Thursday, March 13, 2014

The present is real, the past is gone

Brian Greene has released his World Science U special relativity course, with and without the math. It is slick, free, and appears to be well explained.

He falsely credits and idolizes Einstein, but probably has not read my book, How Einstein Ruined Physics.

In the module on "The Reality of Past, Present, and Future", he makes some faulty philosophical comments about time, that I recently attacked. After explaining some of the difficulty with relativistic simultaneity, he concludes:
So what this collectively tells us is that the traditional way we think about reality -- the present is real, the past is gone, the future is yet to be -- that is without any real basis in physics. What we are really learning from these ideas is that the past, the present, the future, are all equally real.
So does relativity really require us to give up this basic intuition about time? I say no.

The essence of Greene's problem can be understood with pre-relativistic causality. Suppose I am on Earth, an alien is on another planet, and we somehow come to agreement about time. For me, "now" means that I can affect events in the immediate future, and likewise for the alien. But I cannot affect things in the immediate future on the other planet, because anything I cause on Earth will take some time to get to the other planet. So while the alien and I may agree about the meaning of "now" as it relates to our local clocks and our notion of local causality, it will still be the case that I can affect my environment before the alien can, and the alien can affect his before I can.

Relativity makes this more precise by saying that causality is limited by the speed of light, and by giving formulas for how motion can de-synchronize clocks.

The essential point is that the present now makes sense for me, and I can cause changes in the future, but only nearby, because there is no action-at-a-distance. Technically, I can affect my future light cone.

The alien might agree on what now means, and he can affect his future light cone, but my future light cone is different from his.

Thus Greene's conclusion above is entirely wrong. Our traditional notion of time, with its distinction between past, present, and future, does have a real basis in science. I explain this below in terms of time counterfactuals.

While Greene's explanation of relativity is mathematically correct, and his paradoxes might be confusing, the world would be more confusing without relativity. Suppose that my present now was dependent on the whole universe in the immediate past, and my actions affect the entire universe in the immediate future, without any time lag. That alien on another planet could do something to affect me a second later, and I could respond, to affect him in another second. That alien would never make sense of his world because some capricious intelligence in another galaxy could be interfering with his experiments. Relativity puts a lid on that, and ensures that local causes have only local effects.

Relativity gives us more reason to believe that we live in the present, not less. Time is more intuitive when causality has relativistic limits.

1 comment:

  1. How can Mr. Greene believe his own words? I am going to make the assumption that the man can count to ten. If he can do this, then he must acknowledge there was a 'before' he started to count, and an 'after' when he had finished. Likewise, while he was counting, one...two...three...etc. each number preceded the next, until the count was ten. If past, present, and future are all equally real at the same time, how was this progression possible to undertake? If past, present, and future are all one thing, how could any process occur in any particular order at all? How can any operation mathematically occur without logical rules of order? Lack of a before and after also short circuits all possible causality, which is a necessary precondition for all science to function.
    Perhaps Mr. Greene should have studied computer architecture instead of speculative math. If he had done so, he would be more intimately aware of how vital a clock, time, and timing are to making any logical operation or computation even remotely possible. Foolishness like Mr. Greene's 'causality free' time speculations is why physics is becoming increasingly closed and irrelevant to people who aren't willing to jettison their reason just so they can claim to be 'educated'.
    I also fail to see how anyone can be deluded enough to think that if their physics model does not contain an explanation for something (like the direction of time) that the reality therefore must also not contain such a thing. A mathematical or physics model is at best a constructed thing of assumptions, if the model functions at all, it is only in accordance to those assumptions, not the totality of the underlying reality of the model maker.