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Anyone know the answer to this question? OK...so, if multiple wave functions which are overlapped make up the concept of super-position, and we can measure the

Anyone know the answer to this question? OK...so, if multiple wave functions which are overlapped make up the concept of super-position, and we can measure the wave function at any given time, why can't we take enough measurements to formulate a wave theory that will predict where the wave will be at ANY given time?

qwerty_asdf 13y ago
We can predict the behavior of a continuous signal, since it's an ongoing stream of similar events. And we can predict the averages that we can expect to see, but for a single, individual emission of one photon, when we provoke or stimulate the emission of that photon we can't be sure EXACTLY how the photon was emitted, until it bombards the detector, and changes the detectors state. THEN we can infer from the detector, the original state. The reason it's difficult to know the precise situation of a photon, in-flight, is because it's been emitted from a moving target, whose precise state is difficult to control perfectly: a live atom. Without having perfect control of the atom that sends off the spinning, oscillating particle, we have a hard time discerning the exact circumtances of the spin/oscillation imparted upon it. We can hazard guesses, but when we're right, it's only because we get lucky. Not because we controlled it. EDIT: The reason is there are two factors driving the emission: 1. The external behavior of the electon shells 2. The internal nuclear behavior of the protons and neutrons (which do not behave simply as a clump of spherical marbles, the nucleus is it's own volatile, nebulous construct) And, oh yeah... 3. Any other random cosmological events that might sail in from outer space (literally), as fortuitous signals
- FrankenPC 13y ago
  Well, that makes the most sense to me. But, I've always thought this is how the universe worked. Infinitesimal forces acting on a given outcome make precision prediction impossible. I still don't get how quantum mechanics is "spooky". Maybe without a math degree I never will.
  - lutusp 13y ago
    > I still don't get how quantum mechanics is "spooky". Really? Measuring a particle's state at a street corner in Columbus, Ohio instantly causes its partner particle in the Andromeda Galaxy to assume the opposite identity, isn't spooky? http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement Opening a box containing a cat, a vial of poison, and a radioactive sample instantly causes the cat to become either alive or dead, where before the cat was in a superposition of states, i.e. neither alive nor dead. Not spooky? http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat > Maybe without a math degree I never will. No need for a math degree. The weirdness of quantum theories is obvious without a knowledge of advanced mathematics. "If you think you can talk about quantum theory without feeling dizzy, you haven't understood the first thing about it." -- Niels Bohr.
  - qwerty_asdf 13y ago
    Mostly, there are a number of unresolved questions which seem to defy measurement and experimentation, and so instead of getting elbow deep in real world experiments, in an effort to reliably re-create outcomes (experiments that predict what will happen next, when carrying out certain steps), many practitioners of physics have had to spend entire careers "at the drawing board", concocting mathematical theories, on paper, that "add up" to the unexpected, unreliable, confusing things that happen in the real world, even when vacuums, clean rooms, and massive radiation shielding (in the form of miles-deep mine shafts beneath entire mountain ranges sometimes) fail to exert control over. Things like: https://en.wikipedia.org/wiki/Quantum_nonlocality https://en.wikipedia.org/wiki/Quantum_nonlocality (aka: spooky interactions at a distance) Quantum Non-locality seems (seems) to produce scenarios where two particles are stimulated using ostensibly unrelated mechanisms, but then also seem to exhibit cause-and-effect behavior where influencing one particle inexplicably influences the other particle, even though they may be (presumptively) incapable of influencing each other at the point in time and space when the correlating behavior is observed. How did particle A affect particle B? Did you touch it? What happened? No one touched it?! Also unexplained is the: https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment This kind of interference pattern holds up, even at atomic scales, when diffracting x-rays through barriers of crystalline samples. Recently, there has been an experiment developed which may finally explain this behavior: http://web.mit.edu/newsoffice/2010/quantum-mechanics-1020.html http://web.mit.edu/newsoffice/2010/quantum-mechanics-1020.ht... http://www.youtube.com/watch?v=fnUBaBdl0Aw http://www.youtube.com/watch?v=fnUBaBdl0Aw https://en.wikipedia.org/wiki/Pilot_wave https://en.wikipedia.org/wiki/Pilot_wave ...but this would suggest that there are unseen, unmeasuable forces (from parallel dimensions?) influencing our particles in this universe, at all times, and in unexpected ways. If this is true, what does it all mean? Is the sky falling?! Who knows?! These sorts of unexplained behaviors, made physicists very nervous in the early half of the 20th century, since maybe attempts to build city destroying weapons might have horrible, unpredictable triggers or uncontrollable, world-destroying, runaway chain-reaction outcomes, never to be understood (not unlike the black hole fear mongering surrounding the LHC's publicity). Keep in mind that these ideas were kicking around before an atom bomb was anything other than science fiction. The fears and impatience often strike a chord like Dr. Emmett L. Brown's fear of a universe-destroying temporal paradox in Back to the Future.
Xcelerate 13y ago
> we can measure the wave function at any given time We can't. Nobody knows how to measure a wavefunction. Instead, what you measure is one of the eigenvalues of a linear operator that acts on a wavefunction (which particular eigenvalue? You can't always predict this; hence the randomness in QM). For each "observable" you want to measure (position, momentum, spin), there is a specific linear operator associated with it. For instance, in position-space, the position operator is just the identity operator. If you haven't taken linear algebra, I can clarify this further.
- FrankenPC 13y ago
  I have a suspicion what you are trying to tell me is at the root of this. But, no I do not remember any complex math. Yes, I took multiple calculus classes in college, but I don't remember any of it. That was decades ago.
ArbitraryLimits 13y ago
You don't measure the wave function, you measure the state of the underlying system (qubits or whatever). When a measurement is made, the wave function, which gives the probability of finding the system in any particular state, "collapses" so all the probability mass is on the state you just measured. If you keep measuring the system quickly (relative to the time it would take to change significantly) you actually stop if from evolving the way it would have if you'd left it alone, as if you dropped a ball and kept staring at it and it dangled in the air instead of falling.

qwerty_asdf 13y ago

We can predict the behavior of a continuous signal, since it's an ongoing stream of similar events. And we can predict the averages that we can expect to see, but for a single, individual emission of one photon, when we provoke or stimulate the emission of that photon we can't be sure EXACTLY how the photon was emitted, until it bombards the detector, and changes the detectors state. THEN we can infer from the detector, the original state. The reason it's difficult to know the precise situation of a photon, in-flight, is because it's been emitted from a moving target, whose precise state is difficult to control perfectly: a live atom. Without having perfect control of the atom that sends off the spinning, oscillating particle, we have a hard time discerning the exact circumtances of the spin/oscillation imparted upon it. We can hazard guesses, but when we're right, it's only because we get lucky. Not because we controlled it. EDIT: The reason is there are two factors driving the emission: 1. The external behavior of the electon shells 2. The internal nuclear behavior of the protons and neutrons (which do not behave simply as a clump of spherical marbles, the nucleus is it's own volatile, nebulous construct) And, oh yeah... 3. Any other random cosmological events that might sail in from outer space (literally), as fortuitous signals

FrankenPC 13y ago
Well, that makes the most sense to me. But, I've always thought this is how the universe worked. Infinitesimal forces acting on a given outcome make precision prediction impossible. I still don't get how quantum mechanics is "spooky". Maybe without a math degree I never will.
- lutusp 13y ago
  > I still don't get how quantum mechanics is "spooky". Really? Measuring a particle's state at a street corner in Columbus, Ohio instantly causes its partner particle in the Andromeda Galaxy to assume the opposite identity, isn't spooky? http://en.wikipedia.org/wiki/Quantum_entanglement http://en.wikipedia.org/wiki/Quantum_entanglement Opening a box containing a cat, a vial of poison, and a radioactive sample instantly causes the cat to become either alive or dead, where before the cat was in a superposition of states, i.e. neither alive nor dead. Not spooky? http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat http://en.wikipedia.org/wiki/Schr%C3%B6dinger's_cat > Maybe without a math degree I never will. No need for a math degree. The weirdness of quantum theories is obvious without a knowledge of advanced mathematics. "If you think you can talk about quantum theory without feeling dizzy, you haven't understood the first thing about it." -- Niels Bohr.
- qwerty_asdf 13y ago
  Mostly, there are a number of unresolved questions which seem to defy measurement and experimentation, and so instead of getting elbow deep in real world experiments, in an effort to reliably re-create outcomes (experiments that predict what will happen next, when carrying out certain steps), many practitioners of physics have had to spend entire careers "at the drawing board", concocting mathematical theories, on paper, that "add up" to the unexpected, unreliable, confusing things that happen in the real world, even when vacuums, clean rooms, and massive radiation shielding (in the form of miles-deep mine shafts beneath entire mountain ranges sometimes) fail to exert control over. Things like: https://en.wikipedia.org/wiki/Quantum_nonlocality https://en.wikipedia.org/wiki/Quantum_nonlocality (aka: spooky interactions at a distance) Quantum Non-locality seems (seems) to produce scenarios where two particles are stimulated using ostensibly unrelated mechanisms, but then also seem to exhibit cause-and-effect behavior where influencing one particle inexplicably influences the other particle, even though they may be (presumptively) incapable of influencing each other at the point in time and space when the correlating behavior is observed. How did particle A affect particle B? Did you touch it? What happened? No one touched it?! Also unexplained is the: https://en.wikipedia.org/wiki/Double-slit_experiment https://en.wikipedia.org/wiki/Double-slit_experiment This kind of interference pattern holds up, even at atomic scales, when diffracting x-rays through barriers of crystalline samples. Recently, there has been an experiment developed which may finally explain this behavior: http://web.mit.edu/newsoffice/2010/quantum-mechanics-1020.html http://web.mit.edu/newsoffice/2010/quantum-mechanics-1020.ht... http://www.youtube.com/watch?v=fnUBaBdl0Aw http://www.youtube.com/watch?v=fnUBaBdl0Aw https://en.wikipedia.org/wiki/Pilot_wave https://en.wikipedia.org/wiki/Pilot_wave ...but this would suggest that there are unseen, unmeasuable forces (from parallel dimensions?) influencing our particles in this universe, at all times, and in unexpected ways. If this is true, what does it all mean? Is the sky falling?! Who knows?! These sorts of unexplained behaviors, made physicists very nervous in the early half of the 20th century, since maybe attempts to build city destroying weapons might have horrible, unpredictable triggers or uncontrollable, world-destroying, runaway chain-reaction outcomes, never to be understood (not unlike the black hole fear mongering surrounding the LHC's publicity). Keep in mind that these ideas were kicking around before an atom bomb was anything other than science fiction. The fears and impatience often strike a chord like Dr. Emmett L. Brown's fear of a universe-destroying temporal paradox in Back to the Future.

Xcelerate 13y ago

> we can measure the wave function at any given time We can't. Nobody knows how to measure a wavefunction. Instead, what you measure is one of the eigenvalues of a linear operator that acts on a wavefunction (which particular eigenvalue? You can't always predict this; hence the randomness in QM). For each "observable" you want to measure (position, momentum, spin), there is a specific linear operator associated with it. For instance, in position-space, the position operator is just the identity operator. If you haven't taken linear algebra, I can clarify this further.

FrankenPC 13y ago
I have a suspicion what you are trying to tell me is at the root of this. But, no I do not remember any complex math. Yes, I took multiple calculus classes in college, but I don't remember any of it. That was decades ago.

ArbitraryLimits 13y ago

You don't measure the wave function, you measure the state of the underlying system (qubits or whatever). When a measurement is made, the wave function, which gives the probability of finding the system in any particular state, "collapses" so all the probability mass is on the state you just measured. If you keep measuring the system quickly (relative to the time it would take to change significantly) you actually stop if from evolving the way it would have if you'd left it alone, as if you dropped a ball and kept staring at it and it dangled in the air instead of falling.