Researchers have succeeded in measuring the gravitational field of a gold
sphere, just 2 mm in diameter, using a highly sensitive pendulum -- and thus
the smallest gravitational force. The experiment opens up new possibilities
for testing the laws of gravity on previously unattained small scales.
Gravity is the weakest of all known forces in nature -- and yet it is most
strongly present in our everyday lives. Every ball we throw, every coin we
drop -- all objects are attracted by the Earth's gravity. In a vacuum, all
objects near the Earth's surface fall with the same acceleration: their
velocity increases by about 9.8 m/s every second. The strength of gravity is
determined by the mass of the Earth and the distance from the center. On the
Moon, which is about 80 times lighter and almost 4 times smaller than the
Earth, all objects fall 6 times slower. And on a planet of the size of a
ladybug? Objects would fall 30 billion times slower there than on Earth.
Gravitational forces of this magnitude normally occur only in the most
distant regions of galaxies to trap remote stars. A team of quantum
physicists led by Markus Aspelmeyer and Tobias Westphal of the University of
Vienna and the Austrian Academy of Sciences has now demonstrated these
forces in the laboratory for the first time. To do so, the researchers drew
on a famous experiment conducted by Henry Cavendish at the end of the 18th
century.
During the time of Isaac Newton, it was believed that gravity was reserved
for astronomical objects such as planets. It was not until the work of
Cavendish (and Nevil Maskelyne before him) that it was possible to show that
objects on Earth also generate their own gravity. Using an elegant pendulum
device, Cavendish succeeded in measuring the gravitational force generated
by a lead ball 30 cm tall and weighing 160 kg in 1797. A so-called torsion
pendulum -- two masses at the ends of a rod suspended from a thin wire and
free to rotate -- is measurably deflected by the gravitational force of the
lead mass. Over the coming centuries, these experiments were further
perfected to measure gravitational forces with increasing accuracy.
The Vienna team has picked up this idea and built a miniature version of the
Cavendish experiment. A 2 mm gold sphere weighing 90 mg serves as the
gravitational mass. The torsion pendulum consists of a glass rod 4 cm long
and half a millimeter thick, suspended from a glass fiber a few thousandths
of a millimeter in diameter. Gold spheres of similar size are attached to
each end of the rod. "We move the gold sphere back and forth, creating a
gravitational field that changes over time," explains Jeremias Pfaff, one of
the researchers involved in the experiment. "This causes the torsion
pendulum to oscillate at that particular excitation frequency." The
movement, which is only a few millionths of a millimeter, can then be read
out with the help of a laser and allows conclusions to be drawn about the
force. The difficulty is keeping other influences on the motion as small as
possible. "The largest non-gravitational effect in our experiment comes from
seismic vibrations generated by pedestrians and tram traffic around our lab
in Vienna," says co-author Hans Hepach: "We therefore obtained the best
measurement data at night and during the Christmas holidays, when there was
little traffic." Other effects such as electrostatic forces could be reduced
to levels well below the gravitational force by a conductive shield between
the gold masses.
This made it possible to determine the gravitational field of an object that
has roughly the mass of a ladybug for the first time. As a next step, it is
planned to investigate the gravity of masses thousands of times lighter.
The possibility of measuring gravitational fields of small masses and at
small distances opens up new perspectives for research in gravitational
physics; traces of dark matter or dark energy could be found in the behavior
of gravity, which could be responsible for the formation of our present
universe. Aspelmeyer's researchers are particularly interested in the
interface with quantum physics: can the mass be made small enough for
quantum effects to play a role? Only time will tell. For now, the
fascination with Einstein's theory of gravity still prevails. "According to
Einstein, the gravitational force is a consequence of the fact that masses
bend spacetime in which other masses move," says first author Tobias
Westphal. "So what we are actually measuring here is, how a ladybug warps
space-time."
Reference:
Tobias Westphal, Hans Hepach, Jeremias Pfaff, Markus Aspelmeyer. Measurement
of gravitational coupling between millimetre-sized masses. Nature, 2021; 591
(7849): 225 DOI:
10.1038/s41586-021-03250-7
Tags:
Physics
Employee will not require transfer request as money on the old account will automatically transfer to their new account once the present employer verifies the KYC details of the employee EPF Balance with UAN
ReplyDelete