i4
PHYSICS OF THE IMPOSSIBLE
ductor may be discovered tomorrow, next year, or not at all. No one
knows when, or if, such a substance will ever be found.
But if room-temperature superconductors are discovered, a tidal
wave of commercial applications could be set off. Magnetic fields that
are a million times more powerful than the Earth's magnetic field
(which is .5 gauss) might become commonplace.
One common property of superconductivity is called the Meissner
effect. If you place a magnet above a superconductor, the magnet will
levitate, as if held upward by some invisible force. (The reason for the
Meissner effect is that the magnet has the effect of creating a "mirrorimage" magnet within the superconductor, so that the original magnet
and the mirror-image magnet repel each other. Another way to see this
is that magnetic fields cannot penetrate into a superconductor. Instead,
magnetic fields are expelled. So if a magnet is held above a superconductor, its lines of force are expelled by the superconductor, and the
lines of force then push the magnet upward, causing it to levitate.)
Using the Meissner effect, one can imagine a future in which the
highways are made of these special ceramics. Then magnets placed in
our belts or our tires could enable us to magically float to our destination, without any friction or energy loss.
The Meissner effect works only on magnetic materials, such as
metals. But it is also possible to use superconducting magnets to levitate nonmagnetic materials, called paramagnets and diamagnets.
These substances do not have magnetic properties of their own; they
acquire their magnetic properties only in the presence of an external
magnetic field. Paramagnets are attracted by an external magnet,
while diamagnets are repelled by an external magnet.
Water, for example, is a diamagnet. Since all living things are
made of water, they can levitate in the presence of a powerful magnetic
field. In a magnetic field of about 15 teslas (30,000 times the Earth's
field), scientists have levitated small animals, such as frogs. But if
room-temperature superconductors become a reality, it should be possible to levitate large nonmagnetic objects as well, via their diamagnetic property.
In conclusion, force fields as commonly described in science fic-
PHYSICS OF THE IMPOSSIBLE
ductor may be discovered tomorrow, next year, or not at all. No one
knows when, or if, such a substance will ever be found.
But if room-temperature superconductors are discovered, a tidal
wave of commercial applications could be set off. Magnetic fields that
are a million times more powerful than the Earth's magnetic field
(which is .5 gauss) might become commonplace.
One common property of superconductivity is called the Meissner
effect. If you place a magnet above a superconductor, the magnet will
levitate, as if held upward by some invisible force. (The reason for the
Meissner effect is that the magnet has the effect of creating a "mirrorimage" magnet within the superconductor, so that the original magnet
and the mirror-image magnet repel each other. Another way to see this
is that magnetic fields cannot penetrate into a superconductor. Instead,
magnetic fields are expelled. So if a magnet is held above a superconductor, its lines of force are expelled by the superconductor, and the
lines of force then push the magnet upward, causing it to levitate.)
Using the Meissner effect, one can imagine a future in which the
highways are made of these special ceramics. Then magnets placed in
our belts or our tires could enable us to magically float to our destination, without any friction or energy loss.
The Meissner effect works only on magnetic materials, such as
metals. But it is also possible to use superconducting magnets to levitate nonmagnetic materials, called paramagnets and diamagnets.
These substances do not have magnetic properties of their own; they
acquire their magnetic properties only in the presence of an external
magnetic field. Paramagnets are attracted by an external magnet,
while diamagnets are repelled by an external magnet.
Water, for example, is a diamagnet. Since all living things are
made of water, they can levitate in the presence of a powerful magnetic
field. In a magnetic field of about 15 teslas (30,000 times the Earth's
field), scientists have levitated small animals, such as frogs. But if
room-temperature superconductors become a reality, it should be possible to levitate large nonmagnetic objects as well, via their diamagnetic property.
In conclusion, force fields as commonly described in science fic-