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.

Special relativity simplified to its best

                    SPECIAL RELATIVITY

Special relativity postulated by the genius Albert Einstein                                                                                         

Relative velocity

To understand this spooky topic in a simplified and easier way lets clear out topic of relative velocity

Assume We both are on a flight (why train always?) just sitting there and having ice cream, so our both velocities are same and are zero with respect to each other (can also be said as relative to each other). Same case, now when our velocities are considered with respect to the ground(frame of reference is ground)we are in motion with a particular velocity( relative to the ground) and a different velocity when frame of reference is another plane flying across ours cause the velocity of that plane is subtracted from ours . so basically relative velocity pronounces  that speed with which we are moving varies with respect to our frame of reference (hence comes word relative) and also that space is not absolute.

Frame of reference:to the above Paragraph, it is from where one is calculating plane’s velocity

Back to main topic: SPECIAL RELATIVITY

Bottom line of this theory says Speed of light is constant for every observer. Okay I have been listening to this from really long time, what’s spooky about this?

Let me expand and confuse you a little more before clearing it out

For a space ship ‘A’ moving with speed of 2x10⁸m/s  and another space ship ‘B’ moving with speed of 1x10⁸m/s the speeds of light beam travelling parallel to them must be

For A  (3-2)x10⁸=1x10⁸m/s

For B (3-1)x10⁸=2x10⁸m/s  in accordance with relative velocity

But in reality it’s found out to be 3x10⁸m/s for both……does it seem absurd now? Now this appears to defy the concept of relative velocity.

In conclusion speed of light is always constant compared to anyone moving at any speeds, does it now make sense as to why you can’t beat this speed? Because when a particle moves closer to speed of light, light still passes that particle at 3x10⁸m/s.

Okay, all this is cool, but how can it be same?C'mon Something has got to change!

Yes, time compensates it.

TIME DILATION comes to play here.

TIME DILATION:

This basically says that racing of time depends on velocity, the faster you move slower your time runs. As you move with speeds closer to speed of light your time slows down, congrats you will age slowly than your peers. You will have more time in your hand. Same principle is used with various examples, most common one being a pulse bouncing off between 2 surfaces. Similar thing happens with length and this phenomenon is called length contraction.

If you hate Justin Bieber, you might be lucky enough to travel across space at speeds closer to speed of light and come back after a few minutes, few minutes is according to you, but for us on earth it would’ve been years-this is also the main principle of twin paradox(All these paradoxes will be put on soon)

In conclusion:

Special relativity is about speed of light being absolute and constant, doesn’t matter speed of observer, because pacing of time is altered.

Note: Difference between Special relativity and General relativity is that special relativity does not take gravitation into consideration unlike General relativity

And precise value of speed of light is 299792458 m/s