The physicists discussed in The New Time Travelers must deal with problematic situations like the Grandfather Paradox. Say you decide to go back to the days before Dear Old Granddad helped produce Dear Old Dad. Because Granddad has continually been unacceptably stingy with the Werther’s Originals, you off him. This means he cannot produce Dear Old Dad, who in turn cannot have produced you. Therefore, you can’t go back in time to off Granddad. (And there are, therefore, still no more Werther’s Originals in your future or past.)
Einstein’s theory of special relativity allows for an interesting effect. Go faster—as in close to the speed of light—and you’ll experience time dilation. It’s hard to explain the whys, wherefores and what-have-yous, but it all adds up to a curious conclusion. Travel close to light speed for, say, 40 years, then come back to Earth, and it won’t be just 40 years later on Earth. Instead, it’ll be much more. You will have travelled into the future. This is an accepted part of Einstein’s work, so all it should require is a fast enough vessel. (Warning: Going 60 in a 25 mph zone seems to have little to no such effect.)
You fire up the time machine and decide to lend a hand to some great sage of the past like, say, the inventor of googly-eye glasses. You push your chronomobile into third gear and head pastward. You bring a nice pair of googly-eye glasses along and give them to said inventor, who then proudly sallies forth to bring the world “his” googly-eyes. So who exactly invented them? Not you—you just bought them at Acme. Not the inventor—you just showed up and handed them over. An insurmountable paradox?
Thanks to Einsteinian time dilation (see “Arriving Then, Now”), one of the many time machine ideas Toomey discusses in his book requires a trick that sounds simple enough. Physicist Kip Thorne suggested getting a nice wormhole, which is, basically, a shortcut between points in spacetime. Lasso one end of it (with what, nobody knows yet), hook it up to your near-light-speed ship, and travel around for 10 years. One end of the wormhole then exists in a different time than the other. Voila—a handy time machine. Finding or creating a wormhole might prove problematic, but its rewards could be immense for the intrepid chrononaut.