Marks and Remarks
Food for the Mind and Eye

No. 0129, June 30, 2017


"Time Travel"

     Prickles, our resident chronologist, art critic and veritable hedgehog, selected the image below to illustrate our treatise on traveling back in time (which follows). Note: normally, our consciousness is traveling forward in time (at maximum speed, typically the speed of light or close to it, but that's another story...). So is there some special significance here, Prickles? "No," she says.

Copyright 2017 by S.W. Paul Wyszkowski

     The problem with time travel, a well worn staple of science fiction, is two-fold: nobody (I believe I'm justified in using the absolute "nobody"} knows what is the "real" nature of time, and pretty much ditto for travel. Nevertheless, there are things we do know about time and we can define "travel" with some logical rigor. Unfortunately, once we start investigating the logical underpinnings of the concept of "time travel" we blow most s-f time travel plots right out of the water. ("Serves them right," notes Prickles.)

     In our experience, time is the record of a chain of consecutive observations. As somebody (Feinman?) once remarked (I paraphrase) "time is what keeps observations from occurring all at once" thereby making "observation" synonymous with "change" (from what was the case before observation to what is the case after). That distinguishes "before" from "after" and makes "after" contingent on "before". Hence the apparent one-way "flow" of time.

     But is "after" actually contingent on "before"? Could we not run the chain of observations in reverse thus "traveling" backwards in time? There are two problems with that. One is that every observation represents a "choice" from among a number (possibly very large or even infinite) of possible next observations starting with what is the case just "before" the next observation. After an observation has occurred, "after" becomes the new "before". To reverse the process, we necessarily start with this new "before" (formerly "after") and immediately there is another choice to be made among all possible next observations. But this time the one unique observation required for the exact return to the previous "before" must be chosen. That ain't gonna happen by itself, it has to be a conscious, intentional choice. That is not the case moving "forward" where the choosing can be random, subject only to the influence of the statistical probability of any given next observation. So traveling backwards in time involves a stringent requirement that forward travel does not.

     The other, probably insurmountable problem with reversing the "flow" of time, is that it may be impossible to identify the one unique observation that returns from "after" back to the same "before" that preceded it because of inherent and unavoidable errors and inaccuracies in locating the original "before". The "reverse observation" may land in close proximity to the original "before" but it is unlikely to land exactly there. These errors, however small, rapidly accumulate with each such "backward step in time". So it turns out that, rather than returning to the past, what is actually being accomplished by this process is the creation of a new future (one resembling somewhat the recent past but not for long). ("So back to the future?" asks Prickles. Ha ha.)

     Finally, what is usually meant by "travel through time" is not the one-by-one reversal of a chain of observations but an instant translocation from one place on the chain to some other place now in the past. (We won't even consider such translocations to someplace in the future because future does not yet exist except as a conceptual projection). Such instant translocation in time is equivalent to instant teleportation across a distance and there is no known mechanism for accomplishing either with large complex objects (reports of quantum teleportation notwithstanding). Furthermore, two things make achieving such a translocation unlikely: the impossibility of precisely identifying and locating the target location (which becomes more and more indefinite with distance either in time or space), and having to deal with instantaneous displacements of mass and energy at both ends of the translocation. Bottom line (according to Prickles): forget any ideas of becoming your own grandpa or ma.

     That said, there are physical processes that are actually perfectly reversible. They only occur on the scale of the most elementary observations. But that's another story... ("Good," says Prickles.)

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