What is the nature of gravity? That was the question on the minds of researchers at Tohoku University in Sendai, Miyagi, Japan. The team, led by Professor Nobuyuki Matsumoto, set out to discover if gravity is classical or quantum.
“Within the past hundred years, our understanding of nature has deepened based on quantum theory and general relativity. In order to keep moving forward with this progress, it is necessary to understand more about the nature of gravity,” said Matsumoto.
Gravity is one of the most unknown phenomena in modern physics. Its measurement and laws remain somewhat of an enigma. The Tohoku University researchers revealed important information about a new aspect of the nature of gravity by probing the smallest mass-scale.
The team developed a gravity sensor based on monitoring the displacement of a suspended mirror, which allows for measuring the gravity of the smallest mass ever.
Until now the smallest mass for which humans have measured a gravitational field is about 100g, which is surprisingly larger than the mass scale of a common pencil (~10g). Because the gravitational force is much weaker than other forces, such as the electromagnetic force, it is difficult to measure gravity generated by small masses.
The system was constructed based on technology developed for gravitational wave detectors. It uses laser stabilization, a vibration isolation stage, high vacuum, and noise hunting. Unlike gravitational wave detectors, the team used a triangular optical cavity, not a linear optical cavity, to decrease the noise level of the displacement sensor and maintain stable operation of the sensor.
“Our system’s noise level, due to the Brownian motion of the suspended mirror, is one of the smallest in the world,” said Matsumoto.
Development of such a gravity sensor will pave the way for a new class of experiments where gravitational coupling between small masses in quantum regimes can be achieved.