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The article says that one of the attractive qualities if string theory is that it has no free parameters. But then says that the particles a forces of the stand

The article says that one of the attractive qualities if string theory is that it has no free parameters. But then says that the particles a forces of the standard model are determined by the number and size of extra dimensions. Those sound an awful lot like free parameters. Can someone with more than a passing familiarity with the field explain?

AnimalMuppet 8y ago
One might say, given the fundamental particles, there is a unique set of number and sizes of extra dimensions. That is, there are no free parameters if it's going to fit this universe. The same thing happened in relativity. c is not a free parameter; it has to be the speed of light in this universe. You could argue that it could have some other value and relativity would still work correctly. That might be true in some sense, but it wouldn't work as a correct description of this universe. Note well: I do not have more than a passing familiarity with the field. What I am saying here may not be a correct description of the actual state of string theory. Also note that I find "there are no free parameters" and "but it gives rise to this landscape, where there's nothing nailed down in terms of actual physics" to be somewhat difficult to reconcile.
auntienomen 8y ago
Normally in a physical theory, you have some equations describing the dynamics and you go looking for solutions to these equations. The dynamical equations may have some parameters (such as the constant G in Newtonian/Einsteinian gravity), and then there are usually additional parameters required to describe the solutions (such as the mass M of the gravitational field source). String theory has the unusual property that its dynamical equations don't have free parameters. The dynamics is apparently unique. But there are many many solutions to these equations, and so there's a huge space of parameters from that. In particular, if you go looking for ways of embedding the Standard Model in string theory, all of its dynamical parameters (like the electron mass and Newton's constant) are realized as solution parameters.
- kolpa 8y ago
  Can I make Newtonian mechanics into a dyanically 0-free-parameter theory by stating that F == gMm/r^2 , where g is a solution parameter ("the gravity of the universal landscape" ?
  - auntienomen 8y ago
    You can do this -- and indeed, promoting constants to fields is a common technique in the analysis of field theories. But it's cheating if you say the constant is dynamical and then don't say what the dynamics is. In field theory, you have to make additional choices here, and there are a lot of additional parameters that enter. In string theory, you don't have to/get to make a choice at all. The dynamics is uniquely determined. It's not exactly a free lunch, but it's a very unusual feature for a physical theory.
manyoso 8y ago
It is bullocks and just the excuse of a declining number of scientists who have spent their life's work on String Theory and will never admit that the program has utterly failed as a "Theory of Everything"
- throwaway37585 8y ago
  What are your qualifications in the field of theoretical physics?

AnimalMuppet 8y ago

One might say, given the fundamental particles, there is a unique set of number and sizes of extra dimensions. That is, there are no free parameters if it's going to fit this universe. The same thing happened in relativity. c is not a free parameter; it has to be the speed of light in this universe. You could argue that it could have some other value and relativity would still work correctly. That might be true in some sense, but it wouldn't work as a correct description of this universe. Note well: I do not have more than a passing familiarity with the field. What I am saying here may not be a correct description of the actual state of string theory. Also note that I find "there are no free parameters" and "but it gives rise to this landscape, where there's nothing nailed down in terms of actual physics" to be somewhat difficult to reconcile.

auntienomen 8y ago

Normally in a physical theory, you have some equations describing the dynamics and you go looking for solutions to these equations. The dynamical equations may have some parameters (such as the constant G in Newtonian/Einsteinian gravity), and then there are usually additional parameters required to describe the solutions (such as the mass M of the gravitational field source). String theory has the unusual property that its dynamical equations don't have free parameters. The dynamics is apparently unique. But there are many many solutions to these equations, and so there's a huge space of parameters from that. In particular, if you go looking for ways of embedding the Standard Model in string theory, all of its dynamical parameters (like the electron mass and Newton's constant) are realized as solution parameters.

kolpa 8y ago
Can I make Newtonian mechanics into a dyanically 0-free-parameter theory by stating that F == gMm/r^2 , where g is a solution parameter ("the gravity of the universal landscape" ?
- auntienomen 8y ago
  You can do this -- and indeed, promoting constants to fields is a common technique in the analysis of field theories. But it's cheating if you say the constant is dynamical and then don't say what the dynamics is. In field theory, you have to make additional choices here, and there are a lot of additional parameters that enter. In string theory, you don't have to/get to make a choice at all. The dynamics is uniquely determined. It's not exactly a free lunch, but it's a very unusual feature for a physical theory.

manyoso 8y ago

It is bullocks and just the excuse of a declining number of scientists who have spent their life's work on String Theory and will never admit that the program has utterly failed as a "Theory of Everything"

throwaway37585 8y ago
What are your qualifications in the field of theoretical physics?