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Hi, I am a string theorist and a publicist.


Apr
3
comment Prove that $e^{\frac{i\lambda}{\hbar} S_x}S_ze^{-\frac{i\lambda}{\hbar}S_x}=S_z\cos(\lambda)+S_y\sin(\lambda)$
@Paradox101 - it is often useful (but not necessary, as Valter shows) to consider power series for the functions. But if you use them for the exponential, you should probably know what these series (and the factorials and signs in them) look like for the sine and cosine, too.
Apr
2
comment Prove that $e^{\frac{i\lambda}{\hbar} S_x}S_ze^{-\frac{i\lambda}{\hbar}S_x}=S_z\cos(\lambda)+S_y\sin(\lambda)$
You already have it in the form if you know the Taylor expansion of cos and sin! Just put the Sz terms together and Sy terms as well.
Apr
1
awarded  Nice Answer
Mar
30
awarded  Nice Answer
Mar
30
comment What does 400kW(e) mean?
OK, what was meant was 33.3%.
Mar
30
comment Wave on a guitar string, differential equation
It is not, Valter, due to locality. The energy moving through a point is a local quantity related to other local quantities by purely differential operations - so whenever there is an integral sign, it gets cancelled by a derivative.
Mar
30
answered What does 400kW(e) mean?
Mar
30
comment What experiment would disprove string theory?
Yes, we can calculate almost every physical observable in string theory that is well-defined, including many of those that were out of reach of the previous approximate theories. Tens of thousands of papers are full of such calculations.
Mar
29
awarded  Nice Answer
Mar
29
comment Why are the proper time and the proper length not defined in the same frame of reference?
The proper time of a process P (that the object O, e.g. a train, undergoes) and the proper length of object O are defined in the same frame, namely the rest frame of O (in your case the train).
Mar
29
answered Relativity asymmetry?
Mar
25
awarded  Good Answer
Mar
24
awarded  Enlightened
Mar
24
awarded  Nice Answer
Mar
18
awarded  Good Answer
Mar
17
comment Do photons with a frequency of less than 1 Hz exist?
Sorry, the second half of the answer is silly. There is absolutely no problem in producing photons of less-than-one-hertz frequency. Just oscillate with a charge at a frequency less than one hertz and be sure that lots of electromagnetic waves are produced. The waves are composed of many photons - at such low frequencies, we actually produce a huge number of photons. What is hard is to "count" them or experimentally prove that the number is integer - it is not hard to produce them.
Mar
13
comment Why the CMB has not been dispersed so far?
Or alternatively, imagine that the box is as huge as the whole Universe and you're inside it - imagine somewhere near the center. The radiation gets diluted as the box grows but you're still inside it and the radiation is still coming from all directions.
Mar
11
answered Decomposition of group representation using tensor method
Mar
7
awarded  Enlightened
Mar
7
awarded  Nice Answer