What is the doomsday argument?
>
> I appreciate the information that "A-theorists believe that there is
>an ontological (not merely epistemic) asymmetry between past and present, on
>the one hand, and the future on the other. The past and the present are
>real, while the future is not." However, I am slightly confused, since I
>thought Leslie told me today that A-theorists believe the present exists but
>neither the future nor the past. Are such people also A-theorists, or is
>there actually yet a different name for those who believe that only the
>present exists?
There are, in fact, two versions of the A-theory. One is more commonly
called "presentism," for it holds that only the present is real. Sometimes
this is referred to as "temporal solipsism." The more prevalent version of
the A-theory holds that both the past and the present are real, but the
future is not.
> I also appreciate the point that "The fundamental issue here is not
>what can be known but what exists. There is always the danger of conflating
>epistemic with ontological claims." But now I am curious as to what the
>evidence is that leads an A-theorist to claim that the future does not
>exist. Also, for an A-theorist who believes that the past as well as the
>present exists, what is the evidence that the past exists but not the future?
Well, it is just the A-theory itself which claims that the future is not
real. If one is an A-theorist, then ipso facto one believes that there is
the ontological asymmetry in question. If, however, you are asking what
evidence or argument is there for the A-theory, see below.
> In Garry's later posting (Thu, 13 Nov 1997 09:18:07 -0700) on God
>and time he states, "I think we absolutely must distinguish between
>metaphysical time (God's time) and the measured time of the physical
>universe. Even if we cannot do better than an operationalist notion of
>physical time, we still are not forced to give up the idea of absolute
>simultaneity." Similarly, in his posting of Fri, 14 Nov 1997 21:55:45 -0700
>he notes, "Even if people persist in moving relativistically, it seems that
>we only are forced to give up our knowledge of simultaneity, not the thing
>itself." I think I agree that I don't see (at least yet) how to force an
>A-theorist to give up the idea of absolute simultaneity, but I would like to
>ask what the evidence is that there is any such thing. Also, of what use is
>the idea if it can never be known?
I suspect that behind this there is the shadow of operationalism, but I
neeed to let you address that for yourself, Don. As a critical realist, I
am content to admit that there are realities which we do not--and perhaps
cannot in principle--know. I would be quite loath to adopt the
pragmatist's approach either, and see truth as only that which I can use.
I believe that there is an infinite number of true propositions which are
of no "use" whatsoever.
As to "evidence" that there is such a thing as absolute simultaneity, the
evidence is that it is entailed by the A-theory, just as the evidence for
many things in physics is that they are entailed by the best current theory
(e.g. what is the evidence for 10- [or 23-] dimensional superstrings?). No
experimental evidence is available at this time. Conceivably such evidence
could become available, or a better theory could come along which would
shed new light on the issue in question and allow is to redefine,
reconceptualize, or abandon it.
> Perhaps a clue to a possible motivation for an A-theorist is given
>by Garry's final words of his posting of Fri, 14 Nov 1997 21:56:12 -0700,
>"If temporal becoming is not a real feature of the universe, but is only
>psychological, then I believe that it is difficult to give any real meaning
>to the notion of causation, let alone to escape the fatalist dilemma."
>Since I myself don't find these supposed problems with the B-theory nearly
>sufficient to cause me to adopt the A-theory, I am curious as to whether
>there is any more positive evidence for the A-theory than this.
While you have often spoken of "evidence" above, I should make it clear
that a metaphysical theory will be supported by certain arguments, and will
be evaluated by the strength of those arguments, as well as by its power to
explain certain phenomena (not unlike scientific theories in this regard).
I'll offer three lines of argument which support the A-theory. I will only
offer a summary of the arguments here, for reasons of space (the summaries
are long enough!):
(1) Common linguistic practice, while not determinative of reality (as some
postmoderns would say), certainly reflects reality. The use of tensed
language is evidence that temporal becoming is real and that temporal
indexicals cannot be reduced to tenseless language plus a token-reflexive
reference to the time of the utterance. The A-theoretic statement, "A bomb
will explode in the station five minutes from now" conveys information that
the B-theoretic statement, "A bomb explodes in the station five minutes
later than the time of this utterance" does not, for the first will
certainly be action-guiding while the second will not be, unless
accompanied by additional information about the time of the utterance and
what time it is now, a A-determination. Furthermore, expressions such as
"Thank goodness that's over!" uttered after, say, a root-canal, are
incomprehensible if reduced to the B-theoretic expression "Thank goodness
the time of this uterance is later than the time of the root canal." Such
example could be multiplied. There are admittedly deep issues in the
philosophy of language involved here, but the basic point is this: human
thought and action depend inescapably upon tensed determinations. The
ineliminability of tense in guiding our beliefs and actions explains why
tense is so pervasive in common linguistic practice. I suggest that this
is an argument for the conclusion that reality itself is tensed--that is,
that time is dynamic (A-theoretic).
(2) An entity may persist in in time by enduring, in which case it is
conceived as being wholly present at any time at which it exists, or by
perduring, in which case it is conceived as being spread out through time,
and only a part of it--a temporal part--is present at any time at which it
exists. A strong argument can be made that only enduring entities exist in
A-theoretic time, while only perduring entities exist in B-theoretic time.
Another argument then establishes that consciousness is only possible for
enduring entities. Hence, if persons are characterized by (among other
things) persisting consciousness, then they are enduring things, and time
is A-theoretic.
(3) A pervasive part of human experience is that our experience is present
tense. (Of course, my present-tense experience of seeing the sun is the
experience of the sun as it was some 8 minutes ago; nevertheless, the
experience per se is present.) But according to the B-theory there is no
present-tense. Further, consider the class of experiences of mentally
tokening a sequence, such as counting to 50 when playing hide-and-seek, or
counting sheep to fall asleep, or mentally playing the score of a piano
sonata, and so forth. Now whatever might be said about events in the
external world, it does not seem possible to avoid the conclusion that I
experience each successive member of the sequence as first future, in that
I am at least tacitly aware of its "coming," then as present, and then as
past ("I got past the D-flat minor diminished seventh chord this time!").
My experience is of the successive passage of mental states, and is
A-theoretic in nature. But isn't it open to the B-theorist to reply that
my experience of the "passage" of these mental states is itself merely
psychological and not reflective of any ontological reality? Yes, but
only at the pain of infinite regress which does seem to be vicious, for the
psychological states themselves pass in succession, and would need then
ever-higher-order states to explain the apparent succession of the
lower-order states.
One additional point should be made. If time is dynamic, we need a theory
of time which explains its dynamic character as well as its direction. We
need to be able to explain why time "flows" at all, and why it flows in the
direection it does. A causal theory of time answers both questions. A
realist theory of causation can explain why a state of affairs at time t
can bring about another SOA at time t+1. And if formulated properly, a
causal theory can rule out both causal loops and backward causation (the
arguments are significantly different) as being metaphysically impossible,
thus explaining the direction of time (a notable feature of a causal theory
of time, since as we know by now, arguments from statistical thermodynamics
have shown that entropy--which used to be everyone's favorite arrow of
time--cannot do the job).
>
> Since John Leslie told me there are plenty of respected A-theorists,
>I am really just confessing my ignorance of what their arguments are, so now
>I am taking the lazy man's approach (or am I trying to be more efficient?)
>of trying to find what their arguments are without having to take the bother
>of actually reading philosophy texts on what I have thought was a very
>implausible view (especially if the past is supposed to exist but not the
>future; saying that only the present and neither the future nor the past
>exist seems more nearly plausible to me). So perhaps Garry can enlighten me.
>
> Don Page
I doubt that there was any enlightenment above! ;^) Metaphysical arguments
are not easy to abbreviate. I am disturbed by the fact that alomst all
cosmologists I know are B-theorists (like you and Leslie and Davies and
Tipler and others), but at the end of the day, I think this is a
philosophical and not a physical question. But I can recommend a couple of
good texts, if you are interested! (And I am enjoying the discussion.)
Garry DeWeese