"de sitter effect" and cosmology history

[quantumtopology]

I forgot to write the link: http://www.spsnational.org/radiations/2008/ecp_bigbang3.pdf

 

Some discrepancies, You said: "Yeah, certainly a static solution that is consistent with general relativity wouldn't be able to agree with observation." I wouldn't jump to that conclusion yet. We are making theoretical considerations and haven't looked at observational issues in detail so far. What I admitted is that if we accept GR and the conventional assumptions about what is physically possible and what is not, there seems to be not many more options at first sight.

Also, I always considered Minkowski space to be flat, what is hyperbolic about it is its "velocity space" , maybe that's what you implied with the link of your edit.

Anyway It's always a bit confusing to talk about curvatures because often the 3-space manifold gets mixed with 4-spacetime manifold. maybe we should be more specific in this point.

Finally, certainly I find the Big Bang troublesome but this comes from the fact that I find troblesome the expanding hypothesis,and is my belief that before accepting it we have to exhaust the rest of the possibilities. Your opinion being that they have been explored and discarded and mine that there are still options to explore.

Regards

[modest]

I forgot to write the link: http://www.spsnational.org/radiations/2008/ecp_bigbang3.pdf

 

Thank you :D

 

Some discrepancies, You said: "Yeah, certainly a static solution that is consistent with general relativity wouldn't be able to agree with observation." I wouldn't jump to that conclusion yet.

 

I understand.

 

Also, I always considered Minkowski space to be flat, what is hyperbolic about it is its "velocity space" , maybe that's what you implied with the link of your edit.

Anyway It's always a bit confusing to talk about curvatures because often the 3-space manifold gets mixed with 4-spacetime manifold. maybe we should be more specific in this point.

 

Yeah, you'll see Minkowski spacetime referred to as "flat" quite often. In the cosmological sense that "spherical", "flat", and "hyperbolic" are used, it indicates that space takes on those shapes. A big triangle would have angles less than 180º if the space is hyperbolic, greater than 180º if spherical, and exactly 180º if euclidean.

 

Quoting Ned Wright's cosmology tutorial:

One consequence of general relativity is that the curvature of space depends on the ratio of rho to rho(crit). We call this ratio Ω = rho/rho(crit). For Ω less than 1, the Universe has negatively curved or hyperbolic geometry. For Ω = 1, the Universe has Euclidean or flat geometry. For Ω greater than 1, the Universe has positively curved or spherical geometry. We have already seen that the zero density case has hyperbolic geometry, since the cosmic time slices in the special relativistic coordinates were hyperboloids in this model.

Cosmology Tutorial - Part 3

"special relativistic coordinates" in this context is synonymous with Minkowski spacetime. In the absence of mass and lambda general relativity reduces to special relativity / Minkowski spacetime where space is hyperbolic (a big triangle has less than 180 degrees).

 

Finally, certainly I find the Big Bang troublesome but this comes from the fact that I find troblesome the expanding hypothesis,and is my belief that before accepting it we have to exhaust the rest of the possibilities.

 

While I feel like we've exhausted the static options of general relativity, I'm curious why you would approach cosmology from either of these perspectives:

1. Exhaust all static options before considering an expanding option
   
2. Exhaust all expanding options before considering a static option
   

Wouldn't either approach be, perhaps, a little biased? I think we should look at the evidence and see which of all the options (static or dynamic) best fits the evidence.

 

~modest

[quantumtopology]

Well , I'd say the expanding solutions have been privileged in the last 70 years while the non expanding ones where initially supported on philosophycal grounds only to be completely discarded and almost banned a few years later, never to be considered again just like shaking off some amorous letdown.

On the other hand the non-linearity of the redshifts of very distant objects like the supernovae Ia is a big blow to the expanding space hypothesis, certainly it was not predicted and to be frank ,an expansion that changes its pace in such a strange way is not IMO to be taken seriously. I mean the rate of expansion was supposed to be decelarating and suddenly, no , now accelerates. That poor Hubble constant, or parameter as they call it since is anything but a constant, is going to end up feeling dizzy:D

Regards

[modest]

Well , I'd say the expanding solutions have been privileged in the last 70 years

 

Any model that agrees with observation should be privileged over one that does not. This is the backbone of the scientific method.

 

On the other hand the non-linearity of the redshifts of very distant objects like the supernovae Ia is a big blow to the expanding space hypothesis

 

I don't believe so. If something is receding faster than once thought, that is no reason to assume it isn't receding.

 

certainly it was not predicted

 

Sure it was. You can see, for example, Carroll 1992 model C. Section 3 accurately describes the expansion history of such a model 6 years before supernova 1a standard candle observations.

 

This is no surprise considering the Lambda-CDM model is a valid solution of the Friedmann equations and as such, perfectly consistent with general relativity.

 

and to be frank ,an expansion that changes its pace in such a strange way is not IMO to be taken seriously.

 

I'm willing to explore alternative explanations, but I would be weary of anyone not willing to admit that standard cosmology explains observational evidence extremely well.

 

That poor Hubble constant, or parameter as they call it since is anything but a constant, is going to end up feeling dizzy:D

 

It has long been known that the Hubble parameter is time dependent.

 

~modest

[quantumtopology]

Any model that agrees with observation should be privileged over one that does not. This is the backbone of the scientific method.

Indeed but observations are open to interpretations, specially when astronomical evidence is scarce. Otherwise we'd be taking about dogmas o religions.

I'm willing to explore alternative explanations, but I would be weary of anyone not willing to admit that standard cosmology explains observational evidence extremely well.

 

Actually accommodates just too well every observational fact with a little tweak here and a dent there, just enough to make it almos unfalsifiable in Popperian terms.

If questioning the standard model annoys you I understand. But just consider the fact that science is about questioning permanently the current models, no matter how accurate we believe they are, precisely in order not to transform them in a question of faith or belief.

But I feel you adressed me directly about my motives and I tried to be sincere, and in no way meant to offend anyone. If you'd rather keep the conversation focused on technical matters is OK, but you asked....:D

[modest]

I'm not offended.

 

There are many ways to falsify standard cosmology. One could, for a completely arbitrary example, find stars or globular clusters which are significantly older than the universe. In the same vein, one should be able to falsify static models.

 

There are tests that distinguish between expansion and other, unknown, causes of redshift. For example,

 

[astro-ph/0106566] The Tolman Surface Brightness Test for the Reality of the Expansion. IV. A Measurement of the Tolman Signal and the Luminosity Evolution of Early-Type Galaxies

 

The reality of the expansion has been diligently tested at every opportunity.

 

~modest

[quantumtopology]

I thought the Tolman test was not well suited in this case. I read somewhere in the redshift z thread that this test assumed flat geometry and I am talking about hyperbolic geometry.

 

Something I have asked several times in different forums and achieved no answer is the following: Is there some recent conclusive data about the angular size-redshift relation for z>1.6? I have only been able to find a reference from several years ago (Gurvits et al 1999) [astro-ph/9812018] The ``angular size - redshift'' relation for compact radio structures in quasars and radio galaxies which does not show clear evidence for a minimal angular size as predicted by the expansion model, and that is based in assumptions of decelerated expansion (previos to the SNaeIa release) Does anyone have some current information that shows a more conclusive result?

Regards

[modest]

I thought the Tolman test was not well suited in this case. I read somewhere in the redshift z thread that this test assumed flat geometry and I am talking about hyperbolic geometry.

 

Humm...

 

I can't think of why the surface brightness test would be better suited for one geometry over another—although it is probably usually solved in terms of a flat model more often since evidence suggests our universe is approximately flat.

 

The expected results of the SB test depend on the model being solved. I wouldn't know how, then, to say what the results of SB would be for hyperbolic models in general (we would need a specific model to solve for), but de Sitter's hyperbolic model is definitely quite a bit different from what we observe,

For instance a galaxy at redshift z = 3 will appear 9 times brighter in a flat matter dominated universe than it will in de Sitter space (see Fig 4).

The Case for a Positive Lambda-Term - V. Sahni & A. Starobinsky

 

Something I have asked several times in different forums and achieved no answer is the following: Is there some recent conclusive data about the angular size-redshift relation for z>1.6? I have only been able to find a reference from several years ago (Gurvits et al 1999) [astro-ph/9812018] The ``angular size - redshift'' relation for compact radio structures in quasars and radio galaxies which does not show clear evidence for a minimal angular size as predicted by the expansion model, and that is based in assumptions of decelerated expansion (previos to the SNaeIa release) Does anyone have some current information that shows a more conclusive result?

Regards

 

I would say that the SN1a results are the more conclusive result. Supernova light curves are much, much, much better standard candles than angular size.

 

But, to answer your question directly—no. I don't know of any recent redshift-angular size studies that would bound the deceleration parameter.

 

~modest

[quantumtopology]

Hi, Modest

 

I would say that the SN1a results are the more conclusive result. Supernova light curves are much, much, much better standard candles than angular size.

 

I agree here. But I was not thinking of angular size-z relation as a way to measure distance but as a way of checkig a prediction of the L-CDM model

This is from wikipedia:

"The angular size redshift relation describes the relation between the angular size observed on the sky of an object of given physical size, and the objects redshift from Earth (which is related to its distance, d, from Earth). In a Euclidean geometry the relation between size on the sky and distance from Earth would simply be given by the equation:

 

 

tan theta = x/d

 

where θ is the angular size of the object on the sky, x is the size of the object and d is the distance to the object. Where θ is small this approximates to:

 

theta =x/d .

 

However, in the currently favoured geometric model of our Universe, the relation is more complicated. In this model, objects at redshifts greater than about 1.5 appear larger on the sky with increasing redshift." END wikipedia quote

 

 

As it's widely known, this is due to the fact that according to the expansion model from a certain distance calculated to be around z=1.6, objects sending the light we receive now were actually closer ,so that from there on, their angular size should increase instead of decrease.

So this could be a good way to test cosmologic models (of course there are difficulties related to measures at those z numbers)and that is why I'm interested in this relation. But I seem to be the only one :)

 

Regards

[modest]

I agree here. But I was not thinking of angular size-z relation as a way to measure distance but as a way of checkig a prediction of the L-CDM model

 

I understand. They are the same thing.

 

Checking the angular diameter assumes you know two things, 1) the intrinsic size of the object (as measured if you were there at the object) and 2) the apparent, angular, size of the object as viewed from earth. With those two things you have "angular size distance" which is a measure of distance that is independent of redshift and can be plotted against redshift to distinguish between models.

 

That is difficult to do because one can never be entirely sure of the intrinsic size of an object, nor is it very easy to measure angular size with great accuracy over great distance.

 

On the other hand, SN1a tests use luminosity distance as a measure of distance independent of redshift. Again, one needs to know 1) the intrinsic luminosity of the object (as measured if you were there at the object) and 2) the apparent luminosity as measured here on earth. If you know those two things then you have something independent of redshift which can be used to distinguish models.

 

The reason I said that the second option (the luminosity distance) is the better constraint on the deceleration parameter is because we know the intrinsic luminosity of type 1a supernova with good accuracy and certainty and we can measure the apparent luminosity with good accuracy and certainty.

 

This is from wikipedia:

"The angular size redshift relation describes the relation between the angular size observed on the sky of an object of given physical size, and the objects redshift from Earth (which is related to its distance, d, from Earth). In a Euclidean geometry the relation between size on the sky and distance from Earth would simply be given by the equation:

 

tan theta = x/d

 

where θ is the angular size of the object on the sky, x is the size of the object and d is the distance to the object. Where θ is small this approximates to:

 

theta =x/d .

 

However, in the currently favoured geometric model of our Universe, the relation is more complicated. In this model, objects at redshifts greater than about 1.5 appear larger on the sky with increasing redshift." END wikipedia quote

 

Right, but notice the qualifier "of an object of given physical size". Without that intrinsic size one cannot constrain the deceleration parameter with angular diameter. Here is the equation:

[math]\frac{x}{\theta}=\cfrac{c}{H_0 q^2_0} \cfrac{(zq_0+(q_0 -1)(\sqrt{2q_0 z+1}-1))}{(1+z)^2}[/math]

where x is the intrinsic size, theta is the angular size as viewed from earth, z is redshift, and q_0 is the deceleration parameter.

 

Most models act roughly the same way making it difficult to constrain q. Here are some different models of varying matter and cosmological constant values:

 

 

And the plot of their expected angular size distance,

 

 

From: http://preposterousuniverse.com/writings/cpt92.pdf

 

In all models, objects of a fixed size appear smaller with greater redshift up to a point then they start getting larger (angular size is essentially the inverse of angular diameter distance so you would flip the above plot over vertically to plot the angular diameter of something with a fixed size). Model E would be closest to a de Sitter universe and model C is closest to standard cosmology.

 

The SN1a tests do the same thing but with luminosity distance rather than angular size distance.

 

As it's widely known, this is due to the fact that according to the expansion model from a certain distance calculated to be around z=1.6, objects sending the light we receive now were actually closer ,so that from there on, their angular size should increase instead of decrease.

 

Even with a positive deceleration parameter objects of a certain distance would start getting larger in angular diameter. This is simply because the universe is expanding.

 

~modest

[quantumtopology]

 

Even with a positive deceleration parameter objects of a certain distance would start getting larger in angular diameter. This is simply because the universe is expanding.

 

~modest

 

Ok, now supposed they didn't (just for the sake of the argument), we make our observations, calculate things and objects of a certain distance don't start getting larger in angular diameter. Would that be an indication that maybe the universe is not expanding?

[modest]

Ok, now supposed they didn't (just for the sake of the argument), we make our observations, calculate things and objects of a certain distance don't start getting larger in angular diameter. Would that be an indication that maybe the universe is not expanding?

 

Yes, much like the straight line in this:

 

 

~modest

[quantumtopology]

Not quite, since that would be in the case of a Euclidean universe, in a hyperbolic one there would be a an exponential curve, I guess , I'll try to graph it later.

 

Anyway to falsify the LCDM model it would suffice to find that the curve doesn't go up from z about 1.6

 

Regards

[modest]

Not quite, since that would be in the case of a Euclidean universe, in a hyperbolic one there would be a an exponential curve, I guess , I'll try to graph it later.

 

To plot redshift vs. angular diameter for a static universe you must first describe the redshift metric. In other words, you have to explain exactly the cause of redshift and its value at any given distance.

 

Anyway to falsify the LCDM model it would suffice to find that the curve doesn't go up from z about 1.6

 

Clearly the angular size does increase. The graph I just posted and the paper you linked yesterday show this. The luminosity distance of galaxies and SN1a confirm.

 

~modest

[quantumtopology]

So we are back to my link, wich is the one I presented yesterday and that due to some outliers and the intrinsic error was not conclusive. That's why I asked for more recent studies, probably more accurate. I'll try to find something.

[modest]

So we are back to my link, wich is the one I presented yesterday and that due to some outliers and the intrinsic error was not conclusive.

 

Not conclusive enough to constrain the deceleration parameter between like models, but the data clearly shows an increase in angular diameter above z=1.5 showing expansion.

 

~modest

[quantumtopology]

"In principle, the angular-size redshift relation can be used to select the type of space for our universe. However, it is notoriously difficult to collect reliable data in practice because the astronomical yardstick can vary in size and in luminosity over time (the evolutionary and selection effects). In addition, we can only measure the projections on the celestial surface according to the orientation of the objects. All past attempts using data from galaxies, the separation of the lobes of radio sources, quasars, and radio galaxies produced inconclusive results" this is a quote from an interesting page : Relativity

I guess I chose the wrong method to pick out models and that is why nobody seems to use it.

I tried though. It's not time wasted since i learned some things.:)

Regards