Talk:Heisenberg's microscope

message: I recommend a new section be written called "Bohr's Contribution," which would discuss the following three points (comments welcome).
===== Bohr's Criticism =====
The introduction to this article (and a reference in the discussion) suggests that Bohr "criticized" the microscope argument. This is only partially correct. Bohr was critical of Heisenberg's interpretation of "uncertainty" as a mere "human inability" to know some things. So, he might have been critical of this aspect of Heisenberg's *interpretation* of the microscope. But Bohr clearly accepted the argument just fine -- see this p.583 of this 1928 Nature article, in which Bohr gives a rather more sophisticated version of the 1930 microscope argument given by Heisenberg. The main difference, from what I can tell, is that Bohr emphasizes the objective indeterminacy of momentum given a sharp position measurement, and vice versa -- he makes it clear that this is not a mere human ability to know something. Bwr6 20:58, 15 December 2010 (UTC)
thread_title:  Bohr's Contribution 

message: The introduction to this article (and a reference in the discussion) suggests that Bohr "criticized" the microscope argument. This is only partially correct. Bohr was critical of Heisenberg's interpretation of "uncertainty" as a mere "human inability" to know some things. So, he might have been critical of this aspect of Heisenberg's *interpretation* of the microscope. But Bohr clearly accepted the argument just fine -- see this p.583 of this 1928 Nature article, in which Bohr gives a rather more sophisticated version of the 1930 microscope argument given by Heisenberg. The main difference, from what I can tell, is that Bohr emphasizes the objective indeterminacy of momentum given a sharp position measurement, and vice versa -- he makes it clear that this is not a mere human ability to know something. Bwr6 20:58, 15 December 2010 (UTC)
thread_title:  Bohr's Criticism 

message: As pointed out in the uncertainty principle article, Heisenberg's expression of this principle is not mathematically correct -- in this discussion, "change in momentum" \Delta p_x should be replaced with "standard deviation of momentum" \sigma_{p_x}. However, I would suggest keeping the error in the "Heisenberg's Argument" section, since that section does give a literal expression of what Heisenberg said. However, in the 1928 Nature article], Bohr actually does give this correct expression in his discussion of the microscope. This alternative expression (and acknowledgement that it is correct) could be included in the discussion of Bohr. Bwr6 20:58, 15 December 2010 (UTC)
thread_title:  Expression of the Uncertaintly Principle 

message: Is it clear that Heisenberg invented the microscope argument and not Bohr? The first written instance of the microscope that I can find is in the above 1928 article by Bohr. All the expressions of it by Heisenberg that I've been able to find have been later. Some reference should be given here -- or, if none can be found, it should be acknowledged that it's not clear who invented the argument. Bwr6 20:58, 15 December 2010 (UTC)
thread_title:  Historical Origin 

message: "The temperature at which all classical molecular motion stops, equal to 0 Kelvin or -273.15° Celsius. However, quantum mechanically, molecules cannot cease all motion (as this would violate the Heisenberg uncertainty principle), so at 0 K they still vibrate with a certain small but nonzero energy known as the zero-point energy." http://scienceworld.wolfram.com/physics/AbsoluteZero.html
Okay, this is another example where Heisenberg's microscope does not apply.  Is anyone measuring all the atoms in the universe at the same time so that a photon of light is hitting them so that they have an uncertainty of position and cannot reach absolute zero?
In other words, the Uncertainty Principle is applied to the universe even when no measurements are being taken.  Therefore, no disturbance is being made to the measurements.  The Uncertainty Principle is taken to be fundamental.  It says that fundamentally no moving particle can ever have an exact position.  Therefore, no moving particle can ever be said to stop its motion.  Therefore, no atom can cease motion at absolute zero.  This is without measurements being taken to "disturb" the particles.  Therefore, Heisenberg's microscope is wrong.
Now, I want to mention this caveat.  Heisenberg's Uncertainty Principle will in the near future be either proven or disproved.  In creating BECs (Bose-Einstein Condensate) scientists are building better and better instruments to reach absolute zero.  When they build one that reaches absolute zero, HUP will either be debunked or raised to the status of absolute law.--Voyajer 00:28, 4 January 2006 (UTC)
replies: text: Agreed. I had that part wrong. P0M 07:44, 5 January 2006 (UTC)
thread_title: Uncertainty Principle and Absolute Zero

message: Basing himself both on papers by Dirac and Jordan, on contacts with Wolfgang Pauli, Niels Bohr, and others, Heisenberg's first great contribution was the formulation of a theory of quantum mechanics that was expressed in matrix form, and his second great contribution was his indeterminacy or uncertainty principle.  Heisenberg discovered that a natural limit on the certainty or precision of calculated results appeared whenever one attempted to deal with position and momentum of a particle at the same time or the energy and time of a particle at the same time.  The limitations emerged from working through the equations, and were entirely apart from the kind of experimental error that theoretically could be reduced toward a limit of zero by improving measurement tools and procedures. (ab!=ba) The letter that Heisenberg wrote to Pauli in 1927 is the first known record of the communication of this finding to another person.  
Two problems suggested themselves to Heisenberg: What did it really mean to speak of the position of a particle such as an electron? Were the uncertainties that emerged from the mathematics of the theory a kind of mathematical fluke that would find no support for their existence in the empirical world?  Heisenberg worked the problem through in his mind and on paper. One way to determine the position and momentum of a particle would be to observe it with a microscope. When dealing with a sufficiently small particle, such as an electron, the higher the frequency of light one chose in the interest of pinpointing the location more closely, the more energy would be delivered to the particle, and knowledge of Planck's constant allows one to calculate the magnitude of this effect. So even on the assumption of a classical picture in which both the electron and the photons used to measure it were depicted as discrete entities, tiny hard spheres, the idea that a definite position could be known comes into question. This result "solidified in his mind the principle he had already derived without this analogy." (Aczel, 78)  Heisenberg drafted his thought experiment paper in February of 1927. After Bohr read the paper, he wanted Heisenberg to rewrite it to avoid the inaccurate classical depiction of these entities, and to include the idea of complementarity between particles and waves,  but Heisenberg responded only by adding a summary of Bohr's objections to his paper. (http://www.aip.org/history/heisenberg/p09.htm (midpage))
It seems clear that Heisenberg used his thought experiment as a way of introducing his ideas on indeterminacy. The problem is that it intentionally begins where his readers presumably will begin, with a classical picture. It shows them that on its own assumptions the classical picture will not work because while operating under those assumptions you cannot make sense of of the idea of known position and momentum. He uses Planck's constant to quantify the effect that measurement attempts would necessarily have. Making his thought experiment in this way may imply to some readers that the electron that was to come under investigation had a determinate position and momentum, and that after a measurement is attempted the original position and momentum is replaced by some other determinate position and momentum -- which is again unknown. But the thought experiment is intended to show that even if, for the sake of argument, we suppose that these particles have definite positions and momenta, those data cannot be learned by the means proposed in the experiment.
Forgot to sign. P0M 08:18, 5 January 2006 (UTC)
thread_title:  rework draft -- put it here so it won't get lost