[Mike Gale]

Point taken, but Alan was obviously trying to distinguish vectors from numbers, not variants from invariants. With regards to energy conservation, Feynman's sticky bead argument (https://en.wikipedia.org/wiki/Sticky_bead_argument) seems to be the consensus view. The system does indeed lose energy to gravitational waves, which means they can be harnessed to do work.

[timey]

If a system can lose energy due to gravitational waves and these waves can be harnessed to do work, does the reciprocal of this mean that a gravitational wave on the scale of the LIGO event will add energy to a system (earth) that it hits (for the duration of the hit)?

[Mike Gale]

That's the idea. Unlike solar cells, it would work in the dark. But we're talking about very low power levels unless you get up close and personal with the source. Not nearly enough to heat your house or drive your car here on Earth. Not a practical means of communication either because you can't focus the beam or modulate the source signal. It might make a good accident avoidance system for intergalactic travel. I read somewhere that gravitational waves can travel between universes, too. I can't imagine a practical use for that though.

[PmbPhy]

Point taken, but Alan was obviously trying to distinguish vectors from numbers, not variants from invariants.

That was understood. That's why what I posted was a Note. Its intended to be in addition to something. In this case its to warn that when one comes across the term scalar that one understands what it really means in advanced physics and mathematics.

[Mike Gale]

Point taken, but Alan was obviously trying to distinguish vectors from numbers, not variants from invariants.

That was understood. That's why what I posted was a Note. Its intended to be in addition to something. In this case its to warn that when one comes across the term scalar that one understands what it really means in advanced physics and mathematics.

Agreed. Unambiguous terminology is half the battle. I experienced a prime example of that recently when I was schooled by a formally trained expert about the definition of the Schwarzschild event horizon. I thought it was a distance measured in Schwarzschild coordinates, but he said it is in fact the future of the causal past of future null infinity. How's that for terminology? Here's a good reference if you want to decode that definition: https://arxiv.org/pdf/0811.0354v1.pdf