No, that isn't my view, that's what the law states. "stress" is not a notation I'm familiar with, but I see that it is used on Wikipedia too: https://en.wikipedia.org/wiki/Stress–strain_curve One problem is that you cannot have a strain on a particle; a particle's length is by definition so small its irrelevant. But the real issue is that this is just some generic definition of stress, not something specific to this situation. Please give the equation and its derivation of this "Lorentz-stress", where the velocity of the particle is used as an input. Irrelevant. Do you agree with me that a not-straight line isn't necessarily a loop, yes or no? Technically, you are right, but that's really not the point here. A geodesic in GR is what a straight line is in flat space. In that regard, they are the same thing. The "thumb rule" is not a force, so that's wrong. Please give a force. "can be considered as" and "is" are not the same thing. As I already said, that's an imperfect analogue, so it will break down in places. This is a very basic calculus question. Off the top of my head: if a function has a well-defined derivative on its entire domain, it's continuous on that entire domain. f'(x)=1, so yes, that's continuous. A quantized (or as it's called in mathematics, "discreet") function will not be continuous, in general. No, Hubble observed galaxies moving away from us, not the expansion directly. You've missed the point: rulers stretch too, so against what ruler are you measuring this expansion? I'm not saying it's impossible, but one has to be very carefully to define these things properly. The rubber sheet analogue doesn't work properly in these cases. First of all, there's Newton's First Law. But in reality, it's more complicated than that. Pick a ball. The sheet is being stretch in all directions, out from underneath this ball. There is no force pushing the ball around; it remains stationary compared to the sheet directly underneath. The ball doesn't move. Pick another ball. The sheet is being stretch in all directions, out from underneath this ball. There is no force pushing the ball around; it remains stationary compared to the sheet directly underneath. The ball doesn't move. Both balls don't move with respect to the sheet underneath, because there's no force. Yet, the distance between the balls increases! OK, so the first link you gave was indeed wrong. Mechanical energy isn't the same as work, so the quoted part doesn't talk about work either.