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Time Traveler Beware!

(Brief essay on Time Travel Paradoxes)
by Henry Tjernlund
Jan. 29, 1998

One night while lying in a vain attempt to fall asleep I had a sudden realization. The most common argument against time travel is the problem of reverse causality often referred to as the “grandfather paradox.” This states that if one were to travel back in time one could through murder, or other means, prevent oneself from being born in the first place. Thus the argument conclude with the question of how you can do anything, let alone travel back in time, if you were never born.

My “sudden realization” is that once you go back in time and appear in the past the universe doesn’t care where you came from. You simply suddenly exist at that point in time no matter the reason. Your “causality” connection with the future is severed. You can do whatever you want including murdering yourself at an earlier age or even preventing your birth without any paradox occurring. You will continue to live out your life amongst the changes you have made. Your specific past will be memories that only you will have. You will simply be a person that suddenly appeared in the universe with “memories” of a future that will never be.

However, there are other problems with the idea of time travel.

Let me describe a time travel scenario. Imagine we do have a time machine with a chamber or “transported pad” from which we send our ourselves back in time. I see a bigger paradox, not from going back into the distant past, but from going back into the recent past. In fact I speak of the immediate past. Just to keep the argument manageable lets say we set our time machine to send us exactly one second back into the past. The problem of two of us occupying the same space should be immediately obvious and would likely create quite an unpleasant mess. But let us entertain ourselves further and allow a safety feature such that we would travel one second back in time to appear directly “beside” ourself.

So exactly one second before I push the “button” another one of me appears beside me in the chamber. Which means that at the moment I do push the button there are two of us in the chamber or standing on the transporter pad. So now both of us go back in time exactly one second. See the problem?

You can argue both ways for the results being that either three or four of us are now in the chamber, or on the pad, exactly one second before the original me pushed the time travel button. Of course the above process will repeat again and in this loop the number of copies of us will grow either linearly, or geometrically, depending upon how you want to argue. Either way the point is that the machine will have the effect of duplicating me to the capacity of the chamber or pad. And this will all happen “instantly” because we keep looping back through that same one second each time with more and more copies of us on each loop. Talk about mass production.
And this “mass production” is a serious physics problem. Suddenly all this mass would have been created out of nothing violating any such law of conservation. Unless of course the conservation of mass is more just a “suggestion” than an actual physical law of nature.

Anyway, the chance that I would just somehow safely appear off to the side of myself is unlikely. So if you do manage to build yourself a time machine be sure to double, or even triple, check your time destination coordinates or you may meet an unpleasant demise as you reach to press the activation button.