Time and the relative speed of an Expanding Universe

In summary, the existence of time depends on the universe expanding at an accelerated rate. Less fundamental thing, the 'appearance of flow of time for the observers ' is caused by the macroscopic arrow of time. The macroscopic arrow of time exists because of the boundary conditions at the Big Bang (low entropy). So yes, in some sense the TIME has cosmological explanation.
  • #1
markjuliansmi
2
0
I would appreciate assistance in answering the following.

Does the existence of time depend on the universe expanding at an accelerated rate?
 
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  • #2
'existence of time' is something difficult to define

Less fundamental thing, the 'appearance of flow of time for the observers ' is caused by the macroscopic arrow of time. The macroscopic arrow of time exists because of the boundary conditions at the Big Bang (low entropy). So yes, in some sense the TIME has cosmological explanation. Time is always pointing to the direction where entropy increases, so, it is always pointing away from the Big Bang -> BB is always in the 'past'

So the expansion is important. Accelerated expansion is not.
 
  • #3
I think Dmitry67 is correct.I would also point out that you can have time without having an arrow of time -- not sure which notion of time markjuliansmi had in mind.

Re the original question, there is a sense in which the truth is nearly the opposite of what markjuliansmi conjectured. You can have a universe that's dominated by (1) radiation, (2) matter, or (3) the cosmological constant. In cases 1 and 2, you can observe the local conditions in the universe and infer something about "what time it is." In case 3, it turns out that you can't; a cosmology that's purely of this type has a kind of time-translation symmetry that 1 and 2 don't.
 
  • #4
At the point of the Big Bang there was no time outside the singularity. The edge of the universe, from that instant on, represents the moment of creation of time. This is why you can't explain what is outside the universe. There will be stuff there, as soon as time reaches there.

I have no idea how this realtes to acceleration, though.
 
  • #5
jmallett said:
The edge of the universe, from that instant on, represents the moment of creation of time. This is why you can't explain what is outside the universe. There will be stuff there, as soon as time reaches there.

This is incorrect. If you want to understand this kind of thing better, a good nonmathematical book is Gardner's Relativity Simply Explained.
 
  • #6
Thanks everyone for replying. I suppose being rather a scientific novice I wondered, if to be in a position to observe change occurring between two points in time, as we do today, do we need to have the Universe accelerating at the current rather than expanding at a constant velocity or accelerating less than we are observing today.

I suppose I also wondered if what we are observing in regards the expansion of the Universe is more spin than actual expansion – a question most likely emanating from my incapacity to actualise in my mind the enormity of what surrounds us rather than on any actual scientific fact.

If we humans survive for another thousand years I wonder also if we will not require Babel Fish to communicate between the guilds of knowledge one would expect to develop - an absolute necessity for BBQs to save the sanity of both sides.

bcrowell thanks for your suggestion I will order the Gardner's Relativity Simply Explained.
 

1. What is the concept of "time" in relation to the expanding universe?

The concept of time in relation to the expanding universe is complex and is still being studied and debated by scientists. In the theory of general relativity, time is considered a dimension that is intertwined with space. As the universe expands, the fabric of space-time is also expanding, causing time to pass at a different rate in different regions of the universe.

2. How does the expansion of the universe affect the speed of time?

The expansion of the universe affects the speed of time in a phenomenon known as time dilation. This means that the further away an object is from us, the faster it appears to be moving away from us, and the slower time appears to pass for that object. This is due to the stretching of space-time caused by the expansion of the universe.

3. Is the expansion of the universe constant or does it change over time?

The expansion of the universe is not constant and has changed over time. In the early stages of the universe, the expansion was much faster, but as the universe has aged, the expansion has slowed down. However, recent observations have shown that the expansion is actually accelerating, which is still not fully understood by scientists.

4. How does the speed of an object in the universe affect its perception of time?

According to the theory of relativity, the speed of an object affects its perception of time. As an object approaches the speed of light, time appears to slow down for that object. This is known as time dilation and has been observed in experiments with high-speed particles. However, for everyday objects and speeds, the effects of time dilation are negligible.

5. Can time travel be possible in an expanding universe?

There is currently no evidence or scientific theory that supports the possibility of time travel in an expanding universe. While the concept of time dilation may seem similar to time travel, it does not allow for traveling to the past or future in a traditional sense. The idea of time travel in relation to the expanding universe is still a subject of much debate and speculation among scientists and remains a topic of ongoing research.

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