A Brief History of Time

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How I came across this book: In the memory of Stephen Hawking.

Favorite Line from the book:

The mass of the sun curves space-time in such a way that although the earth follows a straight path in four-dimensional space-time, it appears to us to move along a circular orbit in three-dimensional space.

Even Einstein, when he formulated the general theory of relativity in 1915, was so sure that the universe had to be static that he modified his theory to make this possible, introducing a so-called cosmological constant into his equations.

The divine belief that the universe is static was shattered when a champion of humanity, Hubble put us on the correct path. Theories change if something new comes along the way. Objects are in constant motion but time is fixed as per Newton’s law of inertia. This changed too with Einstein’s famous theory of relativity. Time is not fixed anymore, but it is relative to the observer. Stephen Hawking, a theoretical physicist, explains all the theorems in physics which made a difference, and traces the history of time in his amazing book.

The speed of light is constant whereas time is relative. Consider an example of twins where one of the them flies away in a hypothetical spaceship at the speed of light, and the other stays back on the earth. If they meet after ten years, then our space twins will be much younger. It sounds like science fiction, but this is exactly what the theory of relativity tells us – time is relative to the observer. The modern GPS follows the theory of relativity to guide us to the destination point. Einstein summarized this concept as SPACETIME where time is the 4th dimension. Gravity curves SPACETIME, so it is warped. Whereas theory of relativity looks at the cosmological picture, quantum physics evaluates atomic picture. According to the uncertainty principle (Heisenberg), a matter is in a quantum state, i.e., it is impossible to measure their velocity and position accurately, so scientists predict the most likely position. According to quantum physics, some equations will be infinite. For example, there are virtual particles and anti-particles which create energy in the space. Since the space is infinite, this will lead to infinite energy in the universe. According to Einstein’s famous formulae E = MC2, if the energy increase infinitely, then mass has to increase infinitely since the speed of light is constant. With an infinite mass, the universe will collapse secondary to gravity leading to a massive black hole. In essence, quantum physics and theory of relativity cannot go hand in hand. We are just waiting for a new Einstein to come and change all this too.

A star collapses secondary to gravity into a singularity called the black hole when it runs out of energy. According to the second law of thermodynamics, 'entropy' is the tendency towards greater disorder. As entropy increases it leads to increase in temperature. A black hole has virtual pairs of particle and anti-particles which are positively and negatively charged. A black hole sucks in the negative particle and releases the positive particle as heat and radiation. This increases the entropy of the black hole. At a certain point, the negative particle in the black hole will reduce its mass so much that it dies with a massive explosion as large as millions of hydrogen bombs.

SPACETIME WARP

Superman could not have saved Lois Lane even if he had the power to turn the Earth back. Cosmological arrow of time can only go forward. As the universe expands the entropy increases. An intelligent being like human can only exist because of increased entropy which causes the release of energy such as the breakdown of food. So, if you had the power to rotate the earth back, then you may create significant climate change and possibly the earth will cease to exist, but Lois Lane will not come back. I am sorry to break your dreams if you are a Superman fan like me. We have currently accepted Big Bang as the model from which our universe originated. This was the beginning of the time. What was before the Big Bang? We may never know. Stephen Hawking was a genius in mind and spirit. His theoretical models helped to shine a light on black holes. As one of the greatest scientists of the twenty first century, he warped the scientific communities and our lives while sitting in his chair.