[ta92929]

I'm confused. It sounds like they though neutrinos were Weyl points, and neutrinos are real particles. But it also sounds like this experiment created quasiparticles. So are Weyl points still a proposed real particle? Or was it only ever theorized to be some kind of emergent phenomenon? Or did they really create a new type of real particle?

[T-A]

It's one of those cases where condensed matter physicists study a system which satisfies equations known from (more) fundamental theories. Other recurring examples are "black holes" in the lab [1] and "AdS/CFT" (of string theory fame) in solid state and quark-gluon plasma physics [2].

That aside, there is a mathematically well-defined sense in which Weyl fermions are the most "fundamental" fermions: the other kinds you hear about, Dirac and Majorana, can all be written as combinations of Weyl fermions. To make a Dirac, you take two Weyls of opposite helicity and couple them with a common mass term. To make a Majorana, you impose an additional algebraic condition on the two Weyls (take the complex conjugate of Weyl #2, reshuffle it a bit, and you get Weyl #1).

The most significant thing here is the mass term. When you look at the equations, it's immediately obvious that what the mass term does is mix the two Weyls in a Dirac: even if you prepare a pure state of one Weyl, as soon as you set the clock ticking, the mass term will turn it into a mix of two Weyls... unless the mass is exactly 0.

So a less mystifying way to describe the achievement of "making Weyl fermions" is simply "making massless fermions".

[1] http://www.nature.com/nphys/journal/v10/n11/full/nphys3104.h...

[2] https://en.wikipedia.org/wiki/AdS/CFT_correspondence#Applica...

[selimthegrim]

You mean Weyl _fermions_. Weyl fermions obey the Weyl equation, and Majorana fermions the Majorana equation. Majorana fermions are their own anti-particles, while Weyl fermions are not. They are cousins of the Dirac equation (think about how a Dirac point and a Weyl point are related). There is still some debate about whether neutrinos are Weyl or Majorana fermions.

[didgeoridoo]

"I have no doubt that in reality the future will be vastly more surprising than anything I can imagine. Now my own suspicion is that the Universe is not only queerer than we suppose, but queerer than we can suppose." - JBS Haldane

[danieltillett]

This is almost certainly true when you consider almost nobody understands what as humanity we actually know right now about the universe.

The chance that the smartest person in the world is just smart enough to understand exactly how the universe works is very unlikely considering understanding of the universe has never been under evolutional selection. We are going to have to wait for the Singularity to tell us how it really works :)

[selimthegrim]

I misspoke here, I meant Dirac or Majorana fermions.