I could be wrong but i believe they know this as they can see the speed the universe is expanding and using this they can calculate how long (in reverse) it would take to fall back on itself. from this they also believe they know where the centre of the universe is!

Who knows, maybe in 20 years our planet will be destroyed by otherworldly beings to make way for an intergalactic super highway. (Joke on Hitchhiker's Guide to the Galaxy.)

Wow, that was amazing. Good idea, by the way. Is this going to become a huge series of threads with discussions based on mind-boggling videos?

No. It will be a series of threads but i saw this and thought i might as well incorporate the video to add things to talk about!

another thing that always gets me, is whats beyond the universe? there can't just be nothing otherwise the universe couldn't expand anymore?

Ok so they be clever and do diffrent thinks to work out how old it is and they cant get it wrong because no one knoes the truth to start with

This is the way I see things. The universe is a bunch of matter held together by gravity inside a vast blank expansion of nothingness. I think we're in just a complete vastness of absolutely nothing. I don't agree with the Big Bang theory. That couldn't have happened if God created the universe in one week's time.

To me, 'size' is relative.

I believe the universe as in stable energy (matter, you can call it that way) flows through an infinite stream, not in depth or width, but instead infinitely long.

Putting this possibility, many things are possible. The fact that the space is expanding itself every moment as in broadening its 'boundaries' doesn't mean it's infinite, but it scatters using the same torrent through all eternity.

However, assuming space and its respective curvature (time) are infinite, it's a little paradoxical to say it's expanding, isn't it? We can add 1 or 2 to infinite, but we still get infinite.

Does anyone know about the Hubble Ultra Deep Field? It's a picture taken by the Hubble Telescope. It is the deepest image of the universe ever taken in visible light, looking back (to when the universe is thought to have been 800 million years old) approximately 13 billion years ago. The light that was formed back then is still travelling trough space at 300,000km/second. That shows the vastness of space.

Can you believe that? 300000km/s and it's travelling 13 billion years.

^ To above, again I say:

If you film a fish swimming through an infinite river and if it has infinite life span it'll run through it 'all'.

Amplified to my universe theory above, it basically means universe could be curved on a 4D scheme.

Depends if you believe in God or not.