{Hawking [(1)][continued]}[19th July 1988]

[Redbook5:211-212][19880719:0000b]{Hawking [(1)][continued]}[19th July 1988]

(19880719. )

[continued]

On Heisenberg's Uncertainty Principle: *'… The more accurately you try

to measure the position of the particle, the less accurately you can measure its speed, and vice versa. …. This limit does not depend on the way in which one tries to measure the position or velocity of the particle, or on the type of particle: Heisenberg’s uncertainty principle is a fundamental, inescapable property of the world.

(But) **'… We could still imagine that there is a set of laws that determine events completely for some supernatural being, who could observe the present state of the universe without disturbing it. However, such models of the universe are not of much interest to us ordinary mortals. It seems better to employ the principle of economy known as Occam’s razor*** and cut out all the features of the theory that cannot be observed. This approach led ... to ... quantum mechanics […].'

*Ibid, [Stephen Hawking, 'A Brief history of Time', Bantam, 1988] p55 [Chapter 4: ‘The Uncertainty Principle’]

(Having explained how a method of observation disturbs the particle observed....)

[-- as follows: 'The quantum hypothesis explained the observed rate of emission of radiation from hot bodies very well, but its implications for determinism were not realized until 1926, when another German scientist, Werner Heisenberg, formulated his famous uncertainty principle. In order to predict the future position and velocity of a particle, one has to be able to measure its present position and velocity accurately. The obvious way to do this is to shine light on the particle. Some of the waves of light will be scattered by the particle and this will indicate its position. However, one will not be able to determine the position of the particle more accurately than the distance between the wave crests of light, so one needs to use light of a short wavelength in order to measure the position of the particle precisely. Now, by Planck’s quantum hypothesis, one cannot use an arbitrarily small amount of light; one has to use at least one quantum. This quantum will disturb the particle and change its velocity in a way that cannot be predicted. moreover, the more accurately one measures the position, the shorter the wavelength of the light that one needs and hence the higher the energy of a single quantum. So the velocity of the particle will be disturbed by a larger amount. In other words... [– continues at * above]']

**Ibid, [Stephen Hawking, 'A Brief history of Time', Bantam, 1988] p55 [Chapter 4: ‘The Uncertainty Principle’]

*** Actually, 'Non sunt multiplicanda entia praeter necessitem' – entitities are not to be multiplied beyond necessity. (E[ncylopaedia ]B[ritannica ]VIII,867.

(On p125 [in Chapter 8: The Origin and Fate of the Universe], also, he seems to be misusing it)

[continues]

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