This paper posits a path to colonizing/probing the universe with lightweight (30g) or heavyweight (500t) probes based on 3 propulsion methods (fission, fusion, antimatter) by mining a planet like Mercury to make a Dyson swarm to power the effort, and launching probes at 3 speeds (0.5, 0.8c, 0.99)c across the universe with sufficient redundancy to survive intergalactic/cluster dust collisions.

Once arrived at target galaxies/clusters, they build a new factory system to launch another generation of probes to visit locally.

The fact that we have not seen evidence of such an operation does not mean it has not happened - the paper posits hiding such an effort would be trivial and additionally quashing similar efforts by other less careful aliens might be beneficial to a first-mover to avoid paperclip-maximism of the universe. Thus there may be a hidden universal police in place. Or simply too much intergalactic dust to colonize a good chunk before Hubble flow makes targets inaccessible.

Obviously assumptions about technical capability have a wide range of error - can we send smart enough AI with minimal tool sets (in 30g? in 500t?) to start a new Dyson swarm and probe factory? I'm more concerned with the light-speed travel, dust density, Hubble flow, material longevity and other more physical assumptions made.

There are multiple assumptions made, just as in the Drake equation itself, some of which likely have even wider (magnitudes) range than used in the paper.

  • $\begingroup$ I think there have been some more recent Drake equation evaluations, possibly already a question here or in Astronomy SE about it. That may not affect answering your question, but you might find it interesting nonetheless. $\endgroup$
    – uhoh
    Nov 16, 2018 at 18:15
  • $\begingroup$ "What are the issues with this paper" seems like an overly broad question; can you narrow it? $\endgroup$ Nov 16, 2018 at 18:51

1 Answer 1


The first thing I notice is that the paper first handwaves away the difference between the size of the probe and the size of the replicator. It references the Freitas paper (which is itself pretty handwavey) while failing to mention that the probe required to send the 500t replicator masses ten million tons.

The second thing I notice is that the author seems to arbitrarily extrapolate from the fact that an acorn can produce a tree that a 30g replicator can do the same job as the 500t replicator, which calls into question the point of bringing up the 500t replicator in the first place.

Neither paper does much to explain how a replicator would actually be engineered. Naturally occurring replicators (i.e. life forms) take advantage of an environment heavily shaped by earlier, simpler replicators to provide necessary material; an acorn grows into an oak on the backs of billions of years of preparatory work by other plants and animals.

I didn't bother reading any further than that. It's one thing to say that seeding the galaxy with replicators is theoretically possible; it says nothing about the practicality of doing so.

  • $\begingroup$ One practicality is to avoid another civilization paperclip-maximizing the universe. A worthy goal. He does assume the replication would be possible - considering our level of AI or even computer control now, it does not seem impossible that we could have a program build a nuclear power plant, an aircraft carrier or a saturn 5 rocket starting with just a few mining tractors/what we can fit in 500t in under 100 more years technological development - so Im not overly worried about the impossibility of the replicators. More concerned with cosmological assumptions than robotics/AI. $\endgroup$
    – math
    Nov 16, 2018 at 21:02
  • $\begingroup$ I can see a reason for having two types of replicator: The little one might be very slow. $\endgroup$ Feb 27, 2022 at 4:09
  • $\begingroup$ slow is relative unless slow means > 1bn years. even at 10m years per 'hop', even if we only travel 10 light years each hop into 10x the destinations, 1bn years gives an incredibly wide spread. $\endgroup$
    – math
    Jun 23, 2022 at 13:06

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