And today we aregoing to go inside a black hole.
It's not going to be comfortable, but it will be prettyfun.
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 “Schwarzschild radius.
” A tiny, tiny amountof space that, were you to collapse the entire mass of the object into, its density wouldbe so great that its gravitational pull would be so great that not even light could escapefrom it.
You would have a black hole.
If you were to compress Mount Everest intosomething smaller than a nanometer, you would have a black hole.
And if you were to compressthe entire Earth down to the size of a peanut, you would have a black hole.
But, fortunately for us, there is no knownway to compress Everest or Earth in that fashion.
But a star, many, many, many times largerthan our own Sun, has a much larger Schwartzchild radius, and when it runs out of fuel and canno longer keep itself hot enough, it collapses to a single, infinitesimally-small point knownas a “singularity.
” Its density will be infinite and so itsgravitational pull will be so strong that nothing can escape, not even light.
But enough about ways black holes form, let'sjump into one.
First question: what would it look like from the outside? Well, we knowthat gravitational fields bend space and time.
Stars behind our Sun will actually appearto be in slightly different locations from Earth, because the Sun's gravitational fieldbends the light coming from those stars.
When it comes to the gravitational fieldsof larger objects, like entire galaxies or, for that matter, a black hole, the effectis even nuttier.
Light coming from object's behind them is significantly distorted, producing smears and smudges.
As seen from Earth, the blue galaxy behindthis red galaxy is completely distorted, like a fun house mirror.
So, rather than appearingas 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 lightyearsbehind it.
The galaxy's really not in danger of the black hole's “suck, ” but the lightcoming off of that galaxy certainly is.
Watch as the galaxy passes behind the black holeand its light is contorted, twisted and distorted.
Now here's a really fun demonstration.
What if the Earth were to orbit around a blackhole? Looking from the outside, the Earth would look normal at first, but as soon asit passed behind the black hole, the black hole's gravitational field would warp thelight reflecting off the Earth, producing this.
For the sake of simplicity, let's jump intoa simple black hole, one that doesn't have a charge and isn't moving.
And, also, isn'talready sucking up a bunch of matter.
So it's just there on its own.
As we approach, the distortion of the skygrows greater and greater.
A larger and larger portion of our field of view looking forwardinto the black hole will be filled with darkness.
At this point, where half of our field ofview has been swallowed up in darkness, we have reached the “Photon Sphere.
” At this point, light is not going to necessarilyget sucked into the black hole, but it doesn't necessarily leave it either.
Instead, at thismagical point in space, light, photons, can actually orbit the black hole.
If you were to stop here for a moment andlook to the side, you could theoretically see the back of your own head, because lightreflecting off the back of your head would travel all the way around the sphere of theblack 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 worryabout 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 seeyou 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.
Youwould seem almost frozen in space, the light coming off your body becoming increasinglyred-shifted until you simply faded into nothingness.
They would never see you cross the event-horizon.
But for you, of course, everything would seemfine and dandy.
You would continue pass that horizon to your now, inevitable, death.
As you continue to approach the black hole's singularity, your view of the entire universewould get compressed into a smaller and smaller point in space behind you.
If the black hole we're jumping into was largeenough, things actually might be quite comfortable at that event horizon.
We'll know that we'renever going to escape and that our lives are pretty much over, but it might take us hoursto actually reach a point where things started to hurt.
Why would they hurt? Well, the closer you getto the singularity, the more significant the difference in gravitational pull is acrossspace.
And, so, parts of me that are closer to the singularity would be pulled more stronglythan 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 callit “Spaghettification.
” Once you reach this point, you would be dead.
Your molecules would be violently ripped and stretched apart, and when they got to thesingularity, well, we don't really know what would happen.
Perhaps they would completelydisappear in violation of all the laws of physics or maybe they would reappear elsewherein the universe.
It is believed that a moving or spinning black hole might actually createwhat is known as a “wormhole, ” a way of transitioning across space faster than light.
Not in anyway that violates the laws of science, but in a way that takes advantage of the universe'sdimensions.
For instance, if I wanted to get from thispoint to this point, I'd have to travel the distance.
But, theoretically, a wormhole woulddo something really crazy.
For instance, this.
Now, the two points are right next to eachother 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 lightto escape, a Dumbhole is an acoustic black hole.
It won't allow sound to escape.
It doesn'thave to be nearly as powerful and scientists have been able to create Dumbholes in laboratoriesusing special fluids traveling at the speed of sound.
A lot of progress still needs to be made inthe world of acoustic black holes, but we may be able to learn an amazing amount ofinformation about how black holes work by looking at how sound is treated in a Dumbhole.
Now here's another good question: What wouldit look like to travel at the speed of light, say, toward the Sun? Well, surprisingly, youwouldn'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 ofview 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, lookingat the Sun, there's light coming from stuff behind you.
But, if you travel the speed oflight, you will actually reach that light coming from things behind you.
As you reachedlight speed, your field of view would expand like this, concentrating the stuff in themiddle.
But where are you in the universe? Or, here'sa 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 whereyou 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 aballoon getting bigger with all the people inside it.
Instead, it's as if we are thesurface of a balloon.
If you were to put a bunch of dots on a balloon and then blow itup, all the dots would move away from each other at the same rate.
And, on the surfaceof the balloon, there is no center.
Take a look at these two layers.
They areexactly 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 happenswhen I line up a dot in the past and the present.
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 immediatelybecomes 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 matterwhere you are, or who you are, or what your friends or your parents, you really, scientifically, are the center of the universe.
Finally, what if our universe was a googolplexmeters across? It is nowhere near that large.
But, if it was, it would be so voluminousthat, statistically, it would be nearly impossible for there not to be an exact copy of you somewhereelse out there in the universe.
To see why, I highly suggest that you click right thereand 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.