Sorry for the extended delay. Long, stupid story. I temporarily relocated when the remnants of Hurricane Patricia came through town (I hate storms), and then I was having some minor computer troubles for a little bit. It's all back situated now. The "electroshock" line in the last panel on this page was a reference to something Abby said two pages earlier (can't blame you for not remembering, as I've been slow with the updates lately).
I got more than a little bit carried away writing this next science blurb. I wanted to try to explain the significance of light speed in some depth, but I also may have condensed some things down too much because I really want to avoid being overly technical. Of course also I should remind everyone that I'm not an astrophysicist, so my explanations are probably not all that reliable. Use at your own risk, and all that jazz.
So we all know that the speed of light is the fastest anything can travel. But why is that? Well first of all, let's look at the theoretical aspect…
Why “light” speed? Well, that has to do with mass. An object's mass is its ability to resist being accelerated. To overcome an object's inertia – its rest mass – you need to apply force, and to move it faster, you need to apply more force, and so on. That's easy enough to understand, nothing weird going on there. However, something with no mass (or zero “rest mass,” to be more precise) has no resistance to being moved. Unimpeded, it will travel at the maximum velocity allowed by the universe. So, do we know of anything in the universe that has zero rest mass? We do. Photons have zero rest mass. And so photons – light – travel at the universal maximum velocity in a vacuum and require no added force or energy to do so. There are fundamental reasons for all of this, relating to the Higgs field and Minkowski space, but for this science blurb it's not necessary to get into any of that.
Okay, so that sort of explains it… but it still sort of doesn't. Okay, fine, in theory photons travel faster than anything with mass can, because they have no inertia. Buuuuut photons have a finite speed. They “only” travel at about 300 million meters per second. They don't travel instantaneously, so surely if we built a fast enough rocket ship, we can go faster than a measley 300 million meters per second, right? Right?!
But unfortunately the answer appears to be “no.” Weird things start to happen as you approach light speed. Your mass increases. There are mathematical reasons why this is (the speed of light remains constant, so your mass increases to compensate for increasing velocity in order not to violate conservation of momentum), but you don't really need to understand them; just understand that it's a real thing that happens. As you become more massive, it requires exponentially more energy to achieve even an incremental increase in speed. Ultimately, as you get very close to light speed, your mass becomes near infinite, and even applying all the available energy in the universe would only nudge you just a little bit faster… and you'd still be short of light speed. There isn't enough energy in the entire universe to accelerate even one electron to light speed. Nothing with mass can go that fast, and the mass increase would cause it to collapse into a black hole if it got anywhere close. But the problem goes beyond “just” this engineering dilemma. There are very fundamental – and very strange – barriers stemming from the nature of space and time itself.
Time dilation is a real thing. We account for it in our GPS satellites and it causes astronauts to age more slowly than the rest of us. Explaining the how and why of time dilation and special relativity is way too big a task for me, but basically just know that the faster you travel, the more time slows down within your reference frame. It's a wacky but fundamental aspect of how spacetime works, which we generally don't notice in our day-to-day lives because we don't operate at anything close to relativistic speeds.
I said earlier that light doesn't travel instantaneously. That is actually not true, within its own reference frame. If you travel at the speed of light, time effectively stops for you. Your speed is, for all intents and purposes, infinite from your perspective. If you traveled across a billion light years at light speed, it would seem instantaneous to you, even though once you arrived you would find that billions of years had passed in the interim. It's not very intuitive, but this is one of the reasons why it's almost definitely not possible to travel faster than the speed of light. Remember, the faster you go, the slower time moves to compensate for it, and at light speed, time is completely stopped. You can't go slower than zero. If you were to travel faster than light, you would perceive yourself to arrive at your destination before you even left. Time can't go any slower if it's stopped, and your perceived travel time can't be any faster if it's instantaneous. So light speed is the maximum speed that anything can happen because it is, effectively, infinite speed as allowed by the wacky conservation rules of spacetime.
Last, an illuminating illustration. Above, we have a fictional star system with multiple stars orbiting a monster black hole at a distance of several light years. Now, for the sake of argument, lets say something bizarre happens and the black hole instantaneously evaporates, or collapses into an alternate universe. Whatever the case, it vanishes. It's no longer there to exert a gravitational influence on the stars. Do they immediately begin floating away? The answer, oddly, is no. They'll continue orbiting the black hole for years after it left, because the event of the black hole leaving effectively hasn't “happened” for them yet. It can't influence them faster than the speed of light. Astrophysics is weird.
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