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. And if you like this video, please give us a thumbs up, and share it with your friends.
Be sure to check out some of our other popular videos. I'll see you in the next video my friend!
