Heisenberg principle

[hanajack]

Should the [current] inability to "measure" position and momentum mean that a particle at a moment in time does not have a given position and speed?

[ajb]

It is not our inability, the quantum world tells us we cannot.

 

What quantum mechanics tells us that the particle will take all possible values of position and speed, until we try to measure one of these- it has all positions and speeds until we look at it!

 

Even then everything is rather statistical and stated in terms of probability.

[derek w]

Both the uncertainty principle and the observer effect come about because of wave/particle duality.

[swansont]

Both the uncertainty principle and the observer effect come about because of wave/particle duality.

I'd argue that's not strictly true. The observer effect is simply that you have to interact with something in order to observe it, and that interaction changes the system. Heisenberg's argument uses wave properties but as far as I can recall not the duality.

[Ronald Hyde]

Should the [current] inability to "measure" position and momentum mean that a particle at a moment in time does not have a given position and speed?

 

This is so not the way to understand the problems of measurement. To understand a problem in measurement you must at least imagine

an experiment that makes that particular measurement. You may follow that experiment by another that makes another measurement.

Using wave/particle duality and other broad brush principals will not lead to a clear understanding.

[EquisDeXD]

Wait, if you measure a particle at only a particular instant, your only gaining information about a particle when there is only a change in time coordinates of 0, so wouldn't that make sense that if you measure a particle at a single time coordinate that you aren't seeing it travel distance over time?

Edited October 6, 2012 by EquisDeXD

[Ronald Hyde]

Wait, if you measure a particle at only a particular instant, your only gaining information about a particle when there is only a change in time coordinates of 0, so wouldn't that make sense that if you measure a particle at a single time coordinate that you aren't seeing it travel distance over time?

Exactly what experiment are you using to make all these measurements such as a 'particular instant'?

Outside of the context of an experiment your statements have no meaning.

[EquisDeXD]

Exactly what experiment are you using to make all these measurements such as a 'particular instant'?

Outside of the context of an experiment your statements have no meaning.

 

I'm using any particle experiment ever, you only see a particle at a particular moment, according to quantum mechanics, you CANT see the measured particle itself with momentum or with a path it takes, it would be going through multiple time coordinates otherwise which would mean there is force or energy is traveling distance and momentum, but something can't travel distance at only 1 time coordinate or one instant, in order to travel distance you must at least by your own relative clock be traveling through time. I can explain it pretty easily using simple math

 

2x=t, x = potion, t equals time

 

t..........x

1.........2

2.........4

3.........6

4.........8

 

What was the change in position from time=3 to time=3? There wasn't a change, there was no distance traveled just at a particular instant.

Edited October 6, 2012 by EquisDeXD

[derek w]

I'd argue that's not strictly true. The observer effect is simply that you have to interact with something in order to observe it, and that interaction changes the system. Heisenberg's argument uses wave properties but as far as I can recall not the duality.

 

Does wave/particle duality come from the fact that matter and energy distorts space-time,and visa versa distorted space time effects matter?Particles create a field of virtual particles in the local space-time that surrounds them?Particles and space-time interact with each other.

[Ronald Hyde]

Does wave/particle duality come from the fact that matter and energy distorts space-time,and visa versa distorted space time effects matter?Particles create a field of virtual particles in the local space-time that surrounds them?Particles and space-time interact with each other.

 

You can't use 'any experiment whatever' to understand what happens. You have to define a particular experiment.

 

The 'wave particle duality' happens because people are confused about the measurement process. Any experiment that you conduct

must be defined from beginning to end, including any measuring apparatus. If the measuring apparatus measures wavenumber, you

can think of it as a wave. If the measuring apparatus measures the x-position where it is detected, you can think of it as a particle.

[MigL]

I've often said the same thing about wave-particle duality, Ronald.

 

You seem to have a lot of knowledge to pass onto others when you're not on one of your flights of speculation.

Keep it up.

Edited October 7, 2012 by MigL

[Ronald Hyde]

I've often said the same thing about wave-particle duality, Ronald.

 

You seem to have a lot of knowledge to pass onto others when you're not on one of your flights of speculation.

Keep it up.

I don't wish to derail the topic, but I feel a need to reply to MigL. I can work inside the box, I can think outside the box,

and i know when I'm doing either or both. I think you will in time find that my flights of speculation aren't really all that

'flighty', they have a connection with physical reality in areas which are not well understood, like Solar Activity. Because

that's all I'm interested in, understanding stuff.

[O'Nero Samuel]

What then do we have to say about the experiment by Dylan Mahler and Lee Rozema of the University of Toronto? They say they used a "weak-measurement technique". If my conceptions are right, it is the process of measurement that results in the, so to speak, trade-off between accuracy in the measured position and momentum.

[EquisDeXD]

What then do we have to say about the experiment by Dylan Mahler and Lee Rozema of the University of Toronto? They say they used a "weak-measurement technique". If my conceptions are right, it is the process of measurement that results in the, so to speak, trade-off between accuracy in the measured position and momentum.

 

But you don't need to say "weak measurement" then, that trade-off of accuracy was already invented by Warner Heisenberg. If what your saying is their reasoning, it seems like a petty excuse to get in the headlines.

Edited October 9, 2012 by EquisDeXD

[O'Nero Samuel]

But you don't need to say "weak measurement" then, that trade-off of accuracy was already invented by Warner Heisenberg. If what your saying is their reasoning, it seems like a petty excuse to get in the headlines.

I suppose they believe they exceeded Waner Heisenber proposed limit of accuracy. And yes, that did get them in the headline. Why do we always think its something bannal when we happen to knock of a scale from an existing theory, without building something concrete in replacement?

My question really is: what is the new twist to HUP gotten from their experiment?

Edited October 9, 2012 by O'Nero Samuel

[ajb]

My question really is: what is the new twist to HUP gotten from their experiment?

 

The only thing I think of is that the explanation often given to undergraduate students along the original lines of Heisenberg will need some thought. You can derive the uncertainty principle without any hand-waving arguments in a mathematically sound way by thinking in terms of operators, eigenvalues and eigenfunctions. The experiment does not change this deep fact in any way.

 

The bottom line here, which if of course not new, is that no quantum state can be simultaneously both a position and a momentum eigenstate.

[swansont]

I suppose they believe they exceeded Waner Heisenber proposed limit of accuracy. And yes, that did get them in the headline. Why do we always think its something bannal when we happen to knock of a scale from an existing theory, without building something concrete in replacement?

My question really is: what is the new twist to HUP gotten from their experiment?

I think it's pretty clear that the experimenters knew that they had shown only the observer effect limit to be wrong, and not the actual HUP. There is no new twist to the HUP. As ajb notes, the issue here is one of pedagogy.

[O'Nero Samuel]

Then those big headlines like; "

Squeezing What Hasn't

Been Squeezed Before:

Another Victory Over

Uncertainty in Quantum Physics Measurements", "Scientists Cast Doubt On

Heisenberg's Uncertainty

Principle ", " Quantum Uncertainty: Are You Certain, Mr. Heisenberg?", "More Accurate Than Heisenberg

Allows? Uncertainty in the

Presence of a Quantum Memory", etcetra, are overt exagerations by the press to help them sell papers, eh? The least they could do is give, if not the man, the theory some respect. But I suppose these are the hand work of the editors, not scientists.

[mississippichem]

Then those big headlines like; "

Squeezing What Hasn't

Been Squeezed Before:

Another Victory Over

Uncertainty in Quantum Physics Measurements", "Scientists Cast Doubt On

Heisenberg's Uncertainty

Principle ", " Quantum Uncertainty: Are You Certain, Mr. Heisenberg?", "More Accurate Than Heisenberg

Allows? Uncertainty in the

Presence of a Quantum Memory", etcetra, are overt exagerations by the press to help them sell papers, eh? The least they could do is give, if not the man, the theory some respect. But I suppose these are the hand work of the editors, not scientists.

 

Bingo.

 

Bad science journalism are flashy article titles are rampant these days. The science blogosphere seems to agree as well.

Edited October 9, 2012 by mississippichem

[imatfaal]

The only thing I think of is that the explanation often given to undergraduate students along the original lines of Heisenberg will need some thought. You can derive the uncertainty principle without any hand-waving arguments in a mathematically sound way by thinking in terms of operators, eigenvalues and eigenfunctions. The experiment does not change this deep fact in any way.

 

The bottom line here, which if of course not new, is that no quantum state can be simultaneously both a position and a momentum eigenstate.

 

 

I think it's pretty clear that the experimenters knew that they had shown only the observer effect limit to be wrong, and not the actual HUP. There is no new twist to the HUP. As ajb notes, the issue here is one of pedagogy.

 

On the issue of teaching - and hoping that those have taught physics can remember being taught themselves - surely by the point of being a physics undergrad and starting basic quantum mechanics the students will have done basic linear algebra (and know that whilst numbers are commutative under multiplication that matrices are not) and maybe even know of fourier transforms. And given that knowledge would it not be better to start with the mathematically sound explanation?

[hanajack]

The root of my original post lies in the latter part of it - not in the measurement aspect.

 

Simply, does or does not a particle have at a moment in time a given position and momentum?

[Does a rocket, a planet, a comet, a neutrino?]

[Ronald Hyde]

The root of my original post lies in the latter part of it - not in the measurement aspect.

 

Simply, does or does not a particle have at a moment in time a given position and momentum?

[Does a rocket, a planet, a comet, a neutrino?]

For particles no, that's a classical notion, all the particle has is an amplitude and associated probability to have such if you set up an

experiment to measure that observable. And the amplitude and probability can depend upon the time. The function that expresses

that dependency is the Hamiltonian.

[swansont]

On the issue of teaching - and hoping that those have taught physics can remember being taught themselves - surely by the point of being a physics undergrad and starting basic quantum mechanics the students will have done basic linear algebra (and know that whilst numbers are commutative under multiplication that matrices are not) and maybe even know of fourier transforms. And given that knowledge would it not be better to start with the mathematically sound explanation?

You run the risk of the professor not understanding the difference between the observer effect and the HUP, and/or the textbook confusing the two. I remember being taught Heisenberg's argument. Now, it may be that at some point the professor pointed out that this was not, in fact, the correct formulation, but if that happened I forgot. And that's a danger of teaching historical stepping stones that turn out to have been wrong — one of the first things you forget is that it's incorrect. The Bohr atom is perhaps the most famous physics example of this.

[O'Nero Samuel]

Now your are actually begining to sound like HUP should be taught as so-oldschool. But HUP still stand valid, doesn't it?

A nagging question in my mind is; given L. Rozema's procedure of weak measurement, is the product of two measured complimentary quantum quantities now somehow greater than planck's constant?

[EquisDeXD]

Now your are actually begining to sound like HUP should be taught as so-oldschool. But HUP still stand valid, doesn't it?

A nagging question in my mind is; given L. Rozema's procedure of weak measurement, is the product of two measured complimentary quantum quantities now somehow greater than planck's constant?

 

 

The HUP isn't completely wrong, in fact Dalton wasn't completely wrong, there WAS in fact a finite amount of which you could divide matter into, but science doesn't just throw previous models away with new data, it builds off of them, so even if the older HUP doesn't work in every situation, new models of it can be created to fit our current data which still utilize the old HUP.

Edited October 10, 2012 by EquisDeXD