By Dan Hooper, Ph.D., University of Chicago The String theory is considered as one of the future unified field theories. (Image: Natali Art collections/Shutterstock)Einsteins First Attempt at Unified Field Theory
In 1923, Einstein published a series of papers that built upon and expanded on Eddingtons work of affine connection. Later in the same year, he wrote another paper, in which he argued that this theory might make it possible to restore determinism to quantum physics.
These papers of Einstein were covered enthusiastically by the press since he was the only living scientist that was a household name. Although few journalists really understood the theory that Einstein was putting forth, they did understand that Einstein was proposing something potentially very important.
But unfortunately, it was not true. Few of Einsteins colleagues were impressed by this work. And within a couple of years, even Einstein accepted that his approach was deeply flawed. If Einstein was going to find a viable unified field theory, he would have to find another way of approaching the problem.
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Einsteins next major effort in this direction came in the late 1920s. This new approach was based on an idea known as distant parallelism. This approach was very mathematically complex as Einstein treated both the metric tensor and the affine connection as fundamental quantities in this approach, trying to take full advantage of both.
Once again, the press responded enthusiastically. But again, Einsteins colleagues did not. One reason for this was that Einstein was trying to build a theory that would unify general relativity with Maxwells theory of electromagnetism. But over the course of the 1920s, Maxwells classical theory had been replaced by the new quantum theory. Although Maxwells equations are still useful today, they are really only an approximation to the true quantum nature of the universe.
For this reason, many physicists saw Einsteins efforts to unify classical electromagnetism with general relativity as old-fashioned. Einstein seems to have been hoping that quantum mechanics was just a fad. But he was dead wrong. Quantum mechanics was here to stay.
This is a transcript from the video series What Einstein Got Wrong. Watch it now, on The Great Courses Plus.
In the years that followed, Einstein continued to explore different approaches in his unified field theory. He worked extensively with five-dimensional theories throughout much of the 1930s, then moved on to a number of other ideas during the 1940s and 50s. But none of these approaches ever attempted to incorporate quantum mechanics.
In his thirty-year search for unified field theory, Einstein never found anything that could reasonably be called a success. Over these three decades, Einsteins fixation on classical field theories, and his rejection of quantum mechanics, increasingly isolated him from the larger physics community.
There were fewer and fewer thought experiments, and Einsteins physical intuition, once so famous, was pushed aside and replaced by endless pages of complicated interplaying equations. Even during the last days of his life, Einstein continued his search for the unified field theory, but nothing of consequence ever came of it.
When Einstein died in 1955, he was really no closer to a unified field theory than he was thirty years before.
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In recent decades, physicists have once again become interested in theories that could potentially combine and unify multiple facets of nature. In spirit, these theories have a lot in common with Einsteins dream of a unified field theory. But, in other ways, they are very different. For one thing, many important discoveries have been made since Einsteins death. And these discoveries have significantly changed how physicists view the prospect of building a unified field theory.
Einstein was entirely focused on electromagnetism and gravity, but physicists since then have discovered two new forces that exist in naturethe weak and strong nuclear forces. The strong nuclear force is the force that holds protons and neutrons together within the nuclei of atoms. And the weak nuclear force is responsible for certain radioactive decays, and for the process of nuclear fission.
Electromagnetism has a lot in common with these strong and weak nuclear forces. And it is not particularly hardat least in principleto construct theories in which these phenomena are unified into a single framework. Such theories are known as grand unified theories, or GUTs for short. And since their inception in the 1970s, a number of different grand unified theories have been proposed.
Grand unified theories are incredibly powerful, and in principle, they can predict and explain a huge range of phenomena. But they are also very hard to test and explore experimentally. Its not that these theories are untestable in principle. If one could build a big enough particle accelerator, one could almost certainly find out exactly how these three forces fit together into a grand unified theory.
But with the kinds of experiments we currently know how to buildand the kinds of experiments that we can afford to buildits just not possible to test most grand unified theories. There are, however, possible exceptions to this. One is that most of these theories predict that protons should occasionally decay. This is the kind of phenomena that can be tested. So far the limited tests have not been able to prove the Proton decay, but in future bigger tests are planned which could validate these theories.
But even grand unified theories are not as far-reaching as the kinds of unified field theories that Einstein spent so much of his life searching for. Grand unified theories bring together electromagnetism with the strong and weak forces, but they dont connect these phenomena with general relativity. But modern physicists are also looking for theories that can combine general relativity with the other forces of nature.
We hope that such a theory could unify all four of the known forcesincluding gravity. And since the aim of such a theory is to describe all of the laws of physics that describe our universe, we call this theory a theory of everything.
Learn more about problems with time travel.
The focus today, though, is on how to merge the geometric effects of general relativity with the quantum mechanical nature of our world. What we are really searching for, is a quantum theory of gravity.
The most promising theories of quantum gravity explored so far have been found within the context of string theory. In string theory, fundamental objects are not point-like particles, but instead are extended objects, including one-dimensional strings.
Research into string theory has revealed a number of strange things. For example, it was discovered in the 1980s that string theories are only mathematically consistent if the universe contains extra spatial dimensionsextra dimensions that are similar in many respects to those originally proposed by Theodor Kaluza.
Althoughstring theory remains a major area of research in modern physics, there isstill much we dont understand about it. And we dont know for sure whether itwill ever lead to a viable theory of everything.
In many ways, these modern unified theories have very little in common with those explored by Einstein. But in spirit, they are trying to answer the same kinds of questions. They are each trying to explain as much about our world as possible, as simply as they possibly can.
Einsteins unified field theory was an attempt to unify the fundamental theories of electromagnetic and general relativity into a single theoretical framework.
There are at least 10 dimensions of space in string theory, in addition to time which is considered as the 11th dimension. Although some physicists believe there are more than 11 dimensions.
Gravity is not a dimension. Its a fundamental force that is visualized as a bend in space and time.
In everyday life, we encounter three known dimensions: height, width, and depth which are already known for centuries.
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