[QUOTE=Ronald Salmond, MD]
I’ve enjoyed your exposition on Einstein’s special theory of relativity. Could you comment on what Einstein referred to as “spooky”, the concept of ‘action at a distance’? Doesn’t “action at a distance” suggest that there is some speed which exceeds the speed of light? Isn’t there also a theory that the speed of light has not always been fixed at its current speed? Pardon my ignorance if I have mistated these theories.
[/QUOTE]
Einstein was concerned about the apparent instantaneous action between two entangled particles. This behavior is described as being nonlocal–that is, the connection or mechanism between the particles is not transmitted through the intervening continuum, and thus is not subject to the limits of Special Relativity. This isn’t the first time that the notion of “action at a distance” caused some upset; indeed, the action of any fields that we think of as forces (electromagnetic, gravity) falls into the category, but these forces are (to the limits we can test them) well behaved in Special Relativity and General Relativity respectively, and adhere to the invariance of c as the absolute maximum speed for force propagation. (Gravity is kind of tricky on this point because it is so weak and doesn’t tend to vary much, aside from the occasional supernova, but all measurements to date put it around c, and we’d have some serious problems if it ended up being greater than c.)
Anyway, Einstein–never a satisfied customer of quantum mechanics–along with Boris Podolsky and Nathan Rosen came up with the EPR paradox, which was intended to dispute the results of QM as being complete and really explaining what is going on. Real world experimentation has actually demonstrated that there are indeed non-local effects; i.e. a change in the spin of one half of an entangled pair of electrons will have a complementary change in spin of the other member. This sounds like a really exciting way to transmit information faster than light until you realize that the behavior of the particles is only statistically deteminable, so if you modify the behavior of Particle A in order to transmit information, you have to know its instantaneous state at Particle B before you can seperate the data from the random noise…which means that you have to send that correction information by some other means (radio, laser, federal mails, et cetera) thus not really giving you anything useful.
What does this all mean? There are a few different conclusions to be drawn from this; one is that entangled particles are connected “non-locally”, not by fields that only act within the framework of Special and General Relativity. Another is that either reality–at the quantum level–is totally “random” in the sense of being able to predict the specific position, momentum, or orientation of a particle at any given time, though its behavior falls into a very rigid statistical distribution based upon its energy level, so it’s not really random in the general sense of the word. (“We demand rigorously defined areas of uncertainty and doubt!” – The Hitchhiker’s Guide To The Galaxy) The alternative to this is that there are “hidden variables”; underlying rules which explicitly describe the seemingly random (but statistically determinant) behavior of fundamental particles. However, by virtute of the “fundamental interconnectedness of all things” (Douglas Adams is getting quite the workout today) these hidden variables must be nonlocal, i.e. unable to be read by an observer.
The practical upshot is whether you favor interpretations involving utter randomness, simultaneously dead-and-alive cats, Wigner’s uncommunicative friend, alternate timelines full of evil twins sporting goatees, or this hidden variable stuff makes no different whatsoever; the rules of quantum mechanics all work out the same way regardless, or as poster Chronos recently noted, the favored interpretation of most physicists working in the field today is the “shut up and do the math” interpretation. It also means that as long as you don’t stare to hard at it, entanglement does not, in effect violate a liberal reading of Special Relativity, although it does sit uneasily beside it like a canary next to a cat. (Since there is really no good or accepted mechanic for gravity in quantum field theory, General Relativity is perfectly safe…for now.)
On the level of the everyday world, decoherence gives us an experiental reallity in which neither the statistical behavior nor the nonlocality plays a significant part, and you really have to study statistical mechanics, quantum chemistry, or stare really hard at a very small object before it becomes obvious that something seriously screwy is going on. However, you can display a fundimental artifact of quantum mechanics with a very simple exercise; the double slit experiment, which demonstrates the wave nature of photons or electrons. It’s all really nothing to lose sleep over, and I enjoy nothing more than introducing these concepts to friends so that they freak out and have nightmares about angry half-poisoned cats and particles splitting between two slots and interfering with each other.
As for variations in the speed of light, c is defined as being 299,792,458 metres per second. The assumption in Maxwell’s (and others, but for the sake of convenience we’ll assign the blame all to him) electrodynamic theory, which predates Speial Relativty by not quite half a century) is that the speed of light is invariant, and Einstein extended this to demonstrate that time and distance are two aspects of the same fundamental topology, the so-called spacetime continuum. In a sense, when you are inertial (not under acceleration) you are travelling at c on the time axis, and 0 on the x,y, and z (or rho, phi, and theta, or whatever coordinate system you like) axes. Move, and you slow down in time. Move really fast, and your movement through time (from an inertial observer) slows significantly.
Note that this invariance applies to mass and energy, but not the continuum itself. There is nothing in Special Relativity that limits the underlying plenum from stretching at any speed whatsowever, and in fact this whole business about the expansion of the universe, and acceleration thereof (such that points further away from your position are moving away at a faster rate) creates a scenerio in which the relative speed between you and your twin outside of a particular horizon could be greater than the speed of light, even if you and your sibling are standing still in your own reference frames. Note that the speed of light is still invariant; you won’t see light travelling faster, but it will reduce in frequency (redshift) as the space it occupies stretches out, not unlike light infalling into a black hole.
As a practical matter, the only way we know of using energy to actively “stretch” space in a nonsymmetric manner is by binding it up as a lot of mass and moving it around or rotating it, and because the gravity field created by mass is so insubstantial it takes enormous amounts of energy to do these things, perhaps prohibitivly so on scale of real world objects. So, not really an issue unless you have some magic science that allows you to artificially construct gravitational singularities.
Stranger
