Time Travel?

A bunch of smart people (with no other documented credentials) ventured their opinions in response to the question: Do you believe in the possibility of time travel, and if so, how would it be done? These opinions were printed in the 1997 July/August issue of the Mensa Bulletin. Only two of the responses mentioned the theory of relativity. Both of them were inaccurate. This column is dedicated to sorting such things out. I intend to explore the purely philosophical, the scientific, and both bad science and non-science. All of these will have their representatives here.

Bryan Dumka began by opining that time and velocity are related. So far, so good. Brian also gave a good citation that proves this surprising fact. Clocks were flown opposite ways around the earth. The one that travels with the rotation of the earth travels farther and faster than the one whose speed is against the rotation of the earth and is partly cancelled out by it. The clock that has traveled farther and faster is found to be slightly behind the clock that has traveled a shorter distance and therefore at a slower speed. This experiment proves that the faster something goes, the slower it “moves through time” (the more behind its clocks get).

Where Bryan went wrong was in saying that a slow space ship would travel into the past and a fast ship into the future, relatively speaking. This is not true. The fast ship “moves into the future” slower than the slow ship, but they both move into the future. In particular, neither ship moves into the other’s past. If they ever come together, the fast ship will simply not have aged as much. Its clocks will all be slow. Its people will all be younger. Strike one basis for the possibility of time travel.

Doug Sandorf also reported that time and velocity are related. But he went wrong when he extrapolated velocity beyond the speed of light. Bodies traveling faster and faster approach the speed of light as an asymptote. That means they never quite get there. As the speed of light is approached, it takes more and more energy to go the same amount faster. It would take infinite energy to reach the speed of light. Time slows down, but it never quite stops. Nothing that possesses mass can quite get up to the speed of light.

Doug went even further and said that an electron can lose its mass and travel as a photon at the speed of light. This has never been observed. It’s true that energy in the form of photons can be absorbed and released by matter in both nuclear and chemical reactions, but charge is a property that cannot be converted into photons. Electrons, accelerated to nearly the speed of light, get more and more massive, but they do not turn into photons. Strike two for using science as a basis for the notion of time travel.

Two of the Mensans were more philosophical in answering the question “Is time travel possible?” Marvin Cruzan said, “The answer is no … [our] view of time is an artificial, though useful, construct, but [time itself] is the result of the universe in motion.” Gene McDougall stated that “Time exists only as a measurement invented by man … Time travel is therefore impossible.”

Don Million, the editor of the column in which all this appeared, reported that the most common reason given that time travel is impossible is that we would have noticed time travelers among us if it ever did become possible. He also reported that, in his sample, opinions were divided 43 against the possibility of time travel and only five in favor of the possibility.

None of the ten letters published, nor in Don’s opinion any of the other 38 he received but didn’t print, gave any arguments that were truly convincing one way or the other. This seems unfortunate on the one hand, but it makes it that much more appropriate as a topic for this column on the other.

The notion that you could travel through time is based on two assumptions. First, it assumes that time is a measure (or dimension) similar to the measure of length (or a dimension of space). Second, it assumes that there is nothing fundamentally different about moving forward or backward in time, that if you can do one, you can somehow reverse course and do the other.

Consider taking a moving picture of some event and playing it backward. If the event is a two body collision, it might be impossible to tell which is forward and which is reverse. Many simple phenomena are symmetrical with respect to time. Consider, on the other hand, a high-speed collision inside a particle accelerator where atoms are literally smashed. This is how sub-atomic particles are discovered. Many of the pieces that result from such a collision are unstable. They decay into further pieces.

This sequence does not run backwards. In fact, when more than two bodies are involved, almost any interaction does not run backwards. Not always because the physical principles wouldn’t allow it, but because of extreme improbability. The direction of time is the direction of the probable. If you see unlikely things happening in lieu of the commonplace, you are looking at a film being played backwards. Real life ripples outward. Only a plan ever comes together.

Time is a measure of two fairly different basic phenomena. One is how fast things move; the other is how fast they repeat (velocity and frequency). Starting with the concept of simultaneity, you can relate two different speeds by measuring the simultaneous distance covered. Nature was kind enough to provide us with a natural speed constant: the speed of light. But, phenomena that repeat on a regular basis, such as sunrise in the morning or the occurrence of the full moon, historically the basis of our measurement of time, are not fundamental constants. However, some periodic phenomena do appear to be more fundamental, namely the frequencies of atomic vibrations. These have been put to work in our atomic clocks. Time is nothing more than relating one clock-like phenomenon to another.

Velocity and repetition are real phenomena. Motion through space is a real phenomenon. Collisions and interactions are real. Sequences of events are real. But, most sequences don’t play backwards. A sequence involving two particles? Yes. Involving three? Maybe. Involving a handful? Very unlikely. Involving billions? Not in a thousand lifetimes of the universe. Imagine taking sixteen billiard balls scattered all over the table and imparting to each one the exact velocity required to bring all of them together into a triangle at the same moment, perfectly at rest, and have all of their momentum carried away by a single ball, the cue ball. We do this all the time in reverse, but this simple sixteen-body problem will probably remain forever beyond our technology.

Imagine that you could go back in time. The implications are horrendous. Imagine moving back in time just an instant. You would now re-occupy the same space with your former self! Imagine moving back in time a lot. Your matter would cease to exist in the here and now and it would be “created” from the point of view of anyone in the past. In both cases, the principle of conservation of matter and energy would go out the window.

Finally, there is the classical “time paradox.” If you could go back in time, then you would have been in a position to do something that could have prevented your own birth. Certainly, travel backward in time would enable the past to be changed right out from under the present. These are convincing arguments that you can’t go back in time.

So, if physically going back in time is out of the question, we are left with going back in some invisible, incorporeal form. We would establish no presence there, but could we somehow channel information directly out of the past? Once reality has passed through the paper shredder of time can entropy be reversed, bypassed, or negated somehow? Can the shreds be put back together? It takes energy to transmit information, and matter to make a recording of it. Our scientific understanding of the invisible and incorporeal is simply nonexistent. We can prove the possible with a single example, but impossibility can not be demonstrated by the lack of one. The emperor’s new clothes are a hoax! The only logical conclusion I can find is that time is inconsistent with the very notion of travel, and the question of time travel is therefore incoherent at its roots.

One of the Mensans in favor of the idea of time travel, Madelyn Chapple, said “Of course time travel is possible … [but] we will travel only as observers … It will be much like dreaming. In fact, maybe dreaming is time travel.” Perhaps we should admire this free-spirited speculation over the use of bad science. Like the emperor’s clothes (you can’t see ‘em, but they’re there!), her statements are irrefutable. This becomes possible when you side-step science altogether.