Ah, the life of an experimental physicist. Long hours of mind-bending labor, all in service of those few precious moments in which you glimpse one of Nature’s true secrets for the very first time. Followed by the moment when your bosses tell you it was all just a trick.
Not that you didn’t see it coming. As we know, the LIGO experiment and its friend the Virgo experiment are hot on the trail of gravitational waves. They haven’t found any yet, but given the current sensitivity, that’s not too much of a surprise. Advanced LIGO is moving forward, and when that is up and running the situation is expected to change.
But who knows? We could be surprised. It’s certainly necessary to comb through the data looking for signals, even if they’re not expected at this level of sensitivity.
Of course, there is something of a bias at work: scientists are human beings, and they want to find a signal, no matter how sincerely they may rhapsodize about the satisfaction of a solid null result. (Do the words “life on a meteorite” mean anything to you?) So, to keep themselves honest and make sure the data-analysis pipeline is working correctly, the LIGO collaboration does something sneaky: they inject false signals into the data. This is done by a select committee of higher-ups; the people actually analyzing the data don’t know whether a purported signal they identify is real, or fake. It’s their job to analyze things carefully and carry the whole process through, right up to the point where you have written a paper about your results. Only then is the truth revealed.
Yesterday kicked off the LIGO-Virgo collaboration meeting here in sunny Southern California. I had been hearing rumors that LIGO had found something, although everyone knew perfectly well that it might be fake — that doesn’t prevent the excitement from building up. Papers were ready to be submitted, and the supposed event even had a colorful name — “Big Dog.” (The source was located in Canis Major, if you must know.)
Steinn Sigurðsson broke the news, and there’s a great detailed post by Amber Stuver, a member of the collaboration. And the answer is: it was fake. Just a drill, folks, nothing to see here. That’s science for you.
When the real thing comes along, they’ll be ready. Can’t wait.
Physicists are cruel.
They should do this false signal injection to the SETI folks 😉
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That’s really cool, actually.
When the data started rolling in at ATLAS and the agreement with the simulation was so amazingly good, I was momentarily convinced someone had loaded Monte Carlo events into the read-out system. Alas, the folks designing and implementing the simulation are just *that good*.
I wonder what the outcome would be if the ATLAS management stuck some supersymmetry (SUSY) or black hole events into the data stream. Would analysis groups hide their findings until the last moment? Would we work together as a collaboration to figure out what the signal really represented? Would we even find the signal?
A situation like this arose with the first observation of jet quenching in the heavy ion collisions…but for real. The outcome was actually very impressive, with experts from all over the collaboration pooling their resources (and not sleeping!) to make sure that the signal was real.
http://atlas-service-enews.web.cern.ch/atlas-service-enews/2010/news_10/news_Jet%20quenching.php
I can’t help but think that SUSY would be a different story….
This… seems like a complete waste of time. Sure, testing that you can accurately pick up on fake signals is fine, and a normal part of blind physics analyses. But to let it go all the way to having a paper ready to publish? To do that sort of analysis normally takes months of hard work, checking, cross-checking, feedback and alteration.
I took GR from Joe Weber. His papers may have something to do with the crop of gravity wave people being so careful about this sort of test.
I sort of understand how injecting fake events can help test the data analysis process. But how does it guard against the bias towards finding results even where none exist?
Regarding LIGO …I never understood what intellectual issue was at stake in these experiments. Although nothing is ever beyond doubt, classical GR seems pretty well accepted.
Under what circumstance could one imagine a real null result? i.e. finding no gravitational waves. And would it mean? And if they found waves, what would it mean? Would it tell us something about the number of sources within some distance? And that would tell us what exactly? Something about the patterns and rates of formation of large binary systems? Are there any issues of a fundamental nature about space-time at stake here? What will really be learned?
@Chris,
SETI gets huge amounts of false signal detection from terrestrial radio sources. Like all those times they find a signal from a fixed location, that turns out to be a satellite. They don’t need to deliberately give themselves any more negative data.
@Peter,
There is a common misconception that the sole goal of LIGO is to “test” GR. While it is true that the first confirmed detection of a *real* gravitational wave will in some sense be a validation of GR it likely won’t add much new information beyond what we already know. In fact we know a lot about gravitational waves from binary pulsars already. What advanced LIGO and its brethren will do is allow us to start doing astronomy with gravitational waves. This will likely be a boon for astrophysics and possibly for fundamental physics as well (what if we measure a time delay between the gravitational waves and the gamma rays from a neutron star merger?). As far as really testing GR itself, you need to be able to measure the waveform with enough signal to noise to determine whether it is consistent with the predictions of GR. This is best done with black holes rather than neutron stars which will be more rare signals for advanced LIGO. I don’t know what the prospects for doing this is with the ground based detectors but I know that it is something that is very doable with the space-based detector LISA. Hopefully advanced LIGO will get something soon after commissioning and the excitement will prompt ESA and NASA to get LISA going for real.
LIGO is wastage of money. Now they find newr ways of wasting more money! I heard India is building up one too! Another big-time wastage of money. They need hospitals and roads more than this junk science. Down with LIGO and its sisters. They have wastd enourf and now should pass that money to other fields
@ Brad,
No wonder I left you. There are economic implications and job creation associated with large scale science like LIGO. Why build roads if there are no reasons to use them. If LIGO in India is made, they will need to upgrade the local surrounding roads to handle the construction and supplying of the facility. The construction workers will need goods and health care so then one must consider clinics and shops to crop up in small villages/towns near by. Brad I feel your being a bit short sighted…
Angelina
PS. I hope your not this short sighted during the divorce negotiations…
Angelina, that’s the reason you are getting so thin … thinly spred everywhere and not deep anywere. India needs roads even without india’s LIGO — jsut for transporting aggricultural fgoods to cities before those get spoiled, or patients before they die. How long can NSF feed butter to LIGO? give that money to laser scienec, optics science or info technology or mortgage-affected people. ..and do not encourag Indians to go after grav waves leaving their call centres./
Dear Brad and Angelina,
I don’t mean to interrupt your marital fights, which I see with delight, but the latest Indigo plans are not targeted towards building an interferometer in India, but rather to collaborate with LIGO-Australia in raising funding for the Australian detector.
http://www.gw-indigo.org/tiki-index.php?page=The++Indian+Roadmap+for+Gravitational-Wave+Astronomy
It will be a strong commitment from the Indian side, sure, but of an order of magnitude less than building their own instrument.
@Jennifer
Thanks for putting up a link. I just get annoyed so rapidly with Brad and what I see just knee jerk statements. I reacted from an emotional space… It is good to have a level headed girlfriend try to clear the air. Though I do think large scale science offers opportunities for economic stimulus, but I can see how that investment does not translate easily into immediate change like bailing out bad mortgages…
@Brad, I was just making an argument in to opposite logical extreme… and I realize how being a celebrity has detached us from reality so I just leave you to your views… My dad was stubborn and block headed I wonder if there is a correlation there… Maybe I can get research money too… Like you said sweetie that money is better spent on other fields like biomedical research into ED(that could have helped out this marriage) or maybe research into call center retention, as I hear that there is a high turnover rate in North America, maybe LIGO has something to do with that…
@Jenn
Pinky promise… I’ll stop fighting and let the lawyers work it out I swear…
That’s the great thing about well-designed physics experiments, we learn something no matter what the outcome. Even for LIGO it’s possible to find skeptics and naysayers (here’s one), so I share in the sense of excitement at seeing the first traces of measured gravitational waves.
@Nick: “This… seems like a complete waste of time…” I could not disagree more. There is so much to learn from carrying out the process of discovery to the very end. The value of an exercise like the one that was performed is exactly in the fact that it takes “hard work, checking, cross-checking, feedback and alteration.” LIGO folks learned a great deal on what it can go wrong, and are now much more prepared to tackle a real signal, when it will show up.
@melior: Just to clarify. LIGO and Virgo have not seen any “traces of measured gravitational waves”. So far. Analyses of collected data are not over yet. Stay tuned!
The money could have been used to stop rampant cholera in Haiti, for which there is no money.
I’m not sure about it being a complete waste of time, but I do echo some of Nick’s concerns that carrying things to the brink of publication may be overkill. Hopefully most of the content of the preprint(s) are sufficiently portable that rewriting the data content and getting everyone signed off on the final draft isn’t a headache. I don’t know much about big physics collaborations, but in my field, the effort that can go into a big collaborative paper is considerable, so when it has to be scrapped, it’s a pretty big deal.
Wouldn’t it be great if every hundred years or so we built a progressively bigger interferometer to search for a new effect, and each one returned a null result!?
Refutation of theory is worth it of course, it just suddenly strikes me as humorous how similar the current situation is to Michelson & Morely 124 years ago.
Re Doug Watts
And so could all the money we spend watching professional sports. Or buying TVs. Have you got a TV Doug ? What’s your point again ?
Folks in Washington State and Louisiana are encouraged to visit the LIGO interferometers and take a look around. You’ll find that the scientists on-site are friendly and always willing to answer questions and chat with visitors who are interested in LIGO, astronomy, and astrophysics.
Dear Sean:
Take a moment and become better informed. Visit http://www.TheSanta.im.
Santa Claus