For example, there is the "grandmother paradox:" What happens if you go back in time and kill you grandmother before your mother is born? If you killed your grandmother before your mother was born, then you shouldn't have been able to go back in time and kill your grandmother in the first place.
"The world of time travel seems to be a world where the laws of cause and effect get screwed up," said Kraus. "But we learned throughout the 20th century that just because things seem crazy doesn't mean they don't happen, it just may mean that we have to think about them slightly differently."
"While it's highly unlikely that any of it is possible, at least we can say that it isn't impossible," he said.
The transporter system on the Enterprise gave rise to one of the most popular phrases in pop culture ("Beam me up, Scotty!") and was the thing that inspired Krauss' book on "Star Trek."
"The thing that sort of seduced me into thinking about this in the first place was the transporter. ?I travel on a lot of planes [and] it would be wonderful to not have to go through security, among other things," he deadpanned.
According to the television show's writers, the transporter worked by vaporizing a person into a matter stream, moving his atoms to his destination and then putting the atoms back together again.
But, Krauss said, not only is moving atoms difficult, but in order to vaporize a person, you'd have to heat him to 100,000 degrees. And he said the amount of energy released would be about 1,000 hundred-megaton nuclear weapons.
"So it's sort of a little dangerous," he said.
He also said that according to the laws of quantum mechanics, and the Heisenberg Uncertainty Principle, it's not possible to know where every atom in a body is and what it's doing at the same time.
The writers of "Star Trek," aware of the principle, gave their characters "Heisenberg compensators" to address the issue. But we're not as lucky in real life, Krauss said.
"That is one thing, even though it's the thing that seduced me into it, that I believe is impossible," he said.
Creative interpretations of alien life forms were as much a part of "Star Trek" as the high technology that let Enterprise crew members search the galaxy.
"That's, of course, unlikely to be the case," he said. "All you have to do is go to the Bronx Zoo and see that we share a lot of DNA with those critters and they don't look like us. The idea that aliens would look like us really doesn't make any sense."
He also said that it's unlikely that they'd be at our level of technology.
Shostak said that any aliens humans encounter won't be less advanced, because they wouldn't be sending out any detectable signals (such as radio or television waves).
"If you get in touch with someone, they're at least at your level and, statistically, the chance that they'd be even within a thousand years of the same level is almost zero," he said. 'They're going to be way ahead of us. If there really were battles, if Bambi meets Godzilla, we're Bambi."
And though he said it's possible that humans could encounter aliens, he doubts it'll happen the way "Star Trek" proposes.