Inertial Frame of Ref & Forces: Understand Special Relativity

[Lisastronomy]

TL;DR Summary

Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining that eventually the velocity would be constant)? And is that why the speed of light is the same for all observers?

In trying to understand a bit of special relativity, I want to make sure if I understand it correctly, and I came up with the following question: "Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining that eventually the velocity would be constant and with real is meant; not dependent on another observer)? And is that why the speed of light is the same for all observers?"

 

[Ibix]

No. Why would knowing the forces have anything to do with a reference frame? That's little more than a choice of what "at rest" means and a clock synchronisation procedure.

 

[Lisastronomy]

No. Why would knowing the forces have anything to do with a reference frame? That's little more than a choice of what "at rest" means and a clock synchronisation procedure.

Knowing all the forces, would in the end tell you who is really moving, as it seems to me.

 

[Dale]

Summary:: Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining that eventually the velocity would be constant)? And is that why the speed of light is the same for all observers?

doesn't that give away the only real existing frame of reference

No. It defines a class of frames where the acceleration of the object is given by $\Sigma \vec F = m \vec a$ but places no constraints on the initial velocity of the object.

 

[Ibix]

Knowing all the forces, would in the end tell you who is really moving, as it seems to me.

Why? Zero force just means you aren't accelerating, not that you aren't moving.

That there is no such thing as "really" moving is, in fact, one way of reading the principle of relativity, which is one of the postulates of relativity.

 

[PeroK]

Knowing all the forces, would in the end tell you who is really moving, as it seems to me.

What if two objects have zero force acting on them, but they are in relative motion?

The principle of relativity says that the laws of physics are the same in all inertial frames. It's not about "who is really moving".

 

[anuttarasammyak]

Summary:: Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining that eventually the velocity would be constant)? And is that why the speed of light is the same for all observers?

"Imagine you would know all forces in the universe acting upon an object, doesn't that give away the only real existing frame of reference (imagining that eventually the velocity would be constant and with real is meant; not dependent on another observer)? And is that why the speed of light is the same for all observers?"

I think that my body, your body, the Earth, the Sun or everything in the Universe get forces from all the others in the Universe. Then much varieties of motions and frame of reference attached to them take place, e.g. you and I are stack on the Earth, the Earth revolves around the Sun, the solar system revolves in our galaxy, etc. So I am afraid whether what you say about special reference frame really works. Am I taking you wrong ?

 

[Lisastronomy]

Hello, thank you for all your answers! I understand it better now and I was clearly wrong in my assumptions, so thank you for correcting me!