## Wednesday, September 16, 2015

### Advanced LIGO is getting started

Update: observations began on Friday, September 18th, 8 am PDT. I don't want to spread conspiracy theories at any cost but this beginning on September 18th may be just a trick to mask a discovery. They could have discovered a wave e.g. two days ago, on September 14th (such a wave would be called GW150914). Perhaps an Italian postdoc saw it on his screen in Germany at 9:50 UTC. And all this stuff about the beginning on September 18th was done just to legitimize the discovery made on September 14th. Do you think my theory is unlikely? ;-)
LIGO was proposed by Thorne and Drever at Caltech and Weiss at MIT in the early 1990s. The construction between 2002-2010 culminated with some detection run and no gravitational waves have been detected so far.

People who walk there must think that the extraterrestrials have built some bizarre, useless caves here. The LIGO runs two sibling facilities, L-shaped corridors with the vacuum inside whose diameter is 4 km. One of them is in Louisiana, the other one is in the Washington State. At \$0.365 billion, the price tag is nowhere near the LHC but it is the largest single experiment ever funded by NSF, anyway.

Yesterday, Caltech announced and Nature echoed that after years of upgrades, the "Advanced LIGO" is getting started these days.

The sensitivity of Advanced LIGO is 10 times better than was the original LIGO. Because the energy flux decreases as $$1/R^2$$, Advanced LIGO may see approximately 3 times more distant objects of the same kind than the original LIGO could.

Because of other power laws – involving the distribution of the "gravitational wave sources among the celestial objects according to their power" – the number of objects that Advanced LIGO may see is about 1,000 times higher than for the original LIGO. This multiplicative improvement looks particularly striking.

However, the spectrum of possible "orders of magnitude" is much wider still. So even though some calculations suggest that Advanced LIGO should start to see things, it is not quite guaranteed. I am a bit surprised that people can't calculate the moment of the first discovery more precisely. The ignorance about the actual strength of waves that may be expected by widespread celestial objects is probably the main hurdle.

Moreover, we will probably not be told about such a discovery in 2015, on the 100th anniversary of Einstein's general theory of relativity. The press release tells us to be patient. But Einstein only published the papers in 1916 so a discovery in 2016 – which is more conceivable – would be pretty cool, too. The LIGO folks want to have a break, and a coffee, and so on, so the data could also be gradually getting closer for 5 more years, they warn us.

I am obviously no expert in these or other experiments but I don't believe that this slow pace is really justified by some good arguments. I feel that the bureaucracy is organized in such a way that if the people do their work slowly, they accumulate a larger integrated amount of money in the whole process. Sometimes I feel the same about the LHC, too.

It's my impression that some policies encouraging speed – and discouraging deliberate slowdowns – could be useful for all of experimental physics and beyond.

Before the detectors, there have been Apaches or other Indians in Louisiana as well as Washington but the scientists are preparing a third copy of the structure in a place with an even larger number of Indians, namely in India. VIRGO has been running in Italy since 2007 and GEO600 in Germany since 1995. My understanding is that they're not competitive with Advanced LIGO.

LISA, a cousin of LIGO in the outer space, is the music of the 2030s.