Genady

I think we can say any of that or something else, e.g., "the force is from the wall", - as long as we understand the mechanics of it.

If "they" are so advanced then they are over an original excitement of discovery and exploration and perhaps just trying to dump their criminals away, like British used to send their convicts to Australia.

We measure the downward pressure times the area and this is equal the weight, if the wall moves with a constant velocity. The brief moment of the reduced pressure will last while the wall accelerates from the resting state to a constant velocity. When the velocity is constant, the pressure will return to be equal the weight of the fluid divided by the area of the wall, i.e., not reduced.

These words might have a common origin since both English and Persian languages have a common ancestor, Proto-Indo-European language, aka PIE. However, I think that a connection is much more convoluted than the sounds being similar or "squishy and mushy". Look at the etymology of the English word: (worm | Etymology, origin and meaning of worm by etymonline)

I think, they do in the first approximation. But generally, they are more complex because there are other internal forces in the fluids.

Yes, at any point in spacetime where the two waves are present, the resulting field is the sum of two fields. Each one of the two waves continues unchanged. They do not "collide". Their effects simply add up.

Yes, they just go through each other. No, they don't interact.

Maybe it is in principle impossible.

If it were possible, then police work would be very easy. Take a piece of a suspect's skin and listen to all their past conversations.

No. I don't think we do. Even if we could, we would recover a sum of all sounds that hit the object throughout history. That would be just noise.

I don't think we know.

Let's look at it this way. The piston moves down with a constant velocity. Thus, any volume of fluid above it moves down with the same constant velocity. Thus, total force on that unit =0. The force down is its weight. The force up is the pressure difference. Thus, this pressure difference is equal its weight. This is exactly what the "normal" pressure is. Thus, the pressure above the piston is the "normal" pressure.

Yes, you're right. ds2 = dt2 - dx2. (c=1)

They (in the link above) mention but do not emphasize that there is nothing "unique" in visiting mikva. It is a rather mundane and regular thing. E.g., women go there every time after having period.

Yes, here: Event 1: the light hits a point on the Moon. Event 2: the bullet hits the same point on the Moon.

I'll think about the suction, but regarding this: I suggest a mental experiment. What happens if there is vacuum above the piston? When it moves down, the pressure under it gets higher, but the pressure above remains zero. Thus, the overall pressure gets higher.

Here is the diagram. Spatial coordinate is horizontal, temporal is vertical. The light, the ship, and the bullet leave the origin, i.e., the same point in space at the same time. The orange line is the light trajectory, the blue is the ship, and the red is the bullet. (No gravity.)

The points in Minkowski spacetime ARE events. The same point cannot be at a different time or spatial distance, in a given reference frame.

I don't think it will happen. Certainly not the reduced gravitational pull - the latter requires an accelerated fall, but the ball/piston rather moves in the fluid with a constant speed except momentarily at the very beginning. I think, there is a higher pressure under the piston, a normal pressure above it, and a pressure gradient in the gap where the fluid moves up.

Certainly not.

I think I can consider, for simplicity, instead of a sinking ball, a piston with a narrow gap being pushed down. This makes it obvious (to me) that there will be an increased pressure under the piston. Why the pressure above the piston will be lowered?

Got it. Thank you. I looked, by mistake, on the secondary, upside-down rainbow.

Phosphorus is used by life. Life is not used by phosphorus.

This explanation is symmetrical in regard to different colors. Perhaps I miss something. It would explain if the rainbow band were red on the edges and violet in the middle. What makes the violet to appear on the outside edge and the red on the inside edge of the rainbow band?