14 Jul 2016 0:59:58 UTC

Topic 198690

(moderation:

Can anything block a gravity wave? Can gravity waves bounce off of something, and reflect back in the opposite direction? Would the direction reversal create a gravity undertow? Would the undertow seem like antigravity?

When gravity waves intersects with a massive object is something like a standing wave you see when a river flows around a rock created?

Could two gravity waves of the same strength with opposite periods cancel each other out if they intersect?

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## Can Gravity Waves Be Blocked or Reflected

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Nope.

If you mean bounce/reflect as in absorb and re-radiate then in practice no ( to any significance ).

Nope as above.

I'll have to think about whether such an analogy could hold.

In what is called the low field regime ( Earth & hereabouts ) then yes. It is linear. So at the GW detectors very many things are wiggling the gadget and if you exclude non-gravitational reasons, then the remaining signal is the sum of possibly very many influences. So the data segment that gave the good match for the GW150914 event would also contain elements of other unrelated GW generating phenomena. At first this might seem to be an insurmountable annoying problem, but it is not radically different in principle from distinguishing different voices in a room full of people.

Mind you if the scenario is identifying different voices in a sandstorm then that is a more serious challenge. What we seek are non random regularities over and above unrelated noise. The key aspect here is the time frequency of the signal component(s) of interest. Which explains why a chief parameter of the E@H workunits ( all types ) is the frequency we match for with a certain template ( a guess at a prospective signal ). For these types of tasks the signal power of interest is but a fraction of the total power recorded by the instrument. That forces the use of what are labelled 'long integration times', meaning that as the data segment is lengthened the chances increase ( unfortunately only varying like the square root of the time ) that a true signal will become more obvious. For example if you want to be twice as sure then you have to analyse for four times as long! The random influences ( by definition ) will increasingly cancel each other out as we go longer. A legitimate analogy here is the water at a seashore : the waves come and go but if you are patient the tidal variation will be revealed.

{ The mathematical aspect is pretty gorrible, you are welcome to browse my Fourier Stuff threads to confuse yourself more .... :-))) }

Cheers, Mike.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## RE: Could two gravity waves

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By "opposite periods" you mean "180 degrees out of phase of equal effect" or simply, each is the inverse of the other...

Then by my intuition (sorry, too lazy to add up the maths :-) ), then I suspect yes, the gravitational wave effects can cancel out to zero.

However, note that is for the strain effect (stretching/squishing of space and time) on space-time.

That does not say that we have any kind of "anti-gravity" (as known at present...).

To answer again with one word removed:

Note that we see directly such an effect for gravity (note the difference to "gravitational waves") whereby the ocean tides on Earth vary in strength depending on whether our moon aligns with the sun to reinforce or negate the effect of the sun's gravitational influence.

Sorry, but that still is no sign of any 'anti-gravity'...

It's all geometric! (All the way down? :-P )

Keep searchin',

Martin

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