
Physicists observe 'negative mass' - kartikkumar
http://www.bbc.com/news/science-environment-39642992
======
deepnet
It is still an open question as to whether anti-matter falls up or down - e.g.
negative gravitational mass.

The ALPHA experiment is using anti-hydrogen at CERN to find out.

[https://www.nature.com/articles/ncomms2787](https://www.nature.com/articles/ncomms2787)

So far they have made some, but not enough to rule out experimental error.

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CarolineW
Is this the same story as posted here:

[https://news.ycombinator.com/item?id=14147264](https://news.ycombinator.com/item?id=14147264)
(0 comments)

Or here:
[https://news.ycombinator.com/item?id=14135929](https://news.ycombinator.com/item?id=14135929)
(0 comments)

Or here:
[https://news.ycombinator.com/item?id=14131417](https://news.ycombinator.com/item?id=14131417)
(1 comment)

Or here:
[https://news.ycombinator.com/item?id=14130945](https://news.ycombinator.com/item?id=14130945)
(2 comments)

Or here:
[https://news.ycombinator.com/item?id=14093860](https://news.ycombinator.com/item?id=14093860)
(40 comments)

If it's the same as that last one, the comments there are pretty scathing
about the whole thing, so some scepticism advised.

~~~
gus_massa
> _so some scepticism advised._

I think it's a wrong attitude for this article. I prefer to use "beware that
the naïve layman explanation may be misleading and wrong". The research
article is good, the layman explanation is impossible to write.

This is a very technical subject. I don't understand all the details, so I'll
mix some information with guess.

First a similar experiment: Inside a semiconductor, the conduction electrons
are not isolated. You can image that an electron has a cloud of perturbations
around it. So the effective mass of an electron inside a semiconductor is not
the mass of an isolated electron.

Moreover, in some cases the effective mass can be negative. If you push them
with an electric or magnetic field, they will move in the wrong direction.

So it's easier to understand their behavior thinking that they are positively
charged particles with a positive mass, rather than negatively charged
particles with a negative mass. The usual name for them is "holes" and any
Engineer that use semiconductors will use them as if they were real particles.
(A Physicist will be totally convinced that they are real particles, but real
has here not the usual definition.)

So, there are some examples of "things" with negative mass. This case is
different because it's a fluid (a bose condensate?) instead of a solid, and
they are using rubidium atoms that are bosons instead of electrons that are
fermions. So I'm not sure about the details ...

But this is probably a fluid with negative mass that only can live inside some
weird material. It's not a fluid that can be isolated and put in a balance and
get a negative result.

[And it can't be used to build an Alcubierre Drive.]

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squozzer
I think I used the term "negative mass" on a physics pop quiz once. Had
something to do with matter-antimatter reactions. Appears I was 23 years ahead
of my time.

