Quantum Mechanics, and Schrodingers cat.

[Andy Bowden]

What are comrades feelings on Quantum mechanics? I heard that it contradicts dialectical materialism, but ive only just started doing a bit of Physics in Uni so I am not sure. :blink:

And does anyone know how to explain "Schrodingers cat", a theorem which suggests a cat can be both alive and dead in quantum mechanics.


Basically, a thread to bullshit about some of the sexier aspects of Physics and help me out :D

[pedro san pedro]

the cat experiment involves putting a cat into a sealed box with a radioactive actom that has a 50% chance of decaying. if the atom decays, it triggers something that kills the cat. so, while the box is still sealed, there is a 50-50 chance that the cat is alive or dead, so we must accept both as being true - to seperate probablities exist that can only ever be resolved when the box is open.

of course, the experiment is only a theoritical one - theres no need to actually do the experiment to show the two different and contridictory probablities coexisting.

douglas admas (author of the hitchhikers guide to the galaxy) took the experiment one step further by introducing a pyshic into the equation in 'dirk gently's holistic detective agency' :lol:

[ComradeRed]

What are comrades feelings on Quantum mechanics? I actually am a theoretical physicist who works with quantum theory. The problem I have with it is that there is no clear explanation of it.

For example, there are about a half a dozen or so schools of thought ("interpretations") of Quantum Theory. The most famous is the canonical ("Copenhagen") interpretation.

This tells us that "everything" follows the wave-particle duality: sometimes it is better to think of something as a particle, others times it is more beneficial to think of it as a wave.

In turn, this is related to the uncertainty principle. The uncertainty principle originally stated that we can be certain of the frequency or the time of a wave. That is, if I were playing a violin with a bow, you would know the note. On the other hand, if I were to pluck the strings, you would hear "packets" of sound.

The more I do of one, the less I can do of the other. That's it! It's not anything more than this.

The problem is that, although this is fine and dandy, there are no equations that use angular frequency and time(!). So the principle is used for "operators" like position and momentum, Energy and time, etc.

That's all it is in essence. Oh, and there are discrete units to everything. Now, that's it :)

[mikelepore]

I see no relationship between quantum mechanics and dialectics. QM is about the probability of a small particles having certain states, such as momentum and location. Dialectics is a problem-solving technique for identifying trends in very large systems.

The Schrodinger's Cat problem is nonsense. As soon as radiation affects any detector at all, there is no further probability involved. The detector doesn't have to be a human sensory organ. The cat inside the closed box is just as much a detector. An air molecule might be the detector. Outside the so-called Copenhagen school of thought, the vast majority of physicists realize that as soon as a nuclear decay occurs the wave function is resolved. Either an alpha, beta or gamma emission has occurred, or it has not.

Mike Lepore - lepore at bestweb dot net

[ComradeRed]

The Schrodinger's Cat problem is nonsense. As soon as radiation affects any detector at all, there is no further probability involved. The detector doesn't have to be a human sensory organ. The cat inside the closed box is just as much a detector. An air molecule might be the detector. Outside the so-called Copenhagen school of thought, the vast majority of physicists realize that as soon as a nuclear decay occurs the wave function is resolved. Either an alpha, beta or gamma emission has occurred, or it has not. Well, it was originally formulated to demonstrate the absurdity of applying Heisenberg's uncertainty principle to things like position and momentum.

Oddly, people took it as an argument for the Copenhagen interpretation :blink:

As of yet there has been no alternative to the uncertainty principle, although it may come out to be something along the lines of generalizations of quantities just as one generalizes the kinetic energy in thermodynamics.

But not accepting it is not the same as disproving it.

[mikelepore]

I think the uncertainty principle is is pretty much verified. I don't know of any other way to explain the single-slit and double-slit diffraction of protons, neutrons, and, more recently, even atoms and molecules. A particle just has to be more than one place at a given time, no matter how much this may pain us to say it. Also, the tunnel diode certainly works, one way or another.

However, the Schrodinger's Cat "problem" is something else. I can't help thinking that pop-science paperback books are the main thing perpetuating it, and not infrequently with the author's agenda of finding parallels between modern physics and Eastern mysticism.

John Gribbin, in his In Search of Schrodinger's Cat, in all seriousness, quotes the lyric "nothing is real" from the Beatles' song Strawberry Fields Forever. Then he adds a few words: "Nothing is real until we look at it." That's a well-known fallacy, argumentum ad ignorantium. If he were to say he's using a pragmatic definition of truth instead of a correspondence definition of truth, then okay, he would then be clear (although i still wouldn't like it :-), however, one can't, with validity, adopt pragmatism abruptly and only in the case of one scientific branch. Why not, as well, say, "Aliens don't exist on another world until they contact us, and, when they contact us, then they pop into existence"? Why not say that the recent rediscovery of the presumed-extinct ivory-billed woodpecker in fact created what it discovered at that moment? Sorry, but I think that is philosophical idealism, and science should have none of it.

Mike Lepore - lepore at bestweb dot net

[1984]

Originally posted by [email protected] 11 2006, 07:01 AM
Well, it (the Schrodinger's Cat problem) was originally formulated to demonstrate the absurdity of applying Heisenberg's uncertainty principle to things like position and momentum.
Actually, it was originally formulated to demonstrate the absurdity of applying Heisenberg's uncertainty principle to LARGE (multi-molecular) objects.

There IS a probability of a tennis ball to pass right through a tennis racket without piercing the racket's net, but it is "rather small" - like the holes in Blackburn, Lancashire.

:lol:

[bezdomni]

Why couldn't Heisenberg please his wife?

Because when he had the position he didn't have the momentum and when he had the time he didn't have the energy.

:lol:

[TomRK1089]

As I understand it, the uncertanty principle demonstrates that since we cannot empirically prove the location of a particle, we cannot say that it can't be in two places at once. That's just my muddled understanding of it.

[ComradeRed]

Well, it's possible that it could be in two locations; and some interpretations of quantum mechanics certainly argues just that.

But draw a line with several dots on it. Make sure the dots are equal distance from the next dot and the previous one.

A hypothetical particle is moving at a rate of a third of the distance between the dots.

After 1 "turn" the particle's position is probabilistically 2/3 in the original node and 1/3 in the next node; we know its momentum (which is why the position is probabilistic).

But we can take this a step further and more radically which I shan't get into.