The world is not a collection of things, it is a collection of events. The difference between things and events is that things persist in time; events have a limited duration. — Carlo Rovelli, ‘The Order of Time’
You all deny/critique that <all objects are in relative motion>
If you all are right then there is must be an object at absolute rest.
Can you prove that? — TheMadFool
There is no need to prove that. The person who claims that all motion is relative needs to prove that there is no such object as absolute rest. Until it is proven that all motion is relative, the critique of this premise is justified. — Metaphysician Undercover
Ok. So don't come to this forum for help with your physics assignments.
Bloody hell. What a mash. — Banno
There is a need to prove that there exists an object in absolute rest because there are only two contradictory possibilites:
1. An object in absolute rest
or
2. Everything in relative motion
Since you're denying 2 then 1 must be the case. So, prove it. — TheMadFool
Let's try again...
Suppose there is an object, A, in absolute rest i.e. at rest relative to everything else.
But we know that there exists at least 2 objects in relative motion of the displacement kind i.e. the distance between them change e.g. a car moving towards you.
Is it then possible that A is at rest (absolute) relative to both the car and you??
There are three points: object A, the car (B) and you (C) forming a triangle.
We know that the distance BC is changing. Can the distance AC and AB remain constant i.e. can A be at rest relative to both B and C?
I think it's impossible. The pythagorean theorem proves it. — TheMadFool
You ought to see that this is nonsense. "Absolute rest" would be the standard by which all motions are measured. Therefore everything would be in motion relative to "object A" (absolute rest), unless there was something else which was at absolute rest. Only things at absolute rest would be unchanging relative to absolute rest, everything else would be changing relative to absolute rest. — Metaphysician Undercover
You mean the Earth and sun are A and B respectively? The distance between them does change all the time, but not a whole lot. You didn't define what C was. If it's Jupiter for instance, then AC and BC are going to be changing regardless of the stability of AB or not. If its my mailbox, then AC is pretty constant despite the continuous change to AB.What if we assume, in fact it's true that the distance between the earth and the sun keeps changing, that it's the distance AB keeps changing. Doesn't this mean AC and BC should also change? — TheMadFool
Well its pretty easy to make a counterexample of that. Just make AC and BC hinged rods holding those points at a constant separation. AB is free to change (B moving relative to A) without changing the lengths BC or AC. It just changes the angles at each of the 3 vertices.I used the math tool geogebra and what I saw was (taking three vertices of a triangle ABC) if we move B relative to A then even if AC doesn't change BC does change.
The existence of the counterexample is proof that it isn't the case.The mathematical proof would likely use the pythagorean theorem.
Oh, you think absolute rest means that either 1) everything is at rest, or 2) the distance between the one resting object and every other object remains the same.Suppose there is an object, A, in absolute rest i.e. at rest relative to everything else.
In fact, the wording (the i.e. part) is a total contradiction. — noAxioms
If there are only two objects in the universe moving relative to each other, a third object might be stationary relative to one of them, but it would be moving relative to the other at the same velocity as the thing relative to which it is stationary. This is pretty trivial geometry. Yes, you describe this in your lower paragraph.Correct. Thanks for pointing that out. Motion is always relative. What I meant to ask was if there exists an object that's at rest relative to everything else in the universe? There is no such thing, right? — TheMadFool
The speed (not velocity) of light is constant. Each photon has a different frame dependent velocity.What about light? No matter who the observer, where the observer, relative velocity with light is always 186,000 mph. — TheMadFool
Light does not define a valid reference frame, so no, it's not like saying that. If one was to attempt consideration of such a frame, the universe collapses into a singularity and there is no space or time in which to define motion at all.Isn't this kinda like saying that all object in the universe, because they're moving at the same velocity with respect to light,
The speed (not velocity) of light is constant. Each photon has a different frame dependent velocity.
Isn't this kinda like saying that all object in the universe, because they're moving at the same velocity with respect to light,
Light does not define a valid reference frame, so no, it's not like saying that. If one was to attempt consideration of such a frame, the universe collapses into a singularity and there is no space or time in which to define motion at all.
I am wondering what any of this has to do with the topic title. Absolute rest (of a given object) is conceptually possible, and it means that the object's absolute location is unchanging, and has nothing to do with what any of the other objects are doing. It requires a definition of absolute location, which isn't trivial. — noAxioms
Not possible. Beyond a certain distance away, the Hubble expansion prevents any object from being stationary relative to something over here.Just a thought and the connection to the topic title is the possibility of an object/objects that could be at rest relative to everything else in the universe. — TheMadFool
Seems correct to me.If two objects A and B have the same velocity relative to another object C, then the two objects A and B must be at rest relative to each other.
They do not. Read what I said above about light not defining a valid reference frame. Also, light doesn't all have the same velocity since it is moving in all different directionsIf that's the case then since all objects in the universe have the same velocity relative to light
The "absolute" part is meant to take it out of our hands: make it something we discover rather than declare (so changing our minds doesn't alter the situation). — frank
I just evoked absolute rest: a thing that never moves. X-Y axis. Does it exist? — frank
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