Musk, Mars and x-risk

Correct. SIs that only terminally care about a single green button on Earth instrumentally care about optimizing the rest of the universe to prevent anything from threatening that button.

Good point, and this appears to be a general issue with human space settlement.

Suppose that the technology to do it cost-effectively arrives before AI e.g. cheap spaceflight arrives this century, and AI doesn't. Then even if an unfriendly AI shows up centuries later, it can catch-up with and overwhelm the human settlements, no matter how far from Earth they've reached. (The AI can survive higher accelerations, reach higher speeds, reproduce more quickly before launching new settlement missions etc.)

Worse, increasing the number of human settlements most likely increases the chance that someone, somewhere builds an unfriendly AI. So, somewhat surprisingly, space settlement could increase existential risk rather than reduce it.

In many cases, spaceflight may not even be necessary, an uFAI that is still in stealth mode could just transmit itself over.

However (correct me on the jargon), uFAI mindspace certainly contains uFAI's that - for whatever reason - will not concern themselves with anything other than Earth.

For example, a uFAI that uses geometric discounting as part of its utility function (cf. page 6 here) may realize the eventual danger (decades down the line) from a Mars colony, but may invest all its resources to transform Earth into the desired state anyways.

Since the number of uFAI concepts that will also threaten Mars is strictly smaller (even if not much so) than the number of uFAI concepts with no constraints on Mars given, I think the statement that the risk would be somewhat smaller is fair to make (conjunction fallacy otherwise).

Which catastrophic risks does a mars colony mitigate? ... Climate change : yes

If a Mars colony mitigates catastrophic risk (extinction risk?) from climate change,
then climate change is not an existential risk to human civilization on earth.

If humans can thrive on Mars, Earth based humanity will be able to cope with any climate change less drastic than transforming the climate of Earth to something as hostile as the current climate of Mars.

If we can build a self sufficient small scale economy which is independent from earth's ecosystem services and industry base - i.e. an independent martian colony - most listed existential risks a martian colony might mitigate cease to be existential. This is since the mechanism of these existential risks is reduction of ecosystem services provided by earth's biosphere triggering a breakdown of our interconnected world economy with subsequent starvation of most people or even a breakdown of our interconnected world economy without significantly reduced ecosystem services.

This obviously applies to: < 20km diameter impactors, (current tech) wars, famine, super volcanoes, (nearly all) climate change scenarios, global computer failure.

It also applyes to: most pandemics (sub 100% lethality or shelter avaiable or some region spared), most supernova scenarios (breakdown of agriculture due to Ozone layer disruption, far away enough to not instantly fry the earth), some bio- and nanoweapons (sub 100% lethality or shelter avaiable or some region spared).

So a Mars colony will only exclusively survive some highly specific and thus unlikely scenarios: A nano-outbreak which can break into an earthbound shelter, but does not spread through space, a very intense GRB which hits earth but not Mars (is this even possible?), an earth impactor large enough to heat the atmosphere to several hundred °C, perhaps some weird physics disaster.

So what we should do to mitigate x-risks is building a self sufficient small scale economy which is independent from earth's ecosystem services and industry base, not ship it to Mars. Though I fear this is not possible at our current tech level.

Note that if nanoweapons or bad nanotech is released accidentally then Mars may easily be quarantined. Also, it may help that Mars is up gravity well from Earth.

Grey goo?

A miniature black hole, dropped into the centre of the Earth (possibly as some sort of weapon).

An asteroid impact sufficiently large to turn the Earth into another asteroid belt.

An asteroid impact sufficiently large to divert the Earth's orbit, sending it falling into the Sun (admittedly, this would have an effect on a Martian colony as well, but not necessarily a fatal one)

How sure are we that people can stay healthy on Mars?

Not very. We know that no gravity is lethal in the long term for human beings (for a variety of reasons), but we really have no sense of where the cutoff is -- moon gravity is probably too little, but we've no clue if Martian gravity might be enough. Human biology is definitely tuned to Earthly norms for obvious reasons, but it might benefit from greater or smaller g-effects; there simply isn't enough research on the subject, as for obvious reasons it's inordinately difficult to do the relevant studies.

Huh, I wonder how technically feasible it would be to build a base that's rotating fast enough so that it feels like earth gravity inside ... It could be just one large circular Maglev, which shouldn't require too much energy for suspension and maintaining a constant speed - though there's still friction and the fact that it complicates connections to things that are probably better left static.

If we consider malicious actions (like a big war), such colonies on Earth are just too convenient for military installations to be left untouched.

Mars colony is too far away to be able to deal a sneak attack; so wiping it is not as urgent, and after 3 hours there are no rockets anywhere on Earth for next 5 years.

Also, I am not sure that the cheapest way to "filter CO2 and CO, boost O2" is more expensive than "filter all possible chemical weapons and kill all designer bacteria".

Whether a war that realy destroys every human (maybe not immediately, but over the range of a century) is likely is another question.

Of course, intact Mars colony would also have to keep quite a lot of physics, engineering and biology knowledge even if some of it were lost on Earth.

Radiation levels immediately following a nuclear war might be much worse than Martian radiation levels. Moreover, even if is Earth more habitable after the war, if everyone on Earth is dead, this won't matter very much.

I wouldn't see why someone on here could be against it.

Never forget opportunity costs of limited resources. To use a different example saving cute puppies isn't something anyone is against, but there's a question when one has limited resources of whether giving money to animal shelters is a the best use of it.

Opportunity costs. We'd prefer it was spent on a Mars colony than on most things, but if we're spending money on x-risk reduction, it might not be the most cost-effective way to help.

We have no idea if a self sustaining colony is at all feasible. If it cannot eb self sustaining than it doesn't reduce existential risk at all and (as well as opportunity costs mentioned by others) distracts attention and political capital from keeping earth habitable.