BLACK HOLE & SPACE-TIME RELATION

                               

We are all pretty familiar with the term 'Black Hole'. Well, what does it really mean? Firstly, the 'Black Hole' is not black at all. It is a kind of void from which light cannot escape. According to the general theory of relativity, proposed by Sir Albert Einstein, the black hole is that region of space and time, where the gravitational attraction is so strong that nothing can escape from or through it. A huge, enormous amount of mass is concentrated over a very small volume. And, consequently, the density of the black hole becomes incredibly strong.

⮚     Formation of the 'Black Hole': Well, so far as the creation of the black hole is concerned, it is speculated that if the centre of an enormously distributed star collapsed and, as a result, the 'SUPERNOVA EXPLOSION' occurred. Then, the entire mass of the star is found to be concentrated in a very small space,  increasing its density to a great extent. As a result, the 'Giant of the space' is formed.

⮚     Types of  'Black Hole': There are mostly three types of black hole, i.e. 1.Stellar, 2.Intermediate & 3.Supermassive. Supermassive black hole has the highest density out of these three.

⮚     Parts of the Black Hole: There are two major parts of any black hole: 1.Singularity & 2.Event Horizon.

(1) Singularity Point: At the very centre of a black hole, there lies a single one-dimensional point where a huge amount of mass is concentrated, which makes the density of that point infinite. At that point, all laws of physics(space-time curves & gravitational attraction) becomes infinite. And, this singularity is that point of a black hole, where it got created initially.

(2) Event Horizon: This is the point situated on the circumference of the black hole. This is the point where the 'SUPERNOVA Explosion' took place. And, once any object touches the event horizon, it needs a speed higher than that of the speed of light to escape the gravitational pull of the hole, otherwise it gets consumed and is attracted towards the 'Singularity Point'.

What if two Black Holes collide?

If two black holes collide, then, due to both of their tremendous gravitational attraction they will come near each other and start to rotate. At that very moment, the objects around them will go backwards in time. And, at a particular point of time, these holes will crash into each other and combine themselves into one complete black hole.

Hawking Radiation: In the year of 1974, one of the greatest scientists, Sir Stephen Hawking theoretically proved that the Black Hole radiates too. Hawking showed how the strong gravitational field around a black hole can affect the production of matching pairs of particles and anti-particles, as is apparently happening all the time in empty space, according to quantum theory. If the particles are created just outside the event horizon of a black hole, then the positive member of the pair may escape - observed as thermal radiation emitted from the black hole, while the negative particle may fall back into the black hole,  and in this way, the black hole would gradually lose its mass. This was perhaps one of the first-ever examples of a theory which synthesized, at least to some extent, Quantum Mechanics and General Theory of Relativity.

How 'Time Travel' is possible?

There are several ways to time travel. Either one can move at the speed of light in space or one can switch over into the black holes or using the wormholes.

Time travel through Black holes :

●       Say, if any particle or an object falls into the black hole, then what will it experience?  Will it vanish? Or will it be destroyed? When the particle is about to fall into the black hole and after a certain time, when it reaches the range of massive gravitational attraction of the black hole, there will be an imbalance between each and every particle of that object. And, once the object touches the event horizon, it will need to move faster than the speed of light to escape. If not, then it will reach the Singularity Point, where it's density and gravitation pull are infinite. And, in the meantime,  due to enormous and unequal gravitational pull at different particles of the object, they will split from each other.

●       If the particles can move at a speed higher than that of light in that interval, then it will not move towards the singularity point. Instead, it will switch over towards the exact opposite point of the black hole, where it will experience a gravitational repulsion, by which the black hole will tend to throw the body outside of it. At that very opposite side, there lies the wormhole, which is exactly opposite in features than that of the black hole. And, finally, the wormhole will help to throw the object into another universe, often called the 'Multiverse'. This is all still speculation and our imagination, since no object can move faster than the light to our knowledge.

What are  'Wormholes'?

The wormholes are the hypothetical tunnels that join two universes. It is also called the 'Einstein's Rosen Bridge'. Assume two universe, 'Milky Way' and 'Andromeda'(Our neighbour galaxy ). They are situated almost 5-6 googol million distances approximately. If the two galaxies are wrapped to minimize their inner distances by a tunnel to connect those two, this tunnel is called the wormhole. These are made naturally, according to the cosmologists. But, the proof is necessary which is beyond our limit.

‌Time travel by moving faster than light: According to Einstein's general theory of relativity, our mass is completely determined by our speed. The equation known to us, i.e. E= mc^2, was not derived by Einstein. He originally developed the equation m= E/c2, which means that if we move faster than light, then it is possible to travel in time. But, in his theory of relativity, he stated that one can only go forward in time. Going backwards in time is not practically possible. Contradicting it, Stephen Hawking told that it is possible to go backwards and well as forward in time. Consider one train that will rotate the earth at the speed of light. And, during that travel, time will slow down tremendously for the travellers that are staying inside the train. Higher the speed, the slower will be the time. And, when the travellers exits from the train after one rotation, then they will only pass 7 days, whereas the rest of the earth will surpass 65 years. This is also pure speculation because nothing can move faster than the light.

‌An object from Quantum Mechanical POV: Any object has two properties, general properties &  quantum properties. Suppose, when we eat an apple which is assumed to have consisted of a lot of particles, it's general properties vanish. But, what happens to its quantum properties? They never vanish. It's only possible to vanish the quantum properties if the apple crashes into a black hole. In this regard, the scientist, Schrodinger did a brilliant experiment. He put one cat into the box, where the valve systems are present along with the Potassium Cyanide gas. Keeping the box fitted with its cover, he hit the valve systems. The Cyanide gas was released and the cat died. But, is it really so! He theorized that the general property of the cat died not it's quantum properties. When the cyanide gas was released, then there's only one possibility that the cat is alive and dead simultaneously. No 'or' term is linked with it. Because the cyanide gas killed the general property of the cat, not it's quantum property. We saw the cat die but we didn't feel it's aliveness either. It is a very complicated theory to explain. It speculates that maybe we can see the cat alive in a  parallel universe. The 'Schrodinger's Equation' theorized that the quantum property of any object can never be destroyed.

If we consider any particle as the wave, then to determine it's quantum properties, we have to find out its wave function first. And, the wave function is nothing but the complex number(A+iB). If we do the square of its amplitude, then it will reveal the probability of finding that particle within the space. And, if the particles superpose, then the square of their resultant amplitude will give the probability of finding out the whole combination.

Relation between Time and Space: The event that is discussed, the position of the event and the spontaneity of any event are all described as the space. And, on the other hand, time is the measurement of events. Space and time are used simultaneously to describe the events. According to Einstein's general theory of relativity, space and time are relative to each other. And, space-time relation is not linear, but, rather a curve in nature, except at the singularity point of the black hole. The space and time are four-dimensional entities, where time is considered to be the 4th dimension. If one considers any cube (3D) is placed inside another cube, and the outermost cube is constantly rotating then that system will be 4D in nature.

'TIME' is nothing but a stubborn illusion':

It slows down with the massive objects and stops the high speed of light. It completely stops at the speed of light and does not exist at the centre of a black hole. If someone travelled by the rocket, then the passage of time for him will be halved. His watch will be only 10 minutes ahead while for an earthbound observer, more than 20 minutes will have passed. As per Einstein, the space-time does stretch, bend, & twist in response to matter having mass and energy. And, that stretching, bending, etc. are only due to the presence of the gravitational forces. This is what the space-time relation is all about. And, thus the quantum mechanics plays a pivotal role in making the grand design of the universe.

Prithwish Paul

Department-Mechanical

1st Year