When black holes merge,
particles without mass carry
the story at the speed of light
By Helen Gavaghan
Three billion years ago*, around the time oxygen is thought to have appeared on Earth1, two black holes of Solar-mass order of magnitude merged.
The gravitational waves which, in their shape and physical characteristics, tell the story of that event, then began a 28.4 trillion, billion kilometres journey.
For billions of years the gravitational waves of that dynamic event chased each other through the Universe at the speed of light. During that time biology, chemistry,
geology and consciousness evolved on Earth.
Then, on 4th January, 2017, the force of the event from nearly a quarter of the way across the known Universe was felt by the advanced Laser
Interferometer Gravitational-Wave Observatory (aLIGO) in the US.
Consciousness - in this case human - after spending a lot of money, and thought, and scientific international diplomatic effort had observed the
gravitational signal of a binary, solar-mass Black-Hole coalescence, which took place in our long distant past. Energy shed while solid matter was
changing its shape, and size, and orientation - and, in the process, altering the geometry of its immediate enfolding spacetime - began its trip to Earth
in the form of gravitational waves. Having no charge, the gravitational waves had no known interaction with or distraction from electro-magnetism.
The story in these gravitational waves is not something "new under the Sun". This, potentially, is something new before our Sun existed. It heralds a new physics. Around
the world space-based and underground interferometers for the future detection of gravitational waves are under dev-elopment. Only two previous Gravitational Wave events have been detected; both by LIGO.
January's observation is the one which consolidates and affirms a new science is here. Gravitational waves exist at wavelengths hard for the human mind to conceive. From
peak to adjacent peak they can stretch from the Earth's surface to an event which occurred before when the Universe became transparent to visible light**.
Published this June in Physical Review Letters, January's discovery [January 2017] is called GW170104, after the date of its detection.
The first two detections, coming from a different binary black-hole system, were made in 2015 during the interferometer*'s first run, and they provided data which
improved instrument calibration.
aLIGO is now on its third run!!. At the beginning of this month a European collaboration called Virgo joined aLIGO in the hunt for gravitational waves. That particular
Added 5th February, 2018: Minor line edit post publication to prevent repetition of words at the beginning of paragraphs.
For non scientists:
The interference between waves from sources separated from one another by location and/or time creates a combined pattern susceptible to analysis.
A single (or combined) source moving would additionally have a Doppler shift, and that Doppler shift would be constrained by physical realities such as orbital dynamics, or, in
the case of a train whistle, the railway track. A number of factors determine whether Doppler, or interference physics, or a balance of the two are the most apposite technique
for analysing a phenomenon.
3 SCIENCE, PEOPLE & POLITICS [ISSN 1751-598X]