## Wednesday, April 19, 2017

### Diary: negative mass + Tintinhull + Montacute

I was reading the 'Stardrive' book this morning (the part about how the Casimir effect is related to a regime of negative energy between the conducting plates) when the latest news broke about negative mass.
"Washington State University physicists have created a fluid with negative mass, which is exactly what it sounds like. Push it, and unlike every physical object in the world we know, it doesn't accelerate in the direction it was pushed. It accelerates backwards."
The discussion at Physics StackExchange clarified that this does not mean stuff falls upwards. No cavorite then.
"You also asked whether an object with negative mass falls up or down. The equivalence principle tells us that gravity is indistinguishable from uniform acceleration. That means that positive and negative masses have to behave the exact same way under gravity, so negative mass falls down."
If you want a complete explanation ... .

---

This afternoon we took a trip.

 Clare and your author at Montacute House

 Montacute House: an Elizabethan wonder

 Tintinhull Garden

We've been discussing (as a family) who'd we vote for in the first round of the French Presidential election this Sunday. I think we're converging on Jean-Luc Mélenchon: his policies seem to have something for each of us 😎 ... .

1. Actually your Cavorite quote needs to be taken a little carefully. Yes, negative mass will fall down assuming it obeys the Weak Equivalence Principle (extended to negative mass). Generally in discussions this is what is assumed, ie

Gravitational Mass = Inertial Mass

even when that mass is negative.

However in the above experiment one is dealing with "Effective Mass" inside a Quantum Simulation. This effective mass obeys an equation demonstrating that it is negative; and this behaviour has been demonstrated in the experiment. More precisely negative inertial mass has been demonstrated (in the simulation).

There is no claim either way that the Weak Equivalence Principle holds here, in fact the expectation seems to be that the WEP will fail. In short:

¬ WEP: (Negative) Simulated Effective Mass =/= (Negative) Gravitational Mass

and so the Effective mass would move upwards in a Gravitational Field, just like a bubble. So it could be a Quantum Simulation of Cavorite, although that would have to be tested directly.

Overall the "Effective Theory" to be found in material physics has some interesting properties, including negative mass - it transpires that the construct originates in the valence band theory of semiconductors (inspired by Dirac) with negative mass electrons - a form of these "electron holes" (WikiP qv).

1. Re: Complete explanation. You may have noticed that I have contributed to the BackReaction blog in a comment.

Now a later commentator has asked me a related physics question! Will Sabine answer, or should I, or should all this go onto Stack Exchange?

2. The standard of comments was not high. You might get a better class of discussion on StackExchange although Bee would no doubt welcome a more intellectual thread at hers... .