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The very idea of BB is that it initiated spacetime. BB was the beginning of spacetime; none of it existed before BB. Not the three real dimensions. Not the fourth, the imaginary time dimension.
I don't know of any theory suggesting that the dimensions of spacetime arose one by one, that one of them (time) existed before the others.
If it was so: Maybe the universe, after having only the time dimension for a while, was extended to a one-dimensional line (plus time). Then maybe a second real dimension extended universe to a plane. And then some time later, yet another spatial dimension was added, creating the familiar 3D space. Maybe some day another spatial dimension will be added to create a real 4D space (plus time).
No, the theories based on a spacetime model do not dissolve the dimensions into components with separate existences. They are not adding further dimensions to space by and by. Spacetime arrived as a whole that cannot be split up.
You may of course reject the idea that even the three spatial dimensions appeared at BB, that they, too, existed before BB. That is to reject some very basic concepts of the standard model. I am quite sure that breaking spacetime apart into separate components cannot be unified with the standard model. Maybe a pre-BB spacetime can be modeled as an extension.
One problematic point is that, if you move backwards in time so the three spatial dimensions shrink to zero, the time dimension would also shrink to zero. When you reach big bang (in the backwards direction), there would be zero time. Anything before that would have to be negative. You could probably describe anything like that in mathematical terms. You can create a model where you mathematically can brake down your car to zero speed, and then further to negative speeds (which is distinctly different from a speed in the opposite direction), yet you can't brake down you car that much in real life. Standstill is the ultimate braking down. When the universe time has been shrunk to zero, you cannot expect it to go further. Not in the real world. Not even if you claim that it is mathematically possible.
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it is easy so say time before the big bang is meaningless but last i read some physicists are wondering just that . Roger Penrose for one . also it is well known the expansion of the universe is accelerating .
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The standard model does not preclude that there may be other spacetimes. If so, time would appear along with the spatial dimensions (assuming these spacetimes has the same kind of geometry as ours). But our time dimension is completely independent of their time dimensions; there is no meaningful ordering of events in disjunct spacetimes.
I will not claim that there cannot ever be developed a model that includes some higher "meta-time" concept, in a new dimension where each of simple-time spacetimes have distinct coordinates relative to each other. That would be like extending the line to a plane: Line coordinates with X coordinates 3 and 5 are disjunct, but in the new dimension, in the plane, they can have Y coordinates that are identical, or 3 may have a higher Y value than 5, or a lower one. So you can order X=3 and X=5 according to their Y values. But that doesn't unify the X values, they are still distinct on the X axis.
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BernardIE5317 wrote: also it is well known the expansion of the universe is accelerating
But not fast enough! That is one of the current cosmological issues. With the matter that we can observe with our current technologies as the only there are, the gravitational forces would not be strong enough to hold the universe together as well as it seems to - it would expand faster than it does.
Therefore, we assume that there is some matter (or whatever) spread out in the universe that we cannot (currently) observe, but has a gravitational effect, slowing down the expansion. It is referred to as the 'dark matter'.
The universe balances on a thin line: If there was only the currently observable matter, expansion would go on indefinitely; time would never end. However, with a lot more gravitational matter, the expansion would gradually slow down to a halt, after which the universe would start to contract. Gradually, it would collapse, into a final Gnab Gib. Estimates of the amount of dark matter brings the total amount of gravitational matter very close to the balancing point: Maybe it will tip over to the eternity side, maybe it tips over to a Gnab Gib, where time itself ends, along with the collapse of the real coordinates of spacetime.
Personally, I wish for the cosmologists to discover enough dark matter to ensure a Gnab Gib. I am not comfortable with infinities. I would much rather see that there is an end of time (even if if is long after my time). I can relate to things coming to an end, even, or maybe I should say 'especially' when this 'thing' is the universe itself.
(A corollary: I neither worry nor wonder about where I was before I was born. I accept my birth as a beginning. I also accept my death as an end. So I neither worry nor wonder about the concept of eternal life.)
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"Space exists but it is entagled with time."
Graffito on a relativistic bathroom stall.
"In testa che avete, Signor di Ceprano?"
-- Rigoletto
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yes, moving through space takes time as we know it, even at the speed of light. When things are light years apart, time is just that, not instantly.
"A little time, a little trouble, your better day"
Badfinger
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if you are traveling at the speed of light the universe contracts to zero space so the time it takes to travel across it as you measure time on your pocket watch is zero .
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I'll defer physics to you but
but we have measured those distances and time is required by light to traverse them.
Not sure we would be any different except our experience of normal time inside our light machine would be an illusion because when we get to where we are going the time there would have moved ahead. Let's face it light speed travel is not well understood.
We do know that when radio signals travel long distances, even though close to speed of light, there are time delays we must account for. GPS uses such information to triangulate locations.
"A little time, a little trouble, your better day"
Badfinger
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we have measured the time it takes light to travel distances w/ our rulers and our clocks which are not traveling w/ the light . the speed of light is of course finite so a finite non-zero time is required to travel any distance as we measure space and time in our laboratory reference frame .
as for being "different" i assume you are referring wrt to light beam reference frame and our laboratory reference frame. Special Relativity has this all figured out . The Lorentz Transformation Equations (LTEs) give us all the information we require . as a mathematician this of course is trivial to yourself .
as for the time "there" yes of course time there would have elapsed by some duration . but that is not our concern as we travel to there at the speed of light . again the LTEs explain all this . the LTEs have never been found to be wrong .
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Thanx. Not that familiar with TLE's. I'll look at them.
Yes, I do understand special relativity, etc.
But doing the math and doing the deed are not always on the same page.
"A little time, a little trouble, your better day"
Badfinger
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yes, nice video with very clear math. thanx
since we are not photons with regard to time, we can at least project ourselves as such. how weird is that "everywhere at once". God stuff.
"A little time, a little trouble, your better day"
Badfinger
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Space: the final frontier
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yup
"A little time, a little trouble, your better day"
Badfinger
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"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."
-- Douglas Adams
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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I remember that quote from Doug's Hitchhikers Guide. Love his books.
If you have been following NASA's Webb telescope events, space is really, really big. Webb spotted light that is estimated to be 13.1 billion light years away. (don't understand exactly how they measured it, but is a really far away.
NASA’s Webb Delivers Deepest Infrared Image of Universe Yet | NASA[^]
"A little time, a little trouble, your better day"
Badfinger
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Yes, I have been visiting the Webb telescope's web site on a regular basis. Amazing photos!
I don't know enough astronomy to evaluate the other data coming from the telescope, but I expect those results to be just as groundbreaking.
Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.
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jmaida wrote: that is estimated to be 13.1 billion light years away
So the pizza is definitely going to be cold by the time it gets here.
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"A little time, a little trouble, your better day"
Badfinger
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[SPACE IS BIG]
[SPACE IS DARK]
[ITS HARD TO FIND]
[A PLACE TO PARK]
[BURMA SHAVE]
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lol 
"A little time, a little trouble, your better day"
Badfinger
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"The reason time exists is so that everything does not happen at once."
Old Swedish saying
"A little time, a little trouble, your better day"
Badfinger
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"Time is an illusion, lunchtime doubly so".
Old H2G2 saying.
"I have no idea what I did, but I'm taking full credit for it." - ThisOldTony
"Common sense is so rare these days, it should be classified as a super power" - Random T-shirt
AntiTwitter: @DalekDave is now a follower!
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"Time has never moved, only we have moved" - Old Sanskrit saying.
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"When God created time, he made plenty of it."
Irish/Celtic saying.
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