Gravity for Us Dummies

[turtle]

I have one question about gravity…
I am a dummy. I need help from the gravity experts…
A rock is on the ground…it cant move down…
Is there an attraction that the earth exerts on the rock…

[phyllo]

Is there an attraction that the earth exerts on the rock…

Yes.
There is also an attraction between the rock and another one 2 feet away from it.
When you walk by, there is an attraction between your body and the rock.

[turtle]

@phyllo

Is there an attraction that the earth exerts on the rock…

Yes.
There is also an attraction between the rock and another one 2 feet away from it.
When you walk by, there is an attraction between your body and the rock.

phyllo-----i dont understand what this has to do with spacetime curvature…anything??

[phyllo]

phyllo-----i dont understand what this has to do with spacetime curvature…anything??

You don’t need to look gravity from the perspective of spacetime curvature.

Your body is curving space.

Your body is attracted to every mass in the universe.

[PhysBang]

@turtle

phyllo-----i dont understand what this has to do with spacetime curvature…anything??

You have to think about the path of the rock as we might draw it out in space and in time. The path that the rock is trying to make in time is one where it goes, in space, toward the centre of the Earth. This is, essentially, what we might think of as the natural line of how the rock should move through spacetime. It just happens that there is something in the way: the surface of the Earth.

Everything with mass or energy slightly changes these natural lines.

[turtle]

@PhysBang

@turtle

phyllo-----i dont understand what this has to do with spacetime curvature…anything??

You have to think about the path of the rock as we might draw it out in space and in time. The path that the rock is trying to make in time is one where it goes, in space, toward the centre of the Earth. This is, essentially, what we might think of as the natural line of how the rock should move through spacetime. It just happens that there is something in the way: the surface of the Earth.

Everything with mass or energy slightly changes these natural lines.

so there is no such thing as a graviton…this is confusing to this dummy…

[phyllo]

so there is no such thing as a graviton…this is confusing to this dummy…

Which abstraction of gravity are you interested in?
-quantum field theory
-general relativity
-Newtonian gravity

[James_S_Saint]

A “graviton” is a theoretical particle derived by the notion that if EM waves can quantize into particles, then perhaps gravity can also.
I happen to know independently that they can’t, so from me; “no there is no actual such thing as a graviton”.

[PhysBang]

@turtle

so there is no such thing as a graviton…this is confusing to this dummy…

If there are gravitons, then they would be the particle that manages the curving of spacetime.

[turtle]

@phyllo

so there is no such thing as a graviton…this is confusing to this dummy…

Which abstraction of gravity are you interested in?
-quantum field theory
-general relativity
-Newtonian gravity

this is over my head…

[phyllo]

Newton’s law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. (Separately it was shown that large spherically symmetrical masses attract and are attracted as if all their mass were concentrated at their centers.)

Newton explained how these masses interact but he didn’t know why.

While Newton was able to formulate his law of gravity in his monumental work, he was deeply uncomfortable with the notion of “action at a distance” which his equations implied.

He never, in his words, “assigned the cause of this power”. In all other cases, he used the phenomenon of motion to explain the origin of various forces acting on bodies, but in the case of gravity, he was unable to experimentally identify the motion that produces the force of gravity (although he invented two mechanical hypotheses in 1675 and 1717). Moreover, he refused to even offer a hypothesis as to the cause of this force on grounds that to do so was contrary to sound science.

Einstein’s solution

These objections were rendered moot by Einstein’s theory of general relativity, in which gravitation is an attribute of curved spacetime instead of being due to a force propagated between bodies. In Einstein’s theory, masses distort spacetime in their vicinity, and other particles move in trajectories determined by the geometry of spacetime. This allowed a description of the motions of light and mass that was consistent with all available observations. In general relativity, the gravitational force is a fictitious force due to the curvature of spacetime, because the gravitational acceleration of a body in free fall is due to its world line being a geodesic of spacetime.

Go down to the subatomic level and maybe gravity is caused by gravitons.

Gravitons are postulated because of the great success of quantum field theory (in particular, the Standard Model) at modeling the behavior of all other known forces of nature as being mediated by elementary particles: electromagnetism by the photon, the strong interaction by the gluons, and the weak interaction by the W and Z bosons. The hypothesis is that the gravitational interaction is likewise mediated by a – yet undiscovered – elementary particle, dubbed the graviton. In the classical limit, the theory would reduce to general relativity and conform to Newton’s law of gravitation in the weak-field limit.[6][7][8]

Source:Wikipedia

[Farsight]

It’s really simple, turtle. Simpler than you think.

But to see just how simple it is, you have to start with a light beam, then move on to an electron, and then you’ll understand what happens to that rock.