Number 86 : May 1997 |
I share Jonathan's fascination with time. I have put together, and seek to add to, the following list of ideas to help me get to grips with it conceptually. The presentation may be a fraction flippant in parts but I hope it contains no errors. No doubt someone will tell me if there are! I feel sure some great truth is lurking therein. Can you put together the jigsaw and find it?
1) Instantaneous action at a distance (a phenomenon of paired particles): I conceptualise that as a long metal bar with a viewer at each end. One twists the bar clockwise and the other immediately sees it twist anti-clockwise.
2) The timeless photon (a photon’s start and end are simultaneous as far as it is concerned): This looks like it is linked with 1 but I cannot reconcile the different viewpoints.
3) Special Relativity (all observers regardless of their motion arrive at the same measure of the speed of light so a clock moving away from you will appear to run slow): This seems a purely apparent effect as the frequency of the stretched light waves is reduced. It seems part of a different jigsaw but I think you have to deduct this from 4 to get 8.
4) Time dilation (the confirmed prediction of General Relativity that gravity and acceleration, which are equivalent, cause clocks to run slow): This includes an apparent as well as a real effect. Even Stephen Hawking in his 'Brief History..' forgets he is writing for idiots like me when he states, "To someone high up, it would appear that everything down below was taking longer to happen... This prediction was tested... The clock at the bottom ... was found to run slower.". The appearance referred to is from the stretching of the light waves as they move against gravity, but the prediction referred to seems to relate to the retarding effect of gravity on all physical processes, which means that the lower clock really does run slow in addition to the apparent effect. Paul Davis (in ABOUT TIME) really screws your mind up by adding, "Suppose we use the cycles of the light wave as the beats of a clock", which, to my simple mind, makes his lower clock beat faster!
5) Faster than light (also backwards in time): This seems permitted in theory so long as the tachyons which do it don’t slow down. As an invisible jigsaw piece it is difficult to know which puzzle it belongs to.
6) The arrow of time (equally the sledgehammer of the Second Law of Thermodynamics): Does time have direction? If everything was going backwards so would our memory of it; but before any time traveller had a chance to forget how to pilot his craft it would be on its way back to the factory in pieces anyway! This seems as invisible as 5, but see 7.
7) Time travel (taking a short cut through curved space via a wormhole): I am sure that this is the mathematical equivalent of falling off a log but it does seem to assume that past, present, and future exist simultaneously. It is linked with 4 and seems curiously related to 1 via 2. Nevertheless, if anyone has ever done it why haven't they told us? Perhaps if there is a universe for every quantum fluctuation there must be a wide choice of destinations and ours is the equivalent of Scunthorpe.
8) Space-time (the four-dimensional world in which past, present and future co-habit): This seems to be linked with 7 and appears to be a mathematical construction which disposes of the problem of viewpoints (see 2) by not having any. Of course, there is somewhere else which provides a home for past, present and future: the consciousness wherein memory, perception, and prediction combine to give us the idea of time in the first place. Now consider the fact of the same value always being obtained for the speed of light (see 3). The only way I can conceptualise this is if light is not sprayed around at random but attracted. If the attraction is to consciousness via perception then we might be able to link 8, 7, 4, 3, 2, and 1. Note that by this model electromagnetic energy is the reaction to consciousness and essentially the same reaction as referred to in 'The End of the Rainbow’.
Anthony Owens
Anthony - Hmm ... a bold attempt to clarify matters ! I’ll have to leave detailed commentary to others, but I can’t resist a few points. I’m suspicious of the thought in 1. It seems to depend on mathematical idealisations like "rigid rods" that don’t, and maybe cannot, exist. Also 4 : are there really two effects ? I may be totally misunderstanding things, but when authors speak of photons struggling against the gravitational potential of massive bodies, or climbing out of gravitational potential wells, aren’t they speaking metaphorically ? Photons always travel at the speed of light, after all, and are neither like little powered space-rockets nor like unpowered classical bolides that might only just make it into orbit. The time dilation effect occurs at the point of emission of the photon, not while it is on the move through the gravitational field. This effect is demonstrated non-experimentally by a thought experiment that involves two freely falling bodies, one at the point where the photon is emitted, the other at the reference point is being measured. , the two being linked by a Doppler shift (see Kip Thorne, Black Holes & Time Warps). Of course, if we measure the red shift at various points on the photon’s trajectory, it appears to increase with distance from the gravitating body, because our reference point is itself (decreasingly) time dilated with increasing distance from that body. I’ve just invented this argument, by the way, so could be wrong !
My other reservation is the lack of mathematics - the special & general theories of relativity can only be properly appreciated mathematically : and they have quantifiable, testable results. Extensions to, or qualifications of, these theories have to do likewise.
Theo