sábado, 14 de dezembro de 2013

The Day Without Yesterday

Imagine standing outside the universe. Not just outside space, but outside time too. From this spectacular vantage point, you gaze down upon the universe. At one end you see its beginning: the big bang. At the other, you see... whatever it is that happens there. Somewhere in the middle is you, a minuscule worm: at one end a baby, the other end a corpse. From this impossible perspective, time does not flow, and there is no 'now'. Time is static. Immutable. Frozen. Fantastical as it seems, for most physicists today the universe is just like that. We might think of time flowing from a real past into a not-yet-real future, but our current theories of space and time teach us that past, present and future are all equally real – and fundamentally indistinguishable. Any sense that our 'now' is somehow special, or that time flows past it, is an illusion we create in our heads. Physics, in fact, has killed time as we know it. The question is: do we need it back? It was Newton who began to stick the knife into now. His laws of motion, formulated late in the 17th century, were the first to capture time in mathematical equations. Soon it was natural to depict motion on a graph with time on a spatial axis. Once that was done, any special, unique point of 'now' started to look as subjective as a 'here' on a map of space. Einstein landed the fatal blow at the turn of the 20th century. According to his special theory of relativity, there is no way to specify events that everyone can agree happen simultaneously. Two events that are both 'now' to you will happen at different times for anyone moving at another speed. Other people will see a different now that might contain elements of yours - but equally might not. The result is a picture known as the block universe: the universe seen from that impossible vantage point outside space and time. You can by all means mark what you think is 'now' with a red dot, but there is nothing that distinguishes that place from any other, except that you are there. Past and future are no more physically distinguished than left and right. There are things that are closer to you in time, and things that are further away, just as there are things that are near or far away in space. But the idea that time flows past you is just as absurd as the suggestion that space does. According to physics, your life is described by a series of slices of your worm - you as a baby, you as you ate breakfast this morning, you as you started reading this sentence and so on, with each slice existing motionless in its respective time. 'Really there's all these different mes at all these different times,' says Craig Callender. 'But because I think that I'm identical over time, that's why time seems to flow, even though it doesn't.' So do we rally need to mourn time's passing?

Michael Slezak, The now delusion, - Do past, present and future exist only inside our heads, New Scientist, 2 November 2013.

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