Jesse, Yes, that is what I'm saying.
But how you don't understand that actively traveling through spacetime at c doesn't imply everything is at one and only one point in time is beyond me. It's a trivial inference. Edgar On Wednesday, February 5, 2014 5:04:36 PM UTC-5, jessem wrote: > > > > On Wed, Feb 5, 2014 at 4:41 PM, Russell Standish > <li...@hpcoders.com.au<javascript:> > > wrote: > >> On Wed, Feb 05, 2014 at 04:21:47PM -0500, Jesse Mazer wrote: >> > On Wed, Feb 5, 2014 at 3:50 PM, Russell Standish >> > <li...@hpcoders.com.au<javascript:> >> >wrote: >> > >> > > On Wed, Feb 05, 2014 at 07:53:16AM -0800, Edgar L. Owen wrote: >> > > > >> > > > In fact relativity itself conclusively falsifies block time as it >> > > requires >> > > > everything to be at one and only one point in clock time due to the >> fact >> > > > that everything always travels at the speed of light through >> spacetime. I >> > > > find it baffling that so many can't grasp this simple fact. >> > > > >> > > >> > > That is only true for clocks travelling along null geodesics. For all >> > > other geodesics, proper time increases at a rate of 1 second per >> > > second, or c metres per second, where c is the speed of light >> > > expressed in metres per second. >> > > >> > >> > I believe Edgar is referring to the fact that the magnitude (norm) of >> the >> > 4-velocity vector is always c, regardless of what worldline you're >> looking >> > at (Brian Greene explains that this is what he means by "speed through >> > spacetime is always c", and gives a short derivation, on p. 392 of The >> > Elegant Universe). >> > >> > But as I pointed out, this isn't a great revelation. We define >> 4-velocity >> > in natural units (c=1) as (dt/dtau, dx/dtau, dy/dtau, dz/dtau), where >> > t,x,y,z are coordinates of some inertial frame and tau is proper time. >> > Analogously, in a purely spatial scenario involving a curved wire in 3D >> > space we can define a similar vector V=(dx/dL, dy/dL, dz/dL) at every >> point >> > on the wire, where x,y,z are position coordinates and L is a parameter >> > giving distance along the wire (how far an ant would have to walk to get >> > from the end of the wire to any given point). Then the magnitude of this >> > vector V is given by the square root of (dx/dL)^2 + (dy/dL)^2 + >> (dz/dL)^2 >> > which can be rewritten as (dx^2 + dy^2 + dz^2)/dL^2, but dL^2 is just >> equal >> > to (dx^2 + dy^2 + dz^2)--if an ant moves a small distance dL along the >> wire >> > we can treat its path as a straight line segment, and by the Pythagorean >> > theorem the length of any line segment is just the square of the >> coordinate >> > differences between its endpoints--so the magnitude of V is always 1 at >> > every point on the wire, regardless of the shape or orientation of the >> > wire. Greene's derivation of the fact that the magnitude of the >> 4-velocity >> > is always c is pretty much the same, except the analogue of the >> pythagorean >> > theorem in SR spacetime is that dtau^2 = dt^2 - dx^2 - dy^2 - dz^2, and >> you >> > also have to keep track of minus vs. plus signs when you multiply a >> > 4-vector by itself to calculate its norm. >> > >> >> Yes - that is what I meant by proper time advances at 1 second per >> second. As you say, that is not a great revelation, and IIRC, is >> usually taught in introductory relativity courses. >> >> But where Edgar went wrong was to suggest that this implies that all >> points along a path traced out an object moving through space time >> have exactly the same clock time, because everything travels at >> c. This is only true for objects travelling along null geodesics, ie >> objects moving at the speed of light relative to us (or relative to any >> other >> object moving at nonluminal speeds through space). >> > > > Gotcha, I thought you meant that only things on null geodesics could be > said to be "moving through spacetime at c". I don't know if Edgar actually > meant that "all points along a path traced out by an object moving through > space time have exactly the same clock time" though, I think when he said > that everything must "be at one and only one point in clock time due" he > meant that there is an absolute present and that each object has "only one > point in clock time" at the present, not that different points along a path > of an object (or different objects) have the same clock time as one > another. But I don't follow his reasoning in thinking this idea is somehow > implied by the idea that everything "moves through spactime at c". > > Jesse > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/groups/opt_out.
