From: scerir (scerir@libero.it)
Date: Sun Feb 23 2003 - 12:21:59 MST
> > A highly collimated laser radiating into the outer space, with
> > a very very small angle, could show some effect. Because if waves were
> > beamed, at various directions in the outer space, and some power
> > fluctuations in the transmitter were observed, it could mean that the
> > outer space is not uniform. That is to say that sometimes there are,
> > or there are not, out there, "targets" receiving retarded waves and
> > emitting advanced waves.
[Damien]
> My suggestion had been that by using this fact (if it is one!) you could
> establish a code with your future self (or descendents/later
collaborators)
> permitting a message to be sent back to the present, depending on the
> absence or presence of absorbers at various locations. I still think it's
a
> rather nifty idea. But I wonder if I might have lifted it from a Greg Egan
> determinism short story. (I don't have his collections handy, alas.)
The essence of the Feynman-Wheeler absorber theory is the claim
that the source-less field term (of a certain equation) vanishes.
This equation says that
F(k) = F(j,retarded) + F(free) + F(k,retarded) - F(k,advanced)
where F(k) is the field of source j, seen by particle k
where F(j,retarded) is the usual retarded field acting on k from source j
where F(k,retarded) and F(k,advanced) are k's own advanced and retarded
fields
where F(free) is the source-less field term (advanced + retarded)
Wheeler & Feynman gave many reasons for the vanishing of F(free),
and there is little question that there was a cosmological era
in which the universe was opaque, functioning as an absorber.
Even the cosmological background radiation is the result of
gamma-gamma, e+e-, neutrinos, charged particles annihilations,
and not a F(free). In any case the vanishing of F(free) depends
essentially on the present properties of the (near) universe.
Experimental attemps were made to observe a possible failure,
or partial failure of the absorption of F(free).
In example alternately exposing an antenna to the sky, at night,
or shielding it. Figuring that the radiation reaction should be
affected, causing variations in the power or in the current in the
antenna or in something else there. Experiments were not conclusive.
R.B. Partridge, Absorber Theory of Radiation and the Future of
the Universe, 1973, Nature - 244 - p. 263
D.T. Pegg, On a Recent Experiment to Detect Advanced Radiation,
1975, J. Physics, A8 - L60
D.T. Pegg, Absorber Theory of Radiation, 1975, Rep. Progr. Physics,
38 - p. 1339
L.S. Schulman, Formulation and Justification of the Wheeler-
Feynman Absorber Theory, 1980, Found. Physics, 10, p. 841
J.E. Hogart, Cosmological Considerations of the Absorber Theory
of Radiation, 1962, Proc. Royal Soc. London, A267, p. 365
So, yes, there is still hope
for a possible Damienscope!
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