## What is the equation for general relativity?

E = mc² is a scalar equation because energy (E), mass (m), and the speed of light (c) all have only single, unique values.

### What is G in Einstein field equation?

Mathematical form where G is the Newtonian constant of gravitation and c is the speed of light in vacuum. In standard units, each term on the left has units of 1/length2.

**How many Einstein field equations are there?**

The Einstein Field Equations are ten equations, contained in the tensor equation shown above, which describe gravity as a result of spacetime being curved by mass and energy.

**What is the 1915 general relativity?**

General relativity is a theory of gravitation that was developed by Albert Einstein between 1907 and 1915, with contributions by many others after 1915. According to general relativity, the observed gravitational attraction between masses results from the warping of space and time by those masses.

## Why Einstein equations are non linear?

The nonlinearity of the Einstein field equations stems from the fact that masses affect the very geometry of the space in which they dwell. And this is the fundamental insight of (1): mass curves the geometry of spacetime, and the geometry of spacetime in turn tells masses how to move.

### Is general relativity nonlinear?

General relativity: a theory with non-linear laws.

**Why is the speed of light c?**

“As for c, that is the speed of light in vacuum, and if you ask why c, the answer is that it is the initial letter of celeritas, the Latin word meaning speed.”

**What is the variational principle?**

a variational principle seems totally unlike the approach of Newton to ﬁnd- ing the paths of particles subject to forces. Yet we have shown that the 128 CHAPTER 3. THE VARIATIONAL PRINCIPLE associated calculus of variations of functional calculus allows us to con-

## Is the variational principle invariant in free relativistic particles?

We start with the case of a free relativistic particle, and we will require the formalism to be Lorentz invariant from the outset. After all, the variational principle — if general and fundamental — should look the same in all inertial frames. This immediately leads us to write the

### What is the variational principle in inertial frames?

After all, the variational principle — if general and fundamental — should look the same in all inertial frames. This immediately leads us to write the simple candidate functional I = Z d⌧, (3.67) the proper time for a particle to travel between two ﬁxed points in spacetime.

**What is the variation principle in Chapter 3 of 118?**

118 CHAPTER 3. THE VARIATIONAL PRINCIPLE (a) (b) 1 2 3 Figure 3.9: (a) A light ray passing through a stack of atmospheric layers; (b) The same problem visualized as a sequence of adjacent slabs of air of di↵erent index of refraction. a constant everywhere along the path. This result could also have been