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Negative Mass


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#1 geordief

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Posted 19 April 2017 - 01:04 PM

http://www.bbc.com/n...onment-39642992

 

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

 

Seems like it might be a big science story. Is it?

 

Anyone care to  comment?


Edited by geordief, 19 April 2017 - 01:08 PM.

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#2 Strange

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Posted 19 April 2017 - 01:17 PM

There is a good (but short) discussion of this on another forum (https://forum.cosmoq...Negative-masses)

 

The key point is that is is negative effective mass, not really negative mass. Effective mass is shown by a number of things, including for example "holes" in semiconductors (where an electron is missing and so you get a virtual positive charge carrier). 


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#3 imatfaal

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Posted 19 April 2017 - 02:52 PM

A negative effective mass can be realized in quantum systems by engineering the dispersion relation. A powerful method is provided by spin-orbit coupling, which is currently at the center of intense research efforts. Here we measure an expanding spin-orbit coupled Bose-Einstein condensate whose dispersion features a region of negative effective mass. We observe a range of dynamical phenomena, including the breaking of parity and of Galilean covariance, dynamical instabilities, and self-trapping. The experimental findings are reproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the emerging features—shock waves, soliton trains, self-trapping, etc.—originate from a modified dispersion. Our work also sheds new light on related phenomena in optical lattices, where the underlying periodic structure often complicates their interpretation.

https://journals.aps...Lett.118.155301
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#4 swansont

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Posted 19 April 2017 - 05:55 PM

Say you have a helium-filled balloon in a car (I've also seen this done with a cork suspended in a jar of water). When the car accelerates, the balloon accelerates in the opposite direction, relative to the car. One might describe the balloon as having negative mass  — but that's just a way of modeling the behavior, like (as Strange said) modeling a hole in a semiconductor.


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#5 geordief

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Posted 19 April 2017 - 06:07 PM

Say you have a helium-filled balloon in a car (I've also seen this done with a cork suspended in a jar of water). When the car accelerates, the balloon accelerates in the opposite direction, relative to the car. One might describe the balloon as having negative mass  — but that's just a way of modeling the behavior, like (as Strange said) modeling a hole in a semiconductor.

If the car accelerates wrt a stationary observer what does the helium balloon wrt the same observer?  Accelerate less in the same direction?


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#6 swansont

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Posted 19 April 2017 - 08:08 PM

If the car accelerates wrt a stationary observer what does the helium balloon wrt the same observer?  Accelerate less in the same direction?

 

 

Yes, I believe so.


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