Epistemology regarding c

[tezk_4]

TL;DR

How do we know what we know

How do we know that c is the speed limit if our instrument is based on that speed limit, if the "medium" on how we perceive information is only photon then how do we calculate other "medium", isn't it's like relative velocity equation but the c is not constant but variable of the "medium" velocity, Velocity=velocity 1+velocity 2÷1+velocity 1×velocity 2÷medium velocity²

 

[pines-demon]

In PF we try to make sure threads get somewhere. For that we ask users to show what they know and what they have looked so far before asking a question. Have you tried to come up with an answer before asking? What is your current conclusion?

 

[Dale]

TL;DR: How do we know what we know

How do we know that c is the speed limit if our instrument is based on that speed limit

This is a very vague statement. Can you describe a specific experiment for measuring $c$ and what you are concerned about regarding that specific measurement.

If you don’t already have a specific experiment in mind then you can look here https://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html at section 3.4

 

[Sagittarius A-Star]

TL;DR: How do we know what we know

How do we know that c is the speed limit if our instrument is based on that speed limit, if the "medium" on how we perceive information is only photon then how do we calculate other "medium", isn't it's like relative velocity equation but the c is not constant but variable of the "medium" velocity, Velocity=velocity 1+velocity 2÷1+velocity 1×velocity 2÷medium velocity²

Given the assumptions in the paper "Nothing but Relativity", including group properties of a transformation (two boosts in one direction are equivalent to one boost of the same form),
https://arxiv.org/abs/physics/0302045
an experiment is needed to decide between Galilean- or Lorentz-transformation. These are the only possibilities.

For example a twin-paradox experiment (Bailey et al. 1977) is sufficient to decide for Lorentz-transformation.
https://en.wikipedia.org/wiki/Experimental_testing_of_time_dilation#Twin_paradox_and_moving_clocks
The related time-dilation factor contains $v^2/c^2$.

The Lorentz-transformation keeps $c$ invariant, which makes it a speed limit.

 

[berkeman]

The OP is no longer with us (for reasons not directly related to this thread), so the thread is closed now.

 

[bhobba]

TL;DR: How do we know what we know

How do we know that c is the speed limit if our instrument is based on that speed limit,

I can't follow your logic.

However, the modern derivation of relativity has nothing to do with the speed of light; it is derived from the POR (principle of relativity: the laws of physics are the same in any inertial frame). A frame is a conventional standard of rest on which experiments can be done. An inertial frame is a frame, assumed to follow the laws of Euclidean geometry in which the laws of physics are the same at all points and directions in space and at all instants of time, or a frame (again assumed to follow the laws of Euclidean geometry) travelling at constant velocity wrt an inertial frame. The Earth is, for most practical purposes, an inertial frame (although, because it is rotating, mountainous, and has gravity, it is strictly speaking not inertial).

Interestingly, the assumption of Euclidean geometry can be replaced with that of scale invariance, which is equivalent to Euclid's famous parallel postulate (and allowing the definition of an inertial frame by symmetry alone):
https://philarchive.org/archive/ULIAES

From that alone, relativity, except for the value of a constant usually called (for historical reasons) c, can be derived by logic alone:
https://www.physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Now the value of c can be measured in all sorts of ways, many not even involving light. It always turns out to be the speed of light. Which, by the POR, means that speed is the same in all inertial frames.

Apologies to Berkman - penned my reply while you were closing it.

Thanks
Bill

 

[PeterDonis]

One additional note: thread moved to the relativity forum due to subject matter.