Excitement is building as rumors have emerged of multiple detections of gravitational waves. If true, this would be one of the biggest physics breakthroughs so far this century, confirming a central feature of Einstein's Theory of General Relativity.
In September, the first rumors of gravitational wave detections made Nature, but respected Arizona State University physicist and author Lawrence Krauss said at the time, “I give it a 10 to 15 percent likelihood of being right.” No one more confident was willing to go on the record. Yesterday Krauss changed his tune, tweeting: “My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.”
My earlier rumor about LIGO has been confirmed by independent sources. Stay tuned! Gravitational waves may have been discovered!! Exciting.
— Lawrence M. Krauss (@LKrauss1) January 11, 2016
Exciting is an understatement, if the detection is real. Einstein proposed that massive objects curve the fabric of spacetime, in a manner often compared to a heavy object bending a flexible surface. This would alter the movements of other objects, and of light, that passed close to the large object. He also suggested that the acceleration of sufficiently heavy objects would cause ripples in spacetime to propagate outwards.
Orbiting pulsars have been seen to lose energy in exactly the way Einstein predicted, which is regarded as indirect evidence for gravitational waves. Direct evidence, however, remains elusive.
A network of Laser Interferometer Gravitational-Wave Observatories (LIGOs) has been established to search for these waves. LIGOs bounce lasers off a series of mirrors before recombining it in a manner that would be disrupted should a wave pass through. Ultimately, LIGOs are designed to learn something about the sources of waves. Just finding a single indisputable example of a gravitational wave would be a major discovery, but this had so far remained elusive.
A schematic of a LIGO detector. Gravitational waves will minutely lengthen one arm relative to the other, causing the beams to be out of phase when recombined. Public Domain via wikimedia commons
The first LIGOs started operations in 2002, but shut down after eight years without a clear result. They were replaced with more powerful versions, going into operation last September. Almost immediately rumors of multiple detections appeared.
No official announcement has been made, however. Local events such as earthquakes can produce results that would resemble a gravitational wave on a single LIGO machine. Only by comparing data from different LIGOs spread around the world is it possible to confirm a genuine gravitational wave. This is a slow, painstaking process. As a checking mechanism, what are known as “blind signals” are inserted to see whether researchers can spot the difference.
Concern to avoid a false alarm has been particularly high in this field after evidence for gravitational waves by the BICEP2 experiment was reported through a very different mechanism in 2014. Soon after it became clear that the team making the announcement had misunderstood a key part of the data they were using.
No one wants that to happen again, so LIGO teams have been checking their data over and over again to make sure they've got it right. Such thoroughness has left plenty of time for people to talk, inspiring PBS Space Time to make a video.
Discussion, however, stayed largely within the physics community until Krauss' tweet, followed by his expression of confidence that this was not a blind signal. Many have critisized his announcement, claiming that he was taking the glory from those involved in the discovery, and that rumors of this kind discredit science to the public.
@LKrauss1 if true, you are trying to steal their glory; if false, you are damaging scientific credibility. A bit of a no-win really.
— Michael Merrifield (@ProfMike_M) January 11, 2016
When an exciting rumor fizzles it can erode public confidence in science. It might be just a little, but it adds up!
— Robert McNees (@mcnees) January 11, 2016
The official word remains that LIGO is still analyzing the data and will share news, if they have any, when the proper scientific method for discoveries has been followed. Other scientists are cautioning against building hopes unnecessarily. Nevertheless, the more confident team members are willing to say, off the record, that not only is the discovery real, but the announcement will come next week.