Wednesday, January 04, 2006

The Lack of Time Travelers is Disappointing

Back in May, 2005, MIT hosted a Time Traveler convention, inviting any future time travelers to come back in time to attend their convention.

No one showed up.

Or at least, no verified time travelers showed up. Although there were plenty of attendees, none claimed to be an honored guest.

It wasn't until I had too much time on my hands this last week to be alone with my thoughts that it occurred to me that this is disappointing.

The question "If time travel to the past were possible, then where are the time travellers?" is a variation on the Fermi Paradox (If there exist technically advanced alien civilizations, then why haven't we met them?).

Categories of explanatory hypotheses for the Time Traveler paradox are:

  • a) Time travel to the past isn't possible

  • b) Time travel to the past is possible, but

    • b1) no evidence exists because the time travelers are exceptionally good at keeping a secret

    • b2) once one person goes into the past, the timeline is altered

    • b3) the travel can take place only to alternate versions of our universe (multiverse theory)

    • b4) humans never reach the point where they invent this technology

a) Time travel to the past isn't possible. It's tough to prove a negative, so we should keep attempting to "invent" time travel to prove this idea wrong. But this is the likeliest explanation, as you'll see when we examine all the ramifications of the (b) path. And this would be disappointing, because it would mean that there are limits to what we can accomplish, even with infinite time.

b) Time travel is possible. This would be interesting, and cool, if true. But the fact is that we haven't had anyone claim to be from the future in a verifiable way (ie, they regularly make accurate predictions as to events yet to come). And this would tend to discount the variants of this path.

b1) Time travelers are exceptionally good at keeping a secret. Please. There hasn't been a human being alive that could keep a secret that well. Even Deep Throat had to speak out from his death bed to let everyone know who he was. The trouble with just about every conspiracy theory is that in order to encompass more than a couple of people, it has to assume that every single soul in a large group of humans can keep from bragging about "I know something that you don't". Historical evidence weighs heavily on the fact that nothing stays a secret forever. Therefore, if we have had time traveler visitors in our past, the odds are that someone would have talked by now.

I'll grant you that if there have only been a couple of visitors, and only a few visits through history, it is possible that any leaks would have been disbelieved and lost. But this brings up a different problem, which is coming up with an hypothesis as to why, in however many millions of years that exists after time travel is invented in the future, only a couple of visitors ever took advantage of it, and only for a few times? I can only think of a couple decent ideas, which leads us to

b2) once one person goes into the past, the timeline is altered. If there is only one timeline for this universe, and time travel is possible, then this might explain why we haven't heard about any visitors. As I said above, one visitor's single visit could easily go unnoticed, even if they did blab. (Cassandra?) However, if such a visit alters the timeline, then it is statistically unlikely that the timeline would include the invention of time travel and the use of it by that same person. Which means that if time travel is ever invented again, it would be by somebody else, and the first traveler would be somebody else.

If the second traveler went further back in time than the first, then the timeline with the first traveler will no longer exist. so unless every subsequent time traveler only goes to a time after the first one (which eventually gets to be impossible, since you run out of timeline), then inevitably there will be time travelers going back to points in time prior to those visited by "prior" travelers. (The terminology is hard, since english isn't designed to deal with the concept of time very effectively).

So if time travel exists, and was invented and used, then eventually there is only one timeline that would settle out and be stable. This timeline is one where some single time traveler went back in time and no time travel was invented again after that time. Even if the invention of time travel "happened" multiple times, the first time history was altered to the point where time travel wasn't ever invented again, you would have this version of a timeline, "forever onward" so to speak.

So, if there is really only one timeline that can exist, then the only versions that can exist are either one where no time travel was ever invented, or one where it was only invented once and used once. I suppose this is a possibility, and would explain why we haven't heard from anyone travelers. But once again this is disappointing, because it means again that there are limitations to what we can accomplish in the future.

b2) However, say there was more that one timeline. In the many worlds theory of quantum mechanics, our entire universe is just one of an infinite number of universes. Each universe differs by the outcome of a quantum event, where there is a different universe for each of the possible outcomes.

Without doing the math, trust me that this is a lot of universes - more than we can reasonably imagine. And a side effect of the multiverse theory is that there can be universes "right next door" that represent everything the same way as this universe, except that there was a series of quantum events where you were translated from this universe to that one. (This is so because, if time travel were possible, and anyone ever did travel to the past, then there would have to be a version of the universe where this happened, and one where this didn't happen as well).

So perhaps we're just stuck in the one where this didn't happen. And even if we invent time travel in this timeline in the future, and use it to travel back to the past, then the universe we're traveling to is a different one than the one we're living in (since in this universe, no one magically appeared in the past).

But the odds are really against this, because the number of universes where time travel could be invented, and the number of times people would travel to other universes, is dramatically bigger than the instance of a single universe where this never happened. (like 1/infinity). So if the multiverse theory is true, then it is disappointing, because it means we're living in a real backwater universe, out of the mainstream of universes. And living in Podunk Universe is disappointing. (Although I suppose I could take some hope in the fact that, if we really are living in the one single one-in-infinity chance universe that has never had a time traveler visitor, we could still invent time travel in our future, and travel back into the past by visiting one of the other universes in the mainstream...)

But one-in-infinity odds are about as slight as odds get, and those are the odds that this explanation is correct. Which leaves just one other explanation...

b4) Humans never reach the point where they invent time travel technology. This could happen for any number of reasons (we go extinct before we get there; we have a catastrophe that doesn't make us extinct, but we regress too far technologically and since we've used up most of the readily accessible energy sources on this planet, we can't ever crawl back up the technology ladder again; the beings who invent and use time travel look nothing like us, so any visitor isn't one we would recognize or interact with).

Regardless of reason, it would be very disappointing if time travel really were possible, and humans never reach the point where we can invent and use it. Disappointing because most of the reasons that explain why we don't get there are not really attractive to me, as a human being.

So...having given this all of an hour's thought, it is possible that I missed some possible explanations for the lack of known time travelers in our past that are more optimistic.

If you can think of one, please post a comment - I'd love to hear I'm wrong on this one.


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