Accelerating Expansion of Space-Time and Implications for Time Itself

[messyties]

I have had a physics related question buzzing around my head for some time now, but have not been able to find the answer to it. I should state that have no training in physics, but have an interest in science and the universe.

The question; if space is accelerating, what are the implications for time? As space and time are intrinsically linked, I would think that there must be some follow on effect. I know that mass and the speed of mass affects time, but what about the stretching of space itself? If space is accelerating, does that mean that the speed of passing time may be accelerating as well? And, would there even be any way of measuring or calculating this?

Sorry if this question comes across as a bit dim or I am missing out on some vital bit of information.

Thank you in advance.

 

[phinds]

The accelerating expansion of the universe has no effect on time.

 

[WannabeNewton]

The scale factor (which measures the acceleration you speak of) multiplies the spatial measures of distance. It does not affect the time measure, as phinds noted (however the scale factor is itself a function of time of course). You are correct that in general space and time are inextricably "linked" to put it loosely but when speaking of space and time with regards to the history of the universe, what we do is separate the history of the universe into distinct "spatial slices" which represent the universe at an instant of time. We separate the two notions, so to speak.

 

[Naty1]

The question; if space is accelerating, what are the implications for time?

I like the answers to these questions:

Do all observers agree on the age of our Universe?
Crowell:
No, they don’t all agree.

But in an FRW cosmological model, there are preferred observers, who are essentially observers who detect no dipole asymmetry in the CMB….at rest with respect to the CMBR. Such observers agree with one another on the amount of clock time since the Big Bang, and this is what we mean when we speak of the age of the universe in such a model.

In the real universe, a clock on the earth’s surface is not a bad approximation to such a clock. The solar system isn’t moving at any large fraction of c relative to the CMB, and there is not a huge amount of gravitational time dilation between the earth’s surface and a point that is,say, outside the local group of galaxies.

There is not just one such frame for the whole cosmos. There is one such frame for every point in the cosmos. Global frames of reference don’t exist in GR.
But In cosmology, we use the relic radiation as a convenient reference.

when we hear about the age of the universe being 13 billion years, is that 13 billion years of "earth proper time"?

PeterDonis: Not really. It's the proper time that would elapse since the Big Bang {say,for example an observer whose current spatial location is Earth} but who has always seen the universe as homogeneous and isotropic. Such observers are called "comoving" observers. We don't see the universe as isotropic on Earth: we see a dipole anisotropy in the CMBR, for example, indicating that we are not "comoving" observers, even when the effects of the Earth's rotation and orbit about the Sun are corrected for.

 

[Naty1]

A perspective which supports that of posts #2,3 would be via the balloon analogy. It is reasonable to identify the radial [distance from the center to the surface] in the balloon analogy with cosmological time, but it is a non-linear scale. So the universe started at the center, current time in on the surface, the future is to the outside.

This also helps cement the concept that in cosmology one has to be sure that measurements take place at the same time...in the balloon analogy, instantaneously on the surface of the balloon.

phinds explains the balloon analogy here:

www.phinds.com/balloonanalogy