[cinFLA]

The propellor or the jet engine of an aircraft push air backwards to propel the aircraft forward. A ship or boat propellor does the same thing with water. On Earth there is always air or water available to push against.

Was this absurd statement really written by someone with a physics background?

[RightWhale]

Was this absurd statement really written by someone with a physics background?

How is this statement absurd? It seems perfectly true.

[sourcery]

Um, so propellor-driven locomation would actually work in a perfect vacuum?

[PatriotGames]

Was this absurd statement really written by someone with a physics background?

I was thinking the exact same thing as I read the article.

[El Gato]

On Earth there is always air or water available to push against.

Ok so they should have said "push with" or "expel" or somesuch. Give 'em a break. Physicists, like engingeers don't always have the best writing skills. I'm a perfect example of that, my writing skills are pretty minimal, although I do better than many engineers, especially the youngsters.

[CobaltBlue]

OK, we'll accept that you're smarter than we are but only if you prove it by demonstrating it.

Please explain why the statement is absurd.

[Toskrin]

The point seems pretty clear to me. On Earth, travel is usually performed by applying a mechanical force against an external mass - car wheels against the road, a propeller against air against air or water, your foot against the ground. All the travelling object needs is an appropriate form of mechanical linkage to push against the external mass.

In space, there's no external mass, so carrying propellant is the only way to get around.

What space travellers want is a way to get around with a solar powered motor.