A Boost For Quantum Reality 241
Eponymous Hero sends this excerpt from Nature:
"The philosophical status of the wavefunction — the entity that determines the probability of different outcomes of measurements on quantum-mechanical particles — would seem to be an unlikely subject for emotional debate. Yet online discussion of a paper claiming to show mathematically that the wavefunction is real has ranged from ardently star-struck to downright vitriolic since the article was first released as a preprint in November 2011. ... [The authors] say that the mathematics leaves no doubt that the wavefunction is not just a statistical tool, but rather, a real, objective state of a quantum system."
maybe like this... (Score:0, Interesting)
and interesting image http://dequantified.net/preview/factorpreview.gif [slashdot.org]
Re:Heh (Score:5, Interesting)
It certainly knows.
It knows, but you don't. You don't because you haven't measured it yet. And until you measure it, the answer is not the simplified version of the cat being dead and alive at the same time, but that there's a probability it's dead, and a probability it's alive, but it'll never be more than probability until you actually confirm it. Once you confirm it by measurement, the probability of one state goes to one, and the probability of the other state goes to zero.
This goes back to the age-old question: If a tree falls in a forest and no one is around to hear it, does it make a sound? It certainly makes a noise, but does it make a sound?
If there's nothing to observe reality, does it still exist? That's the essence of Schrodinger's cat.
Re:Elephants! (Score:5, Interesting)
the mathematics leaves no doubt that the wavefunction is not just a statistical tool, but rather, a real, objective state of a quantum system.
If that's the case, I would suppose that wavefunctions have wavefunctions.
Yes. That's known as second quantization.
Yet another no-hidden-variables theorem (Score:3, Interesting)
The paper is related to Einsten-Podolsky-Rozen (EPR) paradox and the related "hidden variables" hypothesis which AFAIU states that there are some hidden variables apart from wave function that we can not observe directly. However, under some assumptions it can be proven that their existence affects some statistical properties of a particular type of measurements and therefore can be experimentally tested. One of such theorem was Bell inequalities published in 1964. In the Nature paper in question authors prove similar "no-go" theorem but under different assumptions. To quote:
The result is in the same spirit as Bell’s theorem[13], which
states that no local theory can reproduce the predictions
of quantum theory. Both theorems need to assume that
a system has a objective physical state such that prob-
abilities for measurement outcomes depend only on .
But our theorem only assumes this for systems prepared
in isolation from the rest of the universe in a quantum
pure state. This is unlike Bell’s theorem, which needs
to assume the same thing for entangled systems. Fur-
thermore, our result does not assume locality in general.
Instead we assume only that systems can be prepared
so that their physical states are independent. Neither
theorem assumes underlying determinism.
There is, however, another theorem by Kochen and Specker that is not cited in this paper but also does not assume locality. From wikipedia
The essential difference from Bell's approach is that
the possibility of underpinning quantum mechanics
by a hidden variable theory is dealt with independently
of any reference to locality or nonlocality, but instead
a stronger restriction than locality is made, namely
that hidden variables are exclusively associated with
the quantum system being measured; none are associated
with the measurement apparatus. This is called the
assumption of non-contextuality.
It would be interesting to know what would be the relation of results from the paper to that theorem...
Re:I get it now (Score:5, Interesting)
Re:Heh (Score:5, Interesting)
Try this as a thought experiment. Imagine your brain and your DNA scanned into a computer. This is used to generate a simulated you. This simulated you is placed in a simulated room in which all the known laws of physics are simulated to a high degree of precision.
You are placed in an identical, but real, room. The two rooms are connected via a terminal (or, in the copy's case, a simulated terminal).
You and the simulated you can ask for any scientific equipment that can fit into the room. Both of you can conduct whatever experiments you like. The only requirement is a unanimous agreement between you, your copy and those running the experiment as to which of you is physical and which is virtual.
If no observation, experiment, or set of experiments, exists that can prove which is real, then you cannot prove what is "real" - there'd be nothing so unique to reality that would allow you to unquestionably establish that something belongs to reality and not to something else. If, however, you CAN through experimentation reach a unanimous verdict, then an objective reality is provable.
It is my opinion that it is the first case that would turn out to be true.
Re:It makes sense when compared to string (Score:5, Interesting)
I am not convinced that the particles regarded as fundamental actually are. I'm not even completely convinced that "particles" at that level even exist in the normal sense, since we know interference patterns exist when the gap is in time rather than in space. That makes no logical sense when using a corpuscular model.
It is my suspicion (IANAQMPBTIBO) that in precisely the same way that matter is merely energy that has "condensed" and entangled, particles are merely waves that have "condensed" and entangled. This is based on the fact that fundamental particles of the same type are totally interchangeable and no two particles of the same type are in the same state. To me, that does not appear distinguishable from saying that a single wave appears to be every particle of that type, since that would give you what is observed without having to have any new or excessively complex physics to explain it.
If that is correct, then neither space nor time are particularly important in QM. Which has been theorized by better minds than mine. You would be able to map everything into waveforms and not need spacetime for them to exist in. Rather, spacetime would be one way an observer could interpret those waveforms - it would be subjective, not objective. The waves themselves would be the only "reality". Again, there's a branch of QM based on just such a notion.
To answer your question as to what is "vibrating", in this line of thought there wouldn't be anything TO vibrate, per-se, no time for it to be vibrate in and no space in which the vibrations could take place. You'd simply have a multidimensional waveform where if you made some axis space and another one time, you could treat it as though something was vibrating. In practice, though, it would be a static n-dimensional waveform whose existence was logical rather than physical.
I like this particular branch of QM, as it means physics is a branch of mathematics, a specific group with specific properties and specific operations, and that the universe is a specific set of functions that wholly reside in that group. It makes maths the "ultimate" reality, which means these sorts of philosophical musings about the world can be answered through mathematical analysis (although maths permits that answer to be rigorously undefined).
Thought (Score:4, Interesting)
Re:Thought (Score:3, Interesting)
Indeed, the problem with reversing time is that you suddenly have to change physics to handle the fact that the time has already been used. I remember Einstein expressing the view that we get 3 dimensions of space which can be reused and one dimension of time which can't be reused. And physics generally works and the equations are written for that reality. If suddenly, you can reused time and particles can go back and potentially interfere with themselves, then a ton of work would have to be put into making the equations work.
Re:well, actually... (Score:3, Interesting)
Isn't there a way on slashdot to block "funny" comments? Those years old "jokes" littering almost each science-related thread have no value at all for me.