Re: SETI: SAT Spread Spectrum indistinguishable from normal star? (was Re: Movie ;contact)

Michael Butler (
Mon, 27 Oct 1997 21:57:52 -0800 (PST)

Mea culpa for this shooting from the hip...

On Mon, 27 Oct 1997, Michael Lorrey wrote:
> Michael Butler wrote:
> >
> > Ah, but if the signal is maximally compressed, the signal can't be
> > self-clocking. To recover the signal at the other end, you'd have to have
> > a perfect clock and/or never miss a bit. Nicht wahr?
> Isn't this the same requirement for the previously proposed FTL
> communication, that you'd need the key already on the other end to be
> able to tell what the noise means in the first place?

This is different; I'm saying that even with the key already in place at
both ends, you need either perfect information through the channel (in
both time and frequency domains) or *some* redundancy/pattern, however
small; the latter permits you to resynchronize if that is needed.

> > Also: If the clock is being referenced to say, a pulsar that all can
> observe, then such a compression scheme is possible for widespread use,
> eh?

Something *approximating* it, maybe. Another problem is that (I think) you
have to be able to _resolve_ time to the granularity of the symbol rate.
Methinks there's another engineering limit there. You'd have to know
your position and velocity relative to the pulsar in order to correct for
Lorentz-Fitzgerald effects; h-bar <uncertainty> = delta p x delta v,
right? I am not sure whether all these limits converge, but my gut and
vague memories say they do.

Now, if you have zero-lag action at a distance, then the pulsars could be
clocks for all the "smart" stars. Good luck--I'm not willing to say
it's utterly impossible; I just doubt it's a commonplace across the
universe, and I think the proposition is impossible to falsify, and more
of a bull session topic than something to take action regarding: "What if
there were infinitely powerful beings? Why' they could do... *anything*!"
Fun to yack about, but as unsatisfying as rock-wool candyfloss. IMHO. :)

Carl F. might have a more informed opinion; for sure he's got more math
than I.