Interpritations of Quantum Mechanics

[Alem2000]

Hello ppl. I was wondering how many different interpritations of quantum mechanics there are? I was told there was one called the "many worlds" interpretation. What other ones are there and what do they mean...and what does this one really mean. I wanted to ask this in this Quantum physics forum b/c I was hoping there are ppl that know quantum mechanics very well here.

 

[Alem2000]

MAN! Is this a hard, stupid, or just ignorant question? NO one seems to be replying...whats up with that?

 

[turin]

Alem2000,
I don't think most people hang out here all day on saturday. My experience is that you need to give the post, on average, about a day to get a satisfactory response. Your question is not at all stupid. You have heard something about QM and you are hungry for more info, clarification, and such. That is exactly what most serious posters around like, I think.

I'll get you started, but I'm sure you will get a lot better post from some of the others.

I've found the Schroedinger picture with the Copenhagen interpretation to be the paradigm for traditional physics instruction. What this means is that the Schroedinger equation is taken for granted, that the wave function is the physical thing that undergoes dynamics and operators simply do the telling, and that it doesn't even make sense to consider the wave function's effect on anything else without collapsing.

There is also the Bohm-deBroglie interpretation that says there is actually a little dot flying around, but, since it is so tiny, the effects of its wave come into play. The dot itself only goes through one slit of the two-slit experiment, for example, but the wave is difracted so that the dot still seems to follow a wave-like behavior.

The many worlds interpretation is also known as the Everett interpretation (or something like that). I don't know too much about it.

 

[Olias]

Hello ppl. I was wondering how many different interpritations of quantum mechanics there are? I was told there was one called the "many worlds" interpretation. What other ones are there and what do they mean...and what does this one really mean. I wanted to ask this in this Quantum physics forum b/c I was hoping there are ppl that know quantum mechanics very well here.

Well let's take something from Relativity and ask how QM deals with the same thing?..In Relativity, "Acceleration and Gravity" give out the same effect for something in freefall, they are termed as being Equivilent.

How does QM deal with the same effects?.in QM what is Gravity and what is Acceleration.

 

[selfAdjoint]

QM does not deal with gravity. The reason often given is that gravity is a much weaker forces than the ones dealt with in quantum physics: the electromagnetic force, the weak force that is responsible for radioactivity, and the strong force that holds the nucleus together.

Acceleration, as rate of change of speed, is treated in QM, although physicists usually prefer to work with rate of change of momentum.

I see your point about acceleraation and gravity in relativity (I assume you mean general relativity), but as it could give some confusion to others I'll restate it: it is impossible to tell (locally) whether a given acceleration is due to an imposed force or to gravity.

 

[Olias]

QM does not deal with gravity. The reason often given is that gravity is a much weaker forces than the ones dealt with in quantum physics: the electromagnetic force, the weak force that is responsible for radioactivity, and the strong force that holds the nucleus together.

Acceleration, as rate of change of speed, is treated in QM, although physicists usually prefer to work with rate of change of momentum.

I see your point about acceleraation and gravity in relativity (I assume you mean general relativity), but as it could give some confusion to others I'll restate it: it is impossible to tell (locally) whether a given acceleration is due to an imposed force or to gravity.

Thanks for the clarity SelfAdjoint. My post was meant to instigate thought into the process involved, and how there exists a Macro Force with definate paramiters in GR, and as one approaches the Quantum Domain the Force and effects are reduces to non definate paramiters for local events.

Is it possible to define (locally) whether a given momentum is produced by a Macro or Micro force?..interesting!

 

[meteor]

There are also the collapse theories, this approach is also called Dynamical reduction program. These theories modify the Schroedinger equation, adding to it stochastic and nonlinear terms. Seems that these theories are also able to explain why macroscopic objects exhibit definite characteristics, while microscopic objects do not.

 

[slyboy]

A not-so-short list of interpretations of QM
-----------------------------------------

There are almost as many intepretations of QM as there are physicists/philosophers who work on the foundations of the theory. I have developed my own classification, which is bond to be slightly controversial because not everyone will agree that it is correct. I have also indicated a few names associated with the interpretations. A quick google should get you some more info on them. Note, the list is far from complete.

The classification:
-----------------

Conservative: Takes the standard formalism of QM without modification and seeks to find a language to talk about it that avoids all the paradoxes and conceptual difficulties. Although conservative in that it doesn't do any damage to the maths of QM, it is likely to be radical from a philosophical point of view (so perhaps conservative is not the best word in this sense).

Realist: Takes something in the QM formalism to represent things that really exist in the world. Usual choices are things like position of particles or the wavefunction itself.

Partial-realist: Sometimes takes something in the QM formalism to represent things that really exist, but there are some extra rules that must be satisfied for this to be the case.

Beyond QM: These are really different theories rather than interpretations because they make some predictions that differ from QM. These predictions are likely to be in areas of the theory that have not been adequately tested as of yet.

The list:
--------

Consistent Histories/Decoherent Histories (Conservative, Partial-Realist)
Griffith, Omnes, Gellman, Hartle

Conciousness based (Conservative)
Wigner

Copenhagen (Conservative)
Bohr, Heisenberg et. al.

de-Broglie Bohm (Realist, can be beyond QM if you generalize the allowed initial probability densities)
de-Broglie, Bohm, Valentini, people from southern Europe (for some reason)

Decoherence solves everything (Conservative)
Zurek

Everett Relative State Interpretation (Conservative)
Everett, Wallace

Everything is Information (Conservative)
Wheeler, Fuchs, Zeilinger

Ithica Interpretation (Conservative)
Mermin

Many-worlds (Conservative)
Deutsch, Vaidman (maybe Everett and Wallace depending on your reading)

Modal (Conservative, Partial-Realist)
Mainly philosophers: Bub, Clifton et. al.

Orthodox (Axiomatic) QM (Conservative)
von Neumann

Quantum Logic Interpretations (Conservative, Partial-Realist)
Putnam

Relational Interpretations (Conservative)
Rovelli

The Shut-Up-and-Calculate Interpreatiaion (also known as FAPP) (Conservative)
Most of the physics community

Spontaneous Collapse models, e.g. GRW theory (Realist, Beyond QM)
Gihradi, Rimini, Weber, Pearle

Transactional Interpreatation (Conservative)
Cramer (see also Huw Price)

 

[jnorman]

"The Shut-Up-and-Calculate Interpreatiaion " - certainly this is the most prevalent in normal physics curricula across the nation.

copenhagen seems to still be the preferred general interpretation for theoretical physics, though interpretation in itself is hotly debated everwhere all the time. i still cling to the concept that the simplest explanation is usually the best, and while there isn't any particluar way to "understand" CI logically, it still strikes me as fundamentally the most sound and accurate.

 

[slyboy]

copenhagen seems to still be the preferred general interpretation for theoretical physics, though interpretation in itself is hotly debated everwhere all the time. i still cling to the concept that the simplest explanation is usually the best, and while there isn't any particluar way to "understand" CI logically, it still strikes me as fundamentally the most sound and accurate.

I disagree. Hardly any theoretical physicists subscribe to the Copenhagen interpretation and those that do usually misunderstand what it means. This is not too surprising because it is difficult to find a clear statement of what Niels Bohr's interpretation actually was.

Most physicists believe that QM applies equally well to all systems in the universe, including the whole universe itself. This goes directly against the grain of Copenhagen, which postulates that there must always be a "classical" component of any system, although it is deliberately vague on where this cut between classical and quantum should be placed. In fact, Heisenberg argued that the cut may be placed anywhere that is convenient for describing a particular experiment, but that such a cut must be placed somewhere. Thus, Copenhagen has no place for a "wavefunction of the universe" unless there is somewhere outside of the universe from which to observe it, which is basically a contradiction.

Note also that "textbook quantum mechanics" does not usually give the Copenhagen interpretation. It is actually much closer to von-Neuman's approach.

I think there is no way that the Copenhagen (mis)interpretation should be taken seriously today. Issues from the foundations of QM are becoming of practiacal importance for quantum computing and quantum communication. Also, quantum gravity is difficult to construct partly because we don't have a clear answer to the problems of quantum theory. Thus, the interpretation of QM is no longer a problem with no practical consequences for physics.

 

[jnorman]

in that there are only two basic tenets of CI (there is no underlying reality, and observation creates reality), i don't know exactly what you are finding there to disparage as a "(mis)interpretation." it was early detractors, such as einstein, who calimed there must be a classical component, not bohr and the solvay congress, though Bohr and Heisenberg never totally agreed on how to understand the mathematical formalism of quantum mechanics. and i certainly don't think you can support the comment that it should not be, or isn't taken seriously today, or that it somehow limits research on quantum computing or communication. eric weisstein writes "In the years since its formulation, it (CI) has come to be regarded by many as the "standard" philosophical interpretation of quantum mechanics." even the wikipedia states "The Copenhagen interpretation is the mainstream interpretation of quantum mechanics." quantum gravity is a myth.

 

[slyboy]

in that there are only two basic tenets of CI (there is no underlying reality, and observation creates reality), i don't know exactly what you are finding there to disparage as a "(mis)interpretation." it was early detractors, such as einstein, who calimed there must be a classical component, not bohr

You are confusing two different meanings of "classical component". Einstein thought that the QM formalism was incomplete in that there should be some underlying reality to which the probabilities predicted by QM refer. You might call this reality a "classical component".

Bohr certainly did not believe this, but he did believe that classical concepts were necessary to describe quantum experiments themselves, i.e. the description of the experimental setup and the fact that a particular outcome is obtained is necessarily described in terms of our everyday classical experience.

It is also far from clear that there are only two basic tenents of CI. In fact, each physicist who supposedly subscribed to CI had a different reading of the interpretation. This seems to apply equally well today. One of my reasons for rejecting Copenhagen is this vagueness. Perhaps you should look at http://plato.stanford.edu/entries/qm-copenhagen/

and the solvay congress

Hmm, I think it would be wrong to attriute the Copenhagen Interpretation to the Solvay Congress. This was a meeting of most of the leading physicists of the day, including Einstein, and it is far from clear that the majority subscribed to Bohr or Heisenberg's interpretation of the theory.

and i certainly don't think you can support the comment that it should not be, or isn't taken seriously today

To support the "isn't" part, here are the results from an informal poll of physicists taken by Tegmark in 1999 (http://xxx.soton.ac.uk/abs/quant-ph/0101077 ).

1. Do you believe that new physics violating the Schroedinger equation will make large quantum computers impossible? 1 yes, 71 no, 24 undecided

2. Do you believe that all isolated systems obey the Schroedinger equation (evolve unitarily)? 59 yes, 6 no, 31 undecided

3. Which interpretation of quantum mechanics is closest to your own?

(a) Copenhagen or consistent histories (including postulate of explicit collapse): 4

(b) Modified dynamics (Schroedinger equation modified to give explicit collapse): 4

(c) Many worlds/consistent histories (no collapse): 30

(d) Bohm (an ontological interpretation where an auxilliary "pilot wave" allows particles to have well-defined positions and velocities): 2

(e) None of the above/undecided: 50

For the "should not be" part, I have to admit that it depends on what you mean by the Copenhagen Interpretation. If you mean some sort of interpretation that is operational in nature, i.e. makes no claims to an underlying reality beyond the probabilities predicted by QM, then I think that good arguments can be made for taking it seriously. However, if you mean the explicit positions of Bohr, Heisenberg or other Copenhagenish pioneers of quantum theory, then I do not think they are appropriate for modern physics.

eric weisstein writes "In the years since its formulation, it (CI) has come to be regarded by many as the "standard" philosophical interpretation of quantum mechanics." even the wikipedia states "The Copenhagen interpretation is the mainstream interpretation of quantum mechanics."

I don't think either of these sources are definitive authorities on the subject.

quantum gravity is a myth.

I agree that current theories of quantum gravity are likely to be wrong. In my view, this is because we need to sort out the foundations of quantum theory before the correct path becomes clear. However, that is probably a minority opinion amongst physicists.

What exactly do you mean by "quantum gravity is a myth"? Do you think that a reconcilliation of the two most important theories in physics is impossible? Do you think that there can be no physical theory that accurately describes the early universe at times when both gravity and quantum mechanical effects are equally important? If so, then I would like to know how you can support this position.

 

[jnorman]

"I don't think either of these sources are definitive authorities on the subject." no duh. and no argument about that, but it does point out that for general acceptance, i don't think you can wholesale ignore it as a foundation from which to begin understanding its implications.

i personally have never been impressed by the many worlds interpretation - it just seems so ludicrous, specious, and irrelevant, especially in light of how mind-numbingly incomprehensible observable reality already is. just because an interpretation is "allowed" via certain solutions to equations does not mean that they are reasonable or logically feasible. i also cannot buy into bohm's semi-pilot wave ontological morass - his book, wholeness and the implicate order, was a difficult read at best, and i could not agree with many of his lines of thought - though i admit he is an outstanding thinker. modified dynamics does not seem to offer anything new or valuable, IMHO. which only leaves CI and "undecided" - i can greatly support "undecided" as a safe position :-)

"Do you think that a reconcilliation of the two most important theories in physics is impossible?" hmmm - tough question. surely the extrapolation of energy curves indicates unification of forces, including gravity, at extreme levels may be reasonable. however, quantum mechanics does not appear reconcilable with GR at any fundamental level that i am able to grasp. my long suffering issues with GR lead me to think the whole idea of particles is a primary misconception as entities unto themselves (ie that have some specific reality), and that the solution will only come with a far deeper understanding of fields and their interactions. i know this is contrary to the standard model, which serves us so well for real-world applications, but for an overarching GUT, it may be that we will need to build it on a foundation of field theory, rather than particle/quantum basis. it seems far too common for theorists to speak of particles and fields as separate aspects, even though we are all taught early on that particles are merely the manifestation of fields. this is supported by the simple understanding that as you delve down into the makeup of any particle, you at some point recognize that there is no "thing" there - leptons are point particles, they occupy no volume - what is that? baryons are made up of quarks, which are point particles. the concepts of virtual photons and gluons, and the near-complete non-understanding of the nature of force-carriers in general, do not fit into any frame of comprehension, and as competing theories, do not come anywhere near the elegance and beauty provided by GR. field theory is where it is at. ooops, i am starting to reveal some of my personal bias... you must keep in mind that i am just an old hack who long ago admitted that i shall forever remain confused about the nature of reality. OTOH, it is with great pity that i regard the vast number of humans who never even learn enough to realize how incomprehensible reality actually is - "it is not only stranger than we conceive, it is stranger than we CAN conceive..."

 

[slyboy]

i personally have never been impressed by the many worlds interpretation - it just seems so ludicrous, specious, and irrelevant, especially in light of how mind-numbingly incomprehensible observable reality already is. just because an interpretation is "allowed" via certain solutions to equations does not mean that they are reasonable or logically feasible. i also cannot buy into bohm's semi-pilot wave ontological morass - his book, wholeness and the implicate order, was a difficult read at best, and i could not agree with many of his lines of thought - though i admit he is an outstanding thinker. modified dynamics does not seem to offer anything new or valuable, IMHO. which only leaves CI and "undecided" - i can greatly support "undecided" as a safe position :-)

I couldn't agree more with you about the many-worlds interpretation. It seems to be fairly contentless and to offer little insight into the real problems, since many-worlds would also be "allowed" by classical physics. I also agree that "undecided" is probably the safest position.

However, the options available in the poll do not represent the only possible choices and they are colored by Tegmark's own opinion on the subject. My personal view is that quantum states should be regarded as states of knowledge/information/belief (pick your favourite). This raises the question of what they are states of knowledge about. I haven't discounted the posibility that they are about what might be called "hidden variables", but not of the Bohmian sort. I do not like the guidance role that the wavefunction plays in that theory. I would also prefer the "hidden variables" to respect more of the symmetry that is present in quantum theory, i.e. not to pick out position as a special variable and not to have a preferred reference frame. I am open to the idea that the "hidden variables" might not have a naive realist interpretation, which is why I have put them in quotes.

If such an interpretation proves to be impossible, then I would retreat to the position that quantum states represent knowledge about our possible interventions in the world, which has a much more Copenhagenish flavour.

My own opinion on quantum gravity is that we probably have to go beyond both quantum theory and general relativity. It should probably be based on some sort of discrete structure, in order to have a minimum length scale. However, I don't think it is a good idea to take a discrete structure and then simply attach a Hilbert space to it and say that you then have a quantum theory. Many approaches seem to be basically doing this and it always seems fairly arbitrary to me. Hopefully, investigations into quantum foundations will eventually reveal a better account of what it means to be "quantum" than this.

 

[ZapperZ]

However, the options available in the poll do not represent the only possible choices and they are colored by Tegmark's own opinion on the subject. My personal view is that quantum states should be regarded as states of knowledge/information/belief (pick your favourite). This raises the question of what they are states of knowledge about. I haven't discounted the posibility that they are about what might be called "hidden variables", but not of the Bohmian sort.

We need to be a bit more careful in adopting this view of "states" in QM. If we consider them to be just as what you said, i.e. the state of OUR knowledge of the system (i.e. it is not actually a direct representation of the actual system), then QM is nothing more than ordinary, classical statistical probability. It would be equivalent to saying that we assign the probability of 1/2 in getting a head or a tail when tossing a coin, not because of the inherent randomness in the process, but rather because of our ignorance of the intricate details of the dynamics. But is this really an accurate depiction of QM also?

I used to believe that line of thought until I looked even closer to what exactly can be see that is a direct manifestation of "non-classical, non-statistical" effects of QM. Superposition of states is the clearest example. Is this merely a reflection of our ignorance of the system, or is the system REALLY in a simultaneous combination of states. I would say that there are ample evidence of the latter being the true case. Example: the existence of an energy gap between bonding and antibonding states of H2 molecule. An electron is REALLY spreading itself over BOTH H atom site simultaneously (i.e. the schrodinger cat IS really both dead AND alive), even though upon measurement, it assumes a definite postion. Now you would never see such unusual effects in classical statistics that merely reflect our ignorance or knowledge of the system.

Zz.

 

[selfAdjoint]

But doesn't "reallly" become problematical itself in QM? Some physicists don't believe virtual particles "really" exist, although like your molecular consequences of superposition, they may have "real" effects.

 

[ZapperZ]

But doesn't "reallly" become problematical itself in QM? Some physicists don't believe virtual particles "really" exist, although like your molecular consequences of superposition, they may have "real" effects.

I used the word "really" in the pedestrian sense, not in any deep, philosophical connotation. I hate to think that this string would deterorate into a discussion of the meaning of the word "real".

If you think carefully, ALL of what you accept to be "real" are based on EFFECTS, and the manifestation of the various properties of the "real stuff" via those effects. So to differentiate between "real" and "real effects" is rather strange from my perpespective. I've seen such arguments being used to argue that "electrons" aren't "real".

Zz.

 

[sol2]

Predictive outcomes in a three particle entanglement?

(abc +a'b'c')

That's real :)

 

[slyboy]

Coming from a quantum information makes viewing quantum states as states of knowledge an attractive position for me. It seems to make some of the quantum information protocols slightly less mysterious than if you take the quantum state to be a state of reality. In my opinion, the two best arguments for this position from a modern perspective are:

http://xxx.arxiv.org/abs/quant-ph/0205039
http://xxx.arxiv.org/abs/quant-ph/0401052

There are some key differences between the points of view in these papers and, in particular, the first takes the quantum state to be far more subjective than the second. The second paper is closer to my view onthe subject.

 

[sol2]

Coming from a quantum information makes viewing quantum states as states of knowledge an attractive position for me. It seems to make some of the quantum information protocols slightly less mysterious than if you take the quantum state to be a state of reality. In my opinion, the two best arguments for this position from a modern perspective are:

http://xxx.arxiv.org/abs/quant-ph/0205039
http://xxx.arxiv.org/abs/quant-ph/0401052

There are some key differences between the points of view in these papers and, in particular, the first takes the quantum state to be far more subjective than the second. The second paper is closer to my view onthe subject.

From the issue of "Glast" and the understanding of Quantum Gravity, I am looking for a way in which to describe "geometical realities over a vast distance in space.

One of the ways that I am looking at , putting aside FTL and Vsl characteristics, the issue of high energy photons traveling through space a lot slower then low energy photons. We do understand that the speed of light remains consistent in a absolute vacuum. So for this measure I am looking to the early universe.

Now one of the issue brought up has to do with the interaction with the graviton(theoretcally if such action was to take place how would this action effect the photon) We understand gravity wells may have an effect on the differences of the photon, so if such was the case then, how would you view "entanglement" after the photon has interacted?

Gravitational Lensing :)

Avenues to quantum geometry?

 

[Mike2]

Coming from a quantum information makes viewing quantum states as states of knowledge an attractive position for me. It seems to make some of the quantum information protocols slightly less mysterious than if you take the quantum state to be a state of reality. In my opinion, the two best arguments for this position from a modern perspective are:

http://xxx.arxiv.org/abs/quant-ph/0205039
http://xxx.arxiv.org/abs/quant-ph/0401052

There are some key differences between the points of view in these papers and, in particular, the first takes the quantum state to be far more subjective than the second. The second paper is closer to my view onthe subject.

What is the importance of a quantum state being a choice from many possible states? Is there information gained by the selection of one of the quantum states from the prior existing superpostion of states? Does this somehow balance with the entropy gained in physical processes? Thanks.

 

[Mike2]

What is the importance of a quantum state being a choice from many possible states? Is there information gained by the selection of one of the quantum states from the prior existing superpostion of states? Does this somehow balance with the entropy gained in physical processes? Thanks.

If we start with no information and measure a particular state out of the infinite possibilities of a continuum, then wouldn't that give us an infinite amount of information? How could the entropy of the universe increase if one event could caused an infinite amount of information (infinite negentropy)? So perhaps QM is necessary for entropy.

 

[sol2]

From the issue of "Glast" and the understanding of Quantum Gravity, I am looking for a way in which to describe "geometical realities over a vast distance in space.

One of the ways that I am looking at , putting aside FTL and Vsl characteristics, the issue of high energy photons traveling through space a lot slower then low energy photons. We do understand that the speed of light remains consistent in a absolute vacuum. So for this measure I am looking to the early universe.

Now one of the issue brought up has to do with the interaction with the graviton(theoretcally if such action was to take place how would this action effect the photon) We understand gravity wells may have an effect on the differences of the photon, so if such was the case then, how would you view "entanglement" after the photon has interacted?

From the early universe to now we needed a way in which to talk about the Friedmann equations as well as undertanding the issues of critical density as has been pointed out by Marcus.

Someone mentioned the cloud chamber and about the tracks in regards to dimension, about where the trail begins and ends. Is it not so unlikely that what lies beneath, can still be illucidated upon to help us describe this geometry?

Gravitational Lensing :)

Avenues to quantum geometry?

Looking for a consistent geometical frame work is probably the stuffest thing that I see, and there must be a way in which to gauge this "ordering of geometries."

Looking at the black hole we have gone through a whole history of gravitational conisderations, and know that we have reached a extreme on one level, yet it is also well evident that the early universe held strong gravitational incidences as well, in its expression.

So you know, the geometry at that point is much different then, in what we see of the universe today.

So we look for models that would encapsulate the whole expression of this universe, and if you had understood, "expansion and contraction" in terms of entropic (information) measures how could we not consider the black hole in all its features?

So how much of the universe can we talk about in terms of the black hole? How can such geometry lay out for us the consistancy needed to explain this ordering of geometries?

The first inkling to me came about to me in the pursuate of Heisenberg's collapsing sphere. It wasn't enough just to understand the atom bomb, but to see the dynamics of this realization.

http://www.physics.umd.edu/news/photon/iss026/images/Bosenova.jpg

If such "dynamics" are recognize within context of a cycle in the understanding of the cosmos, how geometrically shall we tackle the enormity of geometrical consisitancy?

http://universe.gsfc.nasa.gov/images/lifecycles/cycles.jpg

We have selected events then out of context of a very dynamcial universe?

So how shall we define this movement? One has to think about this in context of the thread under which we are currently engaged.

Can we not make a basic assumption about the minimum energy of the uncertainty principal?

http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/imgqua/hosc14.gif

We have to accept that the basic Zero point vibration of the Harmonic Oscillator can to speak to the reality of relations of dimensional significance?

How would you do this? IN a weak field measure, matter distinctions recognize the minum energy requirements while. In high energy considerations supergravity speaks to the other end? In between all this...

"http://universe.gsfc.nasa.gov/images/lifecycles/cycles.jpg[/QUOTE]

I added this because I thought the thinking has to change to accomadate this view of continuity in terms of geometrical definition. We still recognize the solidification in these matter distinctions (Our universe now) and the relationship to weak field meausre of gravity, as one end of a spectrum, while in context of the energy, this spectrum is answerable to the basis of harmomic realization ?

How would one answer this, through experimentation?

 

[sol2]

I wanted to add this current expriment to this board for consideration in terms of the Calorimeter

http://glast.gsfc.nasa.gov/images/glast_sa_jan24_03.jpg

The Universe is home to numerous exotic and beautiful phenomena, some of which can generate almost inconceivable amounts of energy. Supermassive black holes, merging neutron stars, streams of hot gas moving close to the speed of light ... these are but a few of the marvels that generate gamma-ray radiation, the most energetic form of radiation, billions of times more energetic than the type of light visible to our eyes. What is happening to produce this much energy? What happens to the surrounding environment near these phenomena? How will studying these energetic objects add to our understanding of the very nature of the Universe and how it behaves?

The Gamma-ray Large Area Space Telescope (GLAST) will open this high-energy world to exploration and help us to answer these questions. With GLAST, astronomers will at long last have a superior tool to study how black holes, notorious for pulling matter in, can accelerate jets of gas outward at fantastic speeds. Physicists will be able to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. And cosmologists will gain valuable information about the birth and early evolution of the Universe.

http://glast.gsfc.nasa.gov/

If we talk about long and short photons, how shall we approach this? Its detailled for us in the way in which this expeirment is set up. I refer to a specific section for consideration, in terms of the tracker module, grid, and calorimeter module.

 

[Mike2]

So we look for models that would encapsulate the whole expression of this universe, and if you had understood, "expansion and contraction" in terms of entropic (information) measures how could we not consider the black hole in all its features?

So how much of the universe can we talk about in terms of the black hole? How can such geometry lay out for us the consistancy needed to explain this ordering of geometries?

The only geometry we can be certain of is the initial singularity. After that we can only consider how the alternative geometries interfered with each other to produce the universe we see. There are no alternatives with a singularity, no other energy levels, no other positions, no other momentums to consider. So the information of the initial singularity is zero. But as soon as the universe starts to expand, we see other places where things can happen. So the expansion is a dissipation, a gain of entropy, and a loss of information. But we gain information by learning where things do happen in this expansion. So does the information content of the universe remain constant? Is this what forces the universe to select out of quantum choices? If so, then you'd expect that the first moments of expansion would be accommpanied by a selection from just a few states. But the more the universe expanded, the more choices would be required to choose from. Is this consistent with any present theory?

Was the energy density of spacetime so great just after the initial singularity that the fabric of space began to tear and small black holes began to appear? They would immediately evaporate and produce other particles.

 

[sol2]

The only geometry we can be certain of is the initial singularity. After that we can only consider how the alternative geometries interfered with each other to produce the universe we see. There are no alternatives with a singularity, no other energy levels, no other positions, no other momentums to consider. So the information of the initial singularity is zero.

How would you explain negative energy? How would you explain the i in Dirac's matrices ( Feynmen understood this in his toy models?).

If it is not undertsood that the size of the black hole can expand(cooling) it will not equally make sense if such a collapse of this black hole could signal fussion. There is a geometrical definiton to it that far exceeds the initial singularity.

If this was cyclical in nature, besides looking at any singularity as part of the many features of this cosmos quantum world, how would you describe it?

But as soon as the universe starts to expand, we see other places where things can happen. So the expansion is a dissipation, a gain of entropy, and a loss of information. But we gain information by learning where things do happen in this expansion. So does the information content of the universe remain constant? Is this what forces the universe to select out of quantum choices? If so, then you'd expect that the first moments of expansion would be accommpanied by a selection from just a few states. But the more the universe expanded, the more choices would be required to choose from. Is this consistent with any present theory?

We see this, even though you have sided with only one side of the universe in expresssion:)

Was the energy density of spacetime so great just after the initial singularity that the fabric of space began to tear and small black holes began to appear? They would immediately evaporate and produce other particles.

Some of the black holes might indeed dissipate, but we have yet to define the context of this critical density, as the singularity, or part of the nature of this cyclical universe?

Still, the geometry remains consistent.

I wanted to add http://superstringtheory.com/forum/bhboard/messages11/74.html for consideration

Quantum Gravity is asking us for a quantum geometry, and from aspect of unification to a fifth dimensinal reality, one had to follow Klein's ordering of geometries. This takes you right through SR and GR to unificatiuon in the aspects of electromagnetism and gravity. You have to speak to that in a geometrical consistancy as Einstein did in GR. Kaluza and Klein become a interesting couple in their perspectives.

This would be consistent with Maxwell and Einstein.

Thanks for responding directly.

 

[Mike2]

Coming from a quantum information makes viewing quantum states as states of knowledge an attractive position for me. It seems to make some of the quantum information protocols slightly less mysterious than if you take the quantum state to be a state of reality. In my opinion, the two best arguments for this position from a modern perspective are:

http://xxx.arxiv.org/abs/quant-ph/0205039
http://xxx.arxiv.org/abs/quant-ph/0401052

There are some key differences between the points of view in these papers and, in particular, the first takes the quantum state to be far more subjective than the second. The second paper is closer to my view onthe subject.

Read your link at:
http://xxx.arxiv.org/abs/quant-ph/0205039

Interesting! He compares quantum mechanics to Bayesian probability theory. He says that the two are almost the same except for some noncommutativity property of quantum mechanics that Bayesian theory does not have. I think that property may be entropy.

He finishes the article by describing how quantum cryptography cannot be eavesdropped upon without detection. The sender prepare quantum message with at least two nonorthogonal states. And if someone trys in intercept the message it produces more noise for any subsequent receiver. What can that be except entropy, no process (of measurement) without causing an increase in entropy (loss of information). So it would seem that the act of covertly gathering information means reducing the emount of information (increasing entropy) in the rest of the signal. Which again leads me to ask: Is entropy conserved, noise somewhere because information gained somewhere else?

 

[tavi_boada]

ballentine's interpretation

Hey

I have read most of the answers to this quetion but no one has mentioned Ballentine's interpretation. Actually, I'm not really sure it's his , but all his(or her) book is written using it.

It basically says that the expected value of a dynamical variable (of it's associated hermitian operator) is the average of the measure on many (idealy infinite) identical systems. That is, QM according to this author, ony makes predictions on ensembles.

What I like about this interpretations is that there are no half-dead cats and other nonsense (F.Salvat).

 

[slyboy]

Ballentine's statistical interpretation is a perfectly good operational way of looking at the theory. However, it has a hard time explaining why quantum statistics are different from classical statistics and it seems difficult to remove the notion of measurement as being fundamental to the theory.

For example, suppose we have the proverbial cat in the state |alive> + |dead>. Ballentine would like to say that it describes a 50/50 mixture of alive cats and dead cats, each cat being actually either alive or dead. However, QM allows us to measure in a different basis, so suppose we could measure in the |alive>+|dead>,|alive>-|dead> basis. Then we would have to say that all the cats are definitely |alive>+|dead>. Similarly, although we would like to say that all |alive> cats are alive, we would have to admit 50% of them are |alive>+|dead> cats and 50% are |alive>-|dead> cats.

Thus, the fundamental question seems to be, what picks out the basis in which we are to regard the state as a mixture. It seems to be dependent on what measurement we perform. This is indeed one possible answer, which has a distinctly Copenhagen flavour. However, this will not satisfy critics who do not wish measurement to play a fundamental role in the theory. Other answers involve invoking things used for the same purpose in other interpretations, such as decoherence, but these also have their drawbacks.

In any case, it seems that a purist version of Ballentine's interpretation, i.e. just saying states represent statistical ensembles without any further qualification, offers little advantage over Copenhagen and its variants.

 

[tavi_boada]

Very interesting insight. But I think that, at most, it puts Ballentine's interpretation on equal footing with respect to the Copenhagen school. WIth Ballentines interpretation things can be modified so it yields nonsensical results, but the other interpretations are nonsensical from the begining!

I must say, that I can live with the exisitence of half alive/dead cats.

 

[Mike2]

...And if someone trys to intercept the message it produces more noise for any subsequent receiver. What can that be except entropy, no process (of measurement) without causing an increase in entropy (loss of information). So it would seem that the act of covertly gathering information means reducing the emount of information (increasing entropy) in the rest of the signal. Which again leads me to ask: Is entropy conserved, noise somewhere because information gained somewhere else?

I don't understand why this is not more interesting. Does this not match the concept of entropy - events and interactions increase entropy which means they reduce the emount of information in the world? Only those events which increase entropy can occur, at least in the average.

But we cannot know how entropy has changed (increase or decrease) unless we make two measurement of a system and see how the state has changed. We take before and after readings; we measure the initial and final states. In the act of making the first measurement, we gain information about the system. The system is then assumed to proceed in a manner of increased entropy. Then we make the final measurement. And we expect that less information is available since the entropy of the system has increased.

How does the emount of available information that can be gained about a system effect the expectation values? Expectation values are probabilistic and so is information. If a measurement randomizes the system, then you'd expect that any measurement would make any subsequent measurement less accurate. You wouldn't know it was less accurate unless you also tried to reverse the order of the two measurements. If the two measurements do not commute, then you'd expect that there would be a limit to the accuracy of the both measurements. Is h-bar a measure of information? Any thoughts or corrections, gentlement?

 

[vanesch]

decoherence!

Thus, the fundamental question seems to be, what picks out the basis in which we are to regard the state as a mixture. It seems to be dependent on what measurement we perform. This is indeed one possible answer, which has a distinctly Copenhagen flavour.

Be careful ! There is a fundamental difference between a superposition of states (which is in fact nothing else but "choosing the wrong basis") and a statistical mixture in the classical sense. The state |dead>+|alive> is a pure state, while the statistical mixture 50% dead and 50% alive is a statistical mixture, and this distinction is INDEPENDENT of the choice of basis, as can easily be seen using the density operator rho: if trace rho^2 = 1, then it is a pure state, else it is a mixture (and this is of course independent of basis).

I would even say that the whole difficulty of QM resides in this distinction (all quantum weirdness comes from superpositions, not from mixtures).

It is exactly the merit of decoherence theory to show under what circumstances the density matrix always evolves into a statistical mixture a la Ballantine when coupled to a macroscopic system (a "thermal bath"), and the preferred basis is the one of the "coherent states".

cheers,
Patrick.

 

[slyboy]

Be careful ! There is a fundamental difference between a superposition of states (which is in fact nothing else but "choosing the wrong basis") and a statistical mixture in the classical sense. The state |dead>+|alive> is a pure state, while the statistical mixture 50% dead and 50% alive is a statistical mixture, and this distinction is INDEPENDENT of the choice of basis, as can easily be seen using the density operator rho: if trace rho^2 = 1, then it is a pure state, else it is a mixture (and this is of course independent of basis).

That is exactly my point. The statistical interpretation of Ballentine seems to want to interpret all states as statistical mixtures rather than superpositions. This is only possible if the measurement basis for the state is somehow fixed (by dechoherence or some other mechanism).

 

[meteor]

I've been always curious about what was exactly Quantum logic, this approach originated in the 30's by Birkhoff and Von Neumann, so I've printed today this paper
"Quantum logic. A brief outline"
http://arxiv.org/abs/quant-ph/9902042
to add to my collection of quantum papers. Although I still don't understand the Hasse diagrams and Greechie diagrams that appear in it, I'm giving to it a try

 

[Feynman]

Hi Alem ur question is too hard