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By Root 949 0

and its content will become clearer as we go. When you think about it for a moment, it is perhaps less bold than it seems at first sight. If we are to lose the age-old certainties of absolute, unvarying distances in space and the unchanging tick-tock of time as the great clock in the sky marks the passing of the years, then maybe the only thing to do is to search for some kind of unification of the two seemingly separate concepts. Therefore, our immediate challenge is to search for a new measure of distance in spacetime that does not change depending on how we move around relative to each other. We will need to tread carefully to understand how the spacetime synthesis works. But what exactly does it mean to search for a distance in spacetime?

Suppose I get out of bed at 7 a.m. and finish my breakfast at 8 a.m. The following statements are true given what we know from experiment: (1) I may measure the distance in space from my bed to my kitchen to be 10 meters, but someone whizzing by at high speed will measure a different distance; (2) My watch indicates that I took 1 hour to eat breakfast, but the high-speed observer will record a different time. Our conjecture is that the distance in spacetime between my getting out of bed and my finishing breakfast is something we can all agree upon—i.e., it is invariant. The existence of this consensus is crucial because we want to build up a set of natural laws using only this type of object. Of course, we just guessed that this might be how things are and we certainly haven’t proven anything yet. We haven’t even decided how to calculate distances in spacetime. But to proceed further, we must first explain what is meant by the second of our three key words, causality.

Causality is another seemingly obvious concept whose application will have profound consequences. It is simply the requirement that cause and effect are so important that their order cannot be reversed. Your mother caused your birth, and no self-consistent picture of space and time should allow you to be born before your mother. To construct a theory of the universe in which you could be born first would be nonsense and lead to contradictions. When put in these terms, nobody could argue with the requirement of causality.

It is worth reflecting, however, that humans seem capable of ignoring it on a daily basis. Take prophesy, for example. Figures like Nostradamus are revered to this day for allegedly being able to see events that happen in the future, either in dreams or some other mystical trancelike state. In other words, events that happened centuries after Nostradamus’ death were visible in his lifetime, at least to him. Nostradamus died in 1566, but he is credited with observing the Great Fire of London in 1666, the rise of Napoleon and Hitler, the September 11, 2001, attacks on the United States, and, our own personal favorite, the rise of the Antichrist in Russia in 1999. The Antichrist hasn’t appeared yet but perhaps he/she is still rising and if he/she does appear before this book goes to print, then we stand corrected.

Putting amusing drivel aside, we need to introduce some important terminology. Nostradamus’s death was an “event,” as were the birth of Adolf Hitler and the Great Fire of London. For Nostradamus to observe an event such as the Great Fire that happened after his death would require the ordering of the two events to be reversed. To say this explicitly is almost a tautology; Nostradamus died before the Great Fire, and therefore he could not have observed it. To observe it, the event that is the Great Fire must have been available for viewing before the event that is Nostradamus’s death, and therefore the order of the events must have been reversed. There is an important subtlety: Nostradamus could have caused the Great Fire. We could imagine that he left a sum of money in a bank account that encouraged someone to light a fire in Pudding Lane shortly after midnight on September 2, 1666. This would establish a causal link between the events associated with the life and death of Nostradamus