On Mon, Dec 24, 2018 at 2:18 PM Jason Resch <[email protected]> wrote:
> On Sun, Dec 23, 2018 at 8:20 PM Bruce Kellett <[email protected]> > wrote: > >> On Mon, Dec 24, 2018 at 12:06 PM Jason Resch <[email protected]> >> wrote: >> >>> On Sun, Dec 23, 2018 at 7:51 PM Brent Meeker <[email protected]> >>> wrote: >>> >>>> >>>> That's what I thought you wanted to conclude. But it doesn't follow. >>>> The specious present is just a mathematical construct and has no physical >>>> significance. It says no more than that one can make a 4D map. >>>> >>> >>> So do you believe that presentism is compatible under relativity? If >>> one puts two synchronized clocks (one at the front, and one at the read) of >>> a rocket, and then the rocket accelerates, the rocket attains a tilted >>> direction in space time, and while the rocket remains at a positive >>> velocity, the rear-ward clock will be "ahead in time" of the forward >>> clock. The rocket is reaching through the dimension of time which explains >>> the discrepancy of the clocks. When the rocket comes to rest, the rocket >>> will have "0" reach through the proper time dimension, and the clocks will >>> again appear synchronized. If something can have an extent through the >>> proper time dimension, how can this be compatible with presentism? >>> >> >> >> Your example does not require any such conclusion. If you have a clock at >> the front of an accelerating rocket, and one at the rear, the rear of the >> rocket has to accelerate at a slightly greater rate or else the rocket will >> fall apart. >> > > How can this be? The rocket is a rigid structure, the front and rear > clocks accelerate at the same rate. > No, that is not the case. In an accelerating rocket, the front and rear accelerate at different rates. This is an important property of the Rindler frame for accelerating systems. Greg Egan has an interesting an informative tutorial on this (as well as other things): http://http://www.gregegan.net/SCIENCE/Rindler/RindlerHorizon.html In the greater acceleration field, the rear clock will run slower than the >> clock at the nose. When the rocket comes to rest again, the two clocks will >> have travelled different non-geodesic paths, so they will no longer be >> synchronized the rear clock will show a smaller elapsed proper time than >> the forward clock. >> > > They will again be synchronized when the rocket comes to a rest. > No. That travel different spacetime paths, so the proper time along each trajectory (clock from) is different. Note that this is specifically for accelerated frames, not inertial frames, which I think you might have in mind. What is it, exactly, that you want to conclude from this? Time is what is >> measured on a clock, and clocks at different relative velocities, or >> different acceleration fields, will record different times. So the only >> reasonably objective "present" is that read on your local clock -- other >> clocks may well record different "presents". >> >> > The idea of time as a dimension separate from the spatial dimensions > explains clock-descynchronization after acceleration (and > re-synchronization when coming to rest), length contraction, time dilation, > etc. If an object can reach through time (just as it reach through space) > then you have clear evidence of the reality of multiple points in time. > This just seems like simple Lorentz transformation stuff. That does not require a block view of space-time. Your diagrams are not actually very helpful. Bruce -- 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
