samedi 23 janvier 2016

Gravityational waves (rumor of direct detection on Earth and its ) reception spectrum on the blogosphere

From the bright side ...
Masses of both black holes exceed 10 solar masses
... many of us eagerly expect the announcement of a hugely exciting discovery (direct detection) of the gravitational waves...

There are several "traps" that may make you think that the {Laser Interferometer Gravitational Waves Observatory} LIGO  shouldn't work at all (I was tempted to be confused by several such traps) and for decades after the discovery of General Relativity, people felt uncertain whether the gravitational waves could have been physical at all (Mach's principle was the primary misconception that drove those who wanted to say that they were unphysical) but at the end, all of them are wrong. Gravitational waves do exist and LIGO-like detectors may detect them. Note that the lengths of the 4-kilometer arms are measured with the accuracy 100,000 times better than the radius of the atomic nucleus. Because it's so, a LIGO discovery will eliminate all conceivable theories that claim that Nature has an unavoidable error margin in positions that would be longer than 10−2010−20 meters (e.g. the nuclear radius). Nature only prevents you from measuring the positions and momenta simultaneously; but it surely keeps track of the position separately and the position makes sense with an arbitrary accuracy – at most, at the Planck scale, there may be some issues (but not the issues that non-stringy quantum gravity babblers are sometimes imagining). 
... A commenter whose name is known to us has told us that there have been two events (short periods with gravitational waves) detected by the LIGO. A new rumor I got yesterday says that LIGO has "heard" a merger of two black holes into one bigger black hole. (I don't know whether this event is one of the two events from the first sentence of this paragraph.) Because black holes are among the heaviest "stellar mass" objects and allow the shortest orbital radii (and therefore strongest gravitational waves), this situation is obviously an event that creates strong enough gravitational waves, especially when both black holes are said to be heavier than 10 Suns (and most black holes in the Universe probably are: the stellar black holes' masses are believed to be between 3 and 50 Suns or so). 
The frequency of the gravitational wave from the two black holes that the LIGO has supposedly detected is comparable to the aforementioned 100 hertz. It's hard to say how many periods of the radiation they will be able to detect. The truly final moments of the merger only correspond to the number of orbital periods comparable to one. But before the black holes merge, they orbit one another for a very long time. The radiation only gets strong enough during the final stages of the merger and whether the LIGO may "hear" the waves long before the final moment (and how long) depends on its actual sensitivity. LIGO got "advanced" so the sensitivity has been improved by an order of magnitude but I don't want to collect all the engineering data and calculate how good the sensitivity has become. 
...At the end, if the rumor is true, what they should have heard is very similar to this LIGO example of inspiral gravitational waves except that the newly actually observed frequency is "somewhat" lower than the frequency in the example (a deeper sound). Note that the frequency of the vibrations as well as their intensity increases with time up to the final moment when the waves almost abruptly disappear.
Posted on monday, january 11, 2016 by Lubos Motl on his blog The Reference Frame

... to its dark one
On the Theory of Gravitational Wave Rumour Sources 
There has been a great deal of excitement almost nowhere in the astrophysics community since it was announced recently that rumours of the detection of gravitational waves had yet again begun to circulate, so I thought I would add here a brief discussion of the theoretical background to these phenomena. 
The standard theoretical model of such rumours is that they are produced from time to time during the lifetime of a supermassive science project after periods of relative quiescence. It is thought that they are associated with a perceived lack of publicity which might threaten funding and lead to financial collapse of the project. This stimulates a temporary emission of hype produced by vigorous gossip-mongering which acts to inflate the external profile of the project, resisting external pressures and restoring equilibrium. This general phenomenon is not restricted to gravitational wave detection, but also occurs across many other branches of Big Science, especially cosmology and particle physics. 
However, observations of the latest outburst suggest support for a rival theory, in which rumours are produced not by the project itself but by some other body or bodies in orbit around it or even perhaps entirely independent of it. Although there is evidence in favour of this theory, it is relatively new and many questions remain to be answered. In particular it is not known what the effect of rumours produced in this way might be on the long-term evolution of the project or on the source itself.
Posted in AstrohypeThe Universe and StuffUncategorized with tags gossipgravitational wavesRumours on January 12, 2016 by Peter Coles aka telescoper on his blog In the Dark

...with several shades of grey (another drill before the next thrill)

An improbable rumour has started that the observatory has already made a discovery — but even if true, the signal could be a drill.
Davide Castelvecchi 30 September 2015 (NATURE | NEWS: EXPLAINER)

Gravitational-wave rumours in overdrive 
Could a signal be a false alarm?

That is also possible. The LIGO detectors have sophisticated systems for reducing unwanted vibrations, but the team needs to carefully check that any detection is not a false alarm — vibrations produced by a passing lorry, for instance. 
But the rumoured signal could also be the result of a deliberate drill. Three members of the LIGO team have access to systems that can secretly nudge the mirrors and simulate all the hallmarks of an astrophysical phenomenon — a procedure called a ‘blind injection’. Only when researchers are ready to reveal that they have spotted something will the blind-injection team announce whether it has created a deliberate signal. Two such exercises occurred in earlier runs of the LIGO, in 2007 and 2010.

But Krauss, at Arizona State University in Tempe, tweeted that he has heard rumours that the team detected a signal during tests of the upgraded detectors last summer, before official data-collection began — and before the blind-injection system was in place. (He did not know any more details when asked by Nature.)

The LIGO researchers would still take their time analysing such an early event, says Laura Cadonati, a physicist at the Georgia Institute of Technology in Atlanta who heads LIGO's data-analysis team; scientists would not be able to assess such an early signal before gaining a better understanding of how often particular types of false alarm are likely to show up in the data.

The LIGO collaboration declined to comment on whether there was any time when both interferometers were active but no blind injection was possible. 
Are LIGO physicists concerned about the rumours?

González is a little miffed. “I am concerned about creating false expectations in the public and the media,” she says.

But Cadonati says that the buzz around the experiment has been “energizing”. “The fact that leaks started early on meant that they were something we had to learn to live with,” she says. “It means that there is excitement around what we are doing.”
Davide Castelvecchi 12 January 2016 (NATURE | NEWS: EXPLAINER)

Steven T. Corneliussen of Physics Today wrote a somewhat critical text about the wave of LIGO rumors that escalated one week ago:
Cosmologist Lawrence Krauss is often cited as a source, mainly because his rumors are relatively quickly spread through a large number of his Twitter followers. Your humble correspondent is often quoted as the propagator of the most precise rumors. Wait for February 11th to hear the announcement. And you will learn about at least two events. And at least one of them will be the detection of a merger of two black holes each of which weighs at least 10 solar masses. ;-) 
... As far as I can say, there are three basic reasons to be concerned when it comes to similar rumors:

  • Accuracy and balance between hype and underlying evidence
  • Fair distribution of fame and credit
  • Discipline and secrecy for their own sake 
Concerning the accuracy, well, people are told that it's "just rumors". But the track record of similar rumors has been extremely good in recent years. On Friday, March 14th, 2014, rumors spread that BICEP2 was going to claim the discovery of primordial gravitational waves on the following Monday. And it did. 

BICEP2 no longer believes that their 2014 paper was quite good but because the rumor was about the announcement, not the perfection of their actual analysis, the controversy about the BICEP2 results doesn't imply that the rumors were inaccurate.
Posted on wednesday, january 20, 2016 by Lubos Motl on his blog The Reference Frame

Even if all this gives you some feeling of déjà-vu let me wish you a happy new year 2016!

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