J.C.MacSwell

Picture yourself in space at the center of a system that includes you, a solar mass 200 million miles away to your right and a 2 solar mass 100 million miles away to your left. You are at the center of mass. Which way would you be pulled by gravity?

If you had a closed system, and chose an inertial frame based on the center of mass being at rest, then the center of mass would stay at rest. The gravitational net force at this point would not necessarily be zero, nor would it necessarily stay zero if it was.

The pressure is highest at the center. The net gravitational force is lowest, goes to zero, at the center. The center of an all one material sphere would be generally denser at the center as you describe The density gradient depends on the bulk/volume modulus of the material, temperature gradients and bulk coefficient of expansion with temperature and any phase changes involved. The Earth is considerably denser at the center as the denser materials gravitate toward the center.

In which direction do you think it should be pulled away?

If entangled communication could work that and the experiment would yield consistent results (disregarding gravity strength anomalies) and if the results produced a "fastest clock" in a particular direction and speed then that would distinguish that reference frame. It's an interesting bit of thinking even though we would expect a null result due to the second if (I think that was Swansont's point) and in fact probably no results at all due to the first if.

Equivalently? Who said equivalently? I said you raised the Earth. You close the distance (sit down) 99.9999999999???????? % and the Earth will close (raise up) the remainder...small as it is. If you want a sense of it being equivalent, then the total mass (mass of the Earth) times distance the Earth moves will be equal and opposite to the mass (your mass) times distance that you move. (all other influences notwithstanding). This is basic conservation of momentum.

So 144 pounds / square feet would convert to 1 pound / square inch?

When you turn on a detecting device the interference pattern disappears, whether it's electrons or photons etc. I think they all "self interfere", the different probabilities of the individual probability wave interfering, and not "with each other", but I am not sure.

You realize your response is unprovable, do you not? The earth doesn't meet the ball unless in the size of the moon, or another stellar object of comparable size and mass. Conservation of momentum. You cannot change the velocity of the centre of mass of a closed system. If you pick a reference frame where the centre of mass is at rest, it must remain at rest unless an outside force acts upon it. If you mean the Earth/ball example is unmeasurable, you are no doubt correct, but if you sit down where you are standing you will have "raised" the Earth relative to where it would have been otherwise and all other things being equal.

Are the two not contradictory on some scale?

You accept the consistency of the math, but not the experimental results? Or not the physical interpretation?

The different elements produce different frequencies, as each photon "package" produced must correspond exactly to an available drop in energy level for the electron/s in the atom. The available drops in energy level vary with each element. This leads me to a question that I think fits well with this thread: Why is the black body radiation curve so common given that the elements behave this way? Also, I know this is probably obvious but when a blackbody radiation curve is redshifted or blueshifted it is still a black body radiation curve?

My motivation was to give an example that I was confident was correct. I did not mean to imply an "if and only if" only that I suspected it could be wrong otherwise. If you and I are at rest or "welded together" in one inertial frame (Let's say you at the start of the Indiannapolis 500 and me on my butt in front of my computer) we are not necessarily at rest in all inertial frames. Given enough spatial separation in one that we are at rest in, you could choose a continuum of inertial frames that correspond to you starting, racing and finishing the Indiannapolis 500 all with me sitting in front of my computer hitting the letter "x" (all the same moment for me, and each frame containing one different moment for you). We of course would not be at rest wrt each other in all those frames.

I think this is the idea. Simultanaeity must be thrown ou the window until an objective standard/absolute reference frame, if it exists can be found/defined. I think this is wrong. Ignorance is key. No observer can measure the speed of light in any direction. Only round trips of light can be measured.

Something like that, yes. However, does it feel no force, in this example, in all inertial frames? I'm sorry, but I missed the context of your last sentence. Are you saying you can rule out your example so that if it had an effect on time it could be accounted for?

Simultaneity is absolute if and only if you can find and define an absolute frame of reference. Noone has done this.