Category Archives: quantum physics

Einstein vs Bohr. Does God throw dice?

In the world of physics, it can be called the Clash of the Titans. Many believe that the upheaval in the scientific world that sparked in the 20th century is unsurpassed by any event or spate of events that pertain to our understanding of the cosmos. The advent of the Planck’s constant, proposed by Max Planck in 1900 would revolutionize our knowledge of atoms and the universe.

In 1905, Albert Einstein, with his sharp visual imagination and youthful energy was able to incorporate Planck’s idea by putting forward the idea that light comes not just in waves but in tiny packets – called quanta (photons). However, as he admitted himself, he struggled to comprehend the unsettling implications of this theory; as it was incongruous with his vision of the underlying reality of the universe (Isaacson, 2007).

Niels Bohr, in 1913 proposed that the electrons in an atom revolve in certain paths called orbits and as an atom agitates under heat, the electrons jump from one orbit to the other and vice versa without ever landing in the space between the two orbits. He defined the quanta as the energy required to displace an electron between two successive orbits.  Einstein, though initially wary succumbed to Bohr’s such proposition in the ensuing years.

The Uncertainty Principle

In 1927, Werner Heisenberg, a student of Niels Bohr pioneered the uncertainty principle which states

The more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa.  

In the words of Walter Isaacson, author of Einstein, his life and universe,

The very act of observing something – of allowing photons or electrons or any other particles or waves of energy to strike the object affects the observation. But Heisenberg’s theory went beyond that. An electron does not have a definite position or path until we observe it.

The uncertainty principle, so simple yet so startling, was a stake at the heart of physics. It asserts that there is no objective reality – not even an objective position of a particle – outside of our observations. Heisenberg’s principle and other aspects of quantum mechanics undermine the notion that the universe obeys strict causal laws. 

This was such a huge blow to Einstein’s reasoning behind the mystics of the universe that he regarded the uncertainty principle as unpropitious, if at best incomplete. As the ensuing experiments continued to demonstrate the uncertain nature of the quanta, Einstein embarked in his quest for a Unified Field Theory that would expound the subatomic world in a way the uncertainty principle did not. His quest itself would remain incomplete if not unavailing.

The impression of a world ruled by probabilities and not by determinism based on Newton’s laws was a concept he would never relent to until his death; as he once famously remarked to his friend and physicist Max Born,

“….but I am convinced that at any rate he (God) does not throw dice.”

There was yet another problem with the quantum mechanics that Einstein could not reconcile with – entanglement; a property where an observation made on a particle instantaneously affects another particle at a distance. His Special Theory of Relativity had ascribed the speed of light as the “cosmic speed limit”. In other words, nothing can travel faster than light. So he considered the idea of entanglement an absurdity as he called it

spooky action at a distance”

The two gangsters of theoretical physics first met in 1920 when Bohr visited Einstein in his Berlin apartment. Following their obverse discussion on the quanta, the two parted; each admiring the other’s personality and intellect. Einstein found the Dane “personally endearing” and the latter, for his part also “revered” him. In their next meeting in Copenhagen, the two got in a streetcar and had an intense intellectual debate as Bohr drove desultorily forgetful of his home where he was supposed to take him to (Cromwell, 2010).

Their biggest clash was at the 1927 and 1930 Solvay conferences with Einstein attacking the quantum interpretation of the world with his witty, astute reasoning and Bohr, with Heisenberg and Pauli’s support, pulling together a rational answer usually pointing the inaccuracies in Einstein’s thought experiment-contrived questions. The detailed description of the two debates can be read here.

One on occasion Bohr responded to Einstein’s adage that God does not play dice by saying

“….stop telling God what to do.”

An excerpt from Isaacson’s biography of Einstein goes as follows:

“More than just a friendship, their relationship became an intellectual entanglement that began with divergent views about quantum mechanics but then expanded into related issues of science, knowledge and philosophy. ‘In all the history of human thought, there is no greater dialogue than that which took place over the years between Niels Bohr and Albert Einstein about the meaning of the quantum’, says the physicist John Wheeler, who studied under Bohr.”

So what do the experiments reveal?

In 1964, after both Einstein and Bohr had died, John Bell, an Irish theorist working at the CERN in Geneva, proposed a way for testing the two approaches. In 1982, Alain Aspect, a French physicist and his co-workers were able to conduct the experiment using two-photon laser excitation and the results conformed with the quantum approach i.e. the entanglement. Other experiments carried out since then have all pointed to the predictions of the quantum theory.

So was Einstein wrong? Perhaps. From what we know until now,

At the fundamental level, we live in a world of uncertainty, of probability rather than predictability. In the everyday world, if we know the initial state of an object then by using Newtonian Laws, its final state can be calculated precisely. At the quantum level, however, no matter how much you know about the present, the future can only be predicted in terms of probabilities.

Our universe is one ruled by uncertainty. At least from what we know until now, God really does play dice.

Bibliography

Cromwell, R. L. (2010). Being Human: Human Being: Manifesto for a New Psychology. Indiana, USA: iUniverse.

Isaacson, W. (2007). Einstein, His Life And Universe. Croydon, UK: CPI Group.

Phys.org. (2010). New light shed on old dispute between Einstein and Bohr. Retrieved from http://phys.org/news183054425.html.

Sarahana. (2012). Einstein vs. Bohr: how their career-long debate led to parallel universes. Retrieved from http://www.imposemagazine.com/bytes/einstein-vs-bohr.