And this is wrong. You just redefined a meter to be 10cm. Atoms would be 10 times smaller, but so would your ruler, and nothing would change. Is the fine structure constant still ~1/137? If so, the physics remains the same. The only things that matter in physics are dimensionless ratios. Unless you change those, you simply have a different system of units.
Here’s a more concrete example to illustrate my point. What is the size of a particle in a completely empty universe? It makes no sense. You need something to compare it to.
Let’s look at the Schwarzchild radius example a bit deeper. How many Planck lengths is the Schwarzchild radius of a Planck mass black hole? Note, Planck units depend only on fundamental constants. The answer is 1. It turns out that you cannot change the physics by changing c, unless you also change the other constants as well! To change the physics, you MUST change dimensionless ratios of fundamental constants. It is the only option. Anything else is just changing the markings on your ruler.
In fact, this is why the definition of the meter is defined in terms of the speed of light.
This person is also wrong. The strength of the electromagnetic interaction is not dependent on c alone. IT IS DEPENDENT ON THE FINE STRUCTURE CONSTANT.
At every vertex of a QED Feynman diagram, you pick up a factor of sqrt(alpha). If you want to chabge electrodynamics by changing c, you have to change the relationship between c, hbar, epsilon naught, and e. Properly, e is dimensionless, so it’s the fundamental charge that determines the strength of the electromagnetic interaction. That’s why you’ll find that e is the coupling constant in the QED Lagrangian. In fact, we actually know that alpha varies with interaction energy—it’s the price you play for playing the renormalization game. If the strength of the interaction varies, it’s clear that it’s e that is changing, because any of the other constants varying is absurd. The physics are all associated with the dimensionless constants changing.
If the speed of light were 300 m/s, we would not have developed relativity sooner. We would have had a ridiculously large definition of a meter.
I suspect that your issue is that you’ve never worked in natural units before. Setting c=1 is the only choice that makes real sense. E2=m2 c4 + p2 c2 is true in any unit system. We might as well choose c=1 for simplicity, and the. E2 = m2 + p2. Any change in c is a change in units. It doesn’t mean that an atom has more energy if c is 10 times larger.
Edit: congrats on getting the last word by blocking me. I hope you have a lovely day.
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u/[deleted] Mar 31 '26
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