[ExI] Von Neumann Probes

[John Clark]

On Sat, Jan 24, 2026 at 5:47 PM Jason Resch via extropy-chat <
extropy-chat at lists.extropy.org> wrote:

*> Computational speed (in operations per second) is a function of mass,
> not of the amount of energy the computer consumes. (in operations per
> second) is a function of mass, not of the amount of energy the computer
> consumes.*


*Since E=MC^2, energy and mass are two different sides of the same thing,
which one is more convenient to use depends on circumstances. If you're
talking about how fast a bit can flip (∆t) then it's energy dependent, the
formula is ∆t≥ h/4E, where h is Planck's constant. But if you're talking
about the maximum possible number of bits a physical object can process
then you're talking about mass and Bremermann's Limit. It's derived from
the relationship between Shannon information entropy and the energy-time
uncertainty principle, it states that the maximum number of bits a physical
object can process is  1.36*1^50 bits per second per kilogram. If you try
to go beyond Bremermann's Limit the energy/mass density would become so
high that your computer would collapse into a Black Hole, and then
information could go in but it couldn't get out so the machine wouldn't be
of much use. *

*John K Clark *







>> *assuming you don't have infinite memory or infinite time available, and
>> by infinite I mean infinite and not just astronomically large. If your
>> memory is finite then after you finish a calculation you're going to need
>> to erase all the scratchpad stuff in memory you use to produce the answer
>> and just keep the answer, but that takes energy. Landauer's principle
>> allows us to calculate the fundamental lower bound of the energy needed to
>> erase one bit of information, it is k*T*ln2, (K is Boltzman's constant, T
>> is the temperature of the computer in kelvin, and ln2 is the natural
>> logarithm of 2). **At room temperature it takes at least 2.9 x 10^-21
>> joules of energy to erase one bit of information. Of course if you had
>> infinite memory at your disposal then you wouldn't need to erase anything,
>> but unfortunately you don't. *
>>
>> *There is one way around this, Landauer’s bound only applies to
>> information erasure not to logic steps, so if your computer is made in a
>> way that allows for reversible computing (everyday computers are not) then
>> once you finish a computation you could keep the answer and then run the
>> computer backwards to get back to the starting state, so no information is
>> erased.*
>>
>
> That's what I was referring to.
>
> * If you do that then, although you could never get to zero, you could
>> perform a calculation using an arbitrarily small amount of energy. But the
>> trouble is thermodynamics tells us the process needs to be as close to
>> adiabatic as possible, so the less energy you use the slower your
>> computation.*
>>
>
> Computational speed (in operations per second) is a function of mass, not
> of the amount of energy the computer consumes.
>
> Unless the computer is wasting energy for something other than
> computation, which is what you seem to be suggesting here.
>
> Jason
>
>
> * Of course if you had infinite time at your disposal it wouldn't matter
>> how slow the computation is, but unfortunately you don't.*
>>
>> *John K Clark*
>>
>>
>>
>>
>>
>>>
>>>
>>>>
>>>>> * > I appreciate the 'von Neumann probe' argument, but not all
>>>>> civilisations are going to go that route*
>>>>
>>>>
>>>> *It would only take one. And I'm not talking about one civilization,
>>>> I'm talking about one individual in a civilization. It is simply not **tenable to
>>>> maintain that precisely 100% of the technologically savvy individuals in
>>>> the observable universe have decided not to make a Von Neumann Probe. I
>>>> think William of Ockham would agree with me that the best explanation of
>>>> the Fermi Paradox is simply we are the first. And as I keep saying,
>>>> somebody has to be. *
>>>>
>>>> *> I have a hunch that we tend to vastly underestimate the difficulty
>>>>> of interstellar travel.*
>>>>
>>>>
>>>> *You don't need interstellar travel to make a Dyson sphere/swarm, and
>>>> something like that should be very noticeable, but we have noticed nothing.
>>>> And any technological civilization worth its salt should be able to get a
>>>> Von Neumann Probe moving at 1% the speed of light because its mass would be
>>>> very small, and so it could get from one side of the galaxy to the other in
>>>> just 10 million years, a blink of the eye cosmically speaking. But just how
>>>> much would a Von Neumann Probe weigh? *
>>>>
>>>>
>>>> *Estimates vary, Freeman Dyson thought it would be about a kilogram but
>>>> George Church and Zaza Osmanov think that's much too high, they think with
>>>> advanced Nanotechnology one Von Neumann Probe could be about the size of a
>>>> bacteria and, depending on various engineering considerations, weigh
>>>> between a trillionth of a gram (10^-12) and a thousandth (10^-3) of a gram;
>>>> and, if it had access to raw materials and light energy from a star, it
>>>> could make a copy of itself in about a year. Then after 79 years there
>>>> would be an Avogadro's number of Von Neumann Probes, 6.02*10^23. And one
>>>> year after that it would be obvious to a blind man in a fog bank that not
>>>> all the technologically knowledgeable minds in the galaxy were on the
>>>> Earth. But we have seen nothing like that. I think I know why. *
>>>>
>>>> *John K Clark*
>>>> _
>>>
>>> ____
>
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