Given the expected rates of significant gravitational wave sources, such as black hole or neutron start mergers etc, (http://iopscience.iop.org/0004-637X/662/1/504/fulltext/21332.tb3.html), eventually if we don't see something above the noise we will have to rethink things. But what assumption would need to be reconsidered first and how?
Dear Stephen,
First assumption of general relativity is that gravity is not a force but a property of space-time geometry, while all other fundamental interactions are the quantum fields in Minkowski space-time.
Honestly speaking the concept of gravitational wave is not intrinsic for geometry because there is no the concept of energy-momentum tensor of gravitational field within general relativity (see previous discussions in the topic “Gravitational physics”).
So one can start from careful consideration of the so-called Feynman’s Field Gravity approach, where tensor and scalar gravitational waves exists and there are several crucial experiments which can distinguish between geometrical and field gravity approaches (see papers http://arxiv.org/abs/0809.2323 and http://arxiv.org/abs/0809.2328).
At some level gravitational waves must exist. Non-detection is purely an instrumental problem. Currently many noise sources (seismic activity, solid Earth-tides etc.) still limits sensitivity and bandwidth of detection. But immense progress has been made, in improving instrumental sensitivity, which is now nearly at the predicted detection limit. If no gravity waves are detected, ever, it would mean that we understand very little of the nature of spacetime (i.e. far less than we thought we did !). As all the 'tests' of GTR has come up positively, to the level that our instruments allow at this stage, we can with fair confidence look towards detecting gravity waves at some stage, and this would become another branch of astronomy, just as radio astronomy was born during the late 1940s. What assumption would need to be re-considered in the event of non-detection? The validity of the General Theory of Relativity.
Dear Ludwig,
there is also another lesson from non-detecting (even with modern sensitivity) GW with such amazing instruments as LIGO and VIRGO. It is the theory of gravitational collapse for the most probable gw sources – massive supernovae in nearby galaxies:
The point is that modern collapse models predict the msec one pulse, while a possibility of pulsating collapse with duration about 1 sec (as neutrino signal from SN 1987A demonstrated) also exists
( see e.g. http://arxiv.org/abs/astro-ph/0104115 ).
Yes Yurij, quite true, perhaps one day there will be a different type of GW detector, which could make use of spacetime curvature variations, then we would be able to see how moving and rotating masses affect spacetime....but then we have to crawl before we can walk !
In general relativity, gravity is due to the curvature of the space-time. And gravitational waves are the ripples in the curved space-time. Non detection of gravitational waves would imply non existence of curved space-time. Under such circumstances alternative explanation for the decay of the orbital period of pulsar would be required. Following article discuss one such alternative explanation.
Research Alternative explanation for orbital period decay of a pulsar
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