# Re: Tegmark's New Book

```On 1/16/2014 7:09 AM, Edgar L. Owen wrote:
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`Brent,`
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Whoa, back up a little. This is the argument that proves every INDIVIDUAL observer has his OWN present moment time. You are trying to extend it to a cosmic universal time which this argument doesn't address. That's the second argument you referenced.
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This argument demonstrates that for every INDIVIDUAL observer SR requires that since he continually moves at c through spactime, that he MUST be at one and only one point in time (and of course in space as well), and thus there is a privileged present moment in which every observer exists,
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That's all ok up to "privileged". The only thing "privileging" the time and location is the observer being at that event. So it is relative to the observer - hence the name "relativity theory".
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and since he is continually moving through time at c he will experience an arrow of time in the direction of his movement.
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I think that's a tautology. Direction of movement assumes a direction of time.

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Once that is agreed we can go on to the 2nd argument to prove that these are universal across all observers....
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So can we agree on that?
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I don't know what "that" refers to, nor what "these" are that are universal. That all observers trace out world lines?...sure.
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Brent

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Edgar

On Wednesday, January 15, 2014 9:19:24 PM UTC-5, Brent wrote:

On 1/15/2014 4:38 PM, Edgar L. Owen wrote:

Brent,

Both DO follow if you understand the argument. Why do you think they
don't follow?

Well the first one is true, if you take time to mean a global coordinate
time.  But
then it's just saying every event can be labelled with a time coordinate.
All that
takes is that the label be monotonic and continuous along each world line.
It'
saying that 'everything can get a time label'.  But it doesn't say anything
how the label on one worldline relates to labels on a different world line.

The SR requirement that the speed of light be the same in all inertial
frames then
implies that the labeling along one line *cannot* be uniquely extended to
other
lines, but must vary according to their relative velocity.

Brent

Edgar

On Wednesday, January 15, 2014 7:27:07 PM UTC-5, Brent wrote:

On 1/15/2014 4:02 PM, Edgar L. Owen wrote:

Brent,

Bravo! Someone actually registered some of my arguments, though
I would
state them slightly differently.

The argument in question, that everyone except Brent seems to
have
missed, is simple.

SR requires that everything moves at the speed of light through
spacetime. This is NOT just "a useful myth", it's a very
important
fundamental principle of reality (I call it the STc Principle).

It's a commonplace in relativity texts.

This is true of all motions in all frames. It's a universal
absolute
principle.
Now the fact that everything continually moves at the speed of
light
through spacetime absolutely requires that everything actually
moves and
continually moves through just TIME at the speed of light in one
direction in their own frame. This movement requires there to
be an
arrow of time,

Not exactly.  It requires that there be a time-axis, but it doesn't
say
anything about which way the arrow points.  It only implies that
bodies
cannot move spacelike (because when they get up to c they've used
all their
speed to move through space and none to move through time).

and this principle is the source of the arrow of time and gives
the
arrow of time a firm physical basis.

Second, because everything is always moving through time at the
speed of
light everything MUST be at one and only one location in time.

That doesn't follow.

That present location in time is the present moment, it's a
unique
privileged moment in time.

That doesn't follow.

Brent

(This argument demonstrates only there must be a present moment
for
every observer. The other argument Brent references is
necessary to
demonstrate that present moment is universal and common to all
observers.) Bravo again Brent, for

...

--
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