What Is the Expansion Limit of Our Universe?

[.ultimate]

I have been sucessful in calculating the limit of expansion of universe.

Conclusion - Universe has expanded to its maximum

Here is my research




Expansion Limit[/size]


According to Hubble's law
v=H_0r

Where r is distance of Galaxies with respect to Center of Galaxy

As v approaches speed of light c

i.e v\to c

r=c/{H_0}

r \approx10^26 m

Where d = 2 * 10^{26} m is Layman Universe Expansion Limit







Observed Time to Reach Expansion limit[/size]

T = r/{H_0.r} \approx 14 billion years









Actual time of Existence of Universe[/size]

T_0 = \frac 1 {H_0. \sqrt{1 - v^2/c^2}} = \infty

 

[marcus]

I have been sucessful in calculating the limit of expansion of universe.

you have succeeded in calculating an important distance in cosmology---which astronomers call the "Hubble radius" and which is not the limit of expansion.
sometimes people mistakenly say it is the present size of the observable universe but it is not that either.

Conclusion - Universe has expanded to its maximum

you have drawn a false conclusion. The observed universe extends beyond the Hubble radius. However you have done a good calculation and found that the Hubble radius is approx 14 billion LY (a useful distance to know even if not the limit of expansion)

According to Hubble's law
v=H_0r

Where r is distance of Galaxies with respect to Center of Galaxy

As v approaches speed of light c

i.e v\to c

r=c/{H_0}

What you have found here is the usual formula for the Hubble radius. Congratulations for finding it.
However typical spatial expansion speeds far exceed c---they are not governed by the speed limit of 1905 special relativity.

T = r/{H_0.r} \approx 14 billion years

You have discovered the usual formula for the so-called "Hubble time" and you have correctly calculated it to be approx 14 billion years.There was a good article in the Scientific American about spatial expansion and the confusions people have about it. It was by Charles Lineweaver and Tamara Davis. Free online. Very clear illustrations. You might like it. I will see if I can get a link.

 

[Maxwells Demon]

the 14 billion years you've found is just the age of the universe right? I've just done this in astronomy class and found it to be 13,8 billion years

 

[Maxwells Demon]

I calculated H0 and then used t = 1/H0 for the age..

 

[marcus]

I calculated H0 and then used t = 1/H0 for the age..

that is not the usual estimated age of the universe

it is CLOSE to what astronomers usually estimate

but it is not equal and it is not how they calculate the age or time since beginning of expansion

 

[Maxwells Demon]

okay, this isn't professional so I knew it wasn't very precise.. Our teacher told us so as well :)

 

[fasterthanjoao]

It's actually a rather difficult exercise to calculate an expression for the age of the Universe. I've worked through calculations umpteen pages long starting with the Friedmann equation. In fact, it's worth noting that almost always it's not possible to obtain an exact expression as often the inevitable integration has no algebraic solution.

(Maxwells- when you cover the Friedmann equation in astronomy, let us know! The above I describe is a very good exercise for covering a good amount in FRW cosmology. (I should think it's also within middle undergraduate level, with a bit of hard work )

 

[.ultimate]

If H_0 is a constant,

then T=1/H_0 i.e Age of the Universe is a constant, and WOULD be a constant in all context.

What I wanted to express was that, according to Relativity, Speed of a particle cannot be greater than speed of light, So the recession of Galaxies will gradually slow down (As S=D/T), when they approach speed of light according to the equation T = T_0 . \sqrt{1 - v^2/c^2}}. And the Universe will stop expanding as it is constant

 

[Wallace]

What I wanted to express was that, according to Relativity, Speed of a particle cannot be greater than speed of light, So the recession of Galaxies will gradually slow down (As S=D/T), when they approach speed of light according to the equation T = T_0 . \sqrt{1 - v^2/c^2}}. And the Universe will stop expanding as it is constant

This is a common misconception. There is no limit in general relativity as to the rate of increase between the proper distance of two objects with respect to proper time. None. Nada.

How can this be the case when we all know that the constancy of the speed of light is so fundamental to Relativity

In special relativity only my first statement is false, i.e. in this case the derivate of the proper distance between any two points with respect to proper time is always less than c. In general relativity however this is not the case. The cut a long story short this is because in special relativity a single Minkowski frame can be created that encompasses the entire universe and all motions can be seen with respect to that frame.

However in a general relativistic universe the presence of the energy within the universe, and particularly the change in that energy ( for instance the reduction in the mean density of matter in the universe at the universe expands ) means that that there is no global Minkowski frame that is common to all parts of the universe at all times. Therefore there is no one frame that all velocities are measured with respect to.

Now this is a very hand waving explanation and only says that proper distance separations can increase at a faster rate than c but dosn't prove that they do. A good reference that is often pointed to on this is "www.mso.anu.edu.au/~charley/papers/DavisLineweaver04.pdf"[/URL] by Davis & Lineweaver. This gives a much fuller and more comprehensive explanation.

In any case, the above is just words used to try and explain how this works. The ultimate proof is that if you solve the general relativistic equations you can easily see these apparently prohibited speeds come out quite naturally. So unless general relativity is wrong you argument does not work.

 

[marcus]

Wallace, I concur completely of course.
As a side comment: sometimes we get posters in this forum who invoke the MILNE UNIVERSE picture as if it were a realistic alternative that could fit the observed data.

I never know how to reply. I think the Lineweaver and Davis dispose of the Milne picture, but it would be nice if there were some quick way to explain that the Milne picture obviously doesn't fit what we see---without going to the length they do.

(AFAIK in that picture there is one Minkowski frame and instead of geometric expansion you have matter actually flying apart. It is a vintage 1930s thing, I believe.)

If someone brings up Milne as if it were a serious possibility, could one say something like the following?

Out past z=1.6 things look larger the farther away they are (i.e. as z increases). In Milne case they would look smaller. So Milne picture is in direct contradiction to what we observe.

or is there some problem with this refutation.

 

[Garth]

Out past z=1.6 things look larger the farther away they are (i.e. as z increases).

Marcus, do you have a reference for that statement?

You are talking about standard rulers are you not?

Garth

 

[Maxwells Demon]

all right, I stepped off :(

 

[marcus]

Marcus, do you have a reference for that statement?

You are talking about standard rulers are you not?

Garth

we've had threads about this before
there was that paper by Hellaby I cited earlier
and "angular size distance" is written up in Wiki

the point about angular size distance is that it has a MAXIMUM

I think this information is widely dispersed.

But if I had to cite one reference it would be Ned Wright's cosmology calculator. z = 1.6 is where the max ang. size dist. comes.
Or somewhere around there to be determined more precisely by future observations as per Hellaby.

I'd prefer not to argue about authorities and so forth. Let's see what Wallace says. My question was to him "can one say something like the following...or is there some problem with [that way of refuting Milne picture]?"

 

[Garth]

Okay, I was well aware of the theoretical maximum in angular diameter distance, I wondered whether there was observational evidence (such as the angular diameter of quasar radio lobes) to confirm the existence of such a maximum, to determine at what red shift it occurred and that therefore could be used to falsify the Mine model.

Garth

 

[Wallace]

The simplest way to falsify the Milne model would be to ask how it explains the observed acceleration of the expansion?

To take this a step back, if one is skeptical about whether the Universe is truly accelerating given the data we have (which I think is unlikely but is none the less a healthy attitude) you can still ask how the Milne model could possibly explain the supernovae data.

 

[MeJennifer]

The simplest way to falsify the Milne model would be to ask how it explains the observed acceleration of the expansion?

Well sorry for being perhaps a bit too simple here and without making any particular claim that the Milne model is in any way valid, how difficult is it to imagine an expansion that is decreasingly limited by curvature, as a form of accelerated expansion?

 

[Wallace]

I'm not sure about how difficult that might be to imagine, however remember that the Milne model describes test particles moving in a global Minkowski frame so there is no curvature. There is no influence on the expansion rate from anything, be it curvature or otherwise.

The Milne model is a very specific and entirely based on kinematic special relativity so any deviation from constant expansion rate cannot be accounted for within that model.

Taking you suggestion on its own, outside of the context of the Milne model, I'm not sure what you mean by "an expansion that is decreasingly limited by curvature, as a form of accelerated expansion?". Could you clarify this?

 

[MeJennifer]

I'm not sure about how difficult that might be to imagine, however remember that the Milne model describes test particles moving in a global Minkowski frame so there is no curvature. There is no influence on the expansion rate from anything, be it curvature or otherwise.

The Milne model is a very specific and entirely based on kinematic special relativity so any deviation from constant expansion rate cannot be accounted for within that model.

Obviously, but nothing prevents us to start from the Milne model and then consider the gravitational impact on it, right?

Taking you suggestion on its own, outside of the context of the Milne model, I'm not sure what you mean by "an expansion that is decreasingly limited by curvature, as a form of accelerated expansion?". Could you clarify this?

Start with a Milne model and observe the expansion of its boundary.
Now add mass-energy to this model.

Then there are three conditions that are interesting:

A. Gravitational convergence slows down the expansion of the boundary but is insufficient to stop it.
B. Gravitational convergence compensates for the expansion of the boundary.
C. Gravitational convergence causes the boundary to contract (a trapped surface condition).

In case of A, the mass-energy density decreases over time and thus the convergence will decrease as well, so the expansion of the boundary accelerates over time.
So this means that, in the limit, A, will approach the pure Mile model.

But feel free to explain where I make an error.

 

[Wallace]

There's still something I'm not quite getting here. Starting with the Milne model and then adding gravity gets you to either a flat, open or closed matter only universe depending on how much mass you put in, i.e. standard non Lambda models. Adding vacuum energy gets you to the LCDM model. I'm not sure how you get anything else from the Milne model, which is just an empty universe with test particles. I'm not sure in what way you are suggesting a Milne model + gravity is any different from a regular FRW model, if indeed that is what you are suggesting?

The other thing I'm not sure about is the speculation of what happens at the 'boundary'? The Milne model describes an infinite universe does it not, so what is the boundary?

 

[MeJennifer]

The Milne model describes an infinite universe does it not, so what is the boundary?

The boundary is simply the surface of the future null cone of the Milne model.

The volumes of all hypersurfaces of constant proper time are obviously infinite.
But is the hypervolume infinite? Did anyone take a crack at that one?

But anyway, the infinity of all hypersurfaces of constant proper time does not preclude space-time from having a boundary or from being closed, as is the case in C.

 

[Wallace]

The boundary is simply the surface of the future null cone of the Milne model.

But who's null cone? If the future light cone of an observer converges then the Universe is closed, which requires the presence of matter (or some kind of w > -1/3 energy at least) to close it. Again I do not comprehend how this is related to the Milne model or some extension of it?

 

[marcus]

The simplest way to falsify the Milne model would be to ask how it explains the observed acceleration of the expansion?
...

Wallace it's really great having you here! I admire your patience and obvious expertise.

What I have found though is if you get a highly verbal and opinionated person who has an idée fixe about the Milne model then it is very difficult to dislodge.

To ordinary clue-ful people who know some GR it is obvious that Milne is a pathetically bad match to nature---it's just obvious. Open and shut prima facie case!

But in a special case where it has become a kind of Cause you may need a sledge-hammer.

so I am asking about the argument where you use the angular size minimum which is in principle OBSERVABLE.

Hellaby says the next generation of instruments are going to be able to pinpoint the minimum with some useful level of accuracy. I expect it will come around z = 1.6.
The idea that everything out beyond z = 1.6 looks bigger and bigger the farther away it is---this idea seems sufficiently graphic that it might make an impression even on a very obstinate person.

Am I missing something. Any comments on this approach to explaining why Milne is bad?

 

[Wallace]

Hellaby says the next generation of instruments are going to be able to pinpoint the minimum with some useful level of accuracy. I expect it will come around z = 1.6.
The idea that everything out beyond z = 1.6 looks bigger and bigger the farther away it is---this idea seems sufficiently graphic that it might make an impression even on a very obstinate person.

I'm not familiar with this kind of test, do you have a useful reference for this? Off the top of my head I would think the biggest problem with this would be finding standard sized objects. If galaxies had the same average size for all cosmic time then this would be easy, but since galaxies evolve, merge and grow in ways we do not fully understand then our measurement of their angular size would be mixed up with our uncertainty over how big in physical size we expect them to be.

On the other hand we would expect galaxies to only get bigger (in physical size) as times goes on, even if the rate at which they do this is unknown. So I guess the presence of the angular size peek should be visible even if galaxy evolution is not completely understood? Considering we have seen galaxies out to z~8-10 via the HUDF surely someone has made a rough measure of this? I havn't thought about this or read anything along these lines before though, so as I say if you have a reference for it I would be interested in reading it!

 

[hellfire]

I'm not familiar with this kind of test, do you have a useful reference for this? Off the top of my head I would think the biggest problem with this would be finding standard sized objects.

From Edmund Bertschinger's tutorial http://ocw.mit.edu/NR/rdonlyres/Physics/8-942Fall2001/2F658E61-68A8-40F4-9168-B7AD0E23CA49/0/cosmog.pdf :

Unfortunately, good meter-sticks are hard to find in cosmology. Gurvits et al (1999, A&A, 342, 378) have used compact radio sources (typically, relativistic jets of plasma emitting synchrotron radiation, powered by massive black holes in quasars and radio galaxies) but they have not demonstrated rigorously that the objects should have the same physical size. A better test will come from measurements of hot gas in clusters of galaxies by combining X-ray emission with the Sunyaev-Zel’dovich effect (shadowing of the microwave background). Birkinshaw (1999, Phys. Rep., 310, 97) gives a detailed review. Finally, other possibilities have been proposed based on the clustering of quasar absorption lines (Hui et al 1999, ApJ, 511, L5) or high-redshift galaxies (Nair 1999, ApJ, 522, 569). These methods are statistical and are based on comparing clustering in the radial and transverse directions, following a suggestion by Alcock & Paczynski (1979, Nature, 281, 358).

 

[Garth]

The simplest way to falsify the Milne model would be to ask how it explains the observed acceleration of the expansion?

To take this a step back, if one is skeptical about whether the Universe is truly accelerating given the data we have (which I think is unlikely but is none the less a healthy attitude) you can still ask how the Milne model could possibly explain the supernovae data.

It is actually remarkable that the (\Omega_M,\Omega_{\Lambda}) = (0,0) model fits the SNe Ia very well out to about z~1, see Perlmutter et al's seminal paper Measurements of Omega and Lambda from 42 high-redshift supernovae Figure 2 page 24

The middle solid curve is for (\Omega_M,\Omega_{\Lambda}) = (0,0). Note that this plot is practically identical to the magnitude residual plot for the best-fit unconstrained cosmology of Fit C, with (\Omega_M,\Omega_{\Lambda}) = (0.73,1.32).

If the 'empty' universe fits the SNe Ia data then DE would have to produce a total pressure equation of
p = -1/3\rho to give a linearly expanding universe. There is one modified GR theory that does just this.

At greater z the fit is not so good, but this could be explained by the SNe Ia not being standard candles at this early epoch. We could also note the remarkable cosmological coincidence of the age of the universe (present best value 13.81 Gyrs.) and Hubble time (present best value 13.89 Gyrs.) especially because with an arbitrary amount of DE the age of the universe could be anything from about 10 Gyrs. to infinity. This does look as if the universe has been expanding linearly!

My original question was asking whether there is any empirical evidence to support the theoretical maximum in angular diameter distance of z ~ 1.6, which would falsify the Milne model as had been previously stated, from hellfire's link paper it looks there is not yet, (unless there is a more recent detection of such a maximum).

Garth

 

[marcus]

I'm not familiar with this kind of test, do you have a useful reference for this? ...

Admittedly it is still at the stage of a research recommendation. There was a paper by Hellaby recommending that the "next generation of redshift surveys" get a handle on it. I will look up the reference

 

[marcus]

I'm not familiar with this kind of test, do you have a useful reference for this? ...

There was a paper by Hellaby suggesting that the "next generation of redshift surveys" could actually determine the maximum of angular size distance.

To refute Milne one would not have to determine the maximum accurately, which is what Hellaby wants. To refute Milne model one only needs observational evidence that such a maximum exists.

I started a thread last year, asking for references, if anyone else had any---here is the Hellaby citation from that thread.

related paper:
http://arxiv.org/astro-ph/0603637
The Mass of the Cosmos
Charles Hellaby
6 pages, 9 graphs in 3 figures. Replacement has very minor changes: puts greek letters on graphs, and adds small corrections made in publication

"We point out that the mass of the cosmos on gigaparsec scales can be measured, owing to the unique geometric role of the maximum in the areal radius. Unlike all other points on the past null cone, this maximum has an associated mass, which can be calculated with very few assumptions about the cosmological model, providing a measurable characteristic of our cosmos. In combination with luminosities and source counts, it gives the bulk mass to light ratio. The maximum is particularly sensitive to the values of the bulk cosmological parameters. In addition, it provides a key reference point in attempts to connect cosmic geometry with observations. We recommend the determination of the distance and redshift of this maximum be explicitly included in the scientific goals of the next generation of reshift surveys. The maximum in the redshift space density provides a secondary large scale characteristic of the cosmos."

for more discussion, the earlier thread was
"got a link for the angular-size redshift relation?"
https://www.physicsforums.com/showthread.php?t=127627
SpaceTiger weighed in at one point.

 

[Wallace]

It is actually remarkable that the (\Omega_M,\Omega_{\Lambda}) = (0,0) model fits the SNe Ia very well out to about z~1, see Perlmutter et al's seminal paper Measurements of Omega and Lambda from 42 high-redshift supernovae Figure 2 page 24

It is 'seminal' because it was the first, and by definition has the least data of any supernovae and cosmology paper. Strange that you should point to it then! Although not so strange when you consider that the data obtained since then have far more significantly ruled out the Milne model...

At greater z the fit is not so good, but this could be explained by the SNe Ia not being standard candles at this early epoch.

So you are happy to use SN to support your theory in the region it agree with it and then just when they diverge suggest that this might is where they cease to be standard candles? :zzz:

We could also note the remarkable cosmological coincidence of the age of the universe (present best value 13.81 Gyrs.) and Hubble time (present best value 13.89 Gyrs.) especially because with an arbitrary amount of DE the age of the universe could be anything from about 10 Gyrs. to infinity. This does look as if the universe has been expanding linearly!

This co-incidence is just that, a coincidence! It means nothing! Think about it for a moment. The age of the universe is not something we can observe it is only something we can derive from our theory, which we obtain by fitting to what we can observe, the data. If two theories give the same derived result for something that is unobservable while one is a good fit to the data and the other is an appalling fit which would you believe?

Take this example. Imagine an Aristotelean physicist and a Newtonian physicist are trying to predict how far a ball thrown at a certain angle will go. The Aristotelean says that the ball will travel in a straight line until a certain point and then will fall vertically downward to the earth. The Newtonian says it will travel on a parabolic path. If they both happen to predict the same final landing point, how can you say which theory is correct? Easy! Watch the ball in flight and observe the parabolic path!

This is just like the universe. We can see the evidence of accelerating and deccelerating eras. Just because you can draw a straight line through an a(t) plot that intersects t=0 and t=1 dosn't mean this is a reasonable model if it does not fit the data!

It's not just about SN. Our models of structure formation work really well for the LCDM model but the Milne model predicts a Universe that looks completely different in terms of the clustering of galaxies etc etc

I find it frustrating that people willfully take one paper detailing one type of measurement and then suggest their pet model fits better than the standard model. The LCDM model is the current standard because it fits all the data with a common set of parameters. It's not perfect, that's for sure, and it might even be completely wrong. However the point is to show how a competing idea fits the whole lot in a better way, not willfully twisting a single out-dated reference into something far more significant than it is!

 

[Garth]

So you are happy to use SN to support your theory in the region it agree with it and then just when they diverge suggest that this might is where they cease to be standard candles? :zzz:

As there is no clear model for SNe Ia is not "happy to use SN to support your theory" just what the standard model does in assuming that their luminosity is constant over cosmological time, because over this time there may have been metallicity evolution?

This co-incidence is just that, a coincidence! It means nothing!

Such as the related coincidental present OOM equality of the densities of baryonic matter, DM and DE in a highly expanded universe? Note: the present derived age of the universe is a function of the exact mix of these components.

Think about it for a moment.

Quite.

The age of the universe is not something we can observe it is only something we can derive from our theory, which we obtain by fitting to what we can observe, the data. If two theories give the same derived result for something that is unobservable while one is a good fit to the data and the other is an appalling fit which would you believe?

I am not advocating the Milne model, although the “Freely Coasting” Cosmology does appear to be more concordant than you allow, however the standard model would be more convincing if Inflation, DM and DE were all verified by laboratory physics. Inflation has explained the coincidental nature of the density, smoothness and flatness problems of old GR cosmology by introducing a new set of non-verified 'entities' with 'coincidental' relative abundances.

Take this example. Imagine an Aristotelean physicist and a Newtonian physicist are trying to predict how far a ball thrown at a certain angle will go. The Aristotelean says that the ball will travel in a straight line until a certain point and then will fall vertically downward to the earth. The Newtonian says it will travel on a parabolic path. If they both happen to predict the same final landing point, how can you say which theory is correct? Easy! Watch the ball in flight and observe the parabolic path!

Apart from the inappropriateness of that example, as we cannot 'observe' the expansion of the universe as one can the trajectory of a ball, the standard model 'R(t)' curve is hardly a simple parabola!

As I said, I am not actually advocating the Milne model, but only pointing out the standard model fits only because of the introduction of components undiscovered in laboratory physics, which until they are discovered, say by the LHC, lead one to keep an open mind on the subject. In the meantime it is intriguing that the simplicity of the Milne model does echo certain features of the universe.

Garth

 

[Wallace]

As there is no clear model for SNe Ia, for example there may be metallicity evolution, is not "happy to use SN to support your theory" just what the standard model does in assuming that their luminosity is constant over cosmological time?

The point is we don't know what evolution effects may or may not exist in the SN we observe, but the best evidence we have suggests that if there are any such effects they are small. Therefore we treat the luminosities as unchanging for all time, for now, until we know any better. This is much more transparent an approach than what you suggest, i.e. requiring that the effect kicks in precisely when it is needed to justify your model.

The key point which you have once again ignored is that the LCDM model is much more than SN. The structure and CMB results are just as crucial and agree with the SN results, hence our guarded confidence in these results.

Such as the related coincidental present OOM equality of the densities of baryonic matter, DM and DE in a highly expanded universe? Note: the present derived age of the universe is a function of the exact mix of these components.

What is the physical significance? So the universe, according to LCDM is 13.8 Gyrs old (or whatever the exact number is). There is nothing significant about this number. It happens to be the inverse of the Hubble time, but there is no significance to this coincidence. It's like saying, wow! my car number plate is 000, what are the odds!

am not advocating the Milne model, although the “Freely Coasting” Cosmology does appear to be more concordant than you allow, however the standard model would be more convincing if Inflation, DM and DE were all verified by laboratory physics. Inflation has explained the coincidental nature of the density, smoothness and flatness problems of old GR cosmology by introducing a new set of coincidental non-verified 'entities'.

I has a quick read of that paper and it dosn't address any issues in structure formation, other than 'structure can form'. I've done simulations of structure in these models before and the clustering statistics are totally different and easily distinguished. Indeed DE and DM are 'non-verified entities' as you suggest, however electrons were also these at some point, as were a host of other physical theories! I wouldn't be that in 10 years we still think these things exist, but inflating the case for alternative models is not the way to go about investigating them.

Apart from the inappropriateness of that example, as we cannot 'observe' the expansion of the universe as one can the trajectory of a ball, the standard model 'R(t)' curve is hardly parabolic!

Why is it inappropriate exactly? We CAN observe the trajectory of R(t)! This is exactly what we do when we study SN! (crossing our fingers that they are standard candles) and also what we do by studying structure at different epochs, since structure is driven by R(t). Of course R(t) is not a parabola, surely you comprehended that this was an analogy, what I'm saying is that is has some curve that we can calculate via our model, and check against observations. The linear coasting (or Milne model) predicts a straight line. The data are incompatible with a straight line and hence we reject the model, even though the staring line passes through the same two end points as the curved one.

 

[hellfire]

I has a quick read of that paper and it dosn't address any issues in structure formation, other than 'structure can form'.

I agree. The paper assumes already some kind of density perturbations and, contrary to inflation, it does not provide a mechanism for their formation.

 

[Garth]

There are about 14 other papers and e-prints on the subject and they certainly do not cover every aspect of the model.

I don't think as much effort has been put into that model as has been put into the standard! It is not surprising there are still unexplained gaps in it.

As I said, I am not myself advocating the freely coasting 'Milne' model but it has some interesting features and, given the large unknowns in the standard model, needs to be kept in mind. IMHO.

Garth

 

[fransic]

I once heard about a pulsing universe. A math professor from Kyoto university had this interesting theory: the universe is expanding and shrinking successively from the very first Big Bang. There was many Big Bangs he said. So, the question will be: what cause it to shrink? He have this theory about the dark matter which would be 98% of universe's mass.
__________________________
http://www.gomvents.com/

 

[Chronos]

A theory is not the same as a philosophy. It is a common weakness shared by all non-GR models. I am partial to the GR interpretation.

 

[Wallace]

I don't think as much effort has been put into that model as has been put into the standard! It is not surprising there are still unexplained gaps in it.

The problem with this kind of argument is that it ignores the reasons why there is more interest in the 'standard' model. If you look at the broad predictions of the Milne model you very quickly see that for every observation we have the theory and data are in complete conflict. Therefore there isn't much motivation for going any further with the model.

The 'standard' model is in agreement with the data in terms of broad predictions. Hence there is a good reason to investigate further. By checking the minute details we have discovered some anomalous aspects of the model in comparison with the data.

'Doing more work' on a model generally means that you are pushing the boundaries to see where it breaks. Of course we won't bother pushing the boundaries on a model that is broken from the start. Such additional work is not necessary, and indeed would not produce any additional insight. The assumption that more work may fill 'the gaps' is groundless when 'the gaps' are fundamental first order (or even zeroeth order) problems with the model.

 

[Garth]

The problem with this kind of argument is that it ignores the reasons why there is more interest in the 'standard' model. If you look at the broad predictions of the Milne model you very quickly see that for every observation we have the theory and data are in complete conflict. Therefore there isn't much motivation for going any further with the model.

The 'standard' model is in agreement with the data in terms of broad predictions. Hence there is a good reason to investigate further. By checking the minute details we have discovered some anomalous aspects of the model in comparison with the data.

'Doing more work' on a model generally means that you are pushing the boundaries to see where it breaks. Of course we won't bother pushing the boundaries on a model that is broken from the start. Such additional work is not necessary, and indeed would not produce any additional insight. The assumption that more work may fill 'the gaps' is groundless when 'the gaps' are fundamental first order (or even zeroeth order) problems with the model.

Others would disagree with you - it seems the standard model is the one that is "a model that is broken from the start" - it is only fixed by invoking Inflation, DM and DE, all as yet undiscovered by 'laboratory' physics...

From Sethi, Kumar, Pandey & Lohiya's 2005 paper A case for nucleosynthesis in slowly evolving models

Summary

In spite of a significantly different evolution, a linear coasting cosmology can not be ruled out by all the tests we have subjected it to so far.
Linear coasting being extremely falsifiable, it is encouraging to observe its concordance ! In standard cosmology, falsifiability has taken a backstage - one just constrains the values of cosmological parameters subjecting the data to Bayesian statistics. Ideally, one would have been very content with a cosmology based on physics tested in the laboratory. Clearly, standard cosmology does not pass such a test. One needs a mixture of hot and cold dark matter, together with (now) some form of dark energy to act as a cosmological constant, to find any concordance with observations. In other words, one uses observations to parametrize theory in Standard Cosmology. In contrast, a universe that is born and evolves as a curvature dominated model has a tremendous concordance, it does not need any form of dark matter and there are sufficient grounds to explore models that support such a coasting.

Garth

 

[Chronos]

Wallace make a pursuasive argument Garth. He might be wrong, but the reasoning is pretty solid, would you not agree? The strength of the 'Standard Model' is it has very loose parameters. In fact, it even allows for additions - like the dark stuff. The evidence in favor of dark stuff is, in fact, fairly compelling. But still, the 'Standard Model' can survive without dark stuff, it merely needs a fairly severe tweak. Surely not all of physics is wrong. The bigger issue is where we draw the line. I stop at GR. GR may only be an approximation, but is much closer to dead on than any lower level physics.

 

[Wallace]

Others would disagree with you - it seems the standard model is the one that is "a model that is broken from the start" - it is only fixed by invoking Inflation, DM and DE, all as yet undiscovered by 'laboratory' physics...

Garth; Inflation, DM and DE ARE the standard model, not 'fixes' tacked onto some model, they are the model!? If you have a theoretical prejudice against these features then that is your prerogative, however the point is that the data, independently, across the range of observables, agrees with the same parameter values, with these features to a high level of precision.

As for the paper you point to, of course there will always be dissenting views to any proposition, that is human nature. I've played with the SN data myself and the Milne model is a poor fit. I don't know how else to say it since you simply disagree. I work in structure formation and I've run the Milne model and frankly you would have to be stark raving and possibly barking mad to think the results look anything like the structure data we have (such as 2dFGRS or SDSS). If you would like me to post some images I'm happy to do so.

 

[Garth]

Hi Wallace,

Yes I am familiar with structure formation in the standard model such as in the Millenium simulation.

The structure formation in that model, together with galactic cluster dynamics and spiral galaxy rotation profiles, requires more density than the standard BBN can provide, hence the need for non-baryonic DM. The smoothness, flatness, density and magnetic monopole problems of GR cosmology requires Inflation. Cosmic acceleration and spatial flatness require DE. It is this exotic non-baryonic DM, the Higgs Boson/Inflaton and DE itself that has not been discovered in the laboratory even after three decades of intense searching, which of course you know all too well.

These have become necessary parts of the standard model, therefore their continued non-detection does become a reason to consider other "dissenting" approaches.

I have no problem with that standard model so long as it is treated as provisional on these entities being discovered.

I am interested in the fact that you have run structure formation in the Milne model. What density were you using?

Garth

 

[Wallace]

A range of densities, nothing fits too well. The problem is that we have to points in which we can normalise the growth amplitude, the CMB (via COBE and WMAP) and today (via 2dFGRS and SDSS). Without bothering with simulations, just looking at linear perturbation theory, there isn't a single set of parameters for the Milne model that gets the correct growth amplitude increase from z=1100 to z=0 as well as being consistent with H_0 and SN data (even the nearby data if we cut of the high z points that do not agree with the Milne model, and may suffer from spurious evolution effects).

We have two differential equations, the distance vs z and growth vs z. For LCDM they both get the same answer between z=1100 and z=0 for a common set of parameter values that also fits other data. The same is simply not true for the Milne model, you just don't get even close to the required growth amplitude increase for complex structures to form.

BTW: I still strongly disagree with the notion that DE and DM will only be 'real' if they can be 'detected in a lab'. If they truly only interact gravitationally this may be literally impossible to do. Does this mean they therefore cannot exist? I just don't understand the theoretical prejudice that demands that if Humans can't make it then it must not exist. A lab experiment is merely the observation of the action of some force on some substance. Astronomy is the same process. I don't understand the fingers in the ears 'LA LA LA' kind of dismissal of the evidence that is staring us in the face due to an anthropocentric notion that something can't be real unless we can play God and make some for ourselves??

 

[Garth]

Thank you for that information.

I believe the Indian team were using values \Omega_{M} = 0.65 ~ 0.69 and h = 0.65 ~ 0.71.

They claim in Cosmological Constraints on a Power Law Universe:

It was also demonstrated that this model is consistent with primordial nucleosynthesis [9]. For
\Omega = 0.65 and \eta = 7.8 × 10⁻⁹, the model with \alpha = 1 yields He⁴ = 0.23 and metallicity of the range 10⁻⁷ [11]. Linear coasting surprising clears preliminary constraints on structure formation and CMB anisotropy [10].

(emphasis mine), where reference [10] is A Concordant "Freely Coasting Cosmology"

About your second point: I am not saying that if we do not discover the Inflaton particle/DM and DE in the lab they do not exist, just that the assumption of their existence is provisional. Our conclusion that they do exist is theory dependent.

That theory (GR) may be modified, especially if/when a quantum gravity theory replaces it.

We just have to keep that in mind.

Garth

 

[Wallace]

Chinese whispers. If you look at the reference [10] all they do, as I have pointed out to you in the past, is show that 'structure can form'. We know a good deal more about structure in our Universe than merely that there is some! They do not attempt to confront the predictions of this model with data. Having done so myself I can see why, though that speaks volumes for their credibility (or lack thereof). It's not a difficult task to do.

On the Lab verification point, I ask you the question of what makes DE and DM 'provisional' theories?? There is no such thing. They are theories that best fit current data. If new data comes along and a new theory is developed (which is certainly occurring on both fronts) and the new theory fits the new data better then the theory will be replaced.

There is no reason to call a theory that is supported by the available evidence 'provisional' apart from, once again, theoretical prejudice. The existence of everything in physics is 'theory dependent' though your toaster doesn't come with a warning 'Danger: The operation of this device is theory dependent, use at your own risk'. Pointing out a banal point about the scientific method in certain cherry-picked cases and not others highlights the fundamental prejudice of the cherry-picker. It's just like Creationists poo pooing Evolution because it is 'just a theory', while happily using the theory of electricity to beam their sermons into your lounge room.

That theory (GR) may be modified, especially if/when a quantum gravity theory replaces it.

We just have to keep that in mind.

Again, no one in cosmology is not bearing this in mind. Pointing it out the way you do implies that this is not the case.

 

[Garth]

I am not disputing the standard model works well, given the addition of these necessary 'entities'. However, if the provisional nature of Inflation/DM/DE is not kept in mind then over-confidence may well close the mind to alternative possibilities.

Garth

 

[Wallace]

But why do you describe them as 'provisional'? Why are these theories any less valid than any other?

 

[Garth]

But why do you describe them as 'provisional'? Why are these theories any less valid than any other?

I am committed to the definition of a scientific study of cosmology that has grown out of the discipline astrophysics as opposed to philosophy or theology. It is astrophysics carried out on the largest scale.

Astrophysics is the knowledge of the physics of the heavenly bodies 'out there' by the understanding of the physics 'down here', in the laboratory.

Occasionally we discover something 'out there' before it is discovered in the laboratory, such as the element helium. However its discovery in 1868 was provisional until verified by Ramsey in 1895 when it was isolated on Earth. Its faint yellow spectral line seen in 1868 was first assumed to be sodium, or it could have been the absorption line of another element under the unusual conditions of the Sun's chromosphere. Of course the laboratory isolation of the new element confirmed it as Helium.

Inflation and the DM particle have been similarly discovered 'out there', I maintain that not until we have discovered these particles 'down here', say by the LHC and if the detection of an axion by Piyare Jain at the University of Buffalo is verified, their properties measured and found to be concordant with cosmological constraints, can we say that we really know what we are talking about.

Garth

 

[Wallace]

Right, so you do hold the anthropocentric view that unless we can make it ourselves we can never be sure it exists. My question stands that how is a lab experiment, in which we observe the action of something on something else fundamentally different to the observation in the cosmos of the same?

Your absurd accusation that LCDM is based on either philosophy or indeed theology(!?) does not become you. Should we ignore the evidence of the cosmos becuase of some history we wish to honour? Should we disregard what is possibly the only evidence we can ever get to study some fundamental physics because the process is somewhat different to what we have used in the past? I think the Aristoteleans had similar issues with a chap named Galileo...

 

[Garth]

Right, so you do hold the anthropocentric view that unless we can make it ourselves we can never be sure it exists. My question stands that how is a lab experiment, in which we observe the action of something on something else fundamentally different to the observation in the cosmos of the same?

How are we ever sure something exists? We have to go by our own observations, either in the laboratory or at a distance as in astrophysics. In the 'laboratory' experiment variables and other effects can be controlled, albeit with difficulty, however that cannot be said about cosmological observations.

If GR, unmodified, could be proven without doubt then its cosmological conclusions could be accepted without doubt. We both know this is not the case.

If the Higgs Boson/Inflaton and DM particle are discovered with the desired properties, then those cosmological observations could be accepted without doubt. Their verification could be 'just around the corner', however, as we both know, this has not yet happened.

Your absurd accusation that LCDM is based on either philosophy or indeed theology(!?) does not become you.

I made no such claim, if it read as such then my post was ambiguous, for which I apologise.

I was simply re-stating the basis of astrophysics as I understand it; i.e. the study of the physics of the stars and other 'heavenly bodies' based on the physics discovered in the 'laboratory'.

The motto of the Royal Astronomical Society, which was founded in1820, is "Quincquid nitet notandum". It means "Let whatever shines be recorded (lit. noted)". It is an interesting observation that some 187 years later it seems that '96%' of our discipline is about recording that which does not shine...

Garth

 

[Wallace]

So you're not prepared to consider that our understanding can evolve to allow us to probe fundamental questions that may be unanswerable 'in the lab'? Are you really not prepared to consider the implications of cosmological data because of what someone said, in a dead language almost 190 years ago?!

I'm not suggesting that DM,DE, inflation etc are locked in stone, neither is the theory of the electron, that's just the way science works. The point I'm making is that if we insist that we will never trust a result unless we can make the stuff ourselves we are potentially blinding ourselves to deeper insight that might not be accessible otherwise.

I see no justification for your position other than appealing to history. I'm not suggesting that cosmological observations, at present, 'seal the deal' but I'm am wary of the attitude that they can never do so, regardless of what we may otherwise be able to learn from the data.

This is not an idle danger. The prejudice against physical laws observed 'in the sky' but not in the lab leads to, amongst other things, the desperate promotion of clearly discordant models, such as the Milne model. Let's use the data we have to do the best we can rather than constraining ourselves for no other reason than homage to the past.

 

[Garth]

Of course I am prepared to consider the development of our understanding of questions unanswerable 'in the lab'. However, mindful of the scientific method I am just aware of the provisional nature of such understanding.

I believe a historical perspective is useful. In order to know where we are going it is instructive to know where we are and how we got here.

Garth

 

[Wallace]

Agreed, but what I see in the history of science is the way in which time and time again understanding stalls due to the confines of particular methodologies, for instance deductive reasoning did not permit empirical data and hence held science back from the wonders of inductive reasoning. Deductive reasoning had achieved a lot and the senses were assumed to be untrustworthy. Eventually the rules were re-written and empirical science bloomed.

That's a simplistic analysis and I'm sure I'm not telling you anything you don't know already, but when I look at the history of science I don't see anything that tells us we need to be able to make something for ourselves before we can be sure (in the scientific sense of the word) that it exists.