Irreducible Fields and their Interaction. E 2 -like little group for massless particles and neutrino polarization as a consequence of gauge invariance. Linear canonical transformations of coherent and squeezed states in the Wigner phase space. JavaScript is currently disabled, this site works much better if you enable JavaScript in your browser. Mathematics Algebra. Fundamental Theories of Physics Free Preview.

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## Is quantum mechanics compatible with general relativity?

Buy Hardcover. Buy Softcover. FAQ Policy. About this book Special relativity and quantum mechanics are likely to remain the two most important languages in physics for many years to come. Show all. Unitary representations of the Lorentz group Pages Dirac, P. A simple method for illustrating the difference between the homogeneous and inhomogeneous Lorentz groups Pages Kim, Y. Time-energy uncertainty relation and Lorentz covariance Pages Hussar, P.

Part I. Free Fields Pages Yukawa, Hideki. Structure and Mass Spectrum of Elementary particles.

General Considerations Pages Yukawa, Hideki. Oscillator Model Pages Yukawa, Hideki. Orthogonality relation for covariant harmonic-oscillator wave functions Pages Ruiz, Michael J. Complete orthogonality relations for the covariant harmonic oscillator Pages Rotbart, F. Covariant harmonic oscillators and the parton picture Pages Kim, Y. Valons and harmonic oscillators Pages Hussar, Paul E.

## Relativistic Quantum Dynamics

Feynman Rules for Any Spin. Massless Particles Pages Weinberg, Steven. E 2 -like little group for massless particles and neutrino polarization as a consequence of gauge invariance Pages Han, D. But these are not the forms of quantum mechanics which are usually taught. By their very existence, they negate many of the arguments that the founders of quantum mechanics gave for their abandonment of realism.

The issue of whether there can be objective truths about the world is also important because it is at the core of a number of key public debates. This book is part of that argument for that point of view, that in the end, we can all be realists and we can have an objective view of nature, even as we are multicultural with expectations in human culture and so forth. The key idea, in society as well as physics, is that we must be relationalists as well as realists. That is, the properties we believe are real are not intrinsic or fixed, rather they concern relationships between dynamical actors or degrees of freedom and are themselves dynamical.

I believe this philosophy also has a role to play in helping us shape the next stage of democracy, one suited to diverse, multicultural societies, which are continually evolving.

So, this book is trying to intervene in both debates about the future of physics and debates about the future of society. This has been true, really, of all six of my books. But years later, when I was 17, I had a kind of magical moment one evening, when I read the autobiographical notes of Albert Einstein, Philosopher-Scientist and got the strong feeling that that was something I would be interested in following and doing. I read that book because I was interested in architecture during those years.

I became pretty interested in architecture after meeting Buckminster Fuller. I got interested in his geodesic domes and the idea of making buildings with curved surfaces, so I began to study the mathematics of curved surfaces. Just kind of out of rebellion, I went through the exams for mathematics even though I was a high school dropout. That gave me the opportunity to study differential geometry, which is the mathematics of curved surfaces, and every book I was studying to do the kind of architecture projects I was imagining had a chapter on relativity and the general theory of relativity.

And I got interested in relativity. There was a book of essays about Albert Einstein, and in it was the autobiographical notes. I basically decided to become a theoretical physicist and work on fundamental problems in space-time and quantum theory that evening. Your decision to drop out of high school propelled you on your path toward theoretical physics. What other circumstances supported your decision to be a physicist?

Then we moved to Cincinnati, Ohio. With the help of a friend of the family who was a professor of mathematics at a little college in Cincinnati, I was able to jump ahead three years and do calculus. And I did that totally as a gesture of rebellion. And then, I dropped out of high school.

My motive was to start taking college courses early because I was very bored with high school. In your book, The Trouble with Physics , you wrote about an additional obstacle that plagues theoretical physicists at the beginning of their career. Yes, but perhaps not quite as much. As always, the job situation for new PhDs in physics is not great. There are some jobs but there are not as many as there are people who are qualified for them. A new PhD student who does their work within a well-defined, well-known framework, where they can be judged on their problem-solving ability rather than their ability to, say, discover new ideas and new directions, is a safer path at the beginning of your career.

So you face much more competition.

At some point, you were a proponent of string theory. When and how did string theory become too problematic in your mind? I would say there are several issues that seemed very difficult to address. One of them is the landscape problem, why there appear to be a vast number of different ways that this world of dimensions can curl themselves up. It says that elementary particles are made up of quarks and other fundamental particles.

Those are free parameters, so you tell the theory what the masses of the different quarks are or what the masses of the neutrinos are, the electrons, what are the strength of the different forces. This is once the basic forces and basic particles are fixed, you still have all this freedom.

And I started to worry about this. When I was in graduate school, and into the s, and then string theory was invented, there was that brief moment when we thought that string theory would resolve those questions because it was believed to be unique—to come into only one version. And all those numbers, such as the masses and the strengths of the forces, would be predictions of the theory unambiguously. So that was for a few weeks in It describes nine dimensions of space. There are six additional dimensions. And to have anything to do with our world, those six extra dimensions have to shrink down and curl up into spheres or cylinders or various exotic shapes.

Sixth dimensional space can curl up into a lot of different things it would take the language of a mathematician to even describe. And there turned out to be at least hundreds of thousands of ways to curl up those six extra dimensions. Additionally, each of those corresponded to a different kind of world with different elementary particles and different fundamental forces.

Then my friend, Andrew Strominger, found that actually, that was a vast undercounting and there were a vast number of possible ways to curl up the extra dimensions leading to a vast number of possible sets of predictions for the properties of the elementary particles. There are also some problems of mathematical consistency where the theory actually predicts infinite answers to questions that should be finite numbers.

### Expertise. Insights. Illumination.

And there are foundational interpretational problems. So it was a kind of crisis. At least, I felt there was a crisis right away, which was I began thinking about this like an evolutionary biologist because at the time I was reading books by the great evolutionary biologists who wrote popular books. Steven J. Gould, Lynn Margulis, Richard Dawkins. And I was very influenced by them, to try to seek a way that the universe could be subject to some kind of process of natural selection that would fix the parameters of the standard model.

The biologists had this notion that they called the fitness landscape. A landscape of different possible sets of genes.

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On top of this set, you imagined a landscape in which the altitude was proportional to the fitness of a creature with those genes. That is, a mountain was taller at one set of genes if those genesresulted in a creature that had more reproductive success. And that was called the fitness. So I imagined a landscape of string theories, a landscape of fundamental theories, and some process of evolution going on on it. And then it was just a question of identifying a process that should work like natural selection. So we required some kind of duplication and some kind of means of mutation and then some kind of selection because there had to be a notion of fitness.

And at that point, I remembered an old hypothesis of one of my postdoctoral mentors, Bryce DeWitt, who had speculated that inside of black holes were the seeds of new universes. Now, ordinary general relativity predicts that to the future of the event horizon is a place that we call singular, where the geometry of space and time break down and time just stops.

So, I imagined that that mechanism, if true, would serve as a kind of reproduction for universes. It just kind of came together. Somebody else will have the same idea. It does make a few predictions, so it is falsifiable. And so far it has yet to be falsified. If you define a major advance as when either a new experimental result verifies a new theoretical prediction based on a new theory or a new experimental result suggests a theory—or interprets a suggested theory that goes on and survives other tests, the last time there was such an advance was the early s.

Since then there have been several experimental findings which were not predicted—like that the neutrinos would have mass; or that dark energy would not be zero. Those are certainly important experimental advances, for which there was no prediction of or preparation for. So in the early s there had been formulated what we call the standard model of particle physics.

The question has been how to go beyond that, because that leaves a number of open questions. A number of theories have been invented, provoked by those questions, which made various predictions. And none of those predictions have been verified. The only thing that has happened in all these years of experiments is better and better and better confirmation of the predictions of the standard model without any insight into what may be behind it.