"Greg Egan - Foundations 4 - Quantum Mechanics" - читать интересную книгу автора (Egan Greg)

The reality is nothing like this, as Figure 3 shows. The observed spectrum
reaches a peak at a certain frequency, then tapers off. Clearly, something prevents the
energy of the field from being equally distributed amongst all possible modes. But what?
The analysis we've given so far assumes that energy can be spread as thinly as
you like; as more and more modes share the energy of the field, each one ends up,
individually, with a smaller amount. But what if energy couldn't be endlessly subdivided
like this? What if you eventually reached a minimum amount, a тАЬparticleтАЭ of energy, as
indivisible as some particles of matter presumably are? Instead of taking on any value
whatsoever, energy would only be found in exact multiples of this amount.
In 1900, Max Planck proposed that this was the case, and called the minimum
amount a quantum. Though it might have been simplest to decree a fixed amount of
energy as the size of one quantum, like the fixed mass of an electron, that wouldn't have
solved the cavity radiation problem: with an infinite number of modes available, the finite
number of quanta would still have been free to тАЬescapeтАЭ to ever higher frequencies. The
only way to prevent this was to propose that higher frequency modes required a greater
minimum energy than lower frequency modes, raising a series of ever higher hurdles to
counteract the tendency for the energy to spread. Planck found that making the energy of
one quantum proportional to the frequency of the electromagnetic wave, as in Equation
(1), would yield a spectrum precisely in agreement with observation, if the constant of
proportionality was chosen correctly. This value, now known as Planck's constant,
is referred to by the letter h, and has a value of 6.625 x 10-34 Joules per Hz.
 Egan: "Foundations 4"/p.5



E = hF (1)


You might be wondering how Equation (1) dictates the nice tapered curve in
Figure 3. What's to stop all the energy in the furnace from going into a single, super-
high-frequency quantum, making the spectrum an isolated peak way off to the right of the
graph? The same thing that stops all the energy in the Earth's atmosphere from ending up
concentrated in a couple of atoms: it's just not very likely. Of all the possible ways a
certain total amount of energy can be distributed between billions of possible modes of
cavity radiation, the vast majority look like the curve in Figure 3.
Over the first three decades of the twentieth century, many other experiments
confirmed the quantisation of light, and led independently to the same value for Planck's
constant. One famous example is the photoelectric effect. When ultraviolet light is
shone on a metal plate in a vacuum tube it blasts electrons off the surface of the metal.
The energy of the individual electrons released this way (as opposed to the total energy
they possess en masse) turns out to be completely independent of the intensity of the
light shone on the plate, and can only be increased by using light of a greater frequency.
This makes sense if the electrons are absorbing individual quanta, rather than gaining
energy from the electromagnetic field as a whole. More intense light of a given frequency
contains more quanta of the same energy, and can blast more electrons off the plate тАФ
but only raising the frequency of the light, and hence the energy of the quanta, can
increase the energy of each individual electron.
Quanta of light, which came to be known as photons, were shown again and
again to behave like localised, indivisible particles. But there was no denying the fact that
light also behaved like a wave, exhibiting interference effects. Neither aspect could be