
#37
Feb612, 11:37 PM

P: 67





#38
Feb712, 12:08 AM

P: 67





#40
Feb712, 12:29 AM

P: 67

The hypothetical spacetime manifold of which we are a part includes all of space and all of time. Its description is static. To be dynamic requires a second dimension of time in which it can change  and that's not in its job description. 



#41
Feb712, 05:37 AM

P: 848

Hermann Weyl's (Einstein's colleague and close friend) picture describes a static 4dimensional universe occupied by static 4dimensional objects (filiamentlike objects strung out along the 4th dimension for billions and trillions of miles, called the world lines). Our bodies are 4D objects of that kind with consciousnesses moving along the world lines at the speed of light (as time passes). The parametric equations for a photon straight world line is: dX4 = cdt dX1 = cdt dX4/dX1 = c The parametric equations for a normal body straight (inertial) world line are: dX4 = cdt dX1 = vdt You can google for "Block Universe" to find more information on this idea. But, now we are approching a subject that may be considered to have zero physics content, subject to lockdown by the forum monitor. So, here is a summary of the concept, after which I will have no more discussion. This block universe model is in the context of a spatial 4th dimension (consciousness moves along the 4th dimension as time passes). 



#42
Feb712, 06:44 AM

P: 3,178

Now about spacetime, he clarified that concept as follows to nonphysicists: (emphasis mine) PS welcome to physicsforums! 



#43
Feb712, 09:32 AM

P: 647





#44
Feb712, 09:37 AM

P: 67

1. Correction: Photon dX4 = cdt (change in time) dX1 = cdt (change in position) dX1/dX4 = 1 (speed of light) Nonphoton dX4 = cdt (change in time) dX1 = vdt (change in position) dX1/dX4 = v/c (speed of nonphoton) 2. Observation: Minkowski's use of the mysterious looking ict has been out of fashion for such a long time that it is probably better not to mention it at all (except for historical reasons). The crucial difference between "ordinary space" and Minkowski space is perhaps best described in terms of the formula describing the interval ("distance"), ds, between two pointevents in Minkowski space (here in x,y,z,t coordinates): [itex]{(ds)}^{2} = {(dx)}^{2} + {(dy)}^{2}+ {(dz)}^{2}  {(cdt)}^{2}[/itex] This is almost the Pythagorian Theorem, but with a perverse minus sign in the last term. If spacetime were Euclidean (i.e. "ordinary", the last term would be [itex]+(cdt)^{2}[/itex]. But it isn't, and that's the end of it. 



#45
Feb712, 09:44 AM

P: 67





#46
Feb712, 10:29 AM

P: 67

Fixed now in the earlier posting. I'm still learning. Sorry! 



#47
Feb712, 06:00 PM

P: 848

dX4/dX1 = c Wrong!! (Don't know what I was thinking while typing that one) Should be: dX4/dt = c 



#48
Feb812, 11:41 AM

P: 366

Space is expanding, time is dilating, while static is an illusion of relative motion. As for the stubbornly persistent illusion of our static universe, it has more to do with the backward view of seeing photons as if at emission instead of absorption, because we do not see the motion of photons in waves we see objects. 



#49
Feb812, 02:21 PM

P: 67

Anything that happens in time is in the spacetime manifold. The manifold itself is not embedded in another time dimension, hence its complete description (all of space and all of time) is static. If it were otherwise, spacetime  all of our space and all of time  would change along that separate time dimension, and past history would be observed to change continuously. 



#50
Feb812, 03:34 PM

P: 65

So, are we safe in asserting that "time" itself is no more measurable than "space" itself is measurable? But rather, it is the EVENTS that occur within spacetime, the dynamic nature of physical phenomena, that necessitate measurement. We don't talk about measuring space (or do we?) but rather things in it. The same should be true for time. I suspect people struggle with the dimension of time more b/c it's more challenging conceptually. It's very possible that I am WAY off (my comprehension is mainly conceptual, not technical). If so, please be gentle. 



#51
Feb812, 03:43 PM

P: 65

sidenote: for some reason, the reference to "clocks measuring time" never sits well with me. it doesn't bother me nearly as much as "rulers measuring distance" which seems slightly more accurate. it's unclear to me what clocks are actually measuring. I find it easier to have a conversation about the nature of time when the whole notion of "clocks" is removed. Perhaps I am just lacking in proper "history of timekeeping" knowledge.




#52
Feb812, 04:47 PM

P: 3,178

Early people recorded events by means of positions of Sun and moon, and thus the "time" concept emerged based on observing (and counting in one direction!) the motion of natural clocks. 



#53
Feb812, 06:01 PM

P: 366

In the fourth dimension, time, we appear as a solid four dimensional object yet in space we see the same object as 3 dimensional and what do both of these objects have in common but the center of their own separate durations. Past history does change continuously from the future through the present into the past, if the present were the surface, or edge of matter I see, then the solid is inside with the signals from some other present waiting to get in, the future. 



#54
Feb812, 08:01 PM

P: 67




Register to reply 
Related Discussions  
Exothermic reaction moves forward with increase in Temp?  Biology, Chemistry & Other Homework  1  
What 'drives' time forward?  General Physics  14  
Backward and forward in time?  High Energy, Nuclear, Particle Physics  10  
Why does time seem to exist only in a forward direction?  Cosmology  16  
Backward or forward in time?  Special & General Relativity  8 