• EinsteinPK
In summary, the conversation discusses the concept of constant or uniform velocity and its relation to the Special Theory of Relativity. It is mentioned that the speed of light remains the same for all inertial frames, but can vary for non-inertial frames. The difference between Special and General Relativity is also mentioned, with General Relativity involving the interaction between space-time geometry and fields or particles. Additionally, it is suggested that an airplane may not be able to maintain constant velocity due to the effects of gravity.

#### EinsteinPK

1. Is there anybody on Earth which can move with constant or uniform velocity?

2. According to Special Theory of Relativity, speed of light is same for all inertial frames. Then can it be different for non-inertial frames?

3. What is General Relativity and what is the difference between Special and General Relativity?

Thank You

(1) If you mean bodies fixed to the surface of the Earth then no; the Earth is not an inertial reference frame. For starters, it rotates about an axis.

(2) Yes. Even in the simple case of a uniformly accelerating frame (the so called Rindler frame) light can move at speeds other than ##c## and even stop (at what is called the Rindler Horizon).

(3) To put it in very simple words, in SR the geometry of space-time is just a backdrop on which fields and particles interact with one another but it itself never interacts at all with the fields or particles. It just sits there in the background as an innocuous stage. In GR, the geometry of space-time interacts with fields and particles (any kind of mass-energy in fact) so as to not only be affected by the propagation of fields and particles in space-time but also to affect the very propagation of these particles and fields. On top of that, gravity becomes nothing more than a manifestation of this "dynamical" space-time geometry.

Thanks a lot @WannabeNewton

(2) Yes. Even in the simple case of a uniformly accelerating frame (the so called Rindler frame) light can move at speeds other than ##c## and even stop (at what is called the Rindler Horizon).

I have a question that If we travel in an airplane, it is not fixed with the earth, but it is in air. Can it move with constant/uniform velocity? Will gravity affect it?

Is there anyone to help me?

EinsteinPK said:
I have a question that If we travel in an airplane, it is not fixed with the earth, but it is in air. Can it move with constant/uniform velocity? Will gravity affect it?
I hope not. The Earth is not traveling with uniform velocity, so if a plane did it would leave Earth's atmosphere quite quickly.

Why are you asking? Perhaps with some context we can be more helpful.

## What is relativity?

Relativity is a theory developed by Albert Einstein that explains the relationship between space and time. It states that the laws of physics are the same for all observers, regardless of their relative motion.

## What are the two types of relativity?

The two types of relativity are special relativity and general relativity. Special relativity deals with the relationship between space and time in the absence of gravity, while general relativity includes the effect of gravity on the fabric of space-time.

## What is the theory of general relativity?

The theory of general relativity explains how gravity works by describing it as the curvature of space-time. According to this theory, massive objects such as planets and stars cause a distortion in the fabric of space-time, which is perceived as the force of gravity.

## What is the difference between special relativity and general relativity?

Special relativity deals with the relationship between space and time in the absence of gravity, while general relativity includes the effect of gravity on the fabric of space-time. Special relativity applies to objects moving at constant velocities, while general relativity applies to objects in any type of motion, including acceleration.

## How has relativity been proven?

Relativity has been proven through numerous experiments and observations, such as the bending of light around massive objects, the slowing down of time for objects in motion, and the prediction and discovery of gravitational waves. These confirmations have solidified relativity as one of the most successful and well-supported theories in physics.