Q & A: Traveling really fast

Is it possible that an underwater train can travel from New York to Paris in less than a hour in the future? And is it also possible to travel faster than Mac 5?
- Derek (age 12)
Seoul, Korea

Yes, it is indeed possible that a train could go from New York to Paris in under an hour, but I'd keep that train away from the water. Maybe a tube with the air taken out under the sea is a good place for such a train. Water is very heavy and would slow down such a train. It would waste lots of energy creating shock waves in either water or air if it were traveling in anything but vacuum. I'd imagine such a project would be both expensive and also difficult to market to the public. People are afraid enough of flying on airplanes. Taking them deep under the sea in an evacuated tube would make them simultaneously afraid of suffocating and drowning. As it is, the Concorde supersonic airplane has been retired more for economic reasons than anything else -- there wasn't enough demand for it to justify the cost of flying the planes.

Underwater tunnels are used routinely for train and auto traffic. Accidents happen, though and fires in these tunnels have created setbacks. Nonetheless, it would be nice to have some mode of transportation from New York to Paris which economizes on fuels.

Travel faster than 5 times the speed of sound is most certainly possible, but again at an expense of energy. There's the unavoidable sonic boom, and friction with the air going past will heat up the skin of an airplane traveling that fast. Astronauts and satellites in low-earth orbit go around the earth once every 90 minutes or so, and you can figure out what that is in terms of the speed of sound (of course the speed of sound means a lot less if there isn't much air).

Tom

(published on 10/22/2007)