One of my favorite daydreams is of being able to travel back into the past – my past – and visit again the places and people that are now gone, as well as warning my younger self of what lay ahead, and of what decisions I should make. Whether my stubborn, self-destructive younger self would listen is another question, but if I had one wish granted, that is what I would want to do! I can identify several decisions in my life that changed its course, most not for the better. In the multiverse or parallel universe theory, that moment where I decided saw a divergence in my timeline, where in one timeline I decided “Yes”, and my life turned out very differently than in the timeline where I decided “No”. So perhaps I can take a peculiar comfort in that my self in a parallel universe might be successful in her life, unlike my self in this timeline!
Time travel to the past in this timeline may not be possible as it would violate causality, and there is no historical evidence of hordes of time travelers visiting past events. Thus, if one could travel back into the past, you would be shunted into a parallel universe, and perhaps be not likely to return to the one in the timeline you left; not an appealing prospect! The book by Michio Kaku that I mentioned in my 29/6/2009 entry, Physics of the Impossible, goes into detail about this, and the multiverse theory is one he finds the most plausible, as described in this interview, “Things We’ll Probably Never See”, NYT, 27/3/2008.
“I call [time travel] a class Ⅱ impossibility, that might be realized centuries or millennia from now. Einstein’s equations, believe it or not, do allow for time travel. But there are still problems with time-travel devices. First of all, energy. Michael J. Fox put plutonium in a DeLorean and rocketed back to the 1950s. You can calculate that plutonium is not enough. You’re talking about the energy, basically, of a black hole or a star. The next dispute is stability – how stable are these time machines? If you go into it, will radiation kill you? Will it close up as you enter it? Now the question of the paradoxes comes in. If you do send an object back in time, what happens if you alter the past? What happens if you shoot your parents before you’re born?
My favorite solution is the many-worlds theory: when you go backwards in time and you save Abraham Lincoln from being assassinated, you’ve actually saved someone else’s Abraham Lincoln. Your past cannot be changed, and you’ve gone to a parallel universe. If the river of time forks into two rivers, you hop across rivers after the fork. Another interpretation is if you go smoothly into the past, you fulfill the past. You didn’t alter the past – it was meant to be this way. And the third interpretation is, I think, the most implausible: you go backwards in time, you’re about to pull the trigger to kill your parents before you were born, but there’s something preventing you from doing it. For example, there’s a law of physics, called gravity, that says you cannot walk on the ceiling. You may want to walk on the ceiling but you can’t do it. Igor Novikov envisions a law of causality that works like this. I tend to disagree. How would you devise a law of physics to prevent causality change when anything can change causality? Just by the fact that you’ve entered the past, you’ve changed the weather pattern. You changed the objects around you. I don’t see that as a very strong possibility.”
This theory is disappointing, though; I want so badly to go back (obsess about it), because my present-day life – the way it has turned out – is a total failure. I occasionally have dreams about this, where I am able to jump back to my past, and the memory of that time is vivid. A dream I recorded for 18/9/2006:
Last night I had a rather vivid dream that I was able to travel back in time, back into my past. In the first jump (I did it by holding something like a rock in my hand and jumping into some sort of cloud) I went back to 31 December 1988. I was outside my parents’ home and saw Dad. I told him I had come from the future. We had a conversation. I then jumped onto the garage roof (it was late afternoon as the sun was behind it) as I prepared to jump back further. I landed in 1998 in my bedroom (there was a desk and computer there, though I didn’t have one then), realized it was the wrong year, then jumped back to 1980 in my home. I woke up then.
Another related daydream, that is closer toward using magic, is of being able to transport the mind I have now back into the mind of my younger self, so that my older self – that has knowledge of my past – could guide my younger self toward making wise decisions, and thus avoid the dismal future I ended up in. I hate my pointless existence, hate the way the world is now, but death is the only way to escape it.
The world of quantum mechanics is bizarre. It exists alongside what we perceive as reality, yet the two worlds do not usually mix; reality rests on top of the quantum world rather like oil on water. Unlike predictable surface reality, in the quantum realm a particle can be in two places at once, or an object can be both alive and dead (before observation makes it decohere into one condition or the other). Maths and physics were, sadly, not my talents at school, so the complex mathematics involved is well beyond my understanding (I can only comprehend the “science for dummies”-type books).
