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From: Physfitfreak <physfitfreak@gmail.com>
Newsgroups: sci.physics.relativity,sci.physics
Subject: Re: S paceTime
Date: Sun, 16 Feb 2025 21:42:24 -0600
Organization: Modern Human
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On 2/16/25 7:23 PM, The Starmaker wrote:
> et me put it simply this way...
> 
> if our Sun were to simply disapear..
> out Earth will feel it's disaperance..immeditaly, ...not minutes later.


Not a bad thought :)

You're nearing the questions I had in last year of high school and first 
year of undergraduate physics.

My guess is that the information of its disappearance will travel 
towards Earth at, or below, the light's speed (i.e. max speed for any 
physical quantity) and when it reaches Earth, the path of Earth motion 
becomes almost linear from that moment on.

But I vaguely remember that in general relativity changes in gravity 
travel _at_ the speed of light although (again claimed) to be not of 
electromagnetic nature.

Another weirder feature of gravity is that the anti particle's gravity 
force is not repulsive toward ordinary particles! They all attract. 
These and other weird questions got us many times busy wondering in 
those years :)

And if you think of it, even the "simple" coordinate systems, say, a 
Cartesian coordinate system, is very weird if you look at it closely. If 
you have an apple hanging from a tree, giving you three coordinates 
components on your system, when you go to the spot where one of the 
components say the apple is, you see no apple there. You'd only see a 
short line segment. And you see none on the other two coordinate axes 
either other than two short line segments. Yet, the three components 
will algebraically give you _all_ the information you can have about 
that apple! Magically, three short pieces of line intervals will give 
you the correct shape of the apple in three dimensions.

These stuff got some of us busy in those good old days.