Welcome to the Club of Wise Children Who Were Anthropically Worried About The Ants. I thought it was just me.

Just saying "it turned out this way, so I guess it had to be this way" doesn't resolve my confusion, in physical or anthropic domains. The boson thing is applicable [not just as a heuristic but as a logical deduction] because in the Standard Model, we consider ourselves to know literally everything relevant there is to know about the internal structures of the two bosons. About the internal structures of minds, and their anthropically-relevant differences, we know far less. Maybe we don't have to call it "randomness", but there is an ignorance there. We don't have a Standard Model of minds that predicts our subjectively having long continuous experiences, rather than just being Boltzmann brains.

it could happen as an accident; with billions of space probes across the universe, random mutations may happen, and the mutants that lost sentience but gained a little speed would outcompete the probes that follow the originally intended design.

This is, indeed, what I meant by "nonsentient mesa-optimizers" in OP:

This mesa-optimizer will then mesa-optimize all the sentience away [this is a natural conclusion of several convergent arguments originating from both computer science and evolutionary theory]

Why do you expect sentience to be a barrier to space travel in particular, and not interstellar warfare? Interstellar warfare with an intelligent civilization seems much harder than merely launching your von Neumann probe into space.

I agree with you that "civilizations get swept by nonsentient mesa-optimizers" is anthropically frequent. I think this resolves the Doomsday Argument problem. Hanson's position is different from both mine and yours.

It sounds to me like you're rejecting anthropic reasoning in full generality. That's an interesting position, but it's not a targeted rebuttal to my take here.

Random vs nonrandom is not a Boolean question. "Random" is the null value we can give as an answer to the question "What is our prior?" When we are asking ourselves "What is our prior?", we cannot sensibly give the answer "Yes, we have a prior". If we want to give a more detailed answer to the question "What is our prior?" than "random"/"nothing"/"null"/"I don't know", it must have particular contents; otherwise it is meaningless.

I was anthropically sampled out of some space, having some shape; that I can say definite things about what this space must be, such as "it had to be able to support conscious processes", does not obviate that, for many purposes, I was sampled out of a space having higher cardinality than the empty set.

As I learn more and more about the logical structure by which my anthropic position was sampled, it will look less and less "random". For example, my answer to "How were you were sampled from the space of all possible universes?" is basically, "Well, I know I had to be in a universe that can support conscious processes". But ask me "Okay, how were you sampled from the space of conscious processes?", and I'll say "I don't know". It looks random.

Huh, I didn't know Hanson rejected the Doomsday Argument! Thanks for the context.

What do you mean [in your linked comment] by weighting civilizations by population?

What do you mean by "update our credences-about-astrobiology-etc. accordingly [with our earliness relative to later humans]"?

Life is really, really rare, because it takes very long to develop, and it's possible that Earth got extremely lucky in ways that are essentially unreplicable across the entire accessible universe.

I am not sure how you think this is different from what I said in the post, i.e. that I think most Kolmogorov-simple universes that contain 1 civilization, contain exactly 1 civilization.

All sampling is nonrandom if you bother to overcome your own ignorance about the sampling mechanism.

Physical dependencies, yes. But past and future people don't have qualitatively more logical dependencies on one another, than multiversal neighbors.

You could make a Grabby Aliens argument without assuming alien sentience, and in fact Hanson doesn't always explicitly state this assumption. However, as far as I understand Hanson's world-model, he does indeed believe these alien civilizations [and the successors of humanity] will by default be sentient.

If you did make a Grabby Aliens argument that did not assume alien sentience, it would still have the additional burden of explaining why successful alien civilizations [which come later] are nonsentient, while sentient human civilization [which is early and gets wiped out soon by aliens] is not so successful. It does not seem to make very much sense to model our strong rivals as, most frequently, versions of us with the sentience cut out.

1. Whichever coordinate system we choose, the charge will keep flowing in the same "arbitrary" direction, relative to the magnetic field. This is the conundrum we seek to explain; why does it not go the other way? What is so special about this way?
2. If I'm a negligibly small body, gravitating toward a ~stationary larger body, capture in a ~stable orbit subtracts exactly one dimension from my available "linear velocity", in the sense that, maybe the other two components are fixed [over a certain period] now, but exactly one component must go to zero.

Ptolemaically, this looks like the ~stationary larger body, dragging the rest of spacetime with it in a 2-D fixed velocity [that is, fixed over the orbit's period] around me - with exactly one dimension, the one we see as ~Polaris vs ~anti-Polaris, fixed in place, relative to the me/larger-body system. That is, the universe begins rotating around me cylindrically. The major diameter and minor diameter of the cylinder are dependent on the linear velocity I entered at [ adding in my mass and the mass of the heavy body, you get the period ] - but, assuming the larger body is stationary, nothing else about my fate in the capturing orbit appears dependent on anything else about my previous history - the rest is ~erased - even though generally-relative spacetime doesn't seem to preclude more, or fewer, dependencies surviving. My question is, why is this? Why don't more, or fewer, dependencies on my past momenta ["angular" or otherwise] survive?

[ TBC, I know orbits can oscillate. However, most 3D shell orbits do not look like oscillating, but locally stable, 2D orbits. ]