1. PHL 356 Philosophy of Physics
Philosophy of Physics II
PHL 356 Philosophy of Physics
Week II
Does Time Pass?

2. Philosophy of Physics II
The issue is this: Is there something that we might call "now" or "the present" that moves through this time series?
The intuitions that we have strongly favour a yes answer.
Consider:
We observe time passing; we feel ourselves moving into the future. In a memorable phrase of Donald Williams, we experience “the grace and whiz of passage.”
Events start out in the future, they become present, then they move into the past. This seems undeniable. So there must be something moving through the time series turning future events into present ones and then into past events.
Before I ate my lunch, I could have chosen either pizza or lasagne. Now that lunch is eaten, my actual choice of pizza is fixed. The choice of pizza went from being possible to actual and the choice of lasagne went from being possible to impossible. The present seems to be moving through the time series converting possibilities into actualities.

3. Time Series

4. The “block” universe (with a moving present)
This picture and next from Internet.

5. Block universe (without a present)

6. Philosophy of Physics II
The Open Future
The block universe is one picture. At each moment it seems like “now,” but this is an illusion. Every moment is equally real.
The open future is another picture. In this account, the present (which is real) turns possibilities into actualities.

7. Philosophy of Physics II
Presentism
Presentism is the view that only the present is real.
All the events that are happening now are real
past events are no longer real
future events are not yet real
The passage of time (the moving present) turns unreal future events into real present events, then into unreal past events.
An argument from special relativity seems to destroy this view.

8. Philosophy of Physics II
Special Relativity
This argument is due to Hilary Putnam and starts from the common sense thought that the present is “real,” while the past has ceased to be real and the future is not yet real, but will become so. To speak of becoming real is just another way of expressing temporal passage.
Putnam introduces a relation R to capture the notion of being equally real. In classical physics, R could be the relation of being simultaneous with. Thus if event A is real (i.e., exists here and now) and event B is simultaneous with A, then B is real, too.
Don’t worry about what “real” means, only “equally real” matters.

9. In special relativity, there is no absolute simultaneity, but only simultaneity in a frame of reference.
Let R be this relation; that is, R is the relation of being simultaneous with in X’s frame of reference. Thus, if A is R to B, then events A and B are equally real (or equally unreal).
Note that R is transitive (if A is R to B and B is R to C, then A is R to C). It is the transitive nature of R that is crucial in Putnam's argument.

10. Philosophy of Physics II
Hyper-planes

11. Philosophy of Physics II
Suppose event 1 is present (here-now) and observed by A.
Thus, event 1 is real according to A, since it is present.
By relation R, everything else on A’s plane of simultaneity is also real.
Suppose observer B is coincident with A.
Event 1 is real according to B, since event 1 is present.
Suppose B is moving relative to A.
Thus, B has a different plane of simultaneity.
By R, everything on B’s plane of simultaneity is real.
Let event 2 be on B’s plane of simultaneity
Thus, event 2 is real.
Event 2 is simultaneous with event 3 in A’s frame
E1 is as real as E2 and E2 is as real as E3, thus, E1 is as real as E3.
Thus, event 3 is real (even though event 3 is in A's future).
Thus, events that are in the future are just as real as those in the present.

12. Philosophy of Physics II
A similar argument could be used to establish the reality of the past.
Conclusion: events in the past, the present, and the future are equally real.
Why does this matter? Because we have a common sense feeling that the future somehow does not really exist (and maybe the past, too). This argument overturns that bit of common sense.
Conclusion: every event in the time series is as real as every other event.
This suggests that the whole idea of now or the present is a kind of subjective illusion.

13. Philosophy of Physics II
A-series vs B-series
J.M.E. McTaggart devised one of the most interesting and controversial arguments concerning time. He claimed that time is unreal. Even though his argument is faulty, it nevertheless influenced future discussion greatly.
Terminology introduced by McTaggart: A-series vs B-series.
There are two common ways to think about time. One way is in terms of past, present, and future. This is known as the A-series. On this view every event (that is, every point of time), is located in the past, or the present, or the future. And, of course, there are gradations: an event might be in the near past, the distant past, the very distant past, and so on.
The other way of characterizing time is in terms of earlier, simultaneous, and later. This is known as the B-series. On this view every event, every point of time, is in the relation of earlier than, simultaneous with, or later than every other event or point of time.

14. Philosophy of Physics II
The question of passage can be expressed in A vs B terms.
Those who deny passage, say that the B-series is sufficient to account for all relevant phenomena involving time.
By contrast, champions of passage claim that the A-series is necessary for understanding time (perhaps in addition to the B-series).

15. Philosophy of Physics II
Analogy: Imagine a film strip; the different frames are different moments of time. The film strip also has a direction. Are these two features sufficient for accounting for time? Or is there something extra, something that is analogous to projection or illumination, one frame at a time? This would be passage, the moving present.
It is important to stress what is not at issue in the A vs B debate.
Both agree that there is a time series.
Both agree that it has a direction.
The only thing that is debated is passage, or the objectivity of past, present, and future.
The A-champions affirm passage.
The B-champions deny passage.

16. Philosophy of Physics II
McTaggart’s Argument
Though he coined the A and B terminology, McTaggart held that time is actually unreal, a kind of illusion. His argument follows below.
A crucial thing you should consider in his argument is his notion of “change.”
McTaggart’s main claim is that the B-series can’t make sense of change, so time requires the A-series; and the A-series is incoherent. His conclusion is that time is unreal, a kind of illusion. (This is claiming much more than claiming that passage is unreal.)

17. Philosophy of Physics II
If time exists, then events are located in the A-series, or in the B-series, or in both.
Events in the B-series are eternal and unchanging. An event such as the death of Queen Anne is eternally after the death of Elizabeth I and before the death of Elizabeth II. This event never changes its location in the time series; as far as the B-series is concerned, it never changes at all.
Change is essential to time. Without change, time would not exist.
In the A-series, the death of Queen Anne is constantly changing; it was in the distant future, then the near future, then the present, then the near past, and so on. Events are fixed with respect to one another in the time series, but they are constantly changing with respect to the moving present.
Thus, if time exists, then events in the B-series must be in the A-series, as well.
Events in the A-series must be past, and present, and future; but this is contradictory.
It won't do to reply that an event is not simultaneously past, present, and future, but is rather future with respect to one event, past with respect to another, and so on. This response, in effect, appeals to the B-series which has already been shown inadequate to explicate time and change.
Thus, the A-series is incoherent. And so is the B-series, because it required the A-series.
Therefore, time is unreal; it does not exist.

18. Philosophy of Physics II
Remarks on McTaggart
McTaggart went on to conclude that since we experience events as happening in time, we do not experience reality as it actually is; we are deceived by appearances.
There are two things to say quickly in reply.
In premiss (3) McTaggart asserts that change is essential to time. Is this true? (Maybe not, but that is a topic for later.)
More problematic is the assertion in premiss (2) about the nature of change. Perhaps it is not events such as the death of Queen Anne that change; it is objects such as Queen Anne herself that change. She changed from being alive to being not alive. That is the only sense of change that we use either in daily life or in science.
Thus, McTaggart’s argument is not sound.

19. Philosophy of Physics II
The B-series View
A champion of the B-series is someone who claims the B-series is the whole story and there is no becoming, no now, no present that moves through the time series. Time does not pass.
All times are equally real.
Earlier, later, simultaneous are objective relations among events.
Past, present, future are subjective, they are relative to times in the B-series.

20. Philosophy of Physics II
B-champions need to explain (or explain away) a few things. So they usually claim the following:
Properties such as past, present, and future, are merely relative. An event is past with respect to some times, future with respect to other times.
We are misled by terms such as “now” or “the present” which seem like nouns that refer to distinct, enduring entities as do “Toronto” or “the prime minister.”
Instead, terms such as “now” or “the present” are so-called indexical terms; they are similar to words such as “I”, “you”, “here”, and “this.” They pick up their meaning in a context and shift their meaning from speaker to speaker or context to context.
“The present” means “the time (in the B-series) simultaneous with the event of saying ‘the present’.”

21. Philosophy of Physics II
All change is of the following form: Entity a has property F at time t and a has property ~F at time t'. (Bob is standing at 12:00 and not standing at 12:01) Objects change, not events.
The case for (or against) the B-series outlook is independent from many of the details of physics. It was first formulated in terms of classical physics, but holds just as well in relativity. (However, the A vs B issue is formulated relative to a frame of reference.)
Metaphors such as the “static” world or the four-dimensional “block” universe in which nothing happens are misleading. These suggest that the universe is “frozen in time.” But remember that time is part of the four-dimension manifold. There is no higher-dimensional spacetime (with its own time axis) in which our 4-dimension spacetime is embedded and where nothing happens.

22. Philosophy of Physics II
The Regress Argument
This argument is due to Williams (1951).
If nowness (the present) moves through the time series, it does so at some speed.
This “moving” through the time series can only be explicated in terms of some external time, a supertime. (For instance, the present moves at the rate of 5 seconds of our time per second of supertime.) (Analogy: Think of events in a film running faster (a flower unfolding) or slower (hummingbird wings beating) than real time.)
If the A-series account is the right account of time, then it must also be the right account of supertime.
Thus, we could ask how fast the present in supertime is moving through the supertime series.
This, obviously, leads to an infinite regress. Consequently, it should be rejected.
Thus, there is no nowness, no present moving through the time series. (In other words, the A-series is absurd.)

23. Philosophy of Physics II
A Simplicity Argument
The B-series is the only account of time we need for science or for daily life
we do not need the extra concepts, past, present, and future, as understood in the A-series.
Notice, for example, that science uses “earlier,” “later,” and simultaneous, and uses temporal intervals between events in describing physical processes.
In science we say “if this happens at t, then that happens at t′.” We do not say that the happenings must be in the future or on a Tuesday.
Laws of nature are indifferent to when something happens; they are oblivious to past, present, and future.
Thus, in the spirit of Occam’s razor, we should eliminate the unnecessary A-series.

24. Philosophy of Physics II
Determinism
One of the objections regularly raised against the B-series concerns determinism and the so-called open future.
The claim is that events in the future are not fixed, unlike events in the past. It has a structure something like a tree.

25. The B-series, by contrast, seems to be committed to a strict determinism.
But if we are not deluded about free will and quantum indeterminacy, then the future is open.
Hence the A-series account is needed. The future can’t exist the way the B-series claims.
Is this a good argument?

26. Philosophy of Physics II
Defining Determinism
This picture of time has been held by a number of notable philosophers, from Aristotle to Whitrow. But it may rest on a confused notion of determinism.
Here is a brief account that will show that the B-series is perfectly compatible with non-determinism (quantum indeterminism and freewill).
Let us characterize a world, W, as deterministic iff (if and only if) every world with the same laws of nature as W and the same initial conditions as W, has the same history as W.
And we will say that a world W is non-deterministic iff there is a world W' that has the same laws and initial conditions as W, but has a different history.

27. Worlds with identical laws and initial conditions, but with different histories

28. Reply to Determinism Argument
Philosophy of Physics II
Reply to Determinism Argument
With this definition in hand, consider my choice of lunch. On a B-series view, it is true at breakfast time that I will choose pizza for lunch. But is my choice determined?
If every world which is like ours in having the same laws and the same set of initial conditions (ie, the various worlds, including me and my counterparts in the other worlds), are exactly the same up to this point) is a world in which I choose pizza, then my choice is deterministic.
But if there is a world in which my counterpart picks lasagne, while I choose pizza in this world, then our choices are not determined.
Of course, finding evidence that my choice is or is not determined is a completely different matter.
Upshot: The B-series account of time is compatible with both freedom and determinism. The A vs B debate is independent from the freedom vs determinism issue.

29. The Perception of Passage
Philosophy of Physics II
The Perception of Passage
It feels like time passes. But if it doesn’t pass, then why do we feel the contrary so strongly? One speculation that is sometimes offered is that the perception of passage is similar to the perception of so-called secondary qualities.
Some properties are completely objective, eg., properties such as mass, charge, and so on. But other properties are subjective, such as colour, flavour, and smell. The first group are called primary properties, and are thought to be in the objective world. The second group are called secondary properties, and are usually thought to be somehow “in the mind.” The rose emits photons which interact with us in such a way as to give rise to the sensation of red. The rose itself, however, has no colour.
The suggestion of some B-series champions (e.g., Grunbaum) is that the perception of passage is actually the perception of a secondary property. There is no passage of time in reality (just as there are no colours or smells), but nature somehow causes the sensation of passage in us. How is this done? We can only speculate. Paul Horwich suggests that it is associated with the growing number of memories that we have, and that we are more confident of our memories (of earlier events) than our anticipations (of later events). This together with some features of our language (tense), somehow give us the sense of moving forward through time.
This is, of course, highly speculative.

30. Einstein’s view Rudolf Carnap reports a conversation with Einstein:
“In Princeton I had some interesting talks with Einstein, whom I had known personally years before....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.” (Carnap, “Autobiographical Notes,” The Philosophy of Rudolf Carnap, P.A Schillp (ed.), La Salle, Ill., Open Court, 1963, 37f.)

31. Einstein expressed an A-series view above, but he expressed a B-series attitude to Now when he wrote to the widow of his old friend Michaelangelo Besso, who had just died.
“... now he has preceded me a little by parting from this strange world. This means nothing. To us believing physicists the distinction between past, present, and future [i.e., between what is now and what is not now] has only the significance of a stubborn illusion.” (Quoted in Folsing, Einstein, A Biography, 741)

32. Philosophy of Physics II
Further Reading
Grunbaum, “The Status of Temporal Becoming”
McTaggart, “Time”
Williams, “The Myth of Passage”
These are classic articles, all reprinted in Gale (ed.) Philosophy of Time. This collection has many additional important articles.
Another good general anthology is Capek (ed) The Concepts of Space and Time.
A recent specialized collection is: Callender (ed), Time Reality, and Experience
Horwich, Asymmetries of Time
Mellor, Real Time
Le Poidevin, Travels in Four Dimensions
Lockwood, The Labyrinth of Time
A new book by Lee Smolin, Time Reborn, argues for something like the A-series, claiming it is necessary for his view of Q-gravity.