Chapter 9: The Arrow of Time

The idea that time could be measured as a set quantity led to the theory of relativity. It is true that time is measured based on perspective. Time for one person that is standing still will be different from time for another person that is in motion or on something that is moving. In "imaginary" time, it is safe to say that if one is moving forward in time, one must also be able to move backward in time. There should not be a difference the back and forth direction of "imaginary time." However, in real time, there is a huge difference between the two directions. We can recall the past but not the future. Time is also directly related to the entropy of the universe. The increase of entropy with time is one example of the arrow of time. There are three known arrows of time. One of the other arrows of time deals with thermodynamics, and the direction of time with a given amount of entropy. As stated in the second law of thermodynamics, the amount of disorder in a system outweighs the amount of order. The early life stages of the universe were probably marked with many disorderly systems and very few orderly systems. If this were true, than it would make sense that the entropy of the universe would be decreasing with time. As time goes on, the entropy of the universe will continue to decrease while the order of the systems in the universe will continue to increase.

As time goes on, the entropy of the universe will continue to decrease while the order of the systems in the universe will continue to increase. The theory of general relativity cannot foretell how the universe began because the laws we have now would be null and void at the point of the big bang. The universe could have started organized and smooth just as easily as could have started out disorderly. Since the amount of disorder has not reached the point of total entropy, we can assume that entropy does not increase with time. It can only decrease or remain constant at the same level. The existence of the thermodynamic arrow of time can be explained if the universe started out with little entropy that steadily increased with time. If the collapse of a star could be compared to the collapse of the universe, than the amount of entropy should decrease as time goes on for both. The conclusion that the universe has no boundary is accurate because it would have had to have orderly when it was created in order for the entropy to decrease with time. The three arrows of time help differentiate the past and the future. They summarize the direction of time and how it relates to the amount of entropy in the universe.