3 ms·
I am sympathetic to the author's thesis. I favor the idea that gravity is a different thing from the other fundamental forces, and possibly an emergent phenomen
by cvoss 2y ago
I am sympathetic to the author's thesis. I favor the idea that gravity is a different thing from the other fundamental forces, and possibly an emergent phenomenon rather than a fundamental thing in its own right.
But, I don't buy the argument made here:
> To call gravity a force, is to privilege flat space as somehow being special.
Flat space is special, and we didn't make it special.
This is taking an important aspect of known physics---that there exist various symmetries and all elements of the corresponding group are equal players (there is no privileged reference frame, positive charge and negative charge are indistinguishable save for their oppositeness, etc.)---and attempting to apply this principle to spacetime curvature. But the zero curvature state is a unique one that is differentiatable from the others. It's the only one where a circle is perfect, having circumference 2 * pi * r. And pi is a fundamental invariant of geometry, curved or otherwise. The mathematics privileges flat space. Further, experiments can be constructed to detected whether we are in flat space or not [1]. That wouldn't be possible if the whole concept of flat were only relative to an arbitrary frame.
[1] https://en.m.wikipedia.org/wiki/BOOMERanG_experiment https://en.m.wikipedia.org/wiki/BOOMERanG_experiment
- TeMPOraL 2y agoI tend to think about this in via a simple 0-1-many heuristic - there's infinitely many ways to have a curved space, but there is exactly one way to have a flat space. That by itself makes it special. Is this heuristic wrong?
- cryptonector 2y ago> Is this heuristic wrong? I would say it is, but in a subtle way. There is only one way in which gravity curves spacetime, and also one set of effects it has when seen from the lens of flat spacetime.
- TeMPOraL 2y ago> There is only one way in which gravity curves spacetime, and also one set of effects it has when seen from the lens of flat spacetime. Is there though? Isn't that the holy grail of science - expressing all of physics, particularly all of "fundamental constants", in a formula where there is one clearly preferred answer? One function with a single global minimum in the parameter space, that defines our universe? Perhaps let me put my heuristic differently: when there exists multiple (especially infinitely many) solutions, you still need to explain why a particular solution would be the solution, and not any of the other ones. A single solution is naturally privileged, because there is only one and there can be no other.
- cryptonector 2y ago> But, I don't buy the argument made here: > > To call gravity a force, is to privilege flat space as somehow being special. > Flat space is special, and we didn't make it special. Neither is curved spacetime. Metrics like the Schwarzschild metric merely let us map between the two. They inherently do this, so flat spacetime seems like inherently as real as -no more, and no less than- curved spacetime. And in flat spacetime gravity is very much a force. We should really not teach that gravity curves spacetime, but that there are equivalent representations of what massive objects do to their surroundings. The reason we should teach both alternatives is that humans have a hard time wrapping their minds around "curved spacetime". Giving a person two different ways to think about the same effects will increase the likelihood that they will understand, and only at a very small cost of increased cognitive load (but since understanding eases the cognitive load, the overall effect should be to reduce cognitive load). Pedagogy matters.