What Is an Element of Reality?

[vanesch]

You think we know nothing, that everything we could believe is an illusion, and the only serious question is whether the illusion you posit is in some superficial sense consistent with your personal mental experience.

Yes, although I would object to the "you think we know nothing". Knowing what is a good illusion is real knowledge that is useful.

I guess this explains why you advocate this strange solipsist version of MWI.

Exactly. I give myself more liberty with the "story" and I am more severe on the principles of the formalism, while you do the opposite.

Try as I might, I can't even bring myself to take that idea seriously. It just isn't a serious theory in the way meant by such scientific realists as Einstein and Bell.

Those whimps don't run in the same category as I do

"Explanatory power" is not a subjective game. It's about what is true, what corresponds to the way the real world actually is. Lies have zero explanatory power.

Hehe, you must be a bad poker player I'd say that there is a whole greyscale between "lies" and "what is true". Given the fact that "what is true" is an unattainable ideal (in my view), there's still stories that work well, stories that work better and stories that are obviously flawed.

And to think, all this time I wasted trying to convince you that your beliefs were a mere illusion. Now you say you knew it all the time. Sigh...

Yes, but YOU don't know that your beliefs are just as well an illusion

I absolutely do not believe that in 500 years we will all believe that the world is flat, that matter is not atomic, that DNA plays no role in inheritance, etc. We actually *know* some things, things about how the world acutally *is*, and science has as its goal finding out *more* things.

When I go hiking, I "believe" that the world is flat and I don't mind taking a flat map of the environment with me. Of course I know that it is an approximation (illusion?) and that this can be explained by the size of the earth. So it is a very useful "illusion" (which is, in your terminology, basically a lie). When I calculate the mechanical vibration modes in a steel structure, I "believe" that steel is a continuum allowing me to use simple equations in continuum mechanics ; even though it is a "lie".
In the same way, I "believe" that matter is made out of individual atoms, although I also think that this is not correct and that they are apparent structures that result from the interactions of quantum fields (yes, we differ here).
What I want to say is that even explanations for which we now KNOW that they are not correct, are still very useful explanations (now understood as approximations of a more "fundamental" explanation). In that sense, indeed, the good old explanations which work up to a point will remain with us for ever, and we will tell them to the kids. "Explanations", "paradigms", "illusions" and so on are like that Iceland cosmology: it is turtles all the way down, and probably at a certain point we will simply stop looking at underlying turtles, because we can't think anymore of any falsifiable statement that could reasonably be tested (and because maybe humankind will face more pressing problems, like total extinction).

All I can say is, if you disagree with that it's no wonder you don't see why Bohm is a serious and promising theory.

Ha, our mutual psycho-analysis has led us to understand each other's viewpoint and mindset, and leads us to fully disagree in peace

Nevertheless, I DO think of Bohm's theory as a useful illusion . First of all because it is an example of a class of theories that certain dumbasses thought couldn't exist (namely a deterministic hidden variable theory with identical predictions as QM), and second, you guys MIGHT be on something. The day that you can come up with a reason why lorentz invariance appears, without putting it in by hand, hence giving us back SR and GR, I will listen very carefully :-)
What I wanted to make you see is that MWI is ALSO a useful illusion, first of all because it is ALSO an example of a class of theories that certain dumbasses thought couldn't exist (namely a theory which fully respects relativity and has identical predictions as QM).

 

[ttn]

I'm not going to bother responding on all the philosophical stuff. I think it's clear to both of us and to anyone else reading what we each think, and how that influences the physics debates.

But one small but important point:

The day that you can come up with a reason why lorentz invariance appears, without putting it in by hand, hence giving us back SR and GR, I will listen very carefully

There is a funny kind of demand here if you think about it. My only claim in all of this has been that Lorentz invariance appears not to be fundamental. That is, Lorentz invariance seems to be a kind of emergent phenomenon that appears in certain situations and/or under certain conditions, rather than a fundamental fact about the causal structure of the world. What this means in practice is that I'm willing to accept some violations of Lorentz invariance in theories so long as they remain consistent with observed facts; you on the other hand want Lorentz invariance to be universal (so that no non-Lorentz-invariant theories or aspects of theories would be acceptable).

My question is: what in the world does any of this have to do with *explaining* Lorentz invariance? Neither one of us has an explanation for it. Taking that formal principle as universal, as a kind of axiom, isn't the same as providing an *explanation* for it. You just accept it and then demand it of theories. I also just accept it (but not as a fundamental) and then demand that theories be consistent with what is known empirically relating to it.

Maybe I'm not being too clear. My point is that I, as an advocate of a Bohm interpretation of QM, have no *special* responsibility to provide some underlying explanation of Lorentz invariance. It's not like you *already have* such an explanation, but that I've pulled the rug out from under it and now I have to provide a new rug. There was never any rug. Lorentz invariance is just something people accepted based on empirical evidence -- namely, the fact that observable effects all seemed to obey a certain kind of transmormation law. It turned out over the last 100 years to be a quite general rule, yes. So people started to believe that it might be or must be universal. But in the absense of some underlying causal argument that it must be universal, that's just plain hasty generalization. That it was hasty is, I think, proved by the prima facie evidence for a non-Lorentz-invariant structure provided by empirical violation of Bell's inequalities.

I fear I've again drifted from the point I actually want to make here. So let me start over. You said: "The day that you can come up with a reason why lorentz invariance appears, without putting it in by hand, hence giving us back SR and GR, I will listen very carefully." My point here is this: The day you can come up with a reason why Lorentz invariance should be accepted as a *universal* and *fundamental* principle, I will listen very carefully. You talk as if there is some special responsibility on my to reject your extrapolation of Lorentz invariance from "works as a description of a number of things so far observed" to "universal fundamental principle of nature". Well I reject that. The burden is on you if you want to extrapolate something into a fundamental law. *You* prove to me (by giving some "reason why lorentz invariance appears, without putting it in by hand") why I shouldn't entertain empirically adequate theories that aren't relativistic.

And on that I'll have to wish you luck given that Bell's inequalities are violated, so we know that no *serious* locally causal theory will be adequate.

 

[vanesch]

*You* prove to me (by giving some "reason why lorentz invariance appears, without putting it in by hand") why I shouldn't entertain empirically adequate theories that aren't relativistic.

Of course you can entertain that view ! But now you should explain to me the APPARENT lorentz invariance of things such as the Maxwell equations, the Dirac equation and so on. HOW COME that all of unitary quantum theory can be formulated in such a way that they can be written in a Lorentz invariant way ?
You can just shrug and say: "well, heh, that's simply how they are ; they could have been different, but they simply happen to be that way." I find that slightly unsatisfying, in the same way as it would have been unsatisfying to say: "equations in Newtonian physics can be written in 3-vector form, it just happens to be that way, it doesn't mean that there is something like isotropy of space."

I could perfectly well accept that Lorentz invariance is not a fundamental principle, but is an "emerging property". Only, you cannot derive that "emerging property" without putting it into ALL the field equations.

I do of course not have to explain WHY Lorentz invariance is a fundamental principle if I TAKE it as basic postulate that all objects in the theory are 4-dim geometrical objects. THIS then implies that all kinds of equations I will write down in a specific coordinate system will be lorentz invariant. So now I have an explanation, for which you can only say "well, it just happens to be that way".

This is where I say that explanatory power is lost in your case.

 

[ttn]

Of course you can entertain that view ! But now you should explain to me the APPARENT lorentz invariance of things such as the Maxwell equations, the Dirac equation and so on. HOW COME that all of unitary quantum theory can be formulated in such a way that they can be written in a Lorentz invariant way ?

You're right that I have no answer to "HOW COME?". My point was that you don't either, so you can't point to my inability to answer this question as a reason to reject my side in favor of your side. Neither side knows *why* Maxwell's equations (etc) are Lorentz invariant.

You can just shrug and say: "well, heh, that's simply how they are ; they could have been different, but they simply happen to be that way."

and I'd add: and hopefully someday we'll have a non-delusional explanation for this.

But my main point was that you shouldn't criticize me for saying "well, that's simply how things are, they happen to be that way." You say the same thing.

I do of course not have to explain WHY Lorentz invariance is a fundamental principle if I TAKE it as basic postulate that all objects in the theory are 4-dim geometrical objects. THIS then implies that all kinds of equations I will write down in a specific coordinate system will be lorentz invariant. So now I have an explanation, for which you can only say "well, it just happens to be that way".

That's precisely what I'm denying. Taking something as a postulate and showing that it is a consequence of something deeper (explaining or proving it) aren't the same thing. You can't *explain* why Maxwell's equations are lorentz invariant by saying "I accepted it as a postulate that all equations should be lorentz invariant." That's just dumb on the face of it. Plus, the only reason you accepted that postulate is because Maxwell's equations (and some other stuff) were lorentz invariant. So not only is the only relevant sense of "explanation" involved here pertaining to the wrong thing (namely, our beliefs rather than the physical facts), the explanation goes the wrong way: it's Maxwell's equations that (partially) explain your belief in some general postulate, not the other way around.

Well, whatever. I think maybe we've talked this one to death. But we've covered a lot of important ground and I've enjoyed it. You can have the last word if you want it.

 

[vanesch]

Taking something as a postulate and showing that it is a consequence of something deeper (explaining or proving it) aren't the same thing. You can't *explain* why Maxwell's equations are lorentz invariant by saying "I accepted it as a postulate that all equations should be lorentz invariant."

I agree with you there, if it were "and the equations are Lorentz invariant" (a certain way of writing formulas). If it were a statement like "and the equations only contain at most 7 terms" that would be an equally silly "principle".
You could write down the Maxwell equations, and show that there are less than 7 terms in it, and just say, "well, I don't know why there are only 7 terms but that's the way it seems to be", and I would be nervously jumping up and down and require you to EXPLAIN my superb postulate that all fundamental field equations in nature have less than 7 terms in them. You'd call me a <fill in derogatory statement about my intelligence> and you would be right. And I have the impression you take the same attitude about the statement of "lorentz invariance". If it were just a "property of the formulas we write down" you would be entirely justified to do so. But what I'm affraid you fail to see is that Lorentz invariance is A CONSEQUENCE of a physical idea, namely that all objects in the theory are 4-dim geometrical objects. This is as fundamental a statement as saying that there are only particles out there. Ok, I cannot tell you WHY the objects should be 4-dim geometrical objects, just as well as you cannot tell me WHY there are only particles out there ; that's always the case with the basic postulates: we cannot explain them. However, once I accept that statement, THERE IS NO OTHER WAY for the theory as to be written down in lorentz invariant equations, so as such, this postulate DOES EXPLAIN the lorentz invariance of the Dirac equation, the maxwell equation, the equations of gravity etc...: they are coordinate expressions of the 4-dim geometrical objects.

 

[metacristi]

"...when you have eliminated the impossible, whatever remains, however improbable, must be the truth." - Sherlock Holmes (Sir Arthur Conan Doyle)

Heh, again that phrase about 'eliminating the impossible' (often seen on forums 'packed' with 'skeptics' :-) )...It might work for detective work or more generally at the macro level (underdetermination is not a serious problem) but I don't think it works at the micro level. Besides even at the macro level there are problems, for example we have to rely on the auxiliary assumption (hidden) but not at all proved (in the sense of having sufficient reasons once and for all) that common sense really gives us a representation of an external reality, for example solipsism is still a perfectly valid solution in spite of the fact that science has a form of realism at its basis (it's laden with the assumption that there exist an external reality which we can perceive/model/understand at least partially).

Returning at the problem of 'nonlocality' the truth is that there is no good reason now to suppose that local realism (in its classical definition) has been thoroughly rejected, indeed nothing impedes the possibility of strong determinism at the most basic level of reality (in which case it is not at all surprising that classical locality still hold, of course to the expense of renouncing at free will). Or even that 'modus tollens' cease to work when applied at quantum level (at least in certain cases, the assumption of uniformity is inductive and no one has produced so far an argument justifying a general inductive method).

This does not mean that there are good reasons to prefer now such a research program (holding classical locality) as the first choice, no, the idea is that we/scientists should be much more humble, there is no crushing evidence that science really lead us to the Truth; Aspect's experiment is considered 'crucial' by many scientists but our actual interpretation might be in reality (not known by us) wrong.

 

[prabhuramkumar]

model question papers and guidance

sir
i have received ur mail on quantum mechanics.it is really nice.
but i want to prefer for iit and iisc.so am in need of model question papers.
pls mail to me at once.it will be helpful for my further studies.
yours
B.prabhu ramkumar