Godot

To respond to scaramallion's op, I doubt even god would know with zero error both values.
By definition, the measurement of the one causes a change in the other. Ergo, knowing both simlutaneously is impossible.
Conversely, (theoretical in an airy-fairy sort of way ) if a trajectory were followed for an infinitely long perios of time, with position and momentum being measures in sequence, then a reasonable approximation of both could be attained. However, this still wouldn't satisfy the zero error requirement.

Mageth

To me, god is superfluous to the question. It's really just "Can the precise position and velocity of a particle be known simultaneously?" If Heisenberg is correct (which he appears to be), the answer is "no".

Jesse

But there's also a separate question about whether, even if it can't be determined by any experiment, the particle actually has a well-defined position and momentum at a particular moment. Whether you think this question is even meaningful is a philosophical issue, I suppose.

Jesse

I'll try to give a slightly shorter version of my long post on the first page.

The question here is whether, when you have an uncertainty relation between quantities like position and momentum, it's possible to imagine that the particle really has a definite position and momentum at all times, and that the uncertainty principle is just a limitation on your ability to measure them, or whether it's somehow more fundamental than that. The main point of my post was that something called the Bell inequality is violated in a certain kind of test known as the "EPR experiment" and that this poses serious problems for anyone who wants to imagine that the uncertainty principle is just a measurement issue and that particle "really" have well-defined quantities of position, momentum, etc. at all times.

Instead of position and momentum, it's more common to use another uncertainty relation when discussing the Bell inequality, one between the "spin" of a particle along various axes. The use of the word "spin" is based on an analogy with spinning classical objects, since you can use the same type of test to measure the spin of something like a charged spinning ball and the "spin" of an electron--this idea is introduced on this page. But all you really need to know is that for a particle like an electron, you can measure its spin in 3 different directions in space, which you could label X, Y, and Z. Unlike for a classical magnetic ball, the spin in each direction will not be a continuous quantity, but will always be found to be either "up" or "down" relative to the axis you chose. And there is an uncertainty relation between these spins--if you choose your X, Y, and Z axes to be at right angles, then measuring any one of them will scramble your knowledge of the the other two (for example, if you measure the X-spin a few times in a row, then if it's "up" the first time it'll be "up" all the other times, but if you then measure the Y-spin and afterwards measure the X-spin again, it'll have a 50% chance of being "up" and a 50% chance of being "down").

So that's spin--now, back to the EPR experiment. In certain circumstances you can have a situation where the spins of two particles will be correlated, a situation known as "entanglement". For example, when two electrons are emitted as a result of radioactive decay, their total spin is always found to be zero, which means that if the first electron is found to be spin-up along the X-axis, then you are guaranteed that if the second electron is measured along the X-axis, it will be spin-down. You will find this even if the two electrons are separated by a large distance and measured at the same time, so that by measuring one you learn information about the result of the same measurement on the other faster than a signal could have passed between the two experimenters. This is partly what Einstein referred to as "spooky action at a distance" but on the surface there's nothing that seems spooky about it--you could just try to explain this in terms of the idea that each had a well-defined spin on each axis when they were first emitted, and the measurements just reveal those preexisting spins. For example, the first might "really" have been UP/DOWN/UP on the X,Y, and Z axes all along, while the second was "really" DOWN/UP/DOWN all along. This would guarantee that when the two experimenters measure both along the same axis, they always find opposite spins.

But the Bell's inequality is a general result about what happens when you randomly pick two different traits to measure on any two objects with well-defined preexisting values of each trait. The page I mentioned above gives a simple example:

This page explains why the inequality must be true for objects whose traits were already set before your measurements; the "Ypiarian twins" scenario in my earlier post also explained the logic. Anyway, the point is that the Bell inequality is violated when you measure spins of correlated electrons along randomly-chosen axes in the EPR experiment. Somehow you find that although the electron spins are always opposite when the experimenters happen to choose the same axis to measure along, you can't explain this just by saying the electrons' spins along all three axes were set and opposite at the moment they were first created.

You can still imagine the electrons have well-defined spins with various strange interpretations in which they do not necessarily have opposite spins along all three axes, only along the axis that is actually measured--for example, they might "know in advance" which axis the experimenter would select, or they might be able to communicate the choice of axis faster than light. These options are covered by the various "interpretations" of QM which I discussed earlier, but here I just wanted to go over EPR and the Bell inequality in terms of actual properties of particles instead of the analogy of the Ypiarian twins from the book I quoted in my other post.

Peter Soderqvist

TO JESSE

Soderqvist1: How many interpretations can deal with a wave equation of the whole universe? If you as a cosmological quantum physicist write down a quantum mechanical wave equation for the whole universe, what causes the collapse of this wave function if everything in your equation is in superposition of states? The only parsimony explanation I know about is the many world's interpretation, because it doesn't need any assumption about collapse of wave function, it is instead wasteful with universes!

The Copenhagen Interpretation can deal with this equation through its offspring, namely john von Neumann's interpretation! Newman's interpretation stems from Bohr's feeling that collapse of wave function happens in the moment when the observer become aware about a measurement! Eugene Wigner has postulated an immaterial mind as collapser of wave function! I have read the Astrobiologist Paul Davies, and Julian Brown's book, The Ghost in the Atom (issued 1986).

Davies has interviewed David Deutsch, and he is enthusiastic about David Deutsch's MWI experiment with quantum computers in a near future, to test Everett's theory! If and only if Everett's theory is proven wrong the von Neumann's interpretation will be the only one! And I firmly believe that the assumption about the immaterial mind cannot be formalized in this equation but must be taken for granted, since all truths cannot be proven according to Godel's incompleteness theorem, because non-computational insights must be taken for granted, or rejected!

The immaterial mind outside the system, can give this equation a consistency proof! I have both Julian Brown's book, The Quest for the Quantum computer, and David Deutsch The Fabric of Reality in my home, but for the moment I am reading Kurt Godel's biography, a Life in Logic; a book about Godel's incompleteness theorem, and I am also reading Carl Sagan 's book, The Demon Hunted world, Science as the candle in the dark!

Soderqvist1: The question I want to ask a computer in a Turing test is; can Godel's incompleteness theorem be formalized in you system? If your answer is no! Why not? And if your answer is yes! Can you describe how this pattern looks like? – However, if you add something to the system in order to give it consistency, what you have added will end up incomplete too, the same it is with more adding, and so on in an infinite regress! This "takes for granted" by professor Keyser is not formalized in the system, therefore; a human mind is something more than a computational system!

There are a lot of different scientific theories! What they all have in common is the same core, which has been experimentally confirmed! But they differ in their extrapolations, so that they all cannot be right, but I am an Darwinian at heart, and I thus firmly believe that, that this high amount of informational entropy from extrapolations (variation), will be reduced by further experiments (Natural selection), since the fittest theory will survive, and the unfit theories rejected! The theory about the conscious mind as the collapser of wave function is my pet theory in the game!

Soderqvist1: some critics of the Darwinian theory, has used the second law of thermodynamics to disprove evolution, and they have failed to do so, but what "some materialists" has ignored, or is ignorant about when they are talking about testability, falsifiability, and that the result must be replicable, in scientific theories and referring to Karl popper about it, is that Karl Popper has debunked materialism and is a genuine dualist, (as quoted from his home side with emphasis in bold type by me). Karl Popper and John Eccles have written a book about it, namely, The Self and its Brain!

John Page

Yes. Where does the certainty of the mind come from? It seems to me that our senses project the perception that objects have "hard edges", circumscibed by (non-existent) lines that may intersect at (non-existent) points, why does anything need to be precisely anywhere?

Our conceptual model of a particle is a delineated mass that has a center of gravity - the latter being an imaginary precise point in space time around which we can calculate its density, size etc. On the othe hand, one's conceptual model of a magnetic field is a phenomenon that acts (invisibly) at a distance and the force of action varies by distance.

That matter and energy can become interchangeable (as per theories of eminent scientists) shows that we need to reconsider the above conceptual models. Apparently, a magnetic field cannot extend to infinity, its force decreases over distance but comes to a quantum point beyond which it can jump no further. At the other end, we suppose that a particle occupies a certain volume of space - how should we consider this different than a particle being in more than one place at a time?

Sorry I don't know the answers. I agree with prior posters that we don't need the miracle ingredient fraudulent (god), which is an invention of our own imaginations, to explain the physical universe.

Cheers, John

Kevbo

Hey, I just wanted to start this post with a little mod request: Do you think we could move all the Seraphim/Jesse posts about whether presupposing the existence of a God in a discussion is possible to an atheist to a new thread discussing exactly that? Those posts seem to be making up the bulk of the thread and it's irrelevant to the topic if we assume that it *is* possible for an atheist to presuppose the existence of a an omniscient God for the purposes of discussion. Anyhow, on to the thought on the actual topic:


My take on QM is that it's possible that particles can or cannot have both a definate momentum and position at a given interval, but that we can never know the answer because our measurement of these qualities comes from indirect observation.

Now, depending on how God observes the world, it may or may not be possible for particles to have these two elusive qualities at the same time. If God observes the world in the sense that God *is* all matter, space, and time (matter is the intersection of God's "fingers" with the plane of reality, or something) then God can have a non-physical "nervous system" that detects these particle qualities, and can know both at once.

If God exists independently of reality or must use physical means to interpret reality, I'd say that God is in the same ark as us mortals.

Kevbo

Thanks mods!

Jesse

Kevbo:
Hey, I just wanted to start this post with a little mod request: Do you think we could move all the Seraphim/Jesse posts about whether presupposing the existence of a God in a discussion is possible to an atheist to a new thread discussing exactly that?

Done! The thread about assumptions needed to answer this question can now be found here.

tensorproduct

Actually this is untrue, Heisenberg's Principle can be derived from mathematical first principles (although it does require some physical defintions afterwards.) The idea that our observation affects the results is a byproduct of uncertainty, but due to the principles of QM a particle does not have exact position or momentum at any time regardless of measurement.