Subatomic particles can be divided into two

[sentencecorrection2]

Manhattan 5lb

Subatomic particles can be divided into two classes: fermions and bosons, terms coined by physicist Paul Dirac in honor of his peers Enrico Fermi and Satyendra Bose. 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 hitherto 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, the seemingly stark division between fermionic and bosonic behavior can be bridged. 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 halfintegral, such as ½ and 1½. As a result, whenever an even number of fermions group together, that group of fermions, with its whole-number total spin, effectively becomes a giant boson. Within certain metals chilled to near absolute zero, for instance, so-called Cooper pairs of electrons form; these pairs flow in precise harmony and with zero resistance through the metal, which is thus said to have achieved a superconductive condition. Similarly, helium-4 atoms (composed of 2 electrons, 2 protons, and 2 neutrons) can collectively display boson-like activity when cooled to a superfluid state. A swirl in a cup of superfluid helium will, amazingly, never dissipate. The observation that even-numbered groups of fermions can behave like bosons raises the corollary question of whether groups of bosons can ever exhibit fermionic characteristics. Some scientists argue for the existence of skyrmions (after the theorist Tony Skyrme who first described the behavior of these hypothetical fermion-like groups of bosons) in superconductors and other condensed-matter environments, where twists in the structure of the medium might permit skyrmions to form.


The example of “a crowd filling seats in a stadium” (line 6) is intended to

1. expand upon one consequence of the Pauli exclusion principle
2. illustrate a behavior of certain fermions
3. describe how electrons circle the nuclei of atoms in concentric, evenly-spaced orbits


Answer is 1&2;

I think 2 is not correct. Because the word "certain" in the option 2 makes it incorrect because the passage doesn't say that behavior is showed only by Certain fermions rather it is showed by all fermions.

[tommywallach]

Hey SC2,

I agree that this is a tough question, but I would stand by the passage. Technically, we don't know that ALL fermions display this behavior. For example, what if the atom in question only has 1 electron? Then the metaphor would not be apt/applicable, because there would only be "one person" in the bleachers.

http://en.wikipedia.org/wiki/Hydrogen-like_atom

Now, you could also argue that a "crowd" is discussed, which implies many electrons. There are certainly plenty of fermions that will not have this "crowd" of electrons.

Make sense? (I still agree with you that it's a toughie, but I think it's still fair...)

-t