Has this idea been explored? Why the universe expands

[twofish-quant]

The following are equivalent:
1) p=0
2) M=constant.
3) The Friedmann equation holds true.

The proof is in Semi-Riemannian Geometry by Barrett O'Neill (1983) p.351

I'll have to take a look at his book, but if he says that then he is wrong (and yes textbooks can be wrong).

6)How do we decide among them? We look at the R-W metric and ask whether there is a canonical (natural) constant rate of expansion associated with that metric. There is. Set dR^2=c^2dt^2. That gives us R=ct where R is to be considered the length of the past world-line of an observer.

Yes. At that point, you calculate redshifts, and find that what you end up with is nothing like what people are observing with supernova and other cosmological observations. We have a lot of precision data for what the universe looks like, and it's very "non-elegant."

That may be true but there is one thing to consider. Any interpretation of data involves assumptions, especially in cosmology. I think the theory I am proposing explains the redshift anomaly without resorting to 'dark energy'.

Right. The trouble is that it doesn't do that.

If you assume that the redshift is caused by something other than straight cosmological expansion, then you get into the dozens of alternative hypothesis for this in the 1960's. Google for "tired light." There's not a small number of people that have tried to come up with things that have nothing to do with redshift, and there are major problems with all of them.

I have tried to follow Occam's Razor - do not add unnecessary entities!

So has everyone else. The trouble is that reality forces you to add necessary entities.

I have proposed a theory that has no parameters but from which you can derive the Hubble Relation.

Which means that it doesn't match reality.

I admit it does require reinterpreting redshift somewhat. Instead of v=cz , I have v=cz/(z+1) and D=cz/H(z+1).

OK, then take a bunch of supernova and then tell me what the brightness/redshift relationship should be. My guess is that it's not going to match.

It's been fun and I'll leave you with the last word.

The basic problem with what you are doing is that you are trying to figure things out with "pure thought" and are not looking at observations at all. If you try to come up with a model of the universe by "pure thought". It's quite easy. The trouble is what happens when you try to match things with observations.

So here is an exercise. I have a bunch of supernova that have identical brightnesses. What is the distance redshift relationship of those supernova. I can tell you based on what you have said that it's not going to match, but all you have to do is to do a few google searches and make the graphs match.

If you can get the graphs to match without any parameters at all, that would be amazing, but I think you will have to add some parameters.

 

[bapowell]

The following are equivalent:
1) p=0
2) M=constant.
3) The Friedmann equation holds true.

The proof is in Semi-Riemannian Geometry by Barrett O'Neill (1983) p.351

Yeah, that's wrong.

If you can get the graphs to match without any parameters at all, that would be amazing, but I think you will have to add some parameters.

Yes, this.

 

[bapowell]

1)Is the p=0 assumption in the three Friedmann models necessary?

I strongly advise that you work through a cosmology textbook and derive the Friedmann Equations from the Einstein Equations. You will see that the Einstein Equations reduce to the Friedmann Equations given two assumptions: homogeneity and isotropy. If you believe that the universe is homogeneous and isotropic, and if you start with GR, then you must end up with the Friedmann Equations.

 

[twofish-quant]

On a positive note, you have all of the math ability to do cosmology. To get to the point where you are able to do useful cosmology work looks like just a matter of taking a course in cosmology, and that can be done in two months...

The two things that you are missing are:

1) knowledge about what the data is
2) knowledge about what has been tried and what is being tried

The good news is to get that knowledge will take you two to three months at the most.

The problem with what you are suggesting is that it has a "been there done that." What you are suggesting is "tired light". It's a model that was done in the 1960's and 1970's and there are a lot of nails in the coffin. In particular once you assume that light behaves in a certain way, lots of things start breaking...

http://en.wikipedia.org/wiki/Tired_light will start, and there are a number of review papers on non-standard cosmologies that will tell you wants wrong with them. Also with enough duct tape and pixie dust, you can get any model to work, but the goal is to get something to work with less duct tape and pixie dust than the current models.

One way out of the mess is to just assume "magic." There is something that magically adds pressure to the universe, but we don't know what it is. At that point we just call it dark energy and you end up where we are not.

The other thing you just can't do is make statements like...

Instead of v=cz , I have v=cz/(z+1) and D=cz/H(z+1).

You just can't do that without some justification. The behavior of distance and velocity come out of GR, and if you start messing with them, then you are saying that GR is invalid. That's not a crazy thing to say, but you have to say it. Once you claim that GR is invalid, then you have to come up with some alternative gravity theory, and there is an industry that is doing that.

Also something you have to realize is that when talking about supernova measurements, people really aren't talking about "distance" and "velocity". When people graph supernova measurements the lower axis is actually a "brightness." When people talk about "distance" in the context of supernova, they are talking about "the number that you get if you assume that 1/r^2 is true which we know that it isn't". When talking about redshift, they are talking about the size of the doppler effect.

One problem with GR is that there is no unique definition of distance or velocity at large distances, so you have to *define* what you mean by distance and velocity. You can come up with a definition of distance and velocity in which the Hubble law is perfectly true throughout the universe, but the tricky part is when you relate your definition to particular experiments.

 

[George Jones]

I'll have to take a look at his book, but if he says that then he is wrong (and yes textbooks can be wrong).

I know that Barrett O'neill is a very careful author, and I am somewhat familiar with the book, so I have had a look.

StateOfTheEqn isn't entirely accurate when StateOfTheEqn writes

The following are equivalent:
1) p=0
2) M=constant.
3) The Friedmann equation holds true.

The proof is in Semi-Riemannian Geometry by Barrett O'Neill (1983) p.351

Actually,

Lemma. Let $M(k,a)$ be a Robertson-Walker spacetime with $a$ nonconstant. Then the following are equilvalent:

(1) The perfect fluid $U$ is a dust.
(2) $\rho a^3 = m$, a positive constant.
(3) (Friedmann-equation) $a'^2 + k = A/a$, where $A = 8 \pi m/3 > 0$.

This is correct. I think that the problem is one of terminology. I think that Friedmann's original models probably were for pressureless dust, but now we lump everything together, including components with pressure, under the term FRW models.

 

[twofish-quant]

This is correct.

It is correct because O' Neill defines what he is calling the Friedmann equation. However, what O'Neill calls the Friedmann equation in that paragraph is not what cosmologists normal use for the term.

see http://en.wikipedia.org/wiki/Friedmann_equations

It's a different equation that includes pressure terms.

 

[leonstavros]

Why can't we assume that the universe is expanding due to centrifugal forces from a spinning universe. If we assume an hour-glass universe with one-half of it being a black hole and the other half connected with our "universe" but still part of the same hour-glass universe. As the black hole spins so does the other half(us). If the black hole universe starts feeding,it will speed up by the extra mass and therefore speed up the rate of spin on our half of the universe. As the rate of spin increases the centrifugal force increases making all the galaxies recede faster from each other.

 

[bapowell]

Why can't we assume that the universe is expanding due to centrifugal forces from a spinning universe. If we assume an hour-glass universe with one-half of it being a black hole and the other half connected with our "universe" but still part of the same hour-glass universe. As the black hole spins so does the other half(us). If the black hole universe starts feeding,it will speed up by the extra mass and therefore speed up the rate of spin on our half of the universe. As the rate of spin increases the centrifugal force increases making all the galaxies recede faster from each other.

Where is the center of rotation? The universe is highly homogeneous and isotropic on large scales -- we simply don't see what you're describing.

 

[leonstavros]

Where is the center of rotation? The universe is highly homogeneous and isotropic on large scales -- we simply don't see what you're describing.

The center would be the same place where the Big Bang occurred.

 

[twofish-quant]

Why can't we assume that the universe is expanding due to centrifugal forces from a spinning universe.

Because we don't see the universe rotating

http://arxiv.org/abs/astro-ph/0702381

A lot of these sorts of questions are like, "how do I know that the bus outside isn't turning into a tiger." Answer: I'm looking at the bus and it isn't turning into a tiger.

If we assume an hour-glass universe with one-half of it being a black hole and the other half connected with our "universe" but still part of the same hour-glass universe. As the black hole spins so does the other half(us). If the black hole universe starts feeding,it will speed up by the extra mass and therefore speed up the rate of spin on our half of the universe. As the rate of spin increases the centrifugal force increases making all the galaxies recede faster from each other.

But you'd see the universe in the direction of the BH to be different than the other direction, which is not what we see.

The basic problem is that you have

assumptions about how the universe works <-> conclusions based on those assumptions <-> actual data

the problem with going

specific assumptions -> conclusions -> data

is that unless you are unusually lucky, your assumptions are not going to match the data.

The direction people are going in

data -> conclusions -> what assumptions work and what doesn't

I look outside my window and I see a mystery, and since I don't have my glasses, I can't tell what it is. So I ask questions. Is it bigger that a car. No, isn't. At that point I know it is not an magic adult elephant, If could be a magic llama from Neptune, but I know it's not a magic adult elephant.

 

[bapowell]

The center would be the same place where the Big Bang occurred.

The Big Bang did not occur at a single location -- it was not an isolated "explosion" occurring within an already existing space. See Marcus's Sticky note on the balloon analogy to get a better understanding of how the Big Bang is viewed.

 

[leonstavros]

The Big Bang did not occur at a single location -- it was not an isolated "explosion" occurring within an already existing space. See Marcus's Sticky note on the balloon analogy to get a better understanding of how the Big Bang is viewed.

I'm confused, how then do we know how old the universe is? Don't cosmologists extrapolated the age and the center of the universe from galaxies receding at a certain direction and velocity?

 

[bapowell]

I'm confused, how then do we know how old the universe is? Don't cosmologists extrapolated the age and the center of the universe from galaxies receding at a certain direction and velocity?

The age can be approximately inferred from the present expansion rate,

$$t \sim H^{-1}_0$$

where $H_0$ is the present-day Hubble parameter. More accurately, the age is determined by starting with $H_0$ and evolving backwards in time with the Friedmann Equation -- the equation that governs the expansion of the universe. This requires a knowledge of the matter and energy content of the universe as well as its curvature. These quantities are given by the densities $\Omega_{M}$ and $\Omega_K$, respectively. Measurements of the cosmic microwave background (CMB) provide an accurate source of the latter two quantities; the most accurate value for the Hubble parameter presently comes from supernova data.

 

[George Jones]

It is correct because O' Neill defines what he is calling the Friedmann equation. However, what O'Neill calls the Friedmann equation in that paragraph is not what cosmologists normal use for the term.

see http://en.wikipedia.org/wiki/Friedmann_equations

It's a different equation that includes pressure terms.

Yes, I know. That is why I wrote

I think that the problem is one of terminology. I think that Friedmann's original models probably were for pressureless dust, but now we lump everything together, including components with pressure, under the term FRW models.