Correct -- as long as they are inertial reference frames. If you are at rest, or moving at a constant velocity v, you will measure the speed of light as c.

Inertia means at rest or moving at a constant velocity. So an accelerated system cannot possibly be 'inertial'.

A non-inertial reference frame could be accelerating, going in uniform circular motion, or at a specific gravitational equipotential surface. An observer in a non-inertial reference frame would observe the speed of light in another reference frame to be changing.

It is a phenomenon of general relativity and it has been proven repeatedly, from navigation systems, black holes and extra-galactic radiations.

It has to do with CONSTANT velocity -- neither the speed nor direction is changing from one moment to the next. An acceleration CHANGES the speed or direction from one moment to the next.

The lorentz factor, lower case gamma, is used to transform quantities like length, mass an time in one reference frame relative to another, co-moving (constant velocity) reference frame.

It is not, however, used in general relativity for the simple reason that the derivation of the lorentz factor was restricted ONLY to inertial reference frames.

It is longer only in 4d space-time, not in 3d.

The analogy is distances in a 2d map (measured as horizontal distance) are different in 3d (measured as slope distance). On a map, everything is flat but in 3d reality, all features on the map have different elevations.

And to take the analogy further, two points on the earth define a straight line (you can connect these two points with a laser) but, when you plot all the points in between on a map, you would discover that it is an s-curve called a geodesic (if the line is sufficiently long). It curves because at each point on the line, the north direction is changing.

A reference frame is merely a cartesian space+time with an arbitrary origin x,y,z,t=0 from which physical phenomena are observed. These reference frame may be at rest, moving at a velocity v, moving at an acceleration g, or moving at a constant speed but changing direction (as in circular or curvilinear motion).

When an observer is at an inertial reference frame (at rest or moving at a constant velocity, v), the speed of light is observed to be constant regardless of the velocity of that rf.

When an observer is at a non-inertial ref frame (accelerating, in uniform circular motion, and in the presence of gravity) the speed of light is observed to be changing depending on the acceleration of that ref frame.

No.

The motion of any physical object is defined in a reference frame using x,y,z,t. In newtonian mechanics x,y,z and t are uniform quantities in any arbitrarily chosen reference frame. One can use any arbitrary unit and their measures will still be the same -- 1 foot=0.3048 meters, 1 minute=60 seconds, etc. In special and general relativity, space and time are not uniform quantities in all reference frames -- a foot in one rf is shorter that 1 foot in another rf. Clocks run slower in one rf than in another.

The laws of physics are based on uniform quantities of mass, space and time, hence a phenomenon at the edge of the universe is exactly repeatable in the other edge of the universe. That is why physical laws are said to be background-independent. However, we already know that mass, space and time are not uniform. They are dependent on the observer's reference frame. So, special and general relativity are means by which we transform measures from one rf to another such that our understanding of natural laws are still the same.

I have already provided an example of this -- the sagnac effect in navigation systems.

My bad.

Precisely. Physics is not political propaganda and it is a scientific fact that the speed of light would change depending on the acceleration of the reference frame from which you are measuring light.

It is invariant ONLY in vacuum and ONLY in inertial reference frames. You can easily google 'speed of light is invariant' it will come up with what I am saying here -- it is invariant in inertial rf and variant in non-inertial rf.

I'm from asia, so.....

Correct. The results of the michelson-morley experiment was counter-intuitive given the galilean transformation. But it was not only accurate, but it brought experimental validation to einstein's postulate of constancy of c.

Galileo formulated the concept.

https://en.wikipedia.org/wiki/Galilean_transformation

In physics, a Galilean transformation is used to transform between the coordinates ofwithin the constructs of Newtonian physics.two reference frames which differ only by constant relative motion