The only known subatomic particles were the proton and the electron: the neutron and the neutrino, for example, were not predicted or discovered until the s.
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The structure of the nucleus was regarded as an interesting but secondary problem, and the unification of forces was considered, in the words of Pais, a minor issue. Electromagnetism then emerged naturally from this extra dimension. Perhaps more so than Pais, we now recognize these early theories as breakthroughs in unification because of their many echoes in the supergravity and string theories of the past 20 years. Kaluza published his idea in , which Einstein pursued in his first unification paper with Jacob Grommer the following year.
Indeed Einstein was to return to 5D theories every few years for the rest of his life. However, even Einstein had to admit that his unification papers were not always ground breaking. For example, after some initial confusion he recognized that the two papers he wrote in were equivalent to the work of Klein. Einstein had hoped to identify quantum fields with such higher components that only arose in the 5D theories. He pursued many apparently blind alleys, such as asymmetric generalizations of the metric, and even postulated that there might be no tensor at all.
Unfortunately, these ideas were unsuccessful.
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For example, in his first unification paper in the antisymmetric part of his tensor field was not suitable for describing all the components of the electric and magnetic fields. However, in his final years following he returned to a theory with a fundamental tensor that was not symmetric and would include both the metric and the electromagnetic tensor, which avoided some of these problems. It is difficult to accuse Einstein of leaving stones unturned — no matter how unpromising they might appear. For example, in the early s he even toyed with the idea that nature might not be described by partial differential equations.
Modern theorists can hardly be accused of excessive conservatism, but even they have not revived this startling speculation! He tried many different ideas, and often returned to earlier theoretical haunts, such as Kaluza-Klein theories, with something new to say. However, the truth is that he was adrift from many of the most important developments in physics at the time. For instance, he was famously sceptical — if not downright hostile — towards quantum physics, and he does not seem to have followed closely the discoveries of new particles and interactions.
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Format: Hardcover Verified Purchase. A fascinating story of how and why as best as one can tell from the record Einstein did what he did. A knowledge of general relativity is useful to follow parts of it. Format: Kindle Edition Verified Purchase. In my opinion, the author didn't achieve a good understanding of Einstein's motivations. The book is however interesting for it's factual contents. The fact that Einstein understood well the role of Science as the attempt to understand the physical world as opposed to Engineering as an attempt to produce formulas that give the same result makes Einstein the only true Physicist in the quantum field of his era.
Everything else would fall into place After 60 years from his dead, we still did not solve that "simple" problem, much less the unification of all forces.
Einstein's revolution: A study of theory unification
It is then premature to say if Einstein was right or wrong in his attempts. Taking an historic sample, we will need another century before developments allows us to judge well Einstein's intuition. And that is not really important He should be considered an hero for fighting for his convictions alone until the end. But much remained to be unified.
In general relativity and classical electrodynamics there were two field theories, both defined on the continuum, both with unlimited range and an inverse square law, both exhibiting static and dynamic effects although the details of gravitomagnetism would not be worked out until later. And yet the theories seemed entirely distinct: gravity was always attractive and worked by the bending of spacetime by matter-energy, while electromagnetism could be either attractive or repulsive, and seemed to be propagated by fields emitted by point charges—how messy. Further, quantum theory, which Einstein's paper on the photoelectric effect had helped launch, seemed to point in a very different direction than the classical field theories in which Einstein had worked.
Einstein never disputed the successes of quantum theory in explaining experimental results, but suspected it was a theory based upon phenomena which did not explain what was going on at a deeper level.
For example, the physical theory of elasticity explains experimental results and makes predictions within its domain of applicability, but it is not fundamental. All of the effects of elasticity are ultimately due to electromagnetic forces between atoms in materials. But that doesn't mean that the theory of elasticity isn't useful to engineers, or that they should do their spring calculations at the molecular level. Einstein undertook the search for a unified field theory , which would unify gravity and electromagnetism, just as Maxwell had unified electrostatics and magnetism into a single theory.
In addition, Einstein believed that a unified field theory would be antecedent to quantum theory, and that the probabilistic results of quantum theory could be deduced from the more fundamental theory, which would remain entirely deterministic. From until his death in Einstein's work concentrated mostly on the quest for a unified field theory. He was aided by numerous talented assistants, many of whom went on to do important work in their own right. He explored a variety of paths to such a theory, but ultimately rejected each one, in turn, as either inconsistent with experiment or unable to explain phenomena such as point particles or quantisation of charge.
As the author documents, Einstein's approach to doing physics changed in the years after While before he was guided both by physics and mathematics, in retrospect he recalled and described his search of the field equations of general relativity as having followed the path of discovering the simplest and most elegant mathematical structure which could explain the observed phenomena.
He thus came, like Dirac, to argue that mathematical beauty was the best guide to correct physical theories.
Einstein's revolution: A study of theory unification | EurekAlert! Science News
In the last forty years of his life, Einstein made no progress whatsoever toward a unified field theory, apart from discarding numerous paths which did not work. In seeking to unify electromagnetism and gravity, he ignored the strong and weak nuclear forces which had been discovered over the years and merited being included in any grand scheme of unification. So great was the respect for Einstein's achievements that only rarely was a disparaging word said about his work on unified field theories, but toward the end of his life it was outside the mainstream of theoretical physics, which had moved on to elaboration of quantum theory and making quantum theory compatible with special relativity.
It would be a decade after Einstein's death before astronomical discoveries would make general relativity once again a frontier in physics.
Einstein’s Methodology, Semivectors and the Unification of Electrons and Protons
What can we learn from the latter half of Einstein's life and his pursuit of unification? The frontier of physics today remains unification among the forces and particles we have discovered.
Now we have three forces to unify counting electromagnetism and the weak nuclear force as already unified in the electroweak force , plus two seemingly incompatible kinds of particles: bosons carriers of force and fermions what stuff is made of.