tisdag 7 september 2010

Light: Waves or Particles?

Is light electromagnetic waves described by Maxwell's equations, or a stream of "light particles" or "photons" as described by Newton? Is heat transfer by radiation an electromagnetic wave phenomenon, or is it a stream of small packets/particles of "energy quanta"?

This is a basic question in physics and also of climate science since our climate is a thermodynamic heat engine powered by radiation from the Sun in the visible spectrum, and cooled by infrared radiation to outer space, with the Earth absorbing high-frequency light and emitting low-frequency light like a blackbody.

Until 1900, the answer was clear: Maxwell's equations was a wonderful gift to humanity as an amazingly compact yet complete description of light and propagation of light, from scientific
point vastly superior to the primitive particle idea of Newton. Educated people would say waves and not particles.

But there was a problem: The phenomenon of blackbody radiation when approached with wave mechanics led to an "ultraviolet catastrophy" with infinite radiated energy in direct contradiction with observation. To save physics from catastrophy something had to be done and it was Max Planck who took on the responsibility, as the successor of the great Kirchhoff at the University of Berlin and a very ambitious member of the newly formed German Physical Society aimed at giving The Kingdom of Prussia a leading role in the scientific world.

After much agony Planck in 1900 gave in and sacrificed rational deterministic wave mechanics, replacing it with irrational statistics of "energy quanta" described by himself as:
  • the whole procedure was an act of despair because a theoretical interpretation had to be found at any price, no matter how high that might be...
And so modern physics was born with the catastrophy elegantly handled by a Salomonic:
  • light is both waves and particles, sometimes this sometimes that, and you are free to chose whatever suits you the best, also referred to as wave-particle duality.
In 1905 the young Einstein used Planck's energy quanta to explain the photoelectric effect,
which added to the success of the revival of Newton's primitive particle theory, requiring wave-particle duality because after all the full particle primitivism of Newton was untenable. But also wave-particle duality is a form of scientific primitivism: Of course you can as a reasonable human being sometimes act like a fool, but duality is here called schizophrenia, and schizophrenic science is crazy science, in our time represented by CO2 climate alarmism ultimately based on radiation as particles.

Both Planck and Einstein struggled to pay the price of introducing particles all through their lives with the logical tragical end:
  • All these fifty years of conscious brooding have brought me no nearer to the answer to the question, “What are light quanta?”. Nowadays every Tom, Dick and Harry thinks he knows it, but he is mistaken. (Einstein shortly before his death 1954)
  • I consider it quite possible that physics cannot be based on the field concept, i.e., on continuous structures. In that case, nothing remains of my entire castle in the air, gravitation theory included, and of the rest of physics. (Einstein 1954)
  • What wanted to say was just this: In the present circumstances the only profession I would choose would be one where earning a living had nothing to do with the search for knowledge. (Einstein's last letter to Born Jan 17 1955 shortly before his death on the 18th of April, probably referring to Born's statistical interpretation of quantum mechanics).
  • Would it not be possible to replace the hypothesis of light quanta by another assumption that would also fit the known phenomena? If it is necessary to modify the elements of the theory, would it not be possible to retain at least the equations for the propagation of radiation and conceive only the elementary processes of emission and absorption differently than they have been until now? (Einstein)
  • We shall now derive strange properties of heat radiation described by electromagnetic wave theory. (Planck 1900)
  • We shall assume that the radiation in one direction is completely independent of the radiation in a different direction, even opposite. (Planck)
  • Either the quantum of action was a fictional quantity,then the whole deduction of the radiation law was essentially an illusion representing only an empty play on formulas of no significance, or the derivation of the radiation law was based on sound physical conception...Mechanically, the task seems impossible, and we will justhave to get used to it (quanta) (Planck 1909).
  • Zur radikalsten Affassung neigt J.J Thompson und A. Einstein, welche glauben, das die Fortpflanzung der elektromagnetischen Wellen nicht genau nach den Maxwellshen Feldgleichungen, sondern nach gewissen Energiequanten h nu erfolgt. Ich meine dagegen, dass man einstweilen noch nicht genötig ist, so revolutionär vorzugehen, sondern das mann damit auskommen durfte, die Bedeutung des Energiequantums h nu lediglich in den Wechselwirkungen zu suchen, mit denen die Resonatoren einander beeinflussen. Eine definitive Entscheidigung uber diese prinzipiellen Fragen können aber erst weiter Erfahrungen bringen. (Planck 1908)
  • Despite the great success that the atomic theory has so far enyoyed, utimately it will have tobe abandoned in favor of the assumption of continuous matter (wave mechanics) (Planck 1882).
  • We therefore regard - and this is the most essential point of the entire calculation - energy to be composed of a very definite number of equal packages (Planck 1900).
  • The wave theory of light, which operates with continuous spatial functions, has worked well in the representation of purely optical phenomena and will probably never be replaced by another theory (Einstein).
  • I do not seek the meaning of “quantum of action” (light quantum) in the vacuum but at the site of absorption and emission (Planck 1907).
  • Despite the apparently complete success of the Einstein equation (for the photoelectric effect), the physical theory on which it was designed to be the symbolic expression, is found so untenable that Einstein himself, I believe, no longer holds to it (Millikan).
  • My futile attempts to fit the elementary quantum of action into classical theory continued for a number of years and cost me a great deal of effort. Many of my collegues saw in this something bordering on a tragedy (Planck shortly before his death).
  • Einstein is increasingly aloof and sceptical (about the quantum discoveries he pioneered). Many of us regards this as a tragedy (Born).
These confessions viewed as deep insights rather than simply expressions of senility, give a pretty grim outlook on "present circumstances" of modern physics, including climate science...What if Einstein and Planck were right?

In Computational Blackbody Radiation I present a way of turning the tragedy into a happy end
by keeping wave mechanics, according to Planck's and Einstein's innermost dream, only
making it more realistic by including an aspect of finite precision computation, instead of resorting to ad hoc particle statistics, which the scientific souls of Planck and Einstein could never accept.

15 kommentarer:

  1. A very good summary of big men´s thoughts. Perhaps the string theory will send some light on the duality.;-)
    I myself is quite satisfied with the wave theory, because it explains my simple questions, for instance the movements of electrons in radio antennas with resonance phenomenas. With higher frequencies yuo need shorter antennas and for infrared light you need molecules to pick up the wave energy. But it must happen something strange when you go further up in the frequencies, in the UV-region and further. But I can´t still se what is so strange with CO2 picking up IR energy from earth and then sending it out spherically, i.e returning some energy to earth making it a little warmer. But how much warmer is a quite different question.
    This is a very nice blog!!

  2. Can you explain how you arrived at your claim in 7:10 of your paper:

    "This means that high-frequency incoming radition is transformed into heat which shows up as low-frequency outgoing infrared radiation, so that the Earth emits more infrared radiation than it absorbs from the Sun.

    This increase of outgoing infrared radiation is not an effect of backradiation, since it would be present also without an atmosphere.

    The second paragraph?

  3. Well, as I tried to explain, it is the absorption of high-freq radiation from the Sun by the Earth (oceans) and emission of low-freq radiation from the Earth, which can be described as transformation of radiation from high to low freq. What is your question?

  4. Here is how the old-fashioned theory goes:

    The cooling to space balances the solar heating. About 240W/m^2, globally annually averaged.

    This cooling to space takes place from somewhere up in the troposphere because the atmosphere absorbs and re-radiates the energy from the earth's surface.

    Without an atmosphere the surface would have to cool to space and would therefore match 240W/m^2 (due to the first law of thermodynamics) - or whatever value the non-reflected solar radiation changes to as a result of the changes in cloud cover, ice caps expanding, etc.

    I think it's quite a good theory.

    So I was quite amazed for you to say "This increase of outgoing infrared radiation is not an effect of backradiation, since it would be present also without an atmosphere."

    I could write "The earth orbiting the sun is not an effect of gravity since it would also happen if the sun had no mass."

    Proof by stating something confidently.

    Surely you understand the old-fashioned theory? But when you write a statement like you did I think you either you never understood it or you are playing some kind of a joke on all your supporters.

    Your statement needs evidence.

    How can the earth's surface - without an atmosphere - radiate 390 W/m^2 directly to space without cooling down?

  5. Without an atmosphere the Earth surface would radiate 240 W/m2 at a temp of -18 C, according to SB. With an atmosphere the temp is 15 C.
    What we seek is to explain the effect of the atmosphere as a coupled
    thermodynamics-radiation system, not simply radiation. Without an atmosphere there would be neither thermodynamics nor atmospheric
    absorption-radiation. Right? To think of an atmosphere with only radiation is scientifically meaningless.

  6. "Without an atmosphere there would be neither thermodynamics nor atmospheric absorption-radiation. Right?"

    Without an atmosphere there would be the first but not the second.

    Without an atmosphere there would be a vacuum, therefore only radiative heating and cooling could possibly take place.

    There would be energy absorbed from the sun and energy radiated from the earth's surface. This is thermodynamics. The first law of thermodynamics would still be in operation.

    So if the earth's surface radiated out 390W/m^2 and received 240W/m^2 it would cool down.

    Correct? Is there any way to disagree with such a basic statement?

    "To think of an atmosphere with only radiation is scientifically meaningless."

    No one does think of it this way. Conduction, of course, is essentially irrelevant, except at the boundary of surface-atmosphere which is how convection "picks up" heat. But convection and radiation are both in operation.

    To think of an atmosphere with only convection is scientifically meaningless - can you sign up to that one?

  7. Agree both rad and thermodyn are req

  8. So back to my question - what is the basis for your amazing claim?

    "This increase of outgoing infrared radiation is not an effect of backradiation, since it would be present also without an atmosphere."

    We measure the backradiation. We measure its minute by minute value at many locations and, from time to time, its spectrum.

    It comes from the atmosphere.

    Your claim needs some support. How do you support your claims?

  9. What I say is that the Earth (including atmosphere if you wish) receives high frequency light from the Sun and delivers low frequency light to
    space. What support would you like to see?

  10. Support your statement: "This increase of outgoing infrared radiation is not an effect of backradiation, since it would be present also without an atmosphere."

    I have explained the problem earlier. Without an atmosphere the earth's surface would cool to space and would cool down to 240W/m^2. With an atmosphere that didn't absorb and emit radiation the earth's surface would cool down to 240W/m^2.

    It's quite fundamental.

  11. Sure, but the effect of the atmosphere is still a combination of thermodynamics and radiation. To consider an atmosphere with only radiation is scientifically meaningless.

  12. Claes, are you having me on?

    Your claim isn't "the Earth (including atmosphere if you wish) receives high frequency light from the Sun and delivers low frequency light to space".

    Your claim is that without an atmosphere (or I would add a radiatively-active atmosphere) the surface temperature of the earth would stay around 15'C.

    I explained the problem with it earlier.

    If you don't understand what you need to defend that's fine as well.

  13. No, without an atm the temp would be -18 C, according to SB.

  14. Excellent, but your article said:

    "This increase of outgoing infrared radiation is not an effect of backradiation, since it would be present also without an atmosphere."

    That is what I am, and have been, seeking an explanation for.

  15. Strange we can't settle this: The Earth receives mainly high freq light
    and emits mainly low freq, in particular emits more low freq rad than
    what is received in the form of low frequency radiation (but not more than
    received as high freq). Maybe I can express this more clearly.