Time and space – a subject of metaphysics?

Question

The entry metaphysics from SEP (Stanford Encyclopedia of Philosophy) also deals with space and time, see chapter 3.2.

I am not convinced that metaphysics does contribute with any new insight to the subject. More, I suspect that the author of the entry, probably an expert in metaphysics, is not familiar with modern physics. He starts the article:

Long before the theory of relativity represented space and time as aspects of or abstractions from a single entity, spacetime, philosophers saw space and time as intimately related. (A glance through any dictionary of quotations suggests that the philosophical pairing of space and time reflects a natural, pre-philosophical tendency: “Had we but world enough, and time …”; “Dwellers all in time and space”.)

The examples cited above consider two separate entities, 1) space and 2) time, which are a “philosophical pairing”. But spacetime is not just adding space and time. One of the main conceptual changes of special relativity was to introduce 4-dimensional spacetime as its basic concept. There is a certain freedom how to decompose spacetime into a component space and a component time. The decomposition depends how the observer chooses its frame of reference.

The single invariant entity in spacetime is the light cone. It separates my future and past from my present. I am causally connected to all events within my light cone, but to none event outside my ligth cone. Hence the special theory of relativity operates with the basic entities spacetime and light cone. From them it derives space and time and the first causal relations.

From this point of view one can easily answer the question raised in SEP about whether space and time are real. If one takes real in the sense of “existing independently from any observer” then the answer is: No, space and time are not real, because they depend on the choice of reference. But spacetime is real, because it is an absolute, not a relative concept. One could ask at this point: Can we close the discussion now?

But the entry in SEP, which runs under the heading “The modern metaphysics”, continues to bring into dicussion the God concept. In my opinion, we should have learnt the lecture from history of science: It it always confusing when mixing scientific questions with theological or even religious ones.

I know that my question makes clear that I neither see nor expect any results from metaphysics concerning spacetime and the derived concepts of space and time. But I am also sure that my question

Should time and space be considered a subject of metaphysics?

will not fit the high estimation of metaphysics by other participants of StackExchange Philosophy. Therefore I hope to learn now the arguments of the adherents of metaphysics.

Answer 1

Space and time are distinct concepts. The fact that relativity makes of time the fourth dimension doesn't mean that space and time are not treated distinctly, as you observe yourself. The metric of relativity makes it clear that one dimension receives a special treatment, in any referential. This is what the concept of time, as opposed to space, subsumes, and the concept remains open to inquiry.

You say that space and time don't exist because of different referentials, but one should not confuse the topology, the metric and a coordinate system. Different referentials assign different space-time coordinates to events. But coordinates are not space or time, they are tools for making calculations. The lesson we should draw from this fact about the concepts of space and time is, again, open to inquiry.

Something is absolute and doesn't depend on the referential: the clock hypothesis, which says that a clock measures the (frame independent) space-time interval along its path. That looks pretty much like an absolute notion of time (since obviously, clock are not meant to measure distances). Arguably this is what the concept of time refers to in relativity.

Even conflating time and the measure of time in a specific referential, the lesson you draw, that space and time are relative to a subject, might be a possible lesson but note that "subject" is not the same as "referential" nor "observer" in the sense of physicists (which really means referential anyway), so you'd have to argue a little more to convince that space and time are not "real". It's really unfortunate that physicists use the term " observer" because it brings confusion: any human observer (=subject) is free to use any coordinate system she wishes to describe the world.

In any case it's certainly not the only lesson to draw. After all, there is also cosmological time, and perhaps there is a priviledged frame of reference, that of the CMB. If quantum mechanics is non-local, maybe that means something for time too, we don't know yet.

Furthermore (to rejoin other answers) the metaphysical questions on space and time are rarely about its existence, rather about its status: is space-time only relations between objects or events, or something more substantive (would it exist without any objects)? Can we account for the passage of time in a block universe, or is change an illusion, to be reframed in terms of different states at different locations in time? What does it imply for our understanding of causation, and the fact that most scientific explanations are causal and time-directed? Is the past hypothesis / entropy account enough to account for all kinds of scientific explanations, even when thermodynamics isn't obviously related? Or is there an intrinsic direction of time associated with "evolution" laws? Or are we merely recording regularities on the distribution of events in a block universe?

All these are meaningful questions which connects science with a broader, big picture of the world, and opinions and intuitions diverge strongly on these topics, even among scientists themselves, so science doesn't have the last word on this. It's a matter of interpreting what science tells us. That's why we are arguing.

Answer 2

Philosophy fledges sciences at a certain point, but does not necessarily expect them to cover the whole range once included in the branch of philosophy they emerge from.

Clearly physics as a scientific discipline is competent to keep its own house and should not have metaphysics injected into it. But there are definitely parts of the metaphysical treatment of time and space that physics is not competent to address.

From Kant's viewpoint: Is spacetime an aspect of animal nature, or is it more basically real? Physics cannot even ask the question properly without involving some of the most abstruse notions ever put forward in psychology. And then it would still need to find a metaphysical basis upon which both sciences have traction. We can just insist there is no answer because physics doesn't need one. But that is a metaphysical position. One without much sense to it.

From Boltzmann's viewpoint: Is entropy something that is basic to all matter, or is it an aspect of our attachment to time? Does entropy exist because of time, or does time exist because of entropy? Physics chooses a position, but not in a way that holds water philosophically, just in a way convenient for modeling. It seems obvious that from within physics, we cannot tell -- we are limited by the perspective of extrapolating backward from memory, a process clearly dependent upon an exothermic chemical reaction.

From Whitehead's viewpoint: Is there a global interpretation that lets us see relativity and quantum mechanics as aspects of the same question, and that motivates a view of the world that will not only capture them more reasonably than our historical view, but give us tools to look at other aspects of the world in a more natural way? Physics can only resist abuse of itself in such questions. It can create theories, but it cannot actually help people make sense of them at a deeper level. Our best references for the 'meaning' of the new science, come mostly from outside it. When voices inside it arise, they tend to rely on totally hopeless metaphysics, or to end up doing metaphysics from scratch that the tradition already contains and rejects.

And these are just my questions. There are plenty of metaphysical aspects of space and time that I personally really don't care about.

Answer 3

I'd suggest that the history of science, which generally takes it's starting point from Galileo, is too narrow a purview to take in the many intricate and various relationships between the subject of philosophy and science.

Badiou, for example takes a much wider view; he suggests that the proper perspective in the contemporary situation is that four domains have been established where truth procedures are found: politics, science, love and art; philosophy has no truth procedure of its own but interweaves with these four domains. This in fact is a Socratic gesture when one recalls the Socratic temper in Platos dialogues.

To a certain extent this agrees with your assessment on the discovery of new concepts in a contemporary discipline such as Modern Physics.

However the actual study of Nature going back to the Milesian cosmologists, shows that there were many intricate relationships between that of metaphysics and that of physical thinking - one need only take a careful look through Lucretious De Rerum Natura, or Aristotles Physics to note this; a wider perspective then would be that of the history of ideas.

In a sense, it is anachronistic to say metaphysics has been of no value (and one should note that metaphysics then meant the investigation of the first principles of Nature, on the things that are: causality, space, time, matter and so on; this differs of course with how it's concieved today, though of course there is an affinity).

Were such a thing as a time-machine were possible; and if you were to use such a machine to go back to Hellenic antiquity when Anaximander, Democritus or Aristotle began their philosophical speculations on nature, would you tell them them: 'guys, don't bother with all that speculation on nature, or on change, or on what is real or not - the one or the void; keep quiet and listen attentatively whilst I tell you all the real truths of space, time and matter; the truths we have discovered in the future'.

And then when you climb back into the time machine to come back to the present moment will you find science as it is now? Or will it all have vanished or been corrupted given all that early work was never done; having been convinced it was worthless?

Answer 4

I like @jobermark's answer, but would like to add an anecdote corresponding to this question; it is a conversation with Einstein as told by Carnap, in which Einstein expressed his belief that "there is something essential about the Now which is just outside the realm of science":

Once Einstein said that the problem of the Now worried him seriously. He explained that the experience of the Now means something special for man, something essentially different from the past and the future, but that this important difference does not and cannot occur within physics. That this experience cannot be grasped by science seemed to him a matter of painful but inevitable resignation. I remarked that all that occurs objectively can be described in science; on the one hand the temporal sequence of events is described in physics; and, on the other hand, the peculiarities of man's experiences with respect to time, including his different attitude towards past, present, and future, can be described and (in principle) explained in psychology. But Einstein thought that these scientific descriptions cannot possibly satisfy our human needs; that there is something essential about the Now which is just outside the realm of science. We both agreed that this was not a question of a defect for which science could be blamed, as Bergson thought. I did not wish to press the point, because I wanted primarily to understand his personal attitude to the problem rather than to clarify the theoretical situation. But I definitely had the impression that Einstein's thinking on this point involved a lack of distinction between experience and knowledge. Since science in principle can say all that can be said, there is no unanswerable question left. But though there is no theoretical question left, there is still the common human emotional experience, which is sometimes disturbing for special psychological reasons.

So Einsteins seemed to believe that an important aspect of the concept of time is outside the reach of science, and if it is outside the reach of science then aren't philosophers entitled [*] to contemplate it?

[*]: I mean entitled in the sense of having permission to, not of having a privilege.

Answer 5

Every concept as important (or primitive) as time and space is subject to metaphysics. For example, I myself consider that time is much more fundamental than space: time is what allows things to change by ordering them, and consequently induces a form of non triviality of existence. Space, on the contrary, seems totally unnecessary to have such non triviality.

One can easily imagine a world without space but time: an abstract mind that can think abstractly does the job (even though it would lack to imagine all geometrical concepts). The reciprocal, on the other hand, would be a dumb picture that has no reason to be because it would lack being non trivial. In particular, the question "why is there time instead of none?" clearly link it with free will: time is here because the universe doesn't yet know where it goes, and is waiting for the guys therein to chose a branch allowed by their present state. In such interactionnist framework, space is understood as an emerging phenomenon (from the successive and past interactions of subjects).

Now, there are also people who believes that space is more fundamental than time, or even that there is no time but just an illusion of it. Such metaphysics are usually deterministic at some level (general relativity is entirely deterministic, while people interpreting QM with multiverses are "globally deterministic" and equalitarists, lacking any authority of "what is" over "what could potentially be"), and deny the existence of freewill of any kind.

That is, your position on free will is necessarily closely related to your metaphysics on time and space. Also, your position on free will is closely related to your position on the "meaning" (in any sense) of existence itself: existence without free will is dumb and meaningless, both for the "things" composing nature, and for nature to realize itself explicitly (it would be simpler if it just didn't realize itself at all), while having freewill usually implies that you believe in some absoluteness of (some) meaning allowing you to chose how to act accordingly to different situations.

PS: I'm pasting an answer I did in physics stackexchange that can be helpful here too.

Now, regardless of what philosophers have to say on space and time, there are also two naive metaphysics physicists share. The substantivalists think that space-time exists by itself, even if its not "made" out of something, and that if you remove all matter from it it is still here (but empty). The relationalists on the other hand, think that space-time is emerging from the relations between matter and that it does not make sense to speak of space-time itself without matter. For substantivalists, space-time has points that "really" do exists, while for relationalists it does not.

I said that these two approach where naive. Why ? If you're a substantivalist, you would have to explain why space-time has points and why, if you do a Leibniz shift of all the matter inside it (that is, you shift all matter by a constant and add some constant velocity with respect to some inertial frame), then the resulting universe we measure is actually indistinguishable from the primer while the configuration of matter is damn different. Is there really a need to believe in points if two different configurations of matter are indiscernible? There is also the hole argument from Einstein in general relativity, but its much subtler (see http://en.wikipedia.org/wiki/Hole_argument).

Now, if you're a relationalist, you would have to explain why is acceleration absolute ? How comes that even if I'm alone in space-time, without referring to anything near or far away from me, I can know for sure if I'm accelerating (say, rotating) or not ? This shows that space-time is not entirely relational, you can look at Newton's bucket for this deep argument.

What we can say, is that space-time is a weird thing we don't really understand. Yet, it is certain that it has an "inertial structure" that allows you to discriminate what it means to accelerate or to be "not moving" (that is, being inertial or following a geodesics in GR). How is that possible to reconcile the presence of an inertial structure without having points ? Nobody knows right now.

Answer 6

I would like to sum up the different answers from jobermark, nir, quen_tin, Mozibur Ullah and from the many comments of others. In order to state, what I have now learned as my answer to my own question. Thank you for your help.

1) All answers and comments as well as nearly all referenced sources express the opinion that metaphysics is a useful addition to physics when dealing with questions of time and space. The notable exception is a paper by a philosopher of physics who states

Without this one is dabbling in pure mathematics, or worse, metaphysics!

All other answers and comments do not show the slightest doubt about this point.

2) It strikes me, that no one attempts to provide a definition of metaphysics. Often the terms metaphysics and philosophy seem to be used without making any difference. Therefore we have no standard to judge which contributions are metaphysical and which are not.

3) Even when some answers and comments accept the term spacetime, they always try to dissolve it into space and time and often advocate an absolute time. Nobody takes the mathematician and physicist Minkowski seriously, who stated about the new concept of spacetime in his paper from Jahresberichte der Deutschen Mathematiker-Vereinigung, Leipzig, 1909:

The views of space and time which I wish to lay before you have sprung from the soil of experimental physics, and therein lies their strength. They are radical. Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.

After such clarification it is of no help to reiterate the question “But what are really space and time?” The philosophical concepts of time and space originate from our every-day experience. They are valid for the meso-cosmic domain. As Special Relativity tells us, they cannot not be stretched without change into the domain of macro-cosmos.

4) In my opinion, the long and iterated discussion from some comments concerning the role of absolute time and proper time in Special Relativity indicates that such discussion must be led within the mathematical framework of Minkowski space – the usual “free-text” arguments from philosophical discussions are not suitable.

5) As an answer to Rovelli’s wish that

the philosophers that are interested in the scientific description of this world would not confine themselves to commenting and polishing the present fragmentary physical theories; but would take the risk of looking ahead

I would expect new ideas from philosophy, which have not been discussed in the physical community before. Where are these ideas?

6) I conclude for myself that there is no help from metaphysics to discuss the problem of spacetime, rather such discussion is misleading.

Note. I do not consider the answer of @sure. His/her choice of wording and emphasis of his/her personal view fall below the standard I consider necessary for a philosophical discussion.