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Author Topic: Why are scientists so sure that the light barrier is impenetrable?  (Read 11217 times)

Offline Good Elf

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Hi diverjohn and JP,

It is nice seeing interest in these matters... diverjohn is new to this thread so I will make a short comment here...
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Another thought about exceeding the speed of light: if it were possible, how would we worry about the acceleration to and from such velocities?
Quantum physics (more specifically... Quantum Electrodynamics) is concerned with events when the wavefunction collapses. The property of velocity is concerned with classical "paths". Acceleration is a classical phenomenon where a particle (with undeniable classical properties) under continuous observation is observed undergoing instantaneous changes in velocity. This incremental "classical" process of acceleration could never enable one to reach or exceed the speed of light. Some other way must be found to achieve any particle relocation in space.

If quantum physics was in anyway a description of "path"... electrons in atoms would "spiral" into the nucleus radiating energy as it goes... this just does not happen. However quantum wavefunctions do not deal with "paths" and is an entirely different physics dealing with "stationary states" of matter waves so it does not specifically need to worry about "speed" or "velocity"... they involve "quantum jumps".
 

Offline JP

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Good Elf,

You may be finished debating quantum mechanics with me, but if you're going to consistently misrepresent it to others, I'm going to reply.  I understand and agree that there is a distinction between quantum properties and classical properties, but your claims that quantum systems are completely undetermined until you measure them is misleading. 

An example of this is what is called an eigenstate in quantum mechanics.  This is just a fancy word saying that the wave function describing the particle has a definite value of some observable.  For example, if an electron is in an energy eigenstate, then it has a definite energy value.
 

Offline Good Elf

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Hi JP, diverjohn, yor_on and all,

Quote from: JP
You may be finished debating quantum mechanics with me, but if you're going to consistently misrepresent it to others, I'm going to reply.
Fine... but please do your research and get your facts as correct as it is known and not just out of elementary texts and their simplified interpretations. I am willing to debate the issue with you but you really must do more work instead of making interpretations based on simplified theories of mechanics because I do not want to repeat myself endlessly if I am not getting across. You got to know to change the way you deal with these issues when speaking about the quantum state.

Quote from: JP
An example of this is what is called an eigenstate in quantum mechanics.  This is just a fancy word saying that the wave function describing the particle has a definite value of some observable.  For example, if an electron is in an energy eigenstate, then it has a definite energy value.
No it does not... wavefunctions are not used to define observables... they describe probability densities. You are sort of suggesting that we have some kind of "probability meter" whereby we are able to "measure" probability... sorry to disappoint... no such device exists.

Regarding atoms and the electron "shells"... There "may" be a definite value for the energy of certain stationary states but what we measure are only the transitions when atoms change state and either emit or absorb photons or electrons. The eigenstates are calculations of the wavefunction and there are no satisfactory explanations of these as classical measurements, they certainly do not satisfactorily address the theoretical problems with simplified models like the "Bohr Atom" for instance. I do not deny that it is possible to determine many things using classical methods of measurement or even calculation but that approach does not address the issues at the base of quantum behavior. Please accept that you need to have a "paradigm shift" to gain a more mature insight into quantum processes. Issues regarding the nature of this stationary state are still unresolved and are still currently satisfied by postulates assuming this "fact"... "a priori". Quantum processes are something that occurs all through all phenomena at this fundamental level and should not be thought of as only a function of atomic transitions. It is also more generally about light and it interactions with matter through electrons. The best way to understand this phenomenon is to read Richard Feynman's Book on Quantum Electrodynamics... "QED - The strange theory of light and matter".. In it all phenomenon at the level of electrons and photons are explained pretty clearly at a simple level... This is still the most accurate theory to describe mostly all known phenomenon. The behavior of atoms is described "loosely" in chapter 3. His approach is pretty casual so you should not expect too much. As a primer to the more general application of these ideas at a elementary level have a look at this short paper...
"Teaching Feynman's Sum Over Paths Quantum Theory" Edwin F. Taylor, Stamatis Vokos, John M. O'Meara, and Nora S. Thornber Computers in Physics, Vol 12, No. 2, Mar/Apr 1998, pages 190 thru 199 [nofollow]

The energy of any system is subject to arbitrary baselines which are defined relative to known repeatable baselines such as the 1S0 lowest energy state for the first bound electron. This is not zero energy.  Between transitions when the electron is in a stable eigenstates there is absolutely nothing to be actually measured. There are no direct measurements of this "level" but only it's relative position in relation to the other levels. "Presumably" electrons and the photons are in superposition with all the other eigenstates possible in the system. At room temperature atoms are mostly "classical" objects forming molecules and allowing us to understand the properties of the outer shells through their chemistry but what makes them very interesting to me is their quantum behavior not this overt "classical behavior".

I would also point out that the theory of atomic orbitals is not entirely soluble being a many body problem. Perturbation Theory does not lead to the "stationary states" but the same old problems classical theory has always been prone to in trying to describe this behavior. All that exists are classical approximations for the systems with multiple electrons simply because this is not the accurate way to solve this problem. The idea that electrons simply "whiz" around the nucleus along spiral paths cannot be maintained.

Cheers
 

Offline JP

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Hi JP, diverjohn, yor_on and all,

Quote from: JP
You may be finished debating quantum mechanics with me, but if you're going to consistently misrepresent it to others, I'm going to reply.
Fine... but please do your research and get your facts as correct as it is known and not just out of elementary texts and their simplified interpretations. I am willing to debate the issue with you but you really must do more work instead of making interpretations based on simplified theories of mechanics because I do not want to repeat myself endlessly if I am not getting across. You got to know to change the way you deal with these issues when speaking about the quantum state.

You're getting your point across.  It's just that the points you're making aren't representative of the mainstream theory of quantum mechanics.  Maybe it's a misunderstanding of language.  Just because physicists say that something is undetermined until they measure it in quantum mechanics doesn't mean that they have zero information about the quantum state before measurement. 

As for textbooks, here are two that I've used that come to mind: Principles of quantum mechanics and Advanced quantum mechanics
 

Offline Good Elf

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Hi JP,

Your books are 1994 vintage. I do not accept that a blanket quote from a large literary work of 650 pages is any form of scholarship. Quite a bit has happened over the intervening years regarding the interpretation of QM. Some bits will still be good but others may become very dated nowadays. I quote papers which are more or less current theory. Try this, along with the other references I have supplied, for a more modern approach to the interpretation...
Heisenberg, Matrix Mechanics, and the Uncertainty Principle - S. Lakshmibala [nofollow] Check out the section on Matrix Mechanics...
Quote from: S. Lakshmibala
We now face an interesting situation. Recall that, by performing an appropriate measurement on the system, we know the state of the system just after the measurement. Was this the state of the system before the measurement? Not necessarily! For, prior to the measurement, the system could have been in a linear superposition of different eigenstates, with unknown (and unguessable) coefficients. It is like saying that in a coin toss experiment whose outcome is a “head”, the coin could have been in a state which was a combination of head and tail before it was tossed! Of course, this would never be the case for actual coins, governed as they are by the laws of classical physics. But then, what was the precise state of the quantum system before the measurement? The answer is: we cannot know. The Copenhagen interpretation is concerned only with outcomes of experiments. Deep philosophical questions, peculiar to quantum mechanics, now arise (Box 4).
My inference is if we as an observer "cannot know" then this same information is also withheld from the universe at large because information at this level is quantized and is not "duplicated" elsewhere. Ultimately this information is transferred to a de facto measuring system while dephasing acting with quantized action and energy transfers...then read Box 4.
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Box 4. Is quantum mechanics complete?
If we can never know the pre-measurement state of a system, is not the theory inadequate, or at least incomplete? For, after all, the system surely has an existence of its own, independent of the act of measurement! (This question is also applicable to wave mechanics, for it too cannot predict the pre-measurement state.) Numerous proposals, including a variety of so-called hidden variable theories, have been made to overcome this inadequacy, but none of these is fully satisfactory. The last word has probably not been said yet in this regard.
The next experimental point to address is the recent experiments which test the validity of Hardy's Paradox [nofollow] (check out the 5th reference for a recent definitive experiment revealing the problem). The Copenhagen Interpretation of this experiment is clearly not correct and leads to "counter-factual results". The meaning of this is in how probability evolves in quantum states... It is possible to have negative values of probability. Negative values of probability are discussed in part here [nofollow]. This appears to be a couple of ways in which this paradox may be resolved (not including a strict Copenhagen Interpretation). A paper that addresses this conundrum can be found here...
Hardy's Setup and Elements of Reality - Louis Marchildon (Submitted on 17 Feb 2009 (v1), last revised 23 Jul 2009 (this version, v2)) [nofollow]
The actual measurement "chooses" the output state. The physical existence before the final measurement is undefined and cannot be resolved using local hidden variables but may be resolved with non-local hidden variables but what this means is not defined (perhaps to do with global values in the external Universe as a whole... perhaps referring to remote entanglement connections as would be the case with Cramer's (Wheeler-Feynman) QM Interpretation. This means no "real valued" local measurables. If some "real" value existed before this state collapse measurement was made it should have had a real positive probability and not a negative value (which is what was found through a partial protective measurement as in the experiment). One conclusion is the "real" value did not exist until the measurement was performed. I take this to mean the "real" value is only determined by the measurement when the wavefunction collapses. Before then the value of a measurable has "no element of reality".
 

Offline JimBob

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I continue to be amazed that a limnologist can take to task a post-doctorate physicist (from one of the most highly regarded schools of physics in the world) for having incorrect ideas in physic when that person is obviously the one who will hold a chair in physics in his old age, while the limnologist, should he survive the waters of Queensland, will still be trying to get grants to count the number of bugs from a canoe. But then, perhaps I have the wrong person and shudder - the actual person is in the field of geology. I am ashamed of my profession if so.

Just who has the training and eduction to most likely have the right answers to the questions being discussed? Did my intro help?

As I tell my students, don't throw a book out. It could be the one that sets the foundation for you future. After all the idiots get through mucking up the subject into an incoherent mess because of the pressure to publish, and publish data that isn't well edited, the roof collapse and that 1994 book that explained in simple literary terms the mystery of quantum mechanics the limnologist so quickly dismissed for pressurr-published quackery will be the source book for a new science based on the ideas it contained. The smart survivor creeps back to seminal 1994 book and start over with the correct assumption. I believe those who threw away William Smith's 1815 Book on The stratification in the canals of England did a bit of backtracking in this manner as newer forces in sciences realized that he had pioneered a completely new field of science. In 1836 William Smith was porclaimed "The Father of English Geology" and was conferred a Doctorate of Laws (LL.D.) from Trinity College, Dublin, for his "Simpleton Work"  Perhaps not as seminal a work as Mr. Smith's, the 1994 book -so recently trashed - can still teach a young non-physicist the value of humility.

The posts of the disaffected dwarf seems an exercise in hubris - the Greeks had this type of behavior well spotted and exceedingly well named. Yet the Greeks were more educated than the a-for-said dwarfed creature of small stature. The Grreks did not find it necessary to vilify, and ascribe habits of ill character to ones verbal sparing partner. The Greeks believed the winner was the one whitch presented the best argument, not the most viscous personal castigations. The winner used his brain, not his power to insult.

I would hope The Good Fairy would re-read the acceptable use policy agreed to when asking for the privilege of posting to the site. Part of that policy prohibits personal attacks.

Any such attack and the elf bites the dust - or is sent to a dwarf as a mining slave. (HEAD THE WORDS OF THE MODERATOR!! ME! The Hornytoaded One) We tolerate fools little here, especially fools that violate the rules. These get hung, drawn, quartered, displayed at the city gates, then banned.

Just so all people know where the rules are - here is the link: http://www.thenakedscientists.com/forum/index.php?topic=8535.0

(I can't speel. Never have been able to. No one hires me a secretary any more!)
« Last Edit: 24/04/2010 17:34:39 by JimBob »
 

Offline JP

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Your books are 1994 vintage. I do not accept that a blanket quote from a large literary work of 650 pages is any form of scholarship. Quite a bit has happened over the intervening years regarding the interpretation of QM.

Quite a bit has happened on the frontiers of quantum field theory and speculative theories like string theory as well as in experimental quantum mechanics.  The postulates of quantum mechanics haven't changed in the past 16 years.  I provided those links to show you that I have actually studied quantum mechanics since rather than debate the science, you seem happier to point out that I haven't done any work to learn the theory.  I have.  But we shouldn't be debating my credentials, we should be talking about the science involved.  

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Try this, along with the other references I have supplied, for a more modern approach to the interpretation...
Heisenberg, Matrix Mechanics, and the Uncertainty Principle - S. Lakshmibala Check out the section on Matrix Mechanics...
I know the matrix formulation of quantum mechanics.  It's used in the sources I cited.  It doesn't support what you're saying.   The paper you cite isn't anything new.  It's a review (for teaching purposes) of existing (vintage 1920s) techniques.  

As for Hardy's paradox, I'm not as familiar with that.  Looking it over briefly, it seems to have nothing to do with the main point of our argument, as it arises from standard quantum mechanics.  Your claims about quantum mechanics are well outside the bounds

Finally, pages 115-118 Principles of quantum mechanics give the basics of eigenstates.
 

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