Does anyone (maybe chronos) know if there has been any progress made in coming up with any of the interaction strength constants from first principals in recent years?
Attempted answer in this thread.
On this one, I was asking about constants like e - the amplitude for a real electron to emit or absorb a real photon.
I know it is around -0.08542455. I think 1/e^2 is seen as a constant more often (137.03597).
I was wondering if anyone has come up with a way to calculate this or other constants from first principals, or is it still just inserted into QED using the measured value.
First principles assume that you have a “first principle”. The value for the fine-structure constant is absolutely derivable from “first principles” in quantum mechanics and is done quite nicely in any Intro text of quantum mechanics. Of course, all kinds of other “ab initio” values are used such as the permitivity of free space, the mass of an electron, and the charge of an electron.
Try http://physics.nist.gov/cuu/Constants/alpha.html
Or are you looking for something with a little more meat on it?
I think I should qualify this statement by saying I don’t know to what precision the constant can be derived. I myself am not a theoretical quantum physicist.
I’ve just started reading the book The Elegant Universe by Brian Greene, and if I understand the question, the book says this is what String Theory is supposed to be. It’s a way to explain all those ugly arbitrary-seeming physical constants by deriving them from an elegant (if complex) theory.
I guess the point was that if it was derived, it would be to perfect precision.
My understanding is that e, j, m, and n pretty much have to be measured. The relationship between them is known well enough that you don’t have to measure all of them. But at least one has to be measure to get the others.
And
This is probably along the lines of what I was asking. I was hoping more progress had been made in the QED side of things and that at least on those constant.
I have looked briefly at some of the string and x-brane theory stuff. I decided I better get some more foundation in QM first.
Been studying QED pretty hard, but the texts are out of date. Still plenty of good stuff to learn though. I’ll look at QCD next.
Meant to add, I pretty well follow QED now except for polarization.
It is getting to be a real bitch to figure this stuff out. Access to people that can MY questions is pretty mjuch non existant for me.
I would love to get to spend a day with a real QM guy… but, that would probably be like heroin and lead to another day, and another, and…
Indeed, you are right about the theory still being tied to measurement. We don’t have any understanding as to why the world scales exactly the way it does. We do, however, have a pretty good idea of the relationships between the various scales.
If you aren’t math-phobic, try starting with David Griffith’s Introduction to Quantum Mechanics if you want to get a good start in the subject. What you will fast realize is that while there is a lot we can do with QM, the world is pretty complex when you try to move beyond the most simple formulations. For example, the hydrogen atom (an electron and a proton) is fairly well understood and solved in most intro texts. The helium atom is usually given a lot of discussion but ends up being too complicated to solve exactly (though I believe an exact solution does exist). Anything beyond helium looks to be nigh on impossible, even using supercomputers.
Thanks JS Princeton!
Sounds like this might be a good follow on to QED by Richard Feynman. I’ll be picking it up I am sure. I’m not math-phobic at all, but I have been finding my math skills could use some expanding to deal with some of the material that I have been getting into with some of this stuff.
String theory is as yet the only set of “first principles” that promises to answer your question. However, after 30 years of string theory, it’s still “promising”…