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I feel I should try to know more about this and possibly grasp some understanding of how it works.

Anyone have a link to a "LIGO for Numpties" page?

It's okay, 20 minutes later and the wonder of the t'interweb, got it now. ;D

Edited by bingevader
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Ben, try these:




As mentioned in my previous post, LISA Pathfinder has been a spectacular success - but I don't think the Wikipedia page reflects that yet.

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Ok, so I had it 2 hours ago and now I've lost it.

Temporarily misplaced, probably with my marbles.

The wonders, delights and then pitfalls of t'interweb! :D

I don't like the use of "ripples" and analogies to ponds when talking about gravity, because they give the impression we are talking about longitudinal waves and not transverse.

However, here's my problem (numpty or otherwise ;) ).

We know that light is affected by gravity, because we can observe it in gravitational lensing.

Why then, isn't the light from the laser in the LIGO experiment affected by the gravitational wave in the same way that the arm of the detector is?

Surely the light waves should be compressed in the same way as space/time is and so come out at the same relative time as the other arm?

I also don't like the rubber sheet and marble analogy for gravity bending space/time as we're only able to picture it in 2D.

However, as in gravitational lensing, the analogy suggests that light can't skip passed the gravitational wave, but must continue in it's straight line following time/space.

If this is the case, then shouldn't the light still travel the same distance in space and time at the same speed?

I'm happy to accept that I have all of this incorrect and would be delighted if someone can put me straight.

Brain Ache! :D


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Sorry, more reading, more brain ache (but I am quite enjoying it)!

Haven't been at this all this time mind you!

Been cleaning the house, but my brain has been trying to fathom it out all this time, and I think it must be beyond me! :D

The Caltech LIGO site suggests that the answer is simply that the speed of light is a constant, and they're the chaps and chapesses who should know.

Space/time is compressed by the gravitational wave, light continues at the same speed, so it gets there quicker, simple!

However, space/time might be compressed, but aren't the arms still 4km long?

Doesn't light still have to travel those 4km at the same speed?

How can it get there quicker unless it's travelling faster than the speed of light?!

My apologies.

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Ok, got it now, Special and General relativity, you could have told me it was that obvious.  :rolleyes2: :D

Special: The results of special relativity hold only as long as we are able to disregard the influence of gravitational fields on a phenomenon.

General: The velocity of light appears to vary with the intensity of the gravitational field and in the presence of a gravitational field the speed of light becomes relative.

Thanks all for your patience.

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Great achievement, and to think it's only taken 18 years (since LIGO first became operational) and between 1/4 and 1/3 of NASA's budget each year plus a major upgrade in 2010 to detect them. And those silly scientists 18 years ago, saying they expect to detect about 100 gravity waves per year :icon_rolleyes:

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