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Physics: Physicists observe 'negative mass'

Introversion

Introversion

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Physicists have created a fluid with "negative mass", which accelerates towards you when pushed.

BBC News said:
In the everyday world, when an object is pushed, it accelerates in the same direction as the force applied to it; this relationship is described by Isaac Newton's Second Law of Motion.

But in theory, matter can have negative mass in the same sense that an electric charge can be positive or negative.

The phenomenon is described in Physical Review Letters journal.

Prof Peter Engels, from Washington State University (WSU), and colleagues cooled rubidium atoms to just above the temperature of absolute zero (close to -273C), creating what's known as a Bose-Einstein condensate.

In this state, particles move extremely slowly, and following behaviour predicted by quantum mechanics, acting like waves.

They also synchronise and move together in what's known as a superfluid, which flows without losing energy.

To create the conditions for negative mass, the researchers used lasers to trap the rubidium atoms and to kick them back and forth, changing the way they spin.

When the atoms were released from the laser trap, they expanded, with some displaying negative mass.

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Click to expand...
 
dickson

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Introversion said:
Physicists have created a fluid with "negative mass", which accelerates towards you when pushed.
Click to expand...

I can't wait to read the Phys. Rev. Lett. about this experiment. There seems to be no end to the clever things you can do with a nice cold Bose-Einstein condensate. And here I can remember reading in a famous graduate-level textbook that the Bose-Einstein condensate "must be one of the most spectacular phenomena in physics to occur purely on paper." (D. Goodstein, States of Matter, Prentice-Hall, Englewood Cliffs, NJ, 1975)

On the basis of the Beeb account, however, what has been demonstrated appears to be a collective phenomenon in normal matter. It's nothing like what would happen if elementary particles with negative mass exist in nature. If memory serves, during the 1950's Hermann Bondi explored what physics would be like if we had some of those. The consequences are certainly bizarre: Gravitational interactions would repel such particles, which would accelerate without bound as they lost energy. I'm certain they would do things, awful things, to the Big Bang. I dunno what they'd be off the top of my head, but I'm sure they would be dire. The effect on relativistic quantum field theories such as comprise the Standard Model would be to hole them below the waterline so completely that there would be no time to launch lifeboats before going down with all hands.

A related issue is the question of in which direction does a positron fall in the Earth's gravitaitonal field. The matter has received both theoretical and experimental attention over the years. It's been a long time, but I recall seeing a Reports on Modern Physics review paper by Martin Nieto maybe twenty years ago. (Twenty-five? My the years grow late.) It is evidently quite a difficult experiment to perform.
 
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