going to be comfortable, but it will be pretty fun. Now, first thing's first: mathematically

speaking, anything could become a black hole if you were to compress it into a small enough

space. That's right, you, me, this camera- everything in the unvierse has what is known

as a "Schwarzchild radius": a tiny, tiny amount of space that, were you to collapse the entire

mass of the object into, it's density would be so great that its gravitational pull would

be so great that not even light could escape from it. You would have a black hole.

If you were to compress Mount Everest into something smaller than a nanometer, you would

have a black hole. And if you were to compress the entire Earth down to the size of a peanut,

you would have a black hole.

But, fortunately for us, there is no known way to compress Everest or Earth in that fashion.

But a star, many, many, many times larger than our own sun, has a much larger Schwartzchild

radius, and when it runs out of fuel and can no longer keep itself hot enough, it collapses

to a single, infinitesimally-small point known as a "singularity."

It's density will be infinite, and, so, it's gravitational pull will be so strong that

nothing can escape- not even light.

But enough about ways black holes form- let's jump into one. First question: what would

it look like from the outside? Well, we know that gravitational fields bend space and time.

Stars behind our sun will actually appear to be in slightly different locations from

Earth because the sun's gravitational field bends the light coming from those stars.

When it comes to the gravitational fields of larger objects, like entire galaxies or,

for that matter, a black hole, the effect is even nuttier. Light coming from object's

behind them is significantly distorted, producing smears and smudges.

As seen from Earth, the blue galaxy behind this red galaxy is completely distorted, like

a fun house mirror. So, rather than appearing as it really should, it looks to us like a ring-

a smudge all the way around the red galaxy.

This is known as "gravitational lensing." Now, take a look at this simulation of a black

hole with a galaxy millions of lightyears behind it. The galaxy's really not in danger

of the black hole's "suck," but the light coming off of that galaxy certainly is. Watch

as the galaxy passes behind the black hole and its light is contorted, twisted, and

distorted.

Now here's a really fun demonstration:

What if the Earth were to orbit around a black hole? Looking from the outside, the Earth

would look normal at first, but as soon as it passed behind the black hole, the black

hole's gravitational field would warp the light reflecting off the Earth, producing

this.

For the sake of simplicity, let's jump into a simple black hole- one that doesn't have

a charge and isn't moving. And, also, isn't already sucking up a bunch of matter- so it's

just there on its own.

As we approach, the distortion of the sky grows greater and greater. A larger and larger

portion of our field of view looking forward into the black hole will be filled with darkness.

At this point, where half of our field of view has been swallowed up in darkness, we

have reached the "Photon Sphere."

At this point, light is not going to necessarily get sucked into the black hole, but it doesn't

necessarily leave it either. Instead, at this magical point in space, light, photons, can

actually orbit the black hole.

If you were to stop here for a moment and look to the side, you could theoretically

see the back of your own head, because light reflecting off the back of your head would

travel all the way around the sphere of the black hole, right back to your face.

A gravitational field not only warps space, it also warps time. Now, for most intensive

purposes here on Earth, we never have to worry about that. But, near a black hole, gravity

would be so strong that an observer standing, watching you jump into the hole, would see

something quite strange. They wouldn't see you get sucked quickly into the hole- instead,

they would see your approach become slower, and slower, and slower, until you reached

a point known as the event-horizon.

This is a point in space where, once crossed, there's no going back. It is at that point

that light can no longer escape. And, so, to a person watching you fall into the hole,

that would be where your journey ended. You would seem almost frozen in space, the light

coming off your body becoming increasingly red-shifted until you simply faded into nothingness.

They would never see you cross the event-horizon.

But for you, of course, everything would seem fine and dandy. You would continue passed

that horizon to your now, inevitable, death. As you continue to approach the black hole's

singularity, your view of the entire universe would get compressed into a smaller, and smaller

point in space behind you.

If the black hole we're jumping into was large enough, things actually might be quite comfortable

at that event horizon. We'll know that we're never going to escape and that our lives are

pretty much over, but it might take us hours to actually reach a point where things started

to hurt.

Why would they hurt? Well, the closer you get to the singularity, the more significant the

difference in gravitational pull is across space. And, so, parts of me that are closer

to the singularity would be pulled more strongly than parts that were facing away, and my entire

body would be stretched toward the singularity. The effect would be so incredible, scientists

don't usually call it stretching, they call it "Spaghettification."

Once you reach this point, you would be dead. Your molecules would be violently ripped and

stretched apart, and when they got to the singularity, well, we don't really know what

would happen. Perhaps they would completely disappear in violation of all the laws of

physics, or, maybe, they would reappear elsewhere in the universe. It is believed that a moving,

or spinning, black hole might actually create what is known as a "wormhole," a way of transitioning

across space faster than light. Not in any way that violates the laws of science, but

in a way that takes advantage of the universe's dimensions.

For instance, if I wanted to get from this point to this point, I'd have to travel the

distance. But, theoretically, a wormhole would do something really crazy. For instance, this.

Now, the two points are right next to each other and I can travel between them almost

instantaneously.

But, again, this is all theoretical. Luckily, we do have a possible way of analyzing black

holes right here on Earth. Enter the "Dumbhole."

Just as a black hole does not permit light to escape, a Dumbhole is an acoustic black

hole. It won't allow sound to escape. It doesn't have to be nearly as powerful, and scientists

have been able to create Dumbhole's in laboratories using special fluids traveling at the speed

of sound.

A lot of progress still needs to be made in the world of acoustic black holes, but, we

may be able to learn an amazing amount of information about how black hole's work by

looking at how sound is treated in a Dumbhole.

Now here's another good question: What would it look like to travel at the speed of light,

say, toward the sun? Well, surprisingly, you wouldn't just see the sun immediately rush

up toward you. No, no, no. In fact, initially, it would look almost as if the sun were receding

away from you. Why? Because your field of view would vastly increase in size. You would

be able to see stuff almost behind you. And here's why:

As you sit there, not moving yet, looking at the sun, there's light coming from stuff

behind you. But, if you travel the speed of light, you will actually reach that light

coming from things behind you. As you reached light speed, your field of view would expand

like this, concentrating the stuff in the middle.

But where are you in the universe? Or, here's a better question: Where is the center of

the universe? Well, this might sound crazy, but, it's everywhere. This is known as the

"Cosmological Principle." No matter where you are in the universe, everything else will

seem to be moving away from you, expanding, at the same rate.

The universe is expanding, but not like a balloon getting bigger with all the people

inside it. Instead, it's as if we are the surface of a balloon. If you were to put a

bunch of dots on a balloon and then blow it up, all the dots would move away from each

other at the same rate. And, on the surface of the balloon, there is no center.

Take a look at these two layers. They are exactly similar, except the top layer represents

a 5% expansion of the bottom layer.

Let's say that you live on one of these dots, and you want to measure where everything is

moving away from. Well, watch what happens when I line up a dot in the past and the present:

Boom. It looks like the center of the expansion. I can do this with any dot. As soon as I choose

a dot to be the frame of reference, it immediately becomes the center of the expansion.

So, while dying in a black hole would be lonely, and scary, and morbid, when you look up into

the sky think instead about this: No matter where you are, or who you are, or what your

parents and friends tell you, you really, scientifically, are the center of the universe.

Finally, what if our universe was a googolplex meters across? It is nowhere near that large.

But, if it was, it would be so voluminous that, statistically, it would be nearly impossible

for there not to be an exact copy of you somewhere else out there in the universe. To see why,

I highly suggest that you click right there and check out Brady Haran's new channel "Numberphile."

It's part of the YouTube original channel's, and I've worked with these guys before. They're

amazing, they're my favorite kind of geeks. So, check out that video, watch their other

stuff, and if you like math, I highly suggest that you subscribe.

And, as always, thanks for watching.