Thanks for your thoughts on this, Wirt, although the answer/conclusions should have been painfully obvious to even the most casual of passersby.  :-)


Ray (Cripes!  Sunset is at 4:12 PM here in Appleton, WI today) Shahan

> -----Original Message-----
> From: HP-3000 Systems Discussion [SMTP:[log in to unmask]] On Behalf Of Wirt Atmar
> Sent: Monday, December 06, 2004 3:30 PM
> To:   [log in to unmask]
> Subject:           Re: [HP3000-L] [Possible SPAM] SETI - Time to Give Up
> 
> Tracy writes:
> 
> > We've been out-foxed, time to give up on the SETI project:
> >
> >  http://www.spacedaily.com/news/seti-04k.html
> 
> I've already been asked about this twice now before. Here's what I wrote in
> my first reply:
> 
> =======================================
> 
> > What do you think of this?  How could a blackbody radiation curve carry any
> > information unless it was modulated somehow?  Just wondered if you had run
> > across this idea.
> 
> Several things seem to have gotten conflated in all of this. It is absolutely
> true that the most compressed signal possible is indistinguishable from
> random noise. It is a signal in which all redundancy has been removed, so that
> nothing is predictable from one transmitted symbol to the next.
> 
> Unfortunately, such a signal is also the most fragile and one that can't be
> transmitted asynchronously. Some form of regular "keying" is necessary so that
> a remote receiver can lock onto it, and that alone would make it
> differentiatible from random noise. Secondly, all information recovery techniques that are
> imbedded in a signal impose some sort of redundancy into the signal. Without
> that redundancy, the information contained in a corrupted packet could not be
> recovered, and that redundancy too would make the signal differentiatible.
> (Without information-recovery capabilities, a corrupted packet would need to be
> asked to be retransmitted, and given the penalties of the speed of light, no one
> would design a long-distance communications network that way).
> 
> Thirdly, although I didn't see how in the text the two were philosophically
> equated, a random source need not be a blackbody source. Blackbody is for
> certain a random assemblage of events, but the inverse isn't true.
> 
> Fourthly, spread spectrum isn't random. The idea was invented during WWII as
> a method to scramble radio communications so as to make the message
> "untappable". The notion was simple enough, and a piano keyboard was the inspiration.
> Transmit a part of the message on one key, then shift to another preplanned key,
> transmit a part of it there, and then shift again, and so on. Unless you knew
> the sequence of frequency hops in advance, you couldn't begin to hear much
> more than a few snippets of the conversation.
> 
> The inventor of spread-spectrum wasn't just another pretty face, btw. It was
> Hedy Lamarr, the actress, and she's received IEEE's highest honors. See:
> 
> http://www.spectrum.ieee.org/careers/careersarchive/careerstrategy/aug04/0804c
> aref1.html
> 
> ========================================
> 
> > Thanks for the very interesting response.  I only thought of blackbody
> >  radiation because they said it would be indistinguishable from star light,
> >  which is pretty close to blackbody radiation if I understand correctly.
> 
> If viewed over a fairly restricted range of frequencies ("one color" or so),
> the radiation from a star is indistinguishable from a random signal. However,
> when sampled over the broad range of frequencies that a star produces, the
> differences would be quite obvious. There would be no reason to transmit over any
> broader range of frequencies than that required by the modulation bandwidth
> of the signal you're transmitting. Anything else would be an enormous waste of
> power and no civilization worth its salt would do such a thing.
> 
> ========================================> 
> 
> Wirt Atmar
> 
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