By now most of you will have heard the rumors. This Thursday the team behind the LIGO experiment are scheduled to give a press conference, and the most likely reason is that they are going to announce the detection of gravitational waves. Of course at this point we do not know how strong the signal is, or even that it is true, but if it is it will be an interesting confirmation of Einstein's general theory of relativity.

According to the general theory of relativity, mass and energy warp spacetime. The reason objects appear to move due to a gravitation force is actually that they are following the shortest path through a warped spacetime. The effects of spacetime warping have been tested in numerous experiments over the past century, and every time they have further confirmed Einstein's predictions.

However there is one prediction that has never been confirmed or refuted - gravitational waves. 

When the distribution of matter and energy changes, the curvature of spacetime in the area changes. And like ripples in a pond, the disturbance propagates out through the rest of the Universe. When these waves encountered matter (such as the detectors on Earth) they cause very slight changes to the positions of the objects. And if the waves are strong enough, these effects can be detected.

For example in LIGO, the gravitational waves cause two sets of mirrors to move back and forth very slightly. by reflecting laser light off of each mirror, and then allowing the laser beams to interfere with each other, scientists can detect these movements in the form of interference patterns. However this is a difficult measurement to make, because the effects of local traffic or weather patterns, or any of a hundred other everyday events can easily overwhelm the signal. For that reason experiments like LIGO try to collect data in multiple locations and go to great lengths to minimize background effects. It is very difficult to obtain a signal as small as a gravitational wave in the midst of all this noise.

And yet if the rumors are true, that is exactly what they have now done. It would appear that some major astrophysical event in some distant part of the Universe has created a ripple which will finally confirm the existence of gravitational waves.

For now, all we can do is anxiously wait for the experimentalists to announce their results.