What does science tell us about the nature of time and space? It is widely claimed that, in relativistic physics, space and time are intertwined in a four-dimensional space-time block universe, where all times co-exist eternally. This seems to challenge the common-sense presentist view of time, where only the present instant exists, moving from a no longer existing past to a yet-to-exist future. How well established is the block universe with its static time?
Absolute space and time
Classical physics is based on Isaac Newton's notions
of absolute space and time, which exist independently of each
other. Newton held that they did not exist by themselves but depended on God's
omnipresence and eternality. There is a universal clock, a universal
"now," so that each location in space follows the same absolute
time.
Absolute space and time accorded well with the notion of
dynamic time or presentism, where only the present moment exists. Absolute
space provided a preferred frame of reference, a God's view of reality,
defining position and motion. This ensured an objective ordering of events (absolute
simultaneity) independent of an observer's position or motion.
Empirically, Newton defined absolute space in terms of a reference frame in which Newton's laws of motion held (called an "inertial frame"). In such a frame the Earth's annual revolution about the Sun, as well as its daily rotation, were deemed to reflect absolute motion. Given, however, that all we can ever observe is relative motion, this raised the question of whether the laws of motion could be reformulated to apply to other conceptions of absolute space, such as, for example, one upholding a stationary Earth.
Relativity, space, and time
Einstein's theory of special relativity, on the other hand,
stressed relative motion between different observers. It
assumed that no observer is privileged but that all have equal standing. Hence,
there is no longer an absolute frame of reference. Further, two observers
moving relative to one another could view the same set of events in different
sequences, so that an event that is past for one observer may be future
for another observer. Consequently, absolute simultaneity (where a set of events has the same absolute order for all observers) is replaced with relative simultaneity
and a universal "now" is replaced with a different local time
for every observer.
In the most popular interpretation of special relativity,
space and time are intertwined into a four-dimensional space-time block
universe where past, present, and future times all co-exist eternally. This static
view of time (eternalism) opposes the dynamic time of presentism, where only
the present time exists.
Our strong commonsense experience of the flow of time is
then reduced to a mere delusion. As Einstein himself said, "To us
believing physicists the distinction between past, present, and future has only
the significance of a stubborn illusion."
Special relativity is somewhat simplistic since it ignores
gravity. Einstein's theory of general relativity generalizes special relativity
to include gravity. General relativity postulates that gravity is exhibited by
warping 4-d space-time so that both space and time are distorted by massive
objects. General relativity, too, is commonly viewed as refuting
presentism.
There are, however, several ways in which special and
general relativity can be reconciled with presentism.
1. Metaphysically preferred frames
Even in theories where there is relative simultaneity, one is
still free to imagine there is a sort of "metaphysically preferred
frame" whose definition of simultaneity is "true" while the
others are "false" in a metaphysical sense. One must then accept that
no possible physical experiment could allow us to empirically prove (or
disprove) that preferred frame to be "true". Such a preferred
frame could, however, be chosen on the basis of philosophical or theological
considerations.
Thus, even if relativity treats all potential observers
equally, we could still choose, for example, a stationary observer in
Greenwich, UK, to have preferred status. We could then define the absolute
reference frame to be centered on Greenwich and define Greenwich time as the
absolute time. Clocks associated with other observers could then be
synchronized with Greenwich time so that a universal "now" is
associated with Greenwich time.
2. Rewrite relativity in absolute terms
Another approach is to rewrite special and general
relativity in terms of absolute time. For example, the
"Neo-Lorentzian" version of special relativity retains absolute
(3-dimensional) space plus an absolute time independent of space. Similarly,
absolute time can be retained in general relativity by using a Hamiltonian
version of general relativity.[1] Such absolute versions of relativity are observationally indistinguishable
from the space-time block universe view. As in the previous case, however, the
absolute frame must generally be chosen on the basis of metaphysical, rather than empirical, considerations.
3. Instrumentalism
One could also contend that, since we can't prove any scientific theory to be true, we should just treat it as a useful fiction. Scientific theories, such as special and general relativity and quantum mechanics can be viewed simply as handy tools that enable us to establish relations among observations and to make predictions, but tell us nothing about reality beyond the observations, such as the nature of time.
Science and time in general
In quantum mechanics, a measurement
performed on one of two entangled particles has an instantaneous effect on the
other particle, even when they are far apart. The two events are simultaneous,
no matter how fast any observer is moving. This supports an
absolute simultaneity, with an objective flow of time.[2]
General relativity, which deals with the very large (e.g.,
stars and galaxies), and quantum mechanics, which deals with the very small
(e.g., atoms), are two of the most successful theories in modern physics. Yet,
they are very difficult to reconcile, suggesting that at least one of these
theories is incomplete. Currently, there is as yet no widely accepted theory of
quantum gravity. One theory of quantum gravity proposed by Petr Horava retains the
notion of absolute time.[3] There seems no
reason to doubt that any future theory of quantum gravity could be interpreted
within a framework of absolute time.
Other scientific disciplines, such as biology and geology, seem more conducive to dynamic time than to static time.
Conclusions
1. We should note that a scientific theory such as general relativity or quantum mechanics, no matter how successful, is just a mathematical model representing a very limited aspect of reality. We must be careful not to commit the fallacy of misplaced concreteness, where our abstract model becomes more real than our concrete experienced reality, upon which the model is based. Thus occurs, for example, when we allow relativity to dismiss the intuitive flow of time we all experience as a mere illusion. After all, science should ultimately serve to explain our observations, not to explain them away.
2. Empirically, physics can deal only with relative motion and position. This leaves one free to choose an absolute frame of reference based on metaphysical or theological considerations. Thus, for example, there can be no scientific objection to choosing, say, the earth as an absolute frame of reference and earth time as universal time, if one so wished.
3. Although some parts of physics, such as special and
general relativity may seem more conducive to eternalism, other parts, such as
quantum mechanics, accord better with presentism. Yet all of physics can be
interpreted within either eternalism or presentism. Thus I conclude that
physics by itself does not conclusively support any particular theory of time.
In short, it offers no compelling grounds for ruling out presentism, or dynamic
time, as a viable view of time.
4. More generally, we must be wary of extracting metaphysical conclusions from any physical theory. Often these merely reflect the metaphysical assumptions upon which the theory is based.
5. Finally, scientific theories, even if they could be proven to be true for the entire observed physical universe, do not extend to the unseen heavenly realm, which seems to have its own laws. Hence, human science, when unaided by divine revelation, is incapable of discovering the true spatial and temporal nature of the universe as a whole.
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[1] J. Brian Pitts 2004, “Some Thoughts on Relativity and the Flow of Time: Einstein’s Equations given Absolute Simultaneity”. Preprint. http://philsci-archive.pitt.edu/2760/. Accessed Nov.16, 2022.
[2] see Jeffrey Koperski 2015, The Physics of Theism. Chichester, UK: Wiley-Blackwell. p.122.
[3] Koperski, op. cit., p.134.
