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US Restarts Hunt For Gravitational Waves With Advanced LIGO
schwit1 writes: The hunt for gravitational waves began again for the Laser Interferometer Gravitational-Wave Observatory (LIGO)-the largest instrument of its kind. The restart follows a five-year-long, US $200-million project to overhaul the experiment's detectors. Many physicists believe the revamped experiment, dubbed Advanced LIGO, will be the first to find direct evidence of gravitational waves: ripples in the fabric of space-time that can be created by, among other things, a pair of neutron stars or black holes orbiting each other.
Gravitational waves were first theorized in 1916 by Albert Einstein as a consequence of his general theory of relativity, which celebrates its centennial this year.
If I remember correctly, the noise floor of the previous instrument was approximately the level of the signal they were looking for.
A better detector may help.
If I remember correctly, the noise floor of the previous instrument was approximately the level of the signal they were looking for. A better detector may help.
Indeed. It's hard to overstate the sensitivity of these instruments, or the vulnerability of these instruments to noise. To take one example, here's an ArXiv preprint that calculates that the original LIGO detectors would need to be physically shielded from tumbleweeds, since the the impact of a wind-borne tumbleweed on the building exterior (100 feet from the detector) could produce a vibrational or gravitational transient sufficient to appear to be a spurious gravitational wave signal.
~Idarubicin
If gravity waves don't actually exist it would be the first prediction of General Relativity to fail, which would be a huge discovery that could help in the search for quantum gravity. Scientists have indirect evidence of gravity waves:
In this current "pre-detection" era it can be difficult to convince those who are not overly familiar with the theory of general relativity that gravitational waves really do exist. Fortunately, the Hulse-Taylor Pulsar (PSR 1913+16) provides firm evidence of a binary system actually emitting gravitational waves! ...
Over the years the period of the pulsar has been measured to high accuracy. General relativity tells us that a binary system will emit energy as gravitational waves and eventually the two objects will inspiral towards each other and merge. As the system evolves towards this merger the period of the orbit will gradually decrease.
The figure (from Weisberg and Taylor (2004)) shows the cumulative shift of periastron time for PSR 1913+16. This shows the decrease of the orbital period as the two stars spiral together. Although the measured shift is only 40 seconds over 30 years, it has been very accurately measured and agrees precisely with the predictions from Einstein's theory of General Relativity. The observation is regarded as indirect proof of the existence of gravitational waves. Indeed, the Hulse-Tayor pulsar is deemed so significant that in 1993 its discoverers were awarded the Nobel prize for their work.
Didn't the "scientists" who built the first experiment know what the noise issues were and that the first equipment couldn't find anything?
There is a range of possible intensities at a given frequency for predicted gravitational waves. The original LIGO project overlapped with potential ranges, so there was a potential possibility of seeing something. It was not built with the certain expectation it would find nothing.
This chart does a really good job of summarizing different predicted sources of gravitational waves, and the sensitivity of current and proposed detectors.
Did anyone else read the headline as "advanced lego"?
Well, not anything that moves, but things that move with a quadrupole moment. In other words, spherically and cylindrical symmetric movements do not radiate. A mass moving linearly by itself, or a sphere spinning will not radiate. However, two masses in orbit around each other will.