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"Causes" in physics
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"Causes" in physics
Paul Stowe (firstname.lastname@example.org) [posting on behalf of Barry Mingst] wrote: One example of a cause and effect theory is Maxwell's equations for electromagnetism. These were explicitly derived from Hemholtz' superfluid aether. Another example is the perfect gas law. Where motion of particles is explicitly the cause of the phenmonena. In these cause-and-effect theories, there is an explicit underlying physical cause of all aspects of the theory. Steve Carlip wrote: This is really a different subject, so I've changed the header. Let's take the perfect gas law as an example, since it's more widely known. The cause of the phenomenon is the motion and interaction of particles, certainly. But what is the "cause" of the interactions? At the simplest level, particles in a gas that collide bounce off each other. Why do they do that, instead of (say) merely passing right through each other? Why, when they interact, do they conserve momentum, and not, say, mv^3? Why do the particles remain stable rather than expanding and dissipating, or shrinking and vanishing? Why don't they stick to each other when they collide? Paul Stowe writes: I would like to comment on these issues since they form the core foundation of what has come to be known as 'Natural Philosophy'. There are of course several approaches to attempting to answer such questions. 1. Just state the above as a postulate, in this vein we would be on the same basis as Einstein's principle of equivalence. 2. State that this IS the observed behavior of all observable matter, and thus, logical reasoning would indicate that therefore, a some fundamental level, this must be a fundamental true property 3. Assume neither, and say, like Bohr, for the system we observe, this characteristic is observed, but who knows about its underlying nature. Tact #1 is what I would designate a "mathematician's" approach and mindset. Tact #2 is the so-called Natural Philosophy approach (the ingrained belief that what we observe can be broken down into fundamental properties that represent an ultimate truth). While tact #3 is what I designate the pragmatic reverse engineering approach, which I've come to call the 'it just does' mentality. What you have done is not to explain the ultimate cause, but to reduce one unexplained phenomenon to another. Not really, we have just reduced them to the Newtonian set. Steve Carlip replies: Which, of course, would look complicated and completely unintuitive to a pre-Newtonian physicist. We don't, after all, see objects moving at constant velocities; they clearly slow down and stop. When we drop a feather and a rock, we don't see them hit the ground at the same time. If we measure the energy in a collision of two macroscopic bodies, we almost never see it conserved. Of course, we understand this all once we accept Newtonian physics---we need to take into account friction, viscosity, heat, etc.---but the only reason it seems "simple" is that we've gotten used to the theoretical framework. Given this, I can say, "Being curved by the presence of matter is the property of all observable spacetime, and thus logical reasoning would indicate that therefore, at some fundamental level, this must be a fundamental true property of spacetime." If this seems unintuitive to you, I suggest that it's for the same reason that Newtonian physics would have seemed unintuitive to earlier scientists. Paul Stowe responds: The said truth is, while we are in fundamentally agreement on the above statement, and the problem is one of both terminology and perspective. Yes, at a fundamental level, there is space (as in physical volume), time as in the observation that things move & change, but this alone and in isolation, cannot produce the effect that is called curvature unless we 'endow' such space (a volume) with some extra physical qualities. Einstein said this, I say this, and refuse to accept the explanation "it just does". There is no fundamental conceptual difference between GR, and viewing the processes of GR as gradient in anisotropic velocities of a physical medium. The retarded 'r' argument of finite propagation in the Newtonian solution was a red herring, just like the Schwarzschild solution, the gradient produced by an attenuation process, once established, is static and propagation speed irrelevant, unless there is a net translational motion between the interacting bodies. Just like the sun's light striking the earth, while it did leave the sun's surface 9+ minutes before encountering the earth, its an continuous process and the earth 'sees' the light at its current position. Likewise, the gradient is always present, and any 'gravitating' body is constantly reacting to its instantaneous presence. This is WHY the Newtonian works for GR, with ITS finite propagation speed. As processes go, the only differences that I see between GR and attenuation gravity is induction heating and translational drag. The drag issue remains unresolved and I might have found a possible solution. But, heaven forbid that there be any really speculative physics discussions in this forum. Steve Carlip continues: What you have done is not to explain the ultimate cause, but to reduce one unexplained phenomenon to another. Such reductions are certainly important in physics. But I think from your examples that you are using "cause and effect" to mean, basically, "something I can easily visualize because it resembles the behavior of ordinary human-scale objects, whose properties seem intuitive." There's no reason to believe physics should be like that. Paul Stowe writes: IMOH I think you're wrong there, because, in the end, if we can't reduce observations to simple fundamental properties, we probably should "pack up our calculators and go home", because the original quest set forth in physics becomes ultimately, unattainable. The best you can hope for is correlations that, at their foundation, will consist of mystical causes such as the 'fields', quantum spin foams, spinors, and twistors, that are considered as only abstract mathematical constructs having no ability to even attempt to ascertain a simpler foundation. Steve Carlip replies: But who gets to decide what a "simple fundamental property" is? Paul Stowe answers: No one, the true test is observations. Things only become 'fundamental' (as in physical laws) if and only if, over a sufficient period of time, no violations have been noted. Steve Carlip continues with the thread ... You gave general relativity as an example of a theory that was not a "cause and effect" theory, and asked, why do masses move along geodesics? Well, in your ideal gas model, why do the particles move in straight lines between interactions? Paul Stowe replies: The answer, because to do otherwise would violate the principle of least action, or in plainer English, would based upon ALL observations collected to date, require an added/extra intervening process. Steve Carlip responds: OK, why doesn't this apply just as well to GR? Masses move along geodesics because to do otherwise would violate the principle of least action, and require added/extra intervening processes. Paul Stowe writes: Yes, the added intervening process is called gravitation. The key question remains, what is this intervening process. Since this discussion is about causes.