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In the course of this very enjoyable press announcement, it is mentioned that inflation can create gravity waves by amplifying gravity fluctuations.

I do not properly understand this statement. I always thought that quantum fluctuations (fluctuation of the metric in this case?) should occur pretty randomly whereas waves are rather coherent motions.

So I understand somehow that inflation can amplify quantum fluctuations, but I don't see how it can convert these random "microscopic" processes into "macroscopically" observable coherent phenomena called gravitational waves. For example, how are the sources of these gravitational waves distributed? Does each point in space-time behave as some kind of a point source? And what is observed at a specific point as the superposition of all these excitations?

In addition, in the same video it is said that not all inflation models produce gravitational waves, the ones that have them are favoured by the data now, etc.

MycrofD
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Dilaton
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    This question may get attention over at http://physics.stackexchange.com/ – David H Mar 24 '14 at 15:00
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    I don't think the title of this question makes much sense. Inflation doesn't cause gravitational waves, inflation blows them up to macroscopic scales. – astromax Mar 31 '14 at 00:59
  • I think the questioner is expecting the waves to be regularly periodic like waves coming in on a shore (the expectation that there is some coherence) but I can't see any evidence of a claim that the waves are coherent. A single pulse travelling is a wave, but it isn't coherent. – Jeremy Apr 07 '14 at 10:48
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    Surely what it means is that waves seen at the very earliest moment are, in a sense, "frozen" into the universe's "shape" by inflation? – adrianmcmenamin Apr 17 '14 at 11:35
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    I'm sure there are people here who could answer it, but this is more of a question for the Physics stack. – Florin Andrei Apr 23 '14 at 16:30
  • the most likely waves have a typical scale ($\pi/50$ or so) just like the way likely waves on the sea would have a typical scale (set by e.g. the strength of the wind). It does not mean all ways have exactly that scale, but visually that scale dominates; 2) the waves were minuscule to start with, but have been blown up to gigantic scales by inflation (hence the name!).
    • – chris Apr 23 '14 at 19:35