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Causation has (has it?) an essential relation to time. If some event caused some other event, then the former was previous. But we hear from scientists that time is just one dimension of space-time and indeed that there may be (or might have been) some more dimensions, other than space and time. Should there be analogues of causation related to the other dimensions? Should there be a wider category than causation encompassing all those analogues? Isn't this all a bit perplexing?

Really, it's not perplexing. The connection between causation and time is that causation implies time. A cause has to precede its effect. Now why is that? Some philosophers have thought that the proposition 'A cause precedes its effect' is synthetic a priori . Others have thought, more plausibly, that it tells us part of what a cause is , so it's analytic. (A cause might be a certain juxtaposition of conditions, for example. In that case the cause and the effect could be almost simultaneous.) Still others have thought that a cause can occur after its effect. Even then, though, causation has a relationship to time. And there is the so-called "bilking" argument. If a cause can occur after its effect, all we have to do is wait for the effect to occur, and then prevent its cause from occurring. The fact that this is possible shows that there cannot be reverse causation, i.e. causation in which the effect comes before the cause. As to other dimensions - is there an analogue to causation in them? (1) Are...

Is the concept of backward causation coherent and is it really taken seriously by philosophers? I doubt whether any scientist would accept the idea and I would like to know what you think.

Is the idea of backwards causation coherent? It seems not, as you could, for example, cause earlier events, such as your own birth, not to have happened. There is also the famous "bilking" (cheating) argument due to Max Black, according to which you can prevent the future cause of something that has already happened from occurring. All the same, philosophers, particularly Michael Dummett, have taken the idea perfectly seriously, and defended it. You write that you doubt that a scientist would take the idea seriously, but plenty of physicists, including Richard Feynman, have indeed used the idea for a variety of purposes, including the remarkable idea of positrons running backwards in time.

Why are philosophers concerned with the nature of time? Isn't this a scientific subject?

Here are some questions about time that are not scientific but are philosophical. Does time flow? Does it pass? What does it pass? Does it move? If so, how fast? If speed (s) = d/t, what is d/t when s is the speed of time? What temporal distance does time travel in a unit time? Surely the unity distance. But then the speed of time is 1 sec. per sec. How can time be measured, as the past does not exist and the future does not exist and the present is merely a point - nothing to measure there! - dividing the past and future? Does time exist? What (if anything) is it made of? Is time travel possible? In a completely unchanging universe, would time pass anyway? If every true statement corresponds to a fact, how can statements about the future be true now, in the present, as there are no facts about the future now, in the present? If there were, they wouldn't be future. Does it mean anything to say that time has a direction? What does it mean? If omelets came first and then eggs afterwards, time would surely...

Is time an independent physical dimension or a human construct designed to compare events to each other ? If it is a physical entity why can we move only in one direction and at an inexorable pace? Is it theoretically possible for a time machine (Hot Tub or any other sort) could exist?

I agree with everything that Allen writes in his last comment. Some time travel scenarios are ruled out a priori : these are the inconsistent ones, and there may be others, for all I know. Are the consistent ones ruled out by anything? I can't see that they are, as the only reason I am clear about for thinking time travel is possible is the grandfather paradox. But it may only rule out the inconsistent cases. So I am in agreement with Allen here too, and in the dark as to whether anything in physics allows or rules out non-contradictory time travel. Time is a dimension, and dimensions are things that allow you to scale. A direction in the structure of the dimension itself seems a slightly incoherent idea to me, as opposed to the direction of the thing moving in the dimension, e.g. a place moving through colour space, such as the sky going from blue to red, or a bullet moving from there to here.
I would like to continue the discussion by saying something about Allen's response. I agree that there might be a question about why position coordinates get bigger and bigger. Answer: we are heading North. But then we are moving. My concern is that if we think in this way, we are already thinking of time as something in which we move and travel. So why not backwards as well as forwards? My orthodox and perhaps crude belief is that time travel is impossible because of the grandmother paradox: if a time machine is possible, then I could use it to travel back two generations, and then kill my maternal grandmother. In that case, my mother would not have existed. But then nor would I. So then I couldn't go back in a time machine and kill my grandmother. So I both would go back in time and kill my grandmother and I would not go back in time and kill my grandmother. This is impossible. The logician Kurt Gödel has a nice version of one response to this paradox. A time machine is possible, but as a matter of...
Time is a physical dimension. The dimension in which something exists is just the minimum number of co-ordinates that are needed to locate the point at which it exists. So three co-ordinates are needed to specify a point in Euclidean space, and accordingly Euclidean space has a dimension of 3. In the physics of relativity theory space and time are not 'independent', as you put it. On a relational or Leibnizian view, such as relativity theory, a space is merely the order of the space occupants. Time, on the other hand time, is one-dimensional. All we need to do to locate an event is to specify one time, say Tuesday: 'The murder happened on Tuesday.' (Some philosophers have discussed the question whether time itself could fork, and whether there could be disjoint times, as distinct from distinct possibilities within time.) Psychological events are also scaled in time. The horrified reaction to Tuesday's murder might take place on Wednesday, say, as one reads the morning newspaper. Accordingly...

Doesn't time travel involve space travel too? If I travel back in time one year, say, in order to be in the same 'place' as I started, I'd need to travel across countless millions of miles of space, since the planet has moved during the last year. Since such instant space travel contradicts Einstein, how come so many philosophers seem to think it's possible? Martin, Wales, UK

You make a very interesting point. If time travel takes a second, then since a later Earth - say Earth in a year - might be zillions of miles away (i.e. more than 186,000), I must travel faster than light, which is impossible. But how long does my time travel take? How do we know that it takes a second? After all, if on the new or later Earth it is a year later, presumably it took me a year to get "there", the same amount of time as it took the Earth itself, even if it felt instantaneous. So there is a difficulty about the meaning of "How long does my time travel take?" If we move in time, or times moves past us, there is a difficulty about the concept of the speed of the movement. Movement in space is distance divided by time, so movement in time, or the movement of time, it seems, is time divided by time; and it is hard (as D.C. Williams pointed out ages ago in "The Myth of Passage") to attach any sense to this idea. This is the interest of your point for me; how do we attach sense to the speed of...

We can only live in this "here&now moment"...in fact, there is no way we can ever live out of "IT"...is it not?

'We can only live in this "here and now" moment . . . in fact , there is no way we can ever live out of it . . . is it not?' I am not sure what is supposed to meant by living in the present instant ("moment" I think has more to do with action). Living at an instant seems as impossible as living at some other time, because there isn't even time to draw breath in an instant. In any case I do not believe that there is something called "the present instant", so I don't see how we could live in it (at it?) It (the present instant) is an abstraction, and it is not, in reality! I do believe there are present times, though, such as the present day or hour. The trouble with the instant is that it is not a time.

How does our approach to knowledge about the past differ from our approach to knowledge about the future, keeping in mind that there is an element of uncertainty in both?

Our knowledge of the past derives from perception, memory and inference, in the sense that these are answers to the question, 'How or by what means do you know?' (There are other ways, for example report or testimony). But our knowledge of the future has in it no elements of memory or perception. So as one might therefore expect it is harder to come by knowledge of the future, and we have less of it per hour, if you want. We typically can know more about a past hour than about a future hour, though by no means all of the past hours, for example those in past centuries. If I know p, and p is a proposition about the future, I cannot know it by memory, special cases apart. (A special case would be that I come to know that I am going to Africa next summer - a piece of knowledge about the future - by remembering that I am going to Africa next summer. 'How do you know?' 'I just remembered it . . .' makes sense as a conversation.) It seems to me, in spite of the assumption you make, however, that in some...

If we move through time, then what is movement? That is to say how is movement, or any change for that matter, possible outside of the context of time?

The idea that we move through time is at best odd, but at worst very confused - no offense at all intended to the author of this fine question, though, as this species of confusion is the motor of philosophy and it is the job of philosophy to describe it and then put it right, among other jobs. The picture is of time around us - and what does this mean? - and us trundling along through it. If indeed this is our conception, the idea of movement has come off its bearings and becomes what lawyers and students call "wordage", as in "we need some wordage to cover this point here". Equally bad, as I see it, is the idea that time moves through us or past us or whatever. You might wonder where it is going, but this question has its own kind of nonsense too. The difficulties here are all due to the A-series conception of time. I agree that the idea of change outside of time is a very interesting one, but I don't see the connection with your first question clearly. What does the question whether we move through...