• #### proper time is invariant

From Mark-T@21:1/5 to All on Fri May 5 10:33:20 2023
Occasionally it's stated that "proper time is invariant",
as if a profundity.

I don't get this. Bob is in Los Angeles, looks at his
watch, it reads 9 AM. He boards a train, two hours
later he arrives in San Diego, his watch reads 11 AM.

A space traveler zooms his telescope into Bob,
observes that Bob is in LA, and Bob's watch reads
9 AM. Later, he sees Bob in San Diego, and sure
enough, Bob's watch reads 11 AM.

So everybody agrees on Bob's proper time interval.
This is profound? It's trivial, with practically no
physics content. Am I missing something?

Mark

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• From Jack Liu@21:1/5 to Mark-T on Fri May 5 10:50:19 2023
On Friday, May 5, 2023 at 12:33:21 PM UTC-5, Mark-T wrote:
Occasionally it's stated that "proper time is invariant",
as if a profundity.

I don't get this. Bob is in Los Angeles, looks at his
watch, it reads 9 AM. He boards a train, two hours
later he arrives in San Diego, his watch reads 11 AM.

A space traveler zooms his telescope into Bob,
observes that Bob is in LA, and Bob's watch reads
9 AM. Later, he sees Bob in San Diego, and sure
enough, Bob's watch reads 11 AM.

So everybody agrees on Bob's proper time interval.
This is profound? It's trivial, with practically no
physics content. Am I missing something?

Mark

When people, especially relativists, say "proper time is invariant" it doesn't mean that proper time is invariant. In fact, it means that the change of proper time is uniform and independent of any physical environment. This concept of proper time is
actually Newton's absolute time. They need to pretend to reject it, so they invented the concept of "proper time".

Re : Chapter six of https://drive.google.com/file/d/1VfhOL63jvB2Dmn4JCRmOx6S8Dh9nRbdC/view

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• From Tom Roberts@21:1/5 to Mark-T on Sat May 6 10:16:29 2023
On 5/5/23 12:33 PM, Mark-T wrote:
Occasionally it's stated that "proper time is invariant", as if a
profundity.

It's not really very profound.

I don't get this. Bob is in Los Angeles, looks at his watch, it
reads 9 AM. He boards a train, two hours later he arrives in San
Diego, his watch reads 11 AM.

A space traveler zooms his telescope into Bob, observes that Bob is
in LA, and Bob's watch reads 9 AM. Later, he sees Bob in San Diego,
and sure enough, Bob's watch reads 11 AM.

So everybody agrees on Bob's proper time interval. This is profound?
It's trivial, with practically no physics content. Am I missing
something?

It's not really profound, and you're not missing anything major. But it
is important to know, as opposed to the coordinate time of a given
coordinate system, which is not invariant [#].

[#] Even it if it implemented with an array of clocks,
each of whose proper time is invariant. The difference
is that proper time exists along each 1-D path of each
clock, while coordinate time exists over the 3-D
region of the coordinate system.

Tom Roberts

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• From Tom Roberts@21:1/5 to Jack Liu on Sat May 6 10:21:40 2023
On 5/5/23 12:50 PM, Jack Liu wrote:
When people, especially relativists, say "proper time is invariant"
it doesn't mean that proper time is invariant.

Nonsense.

In fact, it means that the change of proper time is uniform and
independent of any physical environment.

Well yes, that is part of it, but proper time implies considerably more
than just that.

This concept of proper time is actually Newton's absolute time.

Complete nonsense. Those are VERY different concepts.

Newton's "absolute time" is exactly the same for every observer and
clock, everywhere and everywhen.

Proper time, however, is specific to the path through spacetime of a
single observer or clock; paths moving differently or in different
regions can have completely different proper times.

They need to pretend to reject it, so they invented the concept of
"proper time".

More nonsense. You REALLY need to learn basic physics before attempting

Tom Roberts

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• From Ross Finlayson@21:1/5 to Tom Roberts on Sat May 6 08:56:14 2023
On Saturday, May 6, 2023 at 8:23:44 AM UTC-7, Tom Roberts wrote:
On 5/5/23 12:50 PM, Jack Liu wrote:
When people, especially relativists, say "proper time is invariant"
it doesn't mean that proper time is invariant.
Nonsense.
In fact, it means that the change of proper time is uniform and independent of any physical environment.
Well yes, that is part of it, but proper time implies considerably more
than just that.
This concept of proper time is actually Newton's absolute time.
Complete nonsense. Those are VERY different concepts.

Newton's "absolute time" is exactly the same for every observer and
clock, everywhere and everywhen.

Proper time, however, is specific to the path through spacetime of a
single observer or clock; paths moving differently or in different
regions can have completely different proper times.
They need to pretend to reject it, so they invented the concept of
"proper time".
More nonsense. You REALLY need to learn basic physics before attempting

Tom Roberts

"SR is local."

Einstein's relativity theory assigns a little space to each point in space-time.

The Riemann tensor and its metric vis-a-vis the absolute space-time and
its metric, illustrates that Einstein's inertial systems, are involved, and, he has bridges everywhere, from absolute space time, about, relative velocity.

In this sense Dirac's positronic sea, is also Dirac-Einstein's positronic/white-hole sea.

Mass and charge are quantities, and magnitudes, and so is time.

The space contraction is rather real, though inertial systems in the rotational and inertial systems in the linear, are quite different.

SR is local, and, GR is first.

In "Out of My Later Years" Einstein's "laws of nature" or "Einstein's relativity:
final edition" has that he has a clock hypothesis (that time is universal). Also, he separates clocks from time.

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