Violation of Pauli's Exclusion Principle possible?

1. Nov 15, 2015

Aliasa

I was reading some simplistic explanations of Pauli's Exclusion Principle (PEP) to explain a group of non-science people, and I came across this:

For Fermions, even as pressure builds, no two can be located in the same energy state. This causes them to "stack up" in effect. Only under great force can this(PEP) be overcome.

I have a problem with the last sentence. They go on to talk about Neutron Degeneracy Pressure and formation of black holes, but I'm unsure whether PEP is actually being violated there. Can anyone shed a light?

Last edited: Nov 15, 2015
2. Nov 15, 2015

vanhees71

No the PEP cannot be violated. I think what they want to say is that at too high masses neutron stars become unstable against gravitational collapse. For compact objects you always have a counterbalance between pressure and gravitation. The PEP causes a big pressure, i.e., you cannot squeeze indistinguishable fermions easily together. That's why you can have quite heavy neutron stars (not too long ago one has observed neutron stars with two solar masses!). But at one point this degeneration pressure cannot withstand the gravitation, and the object collapses to a black hole.

3. Nov 17, 2015

stevebd1

From looking at this paper-
Neutron Star Interiors and the Equation of State of Superdense Matter
http://arxiv.org/abs/0705.2708v2

The impression I got is that the increase in equation of state $(w=P/\rho c^2)$ brings on a change in the state of matter (note, for regular matter, w=0). For instance, looking at a typical neutron star, the equation of state (eos) at the centre is predicted to be w=0.59; for a hyperon star (neutron star with hyperons at the core), w=0.42 to 0.31 at the centre; and for a hybrid neutron star (with quark matter at the centre), w=0.21. The interesting thing here is that in the transition from neutron matter to quark matter, the density increases but the pressure seems to actually drop*. This gives the impression that as matter approaches w=1, there's a change in the state of matter, it may be that quarks break down into something else (there is the hypothetical preon) and this process keeps going until reaching Planck density/pressure where w=1 (or at least close to it). It's possible that virtual particles will play some part in halting the collapse before Planck density/pressure is reached.

*According to the paper, the quantities for the hyperon star at the centre are density- 2x109 tonnes/cm3 and the pressure is between 6 to 8x1034 N/m2 while for the hybrid star the density at the centre is 3x109 tonnes/cm3 and the pressure is 5x1034 N/m2.

4. Nov 18, 2015

zonde

I have a problem with that too. From one side it is claimed that PEP can't be violated but from other side it is said that black holes do form despite PEP.

So I have tried to understand what happens according to QM if you try to violate PEP.
One direct conclusion is that distribution of particles across different energy levels changes from Maxwell–Boltzmann statistics to Fermi–Dirac statistics.
Another more speculative conclusion is that particle collisions that involve degenerate matter can't be modeled classically (because "classical collisions" imply Maxwell–Boltzmann statistics).