Time Travel Is Not Possible or Is Near-Impossible to Detect With Current Methods

Time travel is fun to think about, in part because the argument structures involving its effect on the world (if it were real) appear in other kinds of discussions. I'm posting this now because of the fun study that Nemiroff and Wilson did, looking for evidence of time travelers by finding evidence online of people making references to events before they occur. They did not find any such evidence; publication here.

To address the burning public interest in their project, they did an AMA on Reddit, and when asked "Did you receive federal funding for this endeavor?" they responded "Yes. We used funds left over from our study titled: 'Does Tax Payer Money Burn Any Better Than Regular Money?'" (They really did say that but went on to clarify that the real answer was no.)

Let's say time travel in the Back to the Future sense is real. Say that if you go back to the past you can change the present to which you return (no boring branching timeline stuff.) And say that if you remove something from the past, it disappears until you carry it to the present. That is: imagine you have sentimentally precious heirloom silverware. No you don't! I took it from your grandmother when she was a young hottie, and when I get out of the time machine to give it back to you today, you look blankly at me and say "Why are you giving me old forks?"

If that's how it works, shouldn't we expect commodity runs on everything? That is: you realize that gold is valuable. You go back to the pleistocene before people valued it or knew how to pull it out of the ground. You bring back a whole consortium of miners and investors with you, running around the world pulling 50% of the shiny yellow stuff out of the ground, all to the bewilderment of frightened hominids, hiding behind rocks as they watch the incomprehensible doings of these new hairless creatures. You come back to the present and - bammo! Yes the value of gold falls in half overnight, but you still have 50% of that. 25% of the total previous gold market is still nice.

No you don't! Because unless time travel dies with you and your investors, people from YOUR future will sabotage you and take it for themselves. And from their future...and their future...etc. What this means, in economic terms, is that if this kind of time travel is real, then of course it's already happened, and people furthest in the future have perfect information about everything (100% efficient markets) which means everyone has it. Or, that no one has it, because there's no stable reality. (Remember when Bill and Ted said "remember to do X in the future" and got out of a jam? Why can't their enemies say "remember to stop Bill and Ted from doing X"? And so on and so forth ad infinitum. Neither Bill and Ted being the good guys or writers not being able to think their way out of a plot problem can count for your answer.)

So we have either
a) a totally efficient market with everyone knowing the allocation and value of all items throughout time
b) a constant maelstrom of shifting reality

If it's a., the fact that we still see things with apparent value around us instead of in the Big Commodities Exchange at the End of Time (or that we're not getting invaded by people from the End of Time looking for causal high ground) means either that everything "has already happened in order" (the simple Douglas Adams model of time travel), or that time travel of this sort is not possible, or that nothing has any value in a 100% eternally efficient market. (It also means no free will, because we're basically all just watching ourselves in a movie then.) And here's where things start to track other arguments. Here we run into an argument familiar to Singularity buffs, simulation argument maniacs, and Fermi paradox jocks. And it's basically this:

X appears to be an arbitrarily powerful process not provincial to humans. We look around the universe and we do not see evidence of X dominating everything. Therefore, either X is not powerful, or we can't see it, either because it's not see-able (to us), or we don't know what to look for.

Fair enough, except it's very difficult to tell the difference between "it's not see-able (to us)" and "I'm a snake oil salesman insisting that you believe me without evidence". That's also called a PEP, a Pointless Epistemological Problem (see #3 here). Fans of politics, religion and marketing will find these sorts of claims familiar.

Returning to time travel for a moment: the fact that aliens have not used time travel (rather than measly space travel) to visit us (and beat us up!) suggests (again) some combination of: there are no intelligent aliens; we are of little interest to future galactic events because we are boring, weak, or go extinct soon; or that everyone is nice to each other forever. Boy, talk about unrealistic!