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A Boost For Quantum Reality
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."
it is, and it isn't.
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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.
Sheesh, evil *and* a jerk. -- Jade
In practice applying the pop version of quantum theory to everyday life does result in a more cohesive and intuitive reality than trying to go with previous thoughts. It certainly does a better job of handling times when you have to reinterpret events when new information comes into play.
> The philosophical status of the wavefunction [..] would seem to be an unlikely subject for emotional debate
Well not to me. I guess any subject a given amount of people put lots of effort in can arise emotional debates. *Especially* if the subject in question is discussed philosophically.
and interesting image http://dequantified.net/preview/factorpreview.gif
I can see how people could get so passionate over the topic. I myself passionately don't know what the hell they're talking about.
Reality is not a wave function. It's a useful model, but it's absurd to think of it as real and physical.
The cat isn't really both alive and dead. It's either still alive or it died. It certainly knows.
Reality is reality and models are models.
If the wave function has an effect then it what way is it not real? Maybe its the mathematician in me but if reality can only be understood mathematically then I have no problem with that, thats just a problem with our imagination. I have always thought the divided universes interpretation of quantum physics multiple states was reading too much into things, a bit like during the steam age everybody wanted to interpreted things in terms of steam engines, thats useful, but the model implies things which the pure maths itself doesn't.
http://arxiv.org/abs/1111.3328v2
http://arxiv.org/pdf/1111.3328v2.pdf
http://stephan.sugarmotor.org
Most people think of matter as a solid when in fact there is no fundamental solid but matter is in it's base form a vibration which is roughly the same as a wavefunction. In some ways a wavefunction is no different a vibrating string so it's not as crazy as it sounds.
I am a meat wavicle.
I don't get why people get so hung up on these aspects of QM... QM is NOT a complete theory anyway, and treating a particle as a localized field configuration (quantum field theory) neatly fixes many of the seemingly inconsistent aspects of non-relativistic QM (albeit while creating a thousand other problems/questions). It's ultimately irrelevant in some sense...
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...
Its that there's no such thing as an unlikely subject for emotional debate.
Here is thought I had the other day: assume mathematical "function" that defines our universe and underlying physics (function that "theory of everything" is trying to find), works in _reverse_ direction of time. So that every particle (or whatever) at t is calculated from local state at (t+1). We usually thinks of laws of physics going in "natural" direction of time. Now, after the inevitable final end of intelligent civilizations in this universe, surely there will be some artifacts made by durable nanomaterials, that persists long after stars and even black holes evaporate into 'nothing". Universe calculated from backwards will therefore have such "intelligently designed" artifact at the _beginning_, as sort of input parameter, so it have to find a mathematically plausible way going forward (which is backwards in time for us) how these artifacts were created. Intelligent life and physical laws supporting intelligent life might be _result_ of something strange at the function input. That means if you have function where random "state" is input and set of equations ("laws of physics") is output, as soon as you put something looking improbable at input, say set of large prime numbers, function might find it is easier to create universe with intelligent civilization, which created this prime numbers, then to create universe where laws of physics created such improbable outcome by chance.
839*929
The article confused me greatly so I read some of the arxiv preprint linked above. Here's the idea and context as I understand it. I've included some basic quantum background since most people here don't have it.
* Intro to wavefunctions via an example. Electrons have a property called "spin" which has two states, "up" or "down". These can be measured in, for instance, the Stern-Gerlach experiment where those electrons with spin up are deflected up by a magnetic field and those with spin down go down. The wavefunction corresponds to a list of the probability of each outcome occurring. The probabilities evolve through time via the Schrodinger equation which allows predictions to be made. One might prepare an electron where its spin wavefunction corresponds to the list [1/3, 2/3], so 1/3 of the particles go up and 2/3rds go down. [I've oversimplified; wavefunctions are actually elements of an abstract Hilbert space and complex-number amplitudes are used instead of real-number probabilities. I love Hilbert space but it's too much to explain here.]
* Spin is not a classical property. One can measure spin "left" and "right" in addition to "up" and "down" by rotating the Stern-Gerlach (SG) device mentioned above and measuring left/right deflection. Suppose you run a stream of electrons through an up/down SG device which gives 80% of them "up". You then run those "up" electrons through a left/right SG device--it will always come out with 50% "left" and 50% "right". Even more strangely, if you then run the "left" electrons through another up/down SG device, the probabilities will now be 50%/50%, even though you selected only spin up electrons at the first stage so you'd expect 100%/0%. The act of going through the left/right device altered the spin up/down state somehow.
* Hidden variables. Perhaps the electrons above have definite "spin vertical" and "spin horizontal" properties before the experiment starts. The act of going through a device must change the other property, though everything might be deterministic if there is some further hidden property controlling which electrons have their spin up/down states altered in which ways by passing through the "left" SG device. The alternative is that there are no definite properties which determine the wavefunction; the wavefunction is all there is, reality is somehow fundamentally probabilistic, and the wavefunction is "real" instead of a statistical construct.
* Bell's theorem. Suppose spin up/down and spin left/right are definite properties and some hidden variables explain the above results. Using entanglement (which I'll leave undefined) and the assumption that information cannot travel faster than light, one can measure both the spin left/right and spin up/down values of a particle before the hidden variables have a chance to act (note: they might act in a very bizarre, perhaps even non-deterministic, manner, but we get to measure things before they have that chance). This gives a testable prediction which differs from quantum mechanics. If the experiment is performed, the "definite property" theory does not predict reality while the use of wavefunctions does predict reality. This is strong evidence for the reality of wavefunctions, though it's not completely conclusive.
* The paper. It derives Bell's fundamental contradiction from fewer assumptions. In its own words,
The result is in the same spirit as Bell's theorem, which states that no local theory [i.e. one without faster-than-light communication] can reproduce the predictions of quantum theory. Both theorems need to assume that a system has a objective physical state L such that probabilities for measurement outcomes depend only on L. But our theorem only assumes this for systems prepared in isolation from the rest of the universe in a quantum pure state [e.g. a particle measured as spin "up" right after the SG experiment above]. This is unlike
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
Isn't this an oxymoron?
I can't remeber the finer details of Berkeley's argument, but I really don't see his point.
Most likely the world exists as we perceive it. In this case he is just wrong.
In case that the world does not exist, but is just an illusion of some sort, then what? If noone else exists, theres no point in telling them? Let alone spend time on writing a book about it?
You might as well entertain the idea that the world just is. Maybe the illusion will be removed from your eyes and you will see the real reality later on, but discussing it here makes no sense at all to me.
I made it almost through the second paragraph then googled "hilbert space". It's 8:15 and my brain already hurts. I should know by now to just email these to myself to read after work.
Of course it's real. There isn't an imaginary term in the wavefunction equation.
It's about physicists got serious about quantum-wave physics. Thanks to the Copenhagen interpretation, quantum-wave physics have been avoided by almost everyone. It's time for physicists to give up their religious beliefs and get on with it.
Don't stop where the ink does.
The Link in the comment of the article was quite interesting.
http://freespace.virgin.net/ch.thompson1/People/CarverMead.htm
Basically stating that there is nothing statistical about quantum phenomenon and that Bohr got it wrong after all (to my limited understanding).
"we are all atheists about most of the gods that societies have ever believed in. Some of us just go one god further."
not is is not is not
I intend to patent the direct manipulation of the quantum wave function, which will, among other outcomes, be the basis for my infinite improbability drive.
Reality is not a wave function. It's a useful model, but it's absurd to think of it as real and physical.
The cat isn't really both alive and dead. It's either still alive or it died. It certainly knows.
Reality is reality and models are models.
Except that now we are finding the cat is both dead and alive. The question is, which universe do you inhabit? The only way for you to find out is to measure the result, collapse the probability, and determine which reality you inhabit. Your copy (the one you're so desparate to believe doesn't exist, perhaps because s/he threatens your sense of uniqueness, or free will, or whatever), if s/he opens the box and looks, will find s/he inhabits a universe with a different outcome.
As for self determination and uniqueness, this need not really trouble people. In an infinite set of universes, any outcome will be statistical in nature. Like predicting which atom will decay during the half-life of a radioactive material, no prediction can be made as to a particular state (or decision) you or I, as individuals in an indivual timeline, will make. We are still perfectly free to make decisions, and perfectly responisble for their outcomes, regardless of whether the decision we make matches that of 90% of our duplicates, or 0.0001%.
We may not be unique, but that doesn't mean we don't have free will. (Of course, we may not, but that doesn't follow from quantum physics, repetition in an infinite set, or any of the other variations of parallelism that appear more and more to be a fundamental property of our reality).
So people just need to chill, and see where the math and science actually take us. If it turns out we do inhabit a single, unqiue universe, then we get our uniqueness back and those bothered by parallelism are in luck (though it will be a short lived relief, geologically speaking, and ultimately fatal, astrophysically speaking). If it turns out otherwise, then so what? We still live our lives, with or without determinism. Whether we debate that in the context of a single unique timeline, or multiple, perhaps infinite timelines, doesn't really matter.
The only real loser is religion, whic presupposes just the one timeline. But then, religion has a long history of losing out to science and changing its teachings accordingly (like cockroaches, the memes don't die, they just adapt), so even that is unlikely to change if or when the multi-world hypothesis is proven.
So even the most dogmatic mind need not be threatened by either outcome...except perhaps for someone like the character in Star Trek, who is driven mad at the thought of another person in another universe just like them and spends eternity trying to hunt down and kill his duplicate. In which case, if reality is other than what they desire, tough shit.
The Future of Human Evolution: Autonomy
These cretins seem to have forgotten that all physics is an approximation. Deducing things like this from limited observations is not possible. Also, mathematics does only apply to an abstraction of reality. If the abstraction removes anything essential, your mathematical conclusions will not apply to reality.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Stephan Wolfram says it's cellular automata, all the way down.
He also says that Philip Taylor Kramer is stealing his thoughts.
the preceding comment is my own and in no way reflects the opinion of the Joint Chiefs of Staff
I propose a counter thought-experiment:
You are placed in a living room with two televisions and two regular NES controllers, which feed into a wall behind the televisions.
You are told that one of them is a real NES running Super Mario Bros.
You are told that one of them is an i7 running an emulated NES running a ROM dump of Super Mario Bros.
1 Hz green-blink-of-death jokes aside ... Is there anything you can do to tell the difference between the two?
And even more importantly:
1. Does the fact that you can't devise an experiment to tell the difference between the two mean that you should disbelieve in the nature of real vs emulation?
2. If you can't devise an experiment, does "real" vs. "emulation" actually make a difference? Wouldn't it be more accurate to say that both are equally "real" they just reach the same state by different means (which, of themselves are unimportant)?
> If there's nothing to observe reality, does it still exist? That's the essence of Schrodinger's cat.
As basically everyone else, you did not understand what the Cat-example was not about.
It was not about making clear or be an example how QM works in the Kopenhagen interpretation, it was supposed to show how absurd that stance Schroedinger thought it was. He was actually complaining and expressing that "nothing better" came from his equasion. Schroedinger wanted to make QM easier, simpler, more elegant - and instead he created that completely unintiutive probability-mess (as he thought). He was not happy and did not try to explain something.
He said "IF that worked like that, then the cat would be dead as well as alive at the same time. Uhh... THIS IS ABSURD, PEOPLE! This is not what I wanted to create,"
He even stated "If it stays at his quantum-jumping, I regret to ever have been involved with it [QM]".
and post a link to a site with a lot of really interesting thoughts. http://tgdtheory.com/ . flame away punks!
Why do people feel it necessary to answer this question? What good would a resolution do anyone? Outcomes are still the same regardless of what you believe. Even if the "wavefunction" was "real" whatever that means there is still no guarantee we are aware of everything there is to know about it. What good is the label?
So, if I roll a fair, six-sided die, the chance that a given value will come up is 1/6, right?
Is the probability distribution that describes this outcome "real" according to the authors of this paper? I mean, it describes a result that manifests "in reality". The chance that I roll a 3 on any given trial is "really" 1/6. Where is the distribution? Show me it.
I'm somewhat confused about the timing of this article here on the site. The initial response to the PBR paper a couple of months ago was pretty varied, and mostly confused -- both from the lay public as well as from physicists. And so far this discussion also seems to suffer from misunderstandings and misinterpretations of what is the issue here. Frankly, this kind of confusion is unavoidable with an issue as subtle as this, within the constraints of a forum discussion (which is why I won't try to argue my point in detail here), although even some physicist blogs have made a mess of it. Anyway...
The reason I say that the timing is odd is that Slashdot decides to write about the PBR article, coincidental with the appearance of another paper to similar effect (but making different assumptions) on arxiv:
http://arxiv.org/abs/1205.1439 (by Lucien Hardy at Perimeter)
About a month ago, there was another publication by Roger Colbeck and Renato Renner (at PI and Zurich respectively, although Roger Colbeck has just moved to Switherland too, I think):
http://arxiv.org/abs/1111.6597
The upshot of all of these is, crudely speaking, that reality is at least as "complex" as the quantum state (there have been hints of this also from earlier work by Montina, which I think is referenced in Hardy's paper). It does not say that the quantum state as we describe it mathematically is literally a real thing. The background of a lot of these papers is a recent (last 20 years) trend towards statistical/subjective/operationalist interpretations of the quantum state, mostly brought about (in my opinion, anyway) by people working in quantum information/computing.
The abstract isn't saying the wave-function is real, if says if the wave-function isn't real than quantum theory is wrong. Since general theory of relativity and quantum theory are incompatible in some aspects we *know* quantum-theory is partially wrong (like Newtonian physics). So, while mathematically interesting, it's old news.
Hello: The paper in question can be found here: http://arxiv.org/pdf/1111.3328.pdf Apologies if this has been posted already.
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.
No such completely open ended experiment is possible. If it were, any new scientific observation of a previously unknown phenomenon could not be properly modeled on the simulated side and produce the same result as on the real side. In fact, if the results do differ, you have proof of objective reality, or at least that both sides are simulated differently. The simulation cannot have universal knowledge beyond that of its creators. Call that a reasonable postulate.
These arguments are in the same vain as the arguments for Bell's hypothesis.