Is time getting faster?

[gib65]

Hello,

When I think about the expansion of the universe, and how it appears to be accelerating, I understand that the expansion of the universe is more than just galaxies moving apart at greater and greater speeds but space itself expanding at an accelerated rate. But if space is expanding at an accelerated rate, does that mean time is also expanding at an accelerated rate? Or speeding up? Space and time are, after all, part of one continuum called "spacetime", are they not? If so, what does that entail?

[swansont]

16 minutes ago, gib65 said:

But if space is expanding at an accelerated rate, does that mean time is also expanding at an accelerated rate?

Why would it?

[exuczen]

Yes.

Edited July 29 by exuczen

[geordief]

https://www.auckland.ac.nz/en/news/2023/07/04/time-universe.html#:~:text=“Looking back to a time,at the University of Sydney.

 

Is this relevant to the discussion?The link  above  says that astronomers have found that processes  in the early  universe... (and this is their quote)

 

“This expansion of space means that our observations of the early universe should appear to be much slower than time flows today. In this paper, we have established that back to about a billion years after the Big Bang.” 

 

So the cause is "the expansion of space".

Since this (accelerated?**) expansion is ongoing ,it seems to me that future processes should (if we could see them but we can't because by definition they haven't happened yet)  .. should  appear more rapid .

 

In the  actual  frame of reference of the  processes themselves  I think no change in the rate of time passing is observed (or observable?) 

 

This,also  is the relevant  paper in Nature Astronomy from a year ago (I have no subscription)

https://www.nature.com/articles/s41550-023-02029-2

 

**I am unclear as to whether space is/has been  just expanding or undergoing an accelerated expansion and how that would affect the time dilation caused by the phenomenon. 

Edited July 29 by geordief

[exuczen]

@geordief cosmic time dilation is inversely proportional to the CMB redshift z+1. It's much less than one, because its value is like the length of the timestep in computer simulation. The smaller it is, the more steps fit into the base timestep from the time of emission of CMB, and the faster the time goes. Also, the more energy-dense the spacetime is, the slower time goes. It's clear if you look at the 00 term of the energy-momentum tensor and its corresponding term in the metric tensor on the other side of the Einstein's equation.

[geordief]

13 minutes ago, exuczen said:

@geordief cosmic time dilation is inversely proportional to the CMB redshift z+1. It's much less than one, because its value is like the length of the timestep in computer simulation. The smaller it is, the more steps fit into the base timestep from the time of emission of CMB, and the faster the time goes. Also, the more energy-dense the spacetime is, the slower time goes. It's clear if you look at the 00 term of the energy-momentum tensor and its corresponding term in the metric tensor on the other side of the Einstein's equation.

I can't comment as some (most)of those terms are outside  my knowledge bubble.

[exuczen]

@geordief then I recommend you the video I've shared above.

[swansont]

How does time running slower in the past mean that it is expanding? Doesn’t that imply a longer duration? i.e. slowing down?

[exuczen]

@swansont counterintuitively, just the opposite.

[Mordred]

Can you show that using the FLRW metric and not relying on a YouTube video.

The proper time statement is inclusive in the FLRW line element but one has to recognize that we have different time treatments involved (proper time) commoving time, conformal time and look back time.

The common treatment being commoving time  to a commoving observer. 

 

[exuczen]

@Mordred 

https://arxiv.org/abs/astro-ph/0310808

Page 13, equations 7, 8, 9.

[Mordred]

Thank you for providing a solid workable reference +1. That article (well the actual dissertation paper corresponding to that article) is used as a baseline test for the cosmological calculator in my signature. (Just an FYI) on that part.  There is a couple of important lines here that directly relates to how the time components of the FLRW metric is applied and some considerations with regards to blindly treating the recession velocity under strictly SR transformations. 

That is denoted in the the opening statement of the article.  We can see beyond the Hubble sphere and a strictly SR transformation will give infinite redshift at the Hubble horizon. The Z value provided being z=1.46 roughly (depends on the cosmological parameter dataset used).  The article also mentions that standard candles can be used to rule out SR interpretations of redshift. section 4 mentioned on page 6.

section 4 being where the details relating to cosmological redshift under GR becomes essential as opposed to SR the article goes on that the equations in 7,8,9 do not accurately describe expansion due to the treatments applied with recession velocity top of page 15.

section 4.3 now changes the scenario in how expansion is treated by the following statement.

"In this article we have taken proper distance to be the fundamental radial distance measure. Proper distance is the spatial geodesic measured along a hypersurface of constant cosmic time"

So time is now treated differently via the proper time defined by that last statement as supported by statement

"Time can be treated differently eg correctly calculate recession velocities from observed redshifts . However to do this we would have to sacrifice homogeneity of the universe and the synchronous Proper time of commoving object".

lets stop there for the time being ( no pun intended to see how far the OP understands the article and what I just described)

 

 

 

Particularly since a huge set of common misunderstandings of how time is treated by the FLRW metric exists most common trying to apply SR directly to recession velocity

[Mordred]

For aid to the OP cosmic time which is the standard for the FLRW metric used to describe our universe is of the form.

\[d{s^2}=-{c^2}d{t^2}+a({t^2})[d{r^2}+{S,k}{(r)^2}d\Omega^2]\]

\[S\kappa(r)= \begin{cases} R sin(r/R &(k=+1)\\ r &(k=0)\\ R sin(r/R) &(k=-1) \end {cases}\]

An important relation is the critical density relation 

\[\rho_{crit} = \frac{3c^2H^2}{8\pi G}\]

the equations that detail the FLRW metric acceleration equation are below.

\[H^2=(\frac{\dot{a}}{a})^2=\frac{8 \pi G}{3}\rho+\frac{\Lambda}{3}-\frac{k}{a^2}\]

now in the first equation the proper time is the \(-c^2dt^2 \] term above.

However in order to understand how that time component is used by the FLRW metric one has to also understand which class of observers are involved and how the cosmic clock is connected to the Hubble flow (commoving time). As opposed to how SR or GR handles it. GR in this metric the time dependence is directly tied to the scale factor a(t). 

This wiki link actually has a half decent coverage of the time component of the FLRW metric.

https://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric

 

Edited July 30 by Mordred

[exuczen]

I'm giving a screenshot for those who didn't click the link or didn't open pdf (logical or).

If you look carefully, you may recognize Special Relativity's Doppler effect equation, that is the same for both GR and SR, because of the equivalence of the GR and SR time dilation given by this equation. You may even realise, that this equation has a velocity, that must also be identical in GR and SR, if their time dilations are identical. You may even notice the dependence between this velocity and the redshift z+1. A ton of sarcasm is dedicated just for one person, who probably forgot to paste a table to support Friedmann's equation with the values. Your beloved Davis and Lineweaver is self cotradictory, they couldn't even plot the Doppler function properly on the Velocity vs Redshift graph. There are basically wrong values on the velocity axis, that are completely unfit for the Doppler (Special Relativity line). I totally realise that there is a logarithmic scale on the redshift axis, but that doesn't change a thing regarding its invalidity.

Mr. moderator, so far you have shown extraordinary decency by allowing me to defend my point of view instead of banning me and giving the last flood of words and equations to you know who. I count on you to maintain this decency.

[Mordred]

There is no errors in the Lineweaver and Davies article. If their was it would have been pointed out when the dissertation paper was examined in order for the authors to recieve their Ph.D. It also one reference often mentioned as a reliable reference.

You must understand how GR and SR applies in a commoving volume with curvature terms and not just focus on the SR equations and assume thats sufficient.

Secondly mainstream physics section require answers that are mainstream concordance answers.

It is not the place to post personal theories we have a separate forum for that.

Focusing on just the equations you copy pasted is literally ignoring the rest of the article 

 

Edited July 31 by Mordred

[exuczen]

And you must understand the basics of deduction and learn to read with comprehension.

[Mordred]

Here is the complete dissertation paper

https://people.smp.uq.edu.au/TamaraDavis/papers/thesis_complete.pdf

Just now, exuczen said:

And you must understand the basics of deduction and learn to read with comprehension.

No you must understand the entirety of a paper before judging it in error. 

[exuczen]

I really don't have to. If they are wrong in two cases, I don't care about the rest.

[Mordred]

That's your hangup then as you refuse to understand why the authors state what they do. The key difference between SR and GR. Is that SR does not account for the spacetime curvature terms. Where as GR is specifically dealing with the spacetime curvature terms.

The FLRW metric is a very specific coordinate system. That coordinate system is not accounted for strictly by the equations you posted.

By ignoring the rest of the paper your understanding and conclusion is in error.

 

[exuczen]

Sorry, there is no spacetime curvature due to the expansion.

[Mordred]

Wrong our universe does in fact have a slight curvature term. It only approximated as flat. However that curvature term specifies a relation called the critical density formula.

Which isn't quite the same as a GR  curvature term. All in the papers being discussed.

Expansion and contraction does in fact alter the null geodesic paths of massless particles such as photons.  Gr curvature typically involve a center of mass hence it only assists the FLRW metric ( the FLRW metric is a specific class of solution that applies GR ) however the k curvature term itself for the FLRW metric directly involves the critical density relationship. If the actual density precisely matches the critical density term then and only then is our universe critically flat.

 

Edited July 31 by Mordred

[exuczen]

For spacetime to have curvature due to expansion, spacetime itself would have to store the past values of both the metric tensor and the energy-momentum tensor that describe it. It doesn't store them, it has only current values.

[Mordred]

No that's where the equations of state come into play were dealing with the mass distributions of a multi particle field distribution.

All of this being contained in the sections you chose to ignore.

Here is a little for thought. COBE, WMAP and Planck all looked for specific signatures to define and determine the universe curvature term using the CMB.

They looked for distortions that would result from the multiparticle distributions over the expansion history due specifically to how those distortions would result from expansion /contraction of that multiparticle field.

 

Edited August 1 by Mordred

[exuczen]

Equations of state can't help you if there is no spacetime curvature due to expansion for the given reason and there is also the cosmological principle. You choose to ignore my basic logic as well as the plain errors and contradiction in the paper, I choose to ignore the rest of your paper. We're even.

[Mordred]

Every statement you have so far is 100 percent incorrect. You haven't made a single accurate statement.

 Your basic logic chose to ignore what it chose to ignore so is absolutely meaningless because you choose to ignore Any detail that runs counter to your way of thinking.

Literally every single physicist that has ever looked at cosmology would disagree with you.

Edited August 1 by Mordred