[ExI] Wrong frequency? Astronomers rethink where to hunt for alien signals

[Keith Henson]

Hmm.

Long ago, when I was in the geophysics business, we worked with frequencies
in this range. We used two frequencies, typically a high of 3 hertz and a
low of 0.05, both square waves. The low was essentially DC. The difference
between them was called the metallic conduction factor, and was a measure
of how much copper sulfide (or more commonly, iron sulfide) was in the rock
below.

We connected power, up to 15 amps, to the ground using electrode pits
several feet long, dumping several gallons of salt water in them, and
lining the pits with aluminum foil. The voltage readings were taken with
porous ceramic pots with a little copper sulphate in them and a little
splashed on the ground. Typically, the space between electrode pots and
power electrodes was 500 or 1000 feet. I didn't notice any alien signals.

I was once taking readings when I heard something breathing behind me. It
was a black bull with horns about a meter wide. There wasn't anything I
could do, so I finished taking the readings, got up, and walked on to the
next station. Apparently, the bull was just curious.

Keith


On Fri, Jul 24, 2026 at 3:01 PM BillK via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

> On Fri, 24 Jul 2026 at 19:49, <spike at rainier66.com> wrote:
> >
> > BillK, I wrote about this back in the 1990s.  What if... Alien life
> communicates on frequencies far lower than we are accustomed?  We want to
> send a lot of signal in a short time.  What if they don't send a lot of
> information, for there is no need to do that?  The super low frequency
> signals would be appropriate for beings that don't move on our scale, but
> way slower, more like intelligent trees than our warm blooded scurrying
> about with our paltry century lifespans.
> >
> > What kind of receiver would be necessary to extract signals at 5 Hz?
> How about 5 milliHz?  What if a signal is being sent out one bit per week?
> Would we recognize it as a signal?  Have we even watched Tabby's star long
> enough to know if there is information in its dimming cycle?  What if it is
> sending a byte a year?  If one is sending out signals over many light years
> where spanning the distance would take centuries with the best known
> technology, what is the big hurry?
> >
> > Once you have that answer, note that a signal can be sent by rotating a
> group of reflective objects, such as MBrain nodes.  It takes a while,
> but... if you don't need to say much and you have plenty of time... what's
> the big hurry?  For practical purposes, we should speak slowly but listen
> quickly.
> >
> > spike
> > --------------------------------------------------
>
>
> Perplexity AI says that we probably wouldn't notice such signals, as they
> would be lost in the noise of the universe.
> BillK
>
> Perplexity AI -
>
> Yes — in principle, a civilization could use extremely low frequencies,
> but the receiver would have to be built for very long observation times,
> not just high sensitivity. At 5 Hz you are already in the audio range,
> while at 5 mHz the period is about 200 seconds, so the receiver is less
> about “antenna size alone” and more about stable clocks, low drift, and
> long coherent integration over many cycles.
> What a receiver would need
>
> For a 5 Hz signal, a practical receiver could be something like a very
> stable magnetic or electric field sensor, plus filtering and
> time-synchronization. For 5 mHz, the receiver has to wait minutes just to
> see one full cycle, so it needs excellent baseline stability and the
> ability to distinguish a real periodic pattern from slow environmental
> drift.
>
> For something as slow as one bit per week, the main requirement is not
> bandwidth but patience and calibration. A receiver could detect it, but
> only if it continuously monitors the same source for weeks, months, or
> years and has a way to decide that the changes are intentional rather than
> natural variability.
> Would we notice it
>
> Maybe, but not automatically. Humans and many instruments are optimized
> for short-term variability, and slow changes can be mistaken for instrument
> drift, stellar variability, dust, magnetic activity, or plain noise.
>
> That is especially relevant for Tabby’s star: it has shown unusual dimming
> behavior over days to years, including deep dips of up to about 20 percent
> and longer-term fading trends discussed in the literature. But those
> observations have not established any artificial encoding, only that the
> light curve is unusual.
> Time scale versus information
>
> A “byte a year” is not absurd in information-theory terms; it is just an
> extremely low data rate. If the sender expects centuries of travel time,
> then there is no need for speed in the human sense, because the whole
> communication system is operating on geological or evolutionary timescales.
>
> The tradeoff is that low-rate signals become easier to confuse with
> natural variability, and harder to verify as deliberate. The slower the
> message, the more it resembles a process rather than a transmission.
> What kind of antenna
>
> For very low frequencies, the limiting factor is often that a conventional
> resonant antenna becomes impractically large compared with the wavelength.
> At 5 Hz, the wavelength in free space is enormous, so real systems would
> likely rely on non-resonant sensing, near-field coupling, or some exotic
> medium rather than a classic radio-style antenna.
>
> At 5 mHz, you are no longer thinking in “radio station” terms at all. The
> receiver would be more like a precision environmental monitor that looks
> for ultra-slow modulation patterns.
> The big picture
>
> Your core intuition is sound: an alien civilization might have no reason
> to optimize for speed, and a slow receiver-transmitter pair could still be
> meaningful. The hard part is that below a certain rate, the signal stops
> looking like a message unless you already know what structure to expect.
>
> So yes, a week-per-bit or year-per-byte signal could exist, and yes, we
> might miss it. The challenge would be proving that a slow, weak, repeated
> pattern is intentional rather than just the universe being messy.
>
> ===========================
>
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