27 May, 2010

Time, Relativity, Time Travel, and the Great Puzzle of Why the Sun Rose This Morning

There's something wrong with my notion of time.

I used to think it was all subjective - by which I meant relative to one's frame of reference, as general relativity tells us. I am more than happy to accept all the experimental evidence that says moving very fast, or being near a large mass, will slow down the passage of time relative to an observer outside your frame of reference. There is so much evidence for general relativity that it would be ludicrous not to accept it. Yet a simple observation of my own tells me that there must be more to the story than that.

And this is it: the Sun rose this morning. I know that because I saw it.

The problem is that it should not have done. The Sun should not be there at all. The Sun and the Earth were formed at about the same time, some 4.5 billion years ago. However, the mass of the Sun is about 330,000 times that of the Earth. Relatively speaking, time will run a bit more slowly for the Sun than for the Earth. But, after 4.5 billion years, all those nanosecond differences will add up. Yet Earth and Sun seem to be here together. We have both arrived at today at the same time.

So my notion of time - and/or my notion of what general relativity is saying - must be wrong. In fact, the same goes for special relativity too. I cannot account for why anything moving fast relative to me doesn't just wink out of existence. Because its time is slowed down, I should move into its future, it should move into my past, and we should not be able to perceive each other in our respective presents. After all, I know from experience that I cannot see the future, or the past.

So, okay, the fact that relative gravitational potential, or acceleration, or velocity, affects the rate at which time passes for different 'observers' seems to have nothing to do with the way time is actually passing for us all. I can live with that. In fact, I've seen something very like it somewhere else. The speed of light is quite similar. This is a constant and, all intuition aside, light travels at the same velocity (c) relative to you, whatever speed and direction you are travelling relative to its source. What does happen to light, though, is that its frequency shifts. If you are approaching a source of light very fast, it still hits you at exactly c but its frequency is shifted higher - towards the blue end of the spectrum. If you are racing away from the source, light still catches you at exactly c, but now its freuency is lower - shifted towards the red end of the spectrum.

What if time behaves like light? What if the rate of passage of time is also constant? Then, whatever we were doing in the Universe, time would always affect us the same way. But, accelerations, gravitational fields, and relative velocities lead to us perceiving a shift in something equivalent to the frequency of time. Let's call it time's 'colour'. A high gravitational potential, shifts time's colour towards the red end of its spectrum.

This notion (although it explains my problem with time) is an intuitively difficult one because what we normally think of as time - that thing that measures the intervals between ticks of a clock - isn't really time at all. It is just the colour of time. Real time, the thing that has its colour shifted and which ensures the continued coexistence of everything in the present, must be something else. Maybe we should call it 'persistence' or (to borrow a word from H. G. Wells) 'duration'?

So time is a kind of universal persistence and what I used think was time is just the colour of this persistence.

Am I happy now? No, not really. For a start, shifting the colour of persistence is analogous to shifting the colour of light (and is effected in exactly the same ways). So, by the same analogy, there can be no time travel. Shifting the colour of light does not affect its speed. The rate of persistence will be constant regardless of relativistic effects on its colour. You can age less (or more) than other things in the Universe by manipulating your speed, acceleration, or proximity to mass, but you do not change your place in persistence with respect to the rest of the Universe. That's why fast things do not blink out of existence for me. We are persisting at the same rate, even though we are aging at different rates. (Even dragging the exit of a wormhole around at near light-speed won't do the trick any more, because entrance and exit persist at the same rate, the exit may end up younger than the entrance but they will still be there at the same point in persistence at the end of it all!)

Are there any physicists out there who can tell me why all this is wrong and also explain why I saw the Sun this morning?


MrRedwood said...

I'm a little confused — it seems that you are treating an analogy as if it is necessarily true.

Yes, we know that the speed of light is constant, and that this means observers in different frames of reference see frequency shifts.

But "speed" is distance divided by time.

What would the "speed of time" be, in order that it would somehow be "constant"? I'm not sure such an abstraction can be made clear.

It seems to me that by imagining there could be such a thing as the "speed of time", and then applying parallels between light and time... well, you've taken metaphorical thinking to an unwarranted conclusion. There is no paradox because the disparate concepts don't relate to one another the way you arranged them.

graywave said...

Richard, I'm sorry if I confused you. Given how confused I am, though, it's not too surprising, I suppose.

I certainly did not mean to treat the analogy as the litteral truth. I was only saying that thinking of time as having analgous properties to light might provide a way of reconciling the fact that it appears to pass at different rates while at the same time not passing at different rates.

Whatever property of time might be analogous to the speed of light is clearly not speed as such. Similarily, any resemblence between the frequency of light and any property of time whatsoever is purely analogous, not literal.

You'll be pleased to hear I have embarked on a programme of further reading around the matter. If that doesn't clear things up, I'll probably be back here in a few years bemoaning my continued confusion. (Probably with some other hare-brained analogy.)

MrRedwood said...

Well, it certainly is grounds for easy confusion. I'm still trying to figure out simultaneity during and after relativistic travel. I think I understand the situation, then time passes and I can't even remember how to phrase the question.

Thank goodness for hyperspace and wormholes, or so much of scifi would hurt our brains.

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