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View Full Version : Thoughts on Fulvio Melia's R_h = c t "Cosmic Spacetime" theory?



IsaacKuo
2012-May-16, 02:03 PM
I'd like to hear opinions on this arxiv paper:

http://arxiv.org/abs/1205.2713 - The Cosmic Spacetime - Fulvio Melia

Melia claims a shockingly simple formula where the universe's gravitational radius at any point is always equal to ct. He bases this on a combination of the cosmological principle and the Weyl postulate.

Is this a far out idea? Or is it an interesting idea consistent with the mainstream? I'm honestly curious, since I don't really comprehend cosmology theory much beyond layman's terms.

Thanks!

TooMany
2012-May-25, 05:25 AM
According to the author it eliminates the need for inflation (but I certainly don't get it yet). If workable, it would be a big improvement in BBT.

Shaula
2012-May-25, 06:12 AM
Some observations made as I read it:
1) Planck units are not reliant on the Schwarzchild radius. They both contain fundamental parameters only so it is not surprising at all that you can make up an equation which includes it, but you can equally make up one without it.
2) References? Lots of assertions, few references. Poor for a paper. (6 references, 2 himself, one from 81, then two relatively recent ones)
3) His use of Birkoff's theorem must be too subtle for me or very weak.
4) Positive and negative KE? No idea what he is talking about there and because there are not references and it is a throwaway comment, no real hope of getting an idea.
5) The 'amazing coincidence' is basically stating that on average the universe has expanded at a constant rate. H0 is derived from observations of many times and is a measure of this that is heavily skewed by the fact that we can mostly observe the far simpler, recent era.
6) We derive his t0 using H0 so I am rather underwhelmed by the fact that they seem to be related.

I really don't see much in this paper. It appears to be saying something like:
On a long motorway journey cars move at on average 70mph. So if I take the journey time (2 hours) and look at the distance travelled (130mi) I can find this amazing coincidence - that 70 x 2 is nearly equal to 130! This is amazing. In fact it makes me think that all cars must satisfy the equation s = 70t. I mean, people postulate that at the start of the journey the car might have had to speed up from rest but really, what are the odds? What are the odds that the car did all this complex manoeuvring and yet still, today, seems to fit this simple equation s = 70t?

Maybe I am missing something subtle - hope that someone can come along and enlighten me.

TooMany
2012-May-25, 04:31 PM
I don't get it either, but he has some graphs trying to demonstrate something, but what?

caveman1917
2012-May-25, 07:52 PM
On a long motorway journey cars move at on average 70mph. So if I take the journey time (2 hours) and look at the distance travelled (130mi) I can find this amazing coincidence - that 70 x 2 is nearly equal to 130!

You probably mean something like "their average over the last 20 minutes was 70mph".

caveman1917
2012-May-26, 05:33 PM
I'd like to hear opinions on this arxiv paper:

http://arxiv.org/abs/1205.2713 - The Cosmic Spacetime - Fulvio Melia

Melia claims a shockingly simple formula where the universe's gravitational radius at any point is always equal to ct. He bases this on a combination of the cosmological principle and the Weyl postulate.

Is this a far out idea? Or is it an interesting idea consistent with the mainstream? I'm honestly curious, since I don't really comprehend cosmology theory much beyond layman's terms.

Thanks!

In comoving coordinates the gravitational radius is a constant because the enclosed mass remains constant in some constant volume. Likewise the hubble sphere given by ct is in comoving coordinates nearly constant because it depends only on the hubble constant (which changes slightly but not that much). So that a relation of the type r_g \approx k r_h exists is trivial. The point that you can make k=1 is a unit thing, so not all that surprising.