On Thursday, 11 February, 2016, a group of some one thousand scientists co-authored a paper announcing that the LIGO interferometric array had after more than a decade of fruitlessly accumulating data , positively identified the signature of gravitational waves coming from a deep space event. This was a phenomenon predicted by Albert Einstein in 1915 in a landmark paper henceforward known as The General Theory of Relativity. I have known for some time that results are being attributed to observations made with instruments that were inherently incapable of doing so. My scepticism is well known, and I consequently received dozens of requests to publish my view of the matter. In general, layman’s terms, here it is.
On September 14, LIGO observed a “chirp” lasting about a fifth of a second. Analyses of the signal suggest that it was produced by the cataclysmic collision of two black holes a billion light years away. Question: The almighty collision between two supermassive bodies produces a wave lasting just a fifth of second? The instruments that comprise LIGO (Laser Interferometer Gravitational-Wave Observatory) were set up to try to achieve a specific goal, consequent to the predictions of General Relativity Theory. The mirrors in the interferometer are set 4km apart. The expected variation in that distance would be 10^-18 metres or 10^-15 millimetres. In layman’s language, they are looking for a change in distance over the four kilometre separation of ONE THOUSAND TRILLIONTH OF A MILLIMETRE!
The change in distance equates to a required design sensitivity of the LIGO interferometer of one part in 10^21. That is, a resolution of ONE PART in ONE BILLION TRILLION.
Let’s try to put the expected variation into some sort of comprehensible perspective. The diameter of a hydrogen atom is obtained experimentally at 10^-7 mm. Therefore, Ligo seeks to measure a distance that is ONE HUNDRED MILLIONTH of the diameter of a hydrogen atom. Put another way, if the change were one hundred million times greater than the one they claim to have measured, it would be the same as adding or subtracting a SINGLE ATOM to or from the four kilometre distance separating the mirrors.
That is probably unimaginable to most people, so let’s try to add further perspective.
The best precision mirror surfaces are polished to match the ideal, nearly parabolic surface to about 25 nanometres – about 3 ten-thousandths of the width of a human hair. That is incredibly fine tolerance, but let’s compare it with the difference in length that LIGO claims to measure. A nanometre is a unit of spatial measurement that is 10^-9 meter, or one billionth of a meter. Take it down one level – a nanometre is a millionth of a millimetre.
The most precisely polished astrophysical mirrors, like those used in LIGO, can have peaks 25 nm above and below the theoretical surface plane of the mirror. 50 nm is a BILLION TIMES bigger than the gravitational wave signature. In practical terms, it is impossible to measure the distance between the two mirrors in each interferometer (actually said to be 3999.5 metres) to the required tolerances, so they have had to take an average, which is guesswork.
There are other conditions which change the distance between the mirrors by many orders of magnitude greater than the anticipated gravitational wave fluctuation. There is change in ambient temperature as the array goes through day and night cycles, and therefore expansion and contraction. Waves caused by seismic fluctuations are ever present, disturbing the separation. There are also anthropogenic waves, resulting from trucking, blasting, mining, and railroads, for example.
Then there are the influences affecting the light and its frequency that lie between the source of the radiation being measured and the Earth. There are all manner of objects, systems, and force fields in inter-galaxian space. These are not precisely known; some are completely invisible to us, yet they have a profound effect on light signals that simply cannot be quantified by measurement.
The LIGO instruments have all sorts of protective devices shielding them from extraneous kinetics and noise, but to filter those impediments out without fiddling with the sought-after signal, the LIGO scientists would have to guess their magnitude. That is not an empirically sound way to arrive at an accurate answer.
Ligo cost over $620 million US to construct. Research grants and operating costs take that figure to well over one billion US dollars. Hold that thought.
To summarise, paraphrasing the words of Nobel Laureate Steven Weinberg in reference to Edwin Hubble’s initial interpretation of galaxian redshifts, “…it seems they knew the answer they wanted to get.”