# B On what "dark time" might mean

1. Mar 3, 2017

### fwc

I was wondering if someone would kindly point me to reading material that might help to shed some light on the idea outlined below. I'm looking to understand the related concepts in greater depth. Searching for "dark time" is what brought me to PF in the first place, via this forum, and then I also came across this, but neither seem to address the outlined idea. Apologies in advance for the lengthy post--not to mention any errors in my understanding, corrections thereof would be appreciated.
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We think redshift occurs because of how long it takes light to reach us from far away. The assumption here is that the speed of light is constant, even through regions of the universe--between galaxies--that are experiencing accelerated expansion. But what if they aren't experiencing acceleration and light just travels slower through these regions? Or alternatively, perhaps the speed of light is indeed constant, but time moves faster in these regions.

The same argument might be made w.r.t. dark matter. The bodies rotating around the edges of galaxies are moving too fast. It seems like they need to have more mass to keep them tethered to their galaxies. Or maybe they aren't moving as fast as we think; maybe their velocities are lower. A lower velocity could come about one of two ways, by less distance traveled or more time. If time is moving faster for them, then they might be experiencing lower velocity even while we observe them at higher velocities. We know time is local to the observer, so why not?

Could the (perceived) probabilistic nature of quantum mechanics be explained by this also? Perhaps the probabilism is only a matter of perception due to mis-measurement of time. If an atom, from its perspective, experiences no time, or stopped time, this could explain why electrons appear to us to be in all and none of their possible locations simultaneously--distance divided by zero.

Sean Carrol writes, "An unaccelerated trajectory yields the greatest possible time a clock could measure between two events." A clock on a rocketship that zooms away from Earth, circles around, and comes back, will be behind a clock that remains on the surface of the earth during the rocketship's trip. What velocity was the rocketship traveling at? Depends on your perspective. Both the rocketship and the earthling agree on the distance the rocket traveled, but they don't agree on how long it took, so again, velocity is in the eye of the beholder.

As an aside, would a rocketship zooming around like this for, let's say, a billion years, but staying close to Earth all the while, perceive even more redshift from far away galaxies? How much redshift would an atom perceive?

On the surface, all of these seem to point in the same direction of time being faster at larger scales and slower at smaller scales. Scale might not be the operative variable however. Rather, these all point in the direction of time being slower in the presence of accelerating matter and faster in its absence.

2. Mar 3, 2017

### Staff: Mentor

The second one ("Could Dark Matter be Time Itself") does, though that might not be obvious to you. The general idea is that the observations on which our models of dark matter and dark energy are based might instead be due to a difference in "time flow" in different parts of the universe. That idea does not work; to the extent testable models can be made out of it at all, those models make predictions that don't match observations. Your own formulation is much too vague to be testable in any case, and it also appears to be based on basic misunderstandings of the sources you are reading.

See below for some specific examples of the above.

The hypothesis that physical constants could have varied significantly on cosmological time scales has been tested. It does not work. See, for example, here:

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/constants.html

What does "time moves faster" mean?

What does "time is local to the observer" mean?

Please read the PF rules on personal speculations. Your whole post is personal speculation in a sense, but this in particular is very far into that territory and is off limits here.

What does this have to do with the topic?

It would perceive a Doppler shift that had a fluctuating component (due to the ships' motion around the Earth) superimposed on a constant component (the redshift an Earthbound observer would perceive). It would be easy to factor out the fluctuating component, particularly since there would be plenty of other observations that could be used to quantify the motion of the ship relative to the Earth.

In the standard twin paradox in flat spacetime, it is true that the twin who feels acceleration also experiences less time between two fixed events. But this does not generalize to curved spacetime; there are scenarios in curved spacetime where the twin who feels acceleration experiences more time between two fixed events.

A general comment: it is much better to learn our best current theories and what they say before trying to speculate on your own.

3. Mar 3, 2017

### Staff: Mentor

On re-reading, I saw this, it is not correct. The observed redshift of light from a distant galaxy, in the standard cosmological model, depends not on how long the light has traveled, but on the factor by which the universe has expanded from emission to detection. This factor is model-dependent, and our current best fit model does not just use redshift observations; it uses many different observations, and the observed relationships between them. For example, we do not just observe the redshift of the light from distant galaxies; we also observe the brightness and the angular size of the galaxies, and we use the relationship between all three of these to determine the actual expansion history of the universe.

4. Mar 3, 2017

### Chronos

Under GR the speed of light is the basis for defining time. Speaking of the two as separate entities invokes a new paradigm, placing you on slippery soil from a PF perspective. You cannot extrapolate based on unproven assumptions without expecting charges of imbibing from a cracked pot.

5. Mar 3, 2017

### Staff: Mentor

That would not lead to redshift. The approach of a variable speed of light (which is tricky on its own) would need a speed of light that depends on the distance to us. Which would mean we are in a special place in the universe, a "center". Why should we be there? The same problem arises from a different "speed of time".
If time is moving faster for them, we would observe a huge redshift from the time dilation. That is not what we see. A different passage of time would also lead to either redshift or blueshift for all in the same way. This is also not what we see. We have speed measurements both from stars approaching us and receding, and both speed measurements agree. There is also no reason to expect that time behaves differently in the outer parts of a galaxy - apart from the small effect predicted by relativity (which is taken into account where relevant).

I could go on like that, but I hope I showed a general pattern: You speculate without knowing the measurements you want to discuss. You cannot explain measurements you don't even know.

6. Mar 4, 2017

### Staff: Mentor

Fixed it for you....
And seriously, kidding aside, it's one thing for someone to take a wrong turn when they're're finding their way through uncharted and unexplored territory. It's another thing altogether to wander down dead ends and blind alleys because they haven't looked at a map or asked for directions from the people who are already familiar with the territory.

7. Mar 4, 2017