Physicists Prove Einstein Wrong with Observation of Instantaneous Velocity in Brownian Particles

May 20, 2010

AUSTIN, Texas — A century after Albert Einstein said we would never be able to observe the instantaneous velocity of tiny particles as they randomly shake and shimmy, so called Brownian motion, physicist Mark Raizen and his group have done so.

A 5-micrometer glass bead levitated in air by a single laser beam from below. This optical trap is formed by the force from the laser beam and the gravitational force on the bead. Tongcang Li, et. al. used a similar optical trap to study the Brownian motion of a trapped bead in air with ultra-high resolution. Their paper is published in Science. Credit: Tongcang Li.

"This is the first observation of the instantaneous velocity of a Brownian particle," says Raizen, the Sid W. Richardson Foundation Regents Chair and professor of physics at The University of Texas at Austin. "It's a prediction of Einstein's that has been standing untested for 100 years. He proposed a test to observe the velocity in 1907, but said that the experiment could not be done."

In 1907, Einstein likely did not foresee a time when dust-sized particles of glass could be trapped and suspended in air by dual laser beam "optical tweezers." Nor would he have known that ultrasonic vibrations from a plate-like transducer would shake those glass beads into the air to be tweezed and measured as they moved in suspension.

Raizen's research, published in Science, is the first direct test of the equipartition theorem for Brownian particles, one of the basic tenets of statistical mechanics. It is also a step toward cooling glass beads to a state in which they could be used as oscillators or sensors.

The equipartition theorem states that a particles' kinetic energy — the energy it possesses due to motion — is determined only by its temperature, not its size or mass.

Raizen's study now proves that the equipartition theorem is true for Brownian particles; in this case, glass beads that were three micrometers across.

Raizen says he and his colleagues can now push the limits, moving the particles closer to a quantum state for observation.

"We've now observed the instantaneous velocity of a Brownian particle," says Raizen. "In some sense, we're closing a door on this problem in physics. But we are actually opening a much larger door for future tests of the equipartition theorem at the quantum level."

There, he expects that equipartition theory will break down, leading to new problems and solutions surrounding the quantum mechanics of small particles composed of many atoms.

Raizen's coauthors are Tongcang Li, Simon Kheifets and David Medellin of the Center for Nonlinear Dynamics and Department of Physics at The University of Texas at Austin.

For more information, contact: Lee Clippard, College of Natural Sciences, 512-232-0675; Dr. Mark Raizen, professor of physics, 512-471-4753.

7 Comments to "Physicists Prove Einstein Wrong with Observation of Instantaneous Velocity in Brownian Particles"

1.  Brandon Perry said on May 20, 2010

Your title is incredibly vague (and annoying).

2.  Chris said on May 20, 2010

Good article, but you lost me at the end. How can "small particles" be composed of "many atoms"?

3.  Lawrence Kwiat said on May 21, 2010

You haven't proven Einstein wrong, you've just added to his mystery. Einstein was a prince of the mathematics of uncertainty. He was engaged in the exploration of the unknown - and he knew his field was a moving target. That includes you and your explorations, he understood that his own suppositions of the unknown would eventually engage a reality that would, or would not, support them. You're there, but in being there, you are very much a part of Einstein's case in point - that uncertainty evolves though time. The time you and I are in. Relax. Forget "right" and "wrong" and engage in the evolution of events. Much more important subject. Much more engaged with the evolution of certainty from the sea of uncertainty (to which it eventually re-engages anyway).

4.  Christine said on May 21, 2010

Yeah, but that wouldn't be a very good headline, Lawrence.

5.  Josue Osuna said on May 21, 2010

Congratulations to Raizen and his team. I am a proud old friend of David and have witnessed your passion in these findings. Outstanding and magnanimous job, keep pushing humanity knowledge and certainty beyond, we all thank.

6.  max said on May 26, 2010

THANK YOU for an article that isn't dumbed-down to the point of not having information. Too many science write-ups these days don't actually present any science. Well done.

7.  battered Chipmunk said on Sept. 30, 2010

Einstein's e=mc2 is right in the equation but wrong by the constant. The speed of light is ONLY a measurement of speed. Of course, using this as your constant in this equation would lead you to need an infinite amount of energy to reach the speed of light, as you are using the speed of light as the constant. Anyone else see it! Please tell me I'm not alone here. This equation is based on the assumption that the speed of light is the fastest that ANYTHING can travel. Let's redo his equation, shall we, and see what happens... >:)