Thursday, February 11, 2016

Gravitational Waves Detected!

An earlier blog post discusses rumors of the detection of gravitational wave. At the time we had no official confirmation. Now we do.

Early today, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced that it had made a direct observation of a gravitational wave for the first time. LIGO consists of two instruments, and both had recently been upgraded to make them more sensitive (and thus increase the chance of discovery). Back in September 2015, after the upgrade, a signal had been detected by both instruments. After analysis, it was determined that these signals were consistent with two black holes in a close "death spiral." They spiraled closer and closer until they collided and merged to form a single black hole. One of the black holes was 29 times the mass of the sun, the other 36 times the mass of the sun. This occurred about 1 billion years ago and resulted in a gravitational wave that was detected by both of the LIGO instruments. This result was keep secret (except for occasional "leaks" of information) until earlier today (February 11), when LIGO gave a press conference releasing details of the discovery.

This is an important result, but why?

These videos from PBS Digital Studios will be of interest.

A video recorded after the announcement, explaining what the discovery is all about...

LIGO's First Detection of Gravitational Waves

As you may have seen in an earlier blog post, rumors of this result were known for a while, here is a video recorded a few months ago, asking if gravitational waves have already been discovered. The fact is they already had been, but only a few people directly involved with LIGO knew this for sure.

Have Gravitational Waves Been Discovered?

Some other videos discussing different aspects of General Relativity. General Relativity is Einstein's theory of gravity, and it predicts that gravitational waves exist.

"Are Space And Time An Illusion?":

"Is Gravity An Illusion?"

"Can A Circle Be A Straight Line?"

"Can You Trust Your Eyes In Spacetime?":

General Relativity and Curved Spacetime

Sunday, February 7, 2016

Rumor of Gravitational Wave Detection.

One of the predictions of General Relativity (Einstein's theory of gravity) is the existence of gravitational waves. In theory, anytime a massive object accelerates (that is any motion that is not constant straight line motion and not simple rotation) it should generate gravitational waves. So in theory the universe should be filled with gravitational waves.

However despite years of trying, no one has succeeded in detecting them.

But in the past few days rumors have been circulating that LIGO, a project to detect gravitational waves, has finally succeeded.

Einstein thought gravitational waves would be impossible to detect, and in fact they have been difficult to detect. The tiny signals must be separated from other signals (such as earthquakes and passing trucks). Each time a potential signal is detected, a statistic analysis is performed. This in essence asks "What is the likelihood this a real signal, not something that only looks real." This is expressed in terms of "sigma". The higher the sigma, the more likely the signal is real.

According to the rumor, LIGO has in fact detected signals that exceed "five sigma." Normally results like this are not released until solid confirmation has been made, but one of the physicists spilled the beans.

This may prove to be false; but it seems to be real. We should know for sure on February 11th when an official report from LIGO is scheduled to be published.

Those of you living in or near Ann Arbor, might be interested in two upcoming lectures, which by a happy coincidence are on this very topic. Both are by Keith Riles, professor of physics at the University of Michigan.

Saturday, February 13 10:30am: "Gravitational Waves - Einstein's Audacious Prediction."

Saturday, February 20 10:30am: "The Hunt for Gravitational Waves - Was Einstein Right?"

Both events are held in rooms 170 & 182 Weiser Hall (formerly the Dennison Building), University of Michigan Central Campus, 500 Church Street, Ann Arbor, Michigan, 48109

See for more information about these lectures.