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I could see how a universe with such rules could exist. But is it our universe? In the universe you describe, wouldn't we already have seen time travellers from

by im3w1l 6y ago

I could see how a universe with such rules could exist. But is it our universe? In the universe you describe, wouldn't we already have seen time travellers from the future? The only explanation I can think of for why we haven't seen any, if we live in such a universe, is that we need to build an "arrivals hall" first, and that as soon we manage to do that, people from all over start popping in for a visit.

Uehreka 6y ago
I can’t see how a universe like that could exist. Perhaps if some time-traveler was unlucky, their gun might jam, but I can’t figure out how you could successfully thwart a “well-prepared time traveler” who knows all the details of the situation they’re jumping into and has double-checked their gun after making the jump.
- falseprofit 6y ago
  Isn't the point that that guy thwarts himself.
- im3w1l 6y ago
  First consider that a gun is just a dramatic way of illustrating the concept. If a butterfly travels back in time and flaps its wings it could cause a tornado on the other side of the world (butterfly effect). A gun merely jamming solves nothing. Either the time traveler was there "the first time around" or he must be stopped from going back somehow. Because the first and the second time around must be exactly identical.
- tremon 6y ago
  The logical extension of this would be, given how local interactions might affect events across the globe over time, that the entire past becomes immutable. That would reduce time travel to a read-only experience, so it wouldn't have any utility beyond time tourism.
  - account42 6y ago
    Read only time travel would still be immensely useful as there are so many situations where having a clear answer to what happened is interesting - history, solving crimes, analyzing accidents (or bugs as we are on HN), re-measuring experiments, ...
    - diggernet 6y ago
      It would be, but also immensely troubling, as explored in "The Dead Past", by Isaac Asimov.
riffraff 6y ago
I have a short story for this! My solution to "where are all the time travelers" is that we are unable to correct for motion, we send people in the past but they end up million of kilometers away in space. So the past is perfectly accessible, but we can't get to any useful spacetime coordinate.
- AnIdiotOnTheNet 6y ago
  That seems as though it could be solved by making very short trips back and allowing the local gravity to continually correct your velocity and positioning until you reach your destination.
  - riffraff 6y ago
    yes, but you need a lot of energy to move some matter in a single jump, so more jumps mean exponentially more initial energy because of something akin to a "time-rocket-equation" (you need to bring more mass to get energy but that means more mass or spending more time in a place to re-accumulate it). It's a fun idea though, thanks :)

by im3w1l 6y ago

Uehreka 6y ago

I can’t see how a universe like that could exist. Perhaps if some time-traveler was unlucky, their gun might jam, but I can’t figure out how you could successfully thwart a “well-prepared time traveler” who knows all the details of the situation they’re jumping into and has double-checked their gun after making the jump.

falseprofit 6y ago
Isn't the point that that guy thwarts himself.
im3w1l 6y ago
First consider that a gun is just a dramatic way of illustrating the concept. If a butterfly travels back in time and flaps its wings it could cause a tornado on the other side of the world (butterfly effect). A gun merely jamming solves nothing. Either the time traveler was there "the first time around" or he must be stopped from going back somehow. Because the first and the second time around must be exactly identical.
tremon 6y ago
The logical extension of this would be, given how local interactions might affect events across the globe over time, that the entire past becomes immutable. That would reduce time travel to a read-only experience, so it wouldn't have any utility beyond time tourism.
- account42 6y ago
  Read only time travel would still be immensely useful as there are so many situations where having a clear answer to what happened is interesting - history, solving crimes, analyzing accidents (or bugs as we are on HN), re-measuring experiments, ...
  - diggernet 6y ago
    It would be, but also immensely troubling, as explored in "The Dead Past", by Isaac Asimov.

riffraff 6y ago

I have a short story for this! My solution to "where are all the time travelers" is that we are unable to correct for motion, we send people in the past but they end up million of kilometers away in space. So the past is perfectly accessible, but we can't get to any useful spacetime coordinate.

AnIdiotOnTheNet 6y ago
That seems as though it could be solved by making very short trips back and allowing the local gravity to continually correct your velocity and positioning until you reach your destination.
- riffraff 6y ago
  yes, but you need a lot of energy to move some matter in a single jump, so more jumps mean exponentially more initial energy because of something akin to a "time-rocket-equation" (you need to bring more mass to get energy but that means more mass or spending more time in a place to re-accumulate it). It's a fun idea though, thanks :)