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The end of physics has been predicted many times. I remember reading an article in Sci Am about the end of physics a few months before starting my physics under

by spatten 12y ago

The end of physics has been predicted many times. I remember reading an article in Sci Am about the end of physics a few months before starting my physics undergrad in the late 80s. The exciting thing is that it has often been followed by huge breakthroughs -- if I remember correctly, the last time it was widely believed that we had it all figured out was at the turn of the 20th century, just before Quantum Physics and General Relativity were discovered. I'm still patiently waiting for string theory to die and us to start working on something that we can actually do experiments on.

scythe 12y ago
>string theory to die and us to start working on something that we can actually do experiments on. You might already be able to do experiments that would confirm or deny string theory, but we haven't been able to work out the math in sufficient detail to come up with one. The thing about physics is that the deeper we get into the nature of the Universe, the stranger it looks. In the special theory of relativity, Einstein didn't just do strange things to physics. He had to work with a sort of mathematical object -- Minkowski space -- that most mathematicians either had never heard of or ignored, because they thought it was too weird. Turns out we live in Minkowski space. And when he worked with Hilbert on the general theory, they had to go and study Elie Cartan's tensor calculus to make sense of things, and then bring that into Minkowski space. The enterprise spawned a new kind of mathematical notation -- the Einstein repeated index summation convention. And when Dirac tried to quantize the special theory he found himself in the unruly situation of taking the square root of the gradient operator -- the square root of a derivative! The solution relied upon an anticommuting algebra now called the Clifford algebra, represented by Dirac matrices. And when Feynman wanted to quantize action, he had to take an integral over paths. When Schwinger studied particle[1] propagation, the integrals went from the paths of one particle to the paths of all possible particles and particle creation events. When you bring in gravity, the absence of any sort of repulsive action of the field and the number of degrees of freedom mean that any attempt to apply the path integral leads to infinite energies and infinite numbers of particles. String theory appeared as sort of a way, essentially, of restricting the "impact" of new particles by attaching an energy term to the "shape" of the particle. For simplicity particles were 1D manifolds. This led to the Nambu-Goto action. Then they had multiple dimensions, and Witten called it M-theory. It's not going away: you always end up with something like this to fix gravity. In any case, it's not string theory we can't test. It's quantum gravity period. Perhaps another issue is that string theory doesn't work well with QCD, which itself isn't rigorous, etc. http://en.wikipedia.org/wiki/Millennium_Prize_Problems#Yang.E2.80.93Mills_existence_and_mass_gap http://en.wikipedia.org/wiki/Millennium_Prize_Problems#Yang.... http://en.wikipedia.org/wiki/Constructive_quantum_field_theory http://en.wikipedia.org/wiki/Constructive_quantum_field_theo... http://chaosbook.org/fieldtheory/ http://chaosbook.org/fieldtheory/ [1]: There aren't actually any particles, but it makes the math easier to think about.

by spatten 12y ago

scythe 12y ago

>string theory to die and us to start working on something that we can actually do experiments on. You might already be able to do experiments that would confirm or deny string theory, but we haven't been able to work out the math in sufficient detail to come up with one. The thing about physics is that the deeper we get into the nature of the Universe, the stranger it looks. In the special theory of relativity, Einstein didn't just do strange things to physics. He had to work with a sort of mathematical object -- Minkowski space -- that most mathematicians either had never heard of or ignored, because they thought it was too weird. Turns out we live in Minkowski space. And when he worked with Hilbert on the general theory, they had to go and study Elie Cartan's tensor calculus to make sense of things, and then bring that into Minkowski space. The enterprise spawned a new kind of mathematical notation -- the Einstein repeated index summation convention. And when Dirac tried to quantize the special theory he found himself in the unruly situation of taking the square root of the gradient operator -- the square root of a derivative! The solution relied upon an anticommuting algebra now called the Clifford algebra, represented by Dirac matrices. And when Feynman wanted to quantize action, he had to take an integral over paths. When Schwinger studied particle[1] propagation, the integrals went from the paths of one particle to the paths of all possible particles and particle creation events. When you bring in gravity, the absence of any sort of repulsive action of the field and the number of degrees of freedom mean that any attempt to apply the path integral leads to infinite energies and infinite numbers of particles. String theory appeared as sort of a way, essentially, of restricting the "impact" of new particles by attaching an energy term to the "shape" of the particle. For simplicity particles were 1D manifolds. This led to the Nambu-Goto action. Then they had multiple dimensions, and Witten called it M-theory. It's not going away: you always end up with something like this to fix gravity. In any case, it's not string theory we can't test. It's quantum gravity period. Perhaps another issue is that string theory doesn't work well with QCD, which itself isn't rigorous, etc. http://en.wikipedia.org/wiki/Millennium_Prize_Problems#Yang.E2.80.93Mills_existence_and_mass_gap http://en.wikipedia.org/wiki/Millennium_Prize_Problems#Yang.... http://en.wikipedia.org/wiki/Constructive_quantum_field_theory http://en.wikipedia.org/wiki/Constructive_quantum_field_theo... http://chaosbook.org/fieldtheory/ http://chaosbook.org/fieldtheory/ [1]: There aren't actually any particles, but it makes the math easier to think about.