Fermions, which include electrons, protons, and neutrons, obey the Pauli exclusion principle, according to which no two particles can inhabit the same fundamental state. For example, electrons cannot circle the nuclei of atoms in precisely the same orbits, loosely speaking, and thus must occupy more and more distant locations, like a crowd filling seats in a stadium. The constituents of ordinary matter are fermions; indeed, the fact that fermions are in some sense mutually exclusive is the most salient reason why two things composed of ordinary matter cannot be in the same place at the same time.

Conversely, bosons, which include photons (particles of light) and the elusive Higgs boson, do not obey the Pauli principle and in fact tend to bunch together in exactly the same fundamental state, as in lasers, in which each photon proceeds in perfect lockstep with all the others. Interestingly, all particles possess "spin," a characteristic vaguely analogous to that of a spinning ball; boson spins are measured in integers, such as 0 and 1 , while fermion spins are always half-integral, such as $\(\frac{1 }{ 2}\)$ and $\(1\frac{1 }{ 2}\)$. As a result, whenever an even number of fermions group together, that group of fermions, with its whole-number total spin, becomes a giant boson. For example, helium-4 atoms (composed of 2 electrons, 2 protons, and 2 neutrons) can collectively display boson-like activity when cooled to a superfluid state.

The example of "a crowd filling seats in a stadium" is intended to

A. expand upon one consequence of the Pauli exclusion principle
B. illustrate a behavior of certain fermions
C. describe how electrons circle the nuclei of atoms in concentric, evenly spaced orbits



The author's primary purpose in writing this passage is to

(A) explain the mechanism by which fermions can become bosons
(B) describe the two classes of subatomic particles
(C) provide examples of the different forms of matter
(D) explain the concept of particle "spin"
(E) argue that most matter is composed of one type of particle



Which of the following is not mentioned as a characteristic of bosons?

(A) They can be composed of groups of fermions.
(B) They are measured in integer spin.
(C) They are the constituents of ordinary matter.
(D) They tend to bunch together in the same fundamental state.
(E) They include particles such as photons.



According to the passage, which of the following describes a difference between fermions and bosons?

(A) Fermions cannot inhabit the same fundamental state, whereas bosons bunch together in the same state.
(B) Fermions contain many more types of particles than bosons.
(C) Fermions exist in groups, but bosons do not.
(D) Fermions have integral spin values, whereas Bosons have half-integer spin.
(E) Fermions do not obey the Pauli principle, whereas bosons do.



Based on the information in the passage about the Pauli exclusion principle, to which one of the following situations would this principle be most relevant?

(A) Fermi Energy: The maximum energy that electrons in a solid will contain in order to avoid having identical states
(B) Particle Accelerators: Devices that will accelerate charged particles to very high speeds through the application of an external magnetic field
(C) Quantum Entanglement: When particles interact physically and then become separated but still have interdependent properties
(D) Double Slit Experiment: An experiment that revealed the particle and wave duality of photons
(E) The Higgs Field: The field produced by the conjectured Higgs particle that would explain why matter has mass