Is time a constant?

Originally posted by KazetNagorra
You shouldn't look at a particle as having a position and momentum with a certain uncertainty. Rather, the position and momentum of particles are not well-defined as in a classical sense (I hope the distinction is clear).

Its more complicated than that. When they interact with another particle then one particular position or momentum is selected as having existed. With the two slit experiment, the photon goes both ways, but if it is detected en-route it only goes one way. Weird.

Originally posted by twhitehead
Its more complicated than that. When they interact with another particle then one particular position or momentum is selected as having existed. With the two slit experiment, the photon goes both ways, but if it is detected en-route it only goes one way. Weird.

Yes, and actually there is not really a solid theoretical framework to describe the process of wavefunction collapse. If you describe the entire system, including the measurement process, then the system could evolve deterministically.

Originally posted by KazetNagorra
Yes, and actually there is not really a solid theoretical framework to describe the process of wavefunction collapse. If you describe the entire system, including the measurement process, then the system could evolve deterministically.

The universe is a closed system. Therefore it has a wavefunction. If you know it, then everything in the universe is determinable. Does this mean the Heissenberg was wrong?

Originally posted by FabianFnas
The universe is a closed system. Therefore it has a wavefunction. If you know it, then everything in the universe is determinable. Does this mean the Heissenberg was wrong?

Well, that is the question. Is the universe a closed system? I don't know. But even if it is, it doesn't mean Heisenberg was wrong - actually the Heisenberg uncertainty relation does not depend on the act of "measurement".

Originally posted by KazetNagorra
Well, that is the question. Is the universe a closed system? I don't know. But even if it is, it doesn't mean Heisenberg was wrong - actually the Heisenberg uncertainty relation does not depend on the act of "measurement".

What does it depend on? I thought it was the interference with quantum effects that determined which reality shows up.

Originally posted by KazetNagorra
Yes, and actually there is not really a solid theoretical framework to describe the process of wavefunction collapse. If you describe the entire system, including the measurement process, then the system could evolve deterministically.

I disagree. I do not believe that there is any evidence that the universe is deterministic. It might be, but there is no really good reason for believing it is.
I the two slit experiment, the photons hit the screen on the other side in random places with certain probabilities. The probabilities are affected by the number of slits (ie the number of possible paths), but its actual final interaction with the screen remains random and is not determined by initial conditions.

Originally posted by KazetNagorra
Well, that is the question. Is the universe a closed system? I don't know. But even if it is, it doesn't mean Heisenberg was wrong - actually the Heisenberg uncertainty relation does not depend on the act of "measurement".

Doesn't matter if the wave function is known or not, measured or not, only that there exist such a wavefunction, it's complexity doesn't matter.

Originally posted by twhitehead
I disagree. I do not believe that there is any evidence that the universe is deterministic. It might be, but there is no really good reason for believing it is.
I the two slit experiment, the photons hit the screen on the other side in random places with certain probabilities. The probabilities are affected by the number of slits (ie the number of possib ...[text shortened]... al final interaction with the screen remains random and is not determined by initial conditions.

I'm not saying the universe is deterministic, I'm just saying I don't know whether or not it is. The double slit experiment is a nice demonstration of quantum physics but doesn't really answer the question about the nature of the universe because of the question marks surrounding the wavefunction collapse.

Originally posted by sonhouse
What does it depend on? I thought it was the interference with quantum effects that determined which reality shows up.

The Heisenberg uncertainty principle says something about the expectation value of certain operators.

Originally posted by KazetNagorra
The Heisenberg uncertainty principle says something about the expectation value of certain operators.

Does it say anything about destructive decoherence?

Originally posted by KazetNagorra
I'm not saying the universe is deterministic, I'm just saying I don't know whether or not it is. The double slit experiment is a nice demonstration of quantum physics but doesn't really answer the question about the nature of the universe because of the question marks surrounding the wavefunction collapse.

It seems we are in agreement.

My favorite way of looking at things is to throw off the illusion of time moving forward and to look at the universe from a single point in time.
The past and future are both a range of possibilities. There far are more possible futures than there are possible pasts, but apart from that there is little difference between the two. The illusion of time flowing is simply because the small number of possible pasts - especially on the macro scale - results in us being able to 'remember' the past far better than we 'remember' the future. (you could replace 'remember' with 'predict' in both instances of the previous sentence.)

One important point to note, is that if the universe is not fully deterministic, then it may be as impossible to accurately predict the past as it is to predict the future. If that is the case then the 'actual' past is either a forever unknown, or we could see it as a sum of all possible unknowns - which is what quantum mechanics does.

Originally posted by sonhouse
Does it say anything about destructive decoherence?

Not directly I don't think...

Originally posted by amolv06
KellyJay,

How does one define a moment? I would be interested in your definition.

In special relativity, one of the topics I find most interesting is that of simultaneity. For instance, one could use two simultaneous events to define a moment (i.e. a laser hitting two photo-detectors at the same instant). This is a precise moment in time. Relativit ...[text shortened]... tten a chance to check any of them out? They really are great books, and well-worth the read.

Sorry for the long delay in my answer, I was out of town for a few weeks.

I view "the moment" as the same "instant in time"; it is the point where all things
occurred during its durations. So far as relativity goes as I have seen it described
here and else where, it seems more like a perspective than it does a means of
looking at simultaneous occurrences. For me our time line can be captured in a
picture; the moment is seen as the picture was taken; however, I also have to
acknowledge that depending upon the speed of your camera you could still miss a
few things due to some things moving at great rates of speed. So the means of taking
the picture would have to have the ability to get it all at once if a picture were to
taken, and do so with clarity.

I have not had time to look for, or read the books you mentioned. I plan on it, I've
been out of town on business and just barely had time for my chess moves here
let alone anything else. Right now I''m trying to get my sleep back on the same
schedule as everyone else in California.
Kelly

Originally posted by twhitehead
Our measuring devices follow the laws of physics just like the rest of the universe. Many of our measuring devices have very specific very well known laws. For example, some of the most accurate clocks rely on the properties of atoms.
But there are many different ways to measure time, and different ways use different laws. If you move a whole bunch of c ly
My apologies. I was engaging in some totally unnecessary mind reading.[/b]

"My apologies. I was engaging in some totally unnecessary mind reading."

LOL, if that is the worst that happens to us we are in great shape, I do the same
thing with you and others here from time to time as well, you know. No biggie.
Kelly

Originally posted by twhitehead
Our measuring devices follow the laws of physics just like the rest of the universe. Many of our measuring devices have very specific very well known laws. For example, some of the most accurate clocks rely on the properties of atoms.
But there are many different ways to measure time, and different ways use different laws. If you move a whole bunch of c ...[text shortened]... ly
My apologies. I was engaging in some totally unnecessary mind reading.[/b]

You gave me a lot to think about here.
Kelly