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
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
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
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