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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.

Learn more about Einstein and gravitational waves.

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 But over the course of the 1920s, Maxwells classical theory had been replaced by the new quantum theory.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.

Learn more about quantum entanglement.

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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Unified Field Theory: Einstein Failed, but What's the Future? - The Great Courses Daily News

By Dan Hooper, Ph.D., University of Chicago Einstein found it difficult to accept any version of quantum mechanics, in which the universe was probabilistic in nature. (Image: Fankies/Shutterstock)What Is the Copenhagen Interpretation?

The Copenhagen interpretation of quantum mechanics claims that particles behave like waves. These particle-waves are each described by their wave function. The shape of a given particles wave function represents the probability that it will be found at different locations, or with different velocities. The original view of quantum mechanics was that quantum particles simultaneously exist in multiple locations at once, and have multiple velocities. According to the Copenhagen interpretation, whenever a particle is observed its wave function collapses, and the measured quantity takes on a single measured value.

So, prior to any measurement or observation, an electron is simultaneously in locations A and B, where A and B are the two places the wave function peaks sharply. An act of observation causes its wave function to collapse, and its location takes on a single valueeither A or B.

Learn more about how Einstein challenged Newtonian physics.

So, how did scientific consensus form around the Copenhagen interpretation? To begin with, it must be mentioned that quantum mechanics was a rapidly evolving theory between the mid-1920s and late-1920s. So, opinions changed within a matter of months. Its also important to remember that during this period the scientists, who were located across Europe, communicated with each other primarily through letters and publications in scientific journals.

Scientific conferences presented them with an opportunity for in-depth in-person interaction, unlike any other during that time. In fact, scientific conferences played an important role in the development of quantum mechanics. The most important or most influential was the Fifth Solvay Conference on Physics, which was held in Brussels in October 1927.

Almost every single major contributor to the development of quantum mechanics attended this conference, including Albert Einstein, Erwin Schrdinger, Max Born, Niels Bohr, Louis de Broglie, Paul Dirac, and Werner Heisenberg. Also in attendance were Wolfgang Pauli, Marie Curie, and Max Planck. Its worth noting that of the 29 physicists in attendance, 17 had already been awarded a Nobel Prize or would eventually be awarded one.

At the Fifth Solvay Conference, it became clear that a consensus had started to form around the Copenhagen interpretation. Most of those in attendance seemed to have accepted the probabilistic nature of the new theory.

In addition, there was a general acceptance that the Copenhagen interpretation presented the true picture of nature and not a view that would eventually be explained away with a better understanding of the problem. For example, Born, Heisenberg, and Bohr were each fully aware that the universe as described by quantum mechanics was fundamentally probabilistic.

They acknowledged that theres a chance determinism could be restored in some future revision of the theory, but thought the chance was minuscule and unlikely. They were prepared to accept the lack of determinism in the subatomic world.

This is a transcript from the video series What Einstein Got Wrong. Watch it now, on The Great Courses Plus.

A number of respected physicists, including the likes of Bohr, Heisenberg, and Born, had an inkling that the quantum revolution was drawing to an end. They believed their working theory was complete, and that there would be no need for any new elements.

Despite the consensus around the Copenhagen interpretation, Einstein found it difficult to accept any version of quantum mechanics, in which the universe was probabilistic in nature.

To be fair to Einstein, he wasnt exactly arguing that the new theory of quantum mechanics was incorrect. The Schrdinger equation and the other equations of this theory described the phenomena very well, and the successes of quantum mechanics were entirely undeniable. So instead of claiming that quantum mechanics was incorrect, Einstein was arguing that it was somehow incomplete. He was claiming that big pieces of the theory were somehow still missing.

Lets reconsider the example of the electron that is described by a wave function which extends across locations A and B. According to the Copenhagen interpretation, the electron exists in both of these locations simultaneously, but Einstein was skeptical of this conclusion. Its possible that he thought the electron was, in fact, in only one of these two locations at a given time. He might have reckoned that the Schrdinger equation simply failed to identify which of these two locations the electron was present in. If that were true, then the apparent indeterminism of quantum mechanics might just be an illusion.

Einstein imagined there could be another more complete equation that would make it possible to calculate the location of the electron at a given time, without any probabilistic results. Essentially, he was searching for a way to make sense of quantum mechanics that wasnt only deterministic, but in which the properties of each particle or object was always well defined.

Learn more about the Manhattan Project and Einsteins devastating legacy.

With the objective of developing this new complete equation in mind, Einstein began work in early 1927. He started working toward developing a version of quantum mechanics that he hoped could explain all of the observed phenomena of quantum mechanics, while still allowing the laws of nature to be strictly deterministic.

The class of theories he developed and advocated were known as hidden variable theories. According to these theories, the wave function of a particle, as used in the Schrdinger equation, doesnt tell us everything about that particle. These theories claimed that the wave function was, in effect, an incomplete or partial description of the particle.

Einstein hypothesized other variables that were missing from the wave function, in the hope that it would eliminate the need for any indeterminism in the theory. At the Solvay conference, Einstein argued vigorously that the Copenhagen interpretation was fatally flawed, and that a more complete theory was needed. But despite these arguments, he wasnt able to convince many of his colleagues.

In a series of informal but public discussions with Bohr, Einstein raised what he believed to be a series of major flaws with the Copenhagen interpretation. However, Bohr responded effectively to each of Einsteins criticisms. In each case, Bohr found holes in Einsteins arguments, and successfully defended the new consensus view. By the end of this series of discussions, it was clear to most of the scientists in attendance that Bohr had bested Einstein in these debates.

Einstein remained undeterred by his failure at the Solvay Conference to demonstrate any fatal flaws in the Copenhagen interpretation. In the years that followed, he continued to search for a more complete version of quantum mechanics that he hoped would restore determinism to the subatomic world.

The majority of the current generation of quantum physicists still consider the Copenhagen interpretation to be accurate. The Copenhagen interpretation was first proposed by Danish physicist Niels Bohr, and this interpretation was subsequently theoretically proved by the thought experiment known as Schrdingers Cat. In recent years, the Copenhagen interpretation has encountered opposition from the many-worlds interpretation proposed by American physicist Hugh Everett.

Wave functions are mathematical descriptions of the wave properties of particles. If the value of the wave function of a particle for a particular location is high, then the probability of the particle being present at that location at that given time is high.

A total of 29 eminent physicists attended the Fifth Solvay Conference in 1927, including Albert Einstein, Erwin Schrdinger, Max Born, Niels Bohr, Louis de Broglie, Paul Dirac, Werner Heisenberg, Wolfgang Pauli, Marie Curie, and Max Planck, among others.

Bohr believed that the quantum universe was fundamentally probabilistic in nature, whereas Einstein was of the belief that determinism lay at the foundation of the quantum universe. This fundamental disagreement led to a series of public discourses between these two eminent physicists, which are known as the Bohr-Einstein debates.

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How Einstein Failed to Find Flaws in the Copenhagen Interpretation - The Great Courses Daily News

Mumbai, May 7 (IANS): Actress Tisca Chopra is putting her quarantine hours to good use. She says the lockdown has given her time to think about time.

Tisca took to Instagram where she shared a photograph of herself. In the image, she is seen flaunting her perfect skin and is completes a casual statement with a hairband.

Alongside the picture, she wrote: "Lockdown diaries Day: 42. This time has given me time to think about Time. Time is a funny, stretchy thing, years can feel like yesterday. Yet another yesterday can feel like years .. I have always been fascinated by Quantum Physics...

"I have tried to read works of Planck, Heisenberg, Schrdinger and of course Einstein... to understand how time-space works, often failing to understand very much."

She added: "My fascination landed at @netflix_inand #BlackHoleApocalypse .. you must see it if you haven't .. fascinating how absolutely tiny we are .. yet how integrated into the whole..."

Tisca then shared the her menu for dinner.

"On a more mundane note, dinner today will be Pao-Burgers .. check stories later .. Have you got your daru stock while social distancing or are a non-drinker like me? P.S. - This is me in my #WFH office but in my head in field of Hollyhocks in Spain .. how is that for #TimeSpacebending?"

Recently, Tisca shared a stunning photograph of herself and said that she is making the most of staying indoors.

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Tisca Chopra: This time has given me time to think about time - Daijiworld.com