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Author Topic: THE NOW OF THE UNIVERSE  (Read 1588 times)

Offline stelios

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THE NOW OF THE UNIVERSE
« on: 23/07/2009 20:31:30 »
We know telescopes provide a window to the past but the farther we go away (or back in time) the situation becomes pretty sticky.  Consider "looking" (catching the light) from a space object (star, quazar, AGN, whatever) 47 billion years away (that's the farthest we've gazed so far, right?).  The light actually left the object well before that time (has to be less than 13.7 billion years) and then it got stretched due to the expansion of space and reached us only today.  Today, this object is not there any more but its matter is somewhere in a different form or formation.  So, where are today all those particles that took part in the reaction that produced the light that ultimately reached us? For as long as the object they were part of was alive, they should be moving farther away from us with it,so their light path received by us after all those years is the path of the object observed.  Still, this path is 47 billion years away and less than 13.7 billion years back in time.  On the other hand, the object (or its particles) could have moved away from us during all those years faster than light, so we we'll never catch a glimpse even if we wait for ever.  Whatever the case, most probably everything we see today in the sky is not there anymore and they must have moved away from us at some speed.    Plus, almost everybody agree that there is no central point in the universe and all vantage points are equivalent. I suppose this holds if one takes for granted that any point in the universe has the same restrictions as we have, being able to see around it only the evolution of the universe but not the absolute present state of the universe, so this equivalence principle does not hold for any given moment in time (like our absolute NOW or our absolute one hour later etc.).  To make things simpler, I do not consider here the non-existence of absolute time.   
So, is it that TODAY everything sits on the broader (almost) "two-dimensional" surface of a balloon universe (that can be considered to be flat, as far as the number of dimensions is concerned) and everything we look at is just snapshots of the earlier state of that very balloon while it was swelling with the help of space expansion?  In other words, are we just seeing in the sky the evolution of the universe through time (which is the staple notion) and the reality of NOW is sitting around us on the same sphere we are sitting?  If this is the case, is there anything between the surface of the balloon and it's center TODAY, and, does a center even exist TODAY?  The big bang was indeed the center when it all started, but all the light we see now coming from the past and ever closer to the center of space and time should not be there any more. It should follow the same path as the sun and the earth did, and it should sit on the sphere roughly at the same distacne from the primordial center of it all.

All the above are not conclusions of course, they are mere questions of a lay person that has read a few books in his spare time and wants to clear the mess in his head.  If there is anybody out there that can help me sort it out somehow, I'll owe him

Stelios Bakalis


 

Offline LeeE

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THE NOW OF THE UNIVERSE
« Reply #1 on: 24/07/2009 01:01:01 »
There are quite a few questions in there and a full answer would be an essay (where the answers are known).

I'll only comment on one or two things that occurred to me.

Just about everything we see in the sky, with the naked eye, are part of our galaxy or part of the local group, and they'll be with us until we combine.

The balloon analogy for the expanding universe is quite good but the problem with it is that people think of it in three dimensions when it's really only showing two-dimensional expansion.  When you look at the balloon you see its center as being in the middle of the balloon, from a three-dimensional perspective, where there's nothing but air, but the center you see doesn't actually lie on the surface of the balloon, which in the balloon analogy is all that exists; there is no hollow center to the universe.

What you should be wondering about is where is the center of the surface of the (sealed) balloon?

Actually, the balloon analogy is rather good if you use it to visualise space-time instead of just space because then the empty interior of the balloon very nicely represents the time axis.  In that respect, you can then say that while there's no center to the universe, because it would be like trying to establish the center of a spherical surface, there is an origin from the time point of view.  This is an origin though, and not a center.
 

Offline stelios

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THE NOW OF THE UNIVERSE
« Reply #2 on: 24/07/2009 15:44:04 »
We agree on almost everything.  The balloon is indeed two-dimensionsl and it's all there is.  That is how I (try to) visualize it.  There is nothing inside the balloon NOW, the inside of the ballon indeed represents the progression of time and the center of it is the point where it all began back THEN, having no meaning NOW.

There should be no center of the balloon.  The equivalence principle of vantage points holds in somewhat different way for any given moment in time than is generally stated in physics books.  Equivalence of vantage points at any given moment still holds if those points sit on the balloon, so any one point is no different than the others.  But if there is something inside the ballon (unlikely), equivalence breaks and a center is then possible (again, unlikely).

So, my questions remain unanswered.  Corroboration is nice, but confirmation is better

 

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THE NOW OF THE UNIVERSE
« Reply #2 on: 24/07/2009 15:44:04 »

 

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