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> You absolutely can write a formula that matches observations without justifying it or deriving it from first principles, ie. "hacking" Newton's second law is

> You absolutely can write a formula that matches observations without justifying it or deriving it from first principles, ie. "hacking" Newton's second law is totally fine if it works. Physics is an interconnected whole. You cannot simply hack whatever formula you want. Newton's 2nd law is a consequence of Relativity, in the low-velocity limit. You cannot hack Newton's 2nd law without changing Relativity, which means changing basically everything in physics, including extremely precisely measured quantities like the energy levels of the hydrogen atom. That's why MOND itself isn't a theory of nature. You have to modify General Relativity to produce MOND-like effects. It's very difficult to do that without messing up other parts of the theory. > Don't pretend there aren't huge gaping holes you could drive a dump truck through Every precision test of gravity produces results that match GR to within experimental precision. No, these are not just tests within the Solar system. To give you one example, gravitational waves have now been verified to travel at light speed, which rules out large classes of modified GR theories.

naasking 4y ago
> You cannot hack Newton's 2nd law without changing Relativity Yes, changing some aspects of relativity is what will ultimately happen. We already know relativity is technically incorrect because of its singularities. And yes, you absolutely can hack Newton's 2nd law if it's empirically supported. It's frankly bizarre that you keep insisting that you can't do this. > which means changing basically everything in physics Don't be ridiculous, GR absolutely does not have an impact on "everything in physics". > No, these are not just tests within the Solar system. I didn't we've only tested GR within the solar system, I said GR was only well tested within the solar system. There's a big difference and you seem to have a habit of attacking strawman like this.
- naasking 4y ago
  > I didn't we've only tested GR within the solar system Err, I meant "I didn't say we've only tested..."
- DiogenesKynikos 4y ago
  > And yes, you absolutely can hack Newton's 2nd law if it's empirically supported. It's frankly bizarre that you keep insisting that you can't do this. You think it's bizarre that you can't arbitrarily change one prediction in a large, densely interconnected theory? Newton's 2nd law is a consequence of a much larger theory. In order to change it, you have to change the theory that gives rise to it. That will have huge numbers of consequences, but just for Newton's 2nd law, but for pretty much everything else predicted by the theory. > We already know relativity is technically incorrect because of its singularities. No, we don't know this. All modern theories are relativistic. We know that General relativity (a.k.a. gravity) has to have some sort of more fundamental quantum analog, but that quantum theory will also be relativistic. > Don't be ridiculous, GR absolutely does not have an impact on "everything in physics". You don't need GR to get Newton's 2nd law. You only need Special Relativity. You can't "hack" Special Relativity without doing incredible damage all across physics. > I said GR was only well tested within the solar system Wrong. The propagation speed of gravitational waves, the inspiral of binary pulsars, strong gravitational lensing (including around directly imaged black holes), the strong equivalence principle as tested by a triple system with a pulsar, and many other tests.

naasking 4y ago

> You cannot hack Newton's 2nd law without changing Relativity Yes, changing some aspects of relativity is what will ultimately happen. We already know relativity is technically incorrect because of its singularities. And yes, you absolutely can hack Newton's 2nd law if it's empirically supported. It's frankly bizarre that you keep insisting that you can't do this. > which means changing basically everything in physics Don't be ridiculous, GR absolutely does not have an impact on "everything in physics". > No, these are not just tests within the Solar system. I didn't we've only tested GR within the solar system, I said GR was only well tested within the solar system. There's a big difference and you seem to have a habit of attacking strawman like this.

naasking 4y ago
> I didn't we've only tested GR within the solar system Err, I meant "I didn't say we've only tested..."
DiogenesKynikos 4y ago
> And yes, you absolutely can hack Newton's 2nd law if it's empirically supported. It's frankly bizarre that you keep insisting that you can't do this. You think it's bizarre that you can't arbitrarily change one prediction in a large, densely interconnected theory? Newton's 2nd law is a consequence of a much larger theory. In order to change it, you have to change the theory that gives rise to it. That will have huge numbers of consequences, but just for Newton's 2nd law, but for pretty much everything else predicted by the theory. > We already know relativity is technically incorrect because of its singularities. No, we don't know this. All modern theories are relativistic. We know that General relativity (a.k.a. gravity) has to have some sort of more fundamental quantum analog, but that quantum theory will also be relativistic. > Don't be ridiculous, GR absolutely does not have an impact on "everything in physics". You don't need GR to get Newton's 2nd law. You only need Special Relativity. You can't "hack" Special Relativity without doing incredible damage all across physics. > I said GR was only well tested within the solar system Wrong. The propagation speed of gravitational waves, the inspiral of binary pulsars, strong gravitational lensing (including around directly imaged black holes), the strong equivalence principle as tested by a triple system with a pulsar, and many other tests.