Researchers have directly measured the pressure exerted by individual particles for the first time, using a tiny bead suspended in a laser beam. The technique exploits optical trapping, where light radiation pressure holds a microscopic sphere in place while particles bombard it.
The breakthrough enables detection of pressures in the femtonewton range, roughly equivalent to the force a single grain of salt exerts when resting on a surface. Scientists trapped a silica bead about 5 micrometers in diameter using a focused laser. As particles struck the bead, they transferred momentum, creating measurable deflections that reveal the pressure.
This advance opens applications in particle detection. The team proposes using the device to hunt for sterile neutrinos, hypothetical particles that barely interact with ordinary matter and remain one of physics' outstanding mysteries. Sterile neutrinos could constitute dark matter, which comprises 85 percent of the universe's mass yet remains invisible to standard instruments. If sterile neutrinos exist and occasionally collide with ordinary matter, an optical trap could register their presence through the tiny pressure signatures they leave.
Current neutrino detectors rely on indirect methods, observing secondary particles or energy released during interactions. A direct pressure measurement would provide novel confirmation of these elusive particles. However, the approach faces practical hurdles. Optical traps operate in controlled laboratory environments, and differentiating particle pressure from thermal noise requires extraordinary sensitivity.
The research represents a merger of quantum mechanics and classical mechanics. Light itself carries momentum, a phenomenon Einstein predicted and experimentally confirmed over a century ago. Using this principle to measure atomic-scale forces demonstrates how fundamental physics principles yield practical tools.
The sensitivity achieved rivals or exceeds existing particle detectors in specific regimes. Scaling up the system to larger detection volumes and improving background noise rejection remain priorities. Success could reshape how physicists search for beyond-standard-model particles and refine