# B Effect of gravity on time and the age of the universe

1. Oct 15, 2016

### pforeman

In the beginning of the universe, the hot matter of the entire universe was confined to a small volume.
I would guess that compared to our time frame, time flowed slower than it does now.
I would also guess that time has gradually slowed down since then. Is this significant in predicting the age of the universe,or when I see explanations of those first few milliseconds of the universe after the big bang. I would guess that this effect is miniscule now, and virtually unchanged for quite a while now?
Thanks
Paul

2. Oct 15, 2016

### Staff: Mentor

That statement does not make sense. Relative to what would you measure it?

There is no such effect.

3. Oct 16, 2016

### Ibix

Time always runs at one second per second.

With something like a black hole, it's possible to have two clocks next to each other, lower one down near the black hole and raise it again, and show that less time has elapsed for it. This is because the two clocks have taken different routes through spacetime, and the two routes have different "lengths", and it turns out that the "length" of a route through spacetime is the elapsed time for anything following that route. People do say that time runs slower near a black hole, but that's a simplification of the path length explanation (and some related experiments) and sounds more general than it is.

With the big bang, you can't lower one clock close to it and bring it back. So there's no sensible way to ask the question of how fast clocks tick near it - when one clock is near it, all clocks are near it and there's nowhere away from it to compare to. And the mathematical description of it doesn't have the special features (it's not "stationary") that would let you make some analogy to the black hole case, which is what I think you tried to do.

Last edited: Oct 16, 2016
4. Oct 16, 2016

### pervect

Staff Emeritus
Dyson has a "biological scaling hypothesis" in the somewhat dated paper, " TIME WITHOUT END: PHYSICS AND BIOLOGY IN AN OPEN UNIVERSE". This was written, however, before we knew the expansion of the universe was acclerrating.

This hypothesis could be related to what the OP was thinking of. But it's not a question of "physical time" speeding up, it's an unproven but plausible published hypothesis about what one might call "biological time", and how temperature might affect it.

I'm not quite sure I understand the details, such as the sign of the effect, at the moment. It's late. But I thought the ideas might be of interest for the discussion.

Baez's summary in http://math.ucr.edu/home/baez/end.html might be clearer:

The cosmological constant throws a big monkey wrench into Dyson's hopeful picture, as Baez's article points out, but while this is of some interest in it's own right, it's getting off-topic.

5. Oct 16, 2016

### phinds

And @pforeman, just so you know, although ibix's statement

is absolutely correct, you don't have to go to the extreme of a black hole. Just fly an airplane on Earth. It's been done/measured. There is a an aging differential due to speed AND one due to difference in height in the gravity well. Both are tiny, but measurable. The gravitational component does of course depend on different heights in the gravitational well and, as has been pointed out already, there is no "height difference" in the early universe.

6. Oct 16, 2016

### Staff: Mentor

The best atomic clocks are so sensitive they can detect height differences of one meter. You can put one higher in your lab and measure the different gravitational time dilation. It also leads to the interesting effect that you have to specify where in your clock the time measurement happens.

7. Oct 16, 2016

### vanhees71

8. Oct 16, 2016

### Ibix

For clarity, @phinds is referring to the Hafele-Keating experiment. The Pound-Rebka experiment, to which @vanhees71 refers, shows gravitational time dilation without motion.