31:29,920
that for very small creatures,
584
00:31:29,920 --> 00:31:31,920
the world is a completely different place
585
00:31:31,920 --> 00:31:33,600
to the one we experience.
586
00:31:35,163 --> 00:31:38,763
It's as if they're ruled by separate laws of physics.
587
00:31:39,780 --> 00:31:41,120
In terms of their relative strength,
588
00:31:41,120 --> 00:31:43,519
you might almost say that insects are superheroes.
589
00:31:43,519 --> 00:31:45,350
So some of the strongest ants
590
00:31:45,350 --> 00:31:47,560
can easily carry four or five times their own body weight
591
00:31:47,560 --> 00:31:49,960
which for us is the equivalent of of almost a small car
592
00:31:49,960 --> 00:31:52,150
if you're a relatively big human.
593
00:31:52,150 --> 00:31:54,290
This is all because volume, area,
594
00:31:54,290 --> 00:31:56,880
and length change by different amounts
595
00:31:56,880 --> 00:31:58,363
when you make things small.
596
00:31:59,330 --> 00:32:01,770
The overall effect is to make small creatures
597
00:32:01,770 --> 00:32:04,163
relatively much stronger than big ones.
598
00:32:05,490 --> 00:32:08,600
Professor David Labonte carries out tests on ants
599
00:32:08,600 --> 00:32:10,103
to see just how strong.
600
00:32:11,467 --> 00:32:13,180
Ants support the weight of a paintbrush
601
00:32:13,180 --> 00:32:15,010
which is roughly 2.5 grams.
602
00:32:15,010 --> 00:32:17,960
That corresponds to around 500 times its own weight
603
00:32:17,960 --> 00:32:20,860
which would be the equivalent of me for 40 tonnes
604
00:32:20,860 --> 00:32:23,760
which is probably about six, seven lorries.
605
00:32:23,760 --> 00:32:25,480
So it's really quite impressive.
606
00:32:30,667 --> 00:32:32,530
But there's more to being small
607
00:32:32,530 --> 00:32:34,464
than just strength.
608
00:32:34,464 --> 00:32:37,214
(insect buzzing)
609
00:32:38,310 --> 00:32:39,860
As we know, small creatures
610
00:32:39,860 --> 00:32:42,057
have bigger surface area for their weight,
611
00:32:50,070 --> 00:32:52,213
a fact that can be a life saver.
612
00:32:54,370 --> 00:32:55,610
So one of the very first studies
613
00:32:55,610 --> 00:32:57,920
that thought about the question how size matters
614
00:32:57,920 --> 00:32:59,889
and what the right size for an animal is
615
00:32:59,889 --> 00:33:00,980
thought about the problem
616
00:33:00,980 --> 00:33:03,059
of why you can drop an ant down a shaft
617
00:33:03,059 --> 00:33:05,756
and the ant just falls down the ground and walks away,
618
00:33:05,756 --> 00:33:07,562
but if you would do the same to a human,
619
00:33:07,562 --> 00:33:09,000
the human would break.
620
00:33:09,000 --> 00:33:10,590
Because the ant is so small,
621
00:33:10,590 --> 00:33:12,940
air resistance is much more important for the ant.
622
00:33:12,940 --> 00:33:14,880
So the velocity with which the ant hits the ground
623
00:33:14,880 --> 00:33:17,923
is much slower than what would happen to a human.
624
00:33:20,191 --> 00:33:21,520
Taken to an extreme,
625
00:33:21,520 --> 00:33:25,096
it's why rock dust floats in the air but rocks don't
626
00:33:25,096 --> 00:33:28,260
even though they're made of the same stuff.
627
00:33:28,260 --> 00:33:31,160
And there are even more advantages to being so small.
628
00:33:31,160 --> 00:33:32,890
So one of the things we're interested in
629
00:33:32,890 --> 00:33:35,042
is how well insects stick.
630
00:33:35,042 --> 00:33:37,550
And one of the techniques we use to measure that
631
00:33:37,550 --> 00:33:38,628
is a centrifuge.
632
00:33:38,628 --> 00:33:41,600
So we take a little ant, put it on a centrifuge,
633
00:33:41,600 --> 00:33:43,379
and start spinning it around.
634
00:33:43,379 --> 00:33:46,120
And we then try and measure at what acceleration
635
00:33:46,120 --> 00:33:48,270
these ants actually fall of the centrifuge.
636
00:33:49,872 --> 00:33:51,360
Wow.
637
00:33:51,360 --> 00:33:52,470
G-force is the name
638
00:33:52,470 --> 00:33:55,313
for the feeling you might get on a steep rollercoaster.
639
00:33:56,600 --> 00:33:59,443
In the tightest turn, you might experience six G.
640
00:34:00,720 --> 00:34:03,660
But even with much, much higher g-forces,
641
00:34:03,660 --> 00:34:06,210
somehow, the ants hang on.
642
00:34:06,210 --> 00:34:07,250
And during these measurements,
643
00:34:07,250 --> 00:34:09,780
we've seen ants withstand 500 G, 1,000 G
644
00:34:09,780 --> 00:34:11,660
for 10, 20, even 30 seconds,
645
00:34:11,660 --> 00:34:14,740
and then they fall off and walk off as if nothing happened.
646
00:34:14,740 --> 00:34:16,570
It's this same ability to hang on
647
00:34:16,570 --> 00:34:19,980
that allows insects to walk up the smoothest of walls,
648
00:34:19,980 --> 00:34:21,800
even hang on to the ceiling.
649
00:34:21,800 --> 00:34:23,260
So how does it work?
650
00:34:23,260 --> 00:34:25,130
Insects, or geckos, or any animal
651
00:34:25,130 --> 00:34:26,367
that climbs with adhesive feet,
652
00:34:26,367 --> 00:34:27,640
they can't use a glue
653
00:34:27,640 --> 00:34:29,310
because it would take a long time
654
00:34:29,310 --> 00:34:30,810
to activate and deactivate.
655
00:34:30,810 --> 00:34:32,730
So as far as we know, climbing animals
656
00:34:32,730 --> 00:34:35,750
use intermolecular forces to stick to surfaces.
657
00:34:35,750 --> 00:34:36,583
It's still under debate
658
00:34:36,583 --> 00:34:38,640
what exactly these intermolecular forces are.
659
00:34:38,640 --> 00:34:40,023
If you have two molecules and they attract each other,
660
00:34:40,023 --> 00:34:43,050
then you have to convince them to split apart
661
00:34:43,050 --> 00:34:45,363
and that's when helps these animals to stick.
662
00:34:46,250 --> 00:34:47,160
We experience
663
00:34:47,160 --> 00:34:49,836
these intramolecular sticking forces too,
664
00:34:49,836 --> 00:34:51,978
but at our normal human size,
665
00:34:51,978 --> 00:34:53,730
we're not even aware of them
666
00:34:53,730 --> 00:34:55,913
because they're tiny compared to gravity.
667
00:34:56,840 --> 00:35:00,383
But once more, being small changes the rules.
668
00:35:00,383 --> 00:35:04,673
A five millimeter human could climb a wall just like an ant.
669
00:35:06,110 --> 00:35:09,080
But it's not all good news for small creatures.
670
00:35:09,080 --> 00:35:11,760
A five millimeter human may be good at climbing,
671
00:35:11,760 --> 00:35:14,060
but he might not understand why he's doing it.
672
00:35:14,966 --> 00:35:19,040
It's a problem that affects all very small creatures.
673
00:35:19,040 --> 00:35:20,113
Brain size.
674
00:35:21,721 --> 00:35:23,624
Our brains rely on our neurons
675
00:35:23,624 --> 00:35:25,250
and it looks like that neurons
676
00:35:25,250 --> 00:35:28,260
remain relatively constant in size across different animals.
677
00:35:28,260 --> 00:35:30,890
So whether you're a very small or a very big animal,
678
00:35:30,890 --> 00:35:33,460
the neuron is approximately the same size.
679
00:35:33,460 --> 00:35:35,610
Now, this immediately means that if you're very small,
680
00:35:35,610 --> 00:35:37,150
you have fewer neurons,
681
00:35:37,150 --> 00:35:38,590
and that might present you with a problem
682
00:35:38,590 --> 00:35:40,560
regarding your cognitive abilities.
683
00:35:40,560 --> 00:35:41,550
The bottom line is
684
00:35:41,550 --> 00:35:43,240
if you're going to get really small,
685
00:35:43,240 --> 00:35:44,963
you're going to lose brain power.
686
00:35:49,719 --> 00:35:51,020
A five millimeter human
687
00:35:51,020 --> 00:35:53,270
would only have around two million neurons
688
00:35:53,270 --> 00:35:55,940
which puts him somewhere between a cockroach
689
00:35:55,940 --> 00:35:57,542
and a small fish.
690
00:35:57,542 --> 00:35:58,983
Smart enough to spot food,
691
00:36:02,554 --> 00:36:04,440
but probably not smart enough
692
00:36:04,440 --> 00:36:06,693
to worry about the puddle of coffee in the way.
693
00:36:09,070 --> 00:36:10,490
For normal size people,
694
00:36:10,490 --> 00:36:12,463
surface tension is barely noticeable,
695
00:36:13,340 --> 00:36:16,910
but when you're tiny, it's suddenly deadly.
696
00:36:16,910 --> 00:36:17,930
Surface tension is a force
697
00:36:17,930 --> 00:36:19,400
that becomes very, very powerful
698
00:36:19,400 --> 00:36:20,800
if you're very small,
699
00:36:20,800 --> 00:36:23,090
and really unimportant if you're really big.
700
00:36:23,090 --> 00:36:24,451
So for very small animals,
701
00:36:24,451 --> 00:36:26,552
a droplet of water can be very dangerous
702
00:36:26,552 --> 00:36:29,352
while very large animals will hardly notice the droplet.
703
00:36:31,490 --> 00:36:33,040
Super powers or not,
704
00:36:33,040 --> 00:36:35,006
being small has too many downsides
705
00:36:35,006 --> 00:36:38,290
like tiny brains, constantly looking for food,
706
00:36:38,290 --> 00:36:40,170
and of course, if you're that small,
707
00:36:40,170 --> 00:36:42,570
almost everything in the world wants to eat you.
708
00:36:44,152 --> 00:36:47,690
So it's for the best that we return things to how they were
709
00:36:53,140 --> 00:36:54,810
because the size we are now
710
00:36:54,810 --> 00:36:56,960
is a perfect fit for the way we live
711
00:36:56,960 --> 00:36:58,533
and the world we live in today.
712
00:36:59,380 --> 00:37:02,193
Lifespan, health, food, society, resources,
713
00:37:02,193 --> 00:37:05,423
it all goes hand in hand with our size.
714
00:37:10,340 --> 00:37:13,750
We've tried shrinking the planet and even ourselves,
715
00:37:13,750 --> 00:37:17,810
but so far, small has not proved to be beautiful,
716
00:37:17,810 --> 00:37:20,290
but there's one thing we haven't tried,
717
00:37:20,290 --> 00:37:22,030
something so big that surely,
718
00:37:22,030 --> 00:37:23,460
we could make it a little smaller
719
00:37:23,460 --> 00:37:25,173
without ending life as we know it.
720
00:37:26,740 --> 00:37:27,573
The sun.
721
00:37:28,443 --> 00:37:32,060
Perhaps a smaller sun would be a good idea.
722
00:37:32,060 --> 00:37:35,283
Less skin cancer, a cooler climate.
723
00:37:35,283 --> 00:37:37,700
The sun we have is a kind of star
724
00:37:37,700 --> 00:37:40,780
known to astronomers as a G2 drawf,
725
00:37:40,780 --> 00:37:43,750
but it's not really much of a dwarf by human standards.
726
00:37:43,750 --> 00:37:47,470
In fact, it's 1.4 million kilometers wide.
727
00:37:47,470 --> 00:37:50,543
That's 109 times wider than the Earth.
728
00:37:51,860 --> 00:37:54,805
But does it have to be so preposterously large
729
00:37:54,805 --> 00:37:57,980
or would everything work out fine with a smaller,
730
00:37:57,980 --> 00:38:00,540
gentler sun that wouldn't damage our skin
731
00:38:00,540 --> 00:38:03,053
and we can look at without sunglasses?
732
00:38:04,660 --> 00:38:05,900
The key to this question
733
00:38:05,900 --> 00:38:08,563
is understanding what makes a star shine.
734
00:38:09,730 --> 00:38:11,510
Stars are big balls of gas
735
00:38:11,510 --> 00:38:14,210
which have been pulled together by gravity.
736
00:38:14,210 --> 00:38:17,890
At some point, the gases literally fuse.
737
00:38:17,890 --> 00:38:19,540
Subatomic hydrogen particles
738
00:38:19,540 --> 00:38:22,100
get squashed together to make helium.
739
00:38:22,100 --> 00:38:24,462
This is nuclear fusion
740
00:38:24,462 --> 00:38:27,900
which generates such enormous amounts of energy
741
00:38:27,900 --> 00:38:30,400
that we've been trying to replicate the process on Earth
742
00:38:30,400 --> 00:38:32,650
ever since it was discovered.
743
00:38:32,650 --> 00:38:36,563
The problem is that it turns out it's incredibly hard to do.
744
00:38:37,950 --> 00:38:40,930
This is one of the world's best attempts,
745
00:38:40,930 --> 00:38:43,850
JET, Joint European Torus,
746
00:38:43,850 --> 00:38:46,187
based at Culham in the U.K.
747
00:38:46,187 --> 00:38:47,709
The first place on Earth
748
00:38:47,709 --> 00:38:51,133
that they managed to achieve controlled nuclear fusion,
749
00:38:52,599 --> 00:38:56,176
a phenomenally complicated and expensive facility
750
00:38:56,176 --> 00:38:58,850
where they use as much power as a small (mumbling)
751
00:38:58,850 --> 00:39:01,203
to superheat the gases until they fuse.
752
00:39:02,680 --> 00:39:07,170
Jet physicist Ivor Coffey knows just how intense things get.
753
00:39:07,170 --> 00:39:09,350
The fusion takes place inside this chamber.
754
00:39:09,350 --> 00:39:12,390
We actually create a highly ionized gas or plasma.
755
00:39:12,390 --> 00:39:13,620
Sort of the center of the plasma
756
00:39:13,620 --> 00:39:15,852
which is probably roughly just above my head
757
00:39:15,852 --> 00:39:18,270
would be where the temperature
758
00:39:18,270 --> 00:39:20,780
and density are at the maximum temperature.
759
00:39:20,780 --> 00:39:22,084
There could be something in the reads
760
00:39:22,084 --> 00:39:24,643
in between 100 and 150 million degrees centigrade.
761
00:39:26,110 --> 00:39:28,200
Conditions in here are so extreme
762
00:39:28,200 --> 00:39:31,463
that they can only run the machine for 30 seconds at a time.
763
00:39:34,100 --> 00:39:36,030
Today, they're running the fusion test
764
00:39:36,030 --> 00:39:38,807
at even higher power levels than they've tried before.
765
00:39:41,203 --> 00:39:45,363
10, nine, eight, seven, six,
766
00:39:45,363 --> 00:39:48,196
five, four, three, two, one, zero.
767
00:39:51,255 --> 00:39:54,838
(intense orchestral music)
768
00:39:57,280 --> 00:39:59,420
What you are looking at right now
769
00:39:59,420 --> 00:40:01,380
is actual fusion.
770
00:40:01,380 --> 00:40:03,090
This is the very same process
771
00:40:03,090 --> 00:40:05,213
that happens at the heart of a star.
772
00:40:06,131 --> 00:40:09,714
(intense orchestral music)
773
00:40:14,870 --> 00:40:17,420
The problem of making fusion happen on Earth
774
00:40:17,420 --> 00:40:20,870
is no different to the problem of making it happen in space,
775
00:40:20,870 --> 00:40:23,148
but stars manage to solve this problem
776
00:40:23,148 --> 00:40:25,103
by being incredibly big.
777
00:40:26,350 --> 00:40:29,530
The main requirement if you want to trigger fusion
778
00:40:29,530 --> 00:40:30,800
anywhere in the universe,
779
00:40:30,800 --> 00:40:33,550
inside of stars or in a laboratory on Earth
780
00:40:33,550 --> 00:40:35,205
is that you have to create conditions
781
00:40:35,205 --> 00:40:37,440
of very high temperature.
782
00:40:37,440 --> 00:40:40,480
And the problem then is that if you have high temperature,
783
00:40:40,480 --> 00:40:42,350
you will also basically have the problem
784
00:40:42,350 --> 00:40:44,490
that this high temperature ball of material
785
00:40:44,490 --> 00:40:47,670
wants to be pushed out by the pressure.
786
00:40:47,670 --> 00:40:49,770
So you have to somehow overcome the pressure.
787
00:40:49,770 --> 00:40:53,110
And the stars do this by having all the gravity
788
00:40:53,110 --> 00:40:54,130
of the overlying material.
789
00:40:54,130 --> 00:40:55,430
The gravity of the star
790
00:40:55,430 --> 00:40:57,903
is confining the pressure of the hot material.
791
00:40:59,980 --> 00:41:02,420
For stars, size matters.
792
00:41:02,420 --> 00:41:05,260
If they're not big enough, fusion can't happen.
793
00:41:05,260 --> 00:41:07,833
And without fusion, it's not a star at all.
794
00:41:09,910 --> 00:41:12,680
If we make stars smaller, less massive,
795
00:41:12,680 --> 00:41:15,560
and the temperature of the star
796
00:41:15,560 --> 00:41:16,690
in the center will also go down,
797
00:41:16,690 --> 00:41:17,610
and at some point,
798
00:41:17,610 --> 00:41:20,240
the temperature is not sufficient any longer
799
00:41:20,240 --> 00:41:22,552
to ignite nuclear fusion.
800
00:41:22,552 --> 00:41:25,290
And this really is the fundamental limit,
801
00:41:25,290 --> 00:41:26,850
if you like, for stardom.
802
00:41:26,850 --> 00:41:29,030
The very smallest we could make our sun
803
00:41:29,030 --> 00:41:30,450
or indeed any star
804
00:41:30,450 --> 00:41:33,260
is around 10 times the width of the Earth.
805
00:41:33,260 --> 00:41:34,922
But with a sun this size,
806
00:41:34,922 --> 00:41:37,333
what kind of Earth would we wake up to?
807
00:41:40,536 --> 00:41:43,203
(alarm beeping)
808
00:41:44,360 --> 00:41:46,973
For starters, you'd be seeing red.
809
00:41:49,520 --> 00:41:52,560
The reason that this low mass star would be red
810
00:41:52,560 --> 00:41:56,000
is that this star would have much reduced gravity,
811
00:41:56,000 --> 00:42:00,150
and therefore also it would have much reduced temperature.
812
00:42:00,150 --> 00:42:04,830
It would shift the peak wavelength of your photons
813
00:42:04,830 --> 00:42:06,358
that the star is emitting
814
00:42:06,358 --> 00:42:08,550
into longer and longer wavelengths.
815
00:42:08,550 --> 00:42:11,457
This means that we shifted from the yellow that our sun has
816
00:42:11,457 --> 00:42:15,540
into the red that those red dwarf stars would have.
817
00:42:16,610 --> 00:42:17,720
A star this size
818
00:42:17,720 --> 00:42:19,970
would be no brighter than the moon,
819
00:42:19,970 --> 00:42:22,710
but light isn't the only casualty.
820
00:42:22,710 --> 00:42:25,822
Within hours, we'd feel a bigger problem.
821
00:42:25,822 --> 00:42:27,520
What would happen to a planet
822
00:42:27,520 --> 00:42:30,460
around such a red dwarf central star?
823
00:42:30,460 --> 00:42:31,370
The most dramatic thing
824
00:42:31,370 --> 00:42:36,118
is that because of the very, very much reduced temperature,
825
00:42:36,118 --> 00:42:39,293
we would basically experience a deep freeze.
826
00:42:40,430 --> 00:42:42,430
Temperatures would plummet.
827
00:42:43,470 --> 00:42:46,490
A star this size gives off just one six thousandth
828
00:42:46,490 --> 00:42:48,343
of the heat of our sun.
829
00:42:50,176 --> 00:42:54,133
All the liquid water would be converted into ice.
830
00:42:54,133 --> 00:42:58,520
Even our atmosphere would begin to freeze out.
831
00:42:58,520 --> 00:43:02,030
We would enter into a state of complete cold,
832
00:43:02,030 --> 00:43:03,847
deep desperate freeze.
833
00:43:05,200 --> 00:43:06,970
As the Earth cools further,
834
00:43:06,970 --> 00:43:09,300
all the gases in the air solidify
835
00:43:09,300 --> 00:43:11,413
causing the atmosphere to collapse.
836
00:43:13,660 --> 00:43:15,083
So how do we save the world?
837
00:43:16,870 --> 00:43:18,790
The answer may seem obvious.
838
00:43:18,790 --> 00:43:23,033
We move the planet closer to the sun so that things warm up.
839
00:43:24,040 --> 00:43:25,663
But would that actually work?
840
00:43:27,459 --> 00:43:29,060
Earth's normal orbit
841
00:43:29,060 --> 00:43:33,010
is about 150 million kilometers from the sun.
842
00:43:33,010 --> 00:43:35,070
This is the middle of the habitable zone,
843
00:43:35,070 --> 00:43:37,830
the region of the solar system where it's not too hot
844
00:43:37,830 --> 00:43:38,983
and not too cold.
845
00:43:41,270 --> 00:43:42,227
Now, we've moved the Earth
846
00:43:42,227 --> 00:43:45,633
nearly 100 times closer to the tiny sun.
847
00:43:47,066 --> 00:43:50,649
(intense orchestral music)
848
00:43:51,831 --> 00:43:54,590
At this distance, our planet gets the same energy
849
00:43:54,590 --> 00:43:56,090
from the sun as we're used to,
850
00:43:57,310 --> 00:43:58,810
but this is a different world.
851
00:44:01,410 --> 00:44:04,098
The sun may be tiny, but we are so close
852
00:44:04,098 --> 00:44:06,770
that it would look big in the sky.
853
00:44:06,770 --> 00:44:09,193
Around 10 times bigger than we're used to.
854
00:44:12,530 --> 00:44:14,830
But there are problems to face,
855
00:44:14,830 --> 00:44:17,050
problems that the best scientists in the world
856
00:44:17,050 --> 00:44:18,713
are trying to solve
857
00:44:18,713 --> 00:44:22,300
because they've recently discovered a planet just like this
858
00:44:22,300 --> 00:44:24,503
and it turns out it's our nearest neighbor.
859
00:44:25,800 --> 00:44:28,270
If you look at the many stars in the night sky,
860
00:44:28,270 --> 00:44:30,670
you probably won't even notice Proxima Centauri.
861
00:44:31,917 --> 00:44:34,400
It's actually the closest of them all,
862
00:44:34,400 --> 00:44:35,880
but it's very small,
863
00:44:35,880 --> 00:44:40,490
just one seventh the size of the sun, but it's up there.
864
00:44:40,490 --> 00:44:42,905
And at Queen Mary University London,
865
00:44:42,905 --> 00:44:45,210
astronomers have been looking very hard
866
00:44:45,210 --> 00:44:46,925
at the faint light it gives off
867
00:44:46,925 --> 00:44:48,860
to see what they can discover
868
00:44:48,860 --> 00:44:50,793
about the sun's tiny neighbor.
869
00:44:53,720 --> 00:44:56,353
Proxima Centauri is the nearest star to the sun.
870
00:44:57,370 --> 00:44:59,210
This is where astronomy begins.
871
00:44:59,210 --> 00:45:02,910
So it's really the first spot in the next frontier.
872
00:45:02,910 --> 00:45:07,550
So the first place to go when we go beyond our solar system.
873
00:45:07,550 --> 00:45:09,523
So that makes it very special.
874
00:45:10,540 --> 00:45:12,350
In August 2016,
875
00:45:12,350 --> 00:45:14,140
they made an astonishing discovery
876
00:45:14,140 --> 00:45:17,623
by analyzing the light that Proxima Centauri gives off.
877
00:45:18,910 --> 00:45:21,350
So basically what we do, we go to a telescope.
878
00:45:21,350 --> 00:45:24,820
The telescope has an optical fiber sitting at the focus
879
00:45:24,820 --> 00:45:26,310
and then the light from the star
880
00:45:26,310 --> 00:45:27,410
goes through the optical fiber
881
00:45:27,410 --> 00:45:28,834
to the basement of the observatory
882
00:45:28,834 --> 00:45:30,390
where there's a spectrometer.
883
00:45:30,390 --> 00:45:31,709
And what the spectrometer does.
884
00:45:31,709 --> 00:45:33,986
Takes the light coming from the optical fiber
885
00:45:33,986 --> 00:45:36,880
and these two elements here, a prism and a grating,
886
00:45:36,880 --> 00:45:38,648
separate the light into wavelengths.
887
00:45:38,648 --> 00:45:41,688
And we see that there are these dark spots
888
00:45:41,688 --> 00:45:43,750
in the middle of the traces.
889
00:45:43,750 --> 00:45:47,020
These are the footprints of molecules
890
00:45:47,020 --> 00:45:49,730
and atoms in the atmosphere of the star.
891
00:45:49,730 --> 00:45:51,650
When they observed the star again,
892
00:45:51,650 --> 00:45:54,883
they saw that the spectrum of Proxima Centauri was changing.
893
00:45:55,930 --> 00:45:58,887
So we come here to the telescope two months later.
894
00:45:58,887 --> 00:46:00,420
We take more data
895
00:46:00,420 --> 00:46:03,350
and then we see that the measurements start to trend.
896
00:46:03,350 --> 00:46:05,260
Something is happening, whether we don't know what.
897
00:46:05,260 --> 00:46:06,440
We got more measurements,
898
00:46:06,440 --> 00:46:07,970
more measurements, more measurements,
899
00:46:07,970 --> 00:46:09,080
and after two years,
900
00:46:09,080 --> 00:46:12,032
then we see that it reaches a peak
901
00:46:12,032 --> 00:46:14,860
and then you have this signal.
902
00:46:14,860 --> 00:46:15,790
And it's repeating also.
903
00:46:15,790 --> 00:46:17,501
If we keep observing the star,
904
00:46:17,501 --> 00:46:19,601
we see the same thing over and over again.
905
00:46:21,086 --> 00:46:22,829
These wobbles in the spectrum
906
00:46:22,829 --> 00:46:27,020
reveal that the star has been pulled backward and forwards.
907
00:46:27,020 --> 00:46:30,523
It's the telltale sign of a planet orbiting close by.
908
00:46:32,700 --> 00:46:35,952
Further study shows that this planet called Proxima b
909
00:46:35,952 --> 00:46:39,240
has a lot of similarities to our own.
910
00:46:39,240 --> 00:46:42,433
It's roughly Earth-sized and mostly made of rock,
911
00:46:43,570 --> 00:46:48,390
but unlike Earth, which takes 365 days to go around its sun,
912
00:46:48,390 --> 00:46:51,150
the spectrum patterns reveal that Proxima b
913
00:46:51,150 --> 00:46:52,670
takes a mere 11 days
914
00:46:52,670 --> 00:46:55,983
meaning it must be very close to its star.
915
00:46:57,900 --> 00:46:59,600
When the scientists did the maths,
916
00:46:59,600 --> 00:47:01,685
they realized it is at a perfect distance
917
00:47:01,685 --> 00:47:04,242
for the possibility of life.
918
00:47:04,242 --> 00:47:07,760
Not too hot and not too cold.
919
00:47:07,760 --> 00:47:10,010
There are many more factors to consider
920
00:47:10,010 --> 00:47:11,913
before they know if life is possible.
921
00:47:13,310 --> 00:47:14,840
It's only right to the solar system
922
00:47:14,840 --> 00:47:17,456
that we can expect to actually
923
00:47:17,456 --> 00:47:20,069
start to search for evidence of life
924
00:47:20,069 --> 00:47:23,410
in the planets like this one is Proxima Centauri
925
00:47:23,410 --> 00:47:25,010
and also some very nearby stars.
926
00:47:26,644 --> 00:47:29,660
As the search for life on Proxima b begins,
927
00:47:29,660 --> 00:47:33,870
what can we learn from it to help our thought experiment?
928
00:47:33,870 --> 00:47:36,463
Could life survive this close to a small sun?
929
00:47:37,830 --> 00:47:41,170
For a start, plants would have to be a different color.
930
00:47:41,170 --> 00:47:43,560
Plants are green because of the specific wavelength
931
00:47:43,560 --> 00:47:45,367
of light they use.
932
00:47:45,367 --> 00:47:49,258
But if our sun was red like Proxima Centauri,
933
00:47:49,258 --> 00:47:51,739
crucial wavelengths would be missing
934
00:47:51,739 --> 00:47:54,400
and green plants wouldn't work.
935
00:47:54,400 --> 00:47:55,770
They'd have to be black
936
00:47:55,770 --> 00:47:58,970
to absorb as much sunlight as possible.
937
00:47:58,970 --> 00:48:02,200
Our planet would look very different,
938
00:48:02,200 --> 00:48:04,121
but there's a much bigger problem.
939
00:48:04,121 --> 00:48:07,633
A possible side effect of being so close to a star.
940
00:48:08,600 --> 00:48:09,803
Tidal locking.
941
00:48:10,700 --> 00:48:12,800
So basically you have a small star.
942
00:48:12,800 --> 00:48:15,724
The small star makes very little energy.
943
00:48:15,724 --> 00:48:17,470
It's also faint.
944
00:48:17,470 --> 00:48:20,470
So you need to be warm, you need to be close to it.
945
00:48:20,470 --> 00:48:22,150
And the fact of being close to it
946
00:48:22,150 --> 00:48:25,390
means that you also have a very strong tidal forces then
947
00:48:25,390 --> 00:48:26,950
and most likely what will happen
948
00:48:26,950 --> 00:48:30,095
is like what happens with the moon to the Earth.
949
00:48:30,095 --> 00:48:31,940
The rotation of the planet
950
00:48:31,940 --> 00:48:34,340
is synchronized to the orbit of the planet
951
00:48:34,340 --> 00:48:36,823
so the same side faces the star.
952
00:48:38,340 --> 00:48:41,270
With one side frozen in perpetual night
953
00:48:41,270 --> 00:48:43,750
and the other in never-ending sun,
954
00:48:43,750 --> 00:48:46,190
planets that are fully tidally locked
955
00:48:46,190 --> 00:48:48,683
are sometimes called eyeball planets.
956
00:48:50,670 --> 00:48:53,110
The world we are used to isn't possible
957
00:48:53,110 --> 00:48:55,092
around a smaller sun.
958
00:48:55,092 --> 00:48:58,190
Even if we move close enough to the sun to be warm,
959
00:48:58,190 --> 00:49:00,663
Earth would be a very difficult place to live.
960
00:49:02,448 --> 00:49:05,400
(intense orchestral music)
961
00:49:05,400 --> 00:49:09,450
It turns out that the size of our sun is everything.
962
00:49:09,450 --> 00:49:12,760
Any smaller and we can't have a green world,
963
00:49:12,760 --> 00:49:14,577
can't have night and day,
964
00:49:14,577 --> 00:49:17,403
and most of our world becomes deadly.
965
00:49:22,010 --> 00:49:26,040
It seems we are better off with the sun the size it was,
966
00:49:26,040 --> 00:49:30,893
us the size we are, living on a planet that is just right.
967
00:49:33,880 --> 00:49:35,170
Size does matter.
968
00:49:35,170 --> 00:49:37,266
Size determines on the one hand
969
00:49:37,266 --> 00:49:39,400
the height we will achieve,
970
00:49:39,400 --> 00:49:42,905
but on the other hand, size determines our lifespan
971
00:49:42,905 --> 00:49:45,611
because size determines how much energy
972
00:49:45,611 --> 00:49:48,793
we invest in maintaining our body in good shape.
973
00:49:50,470 --> 00:49:52,310
A very large animal and a very small animal
974
00:49:52,310 --> 00:49:53,780
live in completely different worlds,
975
00:49:53,780 --> 00:49:56,180
so they face completely different problems.
976
00:49:56,180 --> 00:49:57,190
Evolution has produced
977
00:49:57,190 --> 00:49:59,160
completely different solutions to these problems.
978
00:49:59,160 --> 00:50:00,740
And for scientists, it's really interesting
979
00:50:00,740 --> 00:50:02,380
to try and understand how things work
980
00:50:02,380 --> 00:50:04,320
at small scales and big scales.
981
00:50:04,320 --> 00:50:05,500
How big you are
982
00:50:05,500 --> 00:50:07,610
determines the scale of the world around you
983
00:50:07,610 --> 00:50:08,637
and how you interact with it.
984
00:50:08,637 --> 00:50:10,483
The smaller you become,
985
00:50:10,483 --> 00:50:13,118
the kinds of things that are dangerous to you change.
986
00:50:13,118 --> 00:50:16,210
But size is also a very mutable variable.
987
00:50:16,210 --> 00:50:18,270
It's flexible and mammals have found a way
988
00:50:18,270 --> 00:50:21,919
to live very successfully at all different sizes.
989
00:50:21,919 --> 00:50:24,690
I think size is important in the universe.
990
00:50:24,690 --> 00:50:25,920
It's a clockwork really.
991
00:50:25,920 --> 00:50:27,860
You have your clock and everything works perfectly,
992
00:50:27,860 --> 00:50:30,137
but if you change the size of one of the cogs,
993
00:50:30,137 --> 00:50:32,370
then it doesn't fit with the rest anymore
994
00:50:32,370 --> 00:50:34,120
and the whole system will collapse.
995
00:50:36,317 --> 00:50:39,613
Size isn't like a color or clothing.
996
00:50:40,905 --> 00:50:42,843
It's not arbitrary.
997
00:50:43,788 --> 00:50:46,823
It goes hand in hand with so many things.
998
00:50:48,290 --> 00:50:53,290
Gravity, intelligence, the evolution of life itself.
999
00:50:55,339 --> 00:51:00,339
Our size is who we are and what we always will be.
1000
00:51:00,969 --> 00:51:04,552
(intense orchestral music)