Many Fermis Revisited

From: Tim May <>
Date: Sun, 12 Jan 2003 16:59:34 -0800

In the interests of doing wild speculation here, which some folks are
asking for more of, here's a followup to a discussion we had a few
weeks ago:

The Fermi Paradox asks the question: "If extraterrestrial civilizations
are at all common, even at the level of a few dozen per galaxy per
galaxy life, why aren't they _here_? Or why don't we see artifacts,
relics, ringworlds, Dyson spheres, evidence of large engineering
projects, and so on?" Fermi used the succinct quip, "Why aren't they
here?," with the details about rate of spread even at slow, sublight
speeds, etc. implicitly obvious.

The Many Fermis Paradox is a variant of this: "If the MWI theory is
correct, AND if there is any communication or movement between the
worlds that is possible, why aren't they here?"

(Note that movement amongst branches is not part of any conventional
MWI interpretations, though it's used in novels and in some of the
wilder interpretations.)

Hal Finney pointed out that the same kind of Fermi Paradox argument is
used to argue against time travel: "If time travel is possible, why
aren't travelers from the future here?" (Arguments that they are here
but they only talk to some people, etc., are trumped by the sheer size
of the future, and by the "defector" argument to the "Cosmic
Quarrantine" solution to the Fermi Paradox: _lots_ of defectors would
violate the quarantine, etc.

Hal further raised the possibility that, like the time travel version,
perhaps the resolution has to do with the need for a "receiver":
neither time travelers nor MWI travelers are here, yet, because we have
not, yet, built the portals or receivers needed by them (opening up
wormholes, a la Visser, etc.).

(The other resolution being, of course, that neither time travel nor
MWI travel is possible, which was Fermi's point about the absence of

I've thought about Hal's point and have this reply:

While we on this earth may not have built the necessary portals or
receivers for either (time travel or MWI travel), some other
civilization surely would have a billion or three billion years ago.
(Assuming the usual crude estimates of distribution of ages of stars,
non-special status of us as observers (a la Boostrum and others), and
crude estimates of likelihood of advanced civilizations elsewhere. If
we are the only form of life in our timelike region of the universe,
i.e., within a few billion light-years, then of course this makes the
odds of another receiver-builder nil.

In this fanciful scenario, the Throgians in a small elliptical galaxy
in Coma Berenices built a MWI receiver in their approximate equivalent
of 4500 A.D., by our measures. This was 2 billion years ago. Once this
MWI receiver was built, the Throgians were the beneficiaries and
traders of vast amounts of MWI knowledge...every discovery made in any
MWI universe they had contact with, including universes filled with
other civilizations, all manner of creatures, and so on.

Call this first construction of such a portal the "MWI Singularity."

(A similar situation, arguably much the same situation, ensues with the
construction of the first time machine portal.)

Steven Baxter has written a series of novels in his future history
which explore this very kind of idea.

With nearly any nonzero chance of building either a time machine or MWI
receiver, a distribution of civilizations would have done this billions
of years ago. (By the usual argument that there is nothing which makes
our emergence about 4.5 billion years after the formation/cooling of
the earth anything special in the cosmic scheme: there should have been
planets which similarly formed and cooled as many as 12 billion years
ago, giving some of them a 6-8 billion year "head start" on us.)

As with other Singularities (AI, nanotech, time travel, MWI) in a
cosmos with civilizations with these kinds of head starts, "why aren't
they here?"

Perhaps in the MWI Singularity, the number of other universes expands
more rapidly than the number of occupants, making the movement of
travelers into any one branch not interesting. (Why would they come
here to our particular branch when endless diversity lies out there in
the multiverse? This was explored by John Barnes in "Finities," where
our branch "empties out" after MWI travel is discovered. Or they
evacuate a la Bear's "Blood Music." Or they do things we cannot

Perhaps there are other types of "cosmic censorship" involved.

But an issue we must face is this: if the MWI worlds--or the future, in
the time travel version--are forever inaccessible to us, then they are
essentially nonexistent to us, of no more value to our lives than
Lewis' "worlds where unicorns exist" or alternate history novels where
Germany won the Second World War.

For if such other branches _are_ accessible, then if we are not in some
special place in the universe these other branches were _also_
accessible to the Throgians in that galaxy in Coma Berenices, enough
time ago for the radical implications of MWI travel/communication to
produce a massive infusion of knowledge and engineering capabilities.

Hal's argument that we have not seen either time travelers or MWI
traveler's because we have not yet built receivers yet. My argument is
"But someone would have by now." And unless we are in a narrow band of
outcomes where some civilizations have done this and are even now
expanding toward us but have not yet reached us or produced engineering
feats we can observe, they should have shown themselves by now.

My hunch is that alien civilizations may well exist, but are not
abundant (else we'd see the Galactic Federation already here, etc.),
and that neither time travel nor MWI travel/communication is possible.

--Tim May
Received on Sun Jan 12 2003 - 20:00:22 PST

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