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

[BillK]

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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