Nor does 20th (21st) -century physics countenance the idea that there is anything ontologically special about the past, as opposed to the present and the future. In fact, it fails to use these categories in any respect, and teaches that in some senses they are probably illusory.[9] So there is no support in physics for the idea that the past is “fixed” in some way that the present and future are not, or that it has some ontological power to constrain our actions that the present and future do not have. It is not hard to uncover the reasons why we naturally do tend to think of the past as special, and assume that both physical causation and physical explanation work only in the past present/future direction (see the entry on thermodynamic asymmetry in time)... I am not referring to the time directions (toward-the-past, toward-the-future), which are certainly legitimate enough in physics and do sometimes play important roles. Rather, I am referring to our intuitive ontological division of history into the past, the present, and the future. “The present” in particular is not to be found in any physical theory's description of the world. And special relativity theory undermines the traditional conception of a non-observer-relative present

I read something in the SEP that suggests that, if you take physics seriously, then time can have a direction, but there is no present and so strictly speaking no future that hasn't happened yet or fixed past. Then A times are nothing in addition to B times: the A series is an illusion.

That could be existentially untenable, much more so than moral anti-realism or even solipsism. Is Bertrand Russell dead, or is he alive until he's 97? How old is Noam Chomsky? What's going on? Are these philosophers just talking the talk? Or is there a present nonetheless, with true utterances about A times, even-though A times are not objective?

In any discussion about whether the now is objective, we need to remember that the term "objective" has different senses. There is objective in the sense of not being relative to the reference frame, and there is objective in the sense of not being mind-dependent or anthropocentric. Proponents of the B-theory say the now is not objective in either sense.

I think part of the problem is that I don't know what "relative to the reference frame" means: whether a time that isn't can still meaningfully exist, and if so what metaphysical commitments we have to make.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – Philip Klöcking
    Commented Sep 9, 2019 at 19:55
  • Does the quote really indicate that such philosophers think there is no past, present or future? It looks to me to be more saying that the past is non-objective or non-fixed. And I'm sure you'd find many philosophers and physicists who disagree too, so asking in the title "How do philosophers believe..." is over generalising. Commented Sep 10, 2019 at 2:02
  • if 20th century physics does not incorporate the past present and future then maybe there's "a reductionist or anti-realist philosophy that does away with these issues". i'm aware that there are so called "A theorists" but, as i said in a previous comment, most reductuionism would surely imply no present, especially given that physics is, i believe, fundamentally an explanation of sense data @curiousdannii
    – user38026
    Commented Sep 10, 2019 at 2:06
  • Can you explain why you think it is "anti-realist" to deny an objective present? Temporal relations are still perfectly real in the B theory or eternalism. Compare to a mathematical platonist, who is a realist about the world of numbers or geometrical objects, and also thinks that arithmetical or geometrical relationships are perfectly real, even if the mathematical realm has no temporal "becoming" in the ontological sense of mathematical forms passing in and out of existence. Why can't one be a realist about spacetime and temporal relations while similarly denying ontological "becoming"?
    – Hypnosifl
    Commented Sep 10, 2019 at 15:35
  • i don't think it's anti-realist, i was wondering whether scientific anti-realism is a condition of the A theory @Hypnosifl
    – user38026
    Commented Sep 10, 2019 at 17:25

5 Answers 5


As far as physics is concerned, modern physics: Relativistic Physics does away with the general notion of temporality which we generally adhere to. Minkowski space-time introduces a 4th axis to the usual 3-space. In that sense, then, we can imagine numerous particles existing independently of each other without any temporal change though when percieved subjectively the particle(s) seems be traversing through time, or perhaps enduring through time.

For example suppose you have a particle x' where (') denotes the temporal coordinate, then you can imagine x'' which immediately succeeds x' in temporality (it is space independent). However, when an observer perceive these particles: x' and x'', it just perceives it as a single particle aging. This was a simple, and highly informal, breakdown of relativistic time.

That said, let us see how that would get rid of the general idea of temporality. As we said earlier, if a particle generally percieved to be aging is not actually aging but it is being succeeded by another particle though with the same essential properties, then there is actually no time. In fact, there is no change, except for infinitely many particles existing tenselessly in an axis. Think of an enduring particle the real number line: 0, 0.000000...1, 0.0000000000...2, and so forth. Each being the "enduring" particle at a particular coordinate in 4-d Minkowski space.

Looking at how rapidly science succeeded, philosophers of the a analytic tradition started basing their metaphysics on science rather than speculation because of which we have numerous philosophic description of time each trying to appease: common sense and science. One theory of time, appeasing more so the former, is eternalism. This is best-suited for, and is much more in-tune with relativity. Eternalists believe every instance; past, present, and future is real. There is nothing special about past, future, or present for that matter. This is more generally referred to as B-Theory of time. On the other hand, theories appealing more to common-sense are categorized as A-Theory of time.

SEP refers to this theory of time.

Reference: look up Eternalism, Relativity, and Minkowski space-time.


Note that they say there is nothing "ontologically special" about the past or future, not that there is no causal order to events or that events do not have different temporal locations. The idea is to just treat time analogously to space, at the ontological level. The phrase "the present" is still meaningful but it is defined relative to when and where it is uttered, similar to the word "here" (I can say that I am 'here' at my current location in space and you are not, but I assume you and I are equally real, and one can take the same perspective on events at different temporal 'locations'). Events and objects at different times have the same ontological status, they "exist" in the same sense, even if you may not be able to influence them (if they are in your past) or know about them (if they are in your future) from your spacetime location. For more on this see wikipedia's articles on eternalism vs. presentism...there's also a SEP article about presentism here, and the time article discusses presentism vs. eternalism in section 6, along with the related notion of the "A theory" and the "B theory" of time in philosophy (the A theory says that events have properties of being in the present or past or future in an objective sense, the B theory says that temporal adjectives like this are only meaningful in a relative sense, as in 'the event of my death lies in the future relative to the event of my birth').

Strictly speaking modern physics does not comment on matters of ontology, but the relativity of simultaneity in Einstein's theory does say that observers using different inertial reference frames can disagree about whether a pair of events at different locations happened at the same time-coordinate or not, and the laws of physics work exactly the same in all inertial reference frames so there can be no basis in the basic laws of physics for seeing one definition of simultaneity as more correct or "natural" than any other. This doesn't rule out the idea that there could be a metaphysically preferred definition of simultaneity that is impossible to determine by any sort of empirical experiment, but I suppose philosophers often a version of Occam's razor to reason that if there is no physically preferred definition of simultaneity, it makes more sense to adopt a metaphysics where there isn't a metaphysically preferred definition either. Note in any case that physics says that when one event A can causally influence another event B via a signal moving at the speed of light or slower, then there are no inertial frames where A and B are simultaneous, and all frames agree on the order of the two events; it's only for events that are outside of one another's light cones, and thus cannot causally influence one another in relativity, that different frames have differing perspectives on their order.

  • are you sure. i highlighted "“The present” in particular is not to be found in any physical theory's description of the world". -1 until you find a reference for your claim
    – user38026
    Commented Sep 10, 2019 at 1:52
  • Reference for what claim? I didn't say "the present" had any meaning in an absolute sense (without any qualifications, as in the quote you mentioned), I said it could only be defined in a relative way. If a particular observer asks "what is happening at present in my inertial rest frame" you can define the set of events that are simultaneous with the event of their asking that question, in their inertial rest frame.
    – Hypnosifl
    Commented Sep 10, 2019 at 3:29
  • "at the ontological level--the phrase "the present" is still meaningful" cf "“The present” in particular is not to be found in any physical theory's description of the world"
    – user38026
    Commented Sep 10, 2019 at 5:09
  • You misread me, I did not intend for 'at the ontological level' and 'the phrase "the present" is still meaningful' to be treated as a single phrase (in fact I argued that physics favors eternalism, where there is no ontological difference between past/present/future any more than between the spatial terms here/there). I just put a dash connecting to two separate phrases 'The idea is to just treat time analogously to space, at the ontological level' and 'the phrase "the present" is still meaningful but it is relative to when and where it is uttered, similar to the word "here".
    – Hypnosifl
    Commented Sep 10, 2019 at 13:56
  • (cont.) I'll replace that dash with a period to make more clear that these are two distinct thoughts.
    – Hypnosifl
    Commented Sep 10, 2019 at 13:57

I see this discussion as deriving from the fact that, once one mathematizes time as a coordinate dimension, like the three coordinate dimensions of space, then everything being 'measured' by the system is in some sense 'all there at once', i.e there is no notion of time 'flowing'. Personally, I think these people are confused, inferring as a property of reality something which in fact is only a property of the model.

  • that's actually an interesting straw man, cheers!
    – user38026
    Commented Oct 11, 2019 at 19:54
  • Hi PMar, welcome to Phil.SE! I'd suggest you to add supporting references or philosophical positions to improve your answer. Currently it is merely philosophical speculation and thus wouldn't be considered a good answer. Commented Oct 13, 2019 at 11:58

People are attached to relativity as the problem with time. But Bell's inequalities and the Quantum Field Theory solution to them are a better example.

Entangled particles seem to put certain aspects of their history 'on hold' until the others entangled with them are tested. If a particle's current state is not yet determined until some point in the future, then the notion of 'present' has real problems beyond mere lack of simultaneity.

This does not prevent the notion of the composite future, however, and I have to disagree with that aspect of the unattributed quote. (BTW -- If you are quoting, attribute.) We can lose the present without losing the future. We just have an indeterminacy problem if we try to measure too closely. But this is no stranger than the indeterminacy problems we already have in spatial terms when we measure too closely.

Thermodynamics requires that the future has aspects of its own -- that it will have higher entropy. But it does not require continuity, being an atomic and statistical theory, so "toward-the-future" is not adequate. There has to be a real future about which the statistical statement is made, not a 'guiding derivative' like in Newtonian inertia. To state the second law properly, you need to refer to a future state and its likely differences from a current state. That future just has to be at a great enough distance to escape quantum effects -- because not everything may get there in a continuous manner.

That still kills most of our feeling about the A-series, in that it kind of makes it non-series-like. Some parts of it flow evenly and others jump forward. What happens to the gaps in the timelines of the entangled particles during which their detailed states were not determined?

At least in relativity, all the things we can reasonably interact with move forward continuously together, just at changing rates. For a QFT particle, some aspect of its state does not move forward, and then suddenly snaps into a determined state when it comes to matter.


Cosmic Time is defined in more realistic models. As the big bang created space itself, there is an absolute reference frame and anything can be dated at "some time after the Big Bang". The non-existence of time became popular with special relativity but the general theory which considers non-stationary cases uses a parameter equivalent to a time coordinate: people ignoring this development are likely to argue against time.

(Note: actually Einstein ''deconstructed'' the classical concept of simultaneity but as Max Jammer noted

The very same concept that in 1905 was instrumental for the creation of the theory of relativity was finally disqualified by the generalized version of the same theory as having lost its general validity. (Jammer M., Concepts of simultaneity, 2006: 285).

The same view is expressed by the editors of Einstein, Relativity and Absolute Simultaneity (Craig W., Simth Q, 2007.)

It has often been commented by physicists that Einstein’s GTR {thus} reintroduced the relations of absolute simultaneity that his STR had denied. (Craig 2007: 8)

  • Cosmic time isn't a preferred frame in the physicist's sense of the dynamical laws of physics obeying different equations in that frame, it's only special due to the matter distribution. Also, it's only precisely defined for a universe that permits slicing of 4D spacetime into a series of 3D spacelike hypersurfaces where the distribution of matter in each 3D slice is perfectly homogenous and isotropic; in the real world this can only be approximate, in a small region that can't be treated as homogenous (a stellar system, say) it doesn't pick out an exact def. of simultaneity in that region.
    – Hypnosifl
    Commented Nov 16, 2019 at 18:44

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