The Universe...

[Platinum]

Right weird one this but can someone possably explain to me.
Scientists tell us that they can use telliscopes to look back at the early universe, but if the universe started off in the same place and expanded, and nothing can move faster than light then surly the light from the early universe should have overtaken us now and what we see now should be much older no?

Yes my head hurts thinking about it as well.

[shaithis]

The universe isn't 3-dimensional. It's about the same shape as a 4-dimensional doughnut and light can "circle" around it.

[Platinum]

Is that proven though?

[Salazaar]

Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.

If you think you understand how the universe works then you really, really don't.

[MaddAussie]

If I understand it correctly Plat, the light(and radio waves etc) we see now left that stars we are viewing millions of years ago so in fact we are seeing into the past as the light takes so long to reach us.

[Platinum]

But if thats the case how did we get so far away without the light from these early galaxys overtaking us?, After all nothing can travel faster than light?

[kalniel]

Is that proven though?

Depends what you define as proven. I don't know of any theories stating the universe has only three dimensions that fit the data we've been able to gather at the moment.

[Salazaar]

But if thats the case how did we get so far away without the light from these early galaxys overtaking us?, After all nothing can travel faster than light?

That presumes that we and the observed galaxy are traveling along the same path, which almost nothing else is. What they're talking about is light coming from objects on a tangential path (almost everything else) to us. The exact time delay we see depends onthe angle between our path and the observed object and our respective distance traveled and speed... And also on some seriously funky 4+ dimensional physics which I can't even begin to comprehend.

[Fraz]

the light from the early universe should ... be much older no?

It's really quite simple, and you've answered your own question sort of.

If something is a million light years away, and is producing light, that light will take a million years to reach us, and hence you are observing what was happening 1 million years ago.

Since the universe is somewhere around 12 billion years old, it's been a very big place for a very long time, so you can extend this principle back a long way back. In fact you can extend it back right to the beginning of time, for exactly the reason you state: nothing* can travel faster than the speed of light.

Modeling the universe as a sphere, the boundary of the sphere will be expanding at the speed of light - i.e. the universe expands at the speed of light in all directions. Hence light from one edge of the sphere can NEVER reach the opposite side of the sphere, because it also is moving away at the speed of light.

This causes a problem known as the "Horizon Problem", which is a real conundrum. Basically, it appears that opposite sides of the universe are in very very close thermal equilibrium - the "temperature" of the left-over radiation from the big bang is 2.725 K on opposite horizons, which is impossible since there is no way it could have equilibriated if opposite horizons are moving away each at the speed of light. Rather bizarrely, the solution to this problem actually involves the very very early universe (when it was about the size of a proton) expanding for a short period of time at a velocity much much greater than the speed of light - the "inflationary stage". I won't go into this though, as it will really break your mind.

* ignoring the early inflationary stage of the early universe.

[Platinum]

My head hurts...

[Tzarbo]

Try this then:

Light travels 1 light year per year.

So summat 6.3 billion light years away from us, if you look at it with a big telescope, will appear as it was 6.3 billion years ago.


IT'S A TIME MACHINE!

To try this for yourself, if you don't have access to the Hubble Ultra Deep Field thingy, go outside and look at the sun (but never look directly at the sun, obviously), but do look at it anyway (but don't it might hurt your eyes), but look at it, and as light from the sun takes about 8 minutes to reach us, you are seeing the sun (never look at the sun) as it was about 8 minutes ago.

IT'S (not really) A TIME MACHINE!

[jim]

Right weird one this but can someone possably explain to me.
Scientists tell us that they can use telliscopes to look back at the early universe, but if the universe started off in the same place and expanded, and nothing can move faster than light then surly the light from the early universe should have overtaken us now and what we see now should be much older no?

Yes my head hurts thinking about it as well.

If the early light overtakes us, we'll be seeing the light that comes after it, hence light from later on.

[iranu]

But if thats the case how did we get so far away without the light from these early galaxys overtaking us?, After all nothing can travel faster than light?

The light is always shining it hasn't been turned off*.

Think of a light bulb. Turn it on. Does the light over take you? Yes of course because someone else standing behind you can see the light. But the light bulb continues to shine and send out light. Now move back slightly, say six billion light years. The light won't have reached you yet because it will take 6 billion years to reach you. Hang around for a bit and wow there's the light. You can now see the light and analyse it. *Now lets imagine that someone turns the light bulb off. What happens? You won't see it switch off because it will take the light 6 billion years to reach you, when one day you'll be viewing the light and it will stop. So in effect what you are seeing is the light as it was 6 billion years ago, hence the back in time bit.

[Fraz]

Now move back slightly, say six billion light years.

Awesome sentence.

[tiggerai]

Plat - could you go back to drinking on saturdays if this is what you're gonna come up with on Monday mornings?!

it's too much!

[IBM]

nothing* can travel faster than the speed of light.

* ignoring the early inflationary stage of the early universe.

Say what?