Right, people, Time Travel Basics.



Like many college professors these days, I find myself having to teach you guys these basic concepts that you really should have mastered already in high school.
Still, I have to face facts: Enough students are having trouble building their Time Machines in this year's class that I thought you all might benefit from a quick review of the basic concepts involved in Time Travel. So I've taken a listing of so-called "Timespeak" from the NOVA Online web site and made dozens of very possibly illegal copies of it, so that I can hand them out after class. The NOVA listing provides a cursory introduction to the basic terminology in the field. Meanwhile, as you see, I have the wordlist in question projected on the unnecessarily huge screen before you by means of this rickety overhead projector. I had asked the A/V department to provide me with a computer and PowerPoint, but they apparently couldn't be bothered. But then what can one expect? When one's own colleagues in the Department treat you like some kind of Mad Scientist, you can scarcely expect the rank-and-file to show you the requisite respect.

(Mad am I? I'll show them who's mad! Why, I'll, I'll... I'll travel back in time and show their young selves that I was right about time travel -- or rather that I was eventually GOING to be right about it. Mind you, that will be a "tough sell," so to speak. For starters, I'd have to introduce myself as a denizen of the future and then give them each a quick a priori history of their own upcoming life in order to provide a context for the "gotcha" revelation that my very presence before them would constitute, if they had but the intellectual capacity and the background information to realize it. But what precisely should I say to them?



It's the sort of thing one better practice before they hit the big green "start" button on their Time Machine, that's for sure. Let's see, I could say:



"Well, if it isn't the eminent Dr. Paisley, the renowned university physicist who took such a dim view of my Time Travel ideas!"



No, that's no good. First of all, I don't know precisely how old (or rather how young) my colleagues will be when I meet them in these new space-time coordinates (given the fact that my Time Machine has a margin of error of as much as 5 years when it comes to landing on any specific date), and I don't want to scare the probable munchkins away before I've even had a chance to taunt them for their future stupidity.



I can see me now: "Well, if it isn't the eminent Dr. Paisley!" And the now-pint-size Dr. Paisley will be like: "Stranger Danger! Stranger Danger!"



Maybe I could get a job teaching the lot of them Physics in a local high-school, and then slowly, class by class, lecture in such a way as to ultimately make them aware of my real identity.



Of course, there's always the chance that I'll teach my future nemeses something that could change the very future from which I myself have just come, rendering my return thither problematic at best! But then I'm sure that Stephen Hawking's hypothesized Chronology Protection Law will kick in just in time to save me from getting hogtied by some logical paradox or other. Mind you, Stephen better be right about my inability to change the past, or my spacio-temporal keister will be cooked!)

Time Travel Terminology:

Absolute space: Our old friend Isaac Newton was wrong, gang. There is no absolute space, thank you very much. So as you're building your Time Machines this semester, remember the mind-blowing corollaries to this fact: namely, that there is no absolute time, length, or even rest. Talk about "no rest for the weary": there's no rest, full stop, period, end of discussion, do not pass go, do not collect $200! (Absolute space, indeed! Perhaps it was an object heavier than an apple that hit the old boy on the noddle outside of his Lincolnshire home in 1666. In retrospect, one wonders if Isaac wasn't sat under one of Gary Larson's "anvil trees" when he had his conceptual breakthrough viz. gravity. Absolute space, quoth he! Oh, nonsense!)




Chronology Protection Conjecture: Notice that this conjecture by our good friend Stephen Hawking does not hypothesize the invalidity of time travel itself. It merely formulates the common-sense conviction that we can't change the past in the course of said time travel because of the Pandora's box of logical paradoxes that would thence obtain. (If you don't understand my use of the word "obtain" here, I'll be teaching a remedial philosophy class tomorrow. Honestly! In my day, we kids already knew the difference between our quarks and our gluons by the fifth grade! Mind you, the local fundamentalists were none too happy with our advanced knowledge in this area, but then again, I've never heard of a Creationist who succeeded in going back in time -- and even if they could, they'd only have 4,000 years or so to go back to, according to their own temporal reckoning, as opposed to the billions of years that we mainstream scientists are at least potentially able to explore.)




Event: Remember, this word has two meanings: It can refer to an actual event in spacetime ("the explosion of a firecracker," to cite NOVA's example here) or an actual point in spacetime.






Freely falling object: an object that is affected only by the force of gravity. (Word.)




General relativity: As NOVA points out, this is Einstein's law of physics according to which gravity is defined by the curvature of spacetime. Of course, don't be misled. That's just a very simple explanation. This concept is actually so complicated that I could probably write a whole PAGE about it right here (maybe even TWO whole pages), but for now, let's just focus on the basics, which are important enough that I'll repeat them even as we speak: General Relativity (remember this, yo) is Einstein's law of physics according to which gravity is defined by the curvature of spacetime.




Geodesic: In a way, this is the simplest concept on Earth, since a geodesic is simply a straight line! In a way, this concept is also tough as nails, since a geodesic is, more specifically, a straight line IN CURVED SPACETIME! Whoo-hoooo! (Ahem. Sorry about that.)



Gravitational time dilation: I won't even go over this, because I'm sure even our poorly educated Freshmen know all about it. What's that? You don't?
Oh, fine: Gravitational time dilation refers to the slowing of time (or what NOVA calls "the flow of time") near a gravitating body. (There! Are we finally all up to speed on that?! Jeez!)



Gravitational wave: NOVA puts this so succinctly, that I'm going to cheat and quote them directly on this one. A Gravitational Wave is "a ripple of spacetime curvature that travels with the speed of light." (Couldn't have said it better myself, all egg-headed as I am!)



Hyperspace: Warning: This concept will be of little use to you in making your Time Machines since "hyperspace" doesn't really exist, except in the amusingly over-reaching minds of our sci-fi authors. (Gene Roddenberry, you silly! There's no such thing as hyperspace, and you know it!) But, for the record, hyperspace is a supposititious flat region of space that somehow "contains" slices of curved spacetime. (Yeah, right, like THAT'S going to happen in the actual universe!)



Mouth: No wisecracks from the inevitably sophomoric Freshmen, please: a mouth is simply an entrance to a wormhole, ladies and gentlemen, nothing more, nothing less. Of course, a wormhole, having two ends, has two mouths. Questions? (I thought not.)



Newtonian laws of physics: The Laws of Physics as established by our old buddy Isaac Newton, which, as NOVA rightly asserts, were "the centerpiece of 19th-century thinking about the Universe." Of course, the problem with this otherwise fine system is that it's based on the now-discredited notion that space and time are absolutes! (We still love ya anyway, Newt! Who's our favorite apple man, huh? Well, apart from Johnny Appleseed, that is? You, sir! YOU!)




Perturbation: Again, no jokes from the kiddies. Perturbation is merely a small distortion of an object's shape (or of the shape of the spacetime curvature surrounding said object).



Planck-Wheeler length: I'm embarrassed even to have to explain this straightforward concept to full-grown physics students such as yourself. Look, it's easy: The Planck-Wheeler length is merely the length scale beneath which space "as we know it" no longer exists and turns instead into a sort of "quantum foam," the suitability of which as a dessert topping has yet to be ascertained. (Sorry. I couldn't resist.) The precise value of this length is something that you might want to seriously consider having tattooed on a conveniently located portion of your anatomy. It comes in handy on many a pop quiz for all you space majors out there. Just be sure to give your chosen tattoo artist the correct formula, which, if I remember correctly, is: 1.62 x 10 to the negative 33 centimeters. That's right, it's almost as small as a Freshman's brain. (Just kidding! Again, I couldn't resist!)



Principle of the absoluteness of speed of light: This is our old friend Einstein's idea that the speed of light is always the same in the absence of gravity (to wit 186,000 miles per second) in every inertial reference frame, and Einstein doesn't care what direction the light is going in either: its speed is always the same, end of discussion.



More terms to be added here in no time!