Making Time Travel Consistent: part 1
In the previous post, I gave you a little teaser about my next writing project: The Causeway. One of the difficult things about writing a story about time travel is the issue of consistency. Time travel is difficult to write about in any way that makes sense. It jumbles up cause and effect into an unintelligible mess, and has a tendency to leave readers passed out in the fetal position, hands fiercely gripping the sides of their head.
What I wish to do in this space is slowly work out my thoughts on the mechanics of time travel in a way that will (hopefully) make sense, or at least be consistent for the purposes of my story. This will be done in a series of posts, tackling one item at a time.
I will not dwell on the specific technology that would be used to implement time travel (more specifically, closed timelike curves that can interact with our normal, causal world,) but on what mechanisms known to science today can be used to explain its possibility.
Item 1: All observations are local.
This is a principle that is easy to ignore when speaking of the so-called paradoxes of quantum mechanics and special relativity. When you see an object (say, a semi-truck bearing down on you), what is it that you really see? You do not see the truck itself, for it is far away and is not directly in contact with you (at least, not yet.) What you see is the image of the truck projected onto your retina. Photons bounce of the surface of the truck, pass through the intervening space, are focused by the lenses in your eyes and strike a screen in the back, slightly altering the nerves there. Electrical signals are then sent to your brain which then interpret what type of object the photons came from, as well as some rough information about how big it is, and what it is made of. Successive bursts of photons hitting the back of your eye can give you more information about your oncoming doom. You can now determine how fast it is moving, whether or not it is slowing down, whether it is coming right at you or is beginning to veer away.
Your eyes (and the part of your brain that processes the incoming information constantly streaming into them) are a fantastically complex and effective bit of measurement and interpretation machinery. They are not, however, perfect. They only have so much resolving power (limited by how many photons can be shoehorned into your eyeball at any given time,) they can only see photons of specific wavelengths, and they require time to process the information input. Much information is thrown out by your brain, leaving you with a highly stylized picture of what is bearing down on you.
In principle, we could make better measuring devices. (And in practice, as well. There are telescopes with much greater resolving power than our eyes, which can see different parts of the electromagnetic spectrum, and can interpret the data they receive into cool, three dimensional false color graphs. See the images taken by the Hubble Telescope, for example.) But every measuring device works essentially the same way. The object being observed sends out “messenger particles” that travel the distance to the measuring device, and the measuring device then measures some properties of these particles: their wavelengths (or equivalently, their energy), the direction it came from, how that direction and energy relates to the direction and energy of all the other messenger particles hitting it, etc…
All we ever really see are the messengers.