Have We Been Interpreting Quantum Mechanics Wrong This Whole Time?
wired.com
wired.com
https://news.ycombinator.com/item?id=8554996
Earlier submissions, but with no discussion:
But look what the article leaves out: You can't, as far as I can tell from the article, demonstrate the collapse effect of detecting which slit the particle passes through. In fact, you can always observe which slit the particle passes through, so measurement has no effect on the wave interference pattern.
If there is a "pilot wave" version of quantum mechanics, these experiments are only a suggestion of some of the mathematics. They appear not to be a macro-scale example.
Did we read the same article? Pilot wave theory has the same mathematics as quantum mechanics. It's a different interpretation of those mathematics - the probability wave is real and physical.
In these droplet experiments, you can measure all you want without affecting the wave and the interference pattern. This might point to an analogous form of quantum mechanics. But it also could be just an interesting but incomplete analogy in classical physics.
The analogy isn't a problem. The fact that there's nothing small enough to observe photons like we can observe the oil is a problem, but it says nothing about the integrity of the analogy.
In the analogy the water is space-time, meaning "observing" the droplet like we observe photons would require shooting another droplet past or into the first droplet.
The first half of that sentence is true, while the second half is not (unless I am misinterpreting what you are trying to say).
Empirically, nobody has (yet) managed to come up with an experiment that measures which slit the photon/electron/other quantum object passes through AND preserves the wave nature of the double-slit effect. In other words, when you set up an experiment to measure which slit is traversed, the characteristic double-slit interference pattern disappears. Again, I'm talking about this purely in practice, or what people observe when they try to perform this experiment[1].
Theoretically, this is result is completely expected. To determine which slit the photon traversed, you must interact with the photon to observe it. Any observation has two results: First, you know the state of the quantum object. Second, the quantum object is in an eigenstate of whatever operator you used to observe it. Since you have forced the photon into an eigenstate, the interference pattern disappears.
[1] Not that you can still see two superimposed single-slit interference patterns, which might confuse some people into thinking they are seeing a double-slit pattern.
The double slit experiment, which this article focusses on, looks at photons. Photons, are carriers of electromagnetic energy – they're their own field.
The field though isn't really a fluid or medium – thinking about ripples moving across a pond won't help you. The field is just the distance over which the photon will travel. It's more about an area of opportunity for something to happen (e.g. in the event that something gets within range of the photon) rather than a big blobby mass actually hanging around in space.
There's no such thing as "pure energy" (although the fundamental forces are probably the simplest forms of energy). Energy is an emergent property of a system (it is a function of how things in one part of a system are arranged with respect to another part of the system).
The problem is that most of the discussions about quantum mechanics interpretation are handwaving without enough linear algebra background. My two favorite questions before starting a discussion are:
* ) What are the eigenvalues of the matrix
/ 0 1 \
\ 1 0 /
I'm sorry I can't answer your question, I only learned about the Schroedinger's Equation
* ) The standard basis B_s = {[1,0],[0,1]} and the Hadamard basis B_h={[1,1],[1,-1]} are a mutually unbiased bases, which means any basis vector lies exactly "in between" the vectors from the other basis.
The use of mutually unbiased bases has applications in quantum crypto: if the same basis is used for encoding and decoding a bit of information the bit will be transmitted faithfully, else if a different basis is used for decoding than the basis used for encoding, the receiver will decode pure noise (i.e. a 50-50% random bit). This "uncertainty about which basis is used to encode the message" is the key idea behind the BB84 protocol.
One thing it should tell you is that we have not been "interpreting quantum mechanics wrong this whole time" because we've made relatively little effort to arrive at an interpretation at all. During my time as a physics student, deeper philosophical issues weren't mentioned in class, and it seemed like the Copenhagen interpretation was grudgingly accepted as a de facto standard in order to just get on with life.
We knew there was some activity in the area of finding a more philosophically pleasing interpretation, and one or two seminar speakers talked about it, but it just wasn't a big deal. Many physicists even questioned the value or physics-ness of the pursuit.
http://www.bbc.co.uk/iplayer/episode/b04tr9x9/the-secrets-of...
This isn't actually the case - Bell's theorem and subsequent verification demonstrate only that a theory of local hidden variables cannot be successful - the local part means that faster than light information transfer doesn't occur. You're allowed to have a pilot wave interpretation if it's nonlocal.
I think this is actually a problem with these experiments - it's nice that they work, but we already knew pilot wave mathematics could describe quantum mechanics, with the caveat that nonlocality is necessary to explain everything. I don't think this nonlocality is (or can be) expressed in the fluid experiments, so presumably they can't actually replicate QM.
Suppose I have a particle at coordinates (0,0) with some velocity in x-direction. Due to symmetry, the trajectory of a pilot-wave particle has to stay on the x-axis, while in QM the heisenberg uncertainty principle results in some momentum in y-direction.
Wouldn't you need to add some kind of imperfection to disturb the pilot-wave in order to reproduce the probabilistic results?
A related problem is that both De Broglie's and Bohm's pilot-wave models leave open the possibility of "empty waves" that carry no momentum or energy and are not related to any particles. Even if we assume that it is space-time through which they propagate, this gives us another piece of math that we need to just throw away, similar to the non-observed probabilities after state collapse, which runs counter to the goal of creating a formalism where the math corresponds to something real in the universe(s).
No it does not. We already have the Schrödinger field, without any notion of an aether. In fact the whole quantum field theory is all about fields and does not require it.