FOSTER THAN LIGHT 205
beyond this strategy so as to be able to travel faster than the speed of
light one would need to change the fuel. A straightforward calculation
shows that you would need "negative mass" or "negative energy," perhaps the most exotic entities in the universe, if they exist. Traditionally,
physicists have dismissed negative energy and negative mass as science fiction. But we now see that they are indispensable for fasterthan-light travel, and they might actually exist.
Scientists have looked for negative matter in nature, but so far
without success. (Antimatter and negative matter are two entirely different things. The first exists and has positive energy, but a reversed
charge. Negative matter has not yet been proven to exist.) Negative
matter would be quite peculiar, because it would be lighter than nothing. In fact, it would float. If negative matter existed in the early universe, it would have drifted into outer space. Unlike meteors that come
crashing down onto planets, drawn by a planet's gravity, negative matter would shun planets. It would be repelled, not attracted, by large
bodies such as stars and planets. Hence, although negative matter
might exist, we expect to find it only in deep space, certainly not on
Earth.
One proposal to find negative matter in outer space involves using
the phenomenon called "Einstein lenses." When light travels around a
star or galaxy its path is bent by its gravity, according to general relativity. In 1912 (even before Einstein fully developed general relativity)
he predicted that a galaxy might be able to act like the lens of a telescope. Light from a distant object moving around a nearby galaxy
would converge as it passed around the galaxy, like a lens, forming a
characteristic ring pattern when the light finally reached the Earth.
These phenomena are now called "Einstein rings." In 1979 the first of
these Einstein lenses was observed in outer space. Since then, Einstein
lenses have become an indispensable tool for astronomers. (For example, it was once thought that it would be impossible to locate "dark
matter" in outer space. [Dark matter is a mysterious substance that is
invisible but has weight. It surrounds the galaxies and is perhaps ten
times as plentiful as ordinary visible matter in the universe.] But NASA
scientists have been able to construct maps of dark matter since dark
beyond this strategy so as to be able to travel faster than the speed of
light one would need to change the fuel. A straightforward calculation
shows that you would need "negative mass" or "negative energy," perhaps the most exotic entities in the universe, if they exist. Traditionally,
physicists have dismissed negative energy and negative mass as science fiction. But we now see that they are indispensable for fasterthan-light travel, and they might actually exist.
Scientists have looked for negative matter in nature, but so far
without success. (Antimatter and negative matter are two entirely different things. The first exists and has positive energy, but a reversed
charge. Negative matter has not yet been proven to exist.) Negative
matter would be quite peculiar, because it would be lighter than nothing. In fact, it would float. If negative matter existed in the early universe, it would have drifted into outer space. Unlike meteors that come
crashing down onto planets, drawn by a planet's gravity, negative matter would shun planets. It would be repelled, not attracted, by large
bodies such as stars and planets. Hence, although negative matter
might exist, we expect to find it only in deep space, certainly not on
Earth.
One proposal to find negative matter in outer space involves using
the phenomenon called "Einstein lenses." When light travels around a
star or galaxy its path is bent by its gravity, according to general relativity. In 1912 (even before Einstein fully developed general relativity)
he predicted that a galaxy might be able to act like the lens of a telescope. Light from a distant object moving around a nearby galaxy
would converge as it passed around the galaxy, like a lens, forming a
characteristic ring pattern when the light finally reached the Earth.
These phenomena are now called "Einstein rings." In 1979 the first of
these Einstein lenses was observed in outer space. Since then, Einstein
lenses have become an indispensable tool for astronomers. (For example, it was once thought that it would be impossible to locate "dark
matter" in outer space. [Dark matter is a mysterious substance that is
invisible but has weight. It surrounds the galaxies and is perhaps ten
times as plentiful as ordinary visible matter in the universe.] But NASA
scientists have been able to construct maps of dark matter since dark