Genady

Normally, yes. But this OPer was not serious and was not really interested and has been banned. So, now we're free to discuss the question in any context. I consider a proton to be a "bag" of two positive and one negative charges. At a small enough distance, the electron would induce the proton to be more positive in the electron direction and more negative in the opposite direction. Increasing the attraction as a result. Perhaps, at a small enough distance electron and neutron also attract, by a similar mechanism. Your thoughts?

Me too. Still?

Maybe at some very small distances?

No. They can only affect a mindset, but they cannot "make" a specific mindset as there are other factors affecting it.

You are absolutely right. It is, however, not what the OP question was about. It depends on the initial conditions.

Expansion of space is a purely gravitational effect. When I walk away from the computer the distance between me and the computer increases. It has nothing to do with the space expansion. Matter is not continuously created in the space expansion.

Because they move in this case under their electrostatic repulsion, not under their gravity.

No, they would not.

So, we're talking about a bunch of ionized hydrogen atoms. Yes, they will repel each other electrostatically, and the group will fly apart. They will move in space. It will be the same space as before. Change in their configuration will change a configuration of their gravitational field.

What is "quantum objects"? Where does the repulsion come from? A bit more specifics, if possible.

@mistermack, There are two time dilations involved. One is a gravitational time dilation. You could call it "actual" as it depends only on a change in gravitational field between events. The other is a relativistic time dilation, due to the observers' relative motion. This one differs "from the perspective of" different observers. (BTW, don't "reunite" the clocks, as the motion will cause the relativistic time dilation and the test will be ruined.) In your scenario, the two effects add in different ways: A and B don't move relative to each other, so there is only the "actual" gravitational time dilation, and it makes A to run slower than B. A and C are in the same place at the same time, so there is no gravitational time dilation between them. But they move relative to each other, which causes a relativistic time dilation. Thus, A is slower than C from the C's perspective, and C is slower than A from the A's perspective. B and C are in different positions in the gravitational field. This causes the gravitational time dilation which makes C to run slower than B. But they also move relative to each other causing the relativistic time dilation. For B, it makes the C to run even slower. However, for C, it makes the B to run slower, compensating for the effect of the gravitational time dilation. In case of B being in infinity and C free falling straight from a rest in infinity, this compensation will be exact, and thus for C, they will be running in sync.

In addition, for the observer C, A will be slower. And (assuming that B is extremely far, and that C is in free radial fall from extremely far) for C, B will be running at the same speed. So, I think that is correct, but only from the C's perspective.

No light is coming from the black letters. Did you see my last post above? What do you think about that solution of the puzzle?

And, of course, "Galilean" (Newtonian) gravity acts instantaneously at any distance.

For an observer with clock A, C will be slower. For an observer with B, C will be slower, too.

I think I got the solution. We don't see light coming from a letter, the letter is black. We see the light from background (white), the letter is where there is no light. Because of the object being out of focus, there is progressively less light coming through as we get closer to the object's edge. So, near the object's edge more light coming through from a bit farther from the object and it gets darker as we get closer. The letter appears where it is dark. The dark area moves progressively closer to the edge. Thus, the lines of the letter appear to move closer to the edge.

This is the curvature I'm talking about. It applies to any "smooth" manifold with any number of dimensions: Riemann curvature tensor - Wikipedia @geordief Let me add an example of the three possibilities for the space of a homogeneous isotropic universe. Take any three points in space, far from each other, for which the distances between them can be measured. They make a triangle. Knowing the distances, calculate the sum of angles of the triangle. If the sum is 1800 then the space is flat. Otherwise, it is curved. If it is less than 1800, the space is "open" or "hyperbolic". If more, it is "closed" or "spherical".

You've replied before my last addition in the post above. Here it is: When the finger is a bit farther away, the letter "i" is definitely vertical:

I think a short answer to the "gravity in flat space" question is that the gravity is a curvature of spacetime, a 4D object, rather than that of space, which is 3D.

I took a snapshot. The line of the "i" appears bent, i.e., not parallel to other "vertical" lines, without a movement. Here is a "before" picture: To put the optical illusion possibility finally to rest, I've rotated the image to make "vertical" lines vertical and have added the vertical grid. "i" is obviously not vertical:

In this lecture Alan Guth explains problems with applying Newton's law of gravity, including the shell theorem, to infinite space. Basically, it boils down to a conditionally convergent integral, which doesn't have a unique answer. Lecture 6: The Dynamics of Homogeneous Expansion, Part II | The Early Universe | Physics | MIT OpenCourseWare Unless, that world contains ether...

To clarify, in GR based cosmology, the flat space (together with open and closed ones) is a possible solution for a homogenous isotropic universe.

In a homogenous isotropic universe flat space with gravity is one of the possibilities, which btw looks like what we in fact got.

Yes, of course.

I guess it would look like Newtonian gravity.