Replies

Nobody has ever successfully detected a gravitational wave. They are a theoretical prediction, but of an effect so small that detecting them is very difficult. If they are there as predicted, and detectors sensitive enough to record them reliably are produced, then you are most of the way there.

The next step is to arrange detectors and use the differences in signal at different ones to map out what waves you are receiving, where and when. But it is obviously much harder to get a good picture of a one-off, transient phenomenon that way, than a picture of a steady source.

Strong gravitational waves are easier to imagine getting produced in a transient rather than a continual source. Gravity tends to rapidly smush things into symmetric shapes that thereafter produce uniform gravity, and only changes in gravity produce gravitational waves. A gravity wave is a propogating "ripple" in space-time itself.

The wildcard is that we know that our theory of gravity probably leaves something out, in details. There is no consistent quantum theory of gravity. We only know our gravity theory checks out for large scale phenomenon. But wave -propagation- may depend in some respects on small scale phenomenon.

Mathematically, they integrate a bunch of infinitessimals without really knowing how the infinitessimal scale looks. For large scale and continuous enough properties, that has always worked so far. But supposedly sensitive gravity wave detectors have been around for a while now, and nobody has actually seen one with them, to date.

The detection schemes are getting better, and obviously as the article shows they have high hopes. We shall see, and that is always fun...

I should add that one can certainly imagine all kinds of continual sources of gravity waves. They just tend to be weaker phenomenon than some potential transient sources. And there is indirect evidence to support the idea of gravitational waves, for instance observed "spin down" of binary pulsars (changes in their period), which are attributed to loss of energy by gravitational radiation. But there is nothing quite like directly detecting a predicted phenomenon, instead of infering it.

But supposedly sensitive gravity wave detectors have been around for a while now, and nobody has actually seen one with them, to date.

And that in itself is rather amazing to me; because doesn't a star collapse into a neutron star or a black hole at least once a day somewhere out there in the universe? Or two black holes merge, say?

Well, I'm looking forward to it, whatever "it" is. I'm sure there will be some surprises; there always are. :-)

Thanks, RW! Makes perfect sense.