“I asked the Zebra,
are you black with white stripes?
Or white with black stripes?
And the zebra asked me,
Are you good with bad habits?
Or are you bad with good habits?
Are you noisy with quiet times?
Or are you quiet with noisy times?
Are you happy with some sad days?
Or are you sad with some happy days?
Are you neat with some sloppy ways?
Or are you sloppy with some neat ways?
And on and on and on and on and on and on he went.
I’ll never ask a zebra about stripes...again.” -Shel Silverstein
When it comes to the classical world -- the world on a macroscopic scale -- we all feel comfortable using the word reality. While we may quibble over the finer, technical points of the definition of the word, you and I know reality when we see it.
There are all sorts of properties we assign to real objects: they have energy, they exist at certain points in space and moments in time, they have certain properties of motion, and are measurable and quantifiable in a variety of other ways.
This ranges from microbes here on Earth to the largest structures in the Universe: all of these are quantifiable as real in terms of energy, position, time, and momentum, among other properties.
But if we head into the quantum realm, down to scales so small that our classical laws and pictures break down, we discover that things are drastically different, and that reality no longer conforms to our expectations.
You might think of an atom the same way you think of a planet orbiting the Sun: an electron moving in orbit around the center-of-mass of the electron/nucleus system. But whereas if you knew a planet's orbital properties and the mass of the star it was orbiting, you'd be able to know with certainty where that planet was and how it was moving (i.e., its position and momentum), the quantum world is a little different.
Okay, a lot different. Because you can no longer predict the position of that electron -- only the probabilities of finding the electron in a certain position -- as time goes on.
If you're like most people, this is going to trouble you. It is so ingrained in us -- by our own experience -- that objects are real, particles are real, and that these real things have definitive properties, that we instinctively start asking questions like, "Okay, where is that particle, really, when we're not looking at it?"
And we assume that this question makes sense. We assume that there is a real position for this real particle at every moment in time, and a real momentum, and a real amount of energy assigned to it. We assume that it's our knowledge that's somehow limited, and so we struggle to fit this troubling observation in with our picture of what reality is.
It's no wonder that quantum mechanics has a number of different interpretations behind it: we're trying to understand reality, and yet the things that we're observing are completely unlike what we experience as reality! Some people, quite understandably, view this as a tremendous problem. After all, there's no consensus as to which interpretation is the "right" one, or even the best one!
There are some interpretations that are demonstrably wrong: the idea that physics is local (things can only affect things they interact with), real (as opposed to complex, or partially imaginary), and deterministic cannot all be simultaneously true. So you might ask which ones are true, and I wouldn't blame you for asking.
The problem is, not only are multiple interpretations equally valid, but none of them tell you anything more or less than any of the others! And there are plenty of valid ones; here's a brief summary.
Rather than go through what the different interpretations are, I prefer to look at it in these terms:
- We have a new set of physical laws that describe the Universe on the quantum level: how things exist, how they evolve in time, how they interact with one another.
- These laws allow us to predict the probability distribution of certain outcomes that we can measure, but not what the outcome of a given measurement is going to be.
- There is an intrinsic amount of uncertainty that is always preserved, and so it is impossible to know certain properties of a system -- in tandem -- to an arbitrary accuracy.
It is what it is, and the only way to develop any sort of intuition for what's going to happen in a given situation is... to figure out what's going to happen in a variety of situations, until you begin to develop an intuition for it! In other words, the most lampooned quote of all time (when it comes to quantum mechanics),
"Shut up and calculate!" -David Mermin,
is actually the one-and-only thing you can actually do for yourself in order to better understand reality.
In other words, it doesn't matter how you arrive at the results, and there are many path there that are equally good. What matters is that, irrespective of how you interpret it (or even whether you interpret it), what you call "reality" at the end of the day matches what your theory predicts.
If you can do that, then your physical theory -- or your favorite interpretation -- is just as valid as any other. And if it doesn't, you're compelled to discard it. However, and you should consider this a warning, this is not without danger.
This carries with it the danger that you can make something as philosophically complex as you want to satisfy as fully as nature will allow whatever preconceptions you have about how reality should behave. If you demand locality, you can force it. If you demand realism, you can force it. If you demand determinism, you can force that, too. If you demand wavefunction collapse, you can make that happen.
And if you demand non-locality, or non-realism, or non-determinism, or wavefunctions that never collapse, you can force those just as easily. Even if you want an interpretation where information travels faster than light, you can make one up, and it still works! But it's no more a mirror of "reality" than one where it doesn't.
In the end, all that matters is that your method of calculating predictions aligns with what you've observed. And if you can get it right, then you'll understand reality as well as anyone.
So let other people be "embarrassed" for quantum mechanics. If you can let go of your classical notions of what an interpretation ought to be, you'll have discovered something even better.
You'll understand the quantum reality of our Universe.
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Interpretation may not change reality, but it has a big effect on how it's described to an audience that doesn't have the chops to understand the equations. QM is somewhat counter-intuitive and if there were one preferred interpretation that most everyone shared, the language and ways of talking about it would be more-or-less unified and more laypeople would be able to understand the basic concepts rather than "quantum" being a catch-all term for anything and everything.
Quantum mechanics is confusing and I accept that. But I do have a question about the double-slit experience. Does the double-slit experiment work with protons or neutrons? The real question is at what point does the double-slit experiment break down? After all, it doesn't work with bowling balls or oranges.
As an undergraduate physics student, I've read a little about the different interpretations of QM. In these interpretations I have found that philosophical speculation is much easier to come by than is a testable scientific model. I think it's unfortunate that these interpretations are often presented as though they are scientific. Wikipedia's table comparing the different interpretations of QM deals with criterion that science does not directly address. In the interest of promoting a greater public understanding of science, I think it would be beneficial to make clear distinctions between a scientific interpretation and a metaphysical interpretation. The former being actually testable, and the latter merely debatable.
@Vern the double-slit experiment has shown a wave-like distribution for objects as large as bacteria. IIRC, the reason we don't see it for bowling balls or oranges is that either the wavefunction associated with objects that big is to small to have a noticeable effect or that in order to get a wave-like distribution, the experiment would have to run for trillions of years. I'm not a physicist, so I could very easily be wrong.
Aether has mass and physically occupies three dimensional space.
A moving particle has an associated aether displacement wave.
In a double slit experiment the particle travels through a single slit and the associated wave in the aether passes through both.
Ethan - if I were to write a text where my implied definition of "real" changes about five times between all kinds of folk-philosophically naive ones (without even scratching on counter factual definiteness), I would shut up and think, not come to the conclusion that "shut up and calculate" is the last answer (is that what you would have concluded about relativity at the very beginning, too?)! Sorry mate, not that you are not a nice guy or anything, but objectively speaking, your kind of scientism (and yes, it is a particular sort of naive scientism that I cannot share as a scientist), is getting worse instead of improving. Since you did not say anything of substance (how could you with five different "real"s all mixed up), there is no more constructive criticism that can be supplied, except the general about that you need to start thinking more seriously or leave the serious questions alone.
You are rude.
@Vern #7: The double-slit experiment works for everything, as near as we can tell, *including* oranges, bowling balls, and you. As laconicsax implied, for truly macroscopic objects, the isolation you need from the environment is too great for the experiment to show any decent results.
Our best understanding is that _everything_ is quantum (c.f. Schrodinger's cat), but as the size of the object increases, the time it can remain in a pure quantum state (unmixed with the environment) decreases, and the magnitude of quantum state differences also decreases.
There are lovely demonstrations of quantum interference with large molecules, for example C_60 (http://www.univie.ac.at/qfp/research/matterwave/c60/index.html and links there, published in Nature in 1999) and organic molecules with up to ~430 atoms (6900 dal) (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3104521/).
@mpc755 
Presenting personal opinions as fact, and especially personal opinions which have been ruled out by other facts (the actual pilot-wave model makes specific predictions which are not supported by experiment) is not a particularly good way to have your opinions accepted in a scientific discussion.
@Colin: Who is rude? You? Ethan? The guy you thought you were texting?
Thanks for another interesting post Ethan. I appreciate that you give up part of your week to educating others. Cheers!
I loved the post, thanks much, for me it was much pedagogic.
"Does the double-slit experiment work with protons or neutrons?"
"The real question is at what point does the double-slit experiment break down? After all, it doesn’t work with bowling balls or oranges."
They would if you had a slit around the same size as the De Broglie wavelength of a bowling ball or orange that the orange or bowling ball could get through. And that would mean either an impossibility (slit smaller than the item) or it going so slow that you'd need quadrillions of lifetimes of the universe to see one go through.
The De Broglie wavelength of an electron or proton or neutron at moderate energies are of a size we can create a diffraction grating for.
And as the energy of the particle (or photon: this is true for photons too!) increases the wavelength (and therefore the size of the slits needed to produce diffraction) decreases.
"Aether has mass and physically occupies three dimensional space."
It can't be seen.
Therefore it can't have any effects on things we CAN see. Such as:
"A moving particle has an associated aether displacement wave"
I enjoy reading your texts and want to thank you for writing them. Thanks for putting so much work into giving us something interesting to read.
Therefore, please allow me to also add a constructive
suggestion: You often add (really nice) images to your text. However, you tend to not really reference and describe them within the text. For instance, people who have already a little bit of knowledge about quantum mechanics, things such as the double slit are easy to recognize and they will know how to put it into the context. A reader not familiar with this will maybe not know how to interpret the image. Therefore, as a thankful reader of your blog, I would be even more thankful if you could couple the images closer to the text.
Again, many thanks.
'Interpretation of quantum mechanics by the double solution theory - Louis de BROGLIE'
“When in 1923-1924 I had my first ideas about Wave Mechanics I was looking for a truly concrete physical image, valid for all particles, of the wave and particle coexistence discovered by Albert Einstein in his "Theory of light quanta". I had no doubt whatsoever about the physical reality of waves and particles.”
“any particle, even isolated, has to be imagined as in continuous “energetic contact” with a hidden medium”
The hidden medium of de Broglie wave mechanics is the aether. The “energetic contact” is the state of displacement of the aether.
"For me, the particle, precisely located in space at every instant, forms on the v wave a small region of high energy concentration, which may be likened in a first approximation, to a moving singularity."
A particle may be likened in a first approximation to a moving singularity which has an associated aether displacement wave.
"the particle is defined as a very small region of the wave"
In a double slit experiment the particle travels a well defined path which takes it through one slit. The associated wave in the aether passes through both. As the aether wave exits the slits it creates wave interference. As the particle exits a single slit the direction it travels is altered by the wave interference. This is the wave piloting the particle of pilot-wave theory. Detecting the particle strongly exiting a single slit turns the associated aether wave into chop. The aether waves exiting the slits interact with the detectors and become many short waves with irregular motion. The waves are disorganized. There is no wave interference. The particle pitches and rolls through the chop. The particle gets knocked around by the chop and it no longer creates an interference pattern.
The Michelson-Morley experiment looked for an absolutely stationary space the Earth moved through. The Michelson-Morley experiment looked for the 'aether wind'. The aether is not an absolutely stationary space. There is no 'aether wind' to detect. Aether is displaced by matter.
'Ether and the Theory of Relativity by Albert Einstein'
"the state of the [ether] is at every place determined by connections with the matter and the state of the ether in neighbouring places, ... disregarding the causes which condition its state."
The state of the aether at every place determined by connections with the matter and the state of the aether in neighboring places is the state of displacement of the aether.
There is no such thing as non-baryonic dark matter. Particles of matter move through and displace the aether.
I'm not a phycisist, but as far as I underdtand, it does work with bowling balls and oranges. It's just that the wavelength of these objects are so massive that you wouldn't be able to see the inference pattern unless you have a detector the size of the universe (or was it larger?).
“any particle, even isolated, has to be imagined as in continuous “energetic contact” with a hidden medium”
No it doesn't.
The aether doesn't exist, chelle.
"The aether doesn’t exist, chelle."
Then explain to us what occurs physically in nature to cause gravity and the observed behaviors in a double slit experiment and while your at it explain to us why there is an offset between the light lensing through the space neighboring galaxy clusters and the galaxy clusters themselves and explain what is outside of the solar system pushing back and exerting inward pressure toward the solar system causing the magnetic field to pile up.
'NASA's Voyager Hits New Region at Solar System Edge'
"Voyager is showing that what is outside is pushing back. ... Like cars piling up at a clogged freeway off-ramp, the increased intensity of the magnetic field shows that inward pressure from interstellar space is compacting it."
It is not the particles of matter which exist in quantities less than in any vacuum artifically created on Earth which are pushing back and exerting inward pressure toward the solar system.
It is the aether, which the particles of matter exist in, which is the interstellar medium. It is the aether which is displaced by the matter the solar system consists of which is pushing back and exerting inward pressure toward the solar system.
'Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies'
"Our data strongly support the idea that the gravitational potential in clusters is mainly due to a non-baryonic fluid, and any exotic field in gravitational theory must resemble that of CDM fields very closely."
The offset is due to the galaxy clusters moving through the aether. The analogy is a submarine moving through the water. You are under water. Two miles away from you are many lights. Moving between you and the lights one mile away is a submarine. The submarine displaces the water. The state of displacement of the water causes the center of the lensing of the light propagating through the water to be offset from the center of the submarine itself. The offset between the center of the lensing of the light propagating through the water displaced by the submarine and the center of the submarine itself is going to remain the same as the submarine moves through the water. The submarine continually displaces different regions of the water. The state of the water connected to and neighboring the submarine remains the same as the submarine moves through the water even though it is not the same water the submarine continually displaces. This is what is occurring physically in nature as the galaxy clusters move through and displace the aether.
Displaced aether pushing back and exerting inward pressure toward matter is gravity.
A moving particle has an associated aether displacement wave. In a double slit experiment the particle travels through a single slit and the associated wave in the aether passes through both.
"Then explain to us what occurs physically in nature to cause gravity"
It isn't aether.
" and the observed behaviors in a double slit experiment "
It isn't the aether.
"offset between the light lensing through the space neighboring galaxy clusters"
It isn't the aether.
"and the galaxy clusters themselves"
It isn't the aether.
"and explain what is outside of the solar system pushing back and exerting inward pressure toward the solar system causing the magnetic field to pile up."
It isn't the aether.
Do you know why?
Because if the aether existed and gave those effects, the michelson-morely experiment would have found an anisotropy in their values.
The did not.
The aether doesn't exist.
If you're going to continue with the bollocks blather, chelle, pop back to the thread for this sort of anti-science shite:
"Because if the aether existed and gave those effects, the michelson-morely experiment would have found an anisotropy in their values."
The Michelson-Morley experiment looked for an absolutely stationary space the Earth moves through. The aether is not an absolutely stationary space. Aether is displaced by matter.
Watch the following video starting at 0:45 to see a visual representation of the state of the aether. What is referred to as a twist in spacetime is the state of displacement of the aether. What is referred to as frame-dragging is the state of displacement of the aether.
The analogy is putting a mesh bag full of marbles into a supersolid and spinning the bag of marbles. If you were unable to determine if the superfluid consists of particles you would still be able to detect the state of displacement of the supersolid.
The supersolid connected to and neighboring the mesh bag of marbles is in the same state throughout the rotation of the bag in the supersolid.
The aether connected to and neighboring the Earth is in the same state, or almost the same state, throughout the Earth's rotation about its axis and orbit of the Sun.
The state of which as determined by its connections with the Earth and the state of the aether in neighboring places is the state of displacement of the aether.
We have a comments policy on this blog, which you can check out here -- http://scienceblogs.com/startswithabang/2012/09/23/weekend-diversion-yo… -- as wow correctly referred you.
If you would like to promote your version of the aether on that thread, you may do so. However, I would appreciate it if you refrained from discussing it here, as it is completely off-topic and has no place in a discussion of the nature of quantum reality and various interpretations of QM.
If you continue to do so here, you will be banned from commenting on this blog.
First I have to point out that the poll that set this web spat of articles off is made at a religious meeting (Templeton founded; Zeilinger is a member of its science panel and a godbotherer on seminars - I have been on one) and purposely filled it with philosophers and other non-scientists.
Then I have to point out that nowhere else is there a science area where people are satisfied with shut-up- and calculate instead of putting "interpretations" as possible and testable theories. If decoherence exists, some of those would fall, for example.
But QM is considered "mysterious" and hands off. This is by the way the religious interest, since it usefully reminds them of their religious mysteries and shut-up closing down of questions by pointing to something and go "godsdiddit". They can implicate religion.
What is reality? To say that it is objects that have properties that are quantifiable is a testable definition, but it works for quantum systems too so is not a dividing line between classical and quantum systems.
I like Deutsch's testable definition of, roughly, "constrained reaction of constrained action" or in other words Samuel Johnson's "I'll refute it this! [kicks stone]". That means every mechanics tests for reality from the start, action-reaction classically and relativistically, observation-observable quantum mechanically.
So as it turns out I have to agree with Siegel on what reality "is" (comes out as). I just don't think “Shut up and calculate!” is the "one-and-only thing you can actually do for yourself in order to better understand reality." For now, perhaps. But not for long.
Italics fail, sorry. :-/
"However, I would appreciate it if you refrained from discussing it here, as it is completely off-topic and has no place in a discussion of the nature of quantum reality and various interpretations of QM."
Quantum reality is a moving particle has an associated aether displacement wave.
so rather than do what's asked by the owner, you prefer to be banned?
PS you're wrong.
I'm discussing the physical nature of quantum reality and that is aether has mass and is physically displaced by the particles of matter which exist in it and move through it and in a double slit experiment the particle travels through a single slit while the associated wave in the aether passes through both.
Why have a blog titled "Quantum Reality" and refuse to understand quantum reality?
No you're talking post-normal non-science.
Ethan, I'm happy with these responses to this idiot being deleted too.
The quantum reality is in a double slit experiment it is the aether which waves.
trolls gotta troll, I guess.
Ignorance has to permeate quantum mechanics, I guess.
All in order to not understand in a double slit experiment it is the aether which waves.
Aaaaaaand there's the ban.
Let's see if it holds. So far so good.
I fixed your italics tag. And yes, ideally some (more) interpretations could be falsified down the road; that would be nice.
Thanks also for the background about this paper; I didn't do enough homework to figure that out. I feel a little bit like a sucker for getting drawn in to a topic that -- if I had all of that information -- I might have stayed away from. I'll know better for next time. :-)
Ironic that they should talk about ignorance whilst espousing ignorance of the MM experiment.
A Brain-Exit failure.
An example of how you need to think things all the way through when it comes to non-classical physics:
"The quantum reality is in a double slit experiment it is the aether which waves."
I could've possibly sat back and watched the physics spanking if it wasn't for the bad grammar.
"Then explain to us what occurs physically in nature to cause gravity and the observed behaviors in a double slit experiment and while your at it explain to us...."
This is what really bothers me, your theory is not correct by default because there are things we can't explain yet, you bear the burden of proof. Gah.
Anyway, interesting post Ethan. Reminds me of when I was a teacher and I ask the class a question, and then I get to say, "well, in a way, you're all right..."
A photon carries energy. When it moves from A to B there has to be a *very very* small change in the curvature of space. So I want to know, (a) does one change start just when the photon leaves A and a second change start when it reaches B – or (b) is it continuous? If the photon goes thru two slits, its final position is not determined until it materializes at B (wherever that turns out to be). That would appear to be a problem if the curvature of space were adjusting continuously -- suggesting that postulate (a) is the correct one. If that logic is correct would that also apply to an electron or an atom of gold?
Ethan, I think your definition of "real" in QM is not right. If I recall correctly, it has nothing to do with complex or imaginary numbers. Rather, a "real" property is one that has a definite value even if the value is not observed. I think that is the definition of "real" needed in the most general form of the proof of Bell's inequality (an inequality which is violated by QM and by the "real" world).
Ethan you say:
"There are some interpretations that are demonstrably wrong: the idea that physics is local ... And there are plenty of valid ones; here’s a brief summary."
And then I assume that all of the interpretations below are valid. The problem is that in the column "Local"; some of those equally valid interpretation of QM have a "Yes" in the local column.
So please clarify. What am I misinterpreting?
Are interpretations with "Yes" in the "Local" column valid or not? Please clarify? Thanks.
I think you would have a better idea of what (I think) Ethan is talking about if you read about Evanescent Waves.
Cliff note version.
Instead of a sine wave for a photon, it can be mathematically described as an imaginary vector of constant length and the Electromagnetic field seen is the real part. This makes some maths easier.
PURELY mathematical trickery.
But plugging an imaginary number in to Maxwell's equations and you get a funny term left over in total internal reflection. The imaginary part of the photon doesn't reflect and continues in the same line, with an exponential decay term.
Purely mathematical trickery.
But put another refracting solid near enough, and the imaginary wave can be turned back into a real photon and this is *actually seen*.
A few other things like that seem to turn up occasionally.
Since we're on some of the difficulties in interpreting QM.
I would sort of like to understand the idea of Wheeler's which I'll call cosmic delayed choice.
In the wikipedia reference above there is a section titled "Wheeler's astronomical experiment" and in that section we see an image of "Einstein's cross" which is an astronomical observation.
But reading the section and doing various searches;I'm not sure if delayed choice experiments have been done at an astronomical scale or not.
I think I understand the basic delayed choice idea. But maybe not.
Any clarification, by someone that understands, would be appreciated.
We have timing well enough to test approximations of true/false to that experiment in the lab on earth, so no need to go astronomical on it. The errors in asserting the scale would likely introduce more error than the accuracy you'd get for the longer transit times.
The universe the wave-particle operates in is different if it's operating in a universe which has two slits looking for a particle or a universe which has two slits looking for a wave.
I don't find it particularly odd that these two different universes have a different result!
Explaining the causality is tricky, and we mostly have to post-hoc rationalise it because we don't have the right language yet to describe it beforehand.
Mind you, reading that it's sad to think I was jawing over with a fellow student in 1990, 10+ years after this was thought up, and wondering the same thing.
I thought I'd thought of something new at the time.
Great question. The problem is that the General Relativity view of the world (where things with mass curve spacetime) and the QR view of the world (where photons 'sniff out' alternative paths) aren't compatible. Both are terrific mathematical representations of certain phenomena and both appear to hint at a view of 'reality'...but they can't coexist the way they are formulated today and that's perhaps the biggest puzzle in physics for the last 90 years or so. Maybe something deeper is going on...extra dimensions, strings, quantum loops..no-one knows (except obviously mpc755 but he's been sniffing the aether).
My off topic opinion in response to Sascha Vongehr comment (above) can be found on Ethan's comment page.
You know Sascha, for a guy who regularly criticizes pretty much anyone who is more famous than yourself for being bad a writer, your own writing style is a big drain to read. You use double negatives, you twist a simple sentence into a complicated phrasal structure that is difficult to parse, you write preambles that seem to have nothing to do with the rest of your articles.
I would love to read criticism of blogs that I read, but they are useless if they are barely readable.
Thanks for the delayed choice explanation.
Wow, in the QM foundational literature, locality and realism (or lack thereof) play essential roles; see for example D'Espagnat's general versions of the proofs of Bell's inequality. This use of the term "real" has nothing to do with the mathematical concept of real (vs complex or imaginary) numbers; it isn't related to the things you mentioned. The definition of realism (as the term is used in foundational debates about QM) is the one I gave above.
Well, it read as you were talking about real in the complex number scheme, as you used "mathematical" there.
And "real" in maths means solely that: the real part of complex numbers.
It is also a very "real" part of what Ethan is talking about (though he'd have to confirm: I'm going by what I can read, and I can't read minds over t'internet).
Mathematical tricks like using complex numbers and proposing only the real part of the complex number is seen in this reality works very VERY often. And it has no reason why.
So to a very large extent, these things can be considered "really a complex number",
Wow, Ethan defined "real" as the opposite of complex, or partially imaginary. It seemed to me that he was making the mathematical distinction between a real variable and a complex number with an imaginary part. Of course I can't read his mind either, so maybe I am wrong about what he intended to mean, but the words he wrote suggest that he was making the mathematical distinction between real numbers and complex numbers (numbers that have an imaginary component, where "imaginary" means the square root of -1). I think you also read it this way, otherwise you wouldn't have brought up the examples you did. But that is NOT the definition that is relevant to QM debates. The three key words he defined in that paragraph, "local", "real", and "deterministic", have precise definitions in QM, since they are at the center of debates on the meaning of QM. Ethan's characterization of "local" and "deterministic" seem ok, but not his characterization of "real".
I call "citation needed" on that for 5 points, Bob.
Wow, it's right in Ethan's post above: "There are some interpretations that are demonstrably wrong: the idea that physics is local (things can only affect things they interact with), real (as opposed to complex, or partially imaginary), and deterministic cannot all be simultaneously true."
I hate to have you feel that I have given you incorrect information. When I wrote that sentence, I was referring to (unfortunately, not very clearly) whether the wavefunction itself was real or not. In some interpretations of quantum mechanics, the wavefunction is a physically real thing, while in others it isn't.
If you want to describe it mathematically, you need both real and imaginary parts, but if it's a physically real thing, it is unknown how one would reconcile that with a mathematically complex object.
But I agree that I should have chosen a better parenthetical synopsis than the one I did; my apologies for any confusion.
Thanks Ethan. Part of the confusion was the context. You were mentioning the three classic things that QM violates: locality, realism, and determinism. Those words each mean something very specific in this context. EPR and Bell's work were concerned with "local realism". "Real" in this context doesn't refer to the problem of getting a real number from a complex function, but rather to the idea that an observable has a definite value independent of our observing it.
Try rephrasing the statement to use "reality". It's not open to such confusion!
I agree that reality and real in QM is very tricky.
Reality is what experiments show us. i.e. electron emitting a photon of a certain value or not emitting (nothing in between), which very different from classical mechanics.
QM is mathematics (very abstract one) that tries to make sense of that reality. I know there proponents that the math is reality. I don't know if it is. But to stay true to Ethan's sentence: "you and I know reality when we see it."
Only experiments are reality. Unless one devises an experiment to test if Wave Function really exists, or if Modal Reality that i.e. Sacha so loves is Reality. No problem, just put forth a thought experiment that proves Many Worlds exist as actual worlds, and I will try to believe it. Untill then IMO it's not science.
My apologies if anyone else has already answered this; I haven't read through all the comments yet. In the historical development of QM, one of the results that came about was that particles and waves are not separate entities, but rather are two different ways of looking at things. That being the case, all particles have a wavelength. This wavelength is inversely proportional to the particle's momentum. (Planck's constant, h, being the constant of proportionality, ie wavelength = h/momentum).
With that in mind, recall that CLASSICAL physics states that a wave will undergo diffraction and interference if it encounters an aperature with a size that is comparable to its wavelength. Particles like apples and oranges have momenta that are many orders of magnitude greater than particles like electrons and protons. Therefore, the wavelength of an apple or orange is much smaller than the wavelength of an electron. In fact, it's so small that we cannot create an aperature small enough to cause oranges and apples to show an interference pattern. That's the reason that the double slit experiment doesn't work with apples and oranges.
Anyone else notice that the responses to the poll question that Ethan posted had a total of 129%? The poll asked what is your favorite interpretation, not what are your favorite interpretations, so this is certainly an inconsistent result. Ironic that the poll respondents were non-scientists. Apparently they aren't mathematicians, either. :)
@ Sean T
it's a quantum fluctuation ;D those 25% are uncertanties in voters count.. lolz
Here's a article that is readable and puts Many Worlds in perspective. It's a pretty balanced sensible explanation.
Are Many Worlds and the Multiverse the Same Idea?by Sean Carroll 2011, http://blogs.discovermagazine.com/cosmicvariance/2011/05/26/are-many-wo…
In the original paper it says, "To ensure representative sample sizes, we required a specic answer A to have been checked by at least 4 participants. Then, if a fraction f of members of this group had also checked a certain answer B, we registered a relationship between the two answers A and B if the following conditions were met..." http://arxiv.org/pdf/1301.1069v1.pdf
So multiple answers were allowed for each of the 16 questions asked.
It's an interesting and readable paper.
just skipped through it quickly now, but will read the papers in the evening. Am specially interested in Suskind's paper. It's something that i gravitate to. "On the one hand, complementarity says that we shouldn’t think about what’s outside our observable universe; every question that it is sensible to ask can be answered in terms of what’s happening inside a single horizon..."
but won't go into it more until I have read the papers. But the problem of interperting QM is still there. To quote mr. Carol: "Quantum mechanics describes reality in terms of wave functions...."
and "describes" is the key word. It's our description of reality. Description and reality aren't same things. To push it and say that our description IS the reality. IMO is too far.
i.e. just by looking at Shroedinger's cat.
"The cat is neither alive nor dead; it is in a superposition of alive + dead. At least, until we observe it. In the simplistic Copenhagen interpretation, at the moment of observation the wave function “collapses” onto one actual possibility."
But that's p.o.v. of observer. From p.o.v. of the cat it's rubbish. Because she's pretty certain of the moment when whatever was in the box killed her or didn't. You pondering about some abstract math outside the box, changes nothing to her. Nor to you for that matter. The math just ends up telling you.. well.. you know.. she's either dead or alive :D.. A bit ironic isn't it :)
Anyways, IMO, we shouldn't assume what reality is. We should go and test it. And I also agree that we should only concern us with our own "reality". If there is no causal link between pocket universes or actual many worlds. Then they are of no reality of ours. And as such don't exist.
I admit, I didn't read the full paper. It just seems that the poll question that they quote is inconsistent with the poll results. Just thought it was a bit ironic, but obviously the result is consistent considering the methodology used.
Yes and no.
Yes, to say it is REALLY real, absolute reality would be too far.
However, when talking to each other, we say things that can be extended to the absurd. And that isn't what;s meant by "real".
A solid isn't "really really" solid. It's mostly empty. But we can't move another solid through it (though hydrogen will diffuse through any solid we can muster up to contain it), so as far as saying what's going on, it really is solid.
We don't bother with the "mostly empty space".
And this idea of "reality" is embedded in science.
To Newton, gravitational attraction REALLY exists.
But when SR said it is REALLY a manipulation of the flat space, it was found not to be REALLY a plain old attractive force.
Science reality is not absolute. It's contingent.
And therefore using "real" like this in science is acceptable.
If someone seems to be getting the "really real" meaning, then correct them. But it's actually fine.
Not really a useful point to bring up. It was a deliberate argument ad absurdium brought up to show how the copenhagen interpretation didn't actually fit in the macro scale.
But it said nothing about the quantum scale. There we have experiments that show that the "cat" really IS alive and dead at the same time.
It just has to be a quantum scale analogue of a cat. Not a macro-scale one.
Agree with you. And that's the most sensible position we should be in. However, to my mind, there are physicists or mathematicians out there who are not of that view.
I agree 100% with your sentence: "Science reality is not absolute. It’s contingent."
but proponents of Modal realism i.e. believe that many worlds are actual REALITIES. This is taking math and QM way beyond it's intended purpose IMO. This is saying that vector spaces of complex numbers in QM are real physical entities. Or whichever interpretation you choose. One shouldn't hold it as faith or whatever. But in debates it almost looks that way. Like it's a religion.
That, again, isn't the problem of the science.
It's the problem of the few extrememly noisy kooks who don't brook kany contention that this reality is contingent.
However, in this case, much like the case in rigid mechanics, where if there's no way of determining the difference, it doesn't exist (so a diatom has no rotational momentum around the longitudinal axis), it doesn't actually make any difference if these parallel universes actually exist or not.
Only if they produce an effect by which their existence can be inferred can they be called "real".
TBH, I feel much the same way about Dark Matter as some use it: "It really exists as real matter!", no, it is contingently proposed. It is currently the simplest most complete explanation, but it's not known what form it takes. Until then, we have a good placeholder for the effect.
Much like Newton's God who causes the planets to be attracted.
Turned out not to be god, but it WAS a scientific force: gravity.
And then once we had an idea precisely what that meant, we progressed to gravitons, Special Relativity, Quantum Gravity, Higgs and so on.
Ethan, I normally enjoy your posts, but this is the first time I've posted a comment. Because in this case, I think you're dead wrong.
I'll start my argument with your conclusion. The idea that there is nothing to choose between the various interpretations of quantum mechanics save taste is equivalent to throwing up your hands and saying "I give up! The universe is incomprehensible!" It's possible that that is the case, though I doubt it. However, that doubt is not sufficient argument that the universe is comprehensible.
That said, regardless of whether or not we can ultimately understand and explain the universe, as scientists, we have a responsibility to assume we can. Why? Because we can only improve our understanding of the nature of the universe if we believe we can.
Since I reject your conclusion, I suppose I have a responsibility to show where I believe you went wrong. I'll start with the wavefunction. Is it real? The equations of quantum mechanics describe it. Using it, we can predict the behavior of physical systems. As with Newton's force of gravity, we must assume it exists unless and until some better theory, a la General Relativity, shows it to be an illusion. It's only rational to assume that things we observe exist.
Next, wavefunction collapse. There is no mechanism in the math of Quantum Mechanics for such a process. Tacking it onto a theory is an error equivalent to Einstein's cosmological constant. (Yes, I know, dark energy exists. However, nothing Einstein knew indicated that it was so. An error is an error, coincidentally proven correct by later discoveries or not.) The equations tell us that the wave describing a particle continues beyond an observed interaction of that particle, so we must assume it does.
Hidden variables are an error of the same category, tacked onto a theory to try to make it behave the way we think it should.
Now, on to the role of the observer. The mind - the observer - is a psychological phenomenon. The laws of psychology emerge from the laws of biology, which in turn emerge from the laws of chemistry, which themselves emerge from the laws of Quantum Mechanics. With so many layers of reality isolating quantum phenomena from psychological ones, we must be leery of any theory that posits a direct causal connection between the two. Not to put too fine a point on it, but if there is ANY rational alternative, we should use it, and if there isn't, we should try harder to think of one.
So, the faculty of reason, which we as scientists must apply if we are to attempt to understand reality, tells us that the wavefunction exists, it does not collapse, there are no hidden variables, and the observer does not directly interact with observed quantum phenomena. If you look at your Wikipedia chart of the interpretations of Quantum Mechanics, you will see that this leaves the Many Worlds interpretation as the most viable. In other words, our knowledge of quantum mechanics tells us that we live in a multiverse, wherein all possible histories of every particle objectively happen. As I have already stressed, future, improved knowledge may modify this understanding in some manner, but that is no excuse for failing to properly apply our best theory of reality, Quantum Mechanics.
I can respect that argument and that point of view. Even if we disagree about our conclusions, I can never say anything bad about taking the approach that says, "I think there's enough information in the Universe to solve this problem."
In this case, the problem that you're talking about is choosing between quantum interpretations. There's the possibility that you're right: it's the approach that people who work on this problem for a living count on! As you can tell from what I've written here, I think that another possibility -- the one that many interpretations are physically and mathematically indistinguishable given the information in our Universe -- is more likely.
MWI is one of my least favorite interpretations, as I think it's very unnecessarily fantastic. There are far "simpler" ensemble interpretations of the vector space of possible outcomes than MWI, and it does not require the assumption of an exponentially increasing number of possible universes to hold the space of outcomes.
But it could be. I just don't think it's necessary, or even educational, to claim it as the interpretation of quantum reality.
In a way, am glad that you believe in MW interpretation and you believe the wave function is real. I don't. And that is fine. But, if you have some time, I would like if you could give some explanation about certain things. Mainly, I would like to know why you interpret certain things the way you do.
You say: " I’ll start with the wavefunction. Is it real? The equations of quantum mechanics describe it."
- I don't understand how you reason this? Equations don't describe it. The results of calculations is a wave function. You don't start with it, you arrive at it. And it is nothing more than probability of certain experimental results. Seems to me you are switching positions of terms. It would like saying that pythagoras' theory describes real numbers. That doesn't mean anything. A real number is the result of the theorem. Nothing more.
then you say: "As with Newton’s force of gravity, we must assume it exists unless and until some better theory,"
- again, I don't understand your view on this. Probability function isn't a force! Quantum Mechanics is a calculus! It's not a force of Nature. It's like alegebra or whatever else. The state space in QM is not real! Why makes to "make it" real? This I don't understand. You are not using real vectors. In fact, I'm pretty sure you wouldn't get valid results if you used real vectors. You need complex numbers, imaginary numbers, in order for QM to calculate. It's not real vector space! And all of it is rooted in experiment. I mean, the matrix is nothing more then mathematical representation of an experimental measurement. It doesn't exist on it's own.
You say "we MUST assume it's real" WHY?? Why in the world do you have to assume that? It's not needed for calculating anything. In fact the math plainly calls it "imaginary".... so why? If you have some personal need, to "believe" in it.. ok, that's fine. But then say.. I MUST believe it's real.. don't say we.
"The equations tell us that the wave describing a particle continues beyond an observed interaction of that particle"
- well, first of all, you are describing only a certain measurement outcome of a certain property of the particle or whichever quantum system, but let's keep it simple. You are not describing the existance of a particle nor what it does in the world. Measuring i.e. the spin of electron is a far cry from saying anything about it's future existance in the real world.
"Now, on to the role of the observer. The mind – the observer – is a psychological phenomenon."
- what are you talking about? The oberver/observable, is just a measurement of an experiment. There is nothing psychological, philosophical or whatever about the observable. And as far as QM it's just a number. A real number. I do an experiment, I get a result. And all the rest of QM is just predicting what results I'll get. Will the light blink or won't it. Or how many times ON AVERAGE will I get tails or heads. There isn't anything mystical about this. Just as there is nothing mystical in measuring a rotational speed of some planet.
The rest of your post is not much about science. But the above interest me very much.
I hadn't spotted this:
“As with Newton’s force of gravity, we must assume it exists unless and until some better theory,”
Newton's laws required some attractive force.
Newtonian gravity was the result of looking at the observations and needing this in there.
(much like DM/DE is there because the observations are inconsistent without them [well, even more inconsistent])
But the many-worlds is an attempt to answer "Why do probabilities work?".
We don't observe probabilities.
And the many-worlds (and string, and brane and ...) don't give any reason why they are right or even definition of why they exist.
Newtonian gravity gave a reason why it exists AND a definition.
So Newton ascribed it to the influence of God. Wrong, but the force is there whether it was God or Gravitons doing the work.
Not the same for Many-Worlds.
"that is no excuse for failing to properly apply our best theory of reality, Quantum Mechanics."
But that best theory doesn't actually include the answers to these questions. That's why these are all called "interpretations" and choosing between them is a matter of preference because they have no additional predictive power (that we can tell, yet). You deride other interpretations for adding things not included in the theory, but QM also has no mechanism for replicating the entire universe on every measurement.
This is not like the Cosmological Constant, which was part of GR from the beginning, and made different predictions for different values. Einstein's error was simply assuming a value that produced the universe he wanted without waiting for the necessary measurements.
At this time, there are no known measurements that could support your favorite interpretation over others, and nothing in the well-verified parts of the theory to suggest that the universe forks. There's no "universe multiplication" factor that you could presume was non-unity.
So we're left with just the philosophical argument for why one is better than the other. One of the oldest tools in such arguments is Occam's Razor. Are you really sure you want to apply it in this case?
Oh and by the way, Ethan was not saying that we should just throw up our hands because we can never figure it out (although, bear in mind, it's possible we live in a universe where we can't).
He's saying that it's not useful for understanding QM today to presume a certain interpretation.
Obviously theorists should continue trying to find out if we could learn more, and if they do find a meaningful, measurable implication of some interpretation then the experimentalists should jump in and do it.
But if you aren't doing that, then just shut up and calculate, because that's how you will figure out what the theory actually implies.
"but QM also has no mechanism for replicating the entire universe on every measurement"
not only that but you can't even measure two things at the same time. Not unless they have totally same eigen values, which is in fact a very specific circumstance.
This is the pitfal. Calling QM a theory of reality. It's not that. Not by a long shot. In order to get expectation values, you need physical experiments. You can't get them just from theory. QM will tell you what a probability of a certain observable will be given some initial parameters, and that's it. It won't tell you what will happen to something 10 minutes from now. It was never meant to do something like that. Maybe to someone a probability of measured value is everything there is in the Universe... but that's their loss. To call it theory of reality is just so wrong.
“Now, on to the role of the observer. The mind – the observer – is a psychological phenomenon.
- what are you talking about? "
He's talking about the pun-based reasoning that New Age woo-shiters use to argue that QM supports the idea of ESP and other psychic nonsense. "Measurement implies observation implies observer implies sentient human brain causing quantum events to occur"
Which, yes, is nonsense, but isn't really relevant to the scientific discussion.
Thanks for finally commenting.
You bring a reasoned and interesting perspective to the table. Please comment more. Look at the interesting discussion you've started.
Good questions and discussion. Well reasoned.
But let me add my point of view
Personally, I like the multiple interpretations of quantum mechanics. Such multiplicity shows that QM is a living active dynamic theory that has much room to grow and which has many more surprises to be discovered.
The other theory, general relativity, that has been as thoroughly tested and confirmed as QM, does not have 10 interpretations. GR is great; it is the best. But like Newtonian Mechanics, it is a dead end. It has 1 interpretation.
QM has been enriched considerably since its founding (in a way that GR has not). Think entanglement, superconductivity, Bose-einstein condensates, quantum computing and quantum cryptology. And I expect many more quantum surprises.
GR is quite static by comparison. And I love GR; but I can't see more than maybe 1 interpretations. (not counting MOND and without adding extra dimensions of space and time).
But then I need string theory is maybe. Or maybe just more QM. I don't know. But they'll tell when they do.
So why would I want to limit myself just to 1 interpretation of QM. No I prefer a dozen interpretations. I want that new insights that explodes into our consciousness from a dozen interpretations of QM. Andthen all of the other interpretations wiggle and transpose and try to accommodate.
In my mind quantum mechanics is a theory of reality; because:
- I need it to try understand the smallest bits of matter
- I need it to try to understand very strange phenomenon
- I need it to understand why a solid is a solid
- I need it to understand how stars work
- I need it to understand the energy levels of atoms
- I need it to understand the energy level states of positronium
What part of Classical reality that has not been re-understood in terms of some quantum interpretation.
-- physical chemistry
-- magnetic resonance imaging of the brain
I dare you to explain virus interactions in the detail without mention of quantum mechanics. Pick a topic.
I just did virus's and quantum mechanics.
Can We Detect Quantum Behavior in Viruses?http://www.sciencedaily.com/releases/2010/03/100311092429.htm
So what part of reality has not been effected and clarified by quantum mechanics? Who ever thought that physicist would be writing papers clarifying what an observer is or is not.
Can we talk about the self without talking about the observer?
Have quantum theorist reached consensus yet on the meaning of observer. Is it only or more than a measurement?
Do you think that quantum weirdness disappears when we aren't measuring?
or do you think that quantum weirdness is there even if we aren't measuring?
Quantum mechanics is our best working theory of reality whether you want to try to understand some tiny little aspect of reality like qluon walls or some giant aspect of reality like the quantum mechanics of cosmic inflation.
There is no theory more fruitful to wrap around the detail of a strange observation than quantum mechanics.That kind of makes it a theory of reality.
I mean Google:
QM and any physical detailed thing and see if interesting research is being done.
GR, or string theory or thermodynamics or .... and any physical detailed thing and see if interesting research is being done.
I think we are going to be struggling with new insights and revolutions in quantum mechanics for another 100 years.
Yep. And macro reality is much the same. I have done and witnessed enough 'impossible' things to know. When people see physical or political laws, I see probabilities. I'm used to being right when everyone else is not. The other way around too. All one can get out of any model of 'reality' is 'how to bet'. It's ALL quantum.
So I place my bets on the horses I WANT to win. Sometimes (entanglement anyone) that seems to make the outrageously implausible merely unusual, especially after it has actually occurred.
" All one can get out of any model of ‘reality’ is ‘how to bet’."
"So I place my bets on the horses I WANT to win. Sometimes (entanglement anyone)"
" that seems to make the outrageously implausible merely unusual, especially after it has actually occurred."
Indeed. It's called Selection Bias.
I'm not sure that you understood my point of view. At least not from reading your post. I will try to explain my position, as well as make some observations of your last post.
First and foremost is I have nothing against QM. It's a brilliant tool and it works extremely well. So not really sure to whom you are addressing: "I dare you to explain virus interactions in the detail without mention of quantum mechanics.". Where did I ever say we don't need QM?
What I do object to is some of the interpretations. Mainly Many Worlds view and mostly Modal Realism. Again, notice I didn't say "I disregard them", I said "object". Meaning I have objections to their logic. And I am asking proponents of that view to describe why they believe that. Because the reasons they give, as you can see, aren't really that solid.
What I object to is calling mathematical constructs physically real. Because that's what they are doing. Not the space in which experiment is happening, but abstract space used to calculate it.
Concerning your comparisons between GR and QM. I don't understand why would you make such a comparison? They are not opposing theories, they have nothing in common. If you want to compare things, then compare QM with classical EM or atomic theory of Bohr.
GR and SR have nothing to do with all this.
then you say: "So why would I want to limit myself just to 1 interpretation of QM?"
- who says you should? I'm having issues with one particular interpretation not all of them. And I don't have an issue with math, only interpretation. Interpretation doesn't mean calculating it differently. There aren't 10-15 different calculus for different interpretations. It's not about that.
As for if it's a theory of reality.. Ok, this really needs it's terms defined in order to not talk pass each other. With the criterium you list, every working theory in physics, be it classical or probabilistic, is theory of reality. Cause it helps us deal more efficiently with nature around us.
What I object to is putting QM on the pedestal as THE THEORY of Reality. It ONLY deals with one part of our experience of reality. Try using QM to calculate how much concrete you need to build a damn, or what's the total resistance of a given macroscopic circuit. It can't. It's wasn't meant to do that. And that is fine by me. Just like we don't call GR theory of reality, or any other theory about anything, likewise we shouldn't call QM that. It's a theory of one small part of reality. But that is, in truth misleading also. Because if you want to stay true to QM, then it's a theory of what happens when you make an experimental observation of the QUANTUM system, because by doing it, you will change what the system was before you made it. And I understand that physicist of that time, and even some of today, find this disturbing. Because looking at something doesn't disturb it in macro world, and want to find a way to interpret it for themselves. Maybe I'm just not that bothered by it. So an electron can be either up or down. But that means we need to change all of our atomic physics... well.. tough luck. The thing is... reality didn't change. We did. Or our understanding did. Electrons always did what they do know. The fact we couldn't understand it 100 years ago is not a question of reality, but our limited knowledge. And I don't mean this in a sense of Hidden Variable Theory, just as a simple statement about our science. In 200 years from now, who knows what theories we'll use.
"Do you think that quantum weirdness disappears when we aren’t measuring?
or do you think that quantum weirdness is there even if we aren’t measuring?"
Come on dude... do you honestly believe that the Sun disappears when it goes below the horizon? Like.. ceases to exist? Of course you don't. So don't make a mistake and go in those waters of QM interpretations.
Because here's a simple concept. Everything existed just fine before we ever began making QM experiments and observations. And will continue to exist long way after we're gone. To be so bold or stupid (sorry, not you.. but I just find that view stupid) and say that nothing really exist until we measure it, is just retarded in my book.
further confusion is introduced because we use the same words (QM) for two things...
We use Quantum Mechanics to imply that atomic and subatomic systems are doing something. And we use the same word/s Quantum Mechanics for the calculus to find probabilities for experimental outcomes. And I think this is the only area of physics with such a problem in terminology.
We don't say that relativity of earth couples to relativity of the Sun. We don't talk about relativity of the Universe... And as such you can clearly distinguish to what you are refering to when talking about calculating something, and what it actually is. In QM, if you just say QM, that distinction is broken. Because you no longer know if one is talking about the actual subatomic world, or of a certain probability calculation. And IMO that's not good.
"Because if you want to stay true to QM, then it’s a theory of what happens when you make an experimental observation of the QUANTUM system"
Though you're mostly correct, this bit needs work.
You can derive F=ma by using Schroedinger's Equation and assuming the values in the macro scale are averages.
The quantum interactions are the basis for the reality that is, but our QM model isn't the quantum interactions. They're our model of them.
Just like Bohr's model of the atom wasn't the atom.
This is a very interesting discussion, but I wonder if all the discussion about interpretation of quantum mechanics isn't just totally fruitless. What I mean by this is that right now we cannot experimentally distinguish the different interpretations. So long as that's the case, there's no scientific basis for favoring one interpretation over any other.
However, assume that at some point in the future someone does devise an experimental way to determine which interpretation is best. It seems to me that the history of QM points to the idea that instead of distinguishing one interpretation from the others, that all of them will gain support, with the experimental design determining which of the interpretations appears to be correct.
That's the case with the debate about whether light is a wave or a particle phenomenon. Phyiscists such as Young and Fresnel seemed to prove that it's a wave, but then Einstein's photoelectric effect explanation came along and treated light as a particle. The problem was that our notions of "wave" and "particle" simply were not representative of reality. Reality just could not be categorized into simple bins like "wave" and "particle".
In a similar vein, isn't it at least possible, if not likely, that reality just can't be categorized into our neat notions of "quantum reality"?
"In a similar vein, isn’t it at least possible, if not likely, that reality just can’t be categorized into our neat notions of “quantum reality”?"
That is as good of a guess as any. It might be.
I did read somewhere about an idea that the observable in QM needn't be fixed. Meaning it might be the case where two observers see different outcomes of same process. Very similar to relativity. I don't know the details, but it's an interesting concept.
I'm looking forward to seeing experiments in the future, at least thought experiments, that could eliminate some possibilities.
"We use Quantum Mechanics to imply that atomic and subatomic systems are doing something. And we use the same word/s Quantum Mechanics for the calculus to find probabilities for experimental outcomes. And I think this is the only area of physics with such a problem in terminology."
Those aren't actually different, as long as you understand as Wow says that it's just a model. A provisional description of reality. QM implies that particles are doing things. Based on that QM gives us math to predict the outcome of experiments. Because it does so correctly to very high precision, we take QM as a provisional model of reality and say that particles are really doing things that QM says they are.
Of course while the model is indeed provisional, we have progressed to the point where we can say with certainty that any model that replaces it cannot get rid of all of the 'quantum weirdness' and instead look like a classical theory.
"We don’t say that relativity of earth couples to relativity of the Sun."
That's because the specific terminology of GR is different, but the actual usage is exactly the same. GR implies that the geometry of space-time curves. It also gives us equations to predict the outcome of experiments with great precision. We therefore take it as a provisional model of reality and say that space-time actually curves.
"Try using QM to calculate how much concrete you need to build a damn, or what’s the total resistance of a given macroscopic circuit."
The reason you can't use QM to calculate the concrete needed to build a damn is the same reason you can't use a non-quantum but nevertheless detailed molecular chemical interaction model to do the same: The math is too hard.
You absolutely can use QM to determine the resistance and other properties of circuits on the scale of nano- and micro- meters, indeed it's absolutely essential for determining the behavior of semiconductor devices. Which we then model using simpler math derived from the QM prediction to determine the behavior of larger circuits, but again that's just because it would take too long otherwise. There are deadlines to meet.
The reason QM seems different than GR or any other physical theory is that it's SO WEIRD that we have a hard time believing it, or even understanding what the theory is actually implying that the particles are doing, or if we can even ever know that because the vexing part is the part that happens *before* the particles interact with anything and that's kind of a problem when it comes to measuring.
But on the other hand, what is actually inside a black hole where the theory of general relativity says there's a singularity, a geometrical discontinuity? What does that actually mean? Is it real? It's beyond the event horizon, so we probably can't ever answer this question.
But that's out of sight, out of mind. QM slaps you in the face with the problem of our intuition versus what our model of reality says. That's the real difference.
First the only thing I said in response to you was, "Good questions and discussion. Well reasoned."
Everything after that was my thoughts, not a response to anything in particular that you said.
Second, we aren't in disagreement. I mostly agree with what you say and your way of thinking, give or take a nit pick here or there. And I am certainly an amateur not an authority.
HERE'S A NIT, an example of my nit picking, which normally I wouldn't even mention.
You say, "So an electron can be either up or down."
And my immediate reaction is No!
Electron spin is an intrinsic property with magnitude of s = 1/2; but it can be in any direction and is constantly changing direction. When we put the experimental apparatus in place; then we force the electron to be in one of two directions which we call up and down. But your statement already assumed the experimental apparatus, situation and such. OK that's a nit.
HERE'S A DISAGREEMENT (i.e. not a nit.)
You say, "Try using QM to calculate how much concrete you need to build a damn."
But how much concrete you use depends upon the strength of the concrete for a specific application. But maybe you assume that nobody is thinking about the strength of concrete in terms of quantum mechanics or the theory of relativity.
So here's a quote:
"Although important advances have been made in understanding the behavior of reinforced concrete columns... the size effect in columns has escape the attention so far. but no phenomenon in physics is understood until the scaling law is understood. This also applies to concrete structures. Discrepancies in the scaling laws at very large and very small distances were the primary impulse for the development of the theories of relativity and quantum mechanics."
Failure of slender and stocky reinforced concrete columns by ZB Bazant 1994
So someone is at least metaphorically (probably not mathematically) considering quantum mechanics when experimentally testing concrete and other materials.
But suppose that I am the engineer in charge of building the biggest dam in the world. A dam so big that it boggles the imagination of engineers. In other words, everybody says that it is impossible, that it will surely fail. But I am going to build it with concrete. But what kind of concrete and how much. Well I better get the experts who understand, in the detail, the strength of concrete.
So I'd start with the authors of this book.
Electronic Basis of the Strength of Materials
John J. Gilman, University of California, Los Angeles, 2003
"This 2003 book relates the complete set of strength characteristics of constituent atoms to their electronic structures. These relationships require knowledge of both the chemistry and physics of materials. The book uses both classical and quantum mechanics, since both are needed to describe these properties, and begins with short reviews of each. Following these reviews, the three major branches of the strength of materials are given their own sections. They are: the elastic stiffnesses; the plastic responses; and the nature of fracture. This work will be of great value to academic and industrial research workers in the sciences of metallurgy, ceramics, microelectronics and polymers. It will also serve well as a supplementary text for the teaching of solid mechanics."
So yes, I think that if you plan to build the biggest dam in the world successfully; then someone applied the knowledge of quantum mechanics to the building materials (e.g. particular steels and concretes).
"What I mean by this is that right now we cannot experimentally distinguish the different interpretations. So long as that’s the case, there’s no scientific basis for favoring one interpretation over any other."
Moreover, there's no point to proposing any of those interpretations.
"What's the sound of one hand clapping?"
Really it's the same thing here. If the interpretations come up with interesting science that differentiates it from the others, then that becomes a discussion.
But if you can't, it's not really worth talking about.
Just do the maths and while they work, use them.
"Electron spin is an intrinsic property with magnitude of s = 1/2; but it can be in any direction and is constantly changing direction. When we put the experimental apparatus in place; then we force the electron to be in one of two directions which we call up and down."
By, for example, putting it next to another electron...
But if there's nothing else there, then we have no preferred direction for up (or down), therefore we say that, by fiat, is pointing up.
Bring another electron along and it won't want to be near the first electron unless it is going the opposite direction, which (by the fiat declaration of up before) must be down. It won't point "a bit down" or "sideways", it'll point down.
@ Michael Kelsey
Has the pilot wave been dis proven? I don't like the term pilot wave but if you mean hidden variables then most people take Bells inequality to disprove hidden variables when in fact it just shows that any hidden variables formulation of quantum mechanics must be non local in fact any single world account of quantum mechanics must be non local.. see http://plato.stanford.edu/entries/qm-bohm/#hv
I avoided clarification on spin of an electron because I was confusing myself and unsure of a concise explanation.
Well done, as concise as can be.
Thanks for that clarification on spin of an electron.
Right, only local hidden variables are out. This doesn't mean there are no hidden variables.
It does mean no classical formulation of hidden variables can work. Even a version of QM with hidden variables is still going to be full of quantum weirdness.
Which is why (this is addressing Sinisa's point, btw) even if you imagine that the QM model is wrong, at some level it really is describing reality. A reality that won't go away even if we replace QM with some other model.
If this is correct: http://arxiv.org/abs/1005.5173
there might not be anything more.. ever :)
That link report considers the possibility of improvement of measurements precision (vis a vis the uncertainty principle) and thus getting more information about a system than current quantum theory allows. And concludes that no improvement is possible, i.e. we are stuck with the uncertainty princip[le.
However, new insights are allowed.
That's why without any improvement in quantum measurement; experiment and new insight led to such as phenomenon as entanglement or superconductivity, etc. And without any improvement in quantum measurement; we may get further insight and predicted and observed and understood phenomenon from a quantum gravity or a string theory or some other theory.
There is a lot more; because we understand so little.
This blog though not nearly as popular as Ethan's
is worth a bookmark. It writes up current exciting experiments about things we don't understand, e.g. gluon walls, high temperature superconductivity. It is experiments like these that inform theorists' next theories.
There is so much more.
My modest prediction is 1,000 years of science discovery at least as rapid as the scientific advances of the last 100 years.
Now back to the link referenced in #92. Is it correct? Probably not. Probably yes. Don't know. Why does it matter?
Yes that's the question, why does it matter?
Well the paper's implied answers is "quantum cryptography."
OK so no one will be able to break a quantum cryptography code. Fine. But I'm not holding my breath waiting for a secure internet in the near future (i.e. next 100 years).
I will not lie and say that I understood completely the math behind the proof, but it's not only about the measurments, that was the point.
It's a proof of general notion of expanding QM, with any kind of additional information, regardless of what it is. It's in a way like bell's inequality proof.
This again has no reference to quantum gravity or strings or etc. This is purely as far as QM results go. Who ever said that means physics wont progress???
or in other words, regardless of new information about the system, the predictive power won't go up. Or in other words, the predictive power of the system is already at maximum. For quantum systems, of course.
At least that's how I understood the paper.
even if we discover new properties of nature, new particles, etc... the probability for spin up or down will still be +-1/2.
OKThen: Neither quantum entanglement nor superconductivity are new discoveries. Superconductivity pre-dated quantum mechanics, in fact. Entanglement was an understood implication of QM theory from the beginning (though it didn't have that name) and was used as part of the EPR parodox to suggest QM was incomplete. But then Bell's Theorem came along and we experimentally verified that nope, it really does behave how the existing QM theory said and EPR isn't a paradox.
So while I too am sure we'll make many more discoveries, the history of QM doesn't really suggest that they will be in the field of QM itself.
That doesn't mean I was expecting a result like that in the paper Sinisa linked. Once again: O_o
"Before the realization of the importance of Bell's theorem, which happened only in the 1970's, the conventional wisdom among physicists was that the "founding fathers" of quantum mechanics had settled all the conceptual questions... I think it is not an exaggeration to say that the realization of the importance of entanglement and the clarification of the quantum description of single objects have been at the root of a second quantum revolution, and that John Bell was its prophet." Alain Aspect, 2004, Introduction to
Speakable and Unspeakable in Quantum Mechanics 2nd edition, by J.S. Bell
Yes, it's Bell's Theorem, introduced in the 60s and tested in the 70s that gave quantum entanglement a newly understood importance. And that importance was in demonstrating -- via experimental violation of Bell's Inequalities -- that quantum entanglement worked just like the Quantum Mechanical theory developed in the 1920s said it did.
Before that, many were convinced that our theory of quantum mechanics had to be incomplete because the implications of quantum entanglement contradicted local realism. Then Bell came along with a way to test this, and then the experiments came back and they said: "Nope! Local realism is out. Entanglement really works the way our theory says it does!"
Quantum entanglement was not a new phenomenon.
What changed is realizing that the phenomenon really did work how QM said it did. That there WASN'T some new aspect to the theory that we just hadn't figured out yet which would get rid of the "spooky action at a distance" and preserve local realism.
That's the opposite of "we discovered new phenomenon which demonstrate that QM was incomplete and that this will happen again in the future."
It's still possible QM is not complete, but the history of QM is actually the opposite: Coming to grips with the uncomfortable truth that it IS.
Well yes, but quantum mechanics said nothing about entanglement in the 1920s.
"Research into quantum entanglement was initiated by a 1935 paper by Albert Einstein, Boris Podolsky, and Nathan Rosen describing the EPR paradox[ and several papers by Erwin Schrödinger shortly thereafter." wikipedia
"So, despite the interest, the flaw in EPR's argument was not discovered until 1964, when John Stewart Bell demonstrated precisely how one of their key assumptions, the principle of locality, conflicted with quantum theory. " wikipedia
So saying "that quantum entanglement worked just like the Quantum Mechanical theory developed in the 1920s said it did" is really beside the point; because obviously nobody clearly understood quantum mechanical theory until Bell's 1964 paper exposed "the flaw in EPR's argument".
"It took him (John Bell) a decade to have his questions taken seriously... With his questions about entanglement, John Bell was able to clarify the Einstein-Bohr debate in an unanticipated manner, offering the opportunity to settle the question experimentally. His work, without a doubt, triggered the second quantum revolution, primarily based on the recognition of the extraordinary features of entanglement, and pursued with efforts to use entanglement for quantum information... Many of the fundamental questions about the measurement problem, including the role of decoherence, are not yet settled, and reading these papers (Bell's) is a source of stimulation and inspiration for contemporary research." Alain Aspect, 2004, Introduction to
Speakable and Unspeakable in Quantum Mechanics 2nd edition, by J.S. Bell
"Quantum entanglement was not a new phenomenon."
But as Wheeler says, "no elementary phenomenon is a phenomenon until it is an observed phenomenon."
And until Bell's 1964 paper there was no "opportunity to settle the entanglement question experimentally." i.e. no one could figure out how to do an entanglement experiment. i.e. entanglement was not a phenomenon because it was not an observed phenomenon, just an conundrum (maybe possible, maybe impossible).
It's worth reading the 2nd edition of Bell's book just to read Alain Aspect's 22 page introduction. And most of Bell's papers are highly readable in large part even for an amateur like me. I don't claim to understand it all.
But when someone finally understands and explains " the fundamental questions about the measurement problem, including the role of decoherence" in quantum mechanics; well then maybe there will be a third quantum revolution.
Of course someone might just say, "quantum decoherence worked just like the Quantum Mechanical theory developed in the 1920s said it did."
Superconductivity is a quantum phenomenon that was not understood until the 1950's.
"Superconductivity... was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911... Since the discovery of superconductivity, great efforts have been devoted to finding out how and why it works. During the 1950s, theoretical condensed matter physicists arrived at a solid understanding of "conventional" superconductivity, through a pair of remarkable and important theories: the phenomenological Ginzburg-Landau theory (1950) and the microscopic BCS theory (1957)... Superfluidity of helium and superconductivity both are macroscopic quantum phenomena." wikipedia
"Well yes, but quantum mechanics said nothing about entanglement in the 1920s."
Of course it did. The potential for correlated systems was right there. It was the possibility of having such a correlated system separated by a space-like distance that provoked the EPR paper with its argument that Quantum Mechanics must be incomplete.
It was the final resolution of the problem that in fact it isn't. The formalism established in the 1920s was (as far as we know even today) complete.
And that's not beside the point. It is rather the point entirely. It's why the "interpretations" of QM are of no consequence. It's why taking the history of QM does not imply that some day they will be, or that there will be modifications made to the theory, because so far, there have not been any.
In a given mathematical framework, there is a set of statements that are true, and they are true regardless of whether you have proven that they are in that set yet. Discovering a new member of that set is not the same as modifying the framework.
For example -- Alan Turing had no idea in the 1930s that the Universal Turing Machine could be used to make voice recognition software or the AI for Aibos. But every time someone creates some new piece of software this doesn't change anything about Turing Machines. We only went beyond the Turing Machine with the development of quantum computing, which required a new framework: the Non-Deterministic Turing Machine. That was something new.
There has been no such advancement in QM. The whole point of Bell's Theorem and subsequent verification was that it wasn't needed. The people who thought that QM was incomplete, that it needed to be modified, were wrong.
While I have no doubt that we will find many, many more novel *applications* for Quantum Theory, I do have my doubts that we will ever have need to extend the theory itself. And it's the history of QM itself that informs this doubt.
"Of course someone might just say, 'quantum decoherence worked just like the Quantum Mechanical theory developed in the 1920s said it did.'"
And if that understanding requires zero changes to the QM formalism established in the 1920s, then that would be completely appropriate to say.
So I think I understand and agree with you. At least you've stated your position clearly and it makes sense to me. Nice.
So I think that means that, from your point of view (which I am accepting), that QED and QCD are not extensions of QM. They are applications of the QM formalism to electroweak and strong forces. And thus in that sense a future quantum gravity (and all approximate quantum gravities) are not new quantum theories; but rather extensions using the exact same fQM ormalism. Is this correct CB?
And further, from your point of view (which I am accepting), the various string theories, supersymmetry theories, etc are/will not be new quantum theories but extensions using the exact same formalism of quantum mechanics. Is this correct?
Can you clarify a little further; and thanks for the education.
I know you are addressing CB, and am sorry to jump in. But one thing you say sort of nags at me.
"from your point of view (which I am accepting), the various string theories, supersymmetry theories, etc are/will not be new quantum theories but extensions using the exact same formalism of quantum mechanics. Is this correct?"
One can't really ask something like that and get a sound answer because part of the answer has to take into account experimental results. And for strings especially, this is impossible in any foreseeable future.
Let me explain.
What theory we'll use depends on how the system behaves. The greatest achievement of QM experiments was to show that there is a part of reality that can't be described classically. How they behave we now call QM.
Now for anything beyond that who knows. Speaking purely theoretically. If we could experiment on strings, and they manifest quantum behavior, then yes. Any theory describing them has to be quantum in nature (meaning probability distributions etc. etc). But just as well, they needn't behave like quantum systems do. They might not behave like QM and not behave classically. Then some new math will come along. So you can't really ask or guess at something like that. QM is at a scale of 10^-15 or something like that. That's our experimental limit. Strings are at plank length (if they exist). Without some kind of experiment, you can't tell how those systems behave.
For SS it's a bit different since SS is already a QM theory. It can't become anything else than QM :)
"So I think that means that, from your point of view (which I am accepting), that QED and QCD are not extensions of QM. They are applications of the QM formalism to electroweak and strong forces."
In my last post I addressed my view of Bell's Theorem -- a mathematical proof of a consequence of the equations of Quantum Mechanics. Discovering a new element of the set of true statements in a given algebra is definitely not an alteration or extension of that algebra.
This is a different case. Quantum Mechanics on its own doesn't predict what quantum particles and forces exist -- that's the Standard Model's job. So you could call QCD an "extension", but it's really a new theory built on the QM framework. And I do still say that is categorically different than modifying the framework.
To help explain my view, consider this: QCD and QED and all quantum theories are Relativistic theories. They obey the rules of Special Relativity. And so far none of those theories or their experimental results (including quantum entanglement) has required that we modify SR or implied that it is incomplete.
So is QCD an extension of SR? I guess I have no problem with you saying that, as long as it's understood that in this context "extension" doesn't mean "filling in a gap in SR" or "modifying SR from its original formulation". It just means building a new theory predicting phenomenon not in the purview of SR on top of an unmodified SR framework.
As far as the future, I don't know. Like Sinisa said, that depends on future developments and experiments. However IF these new theories that are built on QM behave exactly in accordance with the rules of QM, then yes I would say they fall in the same category as QED and QCD.
E.g. if quantum gravity turns out to really just be a new 'graviton' boson behaving like any other QM particle, then that counts.
String Theory is a new framework that happens to reduce to QM in certain regimes and GR in others. I'd say if we ever get confirmation that Strings are a better model of reality, then it will necessarily mean we've replaced the QM (and GR) framework with the String Theory one. But... well, like Sinisa said about that...
Of course jump in, it's an open discussion.
Thanks for your clear explanation.
So in my paraphrase, you seem to be saying that, we have absolutely no experimental or observational motivation to build a theory that in anyway contradicts (or tries to improves upon, i.e. more precision) quantum mechanics. That seems correct.
However, we have to leave the possibility open that future theory explains experiment on phenomenon that "might not behave like QM and not behave classically." OK, hard to imagine; now that you've clarified. But that is the point; the unknown and un-understood remains to be discovered and/or explained.
So m,y last questions. There are a number of unsolved problems in physics.
Obviously theorists and experimentalist are working to understand these various phenomenon. Do any of these problems suggest more strongly than others; the need to extend the formality of QM? Are (and Where are) any new more stringent tests of QM formalism being being proposed? Or is?
Oh well to answer my own question (I always try to find an answer if I can). Here's one answer that makes sense:
"Today there is not one shred of experimental evidence against quantum mechanics and much to be found for it on scales ranging roughly from those probed by the highest energy particle accelarators (10^−17 cm) to delicate experiments on condensed matter systems (10^−5 cm). That is a wide range of scales but still small compared to the range of 10^−33 cm to 10^28 cm that characterize the phenomena considered in contemporary physics. Recent experiments have extended the range on which quantum mechanics has been or will be tested. To motivate and analyze future experiments that probe quantum mechanics at new scales it would be very useful to have alternative theories. These should agree with quantum mechanics where it has been tested so far, but diﬀer from it on scales where it has not yet been tested and be consistent with the rest of modern physics such as special relativity. But as Steve Weinberg puts it: “It is striking that so far it has not been possible to ﬁnd a logically consistent theory that is close to quantum mechanics other than quantum mechanics itself”." Quantum Mechanics with Extended Probabilities
James B. Hartle 2008 http://arxiv.org/pdf/0801.0688v3
Thanks again CB for the discussion and education. Sinisa and others too.
"However, we have to leave the possibility open that future theory explains experiment on phenomenon that “might not behave like QM and not behave classically.” OK, hard to imagine; now that you’ve clarified. "
I don't think it's that hard to imagine. Hard to imagine what it would BE, but not hard to imagine that it exists.
In all honesty despite arguing that the history of QM says we don't need anything more than QM, I still think/thought that some future discovery implying that there is such a need was more likely than the papers linked by Sinisa and you suggest. I'm quite surprised by that.
yes,I'm surprised too.
But the implied assumption, that blocks, new insight is hard to see before the new insight, but obvious after it is seen. E.g. Assumption of flat space
"To look at what everyone has looked, to see what no one has seen. " by someone
Sometimes that assumption is made not because it is thought to be correct, but that the calculations for any other assumption are just not possible to do.
Which is what happened with the flat/open/closed trilogy.
NOTE: it was not assumed it was flat. The maths available only allowed investigation on certain assumptions and those THREE were the three outcomes that the mathematical treatment was able to address.
Many more have been found, some just by throwing computer power at the problem.
non-locality can be understood in terms of scale invariant quantum impedances