Is Absolute Space and Time Really Absolute?

[PeterDonis]

I hadn't realized that energy was being considered truly relative, but I guess it follows from the metaphysical assumption that presentism isn't true.

I'm not sure what you mean by "the metaphysical assumption that presentism isn't true", but if you mean that energy being relative is something that goes with the theory of relativity, as multiple people have pointed out in this thread, that's not the case: energy is relative (i.e., coordinate-dependent) in Newtonian mechanics.

 

[name123]

I'm not sure what you mean by "the metaphysical assumption that presentism isn't true", but if you mean that energy being relative is something that goes with the theory of relativity, as multiple people have pointed out in this thread, that's not the case: energy is relative (i.e., coordinate-dependent) in Newtonian mechanics.

You can use frames of reference for motion in Newtonian mechanics, and only consider relative motion. Though I assume that metaphysically there was supposed to be absolute motion. I assume it was the similar for energy (you could use equations for relative motion or energy but metaphysically absolute motion and energy was assumed).

 

[PeterDonis]

You can use frames of reference for motion in Newtonian mechanics, and only consider relative motion.

It's stronger than that: all motion is relative in Newtonian mechanics, just as in relativity. The relativity of motion was established by Galileo and has been a part of physics ever since; it was not introduced by relativity.

Though I assume that metaphysically there was supposed to be absolute motion.

No. Newtonian mechanics assumed absolute space and time, but not absolute motion. All Galilean coordinate systems (the Newtonian analogue of Einstein's inertial frames with their rods and clocks--the word "Galilean" is used because the transformations between them are called Galilean transformations) are equivalent in Newtonian mechanics, just as all Lorentzian inertial frames ("Lorentzian" because they are related by Lorentz transformations) are equivalent in SR.

 

[A.T.]

You can use frames of reference for motion in Newtonian mechanics, and only consider relative motion.

What do you mean by "you can"? Since there is nothing in Newtonian mechanics that allows you to determine absolute motion, you have to use relative motion.

 

[name123]

[QUOTE="PeterDonis, post: 5007707, member: 197831"
No. Newtonian mechanics assumed absolute space and time, but not absolute motion.[/QUOTE]

Doesn't absolute space and time imply absolute motion? If at any point in absolute time an entity has an absolute location, wouldn't the changes in its absolute spatial location in absolute time count as absolute motion?

 

[jbriggs444]

Doesn't absolute space and time imply absolute motion? If at any point in absolute time an entity has an absolute location, wouldn't the changes in its absolute spatial location in absolute time count as absolute motion?

Under Newtonian mechanics, the distance between two co-moving points is fixed regardless of whether you adopt a frame of reference where those points are moving or one in which they are at rest. In that sense, Newtonian space is "absolute".

 

[A.T.]

Doesn't absolute space and time imply absolute motion?

In Newtonian mechanics distances, clock rates and simultaneity are frame independent, while in Relativity they are frame dependent. Velocities are frame dependent in both models. The first postulate of SR is just restating Galilean relativity, not introducing something new.

 

[name123]

Under Newtonian mechanics, the distance between two co-moving points is fixed regardless of whether you adopt a frame of reference where those points are moving or one in which they are at rest. In that sense, Newtonian space is "absolute".

In the sense that you can imagine whatever coordinate system you like and no matter what frame of reference the human you experience being is in, the experience could be imagined to be an experience of a physical reality in which that distance was manifest as a property (regardless of what method of measurement you use to measure it), and that it's proportion to other physical distances wouldn't be dependent upon the frame of reference of your human.

 

[Nugatory]

Doesn't absolute space and time imply absolute motion? If at any point in absolute time an entity has an absolute location, wouldn't the changes in its absolute spatial location in absolute time count as absolute motion?

No. Google for "Galilean relativity".

 

[PeterDonis]

Doesn't absolute space and time imply absolute motion?

No.

If at any point in absolute time an entity has an absolute location

That's not what "absolute space" means, at least not as that term is used in Newtonian mechanics. "Absolute space" means that spatial distances at a given instant of time are the same for all observers, regardless of their state of motion. (Note that the qualifier "at a given instant of time" is only possible because that phrase has the same meaning for all observers, i.e., because Newtonian mechanics has absolute time.) It does not mean that spatial positions are the same; those are relative. Mathematically, Galilean transformations preserve spatial distances but not spatial positions (whereas Lorentz transformations do not preserve either spatial distances or spatial locations).