General Relativity simplified

GENERAL RELATIVITY

This theory spins around gravity; it is like an extension to special relativity by counting gravity too. Einstein developed it fundamentally based on equivalence principle

EQUIVALENCE PRINCIPLE:

Imagine being locked up in a closed container like an elevator with opaque walls and you are given a tennis ball. As you bounce the ball it touches floor of elevator with acceleration of 9.8m/s (earth’s gravity) as anticipated.

Now your elevator has a fuel tank or you were actually in a rocket, which is accelerating at 9.8m/s (32 feet/sec). When ball is bounced at the moment, what would happen? Would it be same as before?      

Yes to you it would just appear to hit the bottom as before because your body is also accelerating with 9.8m/s. But for an outside observer, it would be the floor accelerating at 9.8m/s towards the ball.

You are shielded inside and you cannot tell if its gravitational frame’s work or accelerating frame’s work that causes ball to touch the floor. In other more scientific and confusing words: laws of physics are same in accelerating (non-inertial) and gravitational frame (inertial) of references, this is called equivalence principle.

Combination of equivalence principle with its analogue in pure mathematics leads to formation of Einstein’s theory of gravitation. (This alone deserves another blog post)

GENERAL RELATIVITY: back to main topic

Einstein’s mathematics consists of 4 dimensions (3 spatial dimensions and 1 time dimension) also called space-time relations. He said “space itself is curved”.

Imagine a rock placed on a spread blanket, there is a depression caused by placing the rock, now a marble shot into blanket will follow an elliptical path around the rock. In analogy, blanket is the space-time fabric, this distortion is formed by matter is called warping of space-time (curving of space time). Imagine is a reference to warping

Proving this:

Light always chooses the least time taking path (hence it’s always straight line), when passing objects as sun (heavy objects that cause warping) light beams bend and the shortest distance it chose being a curved line, articulate us that space-time fabric itself is curved. This phenomena of bending of light is called gravitational lensing

Due to gravitational lensing of sun, light from distant stars is bent and we receive multiple apparent images of them. This was proved during 1919 eclipse; measures of distances of stars were taken at night (absence of sun) and during eclipse (so that sun’s light wouldn’t overwhelm star’s light). Observations obtained were close to Einstein’s theory predicted values. Einstein’s theory overcame, many limitations in newton’s predictions, though it had its own set of difficulties in mathematics domain.

E=MC²

Heard about it too often! But what does it signify?

As Energy is supplied to a particle, it increases its velocity thereby increasing its kinetic energy and mass. This extra mass emanates from energy supplied, it’s also another perspective into saying speed of light is not achievable; as the particle reach speeds close to speed of light, energy supplied is converted to mass gained by the particle.

E=MC² implies

MATTER is condensed form of ENERGY, a storage unit of energy. 

Insignificant amount of matter can generate loads of energy as mass is multiplied by speed of light squared (which is a huge number).

In conclusion: As matter-energy is more ─> curvature of space-time fabric increases hence more the gravitational tug.                    

 Einstein’s relativity theories led to foundation of principles behind motion of black holes, stars, big bang etc.