Luke Muehlhauser: In your paper with Stuart Armstrong, “Eternity in Six Hours,” you run through a variety of calculations based on known physics, and show that “Given certain technological assumptions, such as improved automation, the task of constructing Dyson spheres, designing replicating probes, and launching them at distant galaxies, become quite feasible. We extensively analyze the dynamics of such a project, including issues of deceleration and collision with particles in space.”

You frame the issue in terms of the Fermi paradox, but I’d like to ask about your paper from the perspective of “How hard would it be for an AGI-empowered, Earth-based civilization to colonize the stars?”

In section 6.3. you comment on the robustness of the result:

In the estimation of the authors, the assumptions on intergalactic dust and on the energy efficiency of the rockets represent the most vulnerable part of the whole design; small changes to these assumptions result in huge increases in energy and material required (though not to a scale unfeasible on cosmic timelines). If large particle dust density were an order of magnitude larger, reaching outside the local group would become problematic without shielding methods.

What about the density of intragalactic dust? Given your technological assumptions, do you think it would be fairly straightforward to colonize most of the Milky Way from Earth?

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Luke Muehlhauser: In Weaver (2013) you discuss some paradoxes of rational agency. Can you explain roughly what these “paradoxes” are, for someone who might not be all that familiar with provability logic?

Nik Weaver: Sure. First of all, these are “paradoxes” in the sense of being highly counterintuitive — they’re not outright contradictions.

They all relate to the basic Löbian difficulty that if you reason within a fixed axiomatic system S, and you know that some statement A is provable within S, you’re generally not able to deduce that A is true. This may be an inference that you and I would be willing to make, but if you try to build it into a formal system then the system becomes inconsistent. So, for a rational agent who reasons within a specified axiomatic system, knowing that a proof exists is not as good as actually having a proof.

This leads to some very frustrating consequences. Let’s say I want to build a spaceship, but first I need to be sure that it’s not going to blow up. I have an idea about how to prove this, but it’s extremely tedious, so I write a program to work out the details of the proof and verify that it’s correct. The good news is that when I run the program, it informs me that it was able to fill in the details successfully. The bad news is that I now know that there is a proof that the ship won’t blow up, but I still don’t know that the ship won’t blow up! I’m going to have to check the proof myself, line by line. It’s a complete waste of time, because I know that the program functions correctly (we can assume I’ve proven this), so I know that the line by line verification is going to check out, but I still have to do it.

You may say that I have been programmed badly. Whoever wrote my source code ought to have allowed me to accept “there is a proof that the ship won’t blow up” as sufficient justification for building the ship. This can be a general rule: for any statement A, let “there exists a proof of A” license all the actions that A licenses. We’re not contradicting Löb’s theorem — we still can’t deduce A from knowing there is a proof of A — but we’re finessing it by stipulating that knowing there’s a proof of A is good enough. But there are still problems. Imagine that I can prove that if the Riemann hypothesis is true, then the ship won’t blow up, and if it’s false then there exists a proof that the ship won’t blow up. Then I’m in a situation where I know that either A is true or there is a proof that A is true, but I don’t know which one. So even with the more liberal licensing condition, I still can’t build my lovely spaceship.
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Recently, Eliezer and I had an email conversation with Holden Karnofsky to discuss future-oriented philanthropy, including MIRI. The participants were:

• Eliezer Yudkowsky (research fellow at MIRI)
• Luke Muehlhauser (executive director at MIRI)
• Holden Karnofsky (co-CEO at GiveWell)

We then edited the email conversation into a streamlined conversation, available here.

See also four previous conversations between MIRI and Holden Karnofsky: on existential risk, on MIRI strategy, on transparent research analyses, and on flow-through effects.

Luke Muehlhauser: In a previous interview, I asked Scott Aaronson which “object-level research tactics” he finds helpful when trying to make progress in theoretical research, and I provided some examples. Do you have any comments on the research tactics that Scott and I listed? Which recommended tactics of your own would you add to the list?

John Baez: What do you mean by “object-level” research tactics? I’ve got dozens of tactics. Some of them are ways to solve problems. But equally important, or maybe more so, are tactics for coming up with problems to solve: problems that are interesting but still easy enough to solve. By “object-level”, do you mean the former?
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