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Gravity waves (so please wave back)

There are some ripples passing through the science community and it's all because of gravity.

Einstein theorised that gravity waves should exist but to date, we've not been able to detect them -- or have we?

Back in September of 2015, Lawrence Krauss raised the hackles of more than a few in the physics community by whispering (on Twitter) that these waves had been detected by the Laser Interferometer Gravitational-Wave Observatory.

As events unfolded, it began to appear as if there has been some evidence collected to support the detection of gravity waves but those involved are still a long-way short of publishing a peer-reviewed proof.

So why all the fuss about gravity waves?

Well for a start, the detection of these theoretical waves would be yet another point for Einstein and the robustness of his theory of general relativity.

However, the really exciting thing would be the potential to use gravity waves as a method of communication and another tool for analysing the universe in which we live.

Gravity waves are pretty simple to visualise. If you use Einstein's analog that the ether is like a giant sheet of rubber stretched and supported at the edges then any mass sitting on that sheet will distort that sheet and, in doing so, create gravity. The greater the mass, the more it causes the rubber sheet to sag and thus the more the attractive force (gravity) any other items on the sheet experience.

This analogy however, explains only the static relationship between mass and gravity. To understand gravity waves there needs to be a dynamic component -- either a change in mass or a movement of the mass.

If the mass of the object which was distorting the rubber sheet was to be increased and decreased then obviously it would rise and fall against the tension of the rubber and this would create ripples in time/space (ie: gravity waves) that would radiate out from the mass in the same way that ripples radiate from a stone thrown into a pool of water.

Of course changing the mass of an object is very difficult -- requiring a lot of E=MC2 stuff which means huge amounts of energy are involved.

A much easier way to create gravity waves is simply to move the mass around -- just as you might shake a stick which has its end in a pool of water. The result will be (again) ripples or (in the case of space) gravity waves.

The big problem of course has been detecting these waves. Gravity is a "weak force" and those objects with sufficient mass enough to create sufficiently large waves that our primitive technology can detect them are not likely to be oscillating fast enough to produce gravity waves that have a frequency high enough to be readily detected.

Another problem is that in terms of gravity waves, the universe is probably a really noisy place. There is so much mass out there and so much movement that we'll simply get a whole lot of white noise (at uber-low frequencies) if we listen to these waves. How do we make any sense of them?

The very reason we're able to make such great use of the radio-frequency and light spectrums for communications is that we can use very narrow bandwidths and tune both our transmitters and receivers to ignore everything else. Perhaps we'll be able to do this with gravity waves but it'll be very hard.

Another problem is that of bandwidth. Right now, the only gravity waves we'll be able to detect from any distance will come from huge masses that generate waves with frequencies that will be measured with a calendar. It's a sad law of physics that the lower the frequency of your "carrier" wave, the less data it can carry in a given amount of time.

Our HD TV broadcasts require much, much higher frequencies than the old AM radio broadcasts -- simply because there's so much more data involved in the former than the latter. Now imagine trying to send *any* data at frequencies that may be measured in one cycle per year, per decade. or per millennium. That's 5/8th of bugger all.

If you want higher frequencies then you must use far smaller masses (because of the effects of Newtonian physics) but sadly, since the strength of a gravitational field is directly related to mass -- the strength of those waves will be very, very small.

Who knows... perhaps some time in the future we'll find a way to create ultra-sensitive gravitational wave detectors that can be precisely tuned to the frequency of a transmitter which works by significantly altering the mass of an already massive object. Or perhaps, just perhaps, this work will deliver the technology needed to make practical gravity wave transmitters.

More likely, gravity waves will be a "read-only" medium which simply serve to allow us to map the universe through a different set of eyes.

You have to admit though... if they have been detected, it's another feather in old Albert's cap.

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