"The EmDrive Just Won't Die"

[Guest]

Gravitational lensing is already used for astronomical observations. It's just that we rely on celestial bodies being in just the right position to make an observation. This, in particular, is something we likely wouldn't be able to figure out without a theory predicting it. Relativity does have its uses outside of strictly theoretical research.

[Nuke]

17 hours ago, K^2 said:

Correct, but we don't really need to understand relativity to correct for it. Just measure that time on GPS satellites runs a little faster, observe that the difference is fairly consistent, and compensate for it.

Of course, the fact that we are actually using theoretical values predicted by General Relativity and it gives us the necessary precision is one of the proofs of the theory.

i guess a fudge factor (engineers call them coefficients) you can predict is called science. it always amazed me how aerospace engineers can reduce the complexities of fluid dynamics down to a couple of numbers. 

[NFUN]

On 10/2/2020 at 4:56 AM, magnemoe said:

how very short lived particles could reach the surface after getting created in the upper atmosphere

this is special relativity (and gravitational lensing is pretty easily explicable by saying that light is felt by gravity too, you don't need a whole framework to explain it

Edited October 3, 2020 by NFUN

[Guest]

53 minutes ago, NFUN said:

by saying that light is felt by gravity too, you don't need a whole framework to explain it

Actually, if we didn't have relativity and observed gravitational lensing, that'd be a pretty big WTH that would lead us to relativity in really short order. The principle of least action was already known then, if light was being warped by gravity, we'd have not choice but to conclude that somehow, gravity causes the curved path to be the shortest one. The idea of an external force altering the path of light would be novel indeed. 

Before relativity, we didn't actually know all that much about the nature of light. Classical optics really don't account for things like gravity, and fitting this phenomenon into that framerwork would've been hard.

Edited October 3, 2020 by Guest

[NFUN]

13 minutes ago, Dragon01 said:

Actually, if we didn't have relativity and observed gravitational lensing, that'd be a pretty big WTH that would lead us to relativity in really short order. The principle of least action was already known then, if light was being warped by gravity, we'd have not choice but to conclude that somehow, gravity causes the curved path to be the shortest one. The idea of an external force altering the path of light would be novel indeed. 

Before relativity, we didn't actually know all that much about the nature of light. Classical optics really don't account for things like gravity, and fitting this phenomenon into that framerwork would've been hard.

You need a framework to explain why that happens, obviously, but not a framework to explain the effect, as opposed to stuff like Mercury's orbital precision, which was just magic after other causes were ruled out.

And let's be honest. Basically anything could've toppled our theory of light back then. Hell, the Michelson-Morley experiment already had, two decades before SR was published.

[Guest]

Seeing as light was believed to be massless, then yes, it would have been "magic" until some bright spark connected it to gravity. The leap from there to relativity is basically creating a mathematical formalism (or figuring out how to use the one invented by Poincare) to express that idea. I'm pretty sure people would first go looking at diffraction-related effects, but that would go nowhere, fast.

[K^2]

6 hours ago, Dragon01 said:

Seeing as light was believed to be massless, then yes, it would have been "magic" until some bright spark connected it to gravity. The leap from there to relativity is basically creating a mathematical formalism (or figuring out how to use the one invented by Poincare) to express that idea. I'm pretty sure people would first go looking at diffraction-related effects, but that would go nowhere, fast.

Even if you just assume that light is pulled by gravity like a massive object, you'll quickly find that the angle by which light is bent as it passes massive objects is wrong.

And yeah, we WOULD have derived SR. I mean, it's basically what Einstein did. But GR is another matter. And GR is what's responsible for gravitational lensing, orbit of Mercury, and GPS satellite's clock running fast. And the math on which we would have been able to build GR properly, rather than via the geometric ansatz Einstein pulled out of who knows what inspiration, was only developed in late 50s. Based on when papers were published properly describing GR in terms of Gauge Theory, I estimate we'd have actual GR in the 90s if it weren't for Einstein's work, even if we knew about all of the aforementioned effects.

On the plus side, we wouldn't have that messy differential geometry based theory they still teach in universities. I mean, it works, and it's not wrong, but it feels very arbitrary, and leads to some bad intuition, because people try to think in terms of embedded geometry no matter how well they know that solutions to Einstein Field Equations cannot be embedded in general.