Gravitational waves and rumors

An announcement from LIGO seems to be imminent…

Confirmation or invalidation of a discovery? We will see but it may be time to pause a little and reflect upon the rumors that have plagued the web since last Fall about a potential discovery.

GWvisual_LIGO

Of course, we are all impatient to know more. Obviously also, some scientists imagine that there is fame to gain by announcing in advance a piece of news to which they have not contributed. Fame indeed: a sure way to become infamous…

Only the LIGO collaboration is entitled to announce anything, and at the time they choose proper. Because the time of physics, the time of carefully checking observations and measurements is not the same time as the one at which rumors spread over the web. And we should all be happy for it.

If some event is observed in a detector, one first has to make sure that this is a real cosmic signal and not an accidental injection of some unwanted signal. This may take months. In parallel, one has to analyse this signal in order to understand which cosmic event could have caused it: a supernova explosion, a merger of two neutron stars or two black holes. One has to make sure that this is not some background noise fluctuation that is unfortunately mimicking a real event. One has to identify as much as possible the parameters that can be measured (masses of neutron stars or black holes, distance of the event, etc.) and also the precision at which they are measured.

It is this long process that may eventually lead to what can be called a discovery (or to the realization that there is no significant result). And this process has to be presented in detail to the scientific community at large, which is the body that, in the end, will decide whether this is a discovery.

We can trust the LIGO collaboration to make an announcement only once they are through with this lengthy, but necessary process. This may now be very soon.

And to be frank, I am convinced that, if these rules were followed in some other sectors of our society, the world would be better off.

Pierre Binétruy

5 Comments

  • Alan H Douglas VMD

    Well said, Professor, and there is joy in the anticipation.

  • Anna Skornyakova

    Dear Pierre, while we are looking forward to the LIGO’s announcement, can I ask one more question (sorry if it is ridiculous, I am just curious). Is it possible that instead of gravitational waves their absence will be detected? Just as in 19th century instead of the ether its complete lack was discovered? It would be a new interesting challenge for you physicists.

    • Pierre Binétruy

      Dear Anna,
      It is much more difficult to detect an absence than a presence. In the example of the ether that you mention, the presence of ether implied that the velocity of light would be different in different directions; this fact was proven to be wrong.
      In the case of gravitational waves, one would have to prove that a known source of gravitational waves is not emitting them. For example, the Hulse and Taylor binary pulsar has a period of rotation that is shifting with time, in complete agreement with a loss of energy in the form of gravitational waves. But these gravitational waves are emitted at a frequency which falls in the range of a space detector: the eLISA mission will be able to prove the existence or absence of such waves.
      Unfortunately, there is no such verification source in the case of ground detectors. There are certainly types of sources (supernova explosions, binary systems of neutron stars or black holes) and astrophysicists evaluate their population. But this is a difficult task, and they could prove to be wrong. If one was not finding gravitational waves in ground detectors, one would conclude that the models for estimating these populations were too optimistic. But this remains very unlikely in the context of the increase of sensitivity of these detectors through major improvements over the last years.
      Pierre

      • Anna Skornyakova

        Dear Pierre, thank you, I see. If I understand correctly, there is quite big population of gravitational waves sources, and if the detectors sensitivity is sufficient, they must detect not only one signal, but all existing waves with an appropriate wavelength at once! Is it really possible to separate them and identify certain sources (or at least types of sources) for each wave? What other information or knowledge is expected to be received from the detection, except for the very presence of gravitational waves?
        And, by the way, in the case of Hulse and Taylor binary pulsar – will the space detector be able to find those certain waves emitted by that certain system among all other waves? Sorry for the number of questions, it is just very, very interesting!

      • Anna Skornyakova

        Re-read your post and found the answers to almost all my questions. It’s awful to be such a dummy.

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