Feb. 24, 2005 -- There have been countless accounts of alien visitations around the world, but one of the things that prompts skepticism is how they would get here in the first place.
If aliens are from another world, they must have some extraordinary means of travel -- nothing like what is available anywhere on Earth. It is hard to underestimate the difficulty of going from star to star.
"The distances are so vast, the energy requirements are so extreme, it would be very, very difficult to travel between the stars," said James McGaha, a retired Air Force pilot.
A law of science, determined by Albert Einstein, says nothing can travel faster than the speed of light -- 186,000 miles per second. The fastest object made by man, the Voyager spacecraft is travelling along at 11 miles per second. At that rate, the scientific probe Voyager, launched in 1977, would take 73,000 years to reach the nearest star.
As a result, some scientists think that sort of space travel is a waste of time.
"Scientifically, we have a rule: you want to be alive at the end of your experiment, not dead," said Dr. Neil deGrasse Tyson, director of the Rose Center's Hayden Planetarium at the American Museum of Natural History in New York.
Einstein's Wormhole Loophole
If humans can't travel to the stars, many scientists say extraterrestrial life can't come here either.
However, Michio Kaku, one of the leading theoretical physicists in the world, says many scientists are too quick to dismiss the idea of other civilizations visiting Earth.
Einstein may have said nothing can go faster than the speed of light, but he also left a loophole, said Kaku, a professor at the City University of New York. In Einstein's theory, space and time is a fabric.
Kaku explained: "In school we learned that a straight line is the shortest distance between two points. But actually that's not true. You see, if you fold the sheet of paper and punch a hole through it, you begin to realize that a wormhole is the shortest distance between two points."
A civilization that could harness the power of stars might be able to use that shortcut through space and time, and perhaps bridge the vast distances of space to reach Earth, he said.
"The fundamental mistake people make when thinking about extraterrestrial intelligence is to assume that they're just like us except a few hundred years more advanced. I say open your mind, open your consciousness to the possibility that they are a million years ahead," he said.
Kaku believes that only this type of civilization -- millions of years more advanced that us and capable of using wormholes as shortcuts -- could reach Earth and might be one explanation for UFOs.
"When you look at this handful of [UFO] cases that cannot be easily dismissed, this is worthy of scientific investigation," he said. "Maybe there's nothing there. However, on that off chance that there is something there, that could literally change the course of human history. So I say let this investigation begin."