April 12, 2016 – Dr William Unruh, UBC, Gravitational Radiation – listening to black holes collide

Dr Wiiliam UnruhWilliam Unruh is a Professor of Physics at the University of British Columbia who has made seminal contributions to our understanding of gravity, black holes, cosmology, quantum fields in curved spaces, and the foundations of quantum mechanics, including the discovery of the Unruh effect. His investigations into the effects of quantum mechanics of the earliest stages of the universe have yielded many insights, including the effects of quantum mechanics on computation. Dr. Unruh was the first Director of the Cosmology and Gravity Program at the Canadian Institute for Advanced Research (1985-1996). His many awards include the Rutherford Medal of the Royal Society of Canada (1982), the Herzberg Medal of the Canadian Association of Physicists (1983), the Steacie Prize from the National Research Council (1984), the Canadian Association of Physicists Medal of Achievement (1995), and the Canada Council Killam Prize. He is an elected Fellow of the Royal Society of Canada, a Fellow of the American Physical Society, a Fellow of the Royal Society of London, and a Foreign Honorary Member of the American Academy of Arts and Science.

For more information on Dr Unruh, visit the website of the Perimeter Institute https://www.perimeterinstitute.ca/people/Bill-Unruh


Notes by John Gunn on Dr. Unruh’s presentation

John Madden introduced Dr.  William Unruh, a much decorated physicist from UBC.  Member of the Royal Society and with may other honours.

In his talk, Dr Unruh severely challenged the acumen and the imagination of his audience and it is probably safe to say that the majority of us, having been weaned on Newton’s Laws of Physics, will be left trying to grasp the nature of some of the items put forward by the speaker.  It all runs counter to our intuitive mental picture of our world and our universe. How did our conventional education leave out so much?  However, one can say that his talk emphasized THREE remarkable aspect, these being in no particular order.   (1) The ingenuity and perfection of mankind’s scientific and engineering prowess in the design of the test equipment constructed in Louisiana and Washington to detect gravitational waves (2) the sheer size and content of our universe as seen in relation to our ‘tiny’ solar system  (3) the awesome genius of one person – Albert Einstein – in accurately predicting, among other things, the Gravitational Waves discussed by Dr Unruh today.

(1) The exquisite design of the two sites was amazing.  Two 4km laser beams at right angles and the measurement of the time elapsed and hence the length of the beam – measured to within the diameter if an atomic nucleus – this was done at the same time as to be able to discount any extraneous ‘noise’ such as seismic disturbances or man-made vibrations – this sort of accuracy is truly amazing.  They even have to allow for the effect of varying starlight impinging on the equipment and altering the parameters. Similar experiments to detect these gravitational waves are now being planned by Japan (this one is underground), India, Italy, Germany and several other nations.  Also being mooted is an outer space location, in which case the 4km becomes 1 million km and the sensitivity thereby increased enormously and there is no seismic noise.

(2) The waves which were detected in recent months were deduced as being the result of two black holes – with each of these entities being roughly 30 times the size of our own sun and about 100 km in diameter – the twin entities had been circling each other and they finally coalesced into a single black hole of immense size, and gravitational waves resulted from this event.  It has taken the waves several billion years to traverse the distance from out there to earth!   But the amazing part is that the gravitational waves are so faint after their billion light years of travel that their final effect on the length of the 4km arms means that they are looking for a variation of one part in 1020 (in case that doesn’t print, that number is over a billion billion , or, as already mentioned, less than the diameter of the nucleus of an atom).

(3) Einstein brilliantly proposed his General Theory of Relatively around 1915.  He did this without benefit of Hubble Telescope, or modern computers to solve his amazing equations. At that time he predicted that we would find that light beams will be bent by gravity, that nothing can exceed the speed of light, that the rate of time changes would change with speed of motion, and that there will be gravitational waves.  This final prediction has now been proved – after a delay of 100 years!

Among the other interesting aspects of these measuring experiments was the length to which the scientists went to discount extraneous influences.  There was even a sort of “devil’s advocate” involved to make sure no misleading results accrued which could have been made by someone pining for glory or recognition.  In other words, the results of the experiments are clear, unequivocal and error-free and prove conclusively that Gravitational Waves exist as predicted 100 years ago.

Gravitational Waves are ripples in space-time, a concept which in itself is the foundation of Einstein’s theory.   These waves change distances without requiring any acceleration – again a concept which challenges our intuitive sense of the world around us.  Similar to electromagnetic phenomena, the waves act perpendicularly to the length being affected.   This is a point in the story to explain that you can’t see a black hole because light can’t escape from it, but you can infer its existence by the effect it is having on visible light from stars in the vicinity.  It’s interesting here to point out that these gravitational waves reached each of the two detector system by passing right through the earth itself  from the far side.  Gravity waves don’t care about material in the way so this has no effect on the waves themselves as they head for the detectors.  Incidentally the waves detected thus far have been from black holes but such waves would also result from two neutron stars coalescing.

Questions and Answers

This is great for someone’s ego.  What value  is all this  to society?

Dr Unruh may have had to bite his tongue to respond politely to this question.  It makes you think of the engineer who saw a naturally formed hoop rolling down a hill and said to himself “I think I could make something useful out of that thing.  I think I’ll call it a wheel.” Actually Dr Unruh gave a very full and convincing justification for the 1 billion dollars this experiment cost us to satisfy our curiosity.

Were you and us just lucky with our timing to so quickly detect such an event?

No one knew ahead of time whether it would be days or decades before we got an event.  It now looks like there will be plenty of them.

What is a black hole like?

Well we confirmed in a 1919 eclipse that light is deflected by passing a mass.  If the mass it huge enough (eg a black hole) the light originating within the black hole is passing such a huge mass that the beam is deflected back inside.  In short, light cannot escape, therefore you see nothing.

Will we run out of black holes?

Generally black holes are far apart from one another and so the instances of two black holes orbiting one another and coalescing into this kind of event are probably few and far between.

How do you get these waves to comply with Newtonian physics?

In Newtonian physics there are no gravity waves.  Quite simply, with Relativity, Newtonian physics is superseded and is no longer valid on the large scape of our universe.  It is still useful as an approximation within our solar system which is so small.  Bear in mind that within the concept of General Relativity, gravity is NOT a force as postulated by Newton way back then.

Is there a theory to explain how Einstein figured out General Relativity?

There is a project under way at the moment called the “Einstein Project” to review everything he wrote or said or read, to try and answer that question.  Remember, it took Einstein eight full years to arrive at his famous conclusion.  One of the final observations made which confirmed all his work was the incredibly tiny but important aberration in the elliptical orbit of the planet Mercury which could not be explained by Newton but was exactly in accordance with General Relativity.


The speaker was thanked by Norm Leach.  Norm included one special question of his own – “Is there intelligent life out there?  Yes or No”   He did not get an unequivocal answer.


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