Just a layman question: does this have any implications for theories of quantum gravity, like LQG or String theory?
Equivalence principle of general relativity holds even at gravitational extremes
21–30 of 46 posts
Re: Equivalence principle of general relativity holds even at gravitational extremes
#22Earlier quoted context omitted.
> bending or altering their path of travel probably says something about the photon or the environment being travelled through, more than it does about space and time But the environment they travel through is space and time.
This is a semantic excursion. I'm bailing myself out of trouble by qualifying my statement as " probably " factual somehow, since it's not trivial to back such a concept. Semantic in the sense that the word " environment " is a loaded term. I'll offer this much: photons are particles. As particles, we know them to be part-time resident constituents of massive objects. That massive objects are representative of large…
> I'll offer this much: photons are particles.
Photons are also waves in the EM field.
> As particles, we know them to be part-time resident constituents of massive objects.
I don't think you can say we know that without explain what that means. In no part of physics do we discuss part-time resident constituents.
Your comments use a lot of terms that seem to be of your own creation. Unfortunately, these terms make it hard for your points to be understood because they lack the shared naming conventions that the field of physics uses to discuss these phenomena. Standard naming conventions, both in programming and physics, are enormously important in conveying ideas between people.
Re: Equivalence principle of general relativity holds even at gravitational extremes
#23> Galileo famously (and likely apocryphally) demonstrated the principal by dropping lead balls of different weights off the Leaning Tower of Pisa and observing them hit the ground at the same time.
This never made sense to me as something you'd need to test, once the question had been considered.
Imagine 1000 cannonballs all connected to each other with threads. The result is a single object with 1000x the mass of a cannonball. Would you expect it to fall faster?
Re: Equivalence principle of general relativity holds even at gravitational extremes
#24> Galileo famously (and likely apocryphally) demonstrated the principal by dropping lead balls of different weights off the Leaning Tower of Pisa and observing them hit the ground at the same time. This never made sense to me as something you'd need to test, once the question had been considered. Imagine 1000 cannonballs all connected to each other with threads. The result is a single object with 1000x the mass of a…
It may seem obvious to our modern eyes, but the notion that objects of different mass fall at the same rate is not at all obvious outside of the framework of physics that Galileo helped build.
Without proper notions of force, gravity, mass, density, and the form of the laws of gravity, surely you realize that the answer to your hypothetical is not trivial. This was kind of the whole point of Principia.
Re: Equivalence principle of general relativity holds even at gravitational extremes
#25> Galileo famously (and likely apocryphally) demonstrated the principal by dropping lead balls of different weights off the Leaning Tower of Pisa and observing them hit the ground at the same time. This never made sense to me as something you'd need to test, once the question had been considered. Imagine 1000 cannonballs all connected to each other with threads. The result is a single object with 1000x the mass of a…
Well yes, especially if they fall vertically as the bottom cannonballs would pull the top ones and that would make them fall a lot faster.
Re: Equivalence principle of general relativity holds even at gravitational extremes
#26>with a margin of error of only 30 meters, according to a Amazing they can measure it that accurately
We can do even better some of the time - for example, we can get to ~few nanosecond timing precision for pulsars like J1909-3744 [1], which is equivalent to measuring (changes in) the path length to that pulsar to a few meters or better.
Re: Equivalence principle of general relativity holds even at gravitational extremes
#27This was a measurement of the Nordtvedt parameter which characterizes the difference between a gravitational field and an accelerating reference frame. If there is no difference, as GR predicts, then the parameter is 0. This experiment tests the idea that gravity itself gravitates: gravity imbues very massive bodies with gravitational binding energy, and therefore more inertia. If your inertia is increased due to gra…
Does this mean that gravity is a real form of eneergy and not a simple deformation of space-time?
IOW, if gravity were solely a deformation of space-time, then it would not add inertia? Or am I missing or misunderstanding something?
Re: Equivalence principle of general relativity holds even at gravitational extremes
#28Just a layman question: does this have any implications for theories of quantum gravity, like LQG or String theory?
Yes, the authors discuss the implications for scalar-tensor theories, and it doesn't look great for many of them. The Nature News and Views article by Clifford Will [1] offers a decent overview.
Re: Equivalence principle of general relativity holds even at gravitational extremes
#29Earlier quoted context omitted.
This is a semantic excursion. I'm bailing myself out of trouble by qualifying my statement as " probably " factual somehow, since it's not trivial to back such a concept. Semantic in the sense that the word " environment " is a loaded term. I'll offer this much: photons are particles. As particles, we know them to be part-time resident constituents of massive objects. That massive objects are representative of large…
> I'll offer this much: photons are particles. Photons are also waves in the EM field. > As particles, we know them to be part-time resident constituents of massive objects. I don't think you can say we know that without explain what that means. In no part of physics do we discuss part-time resident constituents. Your comments use a lot of terms that seem to be of your own creation. Unfortunately, these terms make it…
Re: Equivalence principle of general relativity holds even at gravitational extremes
#30The new paper claims to add to the confirmation of "the strong equivalence principle of general relativity."(0) Reading Wikipedia to find which theories are (or were) the alternatives which assumed that principle not to hold: "The strong equivalence principle": "The first part is a version of the weak equivalence principle" "The second part is the Einstein equivalence principle (with the same definition of "local"),…
A gravitational constant that is the same everywhere in the universe and is incompatible with a fifth force. The fallout of this ramification is that, gravity is some sort of ambient side effect of material presence, sort of like a shadow cast, more than an emission radiated. As a constant, that means that its invariance is significant, in the same way the speed of light is significant. There is some externality pegg…
I wouldn't say that general relativity suggests that gravity is an "ambient side effect" of material presence. It means precisely that the geometry of spacetime is determined by the matter-energy content within that spacetime; and that matter moves on geodesics dictated by spacetime. I suppose that I am forced to accept that whether you think gravity is more like a shadow of matter than an active participant in dynamics is somewhat up to you, provided that you get the physics correct. If you don't, then your perspective is wrong.
Glancing at some of the other things you've said in the thread, you seem to be convinced that some waves, like sound waves, are somehow illusory. Let me assure you, there is nothing illusory about wave phenomena, both in general and with gravitational waves in particular. Anything that produces wave-like phenomena can be said to radiate emissions, to paraphrase, and in many cases, there is nothing really more "fundamental" than the wave.
As for the concept of color, I suppose it depends on what you mean by color. Color as defined by the wavelength/frequency of light is perfectly well defined outside of the visible spectrum. As a mental concept, I don't see why it is "irreducible." I suppose you are attempting to say that the universal speed of light is somehow fundamental... but in the same way that a "redder" red is impossible? This is a dubious analogy. It confuses the limitations of the mind with fundamental physics.