I never really understood why people say gravity isn't a force. I understand that gravity is just the motion of objects travelling in a straight line (longest proper time) through space time, but does that really mean it isn't a force?
Justin, first you have to define waht you mean by the term "force"
If you want to say it is a force, it would seem to be something analogous to centrifugal force which most physics texts say does not actually exist
Exactly. It is just the result of not being in an inertial frame, and hence thinking there is a force acting: gravitational, centrifugal, and coriolis forces.
The real force is the earth's up-push on you, accelerating you vertically upwards. The weight of an object in your hand is the upwards force you are exerting on that object, accelerating it out of its preferred inertial frame. Gravity exerts no real force.
Einstein expanded on the concepts of time, space, mass, etc. but I don't see that as causing an incommensurability in any non-trivial sense.
I couln't diasgree more. We are talking paradigm shift of the millenium. GR reduces to Newtonian mathematics, it does not reduce to Newtonian thinking.
Newtonian mechanics is a limiting case of GR from the point of view of the mathematics and the methodology. The change to GR is a total upheaval from the perspective of its metaphysics
The change from Aristotlean science to modern science is profound, not so much because of the change in mathematics and metaphysics, but because of the introduction of systematic empirical methodology.
I think we have another major change this last century that marked the rise of deductive reasoning over empiricism in fundemental physics: GR is probably the precursor of this but it is even more apparent in particle physics, particularly non-Abelian gauge theory leading to electroweak and QCD. String theory is of course the epitome of this approach, but unlike those theories mentioned, it has much to prove...
quote:Justin, first you have to define waht you mean by the term "force"
Yeah, I don't really know. I remember reading in the Principia that force is defined as what causes an acceleration.
quote:I couln't diasgree more. We are talking paradigm shift of the millenium. GR reduces to Newtonian mathematics, it does not reduce to Newtonian thinking.
I might just have a wrong view of incommensurability. When I read that terms, I think uncomparable. I think one guy describes gravitation as the curved space-time, another as as angels pushing inward. They can't even have a valid conversation as to whose views are "correct."
I don't see this in Newtonian/GR. I could just be ignorant of the history. Were scientists saying, wrt SR, "Space is defined as static and unchanging, you are not making any sense!" Are the new concepts completely different than the old ones, or are they just refinements? Is every refinement incommensurable? And what is the difference between a refinement and upheaval?
quote:Einstein expanded on the concepts of time, space, mass, etc. but I don't see that as causing an incommensurability in any non-trivial sense.
quote: I couln't diasgree more. We are talking paradigm shift of the millenium. GR reduces to Newtonian mathematics, it does not reduce to Newtonian thinking.
I don't think it reduces to Newtonian thinking. I'm referring to Kuhn's concept of incommensurability. According to Kuhn, we cannot say that Newtonian thinking was wrong and that GR is correct (or more correct). They are simply paradigms which apply different rules for how to solve different puzzles.
Space is not absolute or relative; these are just different models which have varying degrees of success in describing empirical data. And they don't even have the same empirical data because the paradigms themselves influence our perceptions of reality.
This is according to Kuhn. Do you agree with him with regard to Newtonian dynamics and GR, i.e., they are just different rules for solving the puzzles of the "world," and the "world" isn't even the same because how we view the world hinges on our paradigm?
I don't necessarily see them as incommensurable because SR grew out of the problems of Newtonian dynamics. It wasn't like physicists just said, "Ok, lets throw this garbage out and start from scratch."
This message has been edited by JustinC, 12-14-2005 09:10 AM
Before I stick my head through and exclaim, let me try a nudge first. I hold no grudge against Kuhn or other "paradigmatists" but try not at first to think that "incommensurability" MUST mean NOT COMPARABLE ( the systems of science culture is what are !=, just in the sense that many here say e/c and c/e are never the twixt in twist meeting).
If there are non-algorithmic connections between the nervous system and the bodies’ environment(outside the brain etc but not necessarily outside all soma etc) then law like behavior can still exist. If one assumed that the brain ONLY contains algorithmically relatable operations then one might think whatever might be the relation of irrational and rational numbers overlaying the actual causation they are NOT COMPARABLE. I think this is wrong. This does not speak to the actual theories in physics that you and Cavediver are discussing per say, but I will say something on that if this sledge hammer of a thought only moves sludge and rather than the no-brainer (KNOW BRAIN,errrr) lunged.
This message has been edited by Brad McFall, 12-14-2005 05:17 PM