Could Changing Gravitational Constant Explain Hubble's Law Alternatives?

[gptejms]

I was reading one of John Gribbin's (popular science)books a few days back when I thought if there could be alternative explanation(s) for the Hubble's law.One simple explanation could be that the value of G(universal gravitational constant) could be changing with time--if G were higher in the past(i.e. G increasing as we go into the past),clocks would be moving slower then(than today).Now since clocks are moving faster,light from distant galaxies would appear red-shifted to us---red-shift would be more for more distant galaxies because they are more into the past when G was still higher.My question is:-how is this explanation ruled out by cosmologists before jumping to the expansion model?

Another observation:-(say) G does not change with time.As we go back into the past,things become nearer and nearer--so gravitational fields become higher and higher i.e. clocks get slower and slower leading to the kind of effect mentioned above(even without G changing).So the redshift is now due to two reasons--expansion and 'change of clock rate'.Is the latter effect taken care of in present theories?

Jagmeet Singh

 

[Garth]

I was reading one of John Gribbin's (popular science)books a few days back when I thought if there could be alternative explanation(s) for the Hubble's law.One simple explanation could be that the value of G(universal gravitational constant) could be changing with time--if G were higher in the past(i.e. G increasing as we go into the past),clocks would be moving slower then(than today).Now since clocks are moving faster,light from distant galaxies would appear red-shifted to us---red-shift would be more for more distant galaxies because they are more into the past and G was higher.My question is:-how is this explanation ruled out by cosmologists before jumping to the expansion model?

Another observation:-(say) G does not change with time.As we go back into the past,things become nearer and nearer--so gravitational fields become higher and higher i.e. clocks get slower and slower leading to the kind of effect mentioned above(even without G changing).Is this effect taken care of in present theories?

Jagmeet Singh

Time dilation due to increased gravitaitonal fields is taken care of in the standard theory.

What might present an alternative intepretation of the observation of Hubble red shift is cosmologically increasing particle masses, the variable mass hypothesis, see Non-standard cosmology.

You will also find this interpretation in the Jordan frame of http://en.wikipedia.org/wiki/Self_creation_cosmology experiment.

Garth

 

[Tzemach]

Variable Mass Hypothesis has some merit when we consider the variations in alpha detected by Australian radio astronomers. There are other indications that something is not quite right with the standard model but this is a fairly strong indicator.

 

[gptejms]

Garth:What about my first question:-how do you rule out variations in G?

 

[Garth]

Garth:What about my first question:-how do you rule out variations in G?

G may vary - not in the standard model but in alternative gravitational theories such as the Brans Dicke theory.

But this in itself would not cause red shift, although it would affect the rate of the universe's expansion. Are you confusing gravitational red shift with cosmological red shift perhaps?

Garth

 

[gptejms]

Garth: No,I am not confusing gravitational red shift with cosmological red shift---read carefully the first para of my post no. 1 to understand my question.
One can say that the answer is CMB radiation,which can not be explained by anything other BB.Well,I am not against BB/expanding universe,but the red shift could be due to the expansion plus other reasons(like the changing value of G)--that would have a bearing on the age of the universe.

 

[Garth]

Garth: No,I am not confusing gravitational red shift with cosmological red shift---read carefully the first para of my post no. 1 to understand my question.
One can say that the answer is CMB radiation,which can not be explained by anything other BB.Well,I am not against BB/expanding universe,but the red shift could be due to the expansion plus other reasons(like the changing value of G)--that would have a bearing on the age of the universe.

Yes, I have read your OP, the confusion arises because varying G in itself would not cause atomic clocks to go slow, only gravitational ones such as a pendulum clock, which would actually go faster if G were larger in the past as your OP suggested.

Only a change in atomic constants, such as particle masses, would cause atomic clocks to 'go slow'.

I hope this helps,

Garth

 

[gptejms]

Yes, I have read your OP, the confusion arises because varying G in itself would not cause atomic clocks to go slow, only gravitational ones such as a pendulum clock, which would actually go faster if G were larger in the past as your OP suggested.

Garth

1.I am certainly not talking about Newton's law here.I think I need to repeat what I said in post 1.If clocks were slower in the past(compared to today),light emitted then(i.e. by a distant galaxy) would appear red shifted to us(Agreed?).

2.Now,clocks run slower in higher gravitational fields.One of the reasons why gravitational fields were higher in the past could be that the value of G was higher.My question is:-how do you rule out a changing G?

3.The other reason(for an expanding universe) would be that everything was nearer to everything else(!) in the past,so gravitational fields were higher.So now,in this case,there would be two sources of cosmological red shift---expansion plus changing clock rates.You told me that this effect(changing clock rates due to changing strength of gravitational field) is taken care of in GTR(Right?).

 

[Chronos]

An interesting idea, gptjems. Propose observational evidence that would validate, or falsify it. Try comparing it to this database: http://cdsweb.u-strasbg.fr/viz-bin/Cat?VII/248 . I've already plotted the date. It would be interesting to see how you fit the data to your scheme.

 

[Tzemach]

1.I am certainly not talking about Newton's law here.I think I need to repeat what I said in post 1.If clocks were slower in the past(compared to today),light emitted then(i.e. by a distant galaxy) would appear red shifted to us(Agreed?).

2.Now,clocks run slower in higher gravitational fields.One of the reasons why gravitational fields were higher in the past could be that the value of G was higher.My question is:-how do you rule out a changing G?

3.The other reason(for an expanding universe) would be that everything was nearer to everything else(!) in the past,so gravitational fields were higher.So now,in this case,there would be two sources of cosmological red shift---expansion plus changing clock rates.You told me that this effect(changing clock rates due to changing strength of gravitational field) is taken care of in GTR(Right?).

Have you read the book "The Time Illusion" by Dennis A Wright (ISBN 0-646-02803-0) Published in 1989? The claim in that book was that all time occurs in a single instant, time accelerates as the universe expands a new book is coming soon "Physics God and the End of the World" (ISBN 1-58112-923-8.) due for release (I believe) on 06/06/06.

Not really for the physics purist because of the amount of interconnectivity - science, religion, parapsychology you name it but some interesting concepts. I will look up some of the math and post it here.

 

[gptejms]

An interesting idea, gptjems. Propose observational evidence that would validate, or falsify it. Try comparing it to this database: http://cdsweb.u-strasbg.fr/viz-bin/Cat?VII/248 . I've already plotted the date. It would be interesting to see how you fit the data to your scheme.

I don't have enough time or background in cosmology or GTR to take this up in a serious way.Why don't you take up the problem since you've already plotted the data and know enough GTR to do the calculations--may be we can write a joint paper if you come up with something interesting!

 

[gptejms]

Have you read the book "The Time Illusion" by Dennis A Wright (ISBN 0-646-02803-0) Published in 1989? The claim in that book was that all time occurs in a single instant, time accelerates as the universe expands a new book is coming soon "Physics God and the End of the World" (ISBN 1-58112-923-8.) due for release (I believe) on 06/06/06.

Haven't read it.All time in a single instant---hope it's not crackpot stuff.

I will look up some of the math and post it here.

Please do.

 

[Garth]

1.I am certainly not talking about Newton's law here.I think I need to repeat what I said in post 1.If clocks were slower in the past(compared to today),light emitted then(i.e. by a distant galaxy) would appear red shifted to us(Agreed?).

2.Now,clocks run slower in higher gravitational fields.One of the reasons why gravitational fields were higher in the past could be that the value of G was higher.My question is:-how do you rule out a changing G?

3.The other reason(for an expanding universe) would be that everything was nearer to everything else(!) in the past,so gravitational fields were higher.So now,in this case,there would be two sources of cosmological red shift---expansion plus changing clock rates.You told me that this effect(changing clock rates due to changing strength of gravitational field) is taken care of in GTR(Right?).

[All time in an instant - perhaps Dennis A Wright is traveling at the speed of light! ]

When we talk about 'clocks being slower' we need to be very specific about about what we are talking about.

A clock measures time at 'one second per second' - time for that clock does not slow down or speed up.

Time dilation/acceleration only makes sense when we are talking about comparing one clock with another, that is, comparing the two clocks' measurements of the time interval between two separate events.

The comparison requires a signal has to pass between the two clocks, most often a light/radio signal; hence the way light propagates also affects whether we observe time speeding up or slowing down, or not.

On a space-time diagram draw the world-lines of the two clocks at different epochs and the null-geodesics of light signals between them. These null-geodesics diverge on the space-time diagram and time dilation is observed as red shift.

If particle masses remain constant then cosmological red shift is caused by this divergence of null-geodesics that itself is caused by space-time curvature - the gravitational field of the whole universe. This gravitational curvature is observed as red shift and interpreted as doppler shift of the expanding universe - but note you could interpret it as simply "clocks run slower in higher gravitational fields", actually they don't - they are observed to run slower and that is significantly different to your statement.

"Hubble red shift is caused by the universe expanding" and "clocks are observed to run slower in the higher gravitational fields of the earlier universe" are two equivalent descriptions of the same phenomenon.

You can formulate a theory in which the clocks are observed to run slower for different reasons, such as a change in the atomic constants that determine the frequency of a light emitted or absorbed, for example, but changes in G are affecting the curvature of space-time alone, not the internal workings of the atom.

If G is to vary in a particular theory then that theory requires a field equation and metric from which specific predictions of observables can be made for verification or falsification. The Brans Dicke theory is one such theory but in it both G varies and the also universe expands.

Garth

 

[gptejms]

Time dilation/acceleration only makes sense when we are talking about comparing one clock with another, that is, comparing the two clocks' measurements of the time interval between two separate events.

I had made it clear that clocks were moving slower then(compared to today)--so I don't see why you are objecting.

"Hubble red shift is caused by the universe expanding" and "clocks are observed to run slower in the higher gravitational fields of the earlier universe" are two equivalent descriptions of the same phenomenon.

Are you sure?Even if there were no gravitation between the bodies moving away from each other,there would still be red shift observed--so I don't see how the two are equivalent.

You can formulate a theory in which the clocks are observed to run slower for different reasons, such as a change in the atomic constants that determine the frequency of a light emitted or absorbed, for example, but changes in G are affecting the curvature of space-time alone, not the internal workings of the atom.

If clock rates(one second per 'my (present day) second') have to depend on what clock is used,then time itself loses meaning.Atomic clock rates would also be identical to other clock rates--figure out how.

 

[Garth]

I had made it clear that clocks were moving slower then(compared to today)--so I don't see why you are objecting.

I'm not objecting - just explaining carefully in stages.

Hubble red shift is caused by the universe expanding" and "clocks are observed to run slower in the higher gravitational fields of the earlier universe" are two equivalent descriptions of the same phenomenon

Are you sure?Even if there were no gravitation between the bodies moving away from each other,there would still be red shift observed--so I don't see how the two are equivalent.

They are equivalent in the cosmological case as they are observables deduced from the same R-W metric.

The galaxies/quasars are not moving through space - apart from small proper motions - it is space itself that is expanding with time taking the objects along with it.

If there were no gravitation as in your example any red shift observed would be a Doppler shift caused by their motion through space.

If clock rates(one second per 'my (present day) second') have to depend on what clock is used,then time itself loses meaning.Atomic clock rates would also be identical to other clock rates--figure out how.

Actually time is defined by the method used to measure it, we have atomic time (with Terrestial time & Geocentric Coordinate time subsets), ephemeris time, solar time and sidereal time. They are not all at the same 'rate', but so long as we know how one relates to another we have no problems.

One question is though: "Is there a clock drift between ephemeris and atomic time?" The standard answer is no; however, such a clock drift would be an explanation for the Pioneer Anomaly.

Garth

 

[ratfink]

I was reading one of John Gribbin's (popular science)books a few days back when I thought if there could be alternative explanation(s) for the Hubble's law.One simple explanation could be that the value of G(universal gravitational constant) could be changing with time--if G were higher in the past(i.e. G increasing as we go into the past),clocks would be moving slower then(than today).Now since clocks are moving faster,light from distant galaxies would appear red-shifted to us---red-shift would be more for more distant galaxies because they are more into the past when G was still higher.My question is:-how is this explanation ruled out by cosmologists before jumping to the expansion model?

Another observation:-(say) G does not change with time.As we go back into the past,things become nearer and nearer--so gravitational fields become higher and higher i.e. clocks get slower and slower leading to the kind of effect mentioned above(even without G changing).So the redshift is now due to two reasons--expansion and 'change of clock rate'.Is the latter effect taken care of in present theories?

Jagmeet Singh

I think it is an excellent idea gptejms - and certainly more plausible than the common view. Didn't Arp propose something along these lines but with physical constants changing with time? After all we have only been measuring G, h, etc for a short time and have no way of telling if they are time dependent or not.
Just a thought; Hubble's law is a linear law, when you say:

As we go back into the past,things become nearer and nearer--so gravitational fields become higher and higher

I haven't really thought it through but wouldn't the density increase as the cube of the radius whilst redshift only varies as the first power?
Ratfink.

 

[Garth]

I haven't really thought it through but wouldn't the density increase as the cube of the radius whilst redshift only varies as the first power?
Ratfink.

Nearly correct - actually inversely proportional to the radius cubed etc.

As we go back in time we reach the radiation dominated age when the density of the radiation is greater than that of, and dominates, the matter in the universe and then all the way back to the intense gravitational fields of the Inflation and Planck epochs.

Garth

 

[ratfink]

Nearly correct - actually inversely proportional to the radius cubed etc.

As we go back in time we reach the radiation dominated age when the density of the radiation is greater than that of, and dominates, the matter in the universe and then all the way back to the intense gravitational fields of the Inflation and Planck epochs.

Garth

Probably true, but aren't we mixng models here?
If our original poster (sorry but if i go back to look, i will lose this) if time dependent gravity etc is responsible for redshift then

radiation dominated age when the density of the radiation is greater than that of, and dominates, the matter in the universe and then all the way back to the intense gravitational fields of the Inflation and Planck epochs

all this is a fairy tale and not relevant.
Lets keep on thread and look at time dependent G, h etc being responsible for Hubble's law.
Ratfink

 

[ratfink]

sorry, got this new keyboard and the 'i' key doesn't work too well - bit like misery in Stevens Kings novel!

 

[Garth]

Probably true, but aren't we mixng models here?
If our original poster (sorry but if i go back to look, i will lose this) if time dependent gravity etc is responsible for redshift then

all this is a fairy tale and not relevant.
Lets keep on thread and look at time dependent G, h etc being responsible for Hubble's law.
Ratfink

Well, I was using the standard model to base my argument on.

The relative abundances of the elements and the CMB itself are strong evidences that the universe went through a hot high density phase when everything was tightly compressed in a small volume, it is not a fairy tale. Any alternative theory would have to take these observations into account, I don't think Arp's theory is able to.

If you do propose varying 'constants' in a theory you have to think through the consequences of their variation and often end up with the same total effect.

For example: Fred Hoyle proposed a mass variation theory to explain the CMB in a steady state type universe. ('On the origin of the microwave background', F. Hoyle 1975 ApJ.)

As you went back in time in this theory particle masses decreased until you approached an interface where masses were zero, beyond which they were negative. There was no expansion or contraction, space was static, and this boundary, or interface, was supposed to be that which we incorrectly identify with the BB singularity. The CMB was simply the light from galaxies beyond this interface.

This proposal wanted to avoid the singularity of the BB, however if masses decreased then atomic sizes would increase until at the actual boundary itself they would become infinite.

A BB singularity of finite sized atoms squashed into zero volume was replaced by a universe of infinite sized atoms squashed into a finite size volume.

Either way the material in the universe would be equally squashed! It depended on how you looked at it and what ruler you used.

Certainly if physical constants varied over cosmological time then that would completely turn our understanding upside down. Any such variation would have a knock on effect that would make predictable and falsifiable differences to the universe we observe. To find such a theory that is concordant with observation is the trick - my own offering is http://en.wikipedia.org/wiki/Self_creation_cosmology .

Garth

 

[gptejms]

They are equivalent in the cosmological case as they are observables deduced from the same R-W metric.

You may be right.But tell me:-in the limit of a flat metric,is there no red shift predicted by GTR?

 

[Tzemach]

This thread has some interesting concepts and I must apologise that I haven't turned up the math on Dennis A Wright's Accelerating Time theory but I have a couple of items from the summary.

a) the universe is expanding,
b) it is entropy which generates the concept of time,
c) the universe is becoming less dense therefore its overall gravity must be decreasing
d) Time must accelerate under these conditions.
e) The universe will appear to expand at an accelerating rate as our units of time measurement decrease.

 

[gptejms]

Tzemach:The last point looks good--does it do away with the cosmological term or the dark energy?

 

[Garth]

d) Time must accelerate under these conditions.
e) The universe will appear to expand at an accelerating rate as our units of time measurement decrease.

How do you measure the 'acceleration' of time? Which two clocks are you comparing to detect the acceleration of one clock relative to the other?

(Note: I am not objecting to the idea, it is part of my own SCC model, however that statement d) does not make sense on its own - you need to specify how you measure it.)

Garth

 

[Garth]

You may be right.But tell me:-in the limit of a flat metric,is there no red shift predicted by GTR?

The question is not whether space is flat or not but whether space expands with time or not.

In GR empty space is not flat but hyperbolic - the Milne universe, while flat space contains matter at the critical density.

Both flat space and empty space expand and so distant test particles would exhibit red shift to any observer.

The expansion of flat space in GR is R(t) ~ t^(2/3)

and in empty space R(t) ~ t.

(Note my and does not work. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f641.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":frown:" title="Frown :frown:" data-smilie="3"data-shortname=":frown:" />)<br /> <br /> Garth

 

[ratfink]

This thread has some interesting concepts and I must apologise that I haven't turned up the math on Dennis A Wright's Accelerating Time theory but I have a couple of items from the summary.

a) the universe is expanding,
b) it is entropy which generates the concept of time,
c) the universe is becoming less dense therefore its overall gravity must be decreasing
d) Time must accelerate under these conditions.
e) The universe will appear to expand at an accelerating rate as our units of time measurement decrease.

I am not well up on entropy but I thought that thngs went from being ordered to disordered and that ths jumbling marked the 'arrow of tme'.
In the universe we are going from a bg bang with things whizzng everywhere to ordered Planets, stars, Galaxies.
So, snce the universe is going from disorder to order, does that mean that time is going backwards n the expanding unverse?
Ratfink
P.S Thanks for your earlier post Garth, ddn't know about Hoyle and the CMB.

 

[gptejms]

Garth:I don't see this satisfactorily answered:-'According to your reasoning,'cosmological red shift caused by expanding universe' and 'the same caused by diminishing overall gravitational fields(resulting in clocks becoming faster)' are equivalent statements.If that is the case, then for the hypothetical case where there is no gravitation between the expanding bodies,the two statements should be equivalent.But that is not the case---if there is no graviation then clocks getting faster or slower is meaningless.' What do you have to say to this?
I think I have the answer,but let me hear from you.

Regarding your statement that atomic clocks would be unaffected by the changing gravitational field,I disagree.

 

[gptejms]

Ratfink:Regarding your question addressed to Tzemach:Things can organize,get ordered on a small scale,but on the whole entropy always increases(2nd law).

 

[Garth]

Garth:I don't see this satisfactorily answered:-'According to your reasoning,'cosmological red shift caused by expanding universe' and 'the same caused by diminishing overall gravitational fields(resulting in clocks becoming faster)' are equivalent statements.If that is the case, then for the hypothetical case where there is no gravitation between the expanding bodies,the two statements should be equivalent.But that is not the case---if there is no graviation then clocks getting faster or slower is meaningless.' What do you have to say to this?
I think I have the answer,but let me hear from you.

It is the average gravitational field of the whole (homogeneous and isotropic) universe that causes the expansion of space.

This was the surprising prediction of Einstein's GR field equation (without a cosmological constant) that Einstein himself did not believe until cosmological red shift was discovered by Hubble a decade later.

Note that by gravitational field I mean the curvature of space-time, not gravitational force. Gravitational force between objects within the universe cause that expansion to decelerate. A positive cosmological constant would cause that expansion to accelerate, which is why there is so much interest in it today.

One particular example of this was the empty universe, \rho = 0, with no consmological constant, which is predicted to expand linearly. As there are no gravitational forces there is no deceleration.

Regarding your statement that atomic clocks would be unaffected by the changing gravitational field,I disagree.

I think there may be a common misconception here that I have tried to address above. Let me take it in stages.

First, in SR acceleration on its own does not cause time dilation, i.e. "clocks to run slowly", it is the relative velocity between a clock and an observer of that clock that results in the clock being observed to run slowly. Of course over time acceleration will increase that relative velocity but it is the relative velocity not the acceleration that causes time dilation.

Secondly, in GR as well acceleration does not cause time dilation. By the equivalence principle this means that gravitational fields do not in themselves cause time dilation.

It is untrue, or at least misleading, to say that 'clocks run slow in a gravitational field', one clock has to be compared to another to make any detection at all of time dilation.

The clock at the bottom of a gravitational well is observed to run slowly when its signals, transmitted by light or radio, are compared to a clock at the top of that gravitational well. Those signals diverge as they travel across the space-time curvature that is that gravitational field, and are received at longer intervals apart than when transmitted. This is the observed time dilation.

So it is for cosmological time dilation. The null-geodesics of light rays diverge across curved space-time. So as they leave the intense gravitational field of the early universe they are observed red shifted in the weaker gravitational field of the later universe.

In the standard GR theory atomic masses are constant, the frequency of emission is thereby defined to be the same as that of the process in the apparatus absorbing the photon. Therefore, this red shift is interpeted as doppler red shift, the galaxies 'are rushing away from us'. This is consistent with space expansion.

Garth

 

[gptejms]

One particular example of this was the empty universe, \rho = 0, with no consmological constant, which is predicted to expand linearly. As there are no gravitational forces there is no deceleration.

I remember having read that this is de-Sitter's universe(Gribbin's book)--right?You mean there is an average gravitational field(causing the expansion of space),but no gravitational force.What's the source of the gravitational field i.e. T_{\mu\nu} here?

Coming to the explanation,I thought, for red shift for non-gravitating bodies moving away from each other(an explanation which would not contradict your stand that 'red shift caused by changing clock rates due to changing gravitational field' and 'red shift caused by expansion' are equivalent statements):-
for a body(non-gravitating) to move away from another body with a constant velocity(say),it has to accelerate for some time to achieve that constant velocity.During this period of acceleration,it's as if that two gravitating bodies are moving away from one another---this is where the red shift occurs.So your stand that the two statements(above) are equivalent holds even for this case!

In the standard GR theory atomic masses are constant, the frequency of emission is thereby defined to be the same as that of the process in the apparatus absorbing the photon. Therefore, this red shift is interpeted as doppler red shift, the galaxies 'are rushing away from us'. This is consistent with space expansion.

I think there's nothing like a pure Doppler red shift in GTR(I may be wrong)--you've to trace it back to the acceleration phase(s).

 

[Garth]

One particular example of this was the empty universe, , with no consmological constant, which is predicted to expand linearly. As there are no gravitational forces there is no deceleration.

I remember having read that this is de-Sitter's universe(Gribbin's book)--right?You mean there is an average gravitational field(causing the expansion of space),but no gravitational force.What's the source of the gravitational field i.e. T_{\mu\nu} here?

No, as I said this is the Milne universe, the de-Sitter universe is one with exponential expansion caused by a cosmological constant, or in the Steady State model by an extra 'creation' field. There is no source in the empty Milne universe T_{\mu\nu} = 0, the fact that it expands maybe surprising but it is a prediction of the standard (no cosmological constant) GR field equation.

I think there's nothing like a pure Doppler red shift in GTR(I may be wrong)--you've to trace it back to the acceleration phase(s).

Acceleration itself does not produce time dilation or red shift, only the relative velocity eventually produced by it.

I hope this helps,

Garth

 

[gptejms]

Garth:You haven't commented on my explanation for the two statements being equivalent in the case of non-gravitating bodies moving away from one another.

 

[gptejms]

Acceleration itself does not produce time dilation or red shift, only the relative velocity eventually produced by it.

The reason why I said this was to make the two statements('red shift caused by expansion' & 'red shift caused by changing clock rates due to changing gravitational field') equivalent for the case of non gravitating bodies moving away from one another.I do not see how to make the two statements equivalent otherwise--can you?

Besides,I think 'considering relative velocity to be the primary source of time dilation/red shift' or 'considering the acceleration phase required to get to the constant relative velocity as the primary source' is a matter of choice,of how you look at it----the two statements are equivalent!

 

[Garth]

Garth:You haven't commented on my explanation for the two statements being equivalent in the case of non-gravitating bodies moving away from one another.

I am talking about cosmology, i.e. GR, if you are talking about the empty (zero density) cosmological model than I have commented on it - it expands and mutual red shift would be observed by 'test' (no mass) observers within it. Read up some GR cosmology textbooks, or perhaps here.

Garth

 

[Chronos]

Ouch. Observational evidence suggests the universe includes gravitating matter. Empty universe models are intriguing, but to put it delicately: unphysical.

 

[gptejms]

Garth,Chronos:
I don't think you(Garth) are reading my posts carefully.I asked for your comments on 'my explanation' for the equivalence of the two statements for non-gravitating bodies moving away from one another--you repeat your own explanation!
Anyway,continuing from my post no. 33,I now switch on the gravitation between the bodies moving away from one another.Before gravitation is switched on,the 'two statements' are equivalent in the manner pointed out in post 33.Once gravitation is switched on,there is an additional source of red shift due to changing clock rates(due to diminishing(over time) gravitation).Now are the two statements equivalent?Unless the relative velocity changes(by switching on gravitation)I don't see the two statements to be equivalent.Does the relative velocity change..it should.

So Garth,you could be right that the two statements are equivalent,though I am not 100 per cent sure!What do you have to say,Chronos?

 

[Garth]

I don't have enough time or background in cosmology or GTR to take this up in a serious way.

I am talking about cosmology, i.e. GR, if you are talking about the empty (zero density) cosmological model than I have commented on it - it expands and mutual red shift would be observed by 'test' (no mass) observers within it. Read up some GR cosmology textbooks, or perhaps here.

Ouch. Observational evidence suggests the universe includes gravitating matter. Empty universe models are intriguing, but to put it delicately: unphysical.

I did not intend to be rude but in light of that first quote of gptejms I wanted to set this discussion on the basis of recognised physics and not speculation.

In order to seriously make other hypotheses you do need "to have enough time or background in cosmology or GTR to take this up in a serious way".

Chronos , of course I agree that the universe is not empty, however the Milne model is a recognised cosmological model of the limit of a universe that asymptotically tends to zero density.

In the discussion about non-gravitating observers in an expanding universe the Milne model is the correct one to use, or otherwise, if there is no space-time curvature the discussion is one of SR in which mutally receding observers just observe (relativistic) doppler red shift.

I have located the detail for Dennis A Wright, he has a website where he has some of the math posted, obviously not everything because he wants you to buy the books. It’s not what normally attracts serious science but has some interesting concepts, he took up the study of physics because he is clairvoyant and wanted to understand how time functions. (Don’t we all?)

If this is turning into a discussion of clairvoyance I am out of here...

Garth

 

[Tzemach]

How do you measure the 'acceleration' of time? Which two clocks are you comparing to detect the acceleration of one clock relative to the other?

(Note: I am not objecting to the idea, it is part of my own SCC model, however that statement d) does not make sense on its own - you need to specify how you measure it.)

Garth

Each unit of time is T-t_p or 10^-43 smaller than the unit that preceeded it. So instead of comparing clocks we are examining the behaviour of a single clock.

 

[Garth]

Each unit of time is T-t_p or 10^-43 smaller than the unit that preceeded it. So instead of comparing clocks we are examining the behaviour of a single clock.

How do you propose to do that?
How is the comparison made experimentally of a clock and itself at a later time?

Garth

 

[gptejms]

In order to seriously make other hypotheses you do need "to have enough time or background in cosmology or GTR to take this up in a serious way".

Yours is a valid objection.In fact,I did read about 60% of Dirac's thin book on GR a few years back,though I don't remember all the details--may be I need to re-read it to refresh my knowledge.GR is not my main field, so I read just enough to get a fair idea of the field.

In the discussion about non-gravitating observers in an expanding universe the Milne model is the correct one to use, or otherwise, if there is no space-time curvature the discussion is one of SR in which mutally receding observers just observe (relativistic) doppler red shift.

Milne model must be the correct one to use for non-gravitating observers--even in this model I presume the 'two statements'('red shift caused by expansion'&. 'red shift caused by changing gravitational field') are equivalent--right?

 

[Garth]

Milne model must be the correct one to use for non-gravitating observers--even in this model I presume the 'two statements'('red shift caused by expansion'&. 'red shift caused by changing gravitational field') are equivalent--right?

Yes, and the statements "cosmological red shift is caused by a) the expansion of space, and b) an evolving cosmological (i.e. not local) gravitational field, are equivalent in GR with massive objects and observers.

The questions are:
Precisely what are you measuring?
How is the measurement made?
What standard units of length, time and mass are you comparing them with? and
How is that comparison made over cosmological space and time?

I hope this helps

Garth

 

[gptejms]

Garth:It will be nice if you can do a calculation and show that the two statements are equivalent(for Milne metric or any other metric).

 

[Garth]

Garth:It will be nice if you can do a calculation and show that the two statements are equivalent(for Milne metric or any other metric).

I'll try, my tex/itex get screwed up for some reason since the new server.

The Robertson Walker metric for a homogeneous and isotropic universe is:

d\tau ^2 = dt^2-\frac{R(t)^2}{c^2 }[dr^2+\bar{r}^2 d\Omega^2]

where
d\Omega^2 = d\theta^2+\sin^2\theta d\phi^2

and R(t) is the scale factor describing the expansion of the universe. This is derived from the Field Equation of the gravitational theory (normally GR).

\bar{r} =\begin{cases}<br /> R_C \sinh(r/R_C), &amp;\mbox{for negative curvature}<br /> \\ r, &amp;\mbox{for zero curvature}<br /> \\R_C \sin(r/R_C), &amp;\mbox{for positive curvature}<br /> \end{cases}

[EDIT: here my tex and itex get screwed up again ( - help?), I hope you can understand the following.]

R_C the absolute value of the radius of curvature

r gives the comoving distance from the observer and

\bar{r} gives the proper distance distance.

The cosmological time dilation is given by
dtau/dt and the red shift of an object at time t_1 observed at time t_0 is given by

1 + z = R(t_0)/R(t_1)

now, given a fixed k and R_C, R(t) describes both the 'expansion of the universe' and the 'evolving cosmological gravitational field', they are one and the same.

Garth

 

[Tzemach]

How do you propose to do that?
How is the comparison made experimentally of a clock and itself at a later time?

Garth

If I remember from the first book there was a thought experiment which looked at a hypotheical spaceship which could exceed the speed of light (suspend your relativistic paradigms for a moment) in this spaceship one could not tell whether you were moving in space or time. It made sense but I will have to find and reread it for the full explanation.

I want to wait for the next book to come out because his website says that dark matter, dark energy and the Pioneer Anomaly are all proof that the theory is correct and time accelerates. He also says that gravity is due to the inertia or reluctance of mass to accelerate in time, which is why mass distorts time. (Time moves more slowly in a gravitational Field).

 

[Garth]

If I remember from the first book there was a thought experiment which looked at a hypotheical spaceship which could exceed the speed of light (suspend your relativistic paradigms for a moment) in this spaceship one could not tell whether you were moving in space or time. It made sense but I will have to find and reread it for the full explanation.

I want to wait for the next book to come out because his website says that dark matter, dark energy and the Pioneer Anomaly are all proof that the theory is correct and time accelerates. He also says that gravity is due to the inertia or reluctance of mass to accelerate in time, which is why mass distorts time. (Time moves more slowly in a gravitational Field).

First, here, let us discuss recognised and published physics. Private theories have to pass the criteria and be published in the IR Forum.

You can certainly ask questions, such as: "Does time move more slowly in a gravitational field?" but you then have to respect the answer if given in a clear and logical way.

I'm not against the concept of red shift being an artifact of "time acceleration", indeed it is a feature of my own, published, theory. However you do have to be clear about what you are saying; to detect time acceleration you have to compare one clock with another one and define everything consistently.

All we can do here on Earth is compare our observations of the distant universe with clocks, rulers and standard masses here in the laboratory. One such anomaly that might be indictating the standard understanding requires modification is indeed the Pioneer Anomaly and there has been much discussion on the subject in these Forums.

Garth

 

[Tzemach]

I'm not against the concept of red shift being an artifact of "time acceleration", indeed it is a feature of my own, published, theory.
Garth

This is something I am interested in following further, is there a link to your published theory somewhere? I apologise for being a little too enthusiastic and not observing the protocols properly but I was just a little keen to go further as there seemed to be several people thinking along the same lines.

 

[Garth]

This is something I am interested in following further, is there a link to your published theory somewhere? I apologise for being a little too enthusiastic and not observing the protocols properly but I was just a little keen to go further as there seemed to be several people thinking along the same lines.

The theory is called Self Creation Cosmology, which can be found in a Wikipedia http://en.wikipedia.org/wiki/Self_creation_cosmology .

If you want to discuss the theory please do so there, I don't want it to 'hog' other threads.

[Note: I see the links etc. are all screwed up as well so please find the links to my papers from the bottom of that Wikipedia article if you want to.]
Garth

 

[gptejms]

The cosmological time dilation is given by
dtau/dt and the red shift of an object at time t_1 observed at time t_0 is given by

1 + z = R(t_0)/R(t_1) ...(1)

now, given a fixed k and R_C, R(t) describes both the 'expansion of the universe' and the 'evolving cosmological gravitational field', they are one and the same.

1.R(t) describes 'expansion of the universe',the wavelength gets stretched when the scalefactor expands--this is clear to me.

2.What's not quite clear is the statement:-R(t) describes 'evolving cosmological gravitational field'.First, how do you define cosmological gravitational field?Second,how do you relate it to the scale factor?Why should a gravitational field 'cosmological' or otherwise lead to expansion?
(physical understanding is what I'm looking for)

3. I ask a stupid question here:-I understand your relation(1) (for the red shift)in the spirit of my point 1 above.But you seem to be relating it to the cosmological time dilation dtau/dt...which can be calculated from the RW metric.Is this what you are doing?

 

[gptejms]

He also says that gravity is due to the inertia or reluctance of mass to accelerate in time, which is why mass distorts time. (Time moves more slowly in a gravitational Field).

This seems like circular logic to me.Reluctance of mass to accelerate in time(where acceleration in time is caused by changing gravitational field)...which is why time moves more slowly in a gravitational field(i.e. mass distorts time).

 

[Garth]

1.R(t) describes 'expansion of the universe',the wavelength gets stretched when the scalefactor expands--this is clear to me.

2.What's not quite clear is the statement:-R(t) describes 'evolving cosmological gravitational field'.First, how do you define cosmological gravitational field?Second,how do you relate it to the scale factor?Why should a gravitational field 'cosmological' or otherwise lead to expansion?
(physical understanding is what I'm looking for)

3. I ask a stupid question here:-I understand your relation(1) (for the red shift)in the spirit of my point 1 above.But you seem to be relating it to the cosmological time dilation dtau/dt...which can be calculated from the RW metric.Is this what you are doing?

Consider co-moving galaxies, i.e. those that are carried along with the expansion of space and have no proper motions.

R(t) is the only thing that is evolving with time in the R-W metric.
We are used to the idea that in the Schwarzschild solution, with local static gravitational fields, the field changes with r and not t, in the cosmological solution it changes with t and not r.

It is the average gravitational field of the whole universe that we are talking about. Remember in the cosmological solution we are dealing with a homogeneous density smoothed out over space.

If the expression "evolving cosmological gravitational field" means anything, which is my way of translating your expression in the OP: "As we go back into the past, things become nearer and nearer--so gravitational fields become higher and higher", then it also refers to
R(t).

Garth