A constant speed of light in all reference frames? Surely you can't be serious. [Physics]

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From: Peter Webb on 11 Mar 2010 08:37

"Ste" <ste_rose0(a)hotmail.com> wrote in message
news:860a5e85-6231-4eeb-a3a8-f2b25ced173b(a)x12g2000yqx.googlegroups.com...
> On 11 Mar, 01:58, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> wrote:
>> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>>
>> > except for the fairly
>> > obvious explanation that it is the reference clock which is undergoing
>> > a "real" slowdown.
>>
>> Or, that you have no idea of what SR predicts, and have completely and
>> falsely assumed that observers see clocks jump ahead when turnaround
>> occurs.
>
> I'm merely going off what "experts" here say happens. I didn't say
> there is a "leap ahead". Paul Draper (if I remember correctly) said
> there is a "leap ahead". Now perhaps I misunderstood, but that is what
> was said.

Perhaps that was what he said.

But now you know.

No leap ahead.

From: Dono. on 11 Mar 2010 09:30

On Mar 11, 12:12 am, "Inertial" <relativ...(a)rest.com> wrote:
>
> > You are using the speed composition .
>
> Of course .. that is the correct formula to use to convert a measured speed
> in one frame to a measured speed in another in LET
>

In doing so, you are using the CONCLUION (what you were asked to
prove) in the demonstration.
So, you produced a fake "proof". Congratulations, idiot.

From: PD on 11 Mar 2010 10:10

On Mar 10, 8:51 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote:
> On Mar 10, 11:57 am, PD <thedraperfam...(a)gmail.com> wrote:
>
>
>
> > On Mar 9, 9:41 pm, Paul Stowe <theaether...(a)gmail.com> wrote:
>
> > > On Mar 8, 8:05 pm, "Inertial" <relativ...(a)rest.com> wrote:
>
> > > > "Paul Stowe" <theaether...(a)gmail.com> wrote in message
>
> > > >news:1132a230-92d9-484a-b0c1-d3a97532cad9(a)z10g2000prh.googlegroups.com...
>
> > > > >> >> SR explains it as having to be c due to the geometry of spacetime
>
> > > > >> > That's simply a silly idea...
>
> > > > >> That you think it is silly is your problem, not that of SR
>
> > > > > Something physical may be represented by a geometric description.
>
> > > > And our universe is represented by Minkowski geometry.
>
> > > Yes, you can descibe localized behavior with that format. BUT! to do
> > > so you must depend on finite light speed and its physical
> > > independence. Geometry neither predicts. explains, or has a basis for
> > > that.
>
> > That's incorrect, Paul. The geometric structure of spacetime imposes
> > both a finite speed of light AND makes it frame-independent.
>
> > The geometric structure of spacetime *necessarily* divides pairs of
> > events into three categories: spacelike-separated, timelike-separated,
> > and nullcone-separated. This structure also immediately leads to the
> > result that any wordline that could be traversed by something between
> > timelike-separated events will, in any other inertial reference frame,
> > still be between timelike-separated events. What this means explicitly
> > is that this object can never span two spacelike-separated events.
> > Thus, the universe of events is strictly divided into two completely
> > separated causal domains. The boundary of these domains is the null
> > cone. Since the null cone has a definite slope of space vs time, this
> > imposes a causal speed limit. (This limit does not exist in Euclidean
> > 3D+1D space -- it is a unique feature of the 4D space and its
> > geometry.)
>
> > Furthermore, while transformations between inertial frames will shift
> > the slopes between pairs of timelike events (that is, the speed of an
> > object traveling between the two events), the same transformation
> > between pairs of events on the null cone do not change slope. What
> > this means is that any object that can travel between two events on
> > null cone will have the same speed regardless of inertial reference
> > frame.
>
> > So you see, the geometric structure DOES imply both a causal speed
> > limit and the invariance of that causal speed limit with choice of
> > inertial reference frame. It just so happens that light appears to be
> > one of the candidate objects that can travel between nullcone-
> > separated events.
>
> > If you need to see how the structure does impose those limits
> > formally, I could point you to a reference book or two that derives
> > this unambiguously.
>
> Please provide the reference.

Start with "General Relativity from A to B" by R Geroch. There are a
couple others I can think of, but I'd like to check out which of them
is best before expanding the list. Penrose's book "The Road to
Reality" deals with it beautifully, but that's a big book.

>
> TIA, Bruce
>
> > At the time that Einstein proposed special relativity, he did not
> > understand how such a geometric structure could produce those two
> > conclusions as necessary consequences. And so he just posited the
> > invariance of the speed of light as a postulate (or equivalently,
> > demanded that Maxwell's equations obey the principle of relativity).
> > It was only later that the geometric structure was uncovered and it
> > was understood how the light postulate follows directly from this
> > structure.
>
> > PD- Hide quoted text -
>
> > - Show quoted text -
>
>

From: PD on 11 Mar 2010 10:12

On Mar 11, 6:43 am, Ste <ste_ro...(a)hotmail.com> wrote:
> On 11 Mar, 01:51, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> wrote:
>
> > No, perhaps you didn't understand. As I say, this is *not* the twins
> > paradox, because in the twins paradox only *one* twin leaves Earth.
>
> > ________________________
> > Its functionally the same. It is exactly the twins paradox, but with two
> > twins apparently doing exactly the same thing.
>
> > Even if you cannot see that, the explanation on the Wikipedia page of the
> > Twins Paradox is trivially adapted for two twins.
>
> > I assume that you do not understand the Wikipedia twins paradox page, or
> > else you would know the answers to your questions already. Which parts don't
> > you understand?
>
> Let's just go through it step by step Peter, as we have been doing.
> It's pointless spending 10 more postings arguing about how the
> Wikipedia page does or does not answer the question, or how it is or
> is not relevant. As I've just said in a post to Inertial, the only
> analogy between my scenario and the twins paradox is that, in my
> scenario, both twins leave Earth, and both return the same age as each
> other - hence no paradox, and hence bearing no resemblance at all to
> the twins paradox.

First of all, let's establish what you think is paradoxical at all
about the description of the twins in the twin puzzle. Then let's see
whether this paradox is present in the case you mention.

From: PD on 11 Mar 2010 10:18

On Mar 11, 7:37 am, "Peter Webb"
<webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote:
> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> news:860a5e85-6231-4eeb-a3a8-f2b25ced173b(a)x12g2000yqx.googlegroups.com...
>
>
>
> > On 11 Mar, 01:58, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> > wrote:
> >> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> >> > except for the fairly
> >> > obvious explanation that it is the reference clock which is undergoing
> >> > a "real" slowdown.
>
> >> Or, that you have no idea of what SR predicts, and have completely and
> >> falsely assumed that observers see clocks jump ahead when turnaround
> >> occurs.
>
> > I'm merely going off what "experts" here say happens. I didn't say
> > there is a "leap ahead". Paul Draper (if I remember correctly) said
> > there is a "leap ahead". Now perhaps I misunderstood, but that is what
> > was said.
>
> Perhaps that was what he said.
>
> But now you know.
>
> No leap ahead.

http://scope.joemirando.net/faqs/Relativity/SR/TwinParadox/twin_gap.html

This and the supporting links give some of the context here.