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What about the constants that describe the (relative) rest masses of elementary particles? Since we don’t know the order of magnitude of neutrino masses, it see

by addaon 2y ago

What about the constants that describe the (relative) rest masses of elementary particles? Since we don’t know the order of magnitude of neutrino masses, it seems improbable that even an order of magnitude change of those masses over time would lead to “dramatic changes in the structure of matter.”

adrian_b 2y ago
The masses of the particles and other specific properties, like magnetic moments, are not fundamental constants. They are the properties of those particles. There are such properties for leptons, for hadrons, for nuclei, for atoms, for molecules, for chemical substances, for humans and so on. Any object, either as small as an electron or as big as the Sun is characterized by various numeric properties, such as mass. The fundamental constants are not specific to any particular object. As I have said, after eliminating the fundamental constants that are determined by conventional choices of the system of units, the only fundamental constants that remain are those that characterize the strength of each fundamental interaction, as expressed in a natural system of units. Because most objects are composed of smaller subobjects, it should have been possible to compute their properties from the properties of their components. Starting from the properties of leptons and quarks, it should have been possible to compute the properties of hadrons, nuclei, atoms, molecules and so on. Unfortunately we do not have any theory that can compute the desired properties with enough precision and in most cases even approximate values are impossible to compute. So almost all properties of particles, nuclei, atoms or molecules must be measured experimentally. Besides the question whether the fundamental constants can change in time, one can put a separate question whether the properties of leptons and quarks can vary in time. Some of the properties of leptons and quarks are constrained by symmetry rules, but there remain a few that could vary, for instance the mass ratio between muon and electron. It is likely that a future theory might discover that this mass ratio is not an arbitrary parameter, but the muon is a kind of excited state of the electron, in which case this mass ratio could be computed as a function of the fundamental constants, so the question whether it can vary would be reduced to the question about the variation of the fundamental constants.
- GolDDranks 2y ago
  I think you are wrong; for example the Standard model has 26 (or 25?) fundamental constants that can be made dimensionless, so they are not dependent on the choice of units. Also, the masses of fundamental particles are connected to the strength of the coupling of the particle's field to the Higgs field, and those coupling strengths are fundamental constants.
  - adrian_b 2y ago
    Not all the parameters of the standard model can be made dimensionless, and for most others their dimensionlessness is illusory. When you have 10 absolute masses, you can also represent them by one absolute mass and 9 dimensionless mass ratios. Then you can claim that your model has 9 dimensionless parameters, but this changes nothing, because in any formula that relates different physical quantities you must multiply the mass ratios by an absolute mass. There are cases when using dimensionless mass ratios does not bring any advantage, but there are also cases when using mass ratios can improve the accuracy. For very small things, like particles, nuclei, atoms or molecules, it is possible to measure with much higher accuracy the ratio between their mass and the mass of an electron, than their absolute mass. So in particle/nuclear/atomic physics it is usually the best to express all masses as dimensionless ratios vs. the mass of an electron and to multiply them with the absolute mass of an electron only where necessary. There are methods to measure with high accuracy the absolute mass of an electron, based on measuring the Rydberg constant and the constant of the fine structure. Most parameters of the standard model are dimensionless because they are ratios that eventually need to be multiplied with an absolute value for the computation of practical results. In many research papers about the standard model they get away with using only "dimensionless" parameters because they take advantage of the fact that they cannot continue the computations far enough to obtain practical results, so they use some ad hoc system of units that is not clearly defined and which is disconnected from the remainder of the physics.
    - GolDDranks 2y ago
      > When you have 10 absolute masses, you can also represent them by one absolute mass and 9 dimensionless mass ratios. Then you can claim that your model has 9 dimensionless parameters, but this changes nothing, because in any formula that relates different physical quantities you must multiply the mass ratios by an absolute mass. What? So, what is the mechanism in nature that produces those 9 ratios? If you haven't got one, you haven't got a theory; you've got to admit that those are experimentally confirmed fundamentals. So, I interpret what you're saying like this: you have got a pet theory where the mass ratios are calculable from some other, more fundamental assumptions, but (charitably: because the theory is numerically too hard, or you lack compute resources) you don't have the actual means to calculate them. Otherwise, I scratch my head. If you don't manage to enlighten me, I deem you a crank.

by addaon 2y ago

adrian_b 2y ago

The masses of the particles and other specific properties, like magnetic moments, are not fundamental constants. They are the properties of those particles. There are such properties for leptons, for hadrons, for nuclei, for atoms, for molecules, for chemical substances, for humans and so on. Any object, either as small as an electron or as big as the Sun is characterized by various numeric properties, such as mass. The fundamental constants are not specific to any particular object. As I have said, after eliminating the fundamental constants that are determined by conventional choices of the system of units, the only fundamental constants that remain are those that characterize the strength of each fundamental interaction, as expressed in a natural system of units. Because most objects are composed of smaller subobjects, it should have been possible to compute their properties from the properties of their components. Starting from the properties of leptons and quarks, it should have been possible to compute the properties of hadrons, nuclei, atoms, molecules and so on. Unfortunately we do not have any theory that can compute the desired properties with enough precision and in most cases even approximate values are impossible to compute. So almost all properties of particles, nuclei, atoms or molecules must be measured experimentally. Besides the question whether the fundamental constants can change in time, one can put a separate question whether the properties of leptons and quarks can vary in time. Some of the properties of leptons and quarks are constrained by symmetry rules, but there remain a few that could vary, for instance the mass ratio between muon and electron. It is likely that a future theory might discover that this mass ratio is not an arbitrary parameter, but the muon is a kind of excited state of the electron, in which case this mass ratio could be computed as a function of the fundamental constants, so the question whether it can vary would be reduced to the question about the variation of the fundamental constants.

GolDDranks 2y ago
I think you are wrong; for example the Standard model has 26 (or 25?) fundamental constants that can be made dimensionless, so they are not dependent on the choice of units. Also, the masses of fundamental particles are connected to the strength of the coupling of the particle's field to the Higgs field, and those coupling strengths are fundamental constants.
- adrian_b 2y ago
  Not all the parameters of the standard model can be made dimensionless, and for most others their dimensionlessness is illusory. When you have 10 absolute masses, you can also represent them by one absolute mass and 9 dimensionless mass ratios. Then you can claim that your model has 9 dimensionless parameters, but this changes nothing, because in any formula that relates different physical quantities you must multiply the mass ratios by an absolute mass. There are cases when using dimensionless mass ratios does not bring any advantage, but there are also cases when using mass ratios can improve the accuracy. For very small things, like particles, nuclei, atoms or molecules, it is possible to measure with much higher accuracy the ratio between their mass and the mass of an electron, than their absolute mass. So in particle/nuclear/atomic physics it is usually the best to express all masses as dimensionless ratios vs. the mass of an electron and to multiply them with the absolute mass of an electron only where necessary. There are methods to measure with high accuracy the absolute mass of an electron, based on measuring the Rydberg constant and the constant of the fine structure. Most parameters of the standard model are dimensionless because they are ratios that eventually need to be multiplied with an absolute value for the computation of practical results. In many research papers about the standard model they get away with using only "dimensionless" parameters because they take advantage of the fact that they cannot continue the computations far enough to obtain practical results, so they use some ad hoc system of units that is not clearly defined and which is disconnected from the remainder of the physics.
  - GolDDranks 2y ago
    > When you have 10 absolute masses, you can also represent them by one absolute mass and 9 dimensionless mass ratios. Then you can claim that your model has 9 dimensionless parameters, but this changes nothing, because in any formula that relates different physical quantities you must multiply the mass ratios by an absolute mass. What? So, what is the mechanism in nature that produces those 9 ratios? If you haven't got one, you haven't got a theory; you've got to admit that those are experimentally confirmed fundamentals. So, I interpret what you're saying like this: you have got a pet theory where the mass ratios are calculable from some other, more fundamental assumptions, but (charitably: because the theory is numerically too hard, or you lack compute resources) you don't have the actual means to calculate them. Otherwise, I scratch my head. If you don't manage to enlighten me, I deem you a crank.