CONTENTS

1   INTRODUCTION

2   TECHNICAL DEVELOPMENTS

3   B-THEORY: EXPOSITION

4   A-THEORY: EXPOSITION AND PARADOX

5   ARGUMENTS FOR A-THEORY

6    A-THEORY: REVISED EXPOSITION

7    TIME AND ASSERTION

8    THE PAST-FUTURE ASYMMETRY

9    CONCLUSIONS

5   ARGUMENTS FOR A-THEORY

For all its common-sense plausibility, A-theory seems to face insuperable hurdles. In the above discussion we have encountered four.

In the face of such a barrage of objections, to persist in a defence of A-theory would seem quixotic in the extreme. And yet the basis for such a defence is simple: A-theory is empirically true. The experiment which decides in favour of A-theory is the most fundamental one we can carry out - it is the experience of our day-to-day lives. We carry out the experiment simply by living. The fact that our experience has this day-to-day character is the evidence in favour of A-theory.

To build this into a defence of A-theory requires an argument that the immediate phenomenology of our experience is competent to provide decisive evidence as to the nature of time. Many conclusions drawn by common sense from immediate experience have subsequently been falsified by science: that the sun goes around the earth, that there is an absolute simultaneity relation. However these turned out to be matters which were epistemologically distant from us. Our raw untutored experience was therefore not competent to pronounce on these matters. Experience of motion in our nearby, friction-dominated world turns out to be a bad guide to the laws of motion. Only when we extended our experience scientifically to the motion of the planets through a vacuum did the laws of motion become apparent. And only then could we understand how the earth could be spinning rapidly without our experiencing a sense of motion. Similarly when our experience was confined to relative velocities low compared with the invariant velocity, we could not tell the difference between Galilean and Lorentzian kinematics. For those who work every day with high energy accelerators, the Lorentz transformation and the concomitant existence of an invariant velocity is a matter of common experience.

Conversely there are those experiences which are so epistemologically close to our being that they face us with a choice:

            EITHER these experiences are reliable evidence of reality;

            OR we can have no reliable evidence of reality.

When dealing with this sort of knowledge we have to be very careful not to draw any unwarranted conclusions from it, conclusions which rely on assumptions which do not share the epistemological proximity. Often the reliability of our knowledge of these matters is matched by an almost total failure of understanding. A case in point is our knowledge of mental phenomena. We know directly that there is something there which the word “mind” tries to point at, but our understanding is so poor that almost any attempt to describe the phenomena in words is to be regarded as highly suspect. Therefore we can not derive from our raw experience of mental phenomena any sophisticated ontology of mind, without a level of philosophical analysis which to date no human being has achieved.

The basis of the belief in A-theory is that time, and the passage of time, are such intimate elements of experience that if we were wrong about them we could not use our experience as evidence for anything (except the Cartesian conclusion of our own existence, which may be logically protected from this conclusion). This is not an argument, but rather an act of ostension using words. Readers are pointed in the direction of their experience of time and invited to agree that A-theory is a better description of this experience than B-theory.

Let us see how the four objections fare against this rationale for defending A-theory. As we saw above, the Russell reduction to B-theory is countered by saying that in a A-theoretic world an important piece of reference is lost in this reduction. It has the wrong sort of objects, and leaves out the phenomenology of the Now and of temporal passage.

The counter-attack against McTaggart also begins with the argument from experience. For those who, when examining their personal experience of time, conclude that B-theory is an inadequate description of it, the argument constitutes an existence proof of a way around McTaggart’s argument. If A-theory is true of our experience, then the conclusion that A-theory is impossible must be wrong, even though this argument does not tell us why and where it is wrong.

The same argument can be deployed against objection 4: none of our discoveries about SR can falsify our basic knowledge of time. Everything we claim to know about SR rests ultimately on the same sort of experience which contains the passage of time. If that were untrustworthy, then our conclusions about physical theory, including SR would be compromised. Therefore it must be possible to reconcile the A-theory with SR in some way - but we are still left with the task of turning this possibility into an actual resolution.

The argument from experience leaves open the possibility that passage might  be restricted to the realm of the subjective, leaving the objective world to be described accurately by B-theory. (This assumes that it is possible to glue together a B-theoretic objective world and an A-theoretic subjective experience, which is in itself problematic.) In this case physicists would no longer need to be bothered about passage, and Grünbaum’s observation of the absence of reference to passage in physical theories would be explained. But McTaggart’s argument is too powerful merely to exclude passage from the objective world. If its conclusion were true, then, counter-evidentially, the subjective experience of passage would not be possible. The argument even works for illusion. Even an illusion of passage would be sufficient to show that there must be a way around McTaggart’s argument. Working back from this, we must conclude that McTaggart’s argument can not be used as the basis for excluding passage from the objective world - though there might be other arguments, for example from SR, which do this.

Against Grünbaum the argument is that, while physics does not mention passage explicitly, its entire subject matter concerns things that happen as part of the passage of time. Grünbaum fails to grasp the status of physics as a “modal science”. Physics is based on a split of reality between history, the things which happen, the totality of “what is past, is passing, or to come, and modality, the laws which describe which histories are possible - or, in the case of probabilistic laws, likely. In physics history turns up as the initial conditions and modality is represented by the equations of motion.

It is not the business of physics to describe the historical initial conditions (except perhaps in cosmology, where history and modality may converge). Physics is about the equations of motion, the timeless regularities to be found within history. It is therefore not surprising that physics makes no explicit mention of passage. Implicitly though, all of physics refers to things that could happen historically. All of the experiments on which physics bases its knowledge claims happened at determinate points of history. According to A-theory the reference of this history is finally ensured by relating it to Now. Physics is about things that could or must happen now - without this reference it would not be about anything. This fact is treated in physics textbooks as too obvious to mention, and this can create the illusion that physics is not about passage.

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