viewed dimly through the haze and lights of a city
or in all their glory in a pristine wilderness, the
stars that surround the Earth are magnificent, and
one day Earthlings will travel to some of the new
planets that astronomers are locating. However, the
stars we see are not necessarily where we think they
are, according to an international research team.
"We know that the light from distant stars takes
a very long time to reach the Earth," says Dr.
Akhlesh Lakhtakia, distinguished professor of engineering
science and mechanics, Penn State. "But, taking
into account the distance a star will have moved while
that light travels, we still may not be able to accurately
locate the star.Ó
Negative phase velocity media or materials with negative
refractive index may be responsible for this locational
uncertainty. Recently, materials researchers at the
University of California San Diego, working with micro
and nano materials, developed a metamaterial that
had a negative refractive index for microwaves, proving
that negative phase materials could exist at least
in the microwave part of the electromagnetic spectrum.
Their requirements for this material were that both
the relative permittivity, a measure of the charge
separation in a material, and the relative permeability,
a measure of how electrons loop in materials, of a
substance must be less than zero.
While the implications for negative phase velocity
media in the nano world are the creation of a perfect
lens, a lens with no distortion with applications
for optical transmission devices, CDs, DVDs, microwave
systems, etc., in the universe at large, these media
can disguise the location of a star, according to
A material with negative index of refraction transmits
light or other wave energy differently than one with
positive index of refraction. In all natural materials,
when an energy beam Ð light, radar, microwave
Ð passes through water or glass or some other
material, the beam is displaced in the same direction.
The amount of displacement depends upon how much the
material slows the speed of the beam. In negative
phase velocity media, the displacement is in the opposite
Lakhtakia and Tom. G. Mackay, lecturer in Mathematics,
University of Edinburgh decided to look at why the
permittivity and permeability had to be less than
zero. They found that one or both permeability and
permittivity could be less than zero and negative
phase velocity would occur. They then found that both
could be greater than zero and a negative index of
refraction would occur but only when special relativity
came into play.
The researchers looked at transmission through space,
where high velocities are common.
"First I did the derivations with the observer
moving and the energy source stationary," says
Lakhtakia. " Then Mackay did the derivations
with the observer stationary and the light source
What they found was that it depends on the state of
the observer whether any particular media at any time
has negative or positive index of refraction. The
relative velocity of the observer changes the index
of any material.
"Light coming off a stellar object passes through
many different regions of space filled with different
media and is affected by different gravitational fields,"
says Lakhtakia. "When we finally see it, we cannot
really know where it originated."
While this may be of no consequence today, Lakhtakia
believes it has important implications for when space
travel is common. Because this is a direction dependent
effect, it will change the telemetry of objects and
"The business of space navigation and interpreting
star maps could be a lot more complicated than we
now think it is," says Lakhtakia. "Imagine
mining of extrasolar asteroids. We might not want
to send humans to do the mining, but robots would
have to know where the asteroid is and where on its
surface to mine when it left our solar system."
Calculations would need to be made from Earth on an
asteroid that might not be where we visually see it.
The effects of negative phase velocity media would
need to be taken into consideration.
Another problem would be navigating from somewhere
far away from the Earth in a space ship using information
gathered from the Earth. Depending on the velocity
of the spacecraft and the object aimed for, negative
phase velocity media between the spacecraft and the
destination would also need to be considered.
Contact: Vicki Fong