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Re: new 20K

From: Garmt de Vries <G.deVries~at~phys.uu.nl>
Date: Sun, 16 Oct 2005 08:39:29 +0200 (CEST)
To: Jules Verne Forum <jvf~at~Gilead.org.il>

On Sat, 15 Oct 2005 spaceart~at~att.net wrote:

> The machine used to affect the orbit of the meteor is a truly SF
> device---although Verne (or whoever) apparently ignored the law of
> action and reaction when describing it operating. Any force it applied
> to shifting the meteor would have applied to the machine as well. I
> remember thinking while reading the book that probably the only result
> of shoving on the meteor hard enough to move it would be the flattening
> of the device itself.

It is clear from the text that the meteor was much lighter than the Earth.
What the machine does, is create an absolute vacuum between itself and the
meteor. The non-empty space behind the meteor then pushes it towards
Earth. Of course, the non-empty space behind Earth would push our planet
the other way, but this effect is much smaller, because Earth is larger.

Assuming that the pressure from space is a constant, the ratio between the
forces exerted on Earth and on the meteor goes with the square of the
ratio between their radii, whereas the ratio between their masses goes
with the cube of the ratio of their radii. The meteor thus experiences an
acceleration that is larger than the accelaeration experienced by Earth by
a factor equal to the ratio of the radii.

By the way, the working of the machine is an interesting foreshadowing of
the Casimir effect. In quantum mechanics, empty space is never empty.
There is a constant appearing and disappearing of electron-positron pairs,
which exist for a short time before annihilating again. But they do
contribute to the energy density of the vacuum, which gives rise to a
pressure exerted by the vacuum on everything around it. Another
ingredient we need is the concept of particle-wave duality. Every
particle can, depending on circumstances, behave as a particle or as a
wave. The wavelength is inversely proportional to the momentum. The most
familiar example of this duality concerns photons: light can be a wave
phenomenon (refraction, interference, etc.), but it can also behave as
quantised particles (photo-electric effect). Similarly, you can do
interference experiments with electrons, which you're more used to
thinking of as particles.

Now imagine two parallel, flat, conducting surfaces, close to eachother.
Between them, only certain energies are possible for the electron-positron
pairs: namely those energies for which half of the corresponding
wavelength fits exactly an integer number of times in the distance between
the two surfaces. At the same time, outside the two planes, all energies
are allowed. This means that there are fewer pairs inside the gap than at
the outside. Thus, the pressure inside is lower than outside, and the two
planes are pushed towards each other. Think about it: "empty" space
exerting a real, macroscopic force! It takes a physicist to come with
something like that :) But the effect has been measured, and it is as real
as gravity.

Sorry for the lecture...
Garmt.
Received on Sun 16 Oct 2005 - 08:39:59 IST

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