## Sunday, 18 August 2019

### Common sense tells us that effect of gravity moves at the speed of light

This appears to be an open question; it wasn't until 2002 that they were fairly sure and very recently (2017) that they established that, "assuming a delay of zero to ten seconds, the difference between the speeds of gravitational and electromagnetic waves, vGW − vEM, is constrained to between −3×10−15 and +7×10−16 times the speed of light."

I would have thought it was easier to apply common sense.

The light we see from the sun arrives from where the sun was 8 minutes 20 seconds ago (assuming for simplicity the earth is stationary and the sun moves round it).

If you measure the direction in which the earth is being pulled by the sun, you'd establish that it is being pulled towards where the sun was 8 minutes 20 seconds ago.

The light meter and gravity meter will be pointing in exactly the same direction; if not, there'd be all sorts of apparent weird wobbles (which would make measuring distances and so on a lot easier, as it happens).

And well done to these chaps, while we're on the topic. Instead of chasing non-existent Dark Matter, they are actually measuring and observing exciting stuff that actually happens.

Dinero said...
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Dinero said...

The two opposite ends of a non compressible rod move together with no time lag at all, ie faster than light, and so recognising that and applying it to gravity there is no fundamental reason to postulate that gravity requires a time for affect over distance, ie does not require gravity to have a characteristic speed

Mark said...

The two opposite ends of a non compressible rod move together with no time lag at all,

Not true.

One atom moves because another moves, and the action is electro-magnetic for attraction and repulsion of atoms.

Unless you think the atom at the far end of the rod "knows" which way to go, it has to wait for the information to get to it. At the speed of light.

M, thanks, saved me the bother.

Dinero said...

Yeah OK .

Come to think of it, the the whole uncompressed rod would have to move faster than light, with instant acceleration. So no instantaneous communication with the rod.

View from the Solent said...