The scale of the universe is incredibly

difficult to imagine. think of the biggest thing you can think of – a blue

whale maybe, the Great Pyramids of Giza, the Burj Khalifa in Dubai, Mount Everest.

They may be about as large as you can imagine. But the scale of the universe is

many many orders of magnitude bigger than that. It’s much bigger than you can

probably imagine. And the crazy thing is that the universe is also smaller than

you can ever imagine. Think of the smallest thing you can

imagine – a bacteria maybe, an atom? Keep going because the universe is many

orders of magnitude smaller than that. And that’s the problem. Most of us can’t

grasp the scale of the universe because it’s utterly unrelatable,

to anything that we experience in our daily earthly lives. For example, there

are at least 10 sextillion stars that’s 10 followed by 21 zeroes. That’s

thousands of times more than all the grains of sand on all the beaches of

Earth. But you’ve probably heard this before. What you may not have heard is

that the universe is even smaller than it is large. For example, the smallest

length theorized to be possible, the Planck length, is about 1.6 x 10^-35

meters. This is so small, that if an atom was the size

of the earth, a Planck length would be much smaller than even the head of a pin.

In fact a Planck volume, which is Planck length cubed, or about 4 x 10^-105 cubic meters is so small that there are more Planck volumes

inside a cubic meter, than there are cubic meters in the known universe. Let’s

explore the scale of the universe using some genius animations created by Cari

and Michael Huang, who have generously given us permission to use them. The link

to their website is in the description below. So exactly how long is a Planck

length and how can we visualize something that small. What is the

fundamental reason that this is the smallest length in the universe? That’s

coming up right now… Let’s start with the scale of the human

being because this is probably the most relatable scale we can think of. Just

imagine things that are about the size of your body – things like the giant

earthworm that lives along streams in Australia, or a big each ball which can

be found near oceans and beaches all across America. We’re looking right now

at scales that are 10 to the power 0, or 1 meter in length. Now let’s go smaller

by one order of magnitude. So now we’re looking at things that are on the scale

of about one tenth of a meter or 10 centimeters. these are things like the

Shrew which are some of the smallest mammals found on earth, or a chicken egg

that you might have had for breakfast this morning. Now we’re going to move a bit

faster. Let’s go a thousand times smaller than the scale of a human being, on the

order of one millimeter or one thousandth of a meter. Here you’re going to

find things like a grain of sand, which can be about half a millimeter in length

or dust mites that may be crawling all over your bed, because they love to eat

dead skin cells. Yeah, if you itch in the morning, this could be the culprit. You

can’t usually see them with the naked eye. Let’s go a thousand times smaller

than this scale. Now we’re going a hundred times smaller than the width of

a human hair, or about one millionth of a meter, and ten times smaller than even a

bacteria. Here we’re going to find things like large viruses. Unlike bacteria, 99%

of which are harmless to you, the vast majority of viruses (inside your body) will make you sick.

And our antibiotics are totally ineffective against viruses. Let’s keep

going to a thousand times smaller than this. This is nanometers, or one billionth

of a meter. Now we’re exploring a universe that we can’t see with our

optical microscopes. This is around the order of the size of the DNA molecule,

the blueprint of all life on Earth. This is on the scale of molecules, like the

glucose molecules that your body uses as a source of energy, and the scale of the

biggest atom, cesium. Why is this atom so big even though it doesn’t have the most

electrons? …because it has the best combination of a large valence shell and

low nuclear charge, which allows electrons to wander further away from

the nucleus. Let’s go a thousand times smaller than even this. This is one

trillionth of a meter this is on the scale of the wavelength of gamma rays.

This is the highest energy electromagnetic radiation, consisting of

the most energetic photons. Gamma rays are emitted during nuclear explosions,

and a high-energy cosmological phenomena, such as exploding stars, just before they

collapse into a black hole. Now let’s go a thousand times smaller than this. This

is 1 x 10^-15 m, or 1 quadrillion of a meter. This is the size

of particles that make up the nucleus of atoms, protons and neutrons. The size of a

typical atom, however, is a hundred thousand times larger than its nucleus.

So if an atom was the size of Michigan football stadium, the biggest stadium in

the United States, the nucleus would be a marble sitting in the middle of the

50-yard line. You would think that we’re getting close to the smallest size

theorized to exist, the Planck length. But we are nowhere close. You have to go a

quadrillion times smaller than 1 quadrillion of a meter, or 1 x 10^ -30 meters. And you would still have to go another hundred

thousand times smaller than that, or 1 x 10^-35 meters, then

you would be at the Planck length. In fact if an atom was the size of the

earth, a Planck length would be smaller than the size of an atom. It would be

about the size of a proton. But what exactly is a Planck length? And why is it

the smallest length? Planck length is actually derived from three fundamental

constants of the universe that define the properties of space-time, the speed

of light – C which signifies the maximum speed of communication in the universe.

the gravitational constant – G which signifies the magnitude of gravitational

force between two massive objects. The reduced Planck constant, h-bar

which links how much energy of photon carries depending on its electromagnetic

frequency, defined by this equation. These are really the only constants that

define the fundamental properties of the universe, and all its contents. By taking

different mathematical combinations of these constants, and reducing their units,

you can get a length. So as you can see here, if we take the units of the three

fundamental constants and manipulate them mathematically, we can come up with

a length – L sub p, which is the Planck length. And by a similar mathematical

manipulation, we can also get Planck time, and Planck energy. But what does this

Planck length actually mean? What does it signify? Why is it significant? Well,

cosmologically is the smallest length at which gravity would have an effect. it’s

the scale and size of strings in string theory. It’s also the scale at which

space-time is believed to become quantized in the theory of loop quantum

gravity. Why is this the smallest length? Why isn’t it some other number? Well the

main reason is is because it comes from the fundamental constants of the

universe. And in 1964 C. Alden Mead determined that using the known laws of

quantum mechanics, and the laws of gravitation, it is impossible to

determine the position of an object to a precision smaller than the Planck length.

So from what is currently known about quantum mechanics, a length smaller than

the Planck length, has no meaning. Now note that I said “known laws.” It is

possible that at lengths smaller than the Planck length, gravity or quantum

mechanics behaves completely differently, that we may not yet be aware of. Since we

don’t have a working theory of quantum gravity, this is quite possible. And until

we find out what happens at such small scales, we just need to wait for the next

Einstein to reveal it to us. One of the remarkable things about the Planck

length is that since it’s derived from the fundamental constants of the

universe, which by definition applies to everything, this length is going to be

the same no matter what language you speak, what units you might use, or even

what planet you might come from. So that’s right, if we ever come across

aliens from another world, and compare notes,

we both will have the same length of the smallest length possible in the universe.

So we have a common language already with those shy aliens that only seem to

show up in fuzzy pictures and remote areas of the United States. In part 2 of

this video we’re gonna explore the other end of the scale, how large the universe

is – which by the way, is much larger than you can imagine.

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next video my friend!