“people tend to just ignore relativistic effects, but
relativistic effects are everywhere.” —JAMES CHIn-wEn CHou
It isn’t just for astronauts anymore
By Rachel Ehrenberg
Probing the peculiar effects of Einstein’s
relativity is no longer rocket science.
Tabletop experiments in a Colorado lab
have illustrated the odd behavior of time,
a strangeness typically examined with
space travel and jet planes.
Using superprecise atomic clocks,
scientists have witnessed time dilation—the bizarre slowing of time
described by Einstein’s theories of relativity. The experiments are presented in
the Sept. 24 Science.
“Modern technology has gotten so
precise you can see these exotic effects
in the range of your living room,” says
physicist Clifford Will of Washington
University in St. Louis. The experiments
don’t reveal any new physics, Will says,
but “what makes it cute and pretty cool
is they have done it on a tabletop.”
Time dilation arises in two situations.
In one, time appears to move more slowly
the closer you are to a massive object,
such as the Earth. So a person hovering
in a hot-air balloon, for example, actually
ages faster than someone standing below.
Time also goes faster for someone at
rest relative to someone moving — one
25-year-old twin traveling in a rocket
Still clock
Moving clock
12
9
3
6
High clock
Low clock
Let’s do the time warp Relativity causes
clocks in motion to tick slower than stationary
clocks (top); clocks that are nearer to a massive
object such as earth also run slower (bottom).
near the speed of light for what he perceives as a few months would return to
Earth to find that the other had reached
middle age.
Previous experiments with rockets
and airplanes have demonstrated these
odd aspects of general and special rela-
tivity. The notion of time running slower
closer to Earth has even been tested in a
multistory physics building at Harvard.
A compass that
lights its own way
instrument senses magnetic
field’s direction using optics
By Laura Sanders
A compass made of light shot through
a blob of rubidium atoms can directly
and reliably measure the size and orientation of a magnetic field, physicists
report in the Sept. 13 Physical Review A.
Highly sensitive compasses are needed
for oil discovery, earthquake detection
and other applications. These compasses
typically include a built-in reference magnetic field that allows the instrument to
reconstruct the terrestrial magnetic field,
but the data can vary in quality, says study
coauthor Alexander Zibrov of Harvard.
He and his colleagues trapped
rubidium-87 atoms at 45° Celsius in a
domino-sized chip and shined linearly
polarized laser light into the atoms.
In a magnetic field, the atoms’ orien-
tation changed in a way that could be
detected in the light that came through
the atom cloud. This change allowed the
researchers to measure the precise size
and direction of the field.
