Quote:
Originally Posted by g__day
New Scientist has a great article this edition that looks at the current models theoretical physicists. In essence it repeats what I have said above (no I didn't read it first).
Basically
1. Einstein had horrendously complex equations to solve in relativity
2. He imposed two field constraints to solve them - he said on large scales the universe is homogeneous and isotropic
3. The background radiation studies COBE - and SLOAN Sky surveys shows us that the homogeneous call isn't too bad (although galaxies right up to super clusters tend to show a surprising fractal structure out to a range where they shouldn't (no organising force should have been able to propogiate to 1 million light years or beyond to enforce such observed structure)
4. Examine of type 1A supernovae - a standard candle - showed the Universe appears to be must bigger than we though, especially at far distances - implying if Einstein's two constraints are correct the expansion of the Universe must be accelerating in the last few billion years
5. Dark matter and dark energy are suggested as altering mechanics to this framework to allow it to fit with what we see without changing the underlying model and its two constraints.
The misfit is so large, the basis for the two initial constraints are so arbitary and the lack of a clear model that encompasses dark matter and forces is so vague that a serious group of high end theoretical physicsts are questioning these two initial constriants - asking what slight (or large modification of them) would give us what we observe today with minimal disruption to the standard models and relativity.
Turns out one small change to isotropic would account for what we see without the need for dark matter or energy. Our Hubble sphere is not common and representative - its a bit of a bubble, or put a common way its an underweight weakling (density wise) and its surrounded by more massive, (and more representative of the average density of the entire Universe beyond what we can see).
So if our corner of reality is lighter than average - no need for exotics - gravity drag of the rest of the universe beyond our bubble would explain what we see with conventional physical frameworks.
I like simpler over complex!
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Homogeniety and isotropy are not restraints but postulates for cosmology. Changing the isotropic nature, essentially destroys the mathematics of space-time expansion.
(
http://en.wikipedia.org/wiki/Friedma...-Walker_metric).
The RW metric extends outside the Hubble sphere to the entire Universe. So even a slight change to isotropy (what ever that means), brings down the entire model.
As the Hubble sphere is the observable Universe, we cannot make any comparisons between what is inside and outside the sphere. Anything outside the sphere is pure speculation.
Seems we are making the Universe more complicated.
Regards
Steven