Activity for HDE 226868‭

Type	On...	Excerpt	Status	Date
Edit	Post #285644	Post edited:	—	about 3 years ago
Edit	Post #285644	Post edited:	—	about 3 years ago
Edit	Post #285644	Initial revision	—	about 3 years ago
Question	—	How are the assumptions behind two ways of deriving the Rayleigh-Jeans law related? The Rayleigh-Jeans law does a good job of describing the spectral radiance of a black body at low frequencies: $$B\nu (T)=\frac{2kT{\nu }^2}{c^2}$$ with $T$ the temperature and $\nu$ the frequency. There are a couple of ways to derive it. One, requiring no explicit assumptions about the energy range ... (more)	—	about 3 years ago
Edit	Post #284410	Initial revision	—	over 3 years ago
Question	—	Is it possible to derive the Dieterici equation starting from assumptions about microstates? I was introduced to a somewhat novel derivation of the ideal gas law that starts by thinking about the number of microstates of an ideal gas, $\mathrm{\Omega }$. Say we have a gas with a single particle in a volume $V$. Doubling the volume should double the number of microstates, as it doubles the possible pos... (more)	—	over 3 years ago
Edit	Post #284016	Initial revision	—	over 3 years ago
Answer	—	A: What is semiholonomic? Semi-holonomic constraints look something like the following: $$f(\mathbf{q},t)=\sum {i=1}^{n}fi(\mathbf{q},t)\dot{q}i+f0(\mathbf{q},t)=0$$ with the requirement that $f(\mathbf{q},t)$ be integrable. This expression should look a lot like the total time derivative of some function $F(\mathbf{q},t)$, if... (more)	—	over 3 years ago
Comment	Post #283985	I'm not sure this is really a question about physics - it seems more like a cultural question. (more)	—	over 3 years ago
Edit	Post #283957	Post edited:	—	over 3 years ago
Edit	Post #283957	Initial revision	—	over 3 years ago
Answer	—	A: What does Lagrangian actually represent? There's not really a fundamental interpretation of the Lagrangian because the Lagrangian that describes the dynamics of a system isn't unique - more than one Lagrangian can yield the correct equations of motion. For instance, let's say we have a particle of mass $m$ experiencing a gravitational force... (more)	—	over 3 years ago
Edit	Post #283502	Post edited: I didn't expect this answer to be out of date within a week! New paper by Brown & Batygin on Planet Nine's orbital parameters	—	over 3 years ago
Edit	Post #283502	Initial revision	—	over 3 years ago
Answer	—	A: If planet 9 exists, is it correct to say that it is a "dark planet"? There are perhaps two questions here. The first is whether the planet is intrinsically dark, i.e. it reflects only a small fraction of the light that reaches it from the Sun and emits only a small amount of blackbody radiation. This can be quantified by the planet's albedo, which depends on the compo... (more)	—	over 3 years ago
Comment	Post #283251	I guess I'm a little confused about one of your criteria ("without . . . acceleration"): in this example, the object should always experience a non-zero acceleration because the $\sim 1/r^2$ relation is only 0 at $r\to \mathrm{\infty }$. (more)	—	over 3 years ago