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  • Oshin Mittal

Ch 8: The Conclusion | A Brief History of Time

The concept of our universe started with the assumption that the earth was stationary and other objects orbited around it. Later, Newton came up with the law of gravitation according to which each and every object attracted each other. The fact that objects don’t keep on colliding proves that the forces are somewhere balanced out indicating that there are infinite numbers of celestial objects in the universe. It was also confirmed that the stars and other objects are not present from eternity. Einstein’s theory of relative pointed out that universe is a four-dimension space-time cosmos and each object travelled in a nearest possible straight path, called geodesic, but due to the space-time curvature it appeared to move in circular or elliptical orbits. Edwin Hubble, using the Doppler effect, found that the universe was expanding. Alexander Friedmann made two basic assumptions regarding the universe. Firstly, the universe is identical in all directions and secondly, that this is to hold true from any point in the universe. Arno Penzias and Robert Wilson discovered some weak noises that were unaffected by the earth’s rotation and the direction of the detector, indicating evidence for Friedmann’s first assumption. So, there were three models that followed Friedmann’s two fundamental assumptions:


(1) The rate of expansion of the universe is slow enough for the gravitational force between the galaxies to attract each other and eventually causing the collapsing of the entire universe.


(2) The expansion rate of the universe is too high to be stopped by gravity, although it does slow down a bit. In this case, the universe would continue to expand too rapidly to be countered with.


(3) Expansion of the universe is at a steady rate or speed, that is, it is fast enough to escape re-collapsing while still expanding continuously. This is the most suitable and excepted model for the expansion of the universe


The third model is the most evident to the current situation gave significant consideration to the concept of the big bang.


In an attempt to predict future positions, Werner Heisenberg came up with the uncertainty principle which stated that at a particular point in time, it is impossible to accurately predict both, the position and the velocity. It gave the result that the product of the change in position and momentum is always greater than or equal to a certain constant. This was the base for quantum mechanics.


The life cycle of the star is the base for understanding the formation of the black hole. The gravity between the celestial particles leads to the atomic interaction between the gases which eventual combine to form a star. Further collisions lead to nuclear reactions which in turns balance out the gravity. Once the star runs off the fuel for the reaction is collapses under its own gravity and thus forms a black hole. To define this more appropriately it was accepted that a star with a mass less than Chandrashekhar limit would stop contracting and settle down to a white dwarf. The black hole was believed to be the region from which nothing can escape, not even light! It is believed that the universe had its beginning at the big bang and during its start, the universe was believed to be extremely hot. Slowly and gradually the temperature fall and the corresponding nuclear reactions lead to the formation of the universe that we see today. Now the concept of time is believed to be governed by the second law of thermodynamics, i.e., by entropy. All the three arrows of time, namely, thermodynamic arrow, psychological arrow and the cosmological arrow are governed by the randomness of the universe since the universe tends to be in the disordered state.


This was all from the great book A Brief History of Time -By Stephen Hawkins but that’s not the end of curiosity. Keep Exploring!! Stay Curious and stay updated.

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