4 ms·

For the apple to fall on Newton's head? It could have been dropped by a passing swallow (or possibly two, held on a line between the dorsal guiding feathers).

For the apple to fall on Newton's head? It could have been dropped by a passing swallow (or possibly two, held on a line between the dorsal guiding feathers). For it to fall from the tree? Well, that's a linguistic trick; for it to fall from the tree it must have been hanging on the tree, so that necessary condition is actually a tautology. Physics describes a world with statistical regularities, not absolute laws. Even a clockwork Newtonian universe is not time-reversible; it has multiple pasts that can lead to the observed present.

nytgop77 5y ago
Regarding Newtonian universe. Is that really true, that multiple pasts can exist? Some source would be very welcome.
- svieira 5y ago
  It's not that "multiple pasts can exist", it's that "multiple pasts _would be sufficient to explain_ the effect that is being observed now". E. g. "The apple hit Newton on the head" could be explained by: 1. The apple was hanging on the tree at `t - 1` and the wind shook it loose. 2. The apple was flying through the air because his mother threw it and it collided with his head 3. The apple spontaneously generated due to as-yet-not-understood quantum fluctuations 3 meters above his head.
- scatters 5y ago
  Yes; a simple example is Norton's dome. It is possible to construct a frictionless curve such that a particle that is pushed up the curve with correct initial velocity will reach the top and halt in finite time. Observing a particle sitting at the top of the dome, there is no way to tell when it reached that point or from which direction.
cycomanic 5y ago
It's not a tautology to say for an apple to fall of a tree it has to be on a tree, it's not a tautology for a plane to crash to be flying first or for a car to stop it needs to be in motion first. They are all necessary conditions, in fact this is the definition of a necessary condition. Something to be a necessary condition has nothing to do with time-reversibility, it simply states a logical relationship Let me give you another example: To accelerate a body with mass m it is necessary to exert a force onto it. All mathematical descriptions In fact equivalency, requires conditions to be necessary and sufficient. Your argument that physics describes a world with statistical regularities is a maybe a nice philosophy, however most physicists (and regular people) do not believe we live in a simulation, but physical laws describe the real world.

nytgop77 5y ago

Regarding Newtonian universe. Is that really true, that multiple pasts can exist? Some source would be very welcome.

svieira 5y ago
It's not that "multiple pasts can exist", it's that "multiple pasts _would be sufficient to explain_ the effect that is being observed now". E. g. "The apple hit Newton on the head" could be explained by: 1. The apple was hanging on the tree at `t - 1` and the wind shook it loose. 2. The apple was flying through the air because his mother threw it and it collided with his head 3. The apple spontaneously generated due to as-yet-not-understood quantum fluctuations 3 meters above his head.
scatters 5y ago
Yes; a simple example is Norton's dome. It is possible to construct a frictionless curve such that a particle that is pushed up the curve with correct initial velocity will reach the top and halt in finite time. Observing a particle sitting at the top of the dome, there is no way to tell when it reached that point or from which direction.

cycomanic 5y ago

It's not a tautology to say for an apple to fall of a tree it has to be on a tree, it's not a tautology for a plane to crash to be flying first or for a car to stop it needs to be in motion first. They are all necessary conditions, in fact this is the definition of a necessary condition. Something to be a necessary condition has nothing to do with time-reversibility, it simply states a logical relationship Let me give you another example: To accelerate a body with mass m it is necessary to exert a force onto it. All mathematical descriptions In fact equivalency, requires conditions to be necessary and sufficient. Your argument that physics describes a world with statistical regularities is a maybe a nice philosophy, however most physicists (and regular people) do not believe we live in a simulation, but physical laws describe the real world.