Black Holes - Wonders of the Universe: Falling - BBC Two

More about this programme: http://www.bbc.co.uk/programmes/b00zv39p
Using Zambia's spectacular Victoria Falls, Prof Brian Cox demonstrates what happens as you near a black hole.

Near a black hole space and time do some very strange things because the black holes are probably the most

violent places we know of in the universe. This river provides a beautiful analogy of what happens

to space and time as you get closer and closer to the black hole.

Now upstream the water is flowing pretty slowly.

Let's imagine that it is flowing at three kilometers per hour

and I can swim at 4, so I can swim faster than the flow and can easily escape

But as you go further, further down the stream towards

the waterfall in the distance, the river flows faster and faster.

Imagine that I decided to jump in the river just there at the edge of the falls

The water is flowing far faster than I could swim.

So, no matter what I did, no matter how hard I tried

I would not be able to swim back upstream

I would be carried inextricably towards the edge and I would vanish over the falls

Well, it's the same close to the black hole,

because the space flows faster, faster and faster

towards the black hole.

Literally, this stuff, my space that I am in, flowing over the edge into the black hole.

And then, at a very special point, called the event horizon, the space is flowing

at the speed of light into the black hole.

Light itself, travelling at 300.000km per second is not going fast enough to escape the flow

and light itself will plunge into the black hole.

Well, as you fall into the black hole, across the event horizon, then if you were going feet first, your feet will be

accelerating faster than your head, so you'll be stretched

and you'll be quite literally spaghettified.

Now as you get right into the center,

Then our understanding of the laws of physics breaks down.

Our best theory of space and time, Einstein's theory of general relativity

says that space and time become infinitely curved, that

the center of the hole becomes infinitely dense

That place is called the singularity and it is the place

where our understanding of the Universe stops.