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Friday, September 30, 2022
Dr. Brown: Einstein, relativity, neutron stars and making mistakes
Dr. William Brown
Dr. William Brown

According to the brilliant Cambridge physicist and mathematician Paul Dirac, Albert Einstein was the most brilliant physicist of the 20th century, and possibly all time.

But even Einstein could be stubbornly, even spectacularly wrong.

Several physicists, including Paul Lemaitre, a young Belgian priest with graduate degrees from Cambridge and MIT in physics, pointed out to him that the mathematics Einstein employed to describe the relationships among mass, time and space in his theory of general relativity, also described an expanding universe and hence a very much smaller earlier universe in the past.

To which Einstein brusquely responded to Lemaitre, “Your mathematics may be excellent, but your physics is terrible” and went on to introduce his famous (or infamous depending on your perspective) cosmological constant into his equations to restore stability to the universe.

Later when astronomical observations by Erwin Hubble revealed the universe was indeed expanding, Einstein publicly apologized and withdrew his constant.

Although Einstein was one of the founding fathers of quantum physics based on his work on the quantal nature of light and energy, he resisted the whole notion of uncertainty, and apparent lack of causality and sense of time inherent in quantum physics.

He spent the last 30 years of his life in self-imposed exile at Princeton University looking for a universal field theory that would reconcile general relativity with quantum physics. He didn’t succeed nor have any physicists since, including the likes of Stephen Hawking and Roger Penrose.

Ever since Einstein described general relativity, every attempt to find a flaw in the theory has failed, much to the dismay of some physicists looking for a "theory of everything" in theoretical physics, but so far stymied in their search for such a holy grail.

The failure to reconcile general relativity (the physics of the large) with quantum physics (the physics of the subatomic universe) is a serious stumbling block to progress in understanding two major mysteries in physics: What happens to matter and energy inside black holes? And what happened in those first few seconds when the universe was born?

In 2002, two large neutron stars were spotted circling each other every 2.5 minutes and emitting bursts of radio waves at metronomically precise intervals – every 2.8 seconds for one star and every 23 milliseconds for the other. They are what astronomers call pulsars (short for pulse and stars).

When stars run out of fuel to sustain fusion, they sometimes shed their outer shells and collapse into black holes or neutron stars. Neutron stars are the densest objects in the universe, made up of neutrons jammed together, with, as Dennis Overbye, science writer for the New York Times, put it a few years ago, the mass of the sun crammed into something the size of New York City.

This pair of neutron stars offered the perfect opportunity to precisely test general relativity’s capacity to predict how the mass of neutron stars bend and alter the timing of the radio waves they emit.

Now, years later, after collecting radio-wave data generated by both neutron stars using radio telescopes scattered around the world, the scientists and engineers finally had enough data to analyze and answer the original question: How well did general relativity’s predictions stand up as predictors of mass-related changes in the radio signals from both neutron stars?

In this, the most demanding test of general relativity to date, the answer was a resounding, perfect on all accounts.

As with so many other predictions based on general relativity, including the bending and slowing of light by masses, the generation of gravitational waves in space-time by the collision of black holes and other massive objects (for which studies a Nobel prize was awarded in 2017) and an expanding universe, Einstein turned out to be right or at least his equations turned out to be highly predictive, even if for philosophical reasons, he sometimes shrank from the implications of his own brilliant thought experiments and equations.

Even his cosmological constant turned out to be consistent with the expansile force generated by the as-yet mysterious dark energy and worth belated congratulations to Einstein.

What a paradox Einstein was: visionary, prophet, imaginative and sometimes stubbornly wrong – and except for his brilliance, like us, he made mistakes.

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the InfoHealth series at the Niagara-on-the-Lake Public Library.