Yet off in the fringes of physics there do seem to be things that exert negative pressure. The mysterious “dark energy” that is accelerating the expansion of our universe against the pull of its own gravity might be one. Another is the Casimir effect. It may be possible to build a traversable wormhole using the Casimir effect, so it’s worth covering here.
Physicists believe that at the tiniest-size scales and the briefest flickers of time, our universe is a seething froth of instability, constantly creating pairs of subatomic particles that recombine and vanish before they can be detected. These are called “virtual particles.” Among the virtual particles are photons, the wiggles of electricity and magnetism that make up light, radio, X-rays, and so on. Photons both real and virtual cannot travel very well through electrical conductors such as metals. So if we take two very smooth flat metal surfaces, and place them very close together, they’ll suppress the creation of virtual photons with a wavelength longer than the separation between them. But outside the plates are virtual photons of all wavelengths, which exert a tiny bit more radiation pressure on the back sides of the plates than does the restricted range of wavelengths available between them. If all of this weirdness is really true, then there should be a very tiny force – effectively a negative pressure – pushing the plates toward one another.
This force exists and has been measured in experiments.
There are some difficulties with building wormholes using the Casimir effect. It operates only over very short distances. Also it’s rather weak. It’s not as heavy a hammer for knocking holes in spacetime as, say, the collapsing core of a massive star. But if our kids are terraforming planets and we don’t want to be outdone, we should go for it. We start by building a spherical metal shell with the diameter of the orbit of Pluto, a supersized Dyson sphere. We then build another one surrounding the first, carefully maintaining the gap between them at one Ångstrom unit, roughly the size of an atom. If we accomplish these things, says Dr. Thorne, the Casimir effect will warp space so that we will no longer be able to tell which sphere is the inner one and which is the outer. We will have built a wormhole that allows us to travel the massive distance of one ten-billionth of a meter. Not a practical transportation device, unfortunately. But it’s a real wormhole, and by sending one end on a high-speed trip we might possibly be able to turn it into a real time machine.
Back to the Present
Unfortunately, our own less-than-incredibly-advanced culture won’t be building Matryoshka-doll Dyson spheres and accelerating them to relativistic speeds any time soon. But that doesn’t diminish the appeal of time travel. It remains a fruitful topic for both science fiction and theoretical physics. As in the case of Contact, sometimes the interplay between the two helps make both stronger. And as our train moves inexorably forward at 3600 seconds per hour, the day when we can engineer time machines must be moving just as inexorably closer. Maybe, somewhere up the track, they’re sending people even further along, to still more distant futures where they can send people back.
REACTIONARIES AND REVOLUTIONARIES
A SOUND OF THUNDER
Ray Bradbury
Ray Bradbury was one of the most celebrated twentieth-century American writers. He wrote science fiction, horror, and mystery fiction. Many of Bradbury’s works have been adapted into comic books, television shows, and films. This story was first published in Collier’s magazine in 1952. The term “the Butterfly Effect” was coined because of this famous story – which may be the most reprinted science fiction tale in history.
The sign on the wall seemed to quaver under a film of sliding warm water. Eckels felt his eyelids blink over his stare, and the sign burned in this momentary darkness:
TIME SAFARI, INC.
SAFARIS TO ANY YEAR IN THE PAST.
YOU NAME THE ANIMAL.
WE TAKE YOU THERE.
YOU SHOOT IT.
Warm phlegm gathered in Eckels’ throat; he swallowed and pushed it down. The muscles around his mouth formed a smile as he put his hand slowly out upon the air, and in that hand waved a check for ten thousand dollars to the man behind the desk.
“Does this safari guarantee I come back alive?”
“We guarantee nothing,” said the official, “except the dinosaurs.” He turned. “This is Mr. Travis, your Safari Guide in the Past. He’ll tell you what and where to shoot. If he says no shooting, no shooting. If you disobey instructions, there’s a stiff penalty of another ten thousand dollars, plus possible government action, on your return.”
Eckels glanced across the vast office at a mass and tangle, a snaking and humming of wires and steel boxes, at an aurora that flickered now orange, now silver, now blue. There was a sound like a gigantic bonfire burning all of Time, all the years and all the parchment calendars, all the hours piled high and set aflame.
A touch of the hand and this burning would, on the instant, beautifully reverse itself. Eckels remembered the wording in the advertisements to the letter. Out of chars and ashes, out of dust and coals, like golden salamanders, the old years, the green years, might leap; roses sweeten the air, white hair turn Irish-black, wrinkles vanish; all, everything fly back to seed, flee death, rush down to their beginnings, suns rise in western skies and set in glorious easts, moons eat themselves opposite to the custom, all and everything cupping one in another like Chinese boxes, rabbits into hats, all and everything returning to the fresh death, the seed death, the green death, to the time before the beginning. A touch of a hand might do it, the merest touch of a hand.
“Unbelievable,” Eckels breathed, the light of the Machine on his thin face. “A real Time Machine.” He shook his head. “Makes you think. If the election had gone badly yesterday, I might be here now running away from the results. Thank God Keith won. He’ll make a fine President of the United States.”
“Yes,” said the man behind the desk. “We’re lucky. If Deutscher had gotten in, we’d have the worst kind of dictatorship. There’s an anti-everything man for you, a militarist, anti-Christ, anti-human, anti-intellectual. People called us up, you know, joking but not joking. Said if Deutscher became President they wanted to go live in 1492. Of course it’s not our business to conduct Escapes, but to form Safaris. Anyway, Keith’s President now. All you got to worry about is—”
“Shooting my dinosaur,” Eckels finished it for him.
“A Tyrannosaurus Rex. The Tyrant Lizard, the most incredible monster in history. Sign this release. Anything happens to you, we’re not responsible. Those dinosaurs are hungry.”
Eckels flushed angrily. “Trying to scare me!”
“Frankly, yes. We don’t want anyone going who’ll panic at the first shot. Six Safari leaders were killed last year, and a dozen hunters. We’re here to give you the severest thrill a real hunter ever asked for. Traveling you back sixty million years to bag the biggest game in all of Time. Your personal check’s still there. Tear it up.”
Mr. Eckels looked at the check. His fingers twitched.
“Good luck,” said the man behind the desk. “Mr. Travis, he’s all yours.”
They moved silently across the room, taking their guns with them, toward the Machine, toward the silver metal and the roaring light.
* * *
First a day and then a night and then a day and then a night, then it was day-night-day-night. A week, a month, a year, a decade! A.D. 2055. A.D. 2019. 1999! 1957! Gone! The Machine roared.