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I used to check every question here but not any more. Physics Overflow, which was built from the archives of a defunct "Theoretical Physics Stack Exchange", seems more promising as a place for advanced physics Q&A.


May
5
comment Why do we need complex representations in Grand Unified Theories?
@JakobH I think that some principles of effective field theory are relevant here. One is that every gauge-invariant combination of the field operators should appear in the Lagrangian, the other is that their coefficients should be natural, not too small or large (anything else would be regarded as evidence of new physical mechanisms at higher scales, responsible for the unnatural values).
May
3
comment Real representations of chiral fields
but the masses of charged fermions in the standard model aren't Majorana masses. Anyway see recent question by JakobH for more
May
1
comment Why do we need complex representations in Grand Unified Theories?
... whereas the SM requires Weyl fermions that aren't paired with mirrors, so that mass can instead come from a Higgs-mediated coupling between left-handed weak doublet and right-handed weak singlet.
May
1
comment Why do we need complex representations in Grand Unified Theories?
@JakobH Do you know Weyl fermions (two components) vs Dirac fermions (four components)? The point is that a Weyl fermion and its mirror will combine to make an effective Dirac fermion, because a Dirac-like mass term connecting the two fields is allowed by gauge symmetry...
Apr
30
comment Why do we need complex representations in Grand Unified Theories?
@JakobH In that paper, Adler says his E8 model has mirror fermions. Really, all the reasons on your list are related.
Apr
26
comment Questions about the formalism of Quantum Mechanics
Anyway, I was going to say: Bohmian mechanics is actually easier to explain that quantum mechanics, because it's still just a mathematical state evolving over time. Quantum mechanics has observables and operators and expectation values, the same or similar mathematical formalism takes on different and more complicated meanings.
Apr
26
comment Questions about the formalism of Quantum Mechanics
For some reason, comment editor is stripping OP's name from previous comment. @David
Apr
26
comment Questions about the formalism of Quantum Mechanics
you've relabelled the question as about quantum mechanics, but question 5 is definitely only Bohmian, and questions 4 and 6 have a quite different character if they are read as being about quantum mechanics...
Apr
26
answered Questions about the formalism of Quantum Mechanics
Apr
25
comment What happens in a universe with only two electrons?
I think I saw, in a comment that may have been deleted, @Sharon Salmon say that many of the answers about quantum reality were manifestly statements of opinion rather than knowledge. I just wanted to establish that it is true of the responses here too.
Apr
25
comment What happens in a universe with only two electrons?
@Asher I see from one of your answers physics.stackexchange.com/questions/159308/… that you think electrons don't have a location until they are measured; and I see from your profile that you consider yourself an amateur physicist at best?
Apr
25
comment What happens in a universe with only two electrons?
@Asher, but do you think that the electron has a definite position or definite momentum before you measure it?
Apr
24
comment Physical meaning of quantum interpretations
Apparently based on this Physics Overflow question physicsoverflow.org/29793
Apr
20
comment Where is all the Dark Matter? Theoretical Question
Dark matter is usually thought to form a big sphere around a galaxy, called a halo. The DM particles are everywhere inside the sphere, all the way through. They aren't hiding, but they don't interact much with visible matter, except via gravity.
Apr
9
comment why does string theory require holography?
OK! Holography does help with calculations. Sometimes the alternative description it offers is the only known way. I'll think about what to say about this.
Apr
9
awarded  Revival
Apr
9
comment why does string theory require holography?
That's like saying "why does arithmetic need prime numbers?" The existence of prime numbers is not a starting point, but it follows logically from the definitions of counting, multiplication, etc. The point is that string theory was not designed with holography in mind, it was built step by step according to other criteria, but the resulting theory turned out to have the holographic property.
Apr
8
comment why does string theory require holography?
@John Peterson - Sorry, I don't follow... Holography is not a choice in string theory. You can't have string theory and then decide to add holography, they believe holography is already implied. But it took several decades before this was discovered to be an implication of the theory.
Apr
7
answered why does string theory require holography?
Apr
6
comment Form of the S matrix for interacting scalar field
@Amara, if you ever see this- try asking at Physics Overflow.