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starship-design: Re: A few thoughts on drag & exoitc stuff(was 'still doing stardrives')

Hi Nels:

N. Lindberg wrote:

>         One of the candidates for the 'dark matter' that accounts for 90%
> of our universe and our galaxy is a low-rest mass particle called the
> axion.  This is one of those wierd things that are predicted by SUSY and
> superstring theories.  It has the interesting property that it decays into
> photons in the presence of a strong magnetic field.  Of course, if they
> exist in large quantity in interstellar space, the magnetic field from any
> Bussard scoop would cause their decay.  At low speeds (relative to the
> galactic DM halo) the microwaves produced wouldn't be a big deal, but at
> high speed they could produce enourmous effects.  I have no idea whether
> this would produce drag, thrust, or a force normal to the path.
>         Best Regards,
>         Nels Lindberg

First off, I'm not entirely comfortable with superstring theory. On the one
hand, it's delightfully outrageous enough to be true, but on the other, it's
kind of counterintuitive, to have a hatful of dimensions rolled up into a
microcosm. You have the very direct challenge, whether this theory is
falsifiable, to meet Karl Popper's criterion for a scientific hypothesis.
More deeply, any theory so esoteric has a serious epistemological
concern: say it makes a prediction, and this predicted phenomonon is
actually observed. Does that indeed produce evidence that the theory
has been triumphantly vindicated?

Or does the observation have any connection at all with the theory?
It is possible that the observed phenomonon is utter coincidence, that
the theory is false anyway, and the actual causality of the observation
consists of a mechanism as yet completely unknown to science. So a
cosmology has a tough row to hoe before it can be accepted. No
matter how pretty its exotic math, it must remain a dream castle until
it meets lots of tough tests.

I never heard of the axion. Supposing a magnetic field splits it into
photons, which leave in a hurry. Either they decay isotropically, in
all directions, or they decay anisotropically, with a preferred direction.
Right away, we can assign a higher probability to the isotropic case,
because the alternative seems to violate symmetry, which is one of
the ways Nature likes to keep things neat. (If there were to be a
preferred direction, it seems to make sense that it would be at right
angles to the field lines, though like I said, I doubt there is such a

It seems our ship's field has done work on these particles, to make
them pop. So the field has been weakened, in the amount needed
to catalyze this decay. The effect might produce a visible light in
front of the ship. (An unfortunate consequence of our high velocity
is to blue-shift this light, possibly into unhealthy ranges which would
require additional shielding.)

Overall, a release of energy in front of the ship is necessarily a
detrimental effect, in exactly the same sense that any release of
energy behind the ship must contribute to our acceleration. So I
hope there aren't any axions out there. A possible salvage would
be in contributing to the ionization of neutral hydrogen atoms, to
feed our scoops. We can do lots of things with ions, like making
them jump through hoops, that we can't do with neutral atoms.
A plasma is just what we want to work with, for we can separate
the streams of electrons and protons and accelerate each of them
by appropriate means. To use our extremely limited supply of
reaction mass most effectively, we must push it out within a
gnat's ass of C. That means a proton linac, because electrons
are ridiculously easy to get up to speed. We must do all this while
watching the charge balance of the ship itself, so things don't get
silly aboard.

I hope axions don't exist, because they would be hard to wade

Johnny Thunderbird
heavyLight Books