I was told that there are two kinds gravitational waves. One dies out as 1/r, another one dies out as 1/r^2. The former is what LIGO detected, the latter is not. While I trust the professional qualification of the person very much, as a non-physics professional, I would like to a second person to confirm that. The following is the context of the conversation I had:(adsbygoogle = window.adsbygoogle || []).push({});

Me:

As a non-physics professional, what I am more interested is not GW but what we can learn from GW about the nature of spacetime. Now we have already learned that spacetime can be curved by a mass...we also know that the change of curvature caused by a mass could be propagating at a finite speed of light....

Now if there is a Frequency of a GW and the frequency could be independent of any oscillating source like the characteristic frequency of a matter, then it means that the spacetime also could RESIST the change of its curvature created by mass.....but now the following answer from Jorrie asserts that it is NOT the case:

There will be no GWs seen in the math unless some or other deforming mass is present, at least symbolically, e.g. the mass is just seen as M (or as M1 and M2 in the case of binaries).That is an important assertive information to me :) Thanks a lot.

However, I am still having some concern about the following statement:

The events creating GWs must be oscillating events of a certain type, i.e, in ordinary language it must be changing from "short and fat" to "long and thing" repetitively, at least for some time.as I understand that the spacetime is curved by the presence of a mass....so when the presence of that mass changes (e.g. increase of value or change of location), the curvature in spacetime created by it would change as well...and this change is NOT instantaneously but propagates out at the finite speed of light......Therefore, it seems to me, even if there is just ONE SHOT of change (hypothetically at least) , the change still should be transmitted out at the speed of light, but without any wavy rippling (unlike in a medium of matter like water)......Please correct me if I am wrong.

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RESPONSE from JORRIE:

Yes, any change of the mass distribution will cause a change in curvature that will spread out at 'c' in all directions. This is gravity that changes, not GWs. A good example is the tidal pull of the Moon on Earth that has a period of somewhat over 12 hours. So it is a 'wave', but not a gravitational wave, which has a specific mathematical definition in relativity.

In fact, the Earth/Moon system does emit tiny gravitational waves, but only from somewhat outside the orbit of the Moon. An observer there will obviously see the orbiting system as an alternating "thin body" and a "fat body".

These tiny ripples travel outwards at 'c' and the amplitude fall off with inverse if distance (1/r), while the tidal gravity is a shorter range range phenomenon, because its amplitude falls off with the inverse square of distance (1/r2).

Tidal gravity is much larger than GWs at smaller distances, but there is a point outside the Moon's orbit where the amplitude of the tidal gravity will become smaller than the amplitude of the GWs. This is more or less where gravitational waves is said to originate.

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Regards

Jorrie

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# I About gravitational waves

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