By “optimal expansion speed”, do you mean “maximum possible expansion speed given particle physics, general relativity and thermodynamics (according to our current understanding thereof)”, or do you see some reason that a slower expansion would be beneficial to the ultimate goal (or is that the question)?
Avoiding heat death may be beneficial, for example. As I wrote to Mitchell Porter, to me, the most interesting special case of the question is: if you want to build the fastestest computer in the Universe, should it expand with the speed of light? I’m really not a physicist, so I don’t even know the answer to a very simple version of this question, a version that any particle physicist should be able to answer: Is it possible for some nontrivial information processing system to spread with exactly the speed of light? If not, what about expansion speed converging to c?
what properties are necessary for a structure to seem like a universe to you in the first place?
You (and Mitchell Porter) are completely right . At this point, I don’t have a convincing answer to your obvious question. In the meantime, Tegmark level IV is a good enough answer for me. (Note to Mitchell: it would be very hard to find someone less platonist than me. And I find Tegmark’s focus on computability totally misdirected, so in this sense I am not an intuitionist either.)
I’d be pretty flexible with it, but I think I’d require it to have something timelike, some way for conditions to dynamically evolve over at least one dimension.
I think we disagree here. Please see my answer to Mitchell about the emergence of time from the more basic concept of memory.
I’m not a physicist, but my understanding is that it is not possible for an information processing system to expand at or arbitrarily close to the speed of light; if we neglect the time taken for other activities such as mining and manufacturing, the most obvious limit is the speed to which you can accelerate colony ships (which have to be massive enough to not be fried by collision with interstellar hydrogen atoms). The studies I’ve seen suggest that a few percent of lightspeed is doable given moderate assumptions, a few tens of percent doable if we can get closer to ultimate physical limits, 90%+ doable under extreme assumptions, 99%+ not plausible and 99.9%+ flat-out impossible without some kind of unobtainium.
On the question of ontology, I’m a card-carrying neoplatonist, so you’ve probably heard my position from other people before :-)
Avoiding heat death may be beneficial, for example. As I wrote to Mitchell Porter, to me, the most interesting special case of the question is: if you want to build the fastestest computer in the Universe, should it expand with the speed of light? I’m really not a physicist, so I don’t even know the answer to a very simple version of this question, a version that any particle physicist should be able to answer: Is it possible for some nontrivial information processing system to spread with exactly the speed of light? If not, what about expansion speed converging to c?
You (and Mitchell Porter) are completely right . At this point, I don’t have a convincing answer to your obvious question. In the meantime, Tegmark level IV is a good enough answer for me. (Note to Mitchell: it would be very hard to find someone less platonist than me. And I find Tegmark’s focus on computability totally misdirected, so in this sense I am not an intuitionist either.)
I think we disagree here. Please see my answer to Mitchell about the emergence of time from the more basic concept of memory.
I’m not a physicist, but my understanding is that it is not possible for an information processing system to expand at or arbitrarily close to the speed of light; if we neglect the time taken for other activities such as mining and manufacturing, the most obvious limit is the speed to which you can accelerate colony ships (which have to be massive enough to not be fried by collision with interstellar hydrogen atoms). The studies I’ve seen suggest that a few percent of lightspeed is doable given moderate assumptions, a few tens of percent doable if we can get closer to ultimate physical limits, 90%+ doable under extreme assumptions, 99%+ not plausible and 99.9%+ flat-out impossible without some kind of unobtainium.
On the question of ontology, I’m a card-carrying neoplatonist, so you’ve probably heard my position from other people before :-)