It remains embarrassing that physicists haven’t settled on the best way of formulating quantum mechanics (or some improved successor to it). I’m partial to Many-Worlds, but there are other smart people out there who go in for alternative formulations: hidden variables, dynamical collapse, epistemic interpretations, or something else. And let no one say that I won’t let alternative voices be heard! (Unless you want to talk about propellantless space drives, which are just crap.)
So let me point you to this guest post by Anton Garrett that Peter Coles just posted at his blog:
It’s quite a nice explanation of how the state of play looks to someone who is sympathetic to a hidden-variables view. (Fans of Bell’s Theorem should remember that what Bell did was to show that such variables must be nonlocal, not that they are totally ruled out.)
As a dialogue, it shares a feature that has been common to that format since the days of Plato: there are two characters, and the character that sympathizes with the author is the one who gets all the good lines. In this case the interlocutors are a modern physicist Neo, and a smart recently-resurrected nineteenth-century physicist Nino. Trained in the miraculous successes of the Newtonian paradigm, Nino is very disappointed that physicists of the present era are so willing to simply accept a theory that can’t do better than predicting probabilistic outcomes for experiments. More in sorrow than in anger, he urges us to do better!
My own takeaway from this is that it’s not a good idea to take advice from nineteenth-century physicists. Of course we should try to do better, since we should alway try that. But we should also feel free to abandon features of our best previous theories when new data and ideas come along.
A nice feature of the dialogue between Nino and Neo is the way in which it illuminates the fact that much of one’s attitude toward formulations of quantum mechanics is driven by which basic assumptions about the world we are most happy to abandon, and which we prefer to cling to at any cost. That’s true for any of us — such is the case when there is legitimate ambiguity about the best way to move forward in science. It’s a feature, not a bug. The hope is that eventually we will be driven, by better data and theories, toward a common conclusion.
What I like about Many-Worlds is that it is perfectly realistic, deterministic, and ontologically minimal, and of course it fits the data perfectly. Equally importantly, it is a robust and flexible framework: you give me your favorite Hamiltonian, and we instantly know what the many-worlds formulation of the theory looks like. You don’t have to think anew and invent new variables for each physical situation, whether it’s a harmonic oscillator or quantum gravity.
Of course, one gives something up: in Many-Worlds, while the underlying theory is deterministic, the experiences of individual observers are not predictable. (In that sense, I would say, it’s a nice compromise between our preferences and our experience.) It’s neither manifestly local nor Lorentz-invariant; those properties should emerge in appropriate situations, as often happens in physics. Of course there are all those worlds, but that doesn’t bother me in the slightest. For Many-Worlds, it’s the technical problems that bother me, not the philosophical ones — deriving classicality, recovering the Born Rule, and so on. One tends to think that technical problems can be solved by hard work, while metaphysical ones might prove intractable, which is why I come down the way I do on this particular question.
But the hidden-variables possibility is still definitely alive and well. And the general program of “trying to invent a better theory than quantum mechanics which would make all these distasteful philosophical implications go away” is certainly a worthwhile one. If anyone wants to suggest their favorite defenses of epistemic or dynamical-collapse approaches, feel free to leave them in comments.
The point is, if an electron’s orbital can be shown to be stable to radiation according to classical physics (known as the non-radiation condition), and demonstrated through experiments going back almost a century, why bother with Heisenberg Uncertainty and all of the complicated, out of touch with reality claims, that come along with it?
Is it not more “ontologically simple” to go with the most parsimonious and most accurate theory, which doesn’t require the complete abandonment of thousands of years of accumulated scientific knowledge and observation? 100 years of an academic exercise in QM and the theory still cannot analytically solve for the ionization energy of lithium, indeed it will NEVER be able to analytically solve for any molecule apart from hydrogen; and even then it doesn’t explain the physical basis of spin. Try modelling insulin using a QM approach; it is impossible hence the need for semi-empirical models which more often than not, fail spectacularly. Indeed historically, QM argued against the possibility of the laser as in a laser the precise position and momentum of photons must be theoretically knowable in order for it to function.
“As late as 1956, Bohr and Von Neumann, the paragons of quantum theory, arrived at the Columbia laboratories of Charles Townes, who was in the
process of describing his invention. With the transistor, the laser is one of the most important inventions of the twentieth century. Designed into
every CD player and long distance telephone connection, lasers today are manufactured by the billions. At the heart of laser action is perfect
alignment of the crests and troughs of myriad waves of light. Their location and momentum must be theoretically knowable. But this violates the
holiest canon of Copenhagen theory: Heisenberg Uncertainty. Bohr and Von Neumann proved to be true believers in Heisenberg’s rule. Both denied
that the laser was possible. When Townes showed them one in operation, they retreated artfully. ”
Physicists need to go back to the drawing board and adopt a rational approach, instead of the rationalization approach that has mired mainstream physics for a near century.
@Paul Torek: [[I love the whooshing sound your arguments make as they go over my head. Why is an ontic wavefunction, with electrons and photons mere patterns within it, more troublesome than ontic electrons and photons plus an epistemic wavefunction?]]
It’s simple, really. Electrons, protons, photons, quarks etc. are all concrete residents of spacetime. Now, these entities are not directly observable and they may have various counterintuitive properties. But, metaphysically, they are the same concrete, spatiotemporal entities that physics has always dealt with. Everything in the ontology of fundamental physics (fermionic and bosonic fields, etc) is fully concrete.
Now the wavefunction – if interpreted literally as a physical entity (as in MWI, Bohm, GRW) – would be something else entirely. In fact, it would be a mathematical entity. What does it even mean to attribute physical existence to an abstract mathematical entity? First of all, it cannot live in spacetime. If it can be said to “live” anywhere, it lives in 3N “configuration space”. That is, the psi-ontic position is that physical reality LITERALLY contains mathematical functions from configuration space to complex numbers which somehow causally influence the familiar objects in spacetime that we all know and love. That strikes me as a hard pill to swallow.
On the psi-epistemic view, in contrast, the wavefunction just represents our partial state of knowledge about an underlying concrete spatiotemporal reality. This sounds great until we encounter Bell’s theorem, PBR, and related no-go theorems, which APPEAR to rule out non-ontic interpretations. However, all these no-go theorems assume the absence of retrocausality. And this is precisely the loophole through which the time-symmetric approach carries us into the promise land of “having our cake and eating it”.
To some extent, it’s an issue of philosophical taste. Someone like Max Tegmark – who already believes the physical universe is pervaded by all sorts of mathematical objects and abstracta – might well greet the ontic wavefunction with open arms. Personally I have nominalistic leanings, so if there’s a viable interpretation of QM that requires only concrete elements of spacetime then that’s a path I’d like to explore. As far as I know, the time-symmetric interpretation is the only option compatible with such nominalism.
@Panda,
The problem with your way of thinking is that it doesn’t allow enough wiggle room. You’re suggesting that the universe is described by simple, concrete rules that are easy to explain and useful to make predictions from. If you had your way, there’d be no room left for us philosopher-physicists at all! I say you should be banished from the room before anyone else gets wind of this heresy.
I think the reason Occam’s Razor worked for so many years was because science use to be so simple. Have you tried reading a paper in theoretical physics recently? There is nothing simple and straightforward about it!
How could something, which has had scientist baffled working around the clock to trying to fix it, be elegantly simple? If the solution was simple, we would be endorsing the fact that science has had a giant brain fart for the past century. I am sure there has been plenty of scientist that have tried making simple solutions, since the inception of the idea.
There just cannot be simple solutions to very complex problems. Classical physics has ended. Get over it. Physics is hard now and difficult.
Those guys know plenty about quantum physics, but they have a certain amount to learn about handling exposition and period dialogue…
@Daniel Kerr
@Philophysique
What is meant by an ontic wavefunction with a particle pattern within it? Does a matter wave comprises of a pattern of particles with all the spatial points in wave occupied by particle? Is it possible that all the spatial points in a wave may be occupied by one particle at same instant? If it is not so, what is the stuff of which a matter wave is composed of. If you will state that in case of a charged particle like electron, it is the em field which occupies the spatiotemporal area of wave, this will amount to paraphrasing the query as to what is the stuff of which an em field is composed of. I am struggling since some time to grasp over these issue intuitively though some people may discard such issues being philosophical in nature
@Phiolphysique
“Now the wavefunction – if interpreted literally as a physical entity (as in MWI, Bohm, GRW) – would be something else entirely. In fact, it would be a mathematical entity”
A wave function may be a mathematical description of a wave. In view of this, a wave function can be treated as purely an epismetic concept BUT is wave also an epismetic entity? If a wave has no ontic value, what is the value of a wave function since this will amount to description ( though mathematically elegent) of a non-entity.
My view of the world is that QM stems from more deterministic law that both shares the same eigen values (This might be mathematically possible). Through this process of producing the QM formalism we loose some information and get a few philosophical issues which is well illustrated on this blog. I think that the Aspects experiment (entanglement) could be explained cause this process is far from local hidden variables approach. To actually find out if this hypothesis is true we need to really understand the double slit experiment that hints on a dual nature of particles as both waves and particles. Especially what needs to be rules out is that there cannot be an interaction between the slit and the particle that exchange momentum in quantas and hence produce a pattern on the target screen similar to what the wave formalism would indicate.
Have a nice day!
/Stefan
Great commentary everyone. Personally I don’t believe anyone who claims to be interested in pursuing scientific truth, should be censoring ANY science related commentary obviously related to the topic at hand, no matter how much they may be personally opposed to the materially being presented. That is not science nor is it scientific. That is censorship and many millions have died to defend against such practices. Censorship should NEVER be an issue in science, as long as the commentary is relevant and respectful.
@Panda are you referring to an exchange earlier in this thread, now removed, that began with a proposed alternate explanation for the physical manifestation of the fine structure constant?
There were some other comments in that exchange that were somewhat parsimonious which may have been the target of the removal. While some of the comments in the exchange were clearly ad hominem (“I bitchslapped you”, “you’re a nobody”, “f**k off, dips**t”), I don’t believe any of mine were and I do believe my original comment was removed in error. It was a good faith attempt to propose an alternate formulation and included highly defensible math and scientific thought. It seemed to have rubbed at least one respondent the wrong way and elicited an overreaction. However I don’t believe in the heckler’s veto. In the interest of posterity, I’m going to reproduce the core idea here. I hope Prof. Carroll will understand my intent and elect to respond to the idea or not as he sees fit and not merely delete it a second time.
Here are two definitions for the fine structure constant, alpha. The first is the generally accepted definition and appears Wikipedia. The second, a far more detailed and enlightening definition is, I believe, new to science and should be considered on its own merits.
#1: The fine structure constant is a fundamental physical constant characterizing the strength of the electromagnetic interaction between elementary charged particles.
#2: The fine structure constant is the relativistically corrected ratio to the Bohr radius of a perfect spherical resonator cavity in free space such that the resonant frequency exactly matches the frequency of a photon with energy equal to the rest mass of the electron.
@Vinod Sehgal: [[A wave function may be a mathematical description of a wave. In view of this, a wave function can be treated as purely an epismetic concept BUT is wave also an epismetic entity? If a wave has no ontic value, what is the value of a wave function since this will amount to description ( though mathematically elegent) of a non-entity.]]
We talking about two different things here.
Waves in spacetime are clearly ontic. They are your standard concrete spatiotemporal objects. So any mathematical description of them is obviously going to be epistemic, like every other mathematical construct in physics. For example, going by QFT and GR, ontic reality could be said to consist solely of spacetime-local fields – fermions and bosons. The mathematical equations used to describe this spatiotemporal reality, on the other hand, are purely epistemic – they do not imply that abstract mathematical entities have some sort of physical existence.
When I say “the wavefunction” I am referring specifically to PSI – not to any spatiotemporal field phenomena like electromagnetism or gravitation. PSI – “the wavefunction” – is not defined over spacetime. Rather, PSI is a function from 3N-dimensional configuration space to complex numbers. These complex numbers are supposed to represent “probability amplitudes”, from which expectations of experimental outcomes can be derived. On the ontic view, we thus have a entity that exists outside of spacetime that somehow causally influences the phenomena we observe within spacetime. It’s a bit of a headscratcher. Hence the motivation to interprete it epistemically as a represention of our imperfect information about an underlying spacetime-local reality. Only time-symmetric theories have the potential to deliver on this hope.
@Vinod Seghal “What is meant by an ontic wavefunction with a particle pattern within it? Does a matter wave comprises of a pattern of particles with all the spatial points in wave occupied by particle? Is it possible that all the spatial points in a wave may be occupied by one particle at same instant? If it is not so, what is the stuff of which a matter wave is composed of. If you will state that in case of a charged particle like electron, it is the em field which occupies the spatiotemporal area of wave, this will amount to paraphrasing the query as to what is the stuff of which an em field is composed of. I am struggling since some time to grasp over these issue intuitively though some people may discard such issues being philosophical in nature”
I think philophysique gave a good answer above but I think you wonder what such a wavefunction consists of. It’s not matter, as in the above post, it’s a function which assigns a complex number to every point in a configuration space over spacetime. So if you have one particle it is directly over spacetime, while n particles you have 3n spatial coordinates corresponding to x, y, and z of each particle. The wave itself is not composed of anything material, it is just the distribution that describes the chances of measuring a particle or particles in a given volume of spacetime with a nonperturbative measurement.
I’ve never been bothered by the ‘weird’ aspects of QM, or convinced by the need for hidden variables. On the contrary, the weirdness (in concert with the predictive success of course) is what convinces me that the theory is deep. After all, unless you think it’s cannonballs all the way down, at some point you’d surely expect Whatever’s Going On to violate our macroscopic common sense?
But what does seem unsatisfactory is the internal coherence of the theory. There are at least four central aspects which seem to have little to do with each other: the ‘quantum’ aspect itself (as in energy coming in discrete packets); the non-localness; the ‘sum over histories’ of QED; and the Born Rule.
So for instance, wave-particle duality is not much of a wrench. (I admit this is probably easy for me to say as a layman. For a classical physicist, used to applying the mathematics of waves and particles to completely distinct phenomena, I guess it would be harder to accept.) I can accept that probabilities of particle positions are amplitudes. But why the hell do you then square them? What does it mean, physically, in terms of the ‘probability wave’ that I’m now fairly contentedly imagining… and how does it relate to anything else?
@Philophysique
@ Daniel Kerr
“Waves in spacetime are clearly ontic. They are your standard concrete spatiotemporal objects”.
Thanks dear commentators for taking interest in my queries and responding with very appropriate and detailed replies. I held the view and your comments have reinforced the same that a wave is physical entity with ontic value BUT a wave function is a mathematical epistemic concept devised to describe various properties of particle in wave in terms of probability. But this sort of description of wave does not convinces me completely but on the contrary makes me to go more deep in intricate nature of a wave.
@Philophysoque As you have rightly mentioned that waves ( here by wave I mean matter waves for quantum particles) and I also agree that waves are spatiotemporal concrete realties. It implies waves are composed of some physical stuff ( than only they can be treated as physical realities). Further since waves are spatiotemporal realities, therefore, waves should be residing and acting in our normal 4d spacetime.
Here let me say that we are accustomed to use 4d spacetime for classical world as per SR. It is not necessary if 4d spacetime holds good for quantum world or not? It is our assumption that all the physical laws which holds good at classical world should also hold good at quantum world.
I have not brought wave function yet in picture since wave function is only a mathematical construct to describe probability of properties of particle in Waves did exist prior to formulation of wave function by Schrodinger. Waves can and do exist without wave function but not vice versa. If you agree with above description, a natural and obvious query arises:” What is the physical stuff which constitute a wave?” Since a wave is a concrete physical reality, it should be composed of some thing physical. To elaborate my point of view further, take the example of a single electron circling around the nucleus of a single H atom. As per QM, the single electron will not be positioned rigidly ( as in classical mechanics) at one point but it will be scattered around like a cloud in the form of a wave. This scattering around of electron is an ontic physical concrete reality. Therefore, this scattered cloud or wave should be composed of “something”. What is that “something?” Further does electron behaves both like an particle and wave simultaneously and instantly or it switches over between wave and particle alternatively with some time gap between switching?
” On the ontic view, we thus have a entity that exists outside of spacetime that somehow causally influences the phenomena we observe within spacetime. It’s a bit of a headscratcher”
if I am not mistaken, here you are mentioning Bohm’s interpretation of QM regarding wave function that somehow guides the physical real pilot wave If a wave function is a mathematical construct without any physical base, what is meaning of its ontic existence and that too being taken outside normal 3d space or 4d spacetime and from there guiding or influencing a wave in our normal 3d space? Are you conceding the existence of some extra dimensional space ?
@Daniel Kerr
“The wave itself is not composed of anything material, it is just the distribution that describes the chances of measuring a particle or particles in a given volume of spacetime with a nonperturbative measurement”
I think your above statement does not agrees with description of a wave as given by Philophysique with which I agree. What I want to reiterate that both particle ( say an electron) and its wave in which, as per QM, particle manifest are concrete physical realities I think that is the meaning of saying that wave is ontic in nature. Now if wave is a physical reality — a tangible reality which does exist in our normal 3d or (4d) space, it should be composed of some thing or not? In my above paras, I have elaborated on this aspect. The entity which is not physical is wave function which exist in mathematical formulation to measure the distribution of particle within a spacetime, as you have rightly stated above, but not within empty spacetime but within a physical wave existing within spacetime
Why is it so easy to reject a non local theory of hidden variables? On paper one see that there is a bunch of problems with it, but really is this a sound objection. Don’t get me wrong, I do subscribe to the notion that the fundamental laws are local. But that’s on the right time scale. On the atomic timescale applicable to the Aspect theorem we could very well reach a steady state inside the atom which rule are not local. So the conclusion from the outcome from this test is that modelling through boundary value problems is possible. Let me go deeper with this … If we consider that particles are a crack or a singularity of space, taking parallels to solid state physics means that this crack might very well be two dimensional. Also if this setup should be stable and not radiate we could search for two dimensional surfaces that does not radiate and we get a non radiating boundary condition for which Hauss theorem is applicable. This is a non local theory and searches for such systems have been successful. It is known that we can reproduce quantum solutions for such system just considering Maxwell’s equations and these two dimensional cracks. That means that we can now demonstrate a non local deterministic theory that transformed yield the QM eigen solutions of the Hydrogen. In all this means that the Aspect theorem is not at all strange. That QM can be used to predict things just fine many times if you can solve the equations. Also it is not at all strange that “probabilities” are squared cause the invariant is the integral of phi squared. The question left before accepting this deterministic process is to explain the wave duality attributed to QM because that is not reproduced with this deterministic model. So again, to pose the key question, how well proved is this duality relative alternative explanations?
Regards
Stefan
@Stephan
“Let me go deeper with this … If we consider that particles are a crack or a singularity of space”
Are you trying to convey the idea that space is granular one and space particles create a singularity or crack to give birth to matter particles?
” this crack might very well be two dimensional. Also if this setup should be stable and not radiate we could search for two dimensional surfaces that does not radiate and we get a non radiating boundary condition for which Hauss theorem is applicable”
By your above statement, are you pointing toward hologramic principle of universe?
@Vinod,
Well I have seen and followed equations that basically assumes that for example the electron could be seen as a crack in space that are two dimensional, now exactly how the physics are of the crack is not described, just that it is a disturbance that have a certain geometry. Now what you do is to take Maxwells equations and then introduce a source as a distribution, well the simplest is to try a delta distribution with values on a surface and impose the condition that it should be stable e.g. apply Hauss theorem of non radiation. Typically you would in this setup think about this as a set of charges but that’s the wrong interpretation. The correct one is to find a model that could suite a crack whatever it is. Don’t interpret this as a set of point charges and backpedal, that’s not the only physics that could give up to cracks. So that’s the definition of a crack I ‘ve seen on a blackboard that when I followed the chap doing the analysis gave the correct eigenvalue values.
Granularity …
To find out what space is, like granular etc, you need to be able to have a model of a space that produces electromagnetism, after doing that one can start to introduce non-linearites that can produce cracks and see what can be done.
Holography …
I do think that for simple cases of single particles, information could be condensed on 2 dimensions. So for these cases a holographic principle can hold due to the rule is from a non local steady state. When you resolve the transient I do not think that the holographic principle longer holds. That’s at least my view.
Cheers!
@Anton Garrett
I think the word “non-locality” is misleading. It rings an alarm in people’s mind that you may be challenging relativity’s “no signals faster than light” requirement. Locality as in “local field theory” would be a consequence of relativity. I believe Bell really meant non-factorizability when he used the word “non-locality”
Has it been shown that in spite of “non-locality” which would mean everything is connected to everything else, interpretation of laboratory physics experiments is possible?
@kashyap vasavada
A physics lab experiment with a set of standing waves is an example of a non local theory that show up in your everyday lab. The derivation of these standing waves are generally through boundary value problems which typically connects every point in space with every other point in space. So If you parameterize amongst them you will get a non local theory.
I am writing this now just to say that this page, with its so numerous comments, has a wealth of information of almost astronomical magnitude. (and I am just mentioning this very page, and not the whole of Mr. Sean Carroll’s blog!). I do feel very indebted to this kind of online contributions. So, thank you all, especially the page owner/host.
Best Wishes,
Julio
Hi,
I’m writing SF novels (in French) and the MWI of QM is so far the one I prefer. From the naive perspective where I stand, I’ve tried to come up with a simple formulation of it. Hence the following question…
Would it be right to say, within the context of MWI, that the result of some experiments allow the witness of this result to clearly state in which universe we are in regards to this experiment, while other results/experiments don’t allow us to clearly specify the universe?
For example, in the double slit experiment, when you put an “observer” on one of the paths, this setup allow the witness of the final result to clearly state: “I’m in the universe where the particle went left” or “I’m in the universe where the particle went right.” While without an observer, the result of the experiment doesn’t allow us to clearly say in which universe we are in regards to this experiment. But, it at least allow us to say that there is, for example, a 50% chance that I am in the universe where the particle went left, and the same for the right path.
In other words, QM entanglement would just be a way of saying how good an experiment is at distinguishing amongst two or more universes.
Is this a valid “interpretation” of the MW interpretation, or is this just circular reasoning? O.o
This. Also, Hugh Everett himself believe his theory to mean that we’re all, subjectively, immortal, since for every life and death situation a person faces there exists a world in which he survives (probably alone, after a while), a belief that is apparently shared by at least some MWI supporters. Since I haven’t seen it conclusively refuted that MWI implies quantum immortality, I’m hoping someone manages to eventually falsify MWI itself. However, it’s true that this is no actual argument against MWI and that it’s very much possible that we’re, in fact, all screwed.
Julio,
I too have been away for several days. My disparaging comment about quantum consciousness (ie, here are two things we don’t understand so let’s posit a link) was not entirely serious and was the result of losing patience with Roger Penrose’s output on the subject. I don’t mind pushing things a bit on blog comments. I do treat the subject more seriously, if briefly, in my essay at the telescoper blog to which Sean kindly linked and started this thread.
Kashyap,
Perhaps I should have ben explicit that I was not advocating superluminality, but I do define what I mean by nonlocality in Bell setups and I think that is clear.
J S Bell seems to acquit himself quite well on the topic of hidden variables in his collection: Speakable and Unspeakable in Quantum Mechanics, Cambridge, 1993.