Loving a good argument, I played devil’s advocate.  “I disagree.  By having this conversation, I won’t need to have it with myself again, since I’ll already know what I said on both ends.”

    “Wrong.  My first rule of time travel:  If you interact with yourself, you must repeat all interactions to keep the flow going.  The interaction doesn’t have to be repeated exactly, but it has to occur.  When you are on the other end of this conversation it may be very different, but you still have to have it unless you undo it on another trip, in which case you still have to make that trip.”

    I nodded dumbly even though I was lost.  Older me continued.

    “That’s the reason I asked when you got injected, so I could know when I have to go there and do it.”

    “You’re saying you never injected me?”

    “I didn’t.  Another me did.  But I will.  I just did it in the wrong order, but you can do it in the right order when you play this end, tidying up the flow a bit.”  He stopped his soliloquy, noticing my vacant stare as I smiled and nodded back at him.  “Does that make sense?”

    “Not at all,” I confessed.

    He exhaled a silent sigh and tried again.  “You now have the ability to travel in time because you went back in time and gave yourself that ability.  Therefore, you must go back in time at some point later in life to give yourself that ability again, or else you never would have gotten the ability, and you’re caught in the loop of paradox.”

    I was sure I was wrong, and was not afraid to tell myself.  “I think you’re already in a paradox.  I mean, how did you get the ability to give it to yourself the first time?  It had to start somewhere.”

    “Suppose we were involved in the discovery of time travel, using people as lab rats in a slew of experiments over a period of years before finally getting it right.  Learning from our mistakes, we decide it would be better for everyone’s sanity if this ugly episode never happened.  So I go back in time to before the experiment and give you the ability to travel in time.  From that point on you can do everything differently from what I did so long as you still go back to give yourself the power.  The early experiments are pinched away as if they never happened, but we get to keep the time travel.  Paradox is avoided, and everyone wins!”

    I was still confused on the whole picture, but had to admit it was getting better.  “I think I understand.  You want me to try not to forget about what hasn’t happened yet?”

    “Theoretically.”

    “Then how did we invent time travel?  Did the experiments never happen, or just never happen to us?”

    “That example was hypothetical.  Also, I said we were ‘involved’ in the discovery, not the actual inventor.”  He gave me the same knowing look I was fond of giving before continuing.  “Any more questions?”

    “What did you mean when you said I’d ruin everything before?”

    “Where were you going?”

    “To find you on the day we met.”

    “That would have ruined everything, since you can only go to the same time once.”

    “So I wouldn’t be able to get there?”

    “No you would, since you’re younger.  But I wouldn’t, which would mean I didn’t, which would mean you couldn’t, which would be the big bad paradox.”

    “Why can’t you visit the same day twice?

    “I don’t know.  It just doesn’t work.”

    “But that doesn’t make any sense without a reason.  You should be able to.”

    Old me was becoming impatient.  “Of course you should be able to, and maybe one day we will be able to.  Time travel is still in its infancy.  Once upon a time we could transmit audio signals through the air but not video.  Video was finally figured out, but for the first few years you couldn’t do it in color.  I’m sure everyone will be making repeat trips in time someday, but as of today we cannot.”

    His analogy was reasonable, but I wanted to continue debating. “But if that ability was developed in the future, couldn’t you just go back and pass it on earlier?”

    “I suppose that would be likely.”

    “So since that hasn’t happened, that would mean it never will.  Right?”

    He sighed again, less silently than before.  “I don’t know, but I wouldn’t necessarily want to find out. The inherent risk in disproving the theory is far too great.”

    I gave him a look of half confusion and half fear, still not fully understanding how this worked.

    “Don’t dwell on it too much.  Bottom line is to just be careful.”

    Though not the answer I wanted, it was good enough for the time being. 

    “So, what’s next?  How do we save our sister?”