The size of this universe

Go back to my original drill, if it is 100 light-year away,
the first ray of light that reached here, would it travel >100 light-year distance? and so took > 100 years of time?

 

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In spite of the fact that no one knows the answers to the questions at the heart of Saint's thread, there is an explanation that is not incompatible with the views offered. Our observable universe is a finite subset of the finite Big Bang arena, which is a subset of a greater infinite and eternal universe. Of course there is no way to test such an hypothesis, but it does avoid the explanations that, 1) "God did it", or 2) "Something from nothing".

 

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Short answer, no.
Or in line with what I said in the other post, the light from a star 100 L/years away, would be in our own galaxy and therefor not in space/time undergoing expansion.
[I am ignoring any real proper motion of the star]

 

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You mean the light from that star will reach us in 2114. ?

 

The space in our own galaxy may also expand at a much slower rate!

 

Saint

The effects of Dark Energy(the source of the force driving expansion)are overwhelmed at close distances by the effects of gravity, so no, our galaxy is not appreciably expanding like spacetime is expanding, we are in a gravity bound system and gravity is the dominate force within gravity bound systems. It is the space BETWEEN gravity bound systems where DE becomes the dominate force.

paddoboy

If it had a beginning there is no infinite time(it will always be a finite time from that instant), if it once had no volume then space is finite as well because it has been expanding only since the beginning, a finite size. If it is still expanding then it is by definition not infinite(how do you get bigger when you're already infinite in size?). Our Universe may not be "Everything" that exists, just like your bedroom may not be the only room in the building you live in(on the other hand, you might open your door on empty space). But we are separated from all the rest(if it exists)by "walls" of physical properties, properties that determine the conditions within our Universe and keep us bound within it. We don't know whether there is anything else at all, so we must act as the Universe constrains us to act, it's limits are our limits as well.

Grumpy

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Just wanted to suggest the term "potentially infinite" in regards to your metaphor "near infinite".

 

Assuming that the cosmos doesn't just loop back on itself, in which case, every point -- wherever you are -- is effectively "the center". Which says a lot if you live in The City. You relaly are at the center of the universe.

 

Good explanation.

 

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Just thinking of the reactions I received in another forum re that metaphor, but yeah, OK, I'll accept yours also.

 

Yep to the first question and I see mass/energy densities and subsequently gravity as preventing space/time expansion with regards to the second one.

 

http://en.wikipedia.org/wiki/Metric_expansion_of_space

Regardless of the overall shape of the universe, the question of what the universe is expanding into is one which does not require an answer according to the theories which describe the expansion; the way we define space in our universe in no way requires additional exterior space into which it can expand since an expansion of an infinite expanse can happen without changing the infinite extent of the expanse. All that is certain is that the manifold of space in which we live simply has the property that the distances between objects are getting larger as time goes on. This only implies the simple observational consequences associated with the metric expansion explored below. No "outside" or embedding in hyperspace is required for an expansion to occur. The visualizations often seen of the universe growing as a bubble into nothingness are misleading in that respect. There is no reason to believe there is anything "outside" of the expanding universe into which the universe expands.

Even if the overall spatial extent is infinite and thus the universe can't get any "larger", we still say that space is expanding because, locally, the characteristic distance between objects is increasing. As an infinite space grows, it remains infinite.

 

The distance between objects in our galaxy [or any galaxy] isn't growing because of 'the cosmological expansion of space'. The objects are gravitationally bound and the objects equation of motion describes it's natural path through the gravitational field. The expansion of space is global phenomena over cosmological distances.

You should think about what you said. For instance what force does expanding space put on an object? The answer is none. Space can't push anything so it has NO effect on the motion of anything in the universe.

 

I don't usually quote myself, but no one else has commented, and this presents an interesting picture.

The actual z of the microwave background is not well known, because the decoupling temperature is not well known but estimated to be about 2,990 degrees K; we can thus take the ratio 2990K/2.725K = 1064 to give us the z-factor (1064 representing the degree of redshift in the radiation's spectrum) associated with the recession of the decoupling plasma ( http://bado-shanai.net/map of physics/mopdecodecbr.htm ). Other estimates place it at upwards of z = 1200, utilizing a somewhat higher decoupling temperature, but this is not important for the below discussion.

If one were an observer at that far distant region of the univese that we see when looking in that one direction (which we will for sake of argument assume to have evolved into a galaxy with a sentient observer capability), then that observer when looking towards us would see us not as we are now, but as we were when we were a hot, cooling plasma.

The question for the thoughtful reader, then, is what is the recessional velocity between that region that we see in one direction receding from us at z = 1064, and that other region of space that we see in the opposite direction from us, also receding from us at z = 1064. I.E., how fast are they receding from each other? Hint: it is NOT .999999c + .999999c And for the second question, if an observer in one of those regions were to look in our direction and see us as a receing plasma of some 2990 degrees K, would that observer be able to see that other region of the universe that we see receding from us in the opposite direction?

Food for thought for thoughtful readers with good mathematical ability, such a Rpenner.

 

I'm a bit hungry at this time, and although I hate maths, I'll have a shot at this......

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An observer say at the limit of our observable Universe in a particular direction, [46 L/years distant] would I presume looking back at us, see us receding at the same rate we see him receding.
But what we see receding from us in the other direction [46 L/years distant] would be beyond the observable horizon of the first observer.
Both observers in both directions, would see us at the limit of their observable Universe, but would not be able to view each other, as that would be beyond their observable bubble.
By the same token each observer in opposite directions from us, would be able to observe other observers at the limit of their bubble [in the direct opposite direction from us] that is beyond our bubble.

Eventually though both the observations we make in those direct opposite locations, would in time be beyond our observable bubble as the intervening space expands.

 

can we see that region that is receding from them in the opposite direction? the universe isn't old enough for that to happen and by the looks of it, because of DE, we will never see it.

before DE came on the scene then you would have just doubled it. i don't think relativistic addition needs apply when talking about space expanding and the hubble constant. with DE then it would be double plus whatever the DE contribution to the velocity would be.

of course i may be completely wrong. someone will know though.

 

Again, I would say no.....the region receding from them in the opposite direction is not within our Observational bubble, but lies within there's.

Agreed [that would make two of us wrong]

 

if the universe is expanding, can we say that space-time can be created?
Space-time is a fabric, right?
If it can expand, what happen to time? Does time expand too?

 

The fabric concept is only an analogy to illustrate what happens.
You ask that because space/time is expanding, is that the same as space/time being created......
When we stretch/expand an elastic band, or blow up a balloon, are we creating more rubber/latex??
Einstein has shown that both space and time are not absolute as Newton thought....