[ExI] Von Neumann Probes

[John Clark]

On Sun, Jan 25, 2026 at 11:27 AM <spike at rainier66.com> wrote:


> *> 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. *
>

*I had a hunch that if  a 10^-3 gram von Neumann probe collided with a
10^-3 gram dust particle then 100% of the kinetic energy would be turned
into heat and it would be game over, the probe would be vaporized. However
in interstellar space it is extremely unlikely that it would collide with
something as large as 10^-3 grams, but it would collide with billions of
particles that were far smaller than that, and against that the shield
would be effective. To make sure my hunch was correct I asked Gemini and he
she or it said my hunch was correct. This was my question: *

*Me: If a von Neumann probe with a mass of 10^-3 grams collided with a fast
moving dust particle of about the same mass what percentage of the
energy of the dust particle would be transferred to the probe, and if the
mass of the dust particle was significantly less than mass of the probe
would the percentage of energy transfer belowr lower? I ask this because I
was wondering if a 10^3 gram shield would be sufficient to protect the core
10^12 grams that contained the actual machinery.*

Gemini.  if a 10^-3  g probe hits a  g dust particle at 0.1c, *the probe is
effectively vaporized.*

A shield that has the same mass as the projectile hitting it cannot
"protect" the core at these speeds; instead, the entire system (shield,
core, and dust) becomes an expanding cloud of plasma.
------------------------------
1. The Equal Mass Collision

In physics, when two objects of equal mass collide inelastically (they
"stick" or merge into a debris cloud), the conservation of momentum tells
us what happens to the energy.

   -

   *Mass Transfer:* 100% of the dust particle's mass is "transferred" to
   the system, but since both are likely vaporized, they just become one
   single cloud of plasma.
   -

   *Energy Transfer:* In the center-of-mass frame, *50% of the total
   kinetic energy* is instantly converted into *internal energy* (heat,
   ionization, and structural destruction).

*The TNT Scale:* At $0.1c$ ($30,000\text{ km/s}$), a collision between two
$10^{-3}$ gram objects releases about *900,000 Joules*.

That is the equivalent of exploding *215 grams of TNT* inside a grain of
sand. A $10^{-12}$ gram core (the size of a bacterium) has zero chance of
surviving that internal explosion.

------------------------------
2. If the Dust Particle is Significantly Smaller

If the dust particle is much lighter than the probe (say, 10^-6 g dust hitting
a 10^-3g probe), the results change in a way that favors the probe:

   -

   *Percentage of Energy:* The *percentage* of the *probe's* total energy
   that changes is much *lower*. The probe barely slows down.
   -

   *Energy Dissipation:* However, the *100%* of the dust particle's kinetic
   energy is still deposited into the impact site.
   -

   *Why this is "Higher" or "Lower":* * The *bulk effect* on the probe is
   *lower* (it doesn't knock the probe off course).
   -

      The *local effect* (the "depth" of the hole it punches) is
      *manageable*.

This is why the 10^-3 g shield exists. It isn't meant to stop another
milligram-sized "bullet"; it is meant to absorb millions of *micro-impacts*
from atomic hydrogen and tiny sub-microgram dust grains.
------------------------------
3. Is the 10^-3 g Shield Sufficient?

For the 10^-12 g machinery core to survive, the shield doesn't just act as
a "wall"—it acts as a *diffuser*.

   -

   *The Probability Gap:* In the interstellar medium, large dust grains (
   10^-3 g) are incredibly rare. You might travel light-years without
   hitting one. However, you will hit trillions of hydrogen atoms and
   nano-dust particles (10^-9 g and smaller).
   -

   *Shield Mechanics:* A 10^-3 g graphene shield is *millions of atoms
   thick*. When a 10^-9 g particle hits it, the energy is spread across the
   graphene lattice. The shield "flops" or vibrates, but the machinery at the
   center remains shielded from the radiation and heat.

*The Verdict:** The shield is "sufficient" against the average environment*
(the gas and micro-dust), but it is a "death sentence" if it hits anything
its own size. Osmanov’s model assumes the probes are produced in such high
numbers (trillions) that it doesn't matter if a few thousand hit "large"
dust grains and explode—the rest of the swarm makes it through.

Summary Table: Impact of $10^{-3} Probe at $0.1c$
*Dust Mass* *Outcome for Probe* *Energy Released*

> *10^-3 g (Equal)*

*Total Annihilation* 900,000 Joules
*10^-6 g (1/1000th)* *Severe Damage* 900 Joules
*10^-9 g (Micro-dust)* *Shield Absorbs/Erodes* 0.9 Joules
*John K Clark*
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