Equivalence principle of general relativity holds even at gravitational extremes • Hacker News Board

Re: Equivalence principle of general relativity holds even at gravitational extremes

#11

Post by millstone » Thu, Jul 05, 2018, 8:46 AM UTC

hymenopter4 wrote: post #10

millstone wrote: post #9

Earlier quoted context omitted.

> Since gravity is a symptom of the presence of matter The whole point of the paper is studying the effect of gravity on gravitational self-energy, i.e. NOT matter. You'll find no "matter term" in Einstein's equations.

That does not invalidate the concept. Gravity has not been found to be an incidental phenomenon measurable for anything other than matter's accumulation. In the observable universe (regardless of theories and expressions penned on paper) gravitational forces are always induced by massive material objects, including the remnant artifacts of deceased stars. To suggest otherwise is to walrus the conversation.

Dark matter measurably gravitates and is not a “massive material object.”

Re: Equivalence principle of general relativity holds even at gravitational extremes

#12

Post by neuronic » Thu, Jul 05, 2018, 8:47 AM UTC

saagarjha wrote: post #6

hymen0ptera wrote: post #4

Earlier quoted context omitted.

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…

> 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. But then gravity changes would be felt instantaneously rather than propagating at the speed of light.

Shadows are cast at the speed of light and so is gravity.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#13

Post by neuronic » Thu, Jul 05, 2018, 8:49 AM UTC

hymen0ptera wrote: post #7

saagarjha wrote: post #6

Earlier quoted context omitted.

> 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. But then gravity changes would be felt instantaneously rather than propagating at the speed of light.

Since gravity is a symptom of the presence of matter, gravitational changes ride along with matter travelling as fast as the matter (responsible for this gravitational symptom) can possibly move. At best, only the destruction of matter can move at the speed of light, so a reduction of gravity may propagate, as fast as the dispersal of the dematerialization and subsequent radiation. Accumulation of mass as a knock-on…

> 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.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#14

Post by zerostar07 » Thu, Jul 05, 2018, 9:03 AM UTC

why do they call it Principal?

Re: Equivalence principle of general relativity holds even at gravitational extremes

#15

Post by drjesusphd » Thu, Jul 05, 2018, 9:11 AM UTC

millstone wrote: post #8

This 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…

I've never thought of the equivalence principle like this. I knew gravitational fields have their own mass-energy and can cause a runaway effect (black holes), but I never realized this could mean more inertia too. Neat!

I'm curious about what this means as the event horizon is crossed.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#16

Post by hymenopter4 » Thu, Jul 05, 2018, 9:11 AM UTC

millstone wrote: post #11

hymenopter4 wrote: post #10

Earlier quoted context omitted.

That does not invalidate the concept. Gravity has not been found to be an incidental phenomenon measurable for anything other than matter's accumulation. In the observable universe (regardless of theories and expressions penned on paper) gravitational forces are always induced by massive material objects, including the remnant artifacts of deceased stars. To suggest otherwise is to walrus the conversation.

Dark matter measurably gravitates and is not a “massive material object.”

Dark matter has yet to be defined as anything other than an observed effect on the behavior of matter. Something (and indeed a thing, if anything, ergo matter) we think is probably there.

Being a theoretical hypothesis, formed to explain observations, it remains a side-effect of accounting and inference, and has not been located directly.

Show me why you believe it is a thing. Show me where you have found it. Tell me why it isn't actually matter.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#17

Post by okket » Thu, Jul 05, 2018, 9:14 AM UTC

zerostar07 wrote: post #14

why do they call it Principal?

Double spelling error (first two occurrences), from the third on the article got it right.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#18

Post by hymen0ptera » Thu, Jul 05, 2018, 9:48 AM UTC

neuronic wrote: post #12

saagarjha wrote: post #6

Earlier quoted context omitted.

> 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. But then gravity changes would be felt instantaneously rather than propagating at the speed of light.

Shadows are cast at the speed of light and so is gravity.

Interestingly enough, as a fun side effect of radial motion, the lateral motion of shadows can transit an object exceeding speeds faster than the speed of light constant, C.

From Wikipedia:

  Light spots and shadows

If a laser beam is swept across a distant object, the spot of laser light can easily be made to move across the object at a speed greater than c.

https://en.wikipedia.org/wiki/Faster-than-light

Of course, the shadow must already be cast, in a continuous stream of uniquitous photons, which all need to be arriving upon the reflective surface at the speed of light, before the shadow can transit the surface within the area of effect.

Re: Equivalence principle of general relativity holds even at gravitational extremes

#19

Post by lawlessone » Thu, Jul 05, 2018, 9:58 AM UTC

>with a margin of error of only 30 meters, according to a

Amazing they can measure it that accurately

Re: Equivalence principle of general relativity holds even at gravitational extremes

#20

Post by hymenopter4 » Thu, Jul 05, 2018, 10:25 AM UTC

neuronic wrote: post #13

hymen0ptera wrote: post #7

Earlier quoted context omitted.

Since gravity is a symptom of the presence of matter, gravitational changes ride along with matter travelling as fast as the matter (responsible for this gravitational symptom) can possibly move. At best, only the destruction of matter can move at the speed of light, so a reduction of gravity may propagate, as fast as the dispersal of the dematerialization and subsequent radiation. Accumulation of mass as a knock-on…

> 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 quantities of energy trapped and oscillating in bounded standing waveforms.

We know that the empty vacuum of space really is mostly void, but also that a lot of photons (particles) are still traversing the void quite a bit.

So, space/time, while an empty void, where phenomena transit or conduct themselves theough said empty medium, is still an environment with varying concentrations of activity.

If an neutron manages to be ejected from a supernova, and is directed toward our solar syatem, and is influenced to fall toward the sun, but, miraculously passes straight through the sun, without colliding with any other particles, only to travel onward toward the center of the galaxy, landing in a supermassive black hole some millennia from now, what would you say about the environment this neutron experienced as it fortuitously passed through the center of the sun, without experiencing any collisions?

Would to rob it of all the other qualities, and just label it space and time? Or would you refer to it as an environment, with activity transpiring, in addition to be also being a realm of space and time?