Relativity Revisited

JayCee wants to understand relativity here. So, for the benefit of JayCee and other patrons of My Phenotype, I am attempting to explain one basic proposition of relativity in this post. The proposition, that the velocity of light is constant across all relative frames of reference, is a difficult one to get our head around. We often find this proposition counter intuitive, because we do not travel at speeds anywhere near the velocity of light. Newtonian physics, on the other hand, comes to us intuitively because our intuition was evolved in a Newtonian world where our ancestors were hunting medium sized three dimensional objects travelling at velocities hundred thousand times less than the velocity of light. Had our ancestors inhabited a world where their prey had been eleven dimensional instead of three, string theory would have come to us intuitively. Had they been searching for their food between the lattices of silicon crystals, quantum physics would have been a piece of cake for us. But they hadn’t and therefore JayCee’s trouble with relativity appears more as a matter of heredity than as an issue of intelligence. We recognize his predicament precisely because we also evolved from the same set of ancestors as he did. Here is an interesting sidebar. The most recent common ancestor (MRCA) of JayCee and I, would have lived not more than twenty four generations before us. If we call him (or her) ‘Sam’, Sam’s ancestors are also common ancestors to us and we aren’t interested in them. For Sam to be our MRCA, he should have had at least two children and, JayCee should have come in the lineage of one and I should have come in the lineage of another. The formula to find out the reasonable number of generations, you would have to go back to find your MRCA, is an easy one. You have to take logarithm to the base two of the number of sexually isolated surviving descendents of your MRCA. In this case of JayCee and me, the computation is based on the assumption that our caste is sexually isolated. The logarithmic value came to 23.4. I approximated it to 24 to account for those naughty nadar dudes who could have looked beyond their dudetttes on their Burmese business trips. This calculation is interesting enough to deserve a post in itself and more on that later.

We have digressed too much and we have a business to finish here. Let’s say JayCee is riding a bike at sixty miles per hour. And, there are two girls intending to open up their hearts to JayCee. There is scope for a quick sidebar here. Yes, JayCee is single and available. Readers are perfectly justified in wondering why he is single in spite of having featured in three (1,2)of the ‘My Phenotype’ posts. But, with the recession and all, that’s the situation here and we can only hope things will work out for him soon. Side bar ends. Girl A is waiting for JayCee to come to her, whereas, Girl B decides to chase JayCee down and propose to him on the move. She gets on to her bike and reaches JayCee. As she proposes to JayCee, they both are travelling at sixty miles per hour and are crossing Girl A who is standing still. Now the relative velocity between JayCee and Girl B is zero since they are travelling in the same direction and at the same speed. The relative velocity between JayCee and Girl A is sixty miles per hour. In a physicist lingo, JayCee’s relative velocity from Girl B’s frame of reference is zero and his relative velocity from Girl A’s frame of reference is sixty miles per hour. Now, imagine JayCee and Girl B are travelling in two different beams of light instead of their bikes. Girl A, witnessing this hypothetical chase, would say that JayCee and Girl B are travelling side by side to each other. But JayCee would claim something radically different and tell you that the Girl B is speeding away from him at the velocity of light. So, does Girl B. She would swear in the name of JayCee that he is speeding away at the velocity of light. How can three people have three totally different interpretations of the same event? Einsten’s solved the riddle: He said time beats at different rates, depending on how fast you travel. The faster you travel, the slower the time beats. And, if you reach the velocity of light, time should stand still because the relative velocity of light across all frames of references is a constant.