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General Relativity has identical solutions for forward and reverse time. The Schwarzschild metric for example is expressed in terms of time squared so time its

by kloch 3y ago

General Relativity has identical solutions for forward and reverse time. The Schwarzschild metric for example is expressed in terms of time squared so time itself can take positive or negative values and give the same result. It also allows negative mass but those solutions are not symmetric with positive mass - the rs term that contains mass is not quadratic. One consequence of this combination is if you consider "negative mass" to be just positive mass operating in reverse time (to avoid having to accept the ugly idea of negative mass in positive time), you end up with asymmetric effects.

Nthringas 3y ago
IMO, the fact that GR is time-symmetric is actually a quality of the math underlying the physics i.e. the theory, not reality, is where time symmetry comes from. and this is also exactly why those theories have predictive capabilities but reality is still asymetric in the temporal dimension
- deleted 3y ago
  [deleted]
- chowells 3y ago
  > reality is still asymetric in the temporal dimension That's an interesting claim. Do you have any evidence of it? Oh, wait. Do you actually believe time passes? You're going to need to start by proving we're not in a block universe, then. As far as I know, there is no such thing as an experiment that can disprove either assertion. As such, they're more claims of faith than claims about reality.
  - Nthringas 3y ago
    my argument is more philosophical than scientific, so I can offer no evidence time is asymmetric BY definition. if time weren't asymmetric I would have to call it space instead. (seems like I'm using asymmetry and monotonicity as synonyms) in my definition, passing is all time can ever do, and it must do it only in the 'same direction'. finally, in my view it is space which enables backwards and forwards motion.
    - PrimeMcFly 3y ago
      > time is asymmetric BY definition. if time weren't asymmetric I would have to call it space instead. I don't follow you here. If time were not asymmetric it wouldn't suddenly just be space. What are you actually claiming here?
- fnordpiglet 3y ago
  A wonderful aspect of using math to describe physics is the things admitted as possibly by the math might describe things possible in the physical reality but are very hard to observe given our frame of reference. The fact we’ve really found absolutely nothing observable that contradicts going backwards in time hints that it might in fact be possible under the right conditions. Our sense from our frame of reference that it isn’t doesn’t prove anything, just that we have only observed an asymmetry so far. Sabine made a great episode on this recently, fwiw, and it’s worth watching if the subject interests you. https://youtu.be/4ICIObFtWjM?si=XJ2t0P_I6XCWTl1Q https://youtu.be/4ICIObFtWjM?si=XJ2t0P_I6XCWTl1Q

by kloch 3y ago

Nthringas 3y ago

IMO, the fact that GR is time-symmetric is actually a quality of the math underlying the physics i.e. the theory, not reality, is where time symmetry comes from. and this is also exactly why those theories have predictive capabilities but reality is still asymetric in the temporal dimension

deleted 3y ago
[deleted]
chowells 3y ago
> reality is still asymetric in the temporal dimension That's an interesting claim. Do you have any evidence of it? Oh, wait. Do you actually believe time passes? You're going to need to start by proving we're not in a block universe, then. As far as I know, there is no such thing as an experiment that can disprove either assertion. As such, they're more claims of faith than claims about reality.
- Nthringas 3y ago
  my argument is more philosophical than scientific, so I can offer no evidence time is asymmetric BY definition. if time weren't asymmetric I would have to call it space instead. (seems like I'm using asymmetry and monotonicity as synonyms) in my definition, passing is all time can ever do, and it must do it only in the 'same direction'. finally, in my view it is space which enables backwards and forwards motion.
  - PrimeMcFly 3y ago
    > time is asymmetric BY definition. if time weren't asymmetric I would have to call it space instead. I don't follow you here. If time were not asymmetric it wouldn't suddenly just be space. What are you actually claiming here?
fnordpiglet 3y ago
A wonderful aspect of using math to describe physics is the things admitted as possibly by the math might describe things possible in the physical reality but are very hard to observe given our frame of reference. The fact we’ve really found absolutely nothing observable that contradicts going backwards in time hints that it might in fact be possible under the right conditions. Our sense from our frame of reference that it isn’t doesn’t prove anything, just that we have only observed an asymmetry so far. Sabine made a great episode on this recently, fwiw, and it’s worth watching if the subject interests you. https://youtu.be/4ICIObFtWjM?si=XJ2t0P_I6XCWTl1Q https://youtu.be/4ICIObFtWjM?si=XJ2t0P_I6XCWTl1Q