How can we accurately determine the expansion rate of the Universe?

[Chalnoth]

Nereid,

Do you have a link where I can read up on this equivalence in more detail? I'd be rather surprised if the contracting solution would, for example, produce a cosmic microwave background or an accurate prediction of nucleosynthesis.

 

[Sundance]

Hello

I cannot remember if I posted this link before.

I like to have a remark on this paper.

http://arxiv.org/abs/0810.0153
Expanding Space: The Root of Conceptual Problems of the Cosmological Physics

Authors: Yu. V. Baryshev (Astron.Inst.St.-Petersburg Univ.)
(Submitted on 1 Oct 2008)

Abstract: The space expansion physics contains several paradoxes which were clearly demonstrated by Edward Harrison (1981, 1995, 2000), who emphasized that the cooling of homogeneous hot gas (including photon gas of CBR) in the standard cosmological model based on the violation of energy conservation by the expanding space. In modern version of SCM the term "space expansion" actually means continuous creation of vacuum, something that leads to conceptual problems. Recent discussion by Francis, Barnes, James, and Lewis (2007) on the physical sense of the increasing distance to a receding galaxy without motion of the galaxy is just a particular consequence of the arising paradoxes. Here we present an analysis of the following conceptual problems of the SCM: the violation of energy conservation for local comoving volumes, the exact Newtonian form of the Friedmann equation, the absence of an upper limit on the receding velocity of galaxies which can be greater than the speed of light, and the presence of the linear Hubble law deeply inside inhomogeneous galaxy distribution. The common cause of these paradoxes is the geometrical description of gravity, where there is no a well defined concept of the energy-momentum tensor for the gravitational field, no energy quanta - gravitons, and no energy-momentum conservation for matter plus gravity because gravity is not a material field.

 

[Sundance]

Hello Chalnoth

I have started to read some of the papers on the subject

Equivalance Astrophysics 2008
http://arxiv.org/find/all/1/all:+AND+2008+AND+equivalence+astrophysics/0/1/0/all/0/1

If its any help?

 

[heldervelez]

Perhaps you mean Kepler, or Copernicus, rather than Galileo?

Galileo was the first to introduce Relativity to us. I think we can remember the boat conceptual experience.

Further, there is a critical rider in my post: "even in principle".

Those three words glide over much that we can, and perhaps should, discuss.

We have towsands of pappers about things we can not directly perceive. We do not question when there exist an indirect possibility of reach knowledge.

For example, there have been many attempts to develop a theory, or theories, which reduce to QM (the Standard Model of particle physics) and GR in the appropriate limits. It may well be that, in any - or even all - of these theories it is possible, in principle, to distinguish between an expanding and a shrinking universe. When the universe is viewed through the glasses of those theories, the two are not equivalent.

Continue to explore that link you provide and you can see that it is not a big TOE that is offered. There is no need to go to QM, nor GR is on stress.

IOW, equivalence (in the narrow sense I am using) is theory-dependent; change the theory, and the equivalence may well disappear.

They are not equivalent at all. Only apparently they are equivalent. The assumptions at beginning, the non seen 'objects' and 'artifacts' we get rid, only one single parameter in the theory taken from data.

If you haven't already done so, I'd recommend that you read some of the excellent posts by marcus, in this section of PF; he has done a wonderful job, over several years, of presenting, and in many cases explaining, some of these 'beyond GR' theories, and how interpretations that are equivalent in GR may be distinguishable (though he may not have set out to present this explicitly).

I know that marcus has been devoted to the comunity.

Parts of the universe that we are unable to see, even in principle, are not within the purview of science, by definition. They may be fascinating to speculate about, and may have deep philosophical implications, but they are not, and cannot ever be, science.

What I intended to say was "we can not see that interpretation with our mind". The word see was misleading. Sorry.

If what you say here is to be accounted, then anything that mentions time before the CMB should be avoided (inflation, BB,Dark matter, Dark Energy, now even pre-BB)

 

[Chalnoth]

Hello

I cannot remember if I posted this link before.

I like to have a remark on this paper.

http://arxiv.org/abs/0810.0153
Expanding Space: The Root of Conceptual Problems of the Cosmological Physics

Authors: Yu. V. Baryshev (Astron.Inst.St.-Petersburg Univ.)
(Submitted on 1 Oct 2008)

Honestly, I don't know who Baryshev is, but these objections are just non-issues.

the violation of energy conservation for local comoving volumes

This isn't an issue because General Relativity has no requirement of such energy conservation. It's really easy to understand why this is the case: Newtonian gravity behaves in the exact same way, after all. Just take two test masses initially far away from one another. If you release them, what happens? Naturally they pick up speed and move towards one another.

But where did that energy come from? The standard answer is that it came from gravitational potential energy, which became more negative as the two masses got closer together and picked up speed.

Here's the problem, however: in the normal formulation of general relativity, gravitational potential energy is not considered. If you ignore gravitational potential energy, of course energy isn't going to be conserved.

But there is an alternative: the Hamiltonian formalism. And for a closed FRW universe, it turns out that the total energy is always identically zero: all of the positive energy in matter fields is made up by negative gravitational potential energy.

So that objection is meaningless.

the exact Newtonian form of the Friedmann equation

Well, this is interesting, but I don't see how it's a serious objection. Or even surprising. We know, after all, that whatever equations we make up from Newtonian gravity, those equations must be the same as the prediction for General Relativity as long as the relative speeds remain low and the gravitational fields relatively weak. Since the Friedmann equation assumes a homogeneous, isotropic universe, the gravitational fields are by definition very, very weak. And since the two theories will necessarily have the same prediction locally, where the relative velocities (naively estimated) remain low, while at the same time the assumption of homogeneity is used, the same equation used locally will necessarily also be usable globally. So no, I think we should be more disturbed if this weren't the case, given the particular assumptions used in the derivation.

the absence of an upper limit on the receding velocity of galaxies which can be greater than the speed of light

Given that velocity is only well-defined locally in General Relativity, this is also not an objection. It is slightly unsettling to many people, but it is fully within the predictions of General Relativity, which only states that no massive object can ever outrun a light ray. General Relativity does not guarantee that light rays will be capable of reaching from anywhere to anywhere. In fact, if this were a serious objection, it would also indicate that the prediction of black holes should be considered equally as objectionable.

and the presence of the linear Hubble law deeply inside inhomogeneous galaxy distribution

All this means is that the assumptions of homogeneity and isotropy remain good approximations to the universe on large scales. I have seen nothing to indicate that our current knowledge of structure formation predicts that we should somehow see this Hubble law strongly violated.

So yeah, I am completely unimpressed by these objections.

 

[Old Smuggler]

All this means is that the assumptions of homogeneity and isotropy remain good approximations to the universe on large scales. I have seen nothing to indicate that our current knowledge of structure formation predicts that we should somehow see this Hubble law strongly violated.

Nonsense. The Hubble law is seen right down to the doorstep of the local group of galaxies, i.e.,
below 3 Mpc. The GR prediction is that the Hubble law should become important at the scale of
clusters of galaxies, i.e., about 40 Mpc. Moreover, the local Hubble flow is very cold; the velocity
dispersion is much smaller than that obtained in (straightforward) computer simulations of the local group and its nearby surroundings. This is a problem for GR, and it has been known for some time.

A recent, relevant preprint is arXiv:0811.4610. Please study this paper (and references therein)
before commenting on issues whereof you obviously are ignorant.

 

[Chalnoth]

Nonsense. The Hubble law is seen right down to the doorstep of the local group of galaxies, i.e.,
below 3 Mpc. The GR prediction is that the Hubble law should become important at the scale of
clusters of galaxies, i.e., about 40 Mpc.

As the Hubble constant is near of 72km/s/Mpc, at 3Mpc we would be talking about over 200km/s/Mpc, which is starting to get into the velocity dispersion of less massive regions. Why shouldn't it be apparent?

Furthermore, the Hubble flow is very coherent, while velocity dispersion is much less so.

Moreover, the local Hubble flow is very cold; the velocity
dispersion is much smaller than that obtained in (straightforward) computer simulations of the local group and its nearby surroundings. This is a problem for GR, and it has been known for some time.

A recent, relevant preprint is arXiv:0811.4610. Please study this paper (and references therein)
before commenting on issues whereof you obviously are ignorant.

There is no reason yet to suspect that any problem here is a result of General Relativity. The assumptions that lead to the greater than expected dispersions use linear gravity, and linear gravity is clearly not applicable on these scales. They attempt to correct for this, but these are really small scales. I don't see how we can trust that correction. There are further problems with baryonic physics that are ignored in these calculations.

So no, I see no reason from what you have given me here to suspect there is a genuine problem. Perhaps it will tell us something interesting when more careful work is performed, such as detailed hydrodynamic simulations of structure formation, but it's always going to be really, really difficult to say that we have a genuine misunderstanding of physics here and not just a miscalculation in applying said physics. This is why most of the best data we have in cosmology is on large scales: it's not because we have so much more data, but because the theoretical interpretation of the results is much cleaner.

That said, I fully admit it's possible that this is telling us something interesting. It might, for example, be a hint as to the temperature or decay rate of dark matter. But I'm just not convinced it's genuinely due to new physics, and not just misinterpreting our current theories.

 

[mehul ahir]

what came first chiken or egg? in the other sense universe appears firstly or law governing it?

 

[D-jan]

I'm a little bit puzzled all of a sudden. I don't want to be rude or anything but i just wanted to ask a question to you, Mr. Ahir, how is your post relevant to the origin of the universe? have a good day.

 

[Carid]

Mr. Ahir's comment seems justified though perhaps deserving of its own thread.

Why is our Universe composed of spacetime, matter/energy, and a bunch of forces linking it all together? Why wasn't it just a monochromatic beam of Schrodinger cats passing through two giant superstring slits to create an interference pattern of feline superpositions?

Presumably originally all physical laws and constructs were possible and it was the breaking of symmetries which lead to the dispensation which we are privileged to inhabit.

Purest speculation, of course.

 

[Chalnoth]

Mr. Ahir's comment seems justified though perhaps deserving of its own thread.

Why is our Universe composed of spacetime, matter/energy, and a bunch of forces linking it all together? Why wasn't it just a monochromatic beam of Schrodinger cats passing through two giant superstring slits to create an interference pattern of feline superpositions?

Presumably originally all physical laws and constructs were possible and it was the breaking of symmetries which lead to the dispensation which we are privileged to inhabit.

Purest speculation, of course.

For this sort of speculation, I rather like Max Tegmark's ideas on the subject. You can read about it on his website here:
http://space.mit.edu/home/tegmark/toe.html
(inside is a link to his paper for a more in-depth description)

The basic, basic idea is that his hypothesis is that perhaps all mathematical structures have real existence. The laws of physics in our universe would be one realization of one of these mathematical structures. This idea can be thought of as a more explicit writing down of the statement, "all fully-consistent sets of physical laws exist." In order to bring this idea forward into the realm of reality, one would have to use some sort of anthropic argument.

 

[heldervelez]

Math as to serve Physics, and not the contrary.
Math is a mental construction not a reality of its own.

 

[Chalnoth]

Math as to serve Physics, and not the contrary.
Math is a mental construction not a reality of its own.

Why? I'd say Tegmark's argument is very effective here. We know that as long as the laws which govern our universe are fully self-consistent, then it is necessary that those laws are represented by some mathematical structure. We therefore know that at least one mathematical structure has real existence.

Why can't others?

 

[heldervelez]

... We therefore know that at least one mathematical structure has real existence.

Why can't others?

I do not understand which one you have in your mind.

 

[Dmitry67]

I also agree with the Mark Tegmarks arguments.

I tried to ask several times: if you believe that our universe is not completely equivalent to a purely mathematical structure then please provide an example of a purely *physical* axiom which can not be expressed in mathematical terms.

Nobody succeded...

 

[heldervelez]

I also agree with the Mark Tegmarks arguments.

I tried to ask several times: if you believe that our universe is not completely equivalent to a purely mathematical structure then please provide an example of a purely *physical* axiom which can not be expressed in mathematical terms.

Nobody succeded...

This is a philosophical question and the answer must also be like like this:

We can ommit the observers (we) from the universe and it will continue (or go back in our past 10000 years).
Subtract the Universe and we (the owners of math concepts) will not survive.
Clearly one is not 'equivalent' to the other.

Idem reasoning I apply to the hipotetical 'space is topology'.
Topology is a math construct.

We humans use math concepts to make an understable framework of our knowledge.
The egyptians started to measuring (and triangulating...) to say "this is my land" but the land itself is there in the first hand.

 

[Chalnoth]

I do not understand which one you have in your mind.

None. I don't know which mathematical structure is isomorphic to our universe. Nobody does, yet. But it is enough to know that our universe must be isomorphic to some mathematical structure, because if it weren't, then it wouldn't be consistent. And we obviously can't have that.

 

[Carid]

Math as to serve Physics, and not the contrary.
Math is a mental construction not a reality of its own.

Physics is also a mental construct; in fact everything we know is a mental construct.
Yes, there is a reality out there, and we are part of it, and so are our mental constructs. Plato told us we see shadows on the wall; Newton told us he was picking up pretty shells in front of an ocean of knowledge, etc..

However, the real point of this post is so that I can lay claim to inventing the term "Snowflake Universe" to describe the unique mathematical form that each of Professor Tegmark's universes will adopt.

 

[Sundance]

Hello

What do the actual images tell us?

a) Of all the images that we see the common behaviour is clustering effect.

Matter is drawn into a gravity sink, such as stars and black holes.

Dwarf galaxies cluster around larger galaxies, these cluster and form local cluster of galaxies, these local clusters cluster to form super clusters of clusters of galaxies.


b) That compact objects such as Stars, neutron stars, the theoretical quark stars and black holes form jets that reform their surroundings even effecting the formation of stars and galaxies.

So what we actually see is at random a process that expands and contracts. This is simple enough and yet we try to complicate the observations.

 

[Chalnoth]

So what we actually see is at random a process that expands and contracts. This is simple enough and yet we try to complicate the observations.

It's not complicating the observations. It's just attention to detail.

 

[Sundance]

Hello

Chalnoth said

It's not complicating the observations. It's just attention to detail.

Detail has been the issue for hundreds of years.

Some create a model and try to fit the data to the model and in many cases with ad hoc ideas. EG: Big Bang Theory

 

[heldervelez]

Hello
..
Some create a model and try to fit the data to the model and in many cases with ad hoc ideas. EG: Big Bang Theory

(my bold)

'Had Hoc' is very appropriate, even in the case of BB beeing correct.
It was born after the 'discovery that galaxies are moving apart'. Then all matter had to be in some point of space at the same instant.
If Hubble findings (measure) can be interpreted differently than BB is out.

 

[Chalnoth]

Hello

Chalnoth said

Detail has been the issue for hundreds of years.

Some create a model and try to fit the data to the model and in many cases with ad hoc ideas. EG: Big Bang Theory

So when one single added parameter to the theory not only explains the original observation it was originally used for, but also half a dozen other observations made since, we gain some confidence that it is at least approximately accurate.

 

[Sundance]

Hello


heldervelez said:

'Had Hoc' is very appropriate, even in the case of BB beeing correct.
It was born after the 'discovery that galaxies are moving apart'. Then all matter had to be in some point of space at the same instant.
If Hubble findings (measure) can be interpreted differently than BB is out.

Did I miss something. Actual images show a clustering effect and that galaxies move towards an attractor, a gravity sink so to speak. We see this in the Milky way little group of dwarf galaxies rotaing and gravity bound to the Milky Way. This little group is part of the local group of galaxies with M87 as the centre and this local group is moving towards the great attractor.

If you see galaxies moving away from each other its because they belong to a different group with a different attractor.

 

[Chalnoth]

Did I miss something. Actual images show a clustering effect and that galaxies move towards an attractor, a gravity sink so to speak. We see this in the Milky way little group of dwarf galaxies rotaing and gravity bound to the Milky Way. This little group is part of the local group of galaxies with M87 as the centre and this local group is moving towards the great attractor.

If you see galaxies moving away from each other its because they belong to a different group with a different attractor.

If your supposition here were correct, then galaxies on opposite sides of both attractors would appear to be moving toward one another.

 

[Sundance]

Hello Chalnoth

The movement and clustering is not my idea, its general info.

 

[Chalnoth]

Hello Chalnoth

The movement and clustering is not my idea, its general info.

It appears you have mangled it, then. The idea is that the nonlinear effect of clustering can provide the appearance of an accelerated expansion. It wasn't proposed to explain all expansion, just as an alternative explanation to dark energy. However, so far all such attempts to explain the effect in this way have failed to do so when examined in detail. It is difficult to do the analysis properly, so it isn't yet certain that this is entirely wrong, but it seems unlikely.

 

[Sundance]

Hello Chalnoth

Have a look at as many images as you like

Eg

http://www.spacetelescope.org/news/html/heic0810.html

As for expansion and acceleration, I have questions.

 

[Chalnoth]

Hello Chalnoth

Have a look at as many images as you like

Eg

http://www.spacetelescope.org/news/html/heic0810.html

I don't understand what images of colliding galaxies have to do with your discussion. I mean, they're cool and all, but I really don't see what you think they indicate.

As for expansion and acceleration, I have questions.

Okay...

 

[Sundance]

Hello Chalnoth

The link NASA/ESA has many images

Look at the observation and maybe than you will see what I'm trying to explain.

Expansion and acceleration is in spacetime.

Now look at reality.

You are trying to observe a clustering effect of all star objects.

This does not mean that expansion does not occur, this occurs at the same time throughout the universe. Eg Compact matter as in Black holes and exotic stars such as Neutron Stars in the formation of jets and ejecting matter.

 

[Chalnoth]

Hello Chalnoth

The link NASA/ESA has many images

Look at the observation and maybe than you will see what I'm trying to explain.

Yes, well, this is what I do for a living. And simply glancing at telescope images doesn't provide any significant information about the universe, except that it's pretty. You need to go much deeper than simply glancing at a few images to extract meaningful information.

Expansion and acceleration is in spacetime.

Now look at reality.

You're showing your bias right there. Spacetime is reality.

 

[Sundance]

Hello Chalnoth

Than explain the expansion and acceleration by observation.

I just do not look at nice pics, I also read astrophysics papers.

====================

So tell me about your work

 

[Chalnoth]

Hello Chalnoth

Than explain the expansion and acceleration by observation.

You've got things backwards. Observations do not explain things. Theories explain observations. And one possible explanation, that is so far consistent with all explanations, is that there is a small but non-zero cosmological constant.

So tell me about your work

I've worked on ways to distinguish between varying dark energy and constant dark energy, I've worked on estimation of the power spectrum of the cosmic microwave background, as well as foreground cleaning techniques for the CMB.

 

[Sundance]

Hello Chalnoth

Your work sounds fantastic.

What is the difference between dark matter and dark energy?

 

[Sundance]

Hello Chalnoth

May I have your opinion on this paper

http://arxiv.org/abs/gr-qc/0601033
A darkless space-time

Authors: A. Tartaglia, M. Capone
(Submitted on 9 Jan 2006 (v1), last revised 25 Apr 2007 (this version, v5))

Abstract: In cosmology it has become usual to introduce new entities as dark matter and dark energy in order to explain otherwise unexplained observational facts. Here, we propose a different approach treating spacetime as a continuum endowed with properties similar to the ones of ordinary material continua, such as internal viscosity and strain distributions originated by defects in the texture. A Lagrangian modeled on the one valid for simple dissipative phenomena in fluids is built and used for empty spacetime. The internal "viscosity" is shown to correspond to a four-vector field. The vector field is shown to be connected with the displacement vector field induced by a point defect in a four-dimensional continuum. Using the known symmetry of the universe, assuming the vector field to be divergenceless and solving the corresponding Euler-Lagrange equation, we directly obtain inflation and a phase of accelerated expansion of spacetime. The only parameter in the theory is the "strength" of the defect. We show that it is possible to fix it in such a way to also quantitatively reproduce the acceleration of the universe. We have finally verified that the addition of ordinary matter does not change the general behaviour of the model.