# Were gravitational waves "stronger" long ago?

1. Feb 23, 2016

### Gerinski

In order to detect gravitational waves at our present time and location, aLIGO has required a mind-boggling sensitivity, if I understand well it can detect variations in length in the order of 1/10,000 of the diameter of a proton.

But space has stretched a lot during the universe's history. If I am correct in assuming that gravitational waves redshift in the same way as EM waves, one should expect that the same sort of gravitational waves we have observed now as so weak, if they happened 8 billion years ago, and therefore closer to us, when space was much more "compact", might have been much more easily detectable, they had not yet redshifted. They might have caused a length variation which was detectable more easily back then, and it's only because space has stretched so much that they are so difficult to detect now.

Is this reasoning correct?

And if so, what could that mean if gravitational waves had "macroscopic" effects very early in the universe, because space was still very "compact"? Could gravitational waves have had any influence in the way the universe developed? I mean for example, the passing of a gravitational wave in our epoch on a complex molecule will not change anything, the distance variations it causes are far too small for any interactions between the subatomic particles to vary.

But let's say very early in the universe, a very strong gravitational wave passed a complex molecule and the distance variation it caused between its subatomic particles was enough for the particles to lose their bonding, they became loose from each other and the molecule was broken by the gravitational wave.

Does this make any sense?

TX !

2. Feb 23, 2016

### phyzguy

The gravitational waves detected by LIGO were at a redshift of z=0.09, so they have only redshifted by 9% since they were emitted.

3. Feb 23, 2016

### bcrowell

Staff Emeritus
Like any spherical wave pattern, the gravitational waves aLIGO detected had an intensity that fell off as $1/r^2$, because the energy is getting diluted over a larger and larger area. There is also a cosmological Doppler shift on top of this, but as phyzguy pointed out, that's a relatively small effect.