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14 July, 2010

The Great Puzzle of Why the Sun Rose This Morning: Part 2

You may remember I wrote a couple of months ago about a strange conundrum regarding time. I mentioned this post on a number of lists I belong to, hoping that someone with a better grasp of physics than I would be able to explain it to me. I got many, many responses but, sadly, not one seemed to understand what the issue was and the great majority assumed I just needed a quick primer in special relativity (and then proceeded to give me one, often in a most garbled and peculiar way.) Most people were genuinely interested and tried to be helpful. However, one idiot, on a list I didn't even post to, became quite abusive and accused me of inventing a load of nonsense about relativity in order to make more sales of my book! (Now, how would that work, exactly?) He also threw in a garbled account of special relativity, just to be sure I understood what a genius he was.

It was quite a depressing experience all round.

I have been reading more on the subject since then and I think I have actually found the answer. Gratifyingly enough, the answer is almost exactly the one I came up with. In the language of relativity it is couched in much different terms, however, but I believe it amounts to the same thing.

The conundrum is this: even though time passes at different rates for different frames of reference, we do not experience objects moving in and out of existence as our relative positions in time change. I gave the example of the Sun, which, having a much larger mass than the Earth, should be aging ever so slightly more slowly. In fact, over the 4.5 billion year life of the solar system. the Earth should be 71 years older than the Sun. So why aren't we in the Sun's future? Why is the Sun here with us in this moment in time?

The answer, I suggested, was that we do, in fact, all move at the same rate through time, which would mean that time dilation is something analagous to the way the frequency of light changes depending on the relative velocity of its source. As it turns out, I shouldn't have been talking about space and time separately but about spacetime. Because, as it happens, we are all moving at exactly the same rate through spacetime. When we use spacetime metrics instead of the metrics of space and time, it appears that everything in the Universe is moving at exactly the same rate. That light has a constant velocity is a corollary of this. Light having no mass, there is no time dimension to its motion in spacetime, it must therefore always appear to be moving through space at the maximum velocity possible. Time dilation, under this view, is simply an effect of the projection onto space and time of a spacetime 'velocity' for objects having significant relative speed or mass (or acceleration). All the space and time components as well as mass/acceleration are traded off against one another to maintain a constant spacetime motion. Time can therefore appear to be 'red shifted', in the terminology I made up, for exactly the same geometrical reasons that light appears to be.

And we're all together here and now in spacetime. That's why the Sun keeps coming up in the morning!

Aren't you glad I got that sorted out?

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