First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Alex K]

Okay, my questions are as follows:

1.  Once the wave function is collapsed is it collapsed for all time?  So if I observe light as a particle today do all other observers from this day forth observe it as a particle as well?

I think there is a little bit of confusion about what wave function collapse means. It means that the wave function changes suddenly, and that certain correlations and superpositions are lost in the process. It doesn't mean that the wave function is now gone!
Collapsing the wave function does not mean that now the photon or electron is particle-like instead of wave-like. Whether it behaves like one or the other is always a matter of the type of observation you make, it is not a label sticking to the particle saying "now I'm particle like".

If you measure the location of a particle with a certain precision, what happens in the Copenhagen-picture-wave-function-collapse is that the wave function is now restricted to the area which is still compatible with the result of your measurement, i.e. it is now spread around the location you measured it at, and with a width corresponding to the uncertainty of your measurement. Everywhere else, the wave function vanishes or has a very small value. This wave function which is now restricted to a smaller area will, after the measurement, keep dynamically evolving according to the Schrödinger equation, which in general means that it will spread out again. If you send it through another apparatus, it will again behave as a modified wave.

A good illustration of this is a single slit measurement. If the electron or photon does not hit the barrier, you know it went through the slit and hence you have measured its  location at least in two dimensions (because it was in the slit). After passing the slit, the wave function will spread sideways again:

2.  Is the wave function only collapsed by subjective observation or may it be collapsed by objective observation?  
So if an inanimate object responds to the light as if it were a particle does this reaction constitute an objective "observation" of the light that collapses the wave function?

That is probably not a question that can be answered empirically - it is therefore a matter of interpretation of quantum mechanics, and not actually science in the strict sense.
Generally, there is no distinction between inanimate and animate in the usual interpretations of quantum mechanics, because that would be an unnecessary complication. It is indeed not necessary to make this distinction.

In the Copenhagen interpretation, I would say the collapse is merely a pragmatic recipe which you can use to calculate the outcome of experiments, and the theory is devoid of ontological statements such as whether there really is a wave function, what quantum superposition means and if the wave function is only collapsed when a sentient being looks.

If you insist and try to put an ontological interpretation on top of the Copenhagen interpretation, and interpret it such that wave functions really exist as objects, you almost automatically get something like the Many Worlds interpretation. Let me explain what I mean: if you make an experiment that has another human being as part of the setup, akin to Schrödinger's cat, but where your friend sits in a box and according to some nuclear decay gets sweets or not, and now you perform the quantum calculation predicting the outcome probabilities. You then will do the calculation as if your friend exists in a Schrödinger-like superposition of states where he's got sweets and also doesn't. In the end, when you open the box, your friend either has them or not, and will not have felt that he was in some sort of superposition. If you now insist that the wave function is a real thing ("is ontological", as some say), you will more or less say that there had been two copies of your friend. If you do not take the solipsistic route, the very same treatment is true for you yourself, and after you open the box, the universe will be in a superposition of two states where 1. your friend got the candy and you see him eat it  and 2. your friend didn't get the candy and you see him not eating anything. There are now also two (in this simplified picture) copies of yourself. This is more or less the MWI.

The fact that you will have to treat sentient beings that are part of your experiment as quantum superpositions in order to get the correct results, also means imho that a distinction between sentient and non-sentient does not solve any perceived conceptual problems of quantum physics.

3.  If the wave function is collapsed for all time upon observation and the function may be collapsed by an objective observation (as exhibited in the reaction of the object to the quantum state) of inanimate objects than may it be said all quantum states are determined upon initial interaction with another object for all time?

See above:

- the answer depends on the interpretation you employ
- it is not collapsed for all time in the sense that it is particle-like. But certain properties such as entanglement can be lost permanently.
- as said above, in the Copenhagen interpretation, the objects within the system being studied, when interacting with your experiment, get included into the quantum superposition. The copenhagen picture more or less cuts this process off artificially once we describe a final outcome, thus not including the observer (you) into the quantum superposition by fiat.