5 ms·

1, without having a mechanism for FTL how can we say for certain that it implies CTCs? maybe relativity is an approximation of a more complete theory which allo

1, without having a mechanism for FTL how can we say for certain that it implies CTCs? maybe relativity is an approximation of a more complete theory which allows FTLs without CTCs... 2, didn't the universe itself expand faster than light during inflation? what does relativity have to say about that? if we can't use relativity to explain inflation, why do we so comfortably use it to forbid FTL?

at_a_remove 6y ago
1) Oh, it turns out that the mechanism for getting CTCs out of FTL is completely irrelevant. Construct your light cones, see the results. Warp drive, wormholes, whatever, they all produce CTCs. You can look into it if you don't believe me. 2) None of the matter in the universe was expanding, the spacetime was. You're not the first person to think of this. Probably the first question that popped into anyone's mind when variants of the concept were being kicked around. Anyway, the expansion doesn't generate CTCs because there's no information and/or matter to circle around, it's just the stretch between these. Now, you'll probably ask about -- well, why can't we shrink spacetime selectively to get around all of that? Ah, that requires some exotic matter, matter with negative mass-energy. No, anti-matter does not have negative mass-energy (first thing people reach for). In fact, we've never found anything with negative mass-energy and that concept itself raises a ton of fun paradoxes which I could get into. And you still get CTCs. There's probably a large tree of arguments out there on the Internet somewhere which addresses all of these common objections.
- ikrenji 6y ago
  sure for the mechanisms we have come up with so far. doesn't say anything about things we come up in the future. we don't know what we don't know.
  - at_a_remove 6y ago
    My stock response to that is that we don't know that I can't make a time machine out of some chewing gum wrappers, a rubber band, three transistors, six pipe cleaners, a AAA battery, and it only works while I wear a red hat. We also don't know that I can't use that device to go back in time to the start of the universe and change all of the physical laws so that the previous contraption cannot work. But what are the odds? What would you bet on?
    - guerrilla 6y ago
      You could have used that argument to poo-poo someone proposing anything that was thought to be impossible before it was shown to be possible.
      - at_a_remove 6y ago
        "We don't know what we don't know" is the ultimate gateway to wish fulfillment. It's not fruitful for anything other than fantasy. Who is to say that I cannot write an AI in under 1,000 lines of C? We don't know what we don't know. By all means, pursue that line of inquiry if you feel that the odds are with you. It's just not a useful heuristic for deciding what to spend your resources (time, money, effort, energy, etc.) on.
        guerrilla 6y ago
        You keep mentioning examples people are fully familiar with and comparing it to something nobody is familiar with.
        at_a_remove 6y ago
        I do not know what you mean. I don't know what to tell you other than the following: Nearly every "Can't We Just ...?" is old. It's kind of irritating in a way, because people behave as if their thoughts on FTL (or overunity motors to break conservation of energy, or whatever) are new and unconsidered, but they end up being just about ancient and well-worn, and it's the equivalent of some bright spark saying, "Hey, why don't we just merge the Windows and Linux kernels? Should be easy!" or "Can't you just make it know what I want?" with reference to some program. To be sure there are nuts working in their garages on various projects, but in the scientific community, nobody is holding their breath on these fantastic breakthroughs.

at_a_remove 6y ago

1) Oh, it turns out that the mechanism for getting CTCs out of FTL is completely irrelevant. Construct your light cones, see the results. Warp drive, wormholes, whatever, they all produce CTCs. You can look into it if you don't believe me. 2) None of the matter in the universe was expanding, the spacetime was. You're not the first person to think of this. Probably the first question that popped into anyone's mind when variants of the concept were being kicked around. Anyway, the expansion doesn't generate CTCs because there's no information and/or matter to circle around, it's just the stretch between these. Now, you'll probably ask about -- well, why can't we shrink spacetime selectively to get around all of that? Ah, that requires some exotic matter, matter with negative mass-energy. No, anti-matter does not have negative mass-energy (first thing people reach for). In fact, we've never found anything with negative mass-energy and that concept itself raises a ton of fun paradoxes which I could get into. And you still get CTCs. There's probably a large tree of arguments out there on the Internet somewhere which addresses all of these common objections.

ikrenji 6y ago
sure for the mechanisms we have come up with so far. doesn't say anything about things we come up in the future. we don't know what we don't know.
- at_a_remove 6y ago
  My stock response to that is that we don't know that I can't make a time machine out of some chewing gum wrappers, a rubber band, three transistors, six pipe cleaners, a AAA battery, and it only works while I wear a red hat. We also don't know that I can't use that device to go back in time to the start of the universe and change all of the physical laws so that the previous contraption cannot work. But what are the odds? What would you bet on?
  - guerrilla 6y ago
    You could have used that argument to poo-poo someone proposing anything that was thought to be impossible before it was shown to be possible.
    - at_a_remove 6y ago
      "We don't know what we don't know" is the ultimate gateway to wish fulfillment. It's not fruitful for anything other than fantasy. Who is to say that I cannot write an AI in under 1,000 lines of C? We don't know what we don't know. By all means, pursue that line of inquiry if you feel that the odds are with you. It's just not a useful heuristic for deciding what to spend your resources (time, money, effort, energy, etc.) on.
      - guerrilla 6y ago
        You keep mentioning examples people are fully familiar with and comparing it to something nobody is familiar with.
        at_a_remove 6y ago
        I do not know what you mean. I don't know what to tell you other than the following: Nearly every "Can't We Just ...?" is old. It's kind of irritating in a way, because people behave as if their thoughts on FTL (or overunity motors to break conservation of energy, or whatever) are new and unconsidered, but they end up being just about ancient and well-worn, and it's the equivalent of some bright spark saying, "Hey, why don't we just merge the Windows and Linux kernels? Should be easy!" or "Can't you just make it know what I want?" with reference to some program. To be sure there are nuts working in their garages on various projects, but in the scientific community, nobody is holding their breath on these fantastic breakthroughs.