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Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 18/04/2019 18:32:44

Title: Would dark energy cause negative time dilation?
Post by: jeffreyH on 18/04/2019 18:32:44
If gravity causes time dilation would dark energy cause the opposite effect?
Title: Re: Would dark energy cause negative time dilation?
Post by: yor_on on 18/04/2019 21:44:47
I don't think so Jeffrey. It's an added mass even if we can't measure (as in defining what it consist of) it.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 19/04/2019 01:38:49
If gravity causes time dilation would dark energy cause the opposite effect?
Where would the effect be more pronounced?  Dark energy, if a field of sorts, seems essentially evenly distributed everywhere, and thus would not have a dilation difference from one location to the next, any more than a gravitational field, totally uniform everywhere, would have any dilation difference.
Title: Re: Would dark energy cause negative time dilation?
Post by: Janus on 19/04/2019 02:10:32
If gravity causes time dilation would dark energy cause the opposite effect?
Where would the effect be more pronounced?  Dark energy, if a field of sorts, seems essentially evenly distributed everywhere, and thus would not have a dilation difference from one location to the next, any more than a gravitational field, totally uniform everywhere, would have any dilation difference.
A uniform gravity field would produce a gravitational time dilation between different " heights" in the field.  Gravitational time dilation is due to a difference in potential, not local gravity strength.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 19/04/2019 12:03:48
If gravity causes time dilation would dark energy cause the opposite effect?
Where would the effect be more pronounced?  Dark energy, if a field of sorts, seems essentially evenly distributed everywhere, and thus would not have a dilation difference from one location to the next, any more than a gravitational field, totally uniform everywhere, would have any dilation difference.
A uniform gravity field would produce a gravitational time dilation between different " heights" in the field.  Gravitational time dilation is due to a difference in potential, not local gravity strength.
No, I mean a really uniform gravitational field, one that causes no acceleration at all because mass is uniformly distributed everywhere, as is dark energy.  There would be no 'heights' in such a field.  In fact, discounting minor local distortions, we live in such a uniform gravitational field.  The gravity from everything combined is far more than the gravity from the nearby Earth.  Computing our absolute time dilation needn't even bother with the trivial local contribution from Earth.
Yes, I'm aware that the sun and galaxy each contribute more since the gravitational potential here from each is more than that of Earth, but they're still trivial local contributions compared to the more uniformly distributed 'everything else'.
Nobody works in the dilation from that 'other matter'.  It has no relative meaning, only absolute meaning, so it doesn't pertain to the theory of relativity.  Same for dark energy.  There would be no relative distinction between it having a dilation effect and it not having such an effect, so asking if it has an effect is empirically pointless.
Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 19/04/2019 14:08:53
I asked the question because I have not come across any discussions of what effects dark energy would have on time, or anything else. There is plenty of discussion and work on gravity since it is immediately felt around us. Dark energy seems remote.
Title: Re: Would dark energy cause negative time dilation?
Post by: Janus on 19/04/2019 18:11:02
If gravity causes time dilation would dark energy cause the opposite effect?
Where would the effect be more pronounced?  Dark energy, if a field of sorts, seems essentially evenly distributed everywhere, and thus would not have a dilation difference from one location to the next, any more than a gravitational field, totally uniform everywhere, would have any dilation difference.
A uniform gravity field would produce a gravitational time dilation between different " heights" in the field.  Gravitational time dilation is due to a difference in potential, not local gravity strength.
No, I mean a really uniform gravitational field, one that causes no acceleration at all because mass is uniformly distributed everywhere, as is dark energy.  There would be no 'heights' in such a field.  In fact, discounting minor local distortions, we live in such a uniform gravitational field.  The gravity from everything combined is far more than the gravity from the nearby Earth.  Computing our absolute time dilation needn't even bother with the trivial local contribution from Earth.
Yes, I'm aware that the sun and galaxy each contribute more since the gravitational potential here from each is more than that of Earth, but they're still trivial local contributions compared to the more uniformly distributed 'everything else'.
Nobody works in the dilation from that 'other matter'.  It has no relative meaning, only absolute meaning, so it doesn't pertain to the theory of relativity.  Same for dark energy.  There would be no relative distinction between it having a dilation effect and it not having such an effect, so asking if it has an effect is empirically pointless.
Afterwards, I thought this is what you might have meant, but I wasn't sure.   I figured you would clarify if that is what you meant.



Title: Re: Would dark energy cause negative time dilation?
Post by: PmbPhy on 21/04/2019 00:54:06
No, I mean a really uniform gravitational field, one that causes no acceleration at all because mass is uniformly distributed everywhere, as is dark energy.
Neither of those things are true. A "really uniform gravitational field" causes matter to accelerate anywhere that its placed in the field (at least above the Rindler horizon.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 21/04/2019 04:17:46
No, I mean a really uniform gravitational field, one that causes no acceleration at all because mass is uniformly distributed everywhere, as is dark energy.
Neither of those things are true. A "really uniform gravitational field" causes matter to accelerate anywhere that its placed in the field (at least above the Rindler horizon.
If mass is equally distributed everywhere (which it is on a large enough scale), then it accelerates things in no direction since it cancels out in every direction.  The depth (not strength) of this absolute gravitational field is far more significant than is intuitive, and yet it is completely ignored (even by the absolutists) since it makes no relative difference.

For example, if I compress Earth into a dense but hollow shell, anything inside will not accelerate relative to Earth (and not at all if Earth is all there is) because gravity is balanced in all directions. But clocks inside still run slower than the ones on the outside.  Since all the clocks inside run at the same rate, there is zero relative time dilation. The ones outside are out of reach.

I bring all this up in this thread because it can be similarly argued that any dilation (positive or negative) from dark energy would be absolute and thus completely not distinct from a lack of that dilation.  Anything that can't be distinguished from its absence doesn't exist.
Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 21/04/2019 12:52:41
No, I mean a really uniform gravitational field, one that causes no acceleration at all because mass is uniformly distributed everywhere, as is dark energy.
Neither of those things are true. A "really uniform gravitational field" causes matter to accelerate anywhere that its placed in the field (at least above the Rindler horizon.
If mass is equally distributed everywhere (which it is on a large enough scale), then it accelerates things in no direction since it cancels out in every direction.  The depth (not strength) of this absolute gravitational field is far more significant than is intuitive, and yet it is completely ignored (even by the absolutists) since it makes no relative difference.

For example, if I compress Earth into a dense but hollow shell, anything inside will not accelerate relative to Earth (and not at all if Earth is all there is) because gravity is balanced in all directions. But clocks inside still run slower than the ones on the outside.  Since all the clocks inside run at the same rate, there is zero relative time dilation. The ones outside are out of reach.

I bring all this up in this thread because it can be similarly argued that any dilation (positive or negative) from dark energy would be absolute and thus completely not distinct from a lack of that dilation.  Anything that can't be distinguished from its absence doesn't exist.

Unless you have static Lagrange points, that have a fixed position in spacetime, you will always have an acceleration in one preferred direction. However small that acceleration is. It may well be indistinguishable from being stationary. Galaxies are moving and therefore potentials are changing constantly at spacetime coordinates.

Your argument about the distribution of dark energy may well be true. It doesn't hold for gravity. Dark energy must be weaker than both gravity and electromagnetism. It does not pull apart galaxies and does not disrupt molecular bonding.

No one can state definitively what dark energy is. It is implied from redshift data and the fact that this data indicates an acceleration of the expansion.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 21/04/2019 13:39:24
If you actually understand my post, you will understand my argument about dark energy.  I am not asserting that Earth doesn't accelerate.
Unless you have static Lagrange points, that have a fixed position in spacetime, you will always have an acceleration in one preferred direction.
A fixed position in spacetime is an event.  A Lagrange point is a moving point in space (not spacetime) since it is related to pairs of accelerating (orbiting) objects.  We (Earth, sun, galaxy, whatever) will indeed always have an acceleration in a non-preferred direction because matter nearby is not evenly distributed.  The sun is over there and the moon has no choice but to accelerate towards that always since the sun exerts the greatest force.  The direction of that acceleration changes all the time, so it is not a preferred direction at all.

My comment concerned none of this because there is not a dense ball of dark energy sitting somewhere in the solar system.  My comment presumed a uniform distribution of matter, and only Janus seems to have understood that.

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However small that acceleration is. It may well be indistinguishable from being stationary.
Acceleration is absolute and thus distinguishable from non-acceleration, which is inertial motion, or stationary in a frame.

Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 21/04/2019 14:20:09
Acceleration that is too small to measure cannot be distinguished from a stationary state. Admittedly it is absolute and non inertial. If you can't measure it without it being lost in a margin of error it may as well not exist.

Statistically all the mass of the universe may well be evenly distributed. This does not prevent galaxies from colliding. Their gravitational fields are not cancelled. You cannot depend upon an idealised model to represent the physical universe. The universe will always surprise the modeller.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 21/04/2019 18:25:40
Acceleration that is too small to measure cannot be distinguished from a stationary state. Admittedly it is absolute and non inertial. If you can't measure it without it being lost in a margin of error it may as well not exist.
Fair enough, but the topic is talking about dilation, which tends to be computed rather than measured.  The acceleration from 'everything else' may well be below measurability, but the dilation from that mass is not.  And yet that computation is difficult to find on the web because, for reasons I stated above, it makes no empirical distinction to anything.  Ditto for dark energy.

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The universe will always surprise the modeller.
Yes.  I invite you to make the computation above and be surprised.  How much is time dilated due to the speed and gravity well of Earth, the sun, the galaxy, and everything else, respectively?  None of them are very difficult to figure out.
Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 21/04/2019 21:01:22
 In the context of the solar system and with respect to the sun the dilation at the surface of the earth is around 1 minute per year. I haven't taken into account the effects of the galaxy.

We are not experiencing relativistic effects. That is not the point. The expansion of the universe is thought to be accelerating. Something is accumulating. In other words dark energy has an increasing potential over time. If potential can be said to be a part of dark energy at all.

I don't personally have a clue what dark energy is.
Title: Re: Would dark energy cause negative time dilation?
Post by: PmbPhy on 22/04/2019 00:06:46
If gravity causes time dilation would dark energy cause the opposite effect?
No.

Dark energy is the term used to describe what causes with accelerating expansion of the universe.
Title: Re: Would dark energy cause negative time dilation?
Post by: Halc on 22/04/2019 12:53:09
In the context of the solar system and with respect to the sun the dilation at the surface of the earth is around 1 minute per year.
Not sure where you are getting that.  I got about a 50th of a second per year due to Earth gravity and about 1/3 second per year due to the sun.  These include effects from both gravity and speed.

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I haven't taken into account the effects of the galaxy.
It's the 'everything else' that I was wanting to point out.
Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 22/04/2019 13:05:49
Sorry that should have been 1 second per year. I don't know why I wrote minute.
Title: Re: Would dark energy cause negative time dilation?
Post by: jeffreyH on 22/04/2019 13:15:05
If gravity causes time dilation would dark energy cause the opposite effect?
No.

Dark energy is the term used to describe what causes with accelerating expansion of the universe.


Do you think there will ever be an understanding of what is causing the accelerated expansion?
Title: Re: Would dark energy cause negative time dilation?
Post by: yor_on on 10/05/2019 19:50:33
Pete " Neither of those things are true. A "really uniform gravitational field" causes matter to accelerate anywhere that its placed in the field (at least above the Rindler horizon.)

Would you want to expand on this?