Quantum mechanics is not inconsistent with general relativity, the standard ways of quantizing a theory fail for general relativity. This is not a surprise; physicists knew that these standard methods were not complete, they just produced theories that worked well enough when applied in other areas. Based on your post, it is somewhat likely that you read popular material about loop quantum gravity. If that theory is consistent, has the right long distance limits, etc., then it is both a quantum mechanical and general relativistic theory.
GR and QM are generally agreed to indeed be inconsistent. There are various attempts to come up with theories of quantum gravity. One of these attempts follows particle based physics: string theory and extensions of string theory. The other attempt is GR based, and includes loop quantum gravity and canonical quantum gravity (along with extensions, such as fixed-foliation quantum gravity).
I’ll give you that loop-quantum gravity is “quantum mechnical” and “general realtivistic”. But it isn’t QM or GR. This isn’t a reasonable way of defending your claim that QM and GR are consistent.
And no, I don’t read any popular literature. I hope the above helped explain my previous post a bit.
GR and QM are generally agreed to indeed be inconsistent.
[Citation needed]
I’ll give you that loop-quantum gravity is “quantum mechnical” and “general realtivistic”. But it isn’t QM or GR.
Quantum mechanics is the theory that reality is described by the Schrodinger equation; loop quantum gravity includes the Schrodinger equation. Its proponents claim that it includes the general relativity field equations as a long distance limit; that is what we mean when we say that one theory is a quantization of another, just like quantum and classical electrodynamics.
And no, I don’t read any popular literature. I hope the above helped explain my previous post a bit.
95% probability less than 10% of the physics you read is from journals/arXiv.
GR and QM are generally agreed to indeed be inconsistent
[Citation needed]
So I was somewhat surprised that Wikipedia claims that the above is a “popular claim”, and goes on to cite some yoga involving the quantum mechanics of gravitons, whatever that means. I’m a mathematician, dammit Jim, not a theoretical physicist.
I think a more accurate version of what the grandparent meant is that one cannot merely take QM and GR, stick them together, and hope to get a coherent theory. One needs something more (for example, the above requires the existence of gravitons), and that’s why people go hunting for unified theories.
Relying upon Wikipedia is not advised here. QM and GR, if you stick them together, entail everything. (On the assumption that from a contradiction one can derive anything. Paraconsistent logical systems deny this assumption.) For some proposition, sentence, statement or utterance that P, QM entails P. GR entails not-P. Absent abandoning classical logic (and moving to something like paraconsistent logic), GR and QM are inconsistent.
Let’s assume that a theory is false if the theory entails P and not-P (that is, let’s ignore paraconsistent logical sytstems). Then sticking GR and QM together entails P and not-P. Any theory that entails both P and not-P is false. So sticking them together fails.
Almost all physicists are happy with the above claims, and so there is an ongoing search for theories that preserve what’s supposedly right about QM with what’s supposedly right about GR. Enter theories of quantum gravity. These theories might be in some respects “quantum mechanical”. That is, they preserve some aspects of QM. These theories aren’t QM or GR, however. They’re attempts to preserve what’s right (let’s suppose) about QM and make that compatible with what’s right (let’s suppose) about GR.
We’re utterly in the dark about which such theories might be true. Sadly, that’s the state of the game. If you appeal to QM in defense of some interesting claim, you are failing to appeal to a theory you ought, as an intelligent and well-educated person, place a high degree of credence in. Here our favorite blogger is is screwing up.
Relying upon Wikipedia is not advised here. QM and GR, if you stick them together, entail everything.
I’m confused how you got this out of the above—I didn’t mean to imply that QM+GR was consistent. They need fixing, and the article supports this viewpoint. Grandparent asked for citations; the relevant article has several. I didn’t see the earlier comments between you and endoself, because they’re not in this thread, but in another, for some reason. For what it’s worth, I think you’re misinterpreting statements intended for poetic effect.
So while endoself is wrong when he claims QM isn’t inconsistent with GR, you’re equally wrong for believing EY supports QM over GR, when in fact it’s incredibly likely (based on everything we know about EY’s stance on updating) that for now EY supports QM when it talks about small things and GR when it talks about big things, and that if some better theory would come along that explained the evidence better, EY would update to follow that.
Of course, I can’t speak for him, but I claim the above is a more reasonable interpretation of the state of affairs.
EDIT: So there’s a simpler litmus test to apply here—has EY directly said anything about GR? If so, what evidence is leading you to believe he denies it?
Grandparent asked for citations; the relevant article has several.
The source of your confusion is the meaning of the phrase ‘Citation Needed’. It seldom has anything to do with wanting citations. Actually giving them to him is like answering a (bad) rhetorical question with a literal answer that effectively refutes the rhetorical point of asking it.
“My beliefs are the default and privileged. You have the burden of justifying your beliefs to me.”
“Get back in your place! Who do you think you are?”
“Your momma is inconsistent with General Relativity! But I’m saying it using an intellectual meme rather than the low brow meme.”
Basically, if someone told me ‘Citation Needed!’ in the same conversation that they out of the blue told me I was insane then I would expect them to do whatever they could to find a way to sneer at or dismiss the citations I proceed to give them. I would expect them to feel like their grasp for dominance backfired and try to dig themselves out of what feels like a hole.
This isn’t to say that ‘citation needed’ is never used literally or never appropriate. But I usually find that anyone who is actually interested in whether there are citations available tends to use different language in their reply.
Basically, if someone told me ‘Citation Needed!’ in the same conversation that they out of the blue told me I was insane
Those two things weren’t done by the same person. endoself used [Citation Needed]; PhilosophyFTW called him insane in the followup, for a different reason.
Those two things weren’t done by the same person. endoself used [Citation Needed]; PhilosophyFTW called him insane in the followup, for a different reason.
Ahh. That changes the likely meaning somewhat (greater weight to the first bullet point, less to the last one).
endoself is wrong when he claims QM isn’t inconsistent with GR
I interpreted “QM is inconsistent with GR” as stating that GR cannot be quantized. This is usually what is mentioned in such discussions, as GR is much harder, maybe even impossible, to quantize as compared to other theories. There are very large advantages to only using the word ‘consistent’ in its precise mathematical definition, so I will do that from now on.
In the simplest of terms, theory T is inconsistent with theory T if the conjunction of T and T entails everything in a classical logical system.
Since QM is inconsistent with GR, and since not every proposition is true, either QM or GR is, strictly speaking, false. Perhaps both are false.
The OP, Eliezer, must think that GR is false, since he’s gone out and endorsed QM. This is not a good position to be in. More charitably, the OP has tried to endorse everything in QM that he thinks he needs for his argument, and he’s asserted that all that requisite material will be retained in any future scientific theory.
The OP is then pleading that whatever physical theory turns out to be true will be sufficiently like QM that he’s entitled to rely on QM in the ways he is. Call this quantum mechanical optimism or hopeful thinking. I don’t see the argument here. Sorry.
He can conditionalize his claims. He can say things like, “If QM is true, then...” or “If the true physical theory preserves what there is in QM that I need for my argument, then...” But this isn’t what he’s doing.
And finally, even if the OP were to conditionalize, he’ll still in hot water. Maybe the OP means by “physical nonsense” something like: contradicts claims that follow from QM. But he doesn’t mean this. He’s trotting in his own favorite little philosophical theory, without defense while pretending to rely upon good science (though he’s in fact relying on very probably false science, since QM and GR can’t both be true). This is evident when he writes: “The imaginary identity-tags that read “This is electron #234,567...” don’t affect particle motions or anything else; they can be swapped without making a difference because they’re epiphenomenal.” Let’s suppose that there are such particle-tags. Call them properties. And let’s grant that they don’t affect particle motion. Let’s even grant that they’re epiphenomenal. See how charitable I’m being to the OP?
Now obviously, it doesn’t follow from QM that these epiphenomenal particle tags don’t exist. The OP can beat his brain against the wall for the rest of his life and never manage to show it does so follow. Eliezer believes these particle tags don’t exist, which is why he calls them imaginary, but he has not managed to produce one wit of evidence for that claim. I take it the OP would probably rely upon the following assumption: Nothing epiphenomenal exists. That’s an interesting philosophical claim, and the OP can’t pretend to defend it by giving us more very probably false physical theories. Nor does it follow from any physical theory the OP has mentioned so far.
When reading the OP, I am reminded of William Lane Craig’s attempts to use The Big Bang to defend a central claim he needs for his Cosmological Argument: the universe had a beginning. Craig is in hot water here, for it does not follow from any of our best scientific theories, including all Big Bang Theories, that the universe had a beginning. Craig is using scientific dressing to peddle shoddy arguments that those unfamiliar with the science will be rhetorically overwhelmed by, and I don’t see the difference between what he does and what the OP is doing.
Well, yes. Two theories that make different predictions are logically inconsistent. The standard model of QM is wrong. General relativity is wrong. No-one here disagrees with this. However, the true theory of the laws of physics, when we obtain it, will have to explain all the experimental observations we have so far, which are predicted by the standard model to within 1 part in a billion in some cases. “The wheel of science ratchets forward, but never back” etc etc.
But you’re right, in that all this quantum mechanics stuff is really beside the point anyway. You can apply the generalized anti-zombie principle in a newtonian or any other world just as easily (eg. as done in the first half of the article). Whether or not epiphenomenal particle-tags exist, they can’t affect the physical cause of you saying “yes, I have continuing subjective identity”, so they can’t affect subjective identity. You don’t have to assume that epiphenomenal particle-tags don’t exist to conclude that they are irrelevant by, er, definition.
The only difference QM makes is that it doesn’t talk about “particles” as fundamental entities, and hence “swapping two identical particles” is explicitly a no-op, which is nice, but not much more than an intuition pump.
Philosophers call these particle-tags “haecceities”. The SEP has a good article on identity and individuality in quantum theory. From what I can tell, the parent comment is right except in that classical mechanics can be rephrased to not include particles as fundamental entities, and that quantum mechanics can be interpreted to include particles as fundamental entities (e.g. Bohm). Still, having particles be fundamental seems like a much clearer violation of Occam’s razor in the quantum case than in the classical case.
I didn’t want to come out and talk about haecceitistic properties, since that would have made me sound even weirder (and it is controversial whether there are such), and I was already presenting some arguments in a hostile environment. But I had such properties in mind when responding. Thanks for providing the SEP link.
Quantum mechanics is the theory that reality is described by the Schrodinger equation
You are insane.
95% probability less than 10% of the physics you read is from journals/arXiv.
Feel free to make further claims you have no evidence for. Here’s an article from arXiv you might find interesting: http://arxiv.org/abs/0809.4144
I’m surprised that you put arXiv in the same class you put whatever it is you mean by journals. Maybe I should take the above article seriously? After all, arXiv makes it available. Get out of town.
You win two paper-machine points [1]: one for observing the true nature of arXiv, and the other for implicitly deriding those who argue the countability of the reals.
[1] Probably not redeemable for anything you’d want.
EDIT: Don’t be too harsh on the mantra “QM says reality is described by Schrodinger”. It’s the noble lie they tell undergraduates—or at least, what they told me when I was an undergraduate. In my opinion, it’s slightly unfair to expect the average LW’er to have a better-than-undergraduate knowledge of QM.
Don’t be too harsh on the mantra “QM says reality is described by Schrodinger”. It’s the noble lie they tell undergraduates—or at least, what they told me when I was an undergraduate.
Now I’m interested. In what way are “quantum mechanics” and “vector on a Hilbert space evolving according to Schrodinger’s equation” not the same concept?
They are. I guess the mantra I quoted should have been, “It is true that QM describes reality.” That’s what I assume the grandparent thought you were saying, anyway. It’s not worth calling someone insane over a definition.
Thanks for the points. Yes, ArXiv frequently sucks. And people who argue that the set of real numbers has the same cardinality as the set of natural numbers are morons.. =)
I never stated that every paper on the arXiv was good.
You have neither confirmed nor denied my actual statement.
QM and GR, if you stick them together, entail everything.
I’m not sure what your point is here. If you stick quantum mechanics and Maxwell’s equations together, everything is entailed, but quantum electrodynamics did not give identity back to specific particles. It would be very unlikely for quantum gravity to do that either; certain parts of nature fit perfectly into a very rigid structure and the basic framework of quantum mechanics can be explained but will probably not be eliminated. You can’t point to a specific part of a theory and say “the theory is wrong, so that result is wrong”; theories get improved, but they still have to have enough of the same structure to derive the results already tested by experiment.
Your rebuttal would be more meaningful if you gave us a reason to specifically question the assertion that “identity isn’t in specific atoms”. Something about QM might have to change, OK; but would it be a part of QM which materially affects Eliezer’s argument?
I can’t predict what will have to change to get a scientific theory that is correct. Sorry. I’m also not interested in arguing for a theory of identity here. I’m just pointing out that Eliezer’s argument against a particular theory of identity fails at being less wrong. I don’t have to defend a theory in order to provide a perfectly coherent rebuttal.
In that case, why bring up GR, or even QM? You may as well just say, “Physics might be wrong, ergo, your argument is not deductively valid.”
On the other hand, if empirical evidence does count for something in your epistemology, then you need to be addressing the aspect of QM to which he is appealing.
As I have pointed out, the theory to which he is appealing is very probably false. If he wants to appeal to it in defense of his claims (and even then there are several other reasons why his claims almost certainly don’t follow from the theory), he needs to do so with much more humility. You don’t get to infer P from Q which is probably false, and then assert P with conviction. This is irrational and more wrong (if you know that Q is probably false, which he should), not less wrong. My inference is “The physical theories to which he is appealing are very probably false. This is fact which is widely known. Therefore, his argument is very probably unsound.” And that inference goes through. His argument is very probably a load of garbage since it very probably contains a false premise.
I can truthfully say all of that without even beginning to raise problems for his inferences. Of course, I have done this too. His inferences are deeply problematic for numerous reasons, some of which I have mentioned, some of which are raised in the above-linked SEP article, and others of which can be found by taking a look at some of David Chalmer’s and Galen Strawson’s work.
The post I am commenting on is radically misleading and wildly wrong. Anybody unfamiliar with these issues will be led into error and falsehood by reading it.
As AlephNeil points out, theory unification in physics doesn’t invalidate everything that came before; quite the contrary. In the passage from classical to relativistic mechanics, you lose absolute simultaneity but you retain conservation laws. In that case, it may also be said that the feature of classical physics that was retained—conservation principles—was something for which there was ample empirical evidence, whereas the feature which was lost—the existence of absolute time—was an ontological presupposition which proved to be dispensable.
I consider your argument from the supposed incompatibility of QM and GR to be a bad argument precisely because it has no evident connection to the aspect of QM which is at stake here. In other posts, Eliezer advocates for Julian Barbour’s approach to quantum gravity. There is a small change in the nature of QM here: in Barbour’s theory, there is no time evolution. So the conflict is resolved in a way which does not touch Eliezer’s argument in this post.
You also mention string theory as a unification of QM and GR from the particle physics side, implying, I suppose, that it is GR which has been modified. That would be a very debatable assertion. It is a commonplace of the string versus loop debate to present strings as an outgrowth of particle physics culture, and loop quantum gravity as an outgrowth of the culture of gravitational physics (relativists), and to say that the string theorists neglect general covariance (or “background independence” as it is usually termed in such discussions). This appears to be a historical contingency; it is now a common belief in string theory that the real observables all exist only on the boundary, precisely because the bulk has diffeomorphism invariance; and meanwhile, for practical purposes, diffeomorphism invariance is just another symmetry, which you break by gauge-fixing for the purposes of calculation, but which will still be there in the predictions (i.e. the effects of gauge-fixing must disappear by the end of the calculation).
It would be very unusual to argue that the unification of QM and GR requires a change in how we think about particle statistics. If you actually had such an argument, it would be worth hearing, but you don’t; you just have an argument which bundles the whole of quantum mechanics into one proposition, and the whole of general relativity into another proposition, an argument which claims that the conjunction of these propositions is a contradiction, and that therefore one or the other is false.
Incidentally, how do you get from that to QM is “very probably false”? “The conjunction of A and B is false” does not imply “A is very probably false”! It seems clear that your problem with QM has nothing to do with the alleged incompatibility with GR—this incompatibility (which perhaps you only believe in because of what various authorities say) merely gives you leverage in debate against quantum dogmatists, or hope for a concrete alternative.
Unless you actually have an argument which makes a connection between particle statistics and quantum gravity, you should just stick to particle statistics, and not bring gravity into the picture.
I’m hardly claiming that if we find some true future unified theory of physics, every physical proposition we current believe is false. To assert that would be absurd. The interesting question is which of the propositions that are part of the current packages (at least one of which is false) are in fact false.
If you want to pick some of those propositions and rely upon them, you’d better have independent evidence for their truth (the accurate predictions made by the package isn’t going to count). So rely on that as your evidence, and not on the false package. This is what less wrong people would do.
Barbour is engage more in philosophy than in hard science, and his work is published in either published in poor journals or book form. I could care less whether Eliezer endorse Barbour’s views, if he does. And if he does, then maybe he’d do better to rely upon them than upon QM. If Eliezer does advocate for Barbour’s views, one must wonder why. On the basis of some nice hard scientific evidence? Or on the basis of lots of wishful thinking?
I’m not very interested in getting into a debate about how to properly taxonomize physical theories. That’s irrelevant to any of the points I’ve made, and the debate would be even more irrelevant. Two paragraphs of your response are on this irrelevant subject matter.
It is perfectly acceptable for me to bundle the whole of QM into one proposition, if Eliezer is baselessly relying upon QM. If Eliezer wants to rely on something OTHER than QM, then he can. Something OTHER than QM would be a part of the theory (but not the whole of the theory), or something else like a theory of quantum gravity. If he wants to rely on those things, fine. Then we’ll see what the evidence is for what he relies upon. What, for example, is the evidence for treating Barbour’s odd-ball theories to be more likely true than, say, a fixed-foliation quantum gravity? Well, there isn’t really much evidence. Bad Eliezer.
Your last comment is well worth remarking on. By “very probably false”, I roughly meant that there is a 50% probability that it is false. If there is a 50% epistemic probability that P is false, and your belief that Q is based solely upon your belief that P, then you are irrational if you believe that Q.
You know, I made a mistake at the beginning of this discussion, by conceding your premise that QM and GR are inconsistent. I should have just asked to see the proof.
Usually when people say this, they mean that applying the techniques of perturbative quantum field theory (the techniques which produce Feynman diagams) to general relativity gives rise to an unpredictive theory, because there are infinitely many undetermined quantities associated with higher-order terms in the expansion. The philosophy of renormalization is that you measure such quantities and use them to define the renormalized theory, but that this only makes sense when there are finitely many such quantities.
However, there’s still no proof that this is true for general relativity. There is a research program, “asymptotic safety”, which hopes to find evidence that only finitely many quantities are needed after all. I am skeptical, even though a physicist as good as Steven Weinberg is interested, and as I said, no proof exists. Meanwhile, it does look as if d=4 N=8 supergravity is perturbatively finite. That is a general-relativistic theory—it contains Einstein gravity, coupled to other fields. Although it is perturbatively finite term by term, the Feynman expansion probably doesn’t converge, in which case there need to be other contributions, and most likely N=8 supergravity should be considered a limit of string theory.
Anyway, the bad behavior of general relativity when it is treated using the simplest methods of quantum field theory is by far the main reason that people have for talking about QM and GR as inconsistent, and it’s a theoretical opinion from several decades ago, that is not borne out by more recent developments. If that’s your reason for asserting that QM and GR are inconsistent, I am prepared to rebut that point in as much detail as you wish. If you have some other reason for asserting that they are inconsistent, let’s hear it.
What you put in for P and Q is irrelevant, for a simple reason. If you’re appealing to Q as your only evidence for P, and Q is probably false, then you don’t have good evidence for for P. If Eliezer wants to appeal to some Q as his only evidence for P, and Q is probably false, then he has failed.
Of course, if you have independent evidence for P, then you don’t need to appeal to P as your evidence for Q (and you shouldn’t, since P is very probably false). Here you can appeal to the independent evidence. For example, there is evidence that the earth orbits the sun that is independent of Newton’s theory of gravity. It’s for that reason that you find your toy examples plausible.
This doesn’t work when we’re talking about QM. QM is a package deal that makes predictions. Evidence for the truth of many parts of the package come from the accurate predictions the package makes.
Where there is independent evidence for the parts of the QM package Eliezer wants to appeal to, he should be appealing to those parts of the package and rely upon the independent evidence for them. Appealing to QM is just not rationally acceptable behavior for any reasonably informed persons.
Eliezer might well benefit by thinking about the above-linked SEP article in which this claim is broached: “We now appear to have an interesting situation. Quantum mechanics is compatible with two distinct metaphysical ‘packages’, one in which the particles are regarded as individuals and one in which they are not. Thus, we have a form of ‘underdetermination’ of the metaphysics by the physics (see van Fraassen 1985 and 1991; French 1989a; Huggett 1997). This has implications for the broader issue of realism within the philosophy of science. If asked to spell out her beliefs, the realist will point to currently accepted fundamental physics, such as quantum mechanics, and insist that the world is, at least approximately, however the physics says it is. Of course, there are the well-known problems of ontological change (giving rise to the so-called pessimistic meta-induction) and underdetermination of theories by the data. However, the above underdetermination of metaphysical packages seems to pose an even more fundamental problem, as the physics involved is well entrenched and the difference in the metaphysics seemingly as wide as it could be. These packages support dramatically different world-views: one in which quantal particles are individuals and one in which they are not. The realist must then face the question: which package corresponds to the world? The physics itself can offer no help whatsoever and any justification for choosing one package over the other which appeals to metaphysical considerations, for example, runs the risk of drastically watering down the science in scientific realism.”
GR and QM are generally agreed to indeed be inconsistent. There are various attempts to come up with theories of quantum gravity. One of these attempts follows particle based physics: string theory and extensions of string theory. The other attempt is GR based, and includes loop quantum gravity and canonical quantum gravity (along with extensions, such as fixed-foliation quantum gravity).
I’ll give you that loop-quantum gravity is “quantum mechnical” and “general realtivistic”. But it isn’t QM or GR. This isn’t a reasonable way of defending your claim that QM and GR are consistent.
And no, I don’t read any popular literature. I hope the above helped explain my previous post a bit.
Why did you not write this as a reply to me?
[Citation needed]
Quantum mechanics is the theory that reality is described by the Schrodinger equation; loop quantum gravity includes the Schrodinger equation. Its proponents claim that it includes the general relativity field equations as a long distance limit; that is what we mean when we say that one theory is a quantization of another, just like quantum and classical electrodynamics.
95% probability less than 10% of the physics you read is from journals/arXiv.
So I was somewhat surprised that Wikipedia claims that the above is a “popular claim”, and goes on to cite some yoga involving the quantum mechanics of gravitons, whatever that means. I’m a mathematician, dammit Jim, not a theoretical physicist.
I think a more accurate version of what the grandparent meant is that one cannot merely take QM and GR, stick them together, and hope to get a coherent theory. One needs something more (for example, the above requires the existence of gravitons), and that’s why people go hunting for unified theories.
Relying upon Wikipedia is not advised here. QM and GR, if you stick them together, entail everything. (On the assumption that from a contradiction one can derive anything. Paraconsistent logical systems deny this assumption.) For some proposition, sentence, statement or utterance that P, QM entails P. GR entails not-P. Absent abandoning classical logic (and moving to something like paraconsistent logic), GR and QM are inconsistent.
Let’s assume that a theory is false if the theory entails P and not-P (that is, let’s ignore paraconsistent logical sytstems). Then sticking GR and QM together entails P and not-P. Any theory that entails both P and not-P is false. So sticking them together fails.
Almost all physicists are happy with the above claims, and so there is an ongoing search for theories that preserve what’s supposedly right about QM with what’s supposedly right about GR. Enter theories of quantum gravity. These theories might be in some respects “quantum mechanical”. That is, they preserve some aspects of QM. These theories aren’t QM or GR, however. They’re attempts to preserve what’s right (let’s suppose) about QM and make that compatible with what’s right (let’s suppose) about GR.
We’re utterly in the dark about which such theories might be true. Sadly, that’s the state of the game. If you appeal to QM in defense of some interesting claim, you are failing to appeal to a theory you ought, as an intelligent and well-educated person, place a high degree of credence in. Here our favorite blogger is is screwing up.
I’m confused how you got this out of the above—I didn’t mean to imply that QM+GR was consistent. They need fixing, and the article supports this viewpoint. Grandparent asked for citations; the relevant article has several. I didn’t see the earlier comments between you and endoself, because they’re not in this thread, but in another, for some reason. For what it’s worth, I think you’re misinterpreting statements intended for poetic effect.
So while endoself is wrong when he claims QM isn’t inconsistent with GR, you’re equally wrong for believing EY supports QM over GR, when in fact it’s incredibly likely (based on everything we know about EY’s stance on updating) that for now EY supports QM when it talks about small things and GR when it talks about big things, and that if some better theory would come along that explained the evidence better, EY would update to follow that.
Of course, I can’t speak for him, but I claim the above is a more reasonable interpretation of the state of affairs.
EDIT: So there’s a simpler litmus test to apply here—has EY directly said anything about GR? If so, what evidence is leading you to believe he denies it?
The source of your confusion is the meaning of the phrase ‘Citation Needed’. It seldom has anything to do with wanting citations. Actually giving them to him is like answering a (bad) rhetorical question with a literal answer that effectively refutes the rhetorical point of asking it.
What else does it mean?
“My beliefs are the default and privileged. You have the burden of justifying your beliefs to me.”
“Get back in your place! Who do you think you are?”
“Your momma is inconsistent with General Relativity! But I’m saying it using an intellectual meme rather than the low brow meme.”
Basically, if someone told me ‘Citation Needed!’ in the same conversation that they out of the blue told me I was insane then I would expect them to do whatever they could to find a way to sneer at or dismiss the citations I proceed to give them. I would expect them to feel like their grasp for dominance backfired and try to dig themselves out of what feels like a hole.
This isn’t to say that ‘citation needed’ is never used literally or never appropriate. But I usually find that anyone who is actually interested in whether there are citations available tends to use different language in their reply.
Ah, I see.
Those two things weren’t done by the same person. endoself used [Citation Needed]; PhilosophyFTW called him insane in the followup, for a different reason.
Ahh. That changes the likely meaning somewhat (greater weight to the first bullet point, less to the last one).
I interpreted “QM is inconsistent with GR” as stating that GR cannot be quantized. This is usually what is mentioned in such discussions, as GR is much harder, maybe even impossible, to quantize as compared to other theories. There are very large advantages to only using the word ‘consistent’ in its precise mathematical definition, so I will do that from now on.
In the simplest of terms, theory T is inconsistent with theory T if the conjunction of T and T entails everything in a classical logical system.
Since QM is inconsistent with GR, and since not every proposition is true, either QM or GR is, strictly speaking, false. Perhaps both are false.
The OP, Eliezer, must think that GR is false, since he’s gone out and endorsed QM. This is not a good position to be in. More charitably, the OP has tried to endorse everything in QM that he thinks he needs for his argument, and he’s asserted that all that requisite material will be retained in any future scientific theory.
The OP is then pleading that whatever physical theory turns out to be true will be sufficiently like QM that he’s entitled to rely on QM in the ways he is. Call this quantum mechanical optimism or hopeful thinking. I don’t see the argument here. Sorry.
He can conditionalize his claims. He can say things like, “If QM is true, then...” or “If the true physical theory preserves what there is in QM that I need for my argument, then...” But this isn’t what he’s doing.
And finally, even if the OP were to conditionalize, he’ll still in hot water. Maybe the OP means by “physical nonsense” something like: contradicts claims that follow from QM. But he doesn’t mean this. He’s trotting in his own favorite little philosophical theory, without defense while pretending to rely upon good science (though he’s in fact relying on very probably false science, since QM and GR can’t both be true). This is evident when he writes: “The imaginary identity-tags that read “This is electron #234,567...” don’t affect particle motions or anything else; they can be swapped without making a difference because they’re epiphenomenal.” Let’s suppose that there are such particle-tags. Call them properties. And let’s grant that they don’t affect particle motion. Let’s even grant that they’re epiphenomenal. See how charitable I’m being to the OP?
Now obviously, it doesn’t follow from QM that these epiphenomenal particle tags don’t exist. The OP can beat his brain against the wall for the rest of his life and never manage to show it does so follow. Eliezer believes these particle tags don’t exist, which is why he calls them imaginary, but he has not managed to produce one wit of evidence for that claim. I take it the OP would probably rely upon the following assumption: Nothing epiphenomenal exists. That’s an interesting philosophical claim, and the OP can’t pretend to defend it by giving us more very probably false physical theories. Nor does it follow from any physical theory the OP has mentioned so far.
When reading the OP, I am reminded of William Lane Craig’s attempts to use The Big Bang to defend a central claim he needs for his Cosmological Argument: the universe had a beginning. Craig is in hot water here, for it does not follow from any of our best scientific theories, including all Big Bang Theories, that the universe had a beginning. Craig is using scientific dressing to peddle shoddy arguments that those unfamiliar with the science will be rhetorically overwhelmed by, and I don’t see the difference between what he does and what the OP is doing.
Well, yes. Two theories that make different predictions are logically inconsistent. The standard model of QM is wrong. General relativity is wrong. No-one here disagrees with this. However, the true theory of the laws of physics, when we obtain it, will have to explain all the experimental observations we have so far, which are predicted by the standard model to within 1 part in a billion in some cases. “The wheel of science ratchets forward, but never back” etc etc.
But you’re right, in that all this quantum mechanics stuff is really beside the point anyway. You can apply the generalized anti-zombie principle in a newtonian or any other world just as easily (eg. as done in the first half of the article). Whether or not epiphenomenal particle-tags exist, they can’t affect the physical cause of you saying “yes, I have continuing subjective identity”, so they can’t affect subjective identity. You don’t have to assume that epiphenomenal particle-tags don’t exist to conclude that they are irrelevant by, er, definition.
The only difference QM makes is that it doesn’t talk about “particles” as fundamental entities, and hence “swapping two identical particles” is explicitly a no-op, which is nice, but not much more than an intuition pump.
Philosophers call these particle-tags “haecceities”. The SEP has a good article on identity and individuality in quantum theory. From what I can tell, the parent comment is right except in that classical mechanics can be rephrased to not include particles as fundamental entities, and that quantum mechanics can be interpreted to include particles as fundamental entities (e.g. Bohm). Still, having particles be fundamental seems like a much clearer violation of Occam’s razor in the quantum case than in the classical case.
I didn’t want to come out and talk about haecceitistic properties, since that would have made me sound even weirder (and it is controversial whether there are such), and I was already presenting some arguments in a hostile environment. But I had such properties in mind when responding. Thanks for providing the SEP link.
You are insane.
Feel free to make further claims you have no evidence for. Here’s an article from arXiv you might find interesting: http://arxiv.org/abs/0809.4144
I’m surprised that you put arXiv in the same class you put whatever it is you mean by journals. Maybe I should take the above article seriously? After all, arXiv makes it available. Get out of town.
You win two paper-machine points [1]: one for observing the true nature of arXiv, and the other for implicitly deriding those who argue the countability of the reals.
[1] Probably not redeemable for anything you’d want.
EDIT: Don’t be too harsh on the mantra “QM says reality is described by Schrodinger”. It’s the noble lie they tell undergraduates—or at least, what they told me when I was an undergraduate. In my opinion, it’s slightly unfair to expect the average LW’er to have a better-than-undergraduate knowledge of QM.
Now I’m interested. In what way are “quantum mechanics” and “vector on a Hilbert space evolving according to Schrodinger’s equation” not the same concept?
They are. I guess the mantra I quoted should have been, “It is true that QM describes reality.” That’s what I assume the grandparent thought you were saying, anyway. It’s not worth calling someone insane over a definition.
I’m confused. Are you saying that I got called insane for saying that quantum mechanics is the theory that reality is described by quantum mechanics?
No. I’m saying you got called insane for “saying” (though you didn’t say this) that quantum mechanics describes reality.
But this is just my interpretation of things. I’m having trouble modelling PhilosophyFTW’s beliefs.
Thanks for the points. Yes, ArXiv frequently sucks. And people who argue that the set of real numbers has the same cardinality as the set of natural numbers are morons.. =)
I never stated that every paper on the arXiv was good.
You have neither confirmed nor denied my actual statement.
I’m not sure what your point is here. If you stick quantum mechanics and Maxwell’s equations together, everything is entailed, but quantum electrodynamics did not give identity back to specific particles. It would be very unlikely for quantum gravity to do that either; certain parts of nature fit perfectly into a very rigid structure and the basic framework of quantum mechanics can be explained but will probably not be eliminated. You can’t point to a specific part of a theory and say “the theory is wrong, so that result is wrong”; theories get improved, but they still have to have enough of the same structure to derive the results already tested by experiment.
Your rebuttal would be more meaningful if you gave us a reason to specifically question the assertion that “identity isn’t in specific atoms”. Something about QM might have to change, OK; but would it be a part of QM which materially affects Eliezer’s argument?
I can’t predict what will have to change to get a scientific theory that is correct. Sorry. I’m also not interested in arguing for a theory of identity here. I’m just pointing out that Eliezer’s argument against a particular theory of identity fails at being less wrong. I don’t have to defend a theory in order to provide a perfectly coherent rebuttal.
In that case, why bring up GR, or even QM? You may as well just say, “Physics might be wrong, ergo, your argument is not deductively valid.”
On the other hand, if empirical evidence does count for something in your epistemology, then you need to be addressing the aspect of QM to which he is appealing.
As I have pointed out, the theory to which he is appealing is very probably false. If he wants to appeal to it in defense of his claims (and even then there are several other reasons why his claims almost certainly don’t follow from the theory), he needs to do so with much more humility. You don’t get to infer P from Q which is probably false, and then assert P with conviction. This is irrational and more wrong (if you know that Q is probably false, which he should), not less wrong. My inference is “The physical theories to which he is appealing are very probably false. This is fact which is widely known. Therefore, his argument is very probably unsound.” And that inference goes through. His argument is very probably a load of garbage since it very probably contains a false premise.
I can truthfully say all of that without even beginning to raise problems for his inferences. Of course, I have done this too. His inferences are deeply problematic for numerous reasons, some of which I have mentioned, some of which are raised in the above-linked SEP article, and others of which can be found by taking a look at some of David Chalmer’s and Galen Strawson’s work.
The post I am commenting on is radically misleading and wildly wrong. Anybody unfamiliar with these issues will be led into error and falsehood by reading it.
As AlephNeil points out, theory unification in physics doesn’t invalidate everything that came before; quite the contrary. In the passage from classical to relativistic mechanics, you lose absolute simultaneity but you retain conservation laws. In that case, it may also be said that the feature of classical physics that was retained—conservation principles—was something for which there was ample empirical evidence, whereas the feature which was lost—the existence of absolute time—was an ontological presupposition which proved to be dispensable.
I consider your argument from the supposed incompatibility of QM and GR to be a bad argument precisely because it has no evident connection to the aspect of QM which is at stake here. In other posts, Eliezer advocates for Julian Barbour’s approach to quantum gravity. There is a small change in the nature of QM here: in Barbour’s theory, there is no time evolution. So the conflict is resolved in a way which does not touch Eliezer’s argument in this post.
You also mention string theory as a unification of QM and GR from the particle physics side, implying, I suppose, that it is GR which has been modified. That would be a very debatable assertion. It is a commonplace of the string versus loop debate to present strings as an outgrowth of particle physics culture, and loop quantum gravity as an outgrowth of the culture of gravitational physics (relativists), and to say that the string theorists neglect general covariance (or “background independence” as it is usually termed in such discussions). This appears to be a historical contingency; it is now a common belief in string theory that the real observables all exist only on the boundary, precisely because the bulk has diffeomorphism invariance; and meanwhile, for practical purposes, diffeomorphism invariance is just another symmetry, which you break by gauge-fixing for the purposes of calculation, but which will still be there in the predictions (i.e. the effects of gauge-fixing must disappear by the end of the calculation).
It would be very unusual to argue that the unification of QM and GR requires a change in how we think about particle statistics. If you actually had such an argument, it would be worth hearing, but you don’t; you just have an argument which bundles the whole of quantum mechanics into one proposition, and the whole of general relativity into another proposition, an argument which claims that the conjunction of these propositions is a contradiction, and that therefore one or the other is false.
Incidentally, how do you get from that to QM is “very probably false”? “The conjunction of A and B is false” does not imply “A is very probably false”! It seems clear that your problem with QM has nothing to do with the alleged incompatibility with GR—this incompatibility (which perhaps you only believe in because of what various authorities say) merely gives you leverage in debate against quantum dogmatists, or hope for a concrete alternative.
Unless you actually have an argument which makes a connection between particle statistics and quantum gravity, you should just stick to particle statistics, and not bring gravity into the picture.
I’m hardly claiming that if we find some true future unified theory of physics, every physical proposition we current believe is false. To assert that would be absurd. The interesting question is which of the propositions that are part of the current packages (at least one of which is false) are in fact false.
If you want to pick some of those propositions and rely upon them, you’d better have independent evidence for their truth (the accurate predictions made by the package isn’t going to count). So rely on that as your evidence, and not on the false package. This is what less wrong people would do.
Barbour is engage more in philosophy than in hard science, and his work is published in either published in poor journals or book form. I could care less whether Eliezer endorse Barbour’s views, if he does. And if he does, then maybe he’d do better to rely upon them than upon QM. If Eliezer does advocate for Barbour’s views, one must wonder why. On the basis of some nice hard scientific evidence? Or on the basis of lots of wishful thinking?
I’m not very interested in getting into a debate about how to properly taxonomize physical theories. That’s irrelevant to any of the points I’ve made, and the debate would be even more irrelevant. Two paragraphs of your response are on this irrelevant subject matter.
It is perfectly acceptable for me to bundle the whole of QM into one proposition, if Eliezer is baselessly relying upon QM. If Eliezer wants to rely on something OTHER than QM, then he can. Something OTHER than QM would be a part of the theory (but not the whole of the theory), or something else like a theory of quantum gravity. If he wants to rely on those things, fine. Then we’ll see what the evidence is for what he relies upon. What, for example, is the evidence for treating Barbour’s odd-ball theories to be more likely true than, say, a fixed-foliation quantum gravity? Well, there isn’t really much evidence. Bad Eliezer.
Your last comment is well worth remarking on. By “very probably false”, I roughly meant that there is a 50% probability that it is false. If there is a 50% epistemic probability that P is false, and your belief that Q is based solely upon your belief that P, then you are irrational if you believe that Q.
You know, I made a mistake at the beginning of this discussion, by conceding your premise that QM and GR are inconsistent. I should have just asked to see the proof.
Usually when people say this, they mean that applying the techniques of perturbative quantum field theory (the techniques which produce Feynman diagams) to general relativity gives rise to an unpredictive theory, because there are infinitely many undetermined quantities associated with higher-order terms in the expansion. The philosophy of renormalization is that you measure such quantities and use them to define the renormalized theory, but that this only makes sense when there are finitely many such quantities.
However, there’s still no proof that this is true for general relativity. There is a research program, “asymptotic safety”, which hopes to find evidence that only finitely many quantities are needed after all. I am skeptical, even though a physicist as good as Steven Weinberg is interested, and as I said, no proof exists. Meanwhile, it does look as if d=4 N=8 supergravity is perturbatively finite. That is a general-relativistic theory—it contains Einstein gravity, coupled to other fields. Although it is perturbatively finite term by term, the Feynman expansion probably doesn’t converge, in which case there need to be other contributions, and most likely N=8 supergravity should be considered a limit of string theory.
Anyway, the bad behavior of general relativity when it is treated using the simplest methods of quantum field theory is by far the main reason that people have for talking about QM and GR as inconsistent, and it’s a theoretical opinion from several decades ago, that is not borne out by more recent developments. If that’s your reason for asserting that QM and GR are inconsistent, I am prepared to rebut that point in as much detail as you wish. If you have some other reason for asserting that they are inconsistent, let’s hear it.
(edited to add: undetermined quantities)
What if I were to put P = “there is no such thing as absolute simultaneity” and Q = “special relativity”?
Or P = “the earth orbits the sun” and Q = “Newton’s theory of gravity”?
What you put in for P and Q is irrelevant, for a simple reason. If you’re appealing to Q as your only evidence for P, and Q is probably false, then you don’t have good evidence for for P. If Eliezer wants to appeal to some Q as his only evidence for P, and Q is probably false, then he has failed.
Of course, if you have independent evidence for P, then you don’t need to appeal to P as your evidence for Q (and you shouldn’t, since P is very probably false). Here you can appeal to the independent evidence. For example, there is evidence that the earth orbits the sun that is independent of Newton’s theory of gravity. It’s for that reason that you find your toy examples plausible.
This doesn’t work when we’re talking about QM. QM is a package deal that makes predictions. Evidence for the truth of many parts of the package come from the accurate predictions the package makes.
Where there is independent evidence for the parts of the QM package Eliezer wants to appeal to, he should be appealing to those parts of the package and rely upon the independent evidence for them. Appealing to QM is just not rationally acceptable behavior for any reasonably informed persons.
Eliezer might well benefit by thinking about the above-linked SEP article in which this claim is broached: “We now appear to have an interesting situation. Quantum mechanics is compatible with two distinct metaphysical ‘packages’, one in which the particles are regarded as individuals and one in which they are not. Thus, we have a form of ‘underdetermination’ of the metaphysics by the physics (see van Fraassen 1985 and 1991; French 1989a; Huggett 1997). This has implications for the broader issue of realism within the philosophy of science. If asked to spell out her beliefs, the realist will point to currently accepted fundamental physics, such as quantum mechanics, and insist that the world is, at least approximately, however the physics says it is. Of course, there are the well-known problems of ontological change (giving rise to the so-called pessimistic meta-induction) and underdetermination of theories by the data. However, the above underdetermination of metaphysical packages seems to pose an even more fundamental problem, as the physics involved is well entrenched and the difference in the metaphysics seemingly as wide as it could be. These packages support dramatically different world-views: one in which quantal particles are individuals and one in which they are not. The realist must then face the question: which package corresponds to the world? The physics itself can offer no help whatsoever and any justification for choosing one package over the other which appeals to metaphysical considerations, for example, runs the risk of drastically watering down the science in scientific realism.”