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Robh
20-08-2009, 08:47 AM
Scientists haven't detected gravity waves yet but are happy with the results so far ...
http://www.newscientist.com/article/mg20327222.900-gravity-wave-detectors-home-in-on-their-quarry.html

Rob

renormalised
20-08-2009, 09:09 AM
You always manage to get one of the loony fringe putting their two pennies worth of inane comments into something like this, and this article got one of them as well....sheesh!!!!:screwy: :rolleyes:

sjastro
20-08-2009, 06:47 PM
I'm trying to work out how gravitational waves and Inflation fit into the same picture.....

Steven

renormalised
20-08-2009, 07:48 PM
When gravity froze out from the other three forces just as inflation began.

You could imagine that when the initial symmetry of the universe was broken, that may have produced rather large gravitational disturbances that inflation smoothed out. Remember, according to theory, the cosmological constant at the time was highly non zero, so gravity may have been predominantly repulsive instead of attractive. Inflation would have been driven by this, however in the process of inflation, the expansion would've greatly reduced the initial value of the constant, hence the effects of gravity (or it's antithesis if you consider it not to be gravity, per se).

sjastro
20-08-2009, 09:22 PM
Inflation was initiated by the separation of the nucleur from the electromagnetic/weak forces, gravity was already a separate force.

The cosmological constant is not tied to gravity. The "nuts and bolts" of inflation involves the collapse of a false vacuum into a lower energy state with the subsequent release of energy and expansion of space-time.

From a GR perspective gravitational waves are formed by a change in space-time geometry. This can only if occur if there is a change of mass such as the merging of black holes or a supernova.

During the inflation period the change in space-time geometry is due to simple maths. Assuming spherical symmetry the curvature of space-time is inversely proportional to the square of the radius of the Universe.
A large percentage increase in radius during inflation would have caused a significant flattening of space-time.The Universe at this stage was very much dominated by radiation instead of mass and this is what I am struggling with.

How do you get gravitational waves at this stage of the Universe when mass as we know it only came into existence approximately half a million years later.

Regards

Steven

skwinty
21-08-2009, 02:53 AM
Hi every one,
Been away for a long while but am back again.
Gravitational waves are distortions of space. If you wave a stick around you will cause gravitational waves albeit very tiny ones. When we look at the universe through a telescope back to the 380,000 year mark (after the big bang, we can't see past this mark because the universe was so hot and dense. The universe was opaque then.

The only radiation that can pass through this opaqueness is gravitational waves. If inflation is true, then inflation would have caused a special warp of space due to it's exceptional size and shape. If we eventually manage to detect gravitational waves, they can tell us whether inflation occurred or whether the universe is cyclic. (ie a gentler process)

Inflationary models predict that gravitational waves should be the cause of about 40% of the hot and cold spots of the CMB. The gravitational waves would also have an effect on the polarization of the CMB.
This would show up as E-mode and B-mode patterns similar to electromagnetic waves.

So far we have not had much success in detecting these waves, but when we do, much new information will come to light regarding inflation and or the cyclic (Ekpyrotic universe). This is how I understand it any way.:thumbsup:

Also, remember that energy has mass, and there was a lot of radiation energy. (The Universe at this stage was very much dominated by radiation instead of mass)

renormalised
21-08-2009, 09:32 AM
You're right there...my mistake:P I knew it was symmetry breaking that drove it, just got the two occurrences mixed up:P:D

I was reading in some of the papers...can't remember which, but they believe that the CC was acting much like a form of gravity, except in the anti sense. Probably not strictly correct, though.

Remember, mass and energy are interchangeable and in the conditions that occurred in the early Universe, that energy would've had extremely high density. That alone, would've produced gravitational effects as the energy would've essentially been massive....i.e. acted as mass would.

It would mean that photons and whatever else that was around at the time that constituted the energy budget of the Universe must've been interacting with the Higgs field in some fashion, or maybe under such extreme conditions Higgs bosons act much like photons. Don't ask me how, I'm not Stephen Hawking!!!!. It would mean that the Higgs Field must've come into existence either prior to inflation (maybe when gravity froze out) or during inflation. Now, what they have to do is find the Higgs. Anyway, enough of the conjecture:D:D

sjastro
21-08-2009, 11:27 AM
Energy on its own won't contribute to gravitational waves. Energy converted to mass or vice versa will.

And here lies the problem......
If such an event occurred in the Inflation era we would not be able to measure it as gravitational waves do not exceed the speed of light.

The event is beyond the observable (measurement horizon) of the Universe and will remain so due to the acceleration of space time.

Looking for gravitational waves in the CMB is taking us back to the recombination era about 300,000 years after the end of the inflation era.

Perhaps the article is confusing the CMB as being a product of inflation.

Steven

renormalised
21-08-2009, 12:05 PM
Energy would probably act like mass if the density of the energy were high enough, as it would've been in the very early Universe. Ordinarily it wouldn't. The conditions would've had to have been very extreme in order for it to do so. The problem, though, is as you stated it. However if what they're saying is correct then there must be some mechanism by which we can measure it, despite of inflation. What that is, I don't know.

If there was the influence on the CMB by gravitational waves generated during inflation, then you could expect to see the influence in the smoothness of the CMB. Those gravitational waves would still be present. You'd expect to find minute temp' differences in the CMB as the gravitational waves influence the motions of photons and the density of the Universe at any particular point. But then you still have the thorny question of the rapidity of inflation...makes for a bit of a conundrum!!!.