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Schon 2010 wurde das Team des LIGO-Experiments mit einer Fake-Gravitationswelle getäuscht!

Jocelyne Lopez
Germany

Nov 21, 2018 — 

Eine Mitteilung von Dr. Wolfgang Engelhardt, Physiker, ehemaliger Mitarbeiter des Max-Planck-Instituts für Plasmaphysik in Garching:

 

Die „Gravitationswelle“ GW150914 vom 15. September 2015 war keineswegs die erste ihrer Art. Fünf Jahre vorher hatte das LIGO-Team GW100916 „entdeckt“, allerdings mit einem Verfallsdatum, das schon im März 2011 endete, siehe hier. Diese amüsante Geschichte ist wenig bekannt aber wert, hier in ihren wesentlichen Zügen zitiert zu werden (Zitate):

What kind of merger?

Mergers of black holes and/or neutron stars are very rare, but they can come in many shapes and sizes. What were the masses of the two stars? If one was significantly less than 3 solar masses, it could be a neutron star, not a black hole, and this is an important distinction to astrophysicists. Whether black holes or neutron stars, they might be expected to be spinning; can this be determined from the signal? And where, precisely is the system located on the sky, and at what distance?

All told, there are fifteen parameters that can be extracted from the signals at the LIGO and Virgo detectors, and several different teams of scientists were able to measure them. The result, however, depended on the waveform models used, and the most realistic models were also the most complex.

Documenting the "Evidence":

The scientists gathered all this information together in a paper entitled "Evidence for the Direct Detection of Gravitational Waves from a Black Hole Binary Coalescence". (Coalescence refers to the inspiral of the two stars, their merger into a single perturbed black hole, and the "ringdown" into a final quiet black hole, all through the emission of gravitational waves). A second paper described the parameter estimation procedures and results. A third summarized the search for binary coalescence and the overall results (only one event was observed above the background noise).

Material was prepared for the open release of data relevant to this event, and a whole suite of resources for education and public outreach was assembled. The event was renamed "GW100916", for the year, month and date that it was recorded.

Opening the envelope:

An independent "Detection Committee" reviewed and double-checked all of this work, and reported their findings to the two collaborations. Everyone voted on whether the work, and all the documentation, was sufficient to announce the first detection; the result was a unanimous "yes". The Blind Injection Envelope was opened on March 14, 2011 at a joint meeting of the LIGO Scientific Collaboration and the Virgo Collaboration in Arcadia, CA. There were 300 people in the room and another 100 connecting through a video teleconference. The envelope was opened -- and there was the event: it was a blind injection, not the first direct detection of gravitational waves.

 

Was lernen wir daraus?

1) Ab 2007 verfügte man bereits über Rauschkurven, die es möglich erscheinen ließen, Gravitationswellen zu messen, denn sonst hätte sich das LIGO-Team nicht an die Auswertung und Analyse der Signale gemacht.

2) Ein Team von ca. tausend Wissenschaftlern konnte vom Management hinter die Fichte geführt werden und kam nach halbjähriger Prüfung zu dem einhelligen Schluss, die erste Gravitationswelle direkt gemessen zu haben.

3) Zwischen 2007 und 2015 hat der Kosmos beharrlich geschwiegen, oder keinen Blick durch das „neue Fenster ins All“ erlaubt. Das Upgrade, welches 2015 fertiggestellt war, hatte nämlich nur eine Verbesserung der Rauschkurven um einen Faktor 3 gebracht, so dass spätere Signale mit einem SNR von 30 auch mit SNR 10 gut zu messen gewesen wären.

4) Im September 2015 war es endlich so weit, dass man die Geldgeber mit einer Welle beliefern konnte, wobei aber auch das Team nicht wissen konnte, ob sie echt oder gefälscht war. Dann ging es Schlag auf Schlag: Insgesamt wurden inzwischen sechs Ereignisse gefunden, die ausreichten, den Nobelpreis zu sichern.

Es hätte eine sehr einleuchtende Methode gegeben nachzuweisen, dass man tatsächlich die Breite eines Menschenhaars mit einem Zollstock von vier Lichtjahren Länge vermessen kann (darauf kommt man, wenn man Spiegelauslenkung und Interferometer-Arm mit 10^13 hochskaliert). Diese Methode besteht in der Eichung, die im „discovery paper“ beschrieben ist: Man simuliert eine GW indem man 10 Spiegelauslenkungen von 1 Attometer während 0.15 Sekunden mit Hilfe des calibration-Lasers durch Strahlungsdruck erzeugt und misst gleichzeitig den zugehörigen Detektor-output. Auf diese Weise erhält man eine Eichkurve mit deren Hilfe man aus einem gemessenen Detektorsignal auf die Stärke einer erzeugenden GW schließen kann.

Nur leider gibt es eine solche Eichkurve gar nicht, wie Herr Danzmann mir versichert, siehe hier, Dokument #13. So arbeitet man also mit ungeeichten Instrumenten, findet immer wieder mal ein Osterei, das man selbst im Gras versteckt hat, und verkündet fröhlich der Welt einen neuen Blick ins Weltall, der nur Eingeweihten zugänglich ist, während nicht mal das Forscherteam wissen kann, was echt und was fake ist.

Ein Gutes hat diese Pseudo-Experimentalphysik. Nach dem großen Getöns, das man veranstaltet hat, muss man nun pro Haushaltsjahr eine, besser zwei GW’s fälschen, damit die Geldquellen weiter sprudeln. Es fällt mir schwer, mir vorzustellen, dass dies auf Dauer gut geht. Ich muss allerdings einschränken, dass ich mir auch nicht vorstellen konnte, wie sehr exakte Wissenschaft, die mein geliebter Beruf war, entarten kann.

Dr. Wolfgang Engelhardt

----------------------------

ENGLISH VERSION

Already in 2010 the team of the LIGO experiment was deceived with a fake gravitational wave!

The "Gravitational Wave" GW150914 from September 15, 2015 was by no means the first of its kind. The LIGO team had "discovered" GW100916 five years earlier, but with an expiry date that ended in March 2011, see here. This amusing story is little known but worth quoting here in its essential features (quotes):

What kind of merger?

Mergers of black holes and/or neutron stars are very rare, but they can come in many shapes and sizes. What were the masses of the two stars? If one was significantly less than 3 solar masses, it could be a neutron star, not a black hole, and this is an important distinction to astrophysicists. Whether black holes or neutron stars, they might be expected to be spinning; can this be determined from the signal? And where, precisely is the system located on the sky, and at what distance?

All told, there are fifteen parameters that can be extracted from the signals at the LIGO and Virgo detectors, and several different teams of scientists were able to measure them. The result, however, depended on the waveform models used, and the most realistic models were also the most complex.

Documenting the "Evidence":

The scientists gathered all this information together in a paper entitled "Evidence for the Direct Detection of Gravitational Waves from a Black Hole Binary Coalescence". (Coalescence refers to the inspiral of the two stars, their merger into a single perturbed black hole, and the "ringdown" into a final quiet black hole, all through the emission of gravitational waves). A second paper described the parameter estimation procedures and results. A third summarized the search for binary coalescence and the overall results (only one event was observed above the background noise).

Material was prepared for the open release of data relevant to this event, and a whole suite of resources for education and public outreach was assembled. The event was renamed "GW100916", for the year, month and day that it was recorded.

Opening the envelope:

An independent "Detection Committee" reviewed and double-checked all of this work, and reported their findings to the two collaborations. Everyone voted on whether the work, and all the documentation, was sufficient to announce the first detection; the result was a unanimous "yes". The Blind Injection Envelope was opened on March 14, 2011 at a joint meeting of the LIGO Scientific Collaboration and the Virgo Collaboration in Arcadia, CA. There were 300 people in the room and another 100 connecting through a video teleconference. The envelope was opened -- and there was the event: it was a blind injection, not the first direct detection of gravitational waves.

What do we learn from this?

1) From 2007 there were already noise curves that made it possible to measure gravitational waves, otherwise the LIGO team would not have started evaluating and analyzing the signals.

2) A team of about a thousand scientists was led behind the spruce by management and came to the unanimous conclusion after six months of testing that they had measured the first gravitational wave directly.

3) Between 2007 and 2015 the cosmos persisted, or did not allow a look through the "new window into space". The upgrade, which was completed in 2015, had only improved the noise curves by a factor of 3, so that later signals with a SNR of 30 would also have been easy to measure with a SNR 10. 5

4) In September 2015 it was finally time for the donors to be supplied with a wave, but the team could not know whether it was real or fake. Then everything went quickly: a total of six events have now been found which are sufficient to secure the Nobel Prize.

There would have been a very plausible method to prove that you can actually measure the width of a human hair with a ruler four light years long (that's what you get when you scale the mirror deflection and interferometer arm up to 1013). This method consists of the calibration, which is described in the "discovery paper": You simulate a GW by generating 10 mirror deflections of 1 attometer for 0.15 seconds with the help of the calibration laser by means of radiation pressure and simultaneously measure the associated detector output. In this way, a calibration curve is obtained which can be used to infer the strength of a generating GW from a measured detector signal. Unfortunately, there is no such calibration curve, as Mr Danzmann assures me, see here, document # 13 ). So you work with uncalibrated instruments, you always find an Easter egg that you have hidden in the grass, and cheerfully announce to the world a new look into space that is only accessible to the initiated, while not even the research team can know what is real and what is fake.

This pseudo-experimental physics has a good side. After the big buzz that was held, you now have to fake one, or better two, GW's per household year so that the money sources continue to bubble up. It is difficult for me to imagine that this will work well in the long run. I have to restrict, however, that I also couldn't imagine how very exact science, which was my beloved profession, can degenerate.

Dr. Wolfgang Engelhardt

 

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Bild: © Wolfgang Engelhardt


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