Is it possible to make a Time Machine?
Tidsmaskine, hypotetisk maskine til at rejse frem og tilbage i tiden.....ikke mindst efter at relativitetsteorien ændrede tidsbegrebet. Den almene relativitetsteori tillader strukturer, ormehuller, der fungerer som tidsmaskiner; det er dog et åbent spørgsmål, om de findes i virkeligheden. Selv hvis de findes, vil de ikke kunne anvendes til at ændre fortiden.
HOW TO BUILD A TIME MACHINE
By Paul Davies Viking, $19.95
YOU'VE REFINISHED THE BASEMENT, brewed your own beer, even constructed a one-man ultralight aircraft, and still you feel unsatisfied. You need a real challenge. Paul Davies, a former physics professor at the University of Adelaide in Australia, has just the project for you: Try building a time machine.
Abstract from the book: "Wormhole express: hitch a ride into the past in four easy steps".(How to Build a Time Machine)(Book review)
Einstein established that a limited form of travel into the future is possible. According to the special theory of relativity, rapid motion or a strong gravitational field can noticeably slow the passage of time. If you set out in a very fast spaceship at 87 percent the speed of light--161,000 miles per second--you'll see time pass twice as quickly for the rest of the world as it does for you. Press on closer to the speed of light, and you can race ahead even more rapidly into the future,
Going into the past requires a great deal more work. But Davies approaches the problem with the can-do spirit of those old home-handyman guides. The key to backward time travel is a wormhole, which he compares to a "shortcut between two widely separated places." Scientists these days actually have promising ideas about how to create a wormhole on demand, and Davies describes the process step by step. First, use a particle collider to heat a speck of matter to 10 trillion degrees. Second compress the resulting hot spot by a factor of a billion billion, making a wormhole (smaller than a subatomic particle) that connects two different regions of space. Third, blast the opening of the hole with a million one-terawatt laser beams until it's large enough for at least one passenger. Finally, whip one end of the wormhole around like a lasso at nearly the speed of light to create a time differential between the entrance and the exit. Now hop in, and you're on your way.
Like many instruction manuals, How to Build a Time Machine isn't always easy to understand. The theory of time travel is inherently complex, and the book is quite short--just 128 pages, many of them illustrated--so ideas keep coming at a rapid pace. Davies is an old pro at this topic, and he does a commendable job of keeping the explanations simple. But considering the slightly tongue-in-cheek title of the book, the tone is odd y serious throughout. Many of the illustrations are cartoonish without being playful, and the final section on time-travel paradoxes is too solemn. What's the point of all this work if you can't have a little temporal fun?
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