surreptitious57 wrote:How can the existence of branes be falsified if they are impervious to light ?
Branes can't be falsified by these observations, but the brane-worlds cosmology can. I still haven't had a chance to see if the data impacts it in any way. I get the impression that the observations used only deal with polarisation, so not sure this is going to impact brane-worlds, but it is of course the first experimental observation of gravitational waves, so now we know they're there.
As for how it would be falsified, it's about the mechanism for the instantiation of the cosmos. In inflation, the gravitational waves result from the expansion of spacetime, but they are themselves stretched by the expansion, so their energy is shifted toward the red end of the energy spectrum (just like light waves are shifted toward the red by expansion). In brane-worlds, the gravitational waves are occurring
on the brane itself, which is not expanding, so the waves are expected to be further toward the blue end of the spectrum.
And what exactly is a brane anyway ? I understand it to be multiple dimensional space separate to but part of a larger brane world [ in the same way that a
card in a deck is separate to but part of the deck ] What would be required to cause a brane to come into existence ? Do branes exist inside universes or universes inside branes ? [ I am assuming the latter ]
Not sure that a brane would be required to 'come into existence'. As for what a brane actually is, it's a construct from M-Theory, which is the unification of all the string theories along with 11 dimensional supergravity. In string theory, all the particles are made up of tiny vibrating strings, one dimensional filaments that vibrate in various patterns, and come in open and closed forms. The closed forms are loops of string. In M-Theory, strings still exist, but they form part of a larger landscape of branes (short for membranes, and generally referred to as p-branes, where 'p' refers to the number of dimensions they have). So, a string is a 1-brane because it's 1 dimensional, but you can also have 2-branes (sheets) and 3-branes, etc. So branes are polydimensional strings. In the brane-world, our cosmos resides on a 3-brane. All open strings have their ends tethered to the brane, which means they can't leave the brane they're on, while closed strings are not, and can travel between branes. Photons are open strings, so they're tethered to the brane they reside on, but gravitons are closed strings, which means that gravity can be felt between branes.
Our 3-brane is separated from another 3-brane by an additional dimension of space. The Big Bang occurred when these two 3-branes slammed together. There is, in this model, another cosmos, much like ours, residing on the other brane. Since gravitons can travel between branes, we feel the gravity of the matter on the other brane but, because photons can't travel between branes, it doesn't react electromagnetically in our cosmos, so we can't actually see it anywhere in the electromagnetic spectrum - dark matter.
If the Multiverse hypothesis is falsified by inflation
Well, it's important to be clear what we mean by 'multiverse hypothesis', because there are several hypotheses, and they're extremely different. Under the 'eternal inflation' proposal, inflation is required, so this observation supports a multiverse in that instance. It has no real impact on other multiverse hypotheses.
then does that mean the Big Bang can no longer even be hypothesised as the exact point at which the Universe began ? [ Universe is synonymous with Multiverse here so I mean in all space not just local space ]
In the eternal inflation model, we're just a black hole inside another cosmos. In reality, this doesn't impact any of that, because the observations only support (with the caveats concerning blue shift given above) a post-Planck cosmology at this point. We're still in a standard inflationary cosmology at this point, which is to say that it's the standard BB model with the modifications made by inflationary theory.
Would the laws of physics be different in each one or would they be the same ?
Hard to say at this point. There's Lee Smolin's 'cosmic selection' hypothesis, in which each cosmic expanse that's pinched of from a prior cosmos would inherit the laws of the parent cosmos with slight modifications (yes, a proper evolutionary theory applied to the cosmos), but in reality, I think such things are speculative. I still see no reason to suppose the laws of physics can actually be any different.
If inflation means the Multiverse is in a constant state of expansion does this not invalidate the Second Law Of Thermodynamics ?
Well, that's what some apologists would like to think, which is why they're always running around screaming 'BVG Theorem' at the tops of their lungs as if they know what it implies. In reality, we would need to know the details. It is simple enough to imagine that the formation of the black hole that constitutes the birth of a new cosmos could reasonably bring about the extreme low entropy conditions required. The simple fact is that we have no idea of how to apply the 2LT to the cosmos, and indeed, if eternal inflation is correct, the the cosmos is not an isolated system. It's a closed system at best, and possibly an open one, in which case we can forget about the implications of the 2LT in this regard. It's why I always advise people not to erect thermodynamic arguments to cosmology, because they're always fallacious. I only refer to thermodynamics in this sense to shoot down other references to thermodynamics in this sense.
Would every Universe in the Multiverse be expanding beyond c and would that speed be identical in all of them or different in each one ?
Unknown. My feeling is that
c is constant in all cosmic expanses, because again, there's no reason to suppose that the laws of physics could actually be different.
For more info on 'brane-worlds', read Neil Turoks excellent
The Elegant Universe. Also
Cali's excellent expo of the original papers can be found
HERE.
Hope some of that helps.
Now to have a shufty at the links
Pulsar kindly provided.
Johnny 5 need input!