Assume that a particle is travelling through a slit, immediately prior to its transformation into a wave. What exactly happens when it transforms into a wave? Doesn't the transformation imply a third state besides wave/particle? For some infinitesimally small period doesn't there have to be a third state - where it has some characteristics of both wave and particle? Why is it that the other two states are so stable, compared to this transition phase? Also, what are the particular(ha) features of the wave or particle that cause it to behave this way? For instance, how does a particle 'know' it is travelling through a single slit or a dual slit? How does this ' knowledge' fit in with the collapse of the wavefunction by an observer? Hopefully you folks can help me focus my thinking on this issue?
I'm not sure, but a wave/particle doesn't switch between being a wave and being a particle. The wave/particle duality implies that there isn't any transformation.
As redrover says it doen't switch from one state to another, duality is a fundamental property of it.
But it behaves like a wave and a particle, doesn't it? Something has to change doesn't it - it's expression if not it's essence to wax philosophical So I think my point should still stand - there should be a mid state between the two. Anyway, that's the way my thought experience is leading me.
No – it simultaneously has both a wave nature and a particle nature. That's why it's called 'duality' rather than simply two separate states. You can do experiments that show light being simultaneously both a wave and a particle. Welcome to the strange world of quantum physics.
You have to rembe partiocle and waves ar really macroscopic constructions/visualisations that may seem to be discrete states on the macroscopic level, but not on the microscopic level.
The particle in question will behave like a wave untill you "measure" its position, velocity, energy... ie. force it to interact with a macroscopic system. The particle is a wily little creature. It knows there are two slits, but only behaves wave-like if we do not try to detect which slit it went through. In measuring it, we collapse its wave function and it becomes particle-like. I suppose even saying that it "knows" is a bit misleading because that implies some definate position before the particle is measured. Does an ocean wave "know" it is hitting a double-slit barrier? No. It merely interacts with it in a wave-like manner. You cant assume that it transforms into a wave... That is like saying that the particle had a definate position before it was measured. Quantum physics assures us that we cannot make this assumption--an assumption which Einstein disagreed with-- and so it is not untill we record the particle hitting the measuring screen for our double slit experiment that we can say that it's position is definate. The actual mechanics of the collapse are not really yet know, or even what defines a "macroscopic" system. Experiments to date have certainly proven that the wave-like concept of particles is valid in experiments such as the double-slit.
According to the copenhagen interpretation, a system (the wave/particle) will be a wave until is measured. When it's measured, the wavefunction collapses and the wave transforms to a particle. When the particle is not measured, it transforms another time to a wave. Measure don't necessarily mean the measure of a conscious observer. A device able to measure the particle will collapse the wavefunction (even if there are no persons around) .The question is: how the particle knows that is measured, and what is really a measure?
Lucas, you take what you say as definitive, when it isn't. This question has not been resolved yet. What about many-worlds interpretation or hidden variables (though I believe hidden variables is disproved via Bell's thereom) What's an observer? If you observe or measure for which the wavefunction collapses, and then you do not tell me the result, has the wavefunction collapsed for me. Are my results dictated by what you find?
In the many-worlds interpretation there's no collapse of the wavefunction, but the wavefunction splits in many different little wavefunctions, each of them represent a result of a quantum succes. I don't like very much this idea. The important concept is the concept of measure. If a wave is measured, will collapse, no matter if i do the measure or you do the measure.(or a cat do the measure) Copenhagen interpretation seems me too vague because the concept of measure is not well defined. There's a mental experiment called "quantum suicide" that try to clarify which of the two interpretations is correct But for me, the true interpretation has not been discovered to the moment
you guys ever seen one of those things that have metal bars situated at near parrallel, and an electrical shock rises up between the two bars? What do you think it looks like to people who were living on the 2 dimentional surface of one of the bars? what if you created a slit in some object in the 2D world, and let the electrical charge pass through it, what would happen? I bet it would look alot like a wave/particle duality. I still say that we live in a crumpled up 3-D univers, and that photons are some 4-D energy touching the surface of our three dimentions. like a crumpled peice of paper covered by spiderwebs, all the connection point are connected to other points in our space, though it doesn't look like it from our perspective. It's all about geometry, IMO.
i have a question. do people still consider feynman's sum of paths interpretation of the slit experiment? i think i read that he said there exists an infinite amount of photons and they all travel everywhere prior to going through the slit. or has this been dropped?
contrarian As others observed well a quantum particle does not transform in a wave.According to Copenhagen Interpretation of QM quantum particles have a wave/particle nature.However Bohr's principle of complementarity states that a quantum particle cannot exhibit both characteristics in the same time when they are measured.That's why the Copenhagen Interpretation is a particle OR wave interpretation as opposed to Bohm-de Broglie's particle AND wave hypothesis.Unfortunately we cannot for the moment to make the difference between the two experimentally,the mistery still remain. For example in the two slits experiment (in the acception of the Copenhagen Interpretation) photons show a particle characteristic only when they are emitted and when they hit the screen,in the rest the wave characteristic is shown (useful to explain the patterns of interference observed on the screen).Anyway given that in many cases our succesfull scientific theories are simple models there is still possible that,ontologically speaking,quantum particles are something else:neither particles nor waves...Personally I think that the particle OR wave model is only our simplest way,for the moment,to 'explain' what happens in the two slit experiment and generally at quantum level;a model 'working' for all our actual practical purposes.Epistemically speaking the Copenhagen Intepretation is the simplest now however we do not have yet the right to say that we solved this mistery,ontologically speaking... ryans The violation of Bell's inequalities and its succesfull experimental confirmation (see Alain Aspect's experiment of 1982 and later,improved,versions) only disproved the possibility of existence for local hidden variables;non local hidden variables are still possible.As far as I know there are still many,even in the scientific field,who do not find Aspect's experiment totally sound,accusing different vices of procedure;anyway the majority found it compelling:local hidden variables can be ruled out safely,we have arguments beyond all reasonable doubt for that. But non local hidden variables have not been disproved yet,in fact this is exactly why Bohm's Interpretation became much more persuasive lately apart from the 'shortcomings' of the Copenhagen Intepretation.In fact Bell himself was a staunch proponent of Bohm's Interpretation (practically the only one in the scientific field until the beginning of 1990-th).Still many scientists object to Bohm's interpretation due to the fact that his interpretation seem to contradict Einstein's Special Relativity and due to the momentary lack of a nonlocal hidden variables relativistic version;understandable,given of the huge success of quantum electrodynamics (including the 'natural' explanation of the spin).However,for the moment at least,no data disprove Bohm's interpretation (and more widely the non local 'hidden' variables hypothesis):Bohm's Interpretation and the Copenhagen Interpretation are indistinguishable in what their predictions are concerned (not a surprise given that both have at base the same mathematical formalism,only their ontologies differ).Personally I prefer the hidden variable interpretation (not necessary Bohm's since this hypothesis could still be false nonwithstanding the fact that,possible,we will never be aware of that) due to some personal,strange,experiences that are much more compatible with such an intepretation...
No, Bohm's interpretation does not violate special relativity as relativity says that information cannot travel at speeds greater than c in disconnected regions of space-time. Bohm's interpretation cicumvents this by proposing that it is not 2 distinguishable systems which are present in say quantum entanglement, but one sytem, where both particles contain all information about the whole system (spin, momentum etc) and so there is no transference of information. In the holographic model, all sub-volumes of the universe contain the information about the whole universe, as in a hologram. Bohm's interpretation in fact seems to be the only one compatible with relativity and casuality.
i have another question, i have been reading more on the net about the photon double slit experiment. the sum over paths says that most of the infinite paths that a single photon takes in its journey through the slits will cancel out. how do they cancel out? because they are waves? and just so i am sure i have this right. the ONE photon takes all infinite paths? it's not an infinite amount of photons is it?
Special Relativity is clear:the speed of light is a constant in inertial frames,nothing can travel faster with speeds greater than c.Or the quantum potential of Bohm,pervading all space,is postulated to instantaneously change in all points of space.This is in itself a violation of Special Relativity though WE cannot exchange information with speeds greater than light's.Some proposed to change the postulate in the Special Relativity stating that nothing can travel with speeds greater than c with one which to require only that information cannot be sent with speeds greater than that of light but so far I do not know of any convergence of opinions.The majority of scientists still blame Bohm's Interpretation for violating Special Relativity something which the implicit 'explanation' given by Bohr does not break.
If this is what you think then either you don't understand Bohm's interpretation or you don't have a proper grasp of physics. No information is transferred, the 2 particles are one. You break the oneness of the system by performing a measurement, they are no longer one. Both particles left undissturbed contain all the information the other particle has, but if you change the properties of one particle, the other particles properties will not change.
local hidden variables were disproved by bell. he later extended his proof to include any local theory of QM. thus, bell s theorem is often taken to be a proof that any quantum theory is necessarily nonlocal. i didn t read Lucas post as a definite statement. he leaves his post open ended, "what is a measurement?", "how does the particle know?", which i believe is exactly what know one knows. this is an open question. this is correct. stop to consider that it is possibly you who do not have a proper grasp. both the Copenhagen Interpretation and Bohm s theory involve nonlocal signals. ryans, you are correct that it can be shown that no information can be carried by these nonlocal signals. but metacristi did not dispute this fact. we are all in agreement that information cannot go faster than light. however, metacristi said that people think it is a violation of special relativity for any nonlocal signal to exist. and he is correct. einstein himself believed this. many people disbelieve nonlocality, and find it to be a violation of special relativity. whether the existence of nonlocal signals in quantum theory is a violation of special relativity is a question that is open to interpretation.
O.K. I may have been a bit harsh in my comments to metacristi, I am genuinly sorry about that, but I cannot see how Bohm's interpretation is in contradiction with SR. In Bohm's interpretation remember, there is no collapse of the wave function, as the system (both particles) are in a single conected state. No information transfer.
