Sunday, September 27, 2009

Scott Rebuttal. III. The Importance of Quantum Mechanics

I make comments on Dr. Scott's lack of mention of QM:
Dr. Scott, an electrical engineer, is clearly a victim of this professional isolation himself. I found little mention of quantum mechanics or its impact in astronomical observations and astrophysical understanding and the feedback astrophysics provided to Earth laboratories. Considering that the quantum mechanics that explains the spectra and energy source of the stars is the same quantum mechanics that has made modern microelectronics possible, I suspect Dr. Scott probably has some interesting misconceptions about this subspecialty of his own field. (”The Electric Sky: Short-Circuited”, pg 8)
Dr. Scott has a rather bizarre response
A discussion of quantum mechanics has no place in my book. I intentionally do not discuss the very many subspecialties of electrical engineering. That was not the thrust of my book and I submit comments such as the one above are simply 'red-herrings‘ dragged across the path of that thrust. (”D.E. Scott Rebuts T. Bridgman”, pg 4).
But the quantum mechanics that explains atomic structure and spectra is the exact same quantum mechanics that made modern semiconductor electronics possible!  Does Dr. Scott know this?

One of the few references I provide that Dr. Scott did apparently examine is my paper “The Cosmos in Your Pocket: How Cosmological Science became Earth Technology” (Version 1 was available at that time). Dr. Scott reinforces the appearance of his misunderstanding of quantum mechanics on page 2 of his rebuttal:
At any rate, in one swoop, TB attempts to subsume all of the practical achievements of modern chemistry, solid-state physics, and electronics into owing their origins to astrophysics. This is absurd on its face. If he thinks that Leo Esaki, working for (what is now) Sony Corporation in 1957, had any thoughts about astrophysics in his mind while developing his tunnel diode, I submit he is delusional. What about Brattain, Bardeen, and Shockley while working at Bell Laboratories on their bipolar junction transistor – or the field-effect transistor? Were they thinking about astrophysics too? I very much doubt it. (D. E. Scott Rebuts T. Bridgman, pg 2)
Dr. Scott misses again. My point is the these individuals used the exact same quantum mechanics as Bethe, Teller, Gamow, and others used in solving problems in nuclear astrophysics. These successes in astrophysics also demonstrated the broad range of applicability of quantum mechanics, reinforcing both astrophysics and quantum mechanics as well as the concept that the physical laws we measure on Earth apply in the distant cosmos as well.

But to fully appreciate the quantum connection between astrophysics and modern electronics, one needs to examine some of the history.

These two papers, by Alan Herries Wilson from 1931, are regarded by many as the papers that put semiconductors on a firm theoretical foundation.
These two papers turned semiconductors from a mysterious material (its primary use in electronics was the 'crystal' in crystal radio sets) to a substance that could be understood, and subsequently manipulated, on a fundamental level. John Bardeen and others regard them as the classic papers in semiconductor electronics (see Oral History Transcript — John Bardeen).

While I was originally planning a different approach for this article, another search of the literature revealed a far more interesting connection between semiconductor electronics and astrophysics. Consider this paper, published by the same Alan Herries Wilson earlier in 1931.
This was one of the first papers to use quantum mechanics to in an attempt to understand the nuclear processes that could take place in stellar interiors.

This is a fascinating paper, as it would examine the impact of quantum tunneling on nuclear reaction rates in stars. It did not solve any significant astrophysical problems, for it was a little before it's time, but it outlined the quantum mechanical analyses that later researchers would use. Wilson could not solve the problem because he did not know about the neutron (which would be discovered the following year) nor did he have a way to include the newly-hypothesized neutrino into the reaction computations. A theory of neutrino interactions would not be available until some work by Enrico Fermi a few years later. Both of these discoveries were important to solve the problem of stellar nuclear reactions. It would be another eight years before Hans Bethe would solve the main bottleneck in the formation of hydrogen from helium [Bethe 1939]. Bethe's work would not fully solve the problem until after World War II when the uncertainties in stellar compositions would be resolved.

Even more interesting is the fact that Wilson would note how astrophysicists recognized the implications of the Pauli Exclusion Principle (Wikipedia: Pauli Principle) (the fact that no two electrons, or more generally, identical fermions, can occupy the same quantum state at the same time) before the physicists[Wilson 1980]. Astrophysicists immediately made use of this principle. Ralph Fowler (who was one of Wilson's professors) had already used the Pauli Principle for computing the structure of condensed matter at high densities in the interior of stars [Fowler 1926]. This paper would lay the foundations of later research on degenerate states of matter matter (Wikipedia: Degenerate Matter), a critical development in understanding the structure of white dwarf (Wikipedia: White Dwarf) and neutron stars (Wikipedia: Neutron Stars).

Wilson applied the exact same quantum mechanics in both astrophysics and the development of semiconductor theory. And Wilson wasn't the only physicist to do this. Exploring the publications of Hans Bethe (Nobel Prize, 1967), Edward Teller and others reveal contributions in our understanding of atoms and molecules as well as astrophysics - via the universal application of quantum mechanics.

This only reinforces my original claim, as the great majority of what we know about astrophysical plasmas is determined from their spectra, which can only be understood with quantum mechanics. This is the same quantum mechanics used in understanding technologies from semiconductor electronics to laser emission.

Prior to the discovery of astrophysical spectra, the only thing we knew about the cosmos were positions (mostly 2-D, but 3-D if sufficiently close), colors, motions and variability if we collect the data over time.

Spectra changed all that. With spectra, and the quantum mechanical framework which describes their formation, we can determine:
  • Compositions, ionization levels and temperatures: from lines and intensities of lines
  • Pressure and temperature: from the profile of the spectral lines
  • Radial velocities and intense gravitational fields: from spectral line shifts
  • Electric and magnetic fields: from line splitting, the Zeeman (Wikipedia: Zeeman Effect) and Stark effects (Wikipedia: Stark Effect).
Even on the Earth, quantum mechanics is needed for plasma diagnostics as many high-temerature plasmas of industrial and commercial interest are hot enough to destroy material probes inserted in them. We therefore measure their spectra and use quantum mechanics to determine the temperature and ionization levels.

The quantum mechanics that makes our semiconductor electronics in our homes possible, and enhances our understanding of laboratory plasmas, is the same quantum mechanics that explains the spectra of stars as well as their nuclear energy source.

Did Dr. Scott even bother to check his 'facts' before writing his 'rebuttal'?  Is he attempting to evade acknowledging the role of quantum mechanics in his own field of electrical engineering, as well as in the fields of plasma physics and astrophysics?  Does Dr. Scott understand the role that the concept of Fermi energy plays in semiconductor electronics as well as white dwarf and neutron stars?

  1. J. B. Hearnshaw. The analysis of starlight: One hundred and fifty years of astronomical spectroscopy. Cambridge and New York, Cambridge University Press, 1986.
  2. R. H. Fowler. On dense matter. Monthly Notices of the Royal Astronomical Society, 87:114–122, December 1926.
  3. A. H. Wilson. Solid state physics 1925-1933: opportunities missed and opportunities seized. Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, 371: 39–48, June 1980.
  4. H. A. Bethe and C. L. Critchfield. The formation of deuterons by proton combination. Physical Review, 54: 248–254, August 1938.

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