Time and again

Your concept of time is likely to depend on the sort of society you live in. The ancients, living in what we in our arrogance are wont to call a “primitive” or “unsophisticated” society, often regarded time as cyclical. This made sense when you consider the daily round of dawn, noon and night, the annual cycle of the seasons, the ebb and flow of the tides and even the slow march of the constellations across the night sky.

This fatalistic yet comforting notion of time received a rude shock with the invention of history. Whereas the priest emphasized the endless cycles of life where each ending was merely a return to the beginning, the historian emphasized change, differences, uniqueness of events from which flowed still more change. In a “modern” world of careers, deadlines, meetings and anxiety about the future, we no longer have any doubt about the linear nature of time.

But still we wonder. If it is possible to forecast the weather or say at what time the train from Birmingham will arrive, is it possible to know and even alter the future? Although the present seems to be the effect of which the past is the cause, might it still nevertheless be possible to go back into the past, at least as a visitor and even possibly as an agent of change? But if I change the past, how will I ever know because the present is already the result of the past and therefore contains the effects of any interference.

Such speculation leads to a paradox and both philosophers and scientists generally take paradoxes as a sign that the logic is wrong. Suppose there is something I don’t like about the present and I go back in time to effect a change. But the present is already the result of that change having occurred. So I find myself going back in time to do what has already been done, an apparently pointless exercise. Can I then decide not to go back in time? No, because without my visit, the necessary causes of the present would not be in place, but since they are in place, I necessarily have to go back into the past to bring them about. Even though they have already been brought about.

That’s all very interesting (you mutter) but it’s just speculation and couldn’t really happen. Or could it? It all depends on whether or not it will be (or even is now) possible to travel through time. The fact that we haven’t done so yet (as far as we know) doesn’t prove or disprove the theory. After all, it was only recently that men set foot on the moon after countless aeons during which such a thing was thought to be impossible. Now that we have a lunar landing under our belts, perhaps a “temporal landing” is awaiting us in the not-too-distant future.

Could such a thing happen? It all depends on the nature of time. Several models are being considered though none, as far as I know, has a majority vote. One of these, the one that is perhaps easiest to understand, postulates that Einsteinian space-time forms a kind of 4-dimensional cube. I’ll grant that a 4-dimensional cube is hard to imagine but do your best. As an approximation, think of a fish tank. It is possible to specify any position in the fish tank by measuring its distance along any three edges that meet at a common point or “origin”. Now imagine that our fish tank actually has 4 edges, all perpendicular to one another, that meet in a common origin. 3 of these are our familiar space dimensions and the fourth is time. Easy, isn’t it?

With such a 4-D cube, all events can be specified by their distance along each edge (or “axis”) from the origin. We already do something similar when, having come back from our holidays we say “At this time last week I was sitting having a coffee in the station buffet in Penzance.” We have given the event “having coffee” a precise location in both space and time.

If the world can indeed be seen as a space-time cube, then doesn’t this imply that (in principle at least) we can go to any location within it, that is, visit any place at any moment of time? In other words, does it not imply that we could move about in time as much as we do in space?

It might seem that the answer is no because while we can remain still with respect to any of the space dimensions (I can sit in the station buffet in Penzance as long as I like), we cannot do so with respect to the time dimension (by the time I leave the buffet, it will be later than when I arrived – I will have moved inexorably along the time axis).

But just a minute, I hear you say. Quite rightly you point out the famous time dilation effect predicted by Einstein and proved to exist by many observations since. It seems that if a body accelerates greatly with respect to its surroundings, its clock slows down, leading to the famous “twin paradox”, whereby one twin goes on a journey through space and returns home to find he is younger than the twin who stayed at home. It seems that when we travel along a space axis, this slows our rate of travel along the time axis, just as travelling due south slows our rate of movement along the east-west axis.

Could we ever go so fast in space that our progress along the time axis slowed to zero or even went into reverse, opening the possibility of a voyage into the past? Einstein said no but Einstein’s theory is already showing signs of inadequacy especially in extreme conditions, just as Newton’s did before it. Perhaps we are due for an update.

If we could reverse our direction of travel through space-time (e.g. travel back to London from Penzance and reach London before we originally left it), this would obviously have huge implications, not only for physics and for models of the universe but also for such philosophical questions as free will and determinism. And of course, if it turns out possible in the future, then these implications already apply right at this minute whether we realize it or not.


About SilverTiger

I live in Islington with my partner, "Tigger". I blog about our life and our travels, using my own photos for illustration.
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5 Responses to Time and again

  1. Chris says:

    I always said that Einstein was a troublemaker. At this rate, you’ll be rattling on about parallel universes next. Mind you, if time travel is possible there are a few horses I wouldn’t mind getting some money on – and none of them are going to be each-way bets this time!

  2. emalyse says:

    Always a bit of a brain popper trying to grasp things like this especially a 4-D cube and the like. You have to imagine something that you can’t quite grasp and have no prior experience of. It’s like those supposed stories of the Native Americans being unable to see Columbus’ ships coming in. They could see ripples in the water but they had no previous mind map for the ships themselves and so had to learn slowly to see the ships. I often wonder if this is true for something like time. I have read theories that say we put time in our own order and that an event at aged 50 can occur before or at the same time (really bad use of words here) as an experience that we perceive as happening at 16 or that maybe all experiences happen simultaneously and our mind presents them in an easier to grasp “timeline”. It all gets very theoretical. The ancient Mayan’s seemed to predict that one day we will learn to perceive other dimensions and realities so I wonder if someday we’ll all collectively go “oh yeah, how could we not see that” or more likely just continue to go “Eh, ..”.

  3. SilverTiger says:

    To Chris: Parallel universes are an interesting idea and maybe I’ll get around to them eventually.

    If you could get next week’s racing results, an occasional accumulator would suffice to keep you in clover but you would have to beware of the bookies getting to recognize you. I quite like the idea of investing money in the past and reaping the benefit now.

    To Emalyse: I certainly think we have to learn to perceive. For example, the artist sees differently from ordinary folk. Apparently, some languages don’t have separate words for the colours we call green and blue so for speakers of those languages, these are both the same colour.
    Perhaps we would see more colours if we had names for more wavelengths.

  4. baralbion says:

    Don’t we travel in time whenever we look at a star?

  5. SilverTiger says:

    I would say that it is similar to standing on a mountain top and looking at another mountain top: we see the other mountain but we don’t travel there. Visible distances on earth are small but even so light takes a finite amount of time to travel between mountain tops so we are looking back across space and time, though we don’t usually think in those terms.

    Seeing the light from a star is a bit like looking at Grandpa’s holiday snaps: pictures of places as they were at a time before we were born.

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