Interstellar Information Transmission, was Re: Kurzweil's ...

From: Robert J. Bradbury (
Date: Thu Mar 15 2001 - 21:37:48 MST

On Thu, 15 Mar 2001, Zero Powers wrote:

I said:
> >The only way you send information is by encoding it in matter
> >and send the matter. You can't send matter at the "speed-of-light"
> >because its infinitely expensive to send it at that velocity.
> I'll admit to having little knowledge and no expertise in this area. But
> can't you encode information using only EM waves? Isn't that what fiber
> optics is about? Isn't that how we communicate with satelites?

Zero, always feel free to smack me in the side of the head when
I have jumped one too many tracks (I often don't realize I may
have done it).

This derives from conversations that Spike and I had about the
equivalence of matter and energy due to Einstein's (E = mc^2).
Using this you can assign a real "cost" to losing energy
(due to photon spreading due the inverse square law affecting
the strength of signals being transmitted -- photons you can't
receive with your "detector" are lost energy/matter) and the actual
"matter" lost due to ablation by interstellar particles during
interstellar transit at high velocities.

You *can* encode the information on EM waves, but you lose
the value (read matter or energy) of that depending on the
transmission distance. The further the distance, the more
of your investment you lose (unless you can guarantee
that the receiver is of sufficient size to capture all of
the photons you are transmitting -- across light-year
distances, that gets *really* big).

Now, of course, you can confine the information preventing
it from spreading (by internal reflection) and that *is* what
fiber optics *is* all about. It works great for the connection
of your brain to the NET (a few dozen meters perhaps). It works
less great over a few hundred km (but the clever fiber people
have found ways of pumping up erbium atoms with excess laser
energy and then using this to amplify the actual signals
without converting the optical information stream to electrical
information and back to optical (which gets expensive, causes
losses, etc.) However, a fiber optic cable spanning a few light
years has serious problems (which I'm sure you can imagine).

We do communicate with satellites, but it isn't with fiber
optic cables. It is with directional microwave transmissions
(all those radio-satellite dishes you see on the top of
television stations). They can effectively transmit to
the satellite or receive and focus data from the satellite
sufficiently to provide reliable transmission or reception
of signals. However the question typically "unexplored"
is how much of the energy that is radiated by the transmitters
goes unreceived by the receivers??? Another way to think
about the question is -- how much of the transmission energy that
is radiated by your local cell-phone transmission tower (or your
local television broadcast antenna) is *NEVER* usefully received?

My post was simply a commentary on the fact that if you
transmit your information as a "probe" (read tape/CD/letter)
it doesn't "spread" across interstellar distances. It may
suffer from erosion, but if you send it moderately slowly
you can minimize this. On the other hand if you attempt
to transmit data (as EM wave) at the speed of light, your
information spreads, and unless the receiver has really big
antennas a large fraction of this gets lost.

It all comes down to the fundamental question in communication --
How do you tell someone something at a minimal cost to yourself
and guarantee that they receive all of what you are sending them
(nothing more and nothing less).

Going back to my comment, you cannot send a "letter/tale/CD"
at the "speed-of-light" because it requires an infinite amount
of energy to accelerate it to that speed (this is a consequence
of the relativity equations). So you send information as "matter"
(slowly), or you send information as EM wave (but lose most
of your investment). I've got a spreadsheet that does the
tradeoffs and for the amount of information present in advanced
civilizations (e.g. MBrains) you would rarely use EM waves as your
data information carrier across interstellar distances. Its like
trying funnel the flow from a fire hose into a hypodermic needle.


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