Marc Millis, who manages NASA?s Breakthrough Propulsion Physics Program, says he?s more interested in ways ?to propel spacecraft farther, faster, more efficiently? than in the grand cosmological questions. ?And my ears perk up more when I hear about new experimental evidence than theories,? he says. There are a number of such theories based on experimental evidence. His top three of interest are:

Photon Tunneling.
Some experiments have indicated that photons can appear to tunnel through barriers at speeds faster than light, but researchers are still sorting out the quantum physics behind such phenomena.

Neutrino Rest Mass.
Some experiments have come up with an imaginary number for the rest mass of neutrinos ? a result so baffling that most physicists say the data must be in error. ?If indeed those data are correct, then imaginary mass is a signature characteristic of a tachyon, a faster-than-light particle,? Millis says.

Vacuum Fluctuations.
Quantum physics dictates that even the vacuum of space contains some energy. In fact, some physicists have said a coffee cup full of empty space contains enough energy to boil away Earth?s oceans. But can that energy be extracted or used to propel spaceships? Millis says the outlook is uncertain: ?Very obviously there?s no free lunch in this scheme, but it does provide new clues from which to search for propulsion breakthroughs.?

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