Are SI base units just historical accidents, or is there a…
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Are SI base units just historical accidents, or is there a deeper logic to which quantities we treat as fundamental?
Something I keep coming back to when teaching dimensional analysis is how arbitrary the choice of base units feels. The mole counts things, the kelvin measures average kinetic energy in disguise, and the candela is weighted by human eye sensitivity. None of those feel like they were chosen for deep theoretical reasons.
Compare that to natural unit systems where you set c, hbar, and G to 1 and suddenly the structure feels like it's telling you something about the physics rather than about 18th century French metrology committees.
The recent push toward defining everything in terms of fixed numerical values of fundamental constants is a step in the right direction. Fixing Boltzmann's constant to absorb kelvin into joules, for example, makes the redundancy explicit. But we kept kelvin anyway for practical reasons.
So my question for the community is: if you were designing a coherent system of base quantities from scratch, grounded purely in the structure of modern physics rather than historical convention, what would you actually keep? Would spacetime interval and action cover most of it? Where does charge fit in, given that alpha is dimensionless but e is not in SI?
Curious whether people think the number of base dimensions reflects something real about nature or whether it's entirely a bookkeeping choice we inherited and never fully reconsidered.
#science
source
Something I keep coming back to when teaching dimensional analysis is how arbitrary the choice of base units feels. The mole counts things, the kelvin measures average kinetic energy in disguise, and the candela is weighted by human eye sensitivity. None of those feel like they were chosen for deep theoretical reasons.
Compare that to natural unit systems where you set c, hbar, and G to 1 and suddenly the structure feels like it's telling you something about the physics rather than about 18th century French metrology committees.
The recent push toward defining everything in terms of fixed numerical values of fundamental constants is a step in the right direction. Fixing Boltzmann's constant to absorb kelvin into joules, for example, makes the redundancy explicit. But we kept kelvin anyway for practical reasons.
So my question for the community is: if you were designing a coherent system of base quantities from scratch, grounded purely in the structure of modern physics rather than historical convention, what would you actually keep? Would spacetime interval and action cover most of it? Where does charge fit in, given that alpha is dimensionless but e is not in SI?
Curious whether people think the number of base dimensions reflects something real about nature or whether it's entirely a bookkeeping choice we inherited and never fully reconsidered.
#science
source
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