Force fields; are they possible?

[tonbo0422]

Okay, so Cecil has shot down colonising the planets. But is a force field, ˆ la Star Trek, actually possible without incinerating someone trying to get through it?

I mean the old-fashioned kind that gives you a light buzz when you brush up against it.

Surely the armed forces are working feverishly on such a project.

[MC_Master_of_Ceremonies]

http://www.straightdope.com/mailbag/mforcefield.html

[tonbo0422]

Hmm, did a search and that thread didn’t show up . . . thanks.

[kniz]

[ul]Try this[/ul]

[astro]

They can float a frog on a sufficiently powerful magnetic field so if they can extrapolate that force in some manner it might be possible to push a human away, but the power needed to do this would be absurd vs using more conventional methods.

Some Levity in Physics

Seeing the April 1997 issue of Physics World, a publication of the Institute of Physics in the U.K., many readers chuckled at what they thought was an April Fool’s joke: the report of an antigravity device being used, among other things, to levitate a frog. The appearance of a subsequent notice in a British tabloid, The Sun, probably did little to dispel suspicions of a hoax.

Yet the scientists involved in the work, led by Andrey Geim of the University of Nijmegen in The Netherlands, were being quite serious when they announced that they had floated a live frog using a powerful electromagnet. That a living creature could be lifted in this manner came as a complete surprise even to many knowledgeable physicists. But the flying frog was merely a demonstration of a fundamental property of ordinary materials – and of a technique now being used to perform “low-gravity” biological experiments that might otherwise have demanded a ride on the Space Shuttle.

Most everyday materials – including water and living tissues – are weakly magnetic. They are said to exhibit diamagnetism, a slight tendency to become magnetized in the direction opposite to an applied magnetic field. A diamagnetic object placed in an intense magnetic field that is configured to diminish in strength with height will experience an upward force. So the field of a sufficiently powerful electromagnet can balance the downward tug of gravity – at least over a small volume.

Although materials normally recognized as magnetic (including iron, permanent magnets and so-called paramagnetic substances) can also be lifted with an electromagnet, they cannot hover in midair, unless some feedback mechanism adjusts the surrounding magnetic field constantly to maintain a fixed position. But the levitation of diamagnetic materials is inherently more stable. If the floating diamagnetic object rises slightly, the magnetic force on it diminishes, and it settles back down; if it falls, it automatically gets a boost from the increased magnetic force exerted below its equilibrium position.