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

[Alex K]

We're on the same wavelength in that respect then - I also have no idea what I'm asking
So you're saying that dark matter is most likely composed of multiple different kinds of as yet undiscovered particles, rather than a catchall single kind of matter? In any case it seems to be this decade's 'superpower-giving radiation' in The Flash, and one of the few holdouts in the 'science is spooky and dangerous' genre overall

It could very well be that Dark Matter is composed of several different kinds of undiscovered particles - it's not a given that the "dark sector" has a very simple structure with just one additional particle floating around. However, with the two alternatives I mentioned above, at the simplest level, just having either the one or the other would suffice.

[Alex K]

There is one important class of dark matter particle candidates which do not interact with the weak force - the AXIONs. They can be detected using a peculiar effect: axions can be converted to photons in a strong magnetic field. The ADMX experiment consists of a closed cavity with a resonator and a strong magnetic field. It systematically scans through the resonator frequencies, hoping to observe axion dark matter - to - photon conversions in its cavity.

Would that look to the sensors like a photon just appearing out of nowhere?

Yes, exactly, although I think to make a detection one would need more than one converted photon. You have a closed cavity, and suddenly there would be electromagnetic waves in it:

[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.

[Alex K]

attention: I edited above post just now

[Alex K]

TIL what a neutrino is, methinks that's enough education for this week
thanks for your mostly comprehensible explanation uncle K

Way to make me feel avuncular...

[Anima]

Thank you. I will do a little more research along the lines of your answer while giving it full consideration. As an engineer more inclined to mechanics and aeronautics than electrical I have always found the subjective determination as collapsing the waving function dubious.

This is the first I have heard that determination of the state by subjective observation is not held definitive. If such is the case than it does readily answer my question since the interaction of objects with the photo or electron would be in accordance to it being defined as one state for that interaction while then being rendered an indeterminate state until such time as the next interaction. However, this intern brings up questions about the duration of the determination of said state since an indeterminate state follows. Hmm...

https://youtu.be/BoQ6ZC8EUQ0

[JuliaL]

We're on the same wavelength in that respect then - I also have no idea what I'm asking
So you're saying that dark matter is most likely composed of multiple different kinds of as yet undiscovered particles, rather than a catchall single kind of matter? In any case it seems to be this decade's 'superpower-giving radiation' in The Flash, and one of the few holdouts in the 'science is spooky and dangerous' genre overall

It could very well be that Dark Matter is composed of several different kinds of undiscovered particles - it's not a given that the "dark sector" has a very simple structure with just one additional particle floating around. However, with the two alternatives I mentioned above, at the simplest level, just having either the one or the other would suffice.

Is it intentional that physicists produce only enough experimental data and interpretation to raise more questions and confusion?  Or is it a fortuitous accident that gives good and sufficient reason to continue funding experimental programs.

Dark matter only weakly interacts with the 'real' (anthropic bias noted here) stuff.
Is there any reason to believe that it interacts with itself with the same complex, chaotic results as does real matter?
Could there then be the sort of structure found in our universe, dark suns, dark planets, cladistic trees of evolved dark animals?
Would it coexist in the same spacetime on top of us but because of the weak interactions, we wouldn't know it?

And would it be superman bizzarro universe or the evil Captain Kirk universe?

[Longhorn]

TIL what a neutrino is, methinks that's enough education for this week
thanks for your mostly comprehensible explanation uncle K

Way to make me feel avuncular...

BA-DUM TSSSS

[Alex K]

It could very well be that Dark Matter is composed of several different kinds of undiscovered particles - it's not a given that the "dark sector" has a very simple structure with just one additional particle floating around. However, with the two alternatives I mentioned above, at the simplest level, just having either the one or the other would suffice.

Is it intentional that physicists produce only enough experimental data and interpretation to raise more questions and confusion?  Or is it a fortuitous accident that gives good and sufficient reason to continue funding experimental programs.

Dark matter only weakly interacts with the 'real' (anthropic bias noted here) stuff.
Is there any reason to believe that it interacts with itself with the same complex, chaotic results as does real matter?
Could there then be the sort of structure found in our universe, dark suns, dark planets, cladistic trees of evolved dark animals?
Would it coexist in the same spacetime on top of us but because of the weak interactions, we wouldn't know it?

And would it be superman bizzarro universe or the evil Captain Kirk universe?

Having the Dark matter in the form of a dark world as you propose, is a very exciting thought (I mean, how cool would that be), but unfortunately pretty firmly excluded by observations - we do after all know what the gravitational effects of the dark matter must look like, and your dark parallel world would not satisfy observations.

if dark matter would form dark suns and dark hamsters etc, and it therefore would have to have friction and interaction like our normal matter, it would first of all form disk-like shapes just like our matter, and therefore probably not explain the rotation curves of galaxies for which galaxies need to be embedded in larger clouds of dark matter. Nor would the simulations for large scale structure formation in the early universe come out right.

But, I think, more importantly, such parallel "dark" planets and stars would have been seen in gravitational lensing surveys (you would see a sudden shift in brightness when such a dark star or planet goes in front of one of our ordinary stars because the local curvature of space it induces would act like a lens amplifying the brightness of that star as seen by us).

All this makes it more likely that the Dark Matter behaves mostly like a super-dilute gas that is spread out more evenly.

Is it intentional that physicists produce only enough experimental data and interpretation to raise more questions and confusion? Or is it a fortuitous accident that gives good and sufficient reason to continue funding experimental programs.

What could you possibly mean...
But seriously, the frontier of knowledge is always confusing by definition. There is this funny idea by some old philosopher that knowledge might be like filling a sphere in the sea of all the things we do not know - the more we expand it, the larger becomes the contact area with that which we do not know.

[Longhorn]

if dark matter would form dark suns and dark hamsters etc,

lol