I have a collection of thoughts I carry around in my back pocket that simply fascinate me about reality as it is. And like a ball of string, when I come across a thread of 'knowledge' or 'insight' I add it to the thought. Eventually some of these aggregates reach critical mass and I just have to talk about it. I think this is one of those, and it hooks with the previous phasor post on how our self-ish-ness informs sci-fi representations.
Time travel is an interesting concept. I will not be addressing the whole possibility of it, just one part. The part of where you are when you travel. Have you ever seen the old movie "Time Machine?" A guy had a cool sled with a big roulette-wheel looking thingy on it that would spin. There was a recent remake of the movie that included, I think, Jeremy Irons.
What I liked about that movie is that the machine had an extent of atmosphere around it that would travel with it. A bubble of sorts. The movie took into account geologic activity. When the hero went back in time sometimes he was surround by rock because a nearby erupting volcano covered there place where he was traveling through with lava. As accelerated time went on, we saw the rock erode away from rain etc... I always thought that was spot on.
Some of the sci-fi and sci-fact presentations of time travel represent time as fourth dimension, and posit the possibility of moving in that dimension while the other three remain fixed. That's fine. Keep your same position, just slip down the time axis to earlier or later. I'm cool with that. ...then I started thinking a bit more.
Nothing is still...ever. Of course relative to another object there can be stillness. But time travel presumes an absolute reference frame and in that respect nothing is ever still. Consideration of this stacks up pretty dramatically. Yes, you are sitting still in front a computer reading this (thank you). But...
- The surface of the Earth moves something like 300 miles an hour (depending on your lattitude).
- The Earth orbits around the Sun at something like 67,000 miles an hour.
- The Sun orbits the center of the galaxy at around 490,000 miles an hour.
The point being if you traveled even a few millseconds back in time keeping your current, absolute, position in space, the Earth, and certainly your postion on it, would be far gone. Most likely you would be in space. You most certainly would not be on the same cozy point of this mad pony ride we call Earth that you started from.
It seems that all sci-fi representations of time travel I have seen ignore this fact. They presume, that somehow, the laws of physics let you travel back in time but keep you tethered to your relative, madly changing, location.
There's a lot of relatavistic aspects of this thought experiment I could probably delve into, such as the effects of inertia, but I think the summary outcome is still the same. You might envision a way to slip up and down the time axis, but everything will have moved on (or not be there yet) when you arrive in a new time.