"We move through spacetime at the speed of light"

 OK. Let's tackle this one first. 

OK. The only equation I knew that connects speed and time is from that same freshman lecture about Special Relativity. 





I stared at this. Turned my head sideways, first to the left, then to the right. Upside down. With some algebra, I saw it. It's the equation of a circle!

SIDENOTE: I've wrestled mightily on this. With c as the max, v/c always has to be less than one. So Δt0 has to be less than Δt. Huh? Usually, naught (the subscript 0 in Δt0) indicates some universal thing, which would suggest it would be time at no velocity, i.e. maximum rate of time. But the only way this makes sense (algebraically AND intuitively) is if Δt0, in fact if the whole right-hand side of the top equation is all about ME. MY experience of time when I MYSELF move through space at this velocity. So Δt (left-hand side) is whatever time YOU observe as I whiz past you. So MY time is always less than YOUR time. Time dilation and all. Whew!

ANYWAY. So it's a circle. (I used to be better at Excel. Sorry.)


In this example: If you're moving at 80% of the speed of light (red line), time is passing (green line) at 60% of the rate it would if you were stationary.

I'm mystified why relativity is taught using the equation at the top of this post rather than this far more intuitive circle equation/graph. 


Maybe because it could lead to this insight. When something moves at the speed of light (black line), it does not experience the passage of time.

In other words LIGHT DOES NOT EXPERIENCE THE PASSAGE OF TIME. 

Consider: our telescopes detect photons that have travelled through billions of light-years, billions of years, without any degradation. Without decay, aka entropy. Why? Because light CAN move at the speed of light. Why? Because it has zero mass. If you try to accelerate something with mass (F=ma) toward the speed of light, you run into relativistic mass: the more you push it, the more it resists. So something with mass cannot move at the speed of light, cannot skirt up the vertical axis, and MUST use some of its passage through spacetime as passage through time. And therefore, must experience entropy.

 

Future conundrum: What is Δt? When all motion has stopped, when v=o, when all is homogeneous and there is no entropy yet to be gained, also known as "thermal death", time stops.  Nope, not there yet.

Ahh! Regarding the universe as a whole -- AVERAGE velocity has stopped. All motion is random. But uniformly mixed, so there is no more entropy to be had. Hmm, "thermal death" isn't a good term, implies no kinetic energy. Rather, it's no entropy, no driving force for change, so no passage of time.  OK it's a step. But Nope, not there yet.


try cut-n-paste from word + emoji/special characters

Δt0

 

 

Δt

 

 

v2/c2

 

 

Δt0/Δt

 

 


(c) Carol VanZoeren 2023



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