- #1
Ken G
Gold Member
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Two statements that are often made about degeneracy pressure are:
1) It is a new or special kind of pressure that requires quantum mechanics, in contrast with ideal gas pressure, which in effect involves somewhat mysterious forces that emerge from the Pauli exclusion principle, and
2) it behaves in such a way that degenerate gases do not expand like ideal gases when heat is added to them, which allows the heat to build up and fusion to run away (which causes helium flashes and type Ia supernovae).
For example, these claims can be found in many textbooks, and in Wiki:
http://en.wikipedia.org/wiki/Electro...eracy_pressure
"The Pauli exclusion principle disallows two half integer spin particles (fermions) from simultaneously occupying the same quantum state. The resulting emergent repulsive force is manifested as a pressure against compression of matter into smaller volumes of space."
So that certainly sounds like a "T" for (1). Then we have:
http://en.wikipedia.org/wiki/Type_Ia_supernova
"A main sequence star supported by thermal pressure would expand and cool in order to counterbalance an increase in thermal energy. However, degeneracy pressure is independent of temperature; the white dwarf is unable to regulate the burning process in the manner of normal stars, and is vulnerable to a runaway fusion reaction."
If the point being made here seems unclear, it is often explained further in the quite similar conditions that appear in a helium flash:
http://en.wikipedia.org/wiki/Helium_flash
"A helium flash occurs in these situations because the helium is degenerate, meaning it is supported against gravity by quantum mechanical pressure rather than thermal pressure. Thus an increase in the temperature in the material undergoing fusion does not act to expand the material and by doing so cool it, and there is no regulation of the rate of fusion. "
Certainly there are always idealizations and generalizations needed to simplify complex physics, but do the above two statements about degeneracy pressure really encapsulate the essence of the phenomena encountered, or are they pretty much false myths that are propagated simply because they are not subjected to critical scrutiny? What do people think? The poll possibilities are TT, which is both statements are mostly true, or TF, so statement (1) is mostly true but statement (2) is basically a myth, or FT if the opposite, or FF if both statements are mostly myths that do more to foster misconceptions than bring insights.
1) It is a new or special kind of pressure that requires quantum mechanics, in contrast with ideal gas pressure, which in effect involves somewhat mysterious forces that emerge from the Pauli exclusion principle, and
2) it behaves in such a way that degenerate gases do not expand like ideal gases when heat is added to them, which allows the heat to build up and fusion to run away (which causes helium flashes and type Ia supernovae).
For example, these claims can be found in many textbooks, and in Wiki:
http://en.wikipedia.org/wiki/Electro...eracy_pressure
"The Pauli exclusion principle disallows two half integer spin particles (fermions) from simultaneously occupying the same quantum state. The resulting emergent repulsive force is manifested as a pressure against compression of matter into smaller volumes of space."
So that certainly sounds like a "T" for (1). Then we have:
http://en.wikipedia.org/wiki/Type_Ia_supernova
"A main sequence star supported by thermal pressure would expand and cool in order to counterbalance an increase in thermal energy. However, degeneracy pressure is independent of temperature; the white dwarf is unable to regulate the burning process in the manner of normal stars, and is vulnerable to a runaway fusion reaction."
If the point being made here seems unclear, it is often explained further in the quite similar conditions that appear in a helium flash:
http://en.wikipedia.org/wiki/Helium_flash
"A helium flash occurs in these situations because the helium is degenerate, meaning it is supported against gravity by quantum mechanical pressure rather than thermal pressure. Thus an increase in the temperature in the material undergoing fusion does not act to expand the material and by doing so cool it, and there is no regulation of the rate of fusion. "
Certainly there are always idealizations and generalizations needed to simplify complex physics, but do the above two statements about degeneracy pressure really encapsulate the essence of the phenomena encountered, or are they pretty much false myths that are propagated simply because they are not subjected to critical scrutiny? What do people think? The poll possibilities are TT, which is both statements are mostly true, or TF, so statement (1) is mostly true but statement (2) is basically a myth, or FT if the opposite, or FF if both statements are mostly myths that do more to foster misconceptions than bring insights.
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