2003-01-24 – Measuring the speed of gravity

Two weeks ago, it was reported that the speed of gravity had been measured by a team of two scientists, one a theoretical mathmatician, and one an astronomer. It came out as the speed of light.
(The Proposal and the Results.)
This week, it seems that they got the equations wrong, and accidently measured the speed of light, rather than \”gravity waves\”. (Counter-arguement)

The determination of the \”speed of gravity\” is a very big thing, as it will strengthen the case for Lorentz Relativity being more correct than General or Special Relativity (Paper explaining existing evidence for LR over GR/SR -1998 updated 2002) and may cause a few long-held debates to be settled, including the existence of \”dark matter\” which astronomers have never seen, and no-one has ever detected (in spite of hundreds of millions of pounds worth of research), and still doesn’t explain all the data and observations, but is used to explain/fudge why the galaxies we see in the sky don’t fly apart under their own rotation. The more likely answer is that Lorentz Relativity is more strictly correct the General Relativity, as it includes terms for the long range gravity effect that would explain the structure of galaxies, and do away with the complex corrections for time dialation involving vectors, which are experimentally wrong.

So it is a big issue. As ever, I propose an answer.

I am now going to outline a fairly simple, though quite expensive, experiment that could easily be set up, in order to determine the answer to the question, \”Is the speed of gravity the speed of light?\”.

From my reading of the evidence, we were all lied to in school, and even at university, where my physics degree simply assumed that the speed of gravity was the same as the speed of light, without ever telling us that assumption even existed. Then you read a little of the arguement, and you find that whenever orbital mechanics is being worked out, the speed of gravity is an absolute infinite speed, or the calculations don’t even begin to agree with the observations of the universe, even down to the stable orbit of our satelites, both natural and man-made. However, the existence of some form of already existing, stable gravitational field may preclude this from disproving the \”speed of gravity\”, since the gravity is already there, as it was being \”emitted\” beforehand. Of course, that basic theory falls down when the objects are moving fast enough that they are in an obviously different place when you get to see them, than when they were \”emitting\” from where they were. (Think of the position of the sun in the sky – we see it where it was when the light left, yet the earth is being pulled towards where the sun will be when we look in about 8 minutes time i.e. where the sun actually is now, and not \”now\” in the relativity sense of the word, but now as in instantly!)

So, anyway, we want a hard experiment to look at on earth, to test these things a little more human-scale. So…

Get a mine shaft, a really deep one, or else use a mountain with a tunnel. Whatever.. We want a really big thing that isn’t going to do much over the one second scale, and we want as big a distance as possible. A building wouldn’t be good, since things would be moving all the time on the floors, etc. and the height wants to be as big as possible. Miles if at all possible.

South Africa would be a good place to try this, since they have the deepest mines in the world, the East Rand mine, the world’s deepest, at 3585 m below surface. The Western Ultra Deep Levels, affectionately known as ‘Wuddles’, is planned to go down 5km in the next few years.

Of course, we want the greatest drop from the surface, so other places night be even better.

Next, we get a really big weight. A big truck full of rock would be good, and easy to find. Even better would be an enormous disc of very dense material, such as gold(!) or depleted Uranium (that would be very dense!) which could be put in place. Now, we already have gravitometers that are sensitive enough to detect a change in altitude of less than a metre, so we get two of them, and we check them, and make sure they are as identical as possible. This simply cuts down on the errors we might get.

Now, on the next floor of the mine, we install one of these machines, and we rock the truck back and forth to make sure it is picking things up. Next, we go to the surface, and install machine two, directly above the other machine and our big moveable mass. Now, we move the mass back and forth. Ideally, it would be above 50 tonnes, and it would be on a nice spinner, so we can get a very accurate reading of where it is, and a nice signal for our detectors, which would sweep up and down rather nicely. Now, connected to the two gravitometers are data loggers, with very accurate time-synced clocks. These keep a track of the readings of the gravitometers rather well, for comparison later. After a few hundred rotations, which would be apparent on both machines’ readings, we get the time clocks/data loggers, and which them over, and repeat the experiment. Next we swap the whole set-up, so that the low gravitometer is now the high one, and vice versa, and repeat the whole experiment again.

Now analysis of the data will show that the time it takes for the lower machine to begin to react was exactly the same as the upper machine, to better than a few microseconds (preferably nanoseconds), or, that there was a delay which corresponds to the time taken for light to travel the ~5000 metres, which would prove gravity was moving at 3×10-8 m/s.

That delay would be about a sixty thousandth of a second (~15 microseconds) which should be easily detectable.

Of course, the beauty of my system is, that the gravitometers don’t need to be fast acting, so long as they react at about the same rate. Swapping them over and averaging the results gives us a pair of virtual machines, which reacted at exactly the same rate to the changes, so a quick look at the time stamps on the data should give us an answer.

And we don’t need to worry about accidently measuring c!

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