particleguy
Joined 7 years ago
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Comment · 1 year ago
Yes, Quantum Field Theory can be explained through Lie groups. SU(2) is isomorphic to the quaternions of norm 1, and SU(2) is important if you want to understand the Lorentz group and Poincare group, which represent the symmetries of spacetime and special relativity. Check out the text book Physics From Symmetry by Jakob Schwichtenberg if you would like an approach that derives modern physics primarily from algebra
Comment · 6 years ago
>> ArXiv pre-prints are pretty normal in physics and math.
Correct, and they are usually followed up by a published, peer-reviewed paper as well. I look forward to the day this one also gets reviewed and published.
Higgs boson discovery pre-print: https://arxiv.org/abs/1207.7214 Higgs boson discovery paper: https://www.sciencedirect.com/science/article/pii/S037026931...
It's essentially the same text.
>> BTW, Krasznahorkay is a highly-cited researchers.
Great
Comment · 6 years ago
This result isn't even peer-reviewed yet. All of this hype about the X17 particle is coming from a pre-print on the arXiv.
https://arxiv.org/abs/1910.10459
They claim a 7.2 sigma result, but the distribution of the null-hypothesis (called PDF(exp) in the paper) was determined from simulations of one atomic transition and "external pair creation on the target backing", and the only source of systematic error they took into account was the position of the target relative to the beam-line. It seems a little paltry to me in terms of trying to take into account possible sources of error... And given that the excess appears in only a particular angular region, they seem to be ignoring the Look-elsewhere effect ("oh, no excess signal here? Let me look elsewhere...") and over-stating their significance. The paper also is riddled with spelling and grammar mistakes, and while that doesn't have anything to do with the science, it does say something about the sloppiness of the researcher, I think.
Anyway, I can't imagine this passing the muster of peer-review in its current state. But I'll be curious to see the revised paper with more details included (if they can actually get it published).
EDIT: They did explain how they determined the background distribution, I edited my comment above.
Comment · 7 years ago
Her post linked to in the original blog post makes a good point too: Even if your theory is consistent, it is only as valid as the assumed axioms. Consistency, of course, is necessary in any correct theory of physics, but it is not sufficient and definitely does not make the theory "inevitable". Also, if the consistent axioms are underspecified, you get ambiguous and un-falsifiable theories. Her main target has often been multiverse theories (i.e. how would you define a measure over universes/how could you verify a probability distribution over universes).
In her book "Lost in Math" a target of ire has also been supersymmetry, though she dislikes supersymmetry for another reason, namely the fact that it relies too much on justifications of "beauty" to survive all of its empirical short-comings. In her view, the fact that supersymmetry solves the hierarchy problem is more an aesthetic point (and therefore irrelevant), than a mathematical or logical necessity.
Comment · 7 years ago
I like Physics from Symmetry by Jakob Schwichtenberg as an explanation of how spin arises from a modern understanding of physics. The book was written while the author was a Masters student, and so it is much closer to the way an undergrad physics student would explain it to another student. The author is willing to skip details in favor of more general understanding.
The way the book will describe it is from the perspective of group theory. If you assume that the laws of nature in a relativistic flat spacetime do not change under rotations, translations (in both space and time), and boosts (transformation between frames of reference of constant velocity), then these transformations define a Lie group called the Poincaré group. Representation theory then says that the representations of the Poincare group are characterized by two numbers. These two numbers are identified as a nonnegative mass and a spin. One interpretation is that these representations are indeed what "particles" are in Quantum Field Theory.
Comment · 7 years ago
A small correction- it’s not the small mass of the neutrino that allows it to escape quickly, but the fact that they are electrically neutral, and also do not interact with the strong force and do not get caught by the nucleus of atoms. Photons have no mass, but they arrive after the neutrinos because they are slowed down by being constantly absorbed and remitted by the atoms of the star through the electromagnetic force.