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seen Jul 23 '13 at 10:51

String theory grad student.


Aug
4
comment Relativity - time dilation
You have to be careful about simultaneity, which is not a frame-independent concept. In your original question, you defined simultaneous events in the frame of observer A (whether you intended to or not). As long as you stick with a frame you're fine. But now you launch the second chip in one frame, and want to discuss what it looks like in the first chip's frame, so you have to be careful. For example, in the first chip's frame the new launch does not happen when he is $10^{-6}$ months old, but after that! You have to work it out carefully.
Aug
4
awarded  Commentator
Aug
4
comment How is $\frac{dQ}{T}$ measure of randomness of system?
A microscopic description (like statistical mechanics) considers the underlying degrees of freedom, and should explain how the observed 'macroscopic' phenomena emerge from the detailed model. If you derive the ideal gas law by postulating tiny atoms bouncing around -- that is a microscopic description. Of course a microscopic model at one level may become phenomenological once you go to more detailed observations, so this distinction depends on one's point of view. People who study optics would not call particle physicists 'phenomenologists' -- but strings theorists would.
Aug
4
comment How is $\frac{dQ}{T}$ measure of randomness of system?
I don't know about a 'formal' definition, but a phenomenological description is a description that is at the level of the observations. We observe that a system has certain properties that we can measure, like temperature, pressure, and so on. And we observe certain relations between these properties. When we combine these into a (hopefully simple) model -- that is a phenomenological description. For example, the ideal gas law and Ohm's law are both phenomenological models.
Aug
4
awarded  Revival
Aug
4
answered How is dark energy consistent with conservation of mass and energy?
Aug
4
comment Relativity - time dilation
If you are down voting, it will be nice if you explain your reason for doing so.
Aug
4
revised Relativity - time dilation
Clarified meaning of t(A),t(B),t(C)
Aug
4
answered Relativity - time dilation
Aug
3
comment How is $\frac{dQ}{T}$ measure of randomness of system?
My advice to you, based on personal experience, is to accept these confusions until you learn about the definition of entropy in statistical mechanics (which is what Nathaniel refers to below). Entropy is defined for any system where the specific state is chosen from a probability distribution, and it directly measures our ignorance about which state the system is in ($S=0$ means we know the state exactly, $S$ maximal means all states have equal probability). I find it very confusing to try to understand it through $dQ/T$, since that is a phenomenological rather than microscopic description.
Aug
3
comment Is the Higgs a quantum field or a particle?
I understand; this is why I gave two additional definitions that explain why people think of Higgs excitations as particles. Sorry if this did more to confuse than to clarify.
Aug
3
awarded  Critic
Aug
3
answered Is the Higgs a quantum field or a particle?
Aug
3
comment Taking the continuum limit of $U(N)$ gauge theories
I said it is similar, not the same. It seems to me this discussion has strayed from the original question. Why not post it as a new question?
Aug
2
awarded  Supporter
Aug
1
comment Is spacetime discrete or continuous?
I cannot access the full article because I do not have a scientific american subscription. I will say that statements like "If it works, it could rewrite the rules for 21st-century physics" are generally not indicative of interesting work.
Aug
1
comment Taking the continuum limit of $U(N)$ gauge theories
I don't have a reference but the story is similar to the multiplets in $d=4$, which are derived in any textbook on SUSY. You can repeat this exercise in $d=3$.
Aug
1
revised Is spacetime discrete or continuous?
added 877 characters in body
Aug
1
revised Taking the continuum limit of $U(N)$ gauge theories
Added caution
Aug
1
comment Taking the continuum limit of $U(N)$ gauge theories
As they say, in the $N=3$ theory you can have hypermultiplets, and each hypermultiplet has two chiral multiplets: one in a rep $R$ and one in $\bar{R}$. It is not necessary that $R$ is the adjoint. A bit below the place you mention they consider various possibilities for $R$, only one of which is the adjoint. If you say that a hypermultiplet is 'fundamental' (which I think is not a precise statement although its meaning is clear), it means that you have one chiral multiplet in the fundamental and one in the anti-fundamental.