3 ms·

Gravity is a universal constant. If you reverse time, you just reverse the order of cause and effect, not what the effect is. Does that make more sense to you?

nanidin 4y ago
If we reverse time, would gravitational waves flow backwards?
- dekhn 4y ago
  yes. it's literally like playing a movie in reverse.
  - nanidin 4y ago
    " it's literally like playing a movie in reverse" seems overly authoritative for something we haven't observed. I have seen Tenet, but it's a work of fiction. Have we observed reflected gravitational waves? In reverse-time, where would they originate from if they presumably rippled out into space and didn't collide with anything in forward-time?
    - dekhn 4y ago
      .... they would "originate" from all the locations the gravity waves spread to and converge on the source. Tenet has nothing to do with this- I'm just explaining it as it was covered in my many physics classes that covered the nature of the arrow of time (https://en.wikipedia.org/wiki/Arrow_of_time https://en.wikipedia.org/wiki/Arrow_of_time) and how I interpret it in terms of what seems most likely/least unlikely.
bigbacaloa 4y ago
"gravity is a universal constant" contradicts Newtonian mechanics, special and general relativity.
- nanidin 4y ago
  In these "it's like taking a video of throwing a ball in the air and allowing it to land on the ground, then playing it in reverse" examples, I can't help but think of Newton's first law. If an object at rest stays at rest, how does the ball leap from the ground? Where does the impulse come from? Reverse time seems too far fetched for me, or at least the simplified naïve version of it does.
  - bnralt 4y ago
    It also seems a bit misleading, since in that scenario a ball is intentionally thrown so that it comes down the same way. Let's consider something else - imagine an accretion disk of space dust slowly pulling itself together to form a planet. Play that in reverse, and you have the a planet slowly coming apart piece by piece. Imagine reversing the impact that created the moon. The moon comes apart piece by piece, creating an accretion disk around the earth, which then all moves and hits one area of the earth, and there several parts of it (and part of the earth itself) move together to form a separate planet, which then launches itself from the earths surface into space, flies around the sun a few times, and then slowly breaks apart piece by piece into another accretion disk.

nanidin 4y ago

If we reverse time, would gravitational waves flow backwards?

dekhn 4y ago
yes. it's literally like playing a movie in reverse.
- nanidin 4y ago
  " it's literally like playing a movie in reverse" seems overly authoritative for something we haven't observed. I have seen Tenet, but it's a work of fiction. Have we observed reflected gravitational waves? In reverse-time, where would they originate from if they presumably rippled out into space and didn't collide with anything in forward-time?
  - dekhn 4y ago
    .... they would "originate" from all the locations the gravity waves spread to and converge on the source. Tenet has nothing to do with this- I'm just explaining it as it was covered in my many physics classes that covered the nature of the arrow of time (https://en.wikipedia.org/wiki/Arrow_of_time https://en.wikipedia.org/wiki/Arrow_of_time) and how I interpret it in terms of what seems most likely/least unlikely.

bigbacaloa 4y ago

"gravity is a universal constant" contradicts Newtonian mechanics, special and general relativity.

nanidin 4y ago
In these "it's like taking a video of throwing a ball in the air and allowing it to land on the ground, then playing it in reverse" examples, I can't help but think of Newton's first law. If an object at rest stays at rest, how does the ball leap from the ground? Where does the impulse come from? Reverse time seems too far fetched for me, or at least the simplified naïve version of it does.
- bnralt 4y ago
  It also seems a bit misleading, since in that scenario a ball is intentionally thrown so that it comes down the same way. Let's consider something else - imagine an accretion disk of space dust slowly pulling itself together to form a planet. Play that in reverse, and you have the a planet slowly coming apart piece by piece. Imagine reversing the impact that created the moon. The moon comes apart piece by piece, creating an accretion disk around the earth, which then all moves and hits one area of the earth, and there several parts of it (and part of the earth itself) move together to form a separate planet, which then launches itself from the earths surface into space, flies around the sun a few times, and then slowly breaks apart piece by piece into another accretion disk.