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Maxwell's equations and determinism 
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#19
Sep805, 04:01 PM

P: 355




#20
Sep805, 06:11 PM

P: 1,295

The point is that we can infer the existence of things that we don't see, if it makes our world view more conceptually pleasant. 


#21
Sep905, 06:20 AM

P: 416

In classical physics, systems are not deterministic: e.g. thermodynamics or chemical kinetics. Yes, experiments can prove that the world is undeterministic by measuring random forces, which cannot be reduced to deterministic forces. From a phylosphical view, it is true that nondeterminism is not proved but scientifically it is. You have a random copmponent that cannot be explained in determinisitc terms, that is science. Now you can phylosophically claim that that random component is really caused by an underlying deterministic theory. Yes, phylosophically it is possible. But and scientifically? If you want your hypotesis to be scientific you may prove that can be verified (falsable) in experiments. You may formulate the deterministic final EXACT theory, then derivate random components from it and show that coindice with experiments. This is by definition imposible because by definition the theory may be exact (which may be imposible), you may measure with infinite precision, which is imposible, the proposed state of all universe (even beyond observable universe!), which is imposible, and may compute the EXACT result, which is imposible (except by the use of a perfect computer more larger than universe itself), then and only then if experiment coincides with theory you could prove that universe is determinist. But we compute with imperfect computers, measure with finite precision, develop inexact theories, and cannot know the state of the entire universe. In fact, there is further limitations even for measuring positions and momentum of 10^{24}particles in an ideal gas. Therefore experiments prove that F_{total} = F_{determ} + F_{random} And that is all science can say. You cannot apeal to hidden variables because if are hidden. How do you scientifically show that variables are there? It is like the hyphotesis of "pink elephants" that i said. Personally, I see not problem with the phylosophical interpretation of a world which is non determinist. That mean free will, and love, and ethics, etc. 


#22
Sep905, 06:33 AM

P: 416

http://uts.cc.utexas.edu/~setreal/Pi...20building.jpg You are claiming basically that Empire tate does not exist because i cannot see it entire. I am sited at north i only can see a side, if i am at west i can see another side but like i cannot see all togheter it cannot exist. Moreover like i cannot see a guy sited in the floor 25 from the street but i can the guy if i am inside the Emipre, in the 25 (and then cannot see the Empire), them both Empire state and the guy both do not exist. I cannot see the entire solar system once (in principle I believe that one could) but i can see parts of them at each time and then reconstruct the entire system in a graphical from. Like i can obtain a collection of photos of the Empire and reconstruct it with a graphical package. a = F_{determ} + F_{random} Random components is related to Temperature and strengh "gamma" of interactions, inverse of mass, etc. In Astronomy, "gamma" > 0, and T > 0, and (1/m) > 0... and a > F_{determ} But is only an approximation. For example, T is not zero in space, but is so small that effects are not measured in usual astronomical experiments. The problem of physics is that began with Astronomy and the myth of determinism arised because in astronomy things appears to be deterministic. Chemistry began with condensed matter and newer claimed that world was deterministic. Chemistry always was based in uncertainlty, therein that was did arise like science 100 years after than physics. 


#23
Sep905, 06:34 AM

P: 26

QM doesn't disprove determinism at least for inanimate objects.
It only proves it is incapable of determining specific causes and making nonstatistical predictions for itself. Bohmian Mechanics is of course an excellent formal interpretation of QM theory. Science is after all based upon causality, not witchcraft, and Bohm succeeded in offering a logically rational interpretation of QM effects, carrying out Einstein's hope. The latest installment, the Transactional Interpretation of QM, is also an extension of Einstein's deterministic and logical program, only this time picking up from Feynman's projected agenda. Thus: Einstein > Bohm > Feynman > Cramer > Mead. Offering the best and most scientifically cogent interpretation of QM yet conceived. Mead carried off Feynman's hope of formulating QED without using Maxwell's Equations at all! (and he succeeded where Feynman failed) The final result is Collective Electrodynamics, a short but awesome feat. 


#24
Sep905, 07:09 AM

P: 416

In a more thecnical side, still nobody has shown like probabilities of QM arises from an underliyng phylosophical deterministic evolution. The best example of that Bohm mechanics is not complete or consistent is that there is dozens of different versions of it. E.g. Hilley version of Bohm (Broglie/Bohm) emphasizes that quantum potential is the key, whereas the Dürr School (named Bohmian mechanics) regards the guidance condition as the fundamental equation and avoids the quantum potential. You are confounding causality with determinism. Bohm offered a posibility which was studied but is rather discredited today. There is not logical rationality on Bohm theory. In fact, is more "weird" that usual QM claiming for misterious effects that are hidden and cannot be observed (even in principle). The idea that Bohm theory is carrying out Einstein's hope is complete nonsense. Einstein claimed for a complete determinism based in observable reality. Einsten waited reduce QM to classical physics. Einstein said about Bohm mechanics 


#25
Sep1005, 03:17 AM

P: 1,295

Bohm's theory is much more concrete then standard QM, since it speaks of particles as having trajectories. 


#26
Sep1005, 03:19 AM

P: 576

You really really have to stretch the concept of wave function to call it a hidden variable.



#27
Sep1005, 08:41 AM

P: 416

Of course, Bohm theory is not more concrete than standard QM. This is the reason that is not standard :) In fact, it is so "weird" that only a "dozen of" people follows it. But if you do not understand standard QM, how can you understand Bohm theory? The trajectories of Bohm theory are not real trajectories like in classical mechanics, therefore the supposed "rationality" is lost. Moreover, that trajectories are unobserved. Therefore, if existence is purely a philosophical isssssssssssssuuuuuuueeeeee. That even ignoring that Bohm theory is less useful, consistent, and predictive that standard approach. Even Einstein who rejected QM and loved classical physics rejected Bohm theory 


#28
Sep1005, 03:41 PM

P: 1,295

If you were to read a text on Bohm's theory, you will see that nothing about the trajectories makes them "unobservable in principle", that's totally bogus propaghanda. The only thing which indicates that the trajectories are hidden is one of the traditional postulates of QM: that the wavefunction is the most complete possible description of the system. There is no reason for this, it is postulated. It is just an assumption, and doesn't go anywhere towards proving that Bohmian trajectories are unobservable, QM just assumes there are not. Lets get even more specific. Another postulate of QM is this voodoo: All observations correspond to selfadjoint operators, and the measured quantities correspond to that operator's spectrum of eigenvalues. The problem with this is that it is impossible to construct a time operator in standard QM. In the 1950s Pauli proved that the above postulate is what imposes this limitation. Of course, because Bohm's quantum theory of motion describes particles moving with well defined trajectories, it is relatively straight foward to calculate how much time it takes for various interesting events to occur. It is hoped that one day experimental precision will extend to very short time scales that will allow us to test predictions of Bohm's theory that do not exist in standard QM. Let me repeat myself: Bohm's theory does not involve anything which could be called a "hidden variable". This is a marketing term used by many physicist who do not want to admit that the complexvalued wave function is what is truly hidden from observation. (What we observe are postions, momenta, energy levels and hopefully one day time scales, we certainly don't measure complexvalued wave functions). 


#29
Sep1005, 03:51 PM

Sci Advisor
P: 1,082

There's a lot of really weird stuff in this thread. Planetary orbits? Well, just look in your newspaper for the times of "planetrise" and "planetset", which seem to correspond to reality. These are, of course based on the standard theory of planetary orbits, with, perhaps some perturbations  the data can be found in the ephemeris. And, then there's NASAs various probes which seem to get to where they are going. Crosson, if you have a better theory, lay it on us. For planetary orbits, theory and observation agree nicely. What else do you want?
Bohm to the contrary, QM is the best game in town. Further, it's been around for long enough that many physicists have a very good understanding  for example. lasers, magnetic resonance, optical pumping, and on and on. Bohm has not gotten very far in the physics community because his work, BohmAronof (sp?) as an exception, has not led to any new physics. It's a kluge designed to alleviate philosophical discomfort, rather that confront any empirical situation. It certainly is not Occam friendly. And remember, whether in Newtonian or Einsteinian form, theory gives no clue as to the why of gravitation; who knows the why of electromagnetic fields? There is not a physics theory around that is anything other than descriptive  frankly, some folks claim that classical physics is somehow different in interpretive substance than today's physics. Nothing could be further from the truth. If you are pushing nostalgia for the illusory certainty of past theory, why not go back to the idea of prime mover? Crosson  of course we can measure wave functions, at least up to a phase. We're talking scattering experiments for example. QM will continue to be the best game in town until it fails to explain an experiment or phenomena that it should be able to explain. That's the way science works. Regards, Reilly Atkinson 


#30
Sep1105, 01:33 AM

P: 1,295

My point about orbits was obviously a miss. I am not claiming that copernican/ptolemaic (newtonian really) astronomy does not accurately predict the positions of celestial bodies. I was simply saying that the orbits we imagine the planets to move along cannot be directly observed. Personally I don't give a crap about observation, but if someone attacks the causal (Bohmian) interpretation of QM on the grounds that quantum trajectories are inobservable (the "in principle" part comes from that unfounded assumption of QM that I brought up earlier), then I expect that person to think about which things we discuss in physics are truly observable: the truth is that many are not. Occam says that one should not increase, beyond what is necessary, the number of entities required to explain anything. Bohm's theory does not "increase the number of entities", it simply talks about a particle and a wave associated with the particle (the wave is a generalized Hamilton's statistical function). QM talks about both these things, but in speaks of the particle in a totally inconsistent nonsensical way (as if it teleports around through places it has "no probability of being"). If the particle and its properties do not exist other then when they are measured, what sort of particle is that? Didn't someone accuse me of claiming the empire state building does not exist when we are not looking at it? How ironic that this is the world view of standard QM which I am against. 


#31
Sep1105, 10:00 AM

P: 416

You have no idea of time is. Of course Bohm theory is unnecesary (even if were consistent) for obtain a time operator. Strictly a time superoperator. But are you studied QM some day? do you know what is the Phy> in QM? do you know what is a ray? For you Bohm theory of hidden variables is physical and both QM and planets orbits are hidden variables theories. 


#32
Sep1105, 11:58 AM

P: 1,295

This is my last response to you Juan, because you are an internet troll. You responded to my points with various and that is not enough a discussion to be worth my time.
You seem hung up on the idea that I don't understand basic QM, and even after I try to move on beyond that disgusting obstacle to our discussion, you make a cocky remark like "simple to say" and repeat your groundless accusations. I feel totally disrespected by you, I don't feel that you have read or thought about what I have had to say at all. Here is one of your false characterizations of my point: 


#33
Sep1205, 07:01 AM

P: 416

About "realism" of Bohm mechanics, it is interesting how you omit reference i cited where Bohm mechanics has been experimentally discredited. It is also interesting like you ignore the rest of my arguments and quotes, including Einstein rejection of it. In short, Bohm mechanics is 


#34
Sep1205, 09:39 AM

P: 1,737

Hi Crosson. You posted way back on page one:
Any comments on this? 


#35
Sep1205, 12:14 PM

P: 1,295

After the discovery of chaos in relatively simple nonlinear systems, it is generally agreed that humans will NEVER be able to predict the future Ustate because our measurements only have finite precision, and we only have finite time to calculate. This does not rule out the idea that the universe is deterministic, as in Feynman's famous quote: "The universe integrates empirically", but it absolutely rules out our ability to make even short term weather predictions. 


#36
Sep1205, 03:47 PM

Sci Advisor
P: 1,082

The QM you discuss, and the QM I've known and worked with for many years appear to be rather different. Particles exist only when observed? (David Hume could make a case for that position.) Nope. Most of us do not believe that, as amatter of pragmatism. You totally misstate the "world view of standard QM", and vastly overstate the importance of the arguments about interpretation. Daytoday physics works with a pragmatic BornBohr interpretation, and most physicists are involved in daytoday. It's pretty basic to assume the real objective world exists. And daytoday physics makes the same assumption. I never got back to Bohm because I found high energy theory much more interesting and challenging. (But, of course, I will admit a bias toward observation, which might disqualify my intellectual seriousness.) What in the world do you mean by teleportation? Why does QM upset you so much? The fact that we can participate in this forum is totally based on QM  as in semiconductors,. Have you actually taken a graduate level QM course? Are you aware that with the use of wave packets, trajectories can be defined loosely?  a staple of formal scattering theory. If you wish to cling to your ideas about QM, then if you want to be taken seriously, you will have to cite chapter and verse, rather than handwaving and indignation, about what you consider to be the inadequacies of QM, and give strong support based on observations and or mathematics. But if you really don't give a crap about observations, then as I said above, you are not doing nor talking about physics. Regards, Reilly Atkinson PS By the way, Locrian, your definition of determinism is exactly the one used in physics. Philosophy might well talk a different talk. 


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