Today I watched two episodes on TV that dealt with time travel. The first was Charmed's "Cat House" and the second was Stargate Atlantis's "Before I Sleep." I only realized this after my nitpick with the second made me think of the first. Let me explain.
In Charmed, Piper and Leo are in therapy and Piper casts a spell which lets them literally relive their memories. Unfortunately, her sisters, their familiar and a warlock also get sucked into the time traveling spell. During one of the memories, the warlock steps on the bride & groom figurines from the top of Piper & Leo's wedding cake. The figurines had been on a shelf in the present, and after he stepped on them, they disappeared. Going back and reliving a memory altered the present and that which was destroyed no longer existed in the "new" present time. Based on all the shows and movies I've watched that included time travel, this makes sense to me.
Which brings me to Atlantis. Can someone who understands all this stuff better than I explain to me if what happens in Atlantis is possible (should time travel be possible)?
On Stargate, Dr. Weir and crew find a 10,000 year old woman, who ends up being the same person as Dr. Weir but who had traveled back in time to the time of the Ancients by way of a time machine. Here's how it happens: the Stargate crew gets to Atlantis but most of them drown because the ancient technology doesn't hold up. Weir ends up in a time machine that takes her back to the time of the Ancients. While there, one of the scientists fixes the settings to adjust for the problems Atlantis would face in the future. He also puts Dr. Weir in a stasis chamber to sustain her over the time period during which she would need to switch modules to keep the power going (10,000 years until her crew arrives).
Dr. Weir going back in time changes the past and changes the future. While the technology changed so that Atlantis would survive when the Stargate crew arrived, there would be no guarantee they would even come, that it would be the same people or that anything would be the same. But let's put that aside. Let's assume that the changes made mean that the crew survives. They exist because, due to the technological changes, their deaths didn't happen. That alternative past doesn't exist because the circumstances that gave rise to it don't exist. That makes sense to me.
Here's what doesn't make sense in my mind, and kept me from enjoying the episode as much as I could have. (I know, suspension of reality in TV, but this kept bothering me!) Dr. Weir in the original landing goes in a time machine back in time. How can she exist in the "second" coming of the Stargate crew when she is in the stasis chamber? Are we supposed to believe that everything happened in the normal way and another Dr. Weir grew up in the future and went on the Stargate mission while the other one languished in the stasis chamber in Atlantis? How can she exist in both the stasis chamber and the present time?
Writing this out, it seems like it makes a little more sense to me than it did when I was thinking about it before this post. Before, I couldn't see how she could possibly exist if she went back in time and existed there. But I guess maybe if you think about that as an alternative universe thread (like how they tried to explain it away), maybe we could think that the rest of her lineage would continue along as it would normally and there could be a second Dr. Weir that exists at the same time. But how can they exist together and actually be the "same" person? Maybe it's like the "original" Dr. Weir doesn't exist for the purposes of the present? I'm confused.
Help me understand! :)
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There are generally many many problems with time travel, especially as depicted in pop culture. I won't mention Charmed right now, though.
For Stargate, one way to view it is that for Weir, time progressed linearly. The specific point in absolute time that was her 'present' experienced a jump when she went back, but her perception would be that time was progressing normally. A watch that could track both date and time would have worked normally and have given a time of roughly year 12,000.
The biggest problem I have with these things is that in existing back then, in some sense she would need to have always existed back then. In which case it seems it's basically arguing that things are predestined, since for it to be possible for her to have existed then, in any universe, she necessarily needed to be born and go through a path in life that would have put her on a course to go back in time. That means things like the particular sperm and egg that created her (and all her ancestors) needed to be guaranteed to meet and have the exact same mutations in her development, along with tons of other world events, etc. That also seems to say that going back in time doesn't really end up changing anything since it necessarily happened already anyway.
But more, I'm not a huge fan of predestination (even though I think there's a reasonable chance that if you know the exact state of everything in the universe, you may be able to argue that things are deterministic from there...luckily, it's impossible for anything in the universe to have such knowledge).
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