Thursday, February 11, 2016


Those of us who weren't in the Supernova room watching the feed were probably watching at their desks. There were some funny moments: "This isn't a Hollywood movie, this is a real simulation!" got a lot of laughs around the room. So did the banter about theorists as they introduced Thorne (and a book of his I'd never heard of, though we all read Gravitation by Misner, Thorne, and Wheeler). And we enjoyed the Russian reporter playing to stereotype by claiming that LIGO was invented in 1962 in Russia.
Sorry, I can't resist this oldie. "What is a theoretical physicist? That is a kind of physicist presumed to exist but which has never been seen in the lab."

The big news was the chirp. I was startled at how clear it looked. Look for yourself at what the two detectors saw. You can see the backgrounds that each detector found, and then the signal. I won't try to duplicate the references and animations.

Yes, I read the paper, but most of the details that need explaining are in other papers (like what they mean by "resonant optical cavity, formed by its two test mass mirrors, that multiplies the effect of a gravitational wave on the light phase by a factor of 300". I think it means the light bounces back and forth 300 times but I'm not sure.) Noise is the big issue: reducing it and trying to measure what they can't reduce.

A few details from the paper:

  1. There were 2 events that might be interesting, one much less clear
  2. The data was from a 16-day period, not the whole 4 month time. I don't know if they only used part for analysis convenience or because of detector issues. Can we expect 20x this per year? I hope this wasn't just beginner's luck.
  3. The event was from just before the official start of the run!
  4. They aren't up to full sensitivity yet. They expect another factor of three, which would expand the volume they're sensitive to by a factor of 27
  5. Similar systems are coming online shortly. It might be possible to pinpoint (for some definitions of pinpoint) the source, and if it is close enough maybe use optical telescopes to find out exactly where.
  6. With the festivities 1.3 billion light-years away, and from a merger of black holes at that, IceCube wasn't likely to find any neutrinos from it, and we didn't. (If we had, we'd have probably had a representative at the announcement ourselves.)
  7. "Each test mass is suspended as the final stage of a quadruple-pendulum system, supported by an active seismic isolation platform." That last bit means the platform moved its top to try to compensate for seismic movements of its bottom. The first part means they hung a pendulum from a pendulum from a pendulum from a pendulum.
  8. Did you notice what they estimated from the before/after fits? 3 solar masses turned into gravitational wave energy! (plus or minus half a solar mass) I wonder what it would have been like to view it from a few light-years away...

Note that the Michelson-Morley technique that was used to prove there was no ether, which was the starting point for Einstein's Special Relativity, turns up again in a verification of Einstein's General Relativity. This time they used lasers ( and Einstein wondered if stimulated emission were possible. He just keeps turning up...)

No comments: