Visible Universe

[Oldboy913]

They say there is a limit to our visible universe but why is it that we cannot see any further?

[vascop]

Read this:
http://en.wikipedia.o...i/Observable_universe

[jake-the-peg]

Because light has a fixed speed and the Universe is a certain age.

If two points of the Universe are further apart than light can travel in a period of time equal to the age of the Universe that is the limit beyond which you cannot see.

There are other limits too. As you look back in time you see the Universe as it was younger. At one point there was a phase where light was rapidly absorbed by gas and so is a "dark age"

[factor-fiction]

I always wondered- if we found a very distant mirror-like star which reflected light could be see our reflection of Earth as it was thousands of years ago?

[gen2]

No Factor30 - it would be swamped out by the brightness of the sun.

[factor-fiction]

Oh... even if we put sunglasses on to look in the 'mirror'?
Ah well, that's why I dropped Physics at school.

[jomifl]

More to the point ..How did the stars at the edge of the visible universe get there in the time available without travelling at the speed of light... perhaps time was a bit elastic ansd space a bit bendy.

[factor-fiction]

My head hurts thinking about this.

[vascop]

Are you in the invisible universe old boy?

[ann_h]

jofmil - NB the following is a very layman's explanation, apologies to physicists everywhere...

there were a couple of chaps a while ago who theorised that, very briefly, when the big bang happened, light speed as we know it was not a constraint. Inasmuch as time itself only came into existence then. This conclusion was due to finding new stars (the oldest ones) appearing at the very edge of the visible universe.

Also, a friend of mine (who now works at ESA) told me about an article in 1990 about the theoretical possibility of light faster than light. This is because photons and anti-photons split and rejoin as they travel (imagine the outline of a string of beads); so if this action was not possible eg extreme compression of the space in which the beam is travelling, the light would travel a little faster than it naturally does in our known universe.

[jomifl]

I'm all for changing the theory to fit the facts, but if the facts are deduced using the faulty theory then we have to start again.

[jomifl]

The diameter of the visible universe is 93 billion light years, the age of the universe is 14 billion years (give or take a bit) so the galaxies at the edge would have had to average over 3 times the speed of light to get there so assuming constant acceleration would now be travelling at 6 times the speed of light.. They actually appear to be travelling at a lot less than the speed of light and are accelerating. So how did this come about, have I overlooked something? (this calculation assumes that we are at the centre of the the universe (and the big bang), if we are not then the galaxies at the edge of the universe would have had to travel even faster

[beso]

The space between us and the extreme edge of the Universe has continued to expand after the separation that has occurred since the Big Bang. Consequently the visible edge is well this side of the actual edge because the distance to travel continues to increase.

Where did you get the figure for visible diameter of 93 billion light years?

[jomifl]

Hi Beso ..I got my figures from wiki but have been aware of the time/distance problem for some time, just wondered why nobody has ever picked up on it. Thought I may have misunderstood something, it wouldn't be the first time.

[jomifl]

Hi Oldboy.. I am not intending to nick your thread. to answer your question re. the visible edge of the universe..The further away astronomical objects are then less of their light reaches us because of the inverse square law (twice as far 1/4 the light). they are also travelling away from us very quickly as a consequence of which their light is red shifted so is less energetic. These two factors make extremely distant objects difficult to detect using current technology.

[nightmare]

ann h antiphotons ?

[roger]

Given that the universe is believed to have been created approximately 15 billion years ago then surely the diameter of the visible uiniverse cannot be more than 30 billion lightyears

[jomifl]

Exactly Roger.. but only you and I have noticed..and it should be a lot smaller than that.

[beso]

After the stuff we perceive as on the outside of the BigBang blast travelled through space, that space expanded. Consequently it is now further away from us than it could have been by simply traveling at the speed it is actually moving. Indeed it can be further away than it could travel at the speed of light.

However the light we actually see was emitted long before it got that far away because we only see it at the distance that the original bit between here and there has expanded to since then.

Much of the Universe is now over the horizon and we will never see it. However what we can see is now at a distance greater than you would expect to see given the age of the Universe.

I hope that makes sense.

[jomifl]

Hi Beso..so what you are saying is that the matter at the edge of the visible universe got there so quickly because the fabric of the space that it was in expanded, so it didn't need to have moved quickly relative to that space. A bit like walking along a conveyor belt. Is there any evidece to support this theory or is it still just a theory.That space must have slowed down for those distant objects to be travelling at the speed at which they now appear to be travelling. It might be possible in that case that space might contract back to the origin of the big bang bringing with it all those distant objects that theoreticlly are travelling too fast to be brought back by the universe's gravity. Saying that the distant objects are not where we perceive them to be begs the question of 'when is now?' Surely time travels at the same speed as light effectively?

[society]

"They say there is a limit to our visible universe but why is it that we cannot see any further? "

Our eyes are not 'powerful' enough to see further, well... except for those with a third eye. :-)