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Heisenberg's Uncertainty Principle


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Showing 26-50 of 55 posts in this discussion
In reply to an earlier post on Aug 3, 2010 11:27:50 AM PDT
Arno Arrak says:
Their product, applied to an individual particle, has to obey the uncertainty principle. I did not see the images but check and see if they used some kind of beam whose parameters could be varied instead of an individual particle.

In reply to an earlier post on Aug 3, 2010 12:30:11 PM PDT
[Deleted by the author on Nov 21, 2012 7:14:59 PM PST]

In reply to an earlier post on Aug 3, 2010 1:02:29 PM PDT
I didn't have an actual image in mind, just the general kind that you see in a textbook or on the web.

Posted on Aug 3, 2010 1:41:36 PM PDT
I've read about Stern-Gerlach experiments developed in the early 1920s. Louisa Gilder ("The Age of Entanglement") says, "Silver atoms that pass through an inhomogeneous magnetic field (created by oddly shaped magnets) have a quantized response to the field: they are deflected either up or down, with no range of responses. Designed and performed in 1921 by Otto Stern and Walter Gerlach." That was 89 years ago so detectors have improved greatly since then.

When I was 12 about 50 years ago I ordered a cloud chamber from a scientific supply company. My father who was an engineer loved the idea, but unfortunately we could never get it to work. We would have been able to see the trails that electrons leave in the cloud chamber's vapor, evidence, at least, of their presence. I believe some detectors in the larger accelerators are cloud chambers, although I haven't checked that out on the web.

In reply to an earlier post on Aug 3, 2010 6:55:40 PM PDT
[Deleted by the author on Nov 21, 2012 7:15:16 PM PST]

In reply to an earlier post on Aug 3, 2010 8:19:39 PM PDT
J., I don't know how many experiments were carried before they confirmed the W and Z bosons but it was probably a long and complex series. The LHC has thousands of physicists at work, so as you say, the complications are probably enormous.

There's a good account of the Stern-Gerlach experiment at http://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experiment.

In reply to an earlier post on Nov 12, 2012 1:11:46 AM PST
Charlie T. says:
"Looks as if" because the recording instruments are imperfect.

In reply to an earlier post on Nov 12, 2012 6:18:11 AM PST
Last edited by the author on Nov 12, 2012 6:18:56 AM PST
According to the path integral formulation of quantum mechanics, a particle can take any path, but all the amplitudes for all the paths except those very close to the classical path cancel, so what one observes is the classical path.

In reply to an earlier post on Nov 12, 2012 10:43:21 AM PST
arpard fazakas wrote:
"According to the path integral formulation of quantum mechanics, a particle can take any path, but all the amplitudes for all the paths except those very close to the classical path cancel, so what one observes is the classical path. "
==============================

arpard fazakas,

Your explanation is the best way to screw up physics beyond hope.
As if Physics needs another maniac to make Physics more intolerable.

Where is the logic, clarity, or common sense in your strangulated musings?

Mohamed F. El-Hewie

In reply to an earlier post on Nov 12, 2012 9:11:52 PM PST
looks can be deceiving

In reply to an earlier post on Nov 13, 2012 5:37:55 AM PST
Last edited by the author on Nov 13, 2012 5:40:40 AM PST
I've been thinking more about your very interesting question. The way the detector you describe measures momentum is by the resultant deflection of the charged particle in a constant magnetic field according to the Lorentz force law. The curved path we see is actually a series of measurements of position and momentum over time. Let's imagine we examine a small portion of the path over time dt. Then we have two measurements: of the position x + dx and the deflection dy which reflects the momentum at position x + dx. What the uncertainty principle says is that the standard deviation of the measurement of one of the two variables (position or momentum) can't be less than the standard deviation of the measurement of the other divided by Planck's constant over 4 pi. So imagine we have a microscope and we're looking at the path at greater and greater magnification. What the Heisenberg uncertainty principle says is the finer the width of the line (more precise the measurement of position) the more it will wiggle around (the less precise the measurement of the deflection at each point, which is due to the momentum). Alternatively, the less the line wiggles around (the smoother the curve) the thicker the line will be (less precise the measurement of the position at each point).

In reply to an earlier post on Nov 13, 2012 7:15:40 AM PST
HelVee says:
NNG: pop-Fizick's, for the most part suck

HelVee: I can completely understand this point of view.

However, as a non-scientist and someone who will never, ever be a scientist (just. not. wired. that. way.), they help me get my head around some of the concepts. They also cause me to appreciate the awesome work actual scientists do.

Not all of us take a small amount of knowledge and assume it makes us smart!

In reply to an earlier post on Nov 14, 2012 6:53:26 AM PST
Last edited by the author on Nov 14, 2012 6:54:24 AM PST
Since Heisenberg has come up, I would like to mention the fact that the "uncertainty principle" bearing his name had been formulated previously by Ettore Majorana, a physicist/mathematician who worked with Enrico Fermi, and Emilio Segrè at the University of Rome. This is discussed in Laura Fermi's "Atoms in the Family," Univ. of Chicago Press (1954)

Atoms in the Family: My Life with Enrico Fermi

and in "A Mind Always in Motion: The Autobiography of Emilio Segrè," Univ California Press (1993)

A Mind Always in Motion: The Autobiography of Emilio Segre

Laura Fermi wrote:

"Majorana was a genius, a prodigy in arithmetic, a portent of insight and thinking power, the most profound critical mind at the physics building." [p. 46]

"Majorana had thought out Heisenberg's theory of the nucleus with neutrons and protons as building stones before Heisenberg published it, but he never wrote it." [p. 47]

Unfortunately, Majorana suffered from some type of mental disorder, which worsened after he received an appointment at the University of Naples. He disliked teaching and wanted to do only research. Segrè [pp. 126-127] describes the events leading up to his disappearance, probably by jumping overboard, while traveling from Palermo to Naples.

In reply to an earlier post on Nov 14, 2012 7:43:45 AM PST
uh huh

and leif ericson discovered america

so waht

In reply to an earlier post on Nov 14, 2012 7:49:37 AM PST
Are you sure Majorana came up with the uncertainty principle before Heisenberg? I can't find any confirmation of that in the Wikipedia articles on either the uncertainty principle or Majorana, and your quotes from Laura Fermi's book don't relate to the uncertainty principle.

In reply to an earlier post on Nov 14, 2012 9:46:38 AM PST
yup

if wikipedia doesnt have it
then it doesnt exist

In reply to an earlier post on Nov 14, 2012 10:07:09 AM PST
Re OP: Data from particle accelerators and other machinery shows only an APPROXIMATION to the position and momentum at a particular time. This arises from the wave part of the wave-particle duality properties of such particles. You can measure the values of both position and momentum as precisely as you like, except that the product of the uncertainties in the values of these measurements cannot be less than Planck's constant.

A related issue is that the product of uncertainty of energy and of time cannot be less than Planck's constant. Consider a radio wave of some specified frequency (say 1 MHz). If the wave continues indefinitely, you can measure the frequency as closely as you please, but if it starts and stops, the process of such starting and stopping will introduce uncertainty in the frequency, which uncertainties can be measured by a spectrum analyzer. In the case of radio broadcasting, the uncertainties show up as "sidebands" -- components differing in frequency from the carrier wave.

In reply to an earlier post on Nov 20, 2012 11:38:42 AM PST
Charlie T. says:
Robert A Saunders says:
You can measure the values of both position and momentum as precisely as you like

NO! You can measure EITHER one as precisely as you like, but not both at once.

In reply to an earlier post on Nov 20, 2012 11:41:27 AM PST
Charlie T. says:
Heisenberg's theory of the nucleus with neutrons and protons as building stones is NOT the uncertainty principle

In reply to an earlier post on Nov 20, 2012 2:15:32 PM PST
Last edited by the author on Nov 20, 2012 2:16:19 PM PST
D. Colasante says:
I appreciate your sentiments Charlie but you're quoting RAS out of context. I find him spot on. As it happens, so is your last sentence.

In reply to an earlier post on Nov 20, 2012 2:44:35 PM PST
noman says:
I didn't find anything on the "uncertainty principle" but I did find:

"Exchange forces
It seems that in 1928, Heisenberg had invented a chemical bonding type of electron "exchange force" theory, which posited a purely quantum mechanical force arsing from the exchange of identical electrons, and had assigned Rudolf Peierls, one of Sommerfeld's students, to work on the idea, as applied to Felix Bloch's quantum mechanical electron theory of metals. Heisenberg's "exchange interaction" intuition, supposedly, was the notion of a force generated solely by the exchanging of positions of two totally indistinguishable quantum particles. [2]

Because of the exclusion principle (Pauli exclusion principle), no two electrons can be in the same quantum state. Since, unlike classical particles, quantum electrons are identical, they can be considered to exchange places continually, which gives rise to an additional "attractive exchange force" between electrons.

Heisenberg thus suggested that Peierls examine the effects of this force on Bloch's theory of how electrons are able to propagate long distances in metals.

On 7 July, 1932, Enrico Fermi presented his report in Paris on "The Present State of the Physics of the Atomic Nucleus" (1932) without mentioning the type of force which was subsequently called "Majorana force" and which had actually been thought of, although in a crude form, some months earlier (circa Mar 1932 by Ettore Majorana). The issue of the Zeitschirft für Physick dated 19 July, 1932, contained Heisenberg's first paper on what latter came to be called the "Heisenberg's exchange forces", namely forces involving the exchange of both the space and spin coordinates. [3]

At the 1933 Solvay Congress, Heisenberg had presented his neutron-proton nuclear theory to Fermi and others, according to which the neutron-proton force arises from the virtual exchange of an electron ("virtual" because energy conservation is violated for an instant).

In December of 1933, stimulated by Heisenberg, Fermi showed that both Heisenberg's force and conservation laws could be maintained if the neutron and proton exchange not just an electron but and electron and a neutrino. [2]"

http://www.eoht.info/page/Werner+Heisenberg

In reply to an earlier post on Nov 20, 2012 3:38:59 PM PST
werranth413 wrote:
"Just 'seeing' large atoms was a great accomplishment a few years back. "
==================================
I know that was posted two years ago, which means your claim to seeing atoms must refer to earlier date. Yet, I am not aware that the laws of physics permit seeing atoms. We cannot even see viruses.

Mohamed F. El-Hewie

In reply to an earlier post on Nov 20, 2012 4:46:24 PM PST
The Weasel says:
Mohamed F. El-Hewie says:
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werranth413 wrote:
"Just 'seeing' large atoms was a great accomplishment a few years back. "
==================================
I know that was posted two years ago, which means your claim to seeing atoms must refer to earlier date. Yet, I am not aware that the laws of physics permit seeing atoms. We cannot even see viruses.

Mohamed F. El-Hewie
***
Isn't that what the quotes signify "seeing" - meaning detecting?

In reply to an earlier post on Nov 20, 2012 4:56:43 PM PST
Re Charlie T., 11-20 11:38 AM: You are misquoting me. Please read ALL of the sentence in question.

In reply to an earlier post on Nov 20, 2012 5:21:56 PM PST
Last edited by the author on Nov 20, 2012 5:26:58 PM PST
The Weasel wrote:
"Isn't that what the quotes signify "seeing" - meaning detecting? "
=======================
How hard is it for you to offer an opinion in lieu of a question?

The statement refers to "large" atoms, not just atoms. While, you pretend to know something about the difference between detecting and seeing large atoms, you did not bother to get lazy soul to explain a thing.

Mohamed F. El-Hewie
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Discussion in:  Science forum
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Initial post:  Aug 2, 2010
Latest post:  Nov 21, 2012

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