Does ST provide causation to QM?

csmcmillion

I have a cursory understanding of QM which (as far as I know) fails to provide causation for certain events such as neutron decay and electron leaps to lower orbits. My understanding is that there is (currently) no know "cause" for these, and other, events - they simply happen. We cannot, for example, predict when a particular neutron will decay. I'm wondering if current String Theory provides a causal mechanism for such events?

Demystifier

Standard string theory is probabilistic, just as standard QM and QFT. However, there are also Bohmian versions of those which give a deterministic description of events, including the time of decay. For superstring theory in the Bohmian formulation see
http://xxx.lanl.gov/abs/hep-th/0702060

xristy

I'd be interested in a reference to a work that shows for a given neutron what to measure and how then to compute the time at which the neutron will decay.

mfb

While the process is deterministic (with Bohm), there is no way to predict it - you cannot measure the quantities required for that, without changing the system (here: the neutron).

xristy

In any event is there a reference that clarifies the quantities that are involved and the process by which the decay event occurs based on the quantities. I assume they are related to the quark-gluon process that is a neutron?

Demystifier

True, except perhaps with a weak measurement, recently used to measure photon Bohmian trajectories in a laboratory:
http://www.physicsforums.com/blog.php?b=3077

xristy

So is there a reference that clarifies the quantities that are involved and the process by which the decay event occurs based on the quantities?

Demystifier

Xristy, you probably know that spontaneous decay in QM can be described as tunnelling. A Bohmian description of tunnelling is presented in several sections of the book
P. R. Holland, The Quantum Theory of Motion

xristy

I thought that neutron decay was via the weak force involving (in one mode) the creation of an electron and electron anti-neutrino along with a proton.

I didn't know that it could be explained via QM tunneling.

Holland doesn't talk about the weak force and since there is particle creation I don't understand that a deterministic QM would be immediately applicable.

mfb

Weak decays have a concept similar to tunneling, as they can be described with a short-living virtual W boson, which serves as an energy barrier.

Writing down the DeBroglie-Bohm interpretation with particle creation+annihilation is a bit tricky, but it is possible. MWI is deterministic as well, and particle creation and annihilation are nothing special there.

Demystifier

You are right, that kind of decay requires particle creation and destruction, which Holland does not talk about. As mfb said, Bohmian description of particle creation and destruction is tricky, but possible. See e.g.
http://xxx.lanl.gov/abs/0904.2287 [Int. J. Mod. Phys. A25:1477-1505, 2010]
http://xxx.lanl.gov/abs/1205.1992 [Chapter 8. of a recent book]

xristy

Please provide a reference to this technique. I've searched through various texts on QFT and the Standard Model and can't find an explanation of how to carry through your idea.

mfb

This is not a technique, but a hand-wavy comparison. Howevery, it allows to see why the top-quark is so short-living compared to the other quarks (and their mesons): The top-quark has enough enery to decay into a real b-quark and a real W boson. The other quarks cannot do this, the W in their decay has to be virtual, which supresses the decay (and makes the weak interaction "weak" - at the electroweak scale, it is not weaker than the electromagnetic interaction).