Assignment Versus Equality

[Steven D'Aprano]

On Thu, 30 Jun 2016 10:29 am, Gregory Ewing wrote:

> All your experiment shows is that the last information we had
> about the magnet is that it was nearly stationary just above
> the horizon.
> 
> It doesn't prove that the probe itself is frozen, any more than
> the fact that a photograph you took of something last month
> doesn't move proves that the object you photographed is
> stuck in the state it was in a month ago.

The easy way to see that it isn't frozen in place is to try to fly down to
meet it.


> Keep in mind that changes in the magnetic field propagate at
> the speed of light and are subject to the same redshift, etc.
> as any other signal. It doesn't matter whether you use a
> permanent magnet, an electric charge, or coconuts banged
> together in morse code, relativity still applies.

An electric charge is a much better approach. Because it is a monopole, it
is detectable from a distant more easily than a magnetic bipole, and while
magnets are going to be vaporised into plasma (hence losing their magnetic
field), electrons are electrons (at least until you get into the quantum
gravity regime, at which point we don't know what happens).



-- 
Steven
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.