in quantum physics, is waveform collapse a false idea?

Question

I recently asked why are particles thought of as waves in quantum physics and got a good answer, the probability of their location.

But in fact, is the actual location of said particle finite even if we have yet to discover where it is, and in fact NOT a wave, but a particle at a physical point.

So if I get this right, waveform collapse is the measure of coming to know this finite location of the particle, but the particle was not truly a wave or waveform to begin with, so isn't supposing it as a wave false to begin with, so therefor no collapse happens at all? Isn't it like saying finding my car in a parking lot is car-wave collapse? It's a measure of how much I don't know where my car is (lol). Am I way off?

Answer 1

Contrary to Biofreak's assertion, a majority of quantum physicists today now believe that wave-function collapse does not happen. Biofreak's answer is based on the Copenhagen Interpretation of QM, which asserts that the wave function collapses. However, in the now more widely held view known as Everett's Many Worlds Interpretation of QM, the wave function doesn't collapse. Instead, the universe splits.



Biofreak cites many of the classic experiments in QM: Young's 2-slit experiment, the Stern-Gerlach experiment with electron spin, etc. These experiments illustrate the wave-particle duality that is at the heart of QM and our classical experience of observing quantum systems. The experiments all initialize a quantum system in a state of superposition, wherein the self-interfering wave nature of the system is evident, then make a measurement, wherein the particle nature of the system manifests.



In more recent times, the notion of wave-function collapse has been replaced by a more sophisticated theory called decoherence. Coherence is when the system is in superposition. De-coherence is the process by which the particle nature of the system emerges. Emerges, because decoherence doesn't happen instantaneously, nor is it necessarily irreversible after it begins.



Once a superposition decoheres sufficiently and enough quantum information is lost, the decoherence process is irreversible. To digress slightly, information is lost in this process, not destroyed, because information can neither be created nor destroyed (assuming the amount of space in the universe is fixed). Thorne, Preskill and Hawking settled this debate in recent years as it related to the matter of whether information is destroyed when it falls into a black hole. Hawking thought no, but ultimately conceded a bet he had with Preskill, providing Preskill with a copy of a baseball encyclopedia.



Deutsche, the father of the quantum computer, says that the information is still present, but in a parallel world not accessible to us. Steane relates how there can not be information without a physical representation. And Deutsche states that the computations performed in parallel on a quantum computer of just a few hundred qubits (very very small) can not possibly be done with all the matter in our known universe. Therefore, Deutsche concludes, the information is present in parallel worlds. When the measurement is performed and the quantum superposition decoheres, these worlds split from ours and rapidly become so different from ours that they can no longer interfere with ours.



To conclude, the quantum "measurement problem" is still an active area of exploration. The latest thinking is that there is no wave-function collapse. Instead, there is decoherence and world splitting. The issue of world splitting and what occurs is a topic for a different question, since this answer is already long. Needless to say, the wave-function still exists after decoherence, but we can't access it any longer because we lost the information necessary to reconstruct it. This all suggests that we are of a lower-order dimensionality than really exists in the complete quantum realm. In other words, the universe likely has more dimensions than the 4 space-time dimensions we experience through our ordinary senses. I hope this has been helpful to you.

Answer 2

No, wave function collapse does occur. There are plenty of examples that demonstrate the necessity of this type of behavior. For example, the double slit experiment would not work the way it does without the particle actually filling more than a single point in space. In the double slit experiment, the particle, as a wave, passes through both slits and then interferes with itself. You can't get a particle to interfere with itself if it is a point particle, it must be a wave.



Another example is the Aharonov-Bohm effect where a particle interacts with a field that it doesn't actually pass through, because the wave function still samples that area.



There are other forms of wave function collapse that do not involve position, but involve some other quantity instead. For example, the Stern-Gerlach experiments nicely demonstrate that collapse of electron spin superpositions. Similar experiments with diagonal or circular polarized light passing through appropriate polarizers demonstrate photon polarization collapse. The physics behind these other types of collapse is basically identical to position collapse, thus if they work this way, so should position.



There are many many such examples showing wave function collapse across physics. The idea of collapse (or more correctly, superposition and measurement) is a fundamentally quantum phenomena that does not and will never make sense in the framework of classical physics. It just does not happen in classical physics and there is nothing like it in classical physics. None the less, collapse has been demonstrated and it is not that there is a well defined position that we just do not know.

Answer 3

Best we can do is: It is both. Though I talk about "electromagnetic radiation" this discussion is true for all of Quantum Mechanics.



http://physics.about.com/od/lightoptics/a/waveparticle.htm



WARNING! I am a heretic. According to the Physics Majors, the following is “misleading” or “nonsense.”

Yours is a very profound question. I can tell from your question that you are ready to be let in on the "Dirty Little Secret" of Theoretical Physics: We have NOT yet figured everything out. The universe is governed by whole sets of "Laws" that do NOT agree and are mutually exclusive or illogical ( Google: "Schrodinger's Cat" in case you are interested in the illogic). This is a great embarrassment. We assume we live in an orderly, rational universe that makes sense. Perhaps when Quantum Mechanics and General Relativity are unified we will have a better answer to your question.



For now:



We need the concept of alternating electromagnetic fields (waves) to explain certain physical phenomena, like the interference pattern in the 2 slit experiment. So we keep that. We must somehow explain how a particle orders of magnitude smaller than the distance between the slits somehow passes through both slits and interferes with itself. Problem, we cannot explain this well using "quanta" (Particles, photons). Wave mechanics gives a simple easy to understand explanation.



We need the concept of quanta (particles, photons) to explain other phenomena, like the Photoelectric Effect. So we keep that too. But, this means we use 2 different, mutually exclusive systems of mechanics to explain electromagnetic radiation.



What to do? We cheat! We say that electromagnetic radiation has a dual nature and choose the system of mechanics that works best for the problem at hand.



Quantum Mechanics gets out of this mess by introducing the Uncertainty Principle, Indeterminacy, and the Copenhagen Interpretation of QM. If we do NOT know which slit the particle went through, then the particle is "smeared out in equal parts" and goes through both slits. It turns into a fog. As long as it is a fog, it can pass through both slits. That is: The particle occupies a volume of space with some probability. QM says that so long as the position is not known, the particle occupies the entire volume. If we learn its position, the fog condenses into that location and the particle goes through one slit. (The problem with this is: Fog does not form interference, waves do. Sooner or later, in those problems where appropriate, you must give up particles and fogs and start cranking through the equations of Wave Mechanics) But, Quantum Mechanists prefer “fog” to, "The particle turns into a wave and goes through which ever slits are open. One slit, no pattern. Two slits, pattern. “ Take your choice of which mental picture you form.

Rule of Thumb that got me through QM: If its’ position is known, it is a particle. If its’ position is unknown, it is a wave. This works because the equations of Wave Mechanics work, if the position is unknown. If you don’t tell anybody, no one will know the mental picture you formed to solve the problem. (This may not always work, but I do not remember a case where it failed.)



It is not uncommon for engineers to accept the reality of phenomena that

are not yet understood, as it is very common for physicists to disbelieve

the reality of phenomena that seem to contradict contemporary beliefs of

physics - H. Bauer



PS: Interesting thing about the 2 slit experiment (Google it if you don't know it): If we do it with electrons, we can leave both slits open and put a detector over both slits. Then when the charged electron passes, the detector will tell us which slit the electron went through. Now it gets cool. If we turn the detectors off, we get a pattern (We do not know which slit the electron went through ===> Its a wave and the pattern appears.) Turn the detectors on and the pattern disappears (We know which slit the electron went through ===> Its a particle and the pattern disappears.) Cool huh?

Answer 4

No, the waveform collapse is not a false idea. QM is not Not NOT something you can hope to make logical sense of, and that is not because of your level of education!



Alas, we can actually measure /sense that an electron is both here and there, so to speak, before the waveform collapses. It is detectable at more than one place at a time (and more than one time at a time too, since the waveform includes travel backwards in time.



QM is a very thoroughly tested theory, and it has never failed, but the 'reality' behind it - IF there is a reality behind it - is inscrutable. Einstein spend a lot of time trying to disprove it - unsuccessfully - because he found it, ... well ... distasteful!

Answer 5

I'll stay with your car-parking analogy coz it amuses me:



You find your car based on the mass of information you know about it - and the fact that you make some assumptions based on your model of reality.



When you park your car, you don't expect it to jump randomly into another parking spot, nor do you expect it to travel through time and park itself in the same spot three weeks hence.



You don't expect it to change colour, or shape or size based on the fuel available in the gas tank.



When considering your photon/particle, you are using models to predict a pattern. These models are a imprecise mechanisms for encapsulating what we know - they are not perfect, but they allow us to bring together what we do know and speculate on some furtherance of our knowledge.



The only way to accurately model physics at the quantum level, is to use doctoral-level mathematics - even then, there are still some assumptions made.



Got other things to think about now