What Lies Beyond the Edge of the Universe?

[andrewj]

confusion

Yes and you and your Aussie brethren have been doing a great job clarifying cosmology terms and keeping our language fit.

the bottleneck is that those two Ozlanders Charles Lineweaver and Tamara Davis wrote this fantastically helpful article on common misconceptions and confusion about standard cosmology and it was published in the Scientific American and yet people come and talk as if they HAVEN'T READ IT. It's free.

I won't even give a link to your papers, because I think people should read entry-level SciAm stuff like Lineweaver Davis first.
Aaargh! SciAm website has removed all the illustrations! The article was first posted in 2005 and it is gradually dying
http://www.sciam.com/article.cfm?articleID=0009F0CA-C523-1213-852383414B7F0147&pageNumber=5&catID=2

this is bad. it communicated well partly because the illustrations were so clear

why when its over

 

[andrewj]

Funny you should ask that question as I was just contemplating that very topic - the expanding universe.

First of all...IF we could reach the theorized outer edge of the known universe I believe many would speculate that we might simply find some of the every elusive dark matter. But "no" we would not be able to travel into it.

Oddly enough we would be like the early explorers who thought if they went too far they would reach the edge of the flat Earth and have to turn around or risk falling off.

Personally I don't think there is an end or edge anything like that and I think there is more to this expansion theory then many are willing to admit or can grasp just yet, or maybe they just haven't taken the time to think about it. After all if we can prove the expanded universe why hasn't it change our travel time to say - the moon??

Maybe only the smaller units within the universe are expanding as whole units?

only the space between galaxies expands everything within the galaxy is held by gravity

 

[andrewj]

You were clear, C.F. You have a misconception about what modern cosmology says



in the picture we get in contemporary cosmology such a place does not exist.

the "big bang" is not what the unfortunate words might suggest. It is not an explosion of some material exploding out into empty space. There is no surrounding empty space, in the standard picture.

what we are talking about is an expansion of SPACE ITSELF together with the matter distributed more or less uniformly in it



this has been answered by several of us, but I will recap
if space is finite (that is, space and the matter uniformly distributed in it) then it is analogous to a sphere surface and has no edge or boundary, and if you travel unrealistically fast you eventually come back to starting point----so you eventually see the start

this is assuming you travel very very fast so that we can neglect the fact that space is expanding while you travel.

if space is infinite (with matter more or less uniformly distributed in it according to the usual picture) then no matter how fast you travel the universe looks the same as it would be looking at home. but you never get back home.

=============
the man who made up the phrase "The Big Bang" hated the big bang idea and believed in his baby the Steady State picture. in his anger and contempt he made up a misleading phrase which caught on with journalists and has confused lay people ever since.

the event we are talking about must not be pictured as a comic-book explosion puff-cloud in the middle of empty space.

the event is the beginning of the observed expansion of space (that space being uniformly occupied by matter)

about conditions at or immediately before the start of expansion, people have different models
(a one that is increasingly common nowadays is that the expansion was preceded by a contraction, sort of a mirror image, and that when a certain critical density was reached space stopped contracting and began to expand.
but there are several competing pictures of how the expansion started and no one clear favorite.)

you seem very sure about this

 

[nicky nichols]

hello coldfusion85, are the multiverse ideas by cosmologist max tegmark what you might be looking for?

 

[Chris Hillman]

if the universe is homogeneous and isotropic on large scales according to the FRW model, how can the following, from the WMAP Cosmology page you posted, be a valid statement?
"Because the universe has a finite age (~13.7 billion years) we can only see a finite distance out into space: ~13.7 billion light years. This is our so-called horizon. The Big Bang Model does not attempt to describe that region of space significantly beyond our horizon - space-time could well be quite different out there."

How could it be different beyond the event horizon if we are assuming things are the same everywhere in the universe? It seems that making the statement that "space-time could well be quite different out there" implies that the FRW model might not hold, and therefore, how can we assume it holds now?

This discussion in D'Inverno, Understanding Einstein's Relativity should help you see how to clear up the misconception here (that something must be wrong with the quoted statement).

 

[nicky nichols]

so if space-time topology could be transcended, a presumably non-physical concept within our own universe or perhaps not?, then suppose we travel everywhere far enough, then what might be the average condition of space-time we encounter? ie, what would be the average topology, etc. the average conditions of structure and matter? And what about ending up in those universes in which matter did not decay, or ending up in a place equivalent to somewhere inside our own universe but apparently elsewhere?

 

[Chris Hillman]

Hi, Nicky, I don't know if you were addressing me, but if so, I don't understand your questions.