On 1/2/2019 8:28 AM, John Clark wrote:
On Tue, Jan 1, 2019 at 7:09 PM Brent Meeker <meeke...@verizon.net
<mailto:meeke...@verizon.net>> wrote:
/> And for two spacelike events (as I specified) h^2 < 0 so you
have made the interval along a world line, the proper time,
imaginary. /
The spacetime distance d is *not* the proper time, the
spacetime distance is an invariant, it's the same for all observers,
but proper time is *not* invariant;
Sure it is. It's path dependent, but it's an invariant of a given
path. The "spacetime distance" between two timelike events is the length
of the longest proper time path between them.
your proper time is not my proper time if we're moving relative to
each other, accelerating at different rates, or in different
gravitational fields. But we both always agree on how much we moved
through spacetime since our last meeting.
But obviously if d^2 = r^2 - (ct)^2 (where d is the invariant
distance in spacetime and r the distance in space) then d can be
imaginary if t is large, and that's one reason physicists usually use
d^2 not d when they want a invariant. If it's your position that the
formula given in all books on relativity for that spacetime invariant
are wrong then please inform us of the correct one. If the formula is
correct then the distance through spacetime simply can *not* be the
proper time as you said.
> /You're making a big distinction between spacelike 'distance' and
'proper time'. But it's just muddling the point that the geodesic
followed by a body is the longest interval. /
Yes aclock following a geodesic will show the largest proper time and
yes I am making a big deal about the proper time not being the
spacetime distance because they're not even in compatible units, one
is in seconds and the other is in meters. It's like trying to
subtract acres from nanoseconds, it doesn't make any physical sense.
>>You can never find a distance between anything by subtracting
seconds from meters, that would be gibberish, but you can
subtract meters from meters.
/>That's why the speed of light is now just a conversion factor./
Just? The speed of light is *just* the bridge between two otherwise
incompatible quantities because you *just* can't subtract seconds from
meters! And it's *just* a fact that Google was right and you were
wrong when it said a geodesic was /"the shortest possible line between
two points on a sphere or other curved surface"./
>>Doesn't slow a clock down relative to what?
/> It's a negative, John! It doesn't slow down realtive to
anything. /
Of course it does! If 2 clocks start out synchronized on the Earth and
one stays put but the other is put on a rocket and blasted away into
space at near the speed of light and then accelerated in the opposite
direction so it can return to Earth then the clocks will no longer be
synchronized when they meet again. So obviously *one clock must have
slowed down relative to the other, *or equivalently one clock must
have sped up relative to the other because that's what
"unsynchronized" means.
/> Ideal clocks in relativity are assumed to accurately measure
proper time along their world line. /
And that's why I said "in Relativity, a clock never slows down
relative to an observer in the same reference frame"
> /They never run slow or fast...they just follow different paths./
But that's exactly what clocks slowing down or speeding up between
events means, following different paths through spacetime.
> /You're one that referred to the clock being slowed down. "Then
one twin would encounter a intense gravitational field that the
other twin did not and *gravity will slow down a clock just like
moving fast will.*"/
Yes and in that I was absolutely correct. When the clocks meet again
after one went on its rocket journey the previously synchronized
clocks are now unsynchronized. Unsynchronizedmeans showing different
times, so during the journey one clock *MUST* have run slower than the
other.
That's like saying if two people drove different cars from L.A. to New
York and their odometers registered different distances then one of the
odometers must have measured miles differently than the other...ignoring
the fact that they took different routes.
Brent
John K Clark
--
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 everything-list+unsubscr...@googlegroups.com
<mailto:everything-list+unsubscr...@googlegroups.com>.
To post to this group, send email to everything-list@googlegroups.com
<mailto:everything-list@googlegroups.com>.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
--
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 everything-list+unsubscr...@googlegroups.com.
To post to this group, send email to everything-list@googlegroups.com.
Visit this group at https://groups.google.com/group/everything-list.
For more options, visit https://groups.google.com/d/optout.
