For us believing physicists, the distinction between past, present and future is only a stubbornly persistent illusion." - Albert Einstein (from The Expanded Quotable Einstein. Princeton University Press, 2000). p. 75).
What Einstein was referring to in the quote above, was the impossibility, according to his theory of relativity, of any objective determination of "now," and the lack of a unique objective distinction between past and future for some pairs of events, since these depend on the reference frame. In his words,
"The four-dimensional continuum is now no longer resolvable objectively into sections, which contain all simultaneous events; “now” loses for the spatially extended world its objective meaning. It is because of this that space and time must be regarded as a four-dimensional continuum that is objectively unresolvable." -Einstein, Ideas and Opinions. (New York: Crown Publishers, 1954). p. 371.
I came upon this blog site while researching the topics of presentism and eternalism.
Is Time Travel Possible?
My answer is a resounding "No!" One's answer to that question depends from the start on whether one's philosophy of time is eternalism or presentism. What exactly are these philosophies?
Eternalism is the view that the past, present, and future all exist timelessly and eternally. The cosmos is an eternal four dimensional "block house." In philosophpical terms, spacetime is a completed ontological object -- an actual four dimensaional continuum rather than an abstract four dimensional concept. That notion has its roots in mistaken interpretations of Special Relativity, with an artificial construction and a conventionalist definition of “simultaneity.” Hillary Putnam in his essay "
Time and Physical Geometry" rehearsed in detail an argument for eternalism that relied on that standard misrepresented implication of Special Relativity. His argument in brief rests upon the fact that the Lorentz transformation of SR does not preserve a "now" between observers in relative motion. If I am at rest then my time (i.e. t = 0) slice of spacetime (the set of all events "simultaneous" with me merely because it is assigned the same t coordinate, and what Putnam calls "me-now") does not correspond to your time' (i.e. t' = 0) slice of spacetime (what Putnam calls "you-now"). Putnam then asserts that if what exists in "my-now" is real; and if you and I are collocated at t = t ' = 0 (as you move past me), then me-now and you-now are simultaneously real. Finally, since this property of being real is transitive, it follows that every thing "simultaneous" with you-now is real and everything "simultaneous" with me-now is real, but you are real to me so all of the things real for you must also be real for me. Since some of the things real for you lie to the future of my-now and some to the past. It follows from this (specious) argument that all past, present and future events must be real. And that is eternalism. The attentive reader no doubt noticed the shifting meaning and properties assigned to Putnam's adopted conventional defintions of "simultaneous" and "real."
Presentism, on the contrary, which is the view that only the present exists, future is not yet, and the past is gone. In other words, the past, present and future do not persist in an unchanging four dimensonal "spacetime." There is just space that persists through time. Yesterday's gone. You can’t get to there from now – the past is not a place. It was through the illegitmate wedding of space and time into a single entity known as spacetime that is the core presupposition of eternalism. It was this philosophical view that lead Einstein to declare time as an illusion -- and indeed it would be in eternal spacetime. I call this philosophical presupposition the myth of spacetime
Presentism is the Christian view, but I won’t argue from that at the moment.
Rather, I will critique eternalism and the mistaken idea that time travel is possible.
Clearly, on presentism, time travel is not possible. The past is not a place one can visit in a temporal analog of a spatial trip in an automobile.
This brings me to the specific blog entry by physicalists arguing time travel is possible.
Spatialization of time implies same constraints as a loop of string. A loop of string cannot be a spatial loop and fail to connect to its other end as one traces the loop. The loop is physically constrained to be such. The blog referenced above makes that incisive observation.
Physicalists’ glib declaration that one can’t travel into the past and kill ones grandfather because you didn’t is true but that doesn’t explore the reason and the implications. In the same way that the loop is physically constrained, so is the purported time traveler, as he is a physical system and must obey the dictates of a constrained physical solution. The conclusion is clear. There is no human autonomy from physical causation. Physical systems have to act according to the physical laws.
Time travel paradoxes only arise because their creators conveniently fail to examine the entire set of implications of their physicalist presuppositions. Specifically, they simultaneously embrace human autonomy and also physical determinism of the unchangning block universe. Those two are contradictory. Hence, no autonomy and no paradox.
Such belief in eternalism and possibility of time travel are rather prevalent among non-Christians. However it may come as a surprise that some Christians have uncritically adopted the eternalist view of Einstein. In particular is Jason Lisle and his ill conceived Anisotropic Synchrony Convention (ASC) for accounting for a young earth in an old(?) universe. That Lisle has embraced eternalism is not a mere conjecture since he ascribes to the possibility of time travel as "implied" by Special Relativity (SR). Actually the view of Special Relativity that Lisle holds is more than the mathematical structure of the theory. He has also adopted the assumption of the eternalist. A belief in the myth of spacetime.
That Jason Lisle has succumbed to the eternalist view of special relativity is evident from his book “The Physics of Einstein.” Examples from chapter 10 “How to Build a Time Machine” of that book are:
(1) that he gives lip service to time travel which is impossible in presentism; (2) his claim that time travel is provable using the Lorentz transformation.
The second claim is a false conclusion that is based on an unstated and uncritically examined presupposition of eternalism – i.e. the presupposition that the past still exists and is a place that can be visited. Rejecting that unproven presupposition and adopting presentism (as Christian theism requires) shows that time travel is not provable from the Lorentz transformation. The mathematics of Special Relativity do not prove the possibility of time travel. The possibility of time travel is based on a commitment to a philosophical presupposition.
Here is an extended quote of Lisle:
“As we saw in the previous chapter the theory of relativity allows for the possibility of traveling backward in time if it is also possible to travel faster than the speed of light. That's the good news. The bad news is that there are some compelling reasons to think that faster than light travel is not possible, at least not for information bearing systems. We have seen hints of that in previous chapters, and we will go into greater depth in later chapters. Nonetheless, hypothetically if faster than light travel were possible, then time travel into the past would also be possible. This is provable from the Lorentz transformation, and gives us a much more profound understanding of the nature of space and time. " (emph. added)
The Lorentz transform alone does not prove time travel. It requires the
extra commitment to an eternalist Minkowski spacetime as it requires the past to exist in order to be “revisited.” That is the notion that “time is a place,” which is part-and-parcel of Minkowski’s eternal block universe as espoused by Einstein ("time is an illusion"). Lisle's "profound understanding of the nature of space and time" is infected by eternalism as his inference requires that the past is a place, sitting there waiting to be revisited, if only, we could travel faster than the speed of light. This idea is what has infected and influenced the views of “conventionality” of simultaneity, synchronization and Lisle's “Anisotropic Synchrony Convention” model.
