Rumors that the LIGO interferometers had most likely
detected a gravitation wave (GW) were circulating
in autumn last year. Personally, the direct information
I got quite late, at the beginning of December, was
``we have seen a Monster'', without further detail.
Therefore, when a few days before February 11
quantitative rumors talked of 5.1 sigmas, I was disappointed
and highly puzzled.
How could a Monster have only just a bit more than
five sigmas? Indeed in the past decades we have seen
in Particle Physics
several effects of similar statistical significance
coming and going,
as Alvaro de Rujula
depicted already in 1985 in his famous
Cemetery of Physics of
Fig.2[48].15
Figure:
Alvaro de Rujula's
Cemetery of Physics[48], with graves indicating
`false alarms' in frontier physics,
and not old physics ideas faded out with time,
like epicycles, phlogiston or aether.
 |
Therefore for many of us a five-sigma effect
would have been something worth discussions
or perhaps further investigations but certainly not a
Monster.16This impression was very evident
from the reaction many people had after
seeing the wave form.
``Came on, this is not a five-sigma
effect'', commented several colleagues, more or less using
the same words, ``these are hundreds
of sigmas!'', a colored expression to say that
just by eye the hypothesis
Noise was beyond any imagination.17
The reason of the `monstrosity' of GW150914 was indeed in Table 1
of the accompanying paper on
Properties of the binary black hole merger
GW150914[28]: a Bayes factor
``BBH merger'' Vs ``Noise''18of about
(yes, five times
ten to one-hundred-twenty-five). This means that, no matter
how small the odds in favor of a BBH merger were
and even casting doubt on the evaluation
of the Bayes factor,19
the posterior odds
would be extraordinary large, the probability of
noise being smaller than Shakespeare's drop of water
identically recovered from the sea.20
Giulio D'Agostini
2016-09-06
