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Australian writer and physicist Paul Davis has called time Einstein’s unfinished revolution. Einstein was first to introduce the concept of slowing of time with motion and in gravity. He was also a proponent of block universe view of time in which past present and future all coexist together laid out as a dimension on a time line. The Greek philosopher Aristotle had speculated that time may be related to motion; he however added that motion could be slower or faster but not time. Aristotle did not have the privilege of knowing about Einstein's relativity in which time also becomes amenable to change. Similarly when Einstein published his theory of General Relativity and proposed the revolutionary idea relating time to curvature in space he did not know that the universe was expanding. This discovery by astronomer Edwin Hubble came thirteen years later. One of the most dramatic aspects of the universe is that it is expanding and the presence of motion, forces and curved space-time happens in the expanding space.

The two main concepts of time are presentism and the block universe view of time. In presentism view of time only present is real while past and future do not exist and passage of time is just an illusion. Presentism may appear more intuitive however the block universe view is more popular among physicists and is supported by heavy weights in physics like Einstein. In block universe view time is laid out as a time-scape. This is based on theory of special relativity and an interpretation of Lorentz transformation equations called the Rietdijk– Putnam argument. Physicist Roger Penrose advanced another variation of this argument called the Andromeda paradox. These paradoxes and anomalies arise from lack of simultaneity due to Einstein’s postulate of constancy of the speed of light in theory of special relativity. There is no free will in the block universe of time. All times in past and future already exist. There is however no explanation of lack of visitors from a futuristic technologically advanced civilization. Block universe also cannot explain what causes us to move through time towards the future and why we cannot willfully move back and forth through this time-scape. Neither of the two views on time can explain what time really is and what the cause of time is.


Slowing of time, changes of mass with high velocity, and length contraction are the commonly discussed predictions of special relativity. Theory of relativity is backed by large experimental data in particle accelerators. Length contraction and increase in mass with increase in velocity are reversible changes which normalize when moving object is brought to rest. However time dilation effects lead to permanent deficit in the time of the moving object. Lorentz transformation equations also lead to very interesting predictions based on changes in line of simultaneity the so called Rietdijk–Putnam argument or the Andromeda paradox. Length contraction as well as time dilation is explained by rotation in Minkowski’s space however time dilation is a permanent effect that is measurable afterwards leading to the so called twin paradox. The changes in line of simultaneity for a moving object with its consequences the Andromeda paradox is considered a strong argument for the block universe view of time.

Twin Paradox cannot be explained by acceleration is well known although this argument is still peddled by some relativity books and articles. The best explanation seems to be shift in line of simultaneity of the twins based on Lorentz transformation and Minkowski’s space-time diagrams. However the length contraction which also is similarly explained is not permanent while time dilation is. Another...
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