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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.


Aug
31
comment M-theory and Mathematics
If a D-brane exists, it exists. What would make its existence qualitatively different to the existence of everyday objects like those you list?
Aug
30
comment A few questions about gravity
As for what causes gravity in M-theory, both pictures are available but ultimately some third perspective to do with holographic emergence of space is probably more fundamental. I have to sleep now. Good night
Aug
30
comment A few questions about gravity
Maybe you could if you were Riemann ... But historically it went the other way, mimicking GR with QFT
Aug
30
comment A few questions about gravity
In QFT, classical field states are mimicked by en.m.wikipedia.org/wiki/Coherent_states ... Classical space-time curvature should equal coherent state of gravitons
Aug
30
comment A few questions about gravity
Curved space metric can be described as flat space metric plus an extra field. This extra field that quantifies local deviation from flatness is the graviton field.
Aug
30
comment A few questions about gravity
Dilaton is an example of en.m.wikipedia.org/wiki/Scalar-tensor_theory ... Dilaton field strength equals radius of M-theory 11th dimension
Aug
30
comment A few questions about gravity
Damon, these people have treated you contemptibly. They should be ashamed.
Jun
4
comment What laws are the same in all string theory compactifications?
This question should not be closed.
May
27
comment Does the holographic principle for black holes mean that information is cloned?
Let us continue this discussion in chat.
May
16
comment Could M-Theory explain dark matter as well as dark energy?
@HDE 226868 Actually, you don't know that. They may be related, they may not be.
May
10
comment What does it mean physically if pentagon identity or hexagon identity doesn't have any answers?
@CuriousOne the question is in the title. I interpret it as asking whether all solutions to the fusion rules must obey those identities.
May
5
comment What is the property of neutrino?
The spin and momentum of a particle are affected by other interactions too, Z boson and photon don't have a special role there.
May
5
comment Why do we need complex representations in Grand Unified Theories?
I am a bit puzzled about the relation between this argument and Edward's... is one more fundamental than the other. Further thought required.
May
5
comment Why do we need complex representations in Grand Unified Theories?
If $\psi$ is real, then a term of the form $m \psi^* \psi$ should automatically exist - whereas, if $\psi$ is complex, that term exists only if a separate, complex-conjugate field is part of the theory. And then I think naturalness is used to argue that the coefficient will be large enough to matter.
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.