[ExI] Von Neumann Probes

[spike at rainier66.com]

From: John Clark <johnkclark at gmail.com> 
Sent: Sunday, 25 January, 2026 5:23 AM
To: ExI chat list <extropy-chat at lists.extropy.org>
Cc: spike at rainier66.com; Ben Zaiboc <benzaiboc at proton.me>
Subject: Re: [ExI] Von Neumann Probes

 

 

 

On Sat, Jan 24, 2026 at 6:11 PM spike jones via extropy-chat <extropy-chat at lists.extropy.org <mailto:extropy-chat at lists.extropy.org> > wrote:

 

> The other thing I'm trying to understand is how a bacterium-sized probe
travelling at 1%c would last more than a few decades in interstellar space.
Just one single collision with a grain of dust would destroy it.

 

According to Osmanov, although the logic (machinery) of A Von Neumann probe would theoretically only need a picogram of mass (10^-12 grams), to be practical the probe would require about 10^-3 grams, the size and mass of a grain of coarse sand. The extra mass would be used to make a Graphene shield needed to protect the probe from collisions with dust particles.

 

John K Clark

 

 

 

At .01c any collision with a dust particle or any particle consisting of even a few thousand atoms would make the material in the shield irrelevant.  Reasoning: do a calculation or even a reasonable estimate on the energy of collision, compare with the chemical bonding energy of whatever material you want or can plausibly imagine.

 

Here’s a paper on high speed collision, which is behind a paywall, but the introduction gives you an idea of what I am talking about:  

 

https://asmedigitalcollection.asme.org/fluidsengineering/article-abstract/95/2/276/412692/Hydrodynamic-Phenomena-During-High-Speed-Collision?redirectedFrom=fulltext

 

More relevant than drag is erosion during interstellar travel, never mind what shield material is used (Arthur C Clarke proposed water ice.)  Consider a comment Keith made a few days ago about how leaking steam behaves in a powerplant.  Estimate the velocity of steam escaping from a small leak, then consider his description of the escaping steam sawing off broomsticks.  The local machine shop had a tool for carving metal blocks using a hypervelocity water jet.  How many C is that?  Any reasonable estimate will do: a kilometer per second?  Two?  Ten?  Regardless of your reasonable estimate, it is still down in the range of a few micro-C.  

 

In light of that thought experiment, think of how absurd was my own calculation yesterday on the deceleration of the cubic millimeter one milligram probe from drag (sheesh, do I feel silly now.)  The drag from interstellar hydrogen is irrelevant if the probe burns up or erodes away long before its centuries-long journey at 10 milli-C.  

 

The energy in a collision increases as the square of the velocity.  Even intentionally overestimating the velocity of the water jet cutter gives us at least a three order of magnitude velocity ratio, which means a six order of magnitude ratio in energy of collision, taking us into energy levels far greater than the piddly covalent bond energy in diamond or whatever other material you prefer.  Ja I know the water jet is orders of magnitude more particles, however it does its precision erosion is orders of magnitude less time than the interstellar probe will be in flight.

 

Do offer a mathematically based refutation to my conclusion that any millimeter scale von Neumann probe at anywhere near .01C is completely impossible, regardless of any plausible future materials breakthroughs.  I might buy the notion of a micro-C however, and if so, it is much easier to imagine accelerating that milligram mass to that velocity and decelerating upon arrival.  It shouldn’t matter much if it takes millions of years to span the distance between the closest stars, ja?  What’s the big hurry?

 

John, Keith, Ben, others, what say ye?

 

spike  

 

 

 

 

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