If this was true, how could we tell? In other words, is this a testable hypothesis?
This. Physics runs on falsifiable predictions. If ‘consciousness can affect quantum outcomes’ is any more true than the classic ‘there is an invisible dragon in my garage’, then discovering that fact would seem easy from an experimentalist standpoint. Sources of quantum randomness (e.g. weak source+detector) are readily available, so any claimant who thinks they can predict or affect their outcomes could probably be tested initially for a few 100$.
General remark:
One way this could turn out to be true is if it’s a priori more likely that there are special, nonrandom portions of the quantum multiverse we’re being sampled from. For example, if we had a priori reasons for expecting that we’re in a simulation by some superintelligence trying to calculate the most likely distribution of superintelligences in foreign universes for acausal trade reasons, then we would have a priori reasons for expecting to find ourselves in Everett branches in which our civilization ends up producing some kind of superintelligence – i.e., that it’s in our logical past that our civilization ends up building some sort of superintelligence.
It is not clear to me that this would result in a lower Kolmogorov complexity at all. Such an algorithm could of course use a pseudo-random number generator for the vast majority quantum events which do not affect p(ASI) (like the creation of CMB photons), but this is orthogonal to someone nudging the relevant quantum events towards ASI. For these relevant events, I am not sure that the description “just do whatever favors ASI” is actually shorter than just the sequence of events.
I mean, if we are simulated by a Turing Machine (which is equivalent to quantum events having a low Kolmogorov complexity), then a TM which just implements the true laws of physics (and cheats with a PNRG, not like the inhabitants would ever notice) is surely simpler than one which tries to optimize towards some distant outcome state.
As an analogy, think about the Kolmogorov complexity of a transcript of a very long game of chess. If both opponents are following a simple algorithm of “determine the allowed moves, then use a PRNG to pick one of them”, that should have a bound complexity. If both are chess AIs which want to win the game (i.e. optimize towards a certain state) and use a deterministic PRNG (lest we are incompressible), the size of your Turing Machine—which /is/ the Kolmogorov complexity—just explodes.
Of course, if your goal is to build a universe which invents ASI, do you really need QM at all? Sure, some algorithms run faster in-universe on a QC, but if you cared about efficiency, you would not use so many levels of abstraction in the first place.
Look at me rambling about universe-simulating TMs. Enough, enough.
You quoted:
This is not how Mach works. You are subsonic iff your Mach number is smaller than one. The fact that you would be supersonic if you were flying in a different medium has no bearing on your Mach number.
I would also like to point out that while hydrogen on its own is rather inert and harmless, its reputation in transportation as a gas which stays inert under all practical conditions is not entirely unblemished.
The beings travelling in the carriages are likely descendants of survivors of the Oxygen Catastrophe and will require an oxygen-containing atmosphere to survive.
Neglecting nitrogen, you have oxygen surrounded by hydrogen surrounded by oxygen. If you need to escape, you will need to pass through that atmosphere of one bar H2. There is no great way to do that, too little O2 means too little oxidation and suffocation, more O2 means that the your atmosphere is explosive. (The trick with hydrox does not work at ambient pressure.)
Contrast with a vacuum-filled tunnel. If anything goes badly wrong, you can always flood the tunnel with air over a minute, going to conditions which are as safe as a regular tunnel during an accident which is still not all that great. But being 10km up in the air is also not great if something goes wrong.
Barlow’s formula means that the material required for a vacuum tunnel scales with the diameter squared. For transporting humans, a diameter of 1m might be sufficient. At least, I would not pay 42 times as much for the privilege of travelling in a 6.5m outer diameter (i.e. 747 sized) cabin instead. Just lie there and sleep or watch TV on the overhead screen.