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I've never understood why "paradoxes make cause-and-effect-reasoning difficult" concerns are a valid argument that something could not be possible. Does physics

I've never understood why "paradoxes make cause-and-effect-reasoning difficult" concerns are a valid argument that something could not be possible. Does physics care whether the workings of the universe are accessible to our logic?

gpderetta 7y ago
> Does physics care whether the workings of the universe are accessible to our logic? the universe itself doesn't care, but physics, that is, our math based theories, certainly they do, in fact they require it.
- garmaine 7y ago
  Not in the way the post you are replying to means. Our “math based theories” of physics do not require a world without cause-effect paradoxes. Indeed they seem to explicitly permit them.
  - deleted 7y ago
    [deleted]
cartoonworld 7y ago
If I look at a random numeric oracle of 1-10, and consider the result as N, and apply to it some kind of mathematical formalism of: If ( N + 10 = 20 ) then eat(last_bagel) My wife comes home and is cross with me for eating the last_bagel. So, I hop in my handy time machine, travel back to before the time where I access the oracle, and alter it to only produce a random number from 1-9. If I succeed, my wife is no longer cross with me. But, if she is no longer cross with me, then why would I alter past events? Likely, I would have no cause to travel back in time in this scenario, so the oracle remains programmed to produce up to 10. Now my wife is cross with me again. Which one happens?
- vokep 7y ago
  Of course there is no answer to this question yet, but thats the point. Just because a thought experiment doesn't solve it, doesn't mean it cannot be physically produced. For all we know in actual implementation you would simply eat the bagel, time travel back and bias the oracle, but your conscious experience only ever consists of finding that your oracle was modified and has your fingerprints on it somehow.
- jbattle 7y ago
  Yet quantum mechanics is full of phenomenon that operate counter to our understanding of cause and effect. Physicists accept things like double slit interference - why do they seem to consider these time travel induced causal paradoxes so off-limits?
  - cartoonworld 7y ago
    Mostly because a bagel is not an electron, and slit experiments illustrate wave-particle duality, do they not? Anyhow, the message was about how paradoxes make reasoning hard, not about how we can wave away the uncertainties. Next time I'll just skip all the time machine nonesense and head to the nearest rectory.
    - garmaine 7y ago
      I think the point made by user jbattle is that physics already allows, for example, causal relationships that go either “back in time” or “faster than light” from certain valid reference frames. Physicists have found ways of coping with this reality. Why should the introduction of a time machine make it fundamentally any different?

gpderetta 7y ago

> Does physics care whether the workings of the universe are accessible to our logic? the universe itself doesn't care, but physics, that is, our math based theories, certainly they do, in fact they require it.

garmaine 7y ago
Not in the way the post you are replying to means. Our “math based theories” of physics do not require a world without cause-effect paradoxes. Indeed they seem to explicitly permit them.
- deleted 7y ago
  [deleted]

cartoonworld 7y ago

If I look at a random numeric oracle of 1-10, and consider the result as N, and apply to it some kind of mathematical formalism of: If ( N + 10 = 20 ) then eat(last_bagel) My wife comes home and is cross with me for eating the last_bagel. So, I hop in my handy time machine, travel back to before the time where I access the oracle, and alter it to only produce a random number from 1-9. If I succeed, my wife is no longer cross with me. But, if she is no longer cross with me, then why would I alter past events? Likely, I would have no cause to travel back in time in this scenario, so the oracle remains programmed to produce up to 10. Now my wife is cross with me again. Which one happens?

vokep 7y ago
Of course there is no answer to this question yet, but thats the point. Just because a thought experiment doesn't solve it, doesn't mean it cannot be physically produced. For all we know in actual implementation you would simply eat the bagel, time travel back and bias the oracle, but your conscious experience only ever consists of finding that your oracle was modified and has your fingerprints on it somehow.
jbattle 7y ago
Yet quantum mechanics is full of phenomenon that operate counter to our understanding of cause and effect. Physicists accept things like double slit interference - why do they seem to consider these time travel induced causal paradoxes so off-limits?
- cartoonworld 7y ago
  Mostly because a bagel is not an electron, and slit experiments illustrate wave-particle duality, do they not? Anyhow, the message was about how paradoxes make reasoning hard, not about how we can wave away the uncertainties. Next time I'll just skip all the time machine nonesense and head to the nearest rectory.
  - garmaine 7y ago
    I think the point made by user jbattle is that physics already allows, for example, causal relationships that go either “back in time” or “faster than light” from certain valid reference frames. Physicists have found ways of coping with this reality. Why should the introduction of a time machine make it fundamentally any different?