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

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From: PD on 1 Mar 2010 09:53

On Feb 27, 9:20 pm, Ste <ste_ro...(a)hotmail.com> wrote:
> On 27 Feb, 13:00, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> wrote:
>
>
>
> > "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> >news:2726fc2b-b860-4c84-96a9-3776df684de4(a)e7g2000yqf.googlegroups.com...
>
> > > On 27 Feb, 07:02, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> > > wrote:
> > >> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> > >>news:f1c82fe9-c833-4262-9bca-d62d9181c8b0(a)i39g2000yqm.googlegroups.com...
> > >> On 26 Feb, 12:52, "Inertial" <relativ...(a)rest.com> wrote:
>
> > >> > "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> > >> > > Of course I'm not claiming to know anything profound about the solar
> > >> > > system. The conceptual model has been accepted for centuries, and I'm
> > >> > > not pretending to add anything new to it. The point I was making
> > >> > > about
> > >> > > it is that the conceptual model is required to give any real meaning
> > >> > > to the equations.
>
> > >> > We already have such model .. that's the whole POINT of physics .. it
> > >> > is
> > >> > modeling reality. How reality behaves is the meaning to the equations
> > >> > ..
> > >> > they describe what is going on.
>
> > >> Then show the equations to a child. Ask him if he understands what is
> > >> going on. And remember, you're not allowed to mention the conceptual
> > >> aspect, or appeal to sensory perception. You must only use the
> > >> equations. If these equations alone describe what is going on
> > >> meaningfully, then the child ought to understand immediately.
>
> > >> ___________________________________
> > >> Why a child?
>
> > >> Why not try and explain the equations of SR to a nematode worm? If they
> > >> really do encompass SR, then the nematode worm should understand SR
> > >> immediately. Or so your logic would suggest.
>
> > > No, my logic wouldn't suggest that. My logic says that these equations
> > > are meaningless without a conceptual model that gives them meaning.
>
> > What's wrong with Minkowski space-time? It gives me and lots of other people
> > a very clear conceptual model of SR.
>
> > >> Here are the facts. To fully understand SR, you need to be reasonably
> > >> intelligent, have a basic maths ability, and have some knowledge of
> > >> physics.
>
> > >> A child, a nematode worm, and yourself all miss out on some or all of
> > >> these.
>
> > >> If you want to understand SR, you are going to need to learn some maths
> > >> and
> > >> physics. Some things actually require work. Sorry.
>
> > > You can teach the child maths. But you can't tell him anything about
> > > the nature of the universe (because otherwise you're providing the
> > > conceptual model by the back door, when it is your argument that this
> > > is not necessary to understand physics, only the maths is required).
>
> > That was not my argument.
>
> Then can we revise, what is your argument? As I understood your
> argument, it was that the mathematical descriptions which account for
> what is observed is to paraphrase the "full extent of physics", and
> that anything else to do with the conceptual basis is "just
> philosophy".
>
> > But I still don't get what your problem is with the conceptual model of SR
> > provided by Minkowski space-time? It is isomorphic to SR, uses only simple
> > geometry, and all the key equations of SR become simple geometric
> > constructs. Minkowski contributed nothing to SR except a superb conceptual
> > model, apparently exactly the thing you want.
>
> > So why not learn it?
>
> Because you still don't seem to fully comprehend my plain words, that
> a mathematical model of SR is quite different from a physical model.
> You repeat over that "Minkowski is a physical model", but it isn't
> according to the requirements of what I (and of course, many others in
> society) hold to be "physical". Minkowski doesn't rest on physical
> concepts. It doesn't lay any claim as to what "time" is, for example,
> in a qualitative sense.

Nor does classical mechanics explain what "space" is. Is that a fault?
Nor does Newtonian mechanics explain what "energy" is. Is that a
fault?

> Nor does SR explain qualitatively what
> electromagnetic radiation is, or what its effects are.

Nor does the Lewis theory of acids and bases explain genetics. Why
should it?

> It necessarily
> doesn't, as a purely mathematical theory, detail whether what you are
> seeing is "reality", or whether it is merely an optical illusion, or
> whether SR is a combination of "real" effects and optical illusions.
>
> These are all significant questions to anyone with a sensible view of
> "physics". After all, there are mathematical models that will describe
> what you see in a curved mirror, and yet according to your argument
> there is no need to go further in detailing whether you are seeing
> "reality" or merely an illusion. Indeed it seems to me that, according
> to your argument, the question of whether a curved mirror causes an
> optical effect, or whether there is really another copy of my body
> inside an alternate universe, is a question of "mere philosophy".
>
> Of course, I await correction on my interpretation of your arguments,
> but you can see just how spectacularly obtuse and narrow-minded it is
> to say (if indeed you are saying) that the physical nature of various
> observations are "a question of philosophy, not physics".

From: PD on 1 Mar 2010 09:58

On Feb 27, 11:22 pm, Ste <ste_ro...(a)hotmail.com> wrote:
> On 27 Feb, 15:44, PD <thedraperfam...(a)gmail.com> wrote:
>
>
>
> > On Feb 26, 6:34 pm, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > > > The fact that this conceptual model in a raw form
> > > > > can permit predictions that are so permissive as to make almost no
> > > > > prediction at all, does not mean they are not an essential component
> > > > > to scientific enquiry and advance.
>
> > > > No testable predictions = not science. Possibly philosophy, possibly
> > > > fiction, possibly drug induced free association speech, possibly gibberish,
> > > > possibly an incredibly profound insight into human emotions, possibly
> > > > masturbation. But not science. Science makes testable predictions. (Note
> > > > that this is a necessary but not sufficient condition. Astrology also makes
> > > > predictions, just very poorly).
>
> > > I think you're attributing an absurd definition to "science". Paul
> > > Draper probably had a more tenable argument when he said that string
> > > theorists are scientists doing science, but that they do not yet have
> > > a "scientific theory". But I know from talking to him that he
> > > attributes a very contorted meaning to the phrase "scientific theory",
> > > that would condemn a lot of scientific knowledge, both historical and
> > > current, as being "unscientific".
>
> > Examples, please.
>
> In physics I would raise the same old example: string theory .

We've already discussed this.

> But
> there are certainly more. We have things like "dark matter".

And dark matter IS a theory. It has definite, quantitative
predictions. And those predictions are now undergoing experimental
test. In what way is it not a theory in the sense that I described it?

> Or even
> Newton.

And in what way is Newtonian physics not a theory?

> Or Galileo. And more broadly, in biology we have evolution,
> and in economics, rational choice theory.
>
> All managed to fail

Alright, we'll take just two: dark matter and Newtonian physics to
test your contentions?

> your previously stated requirement of a
> "scientific theory", which (amongst other things) is being falsifiable
> (in a practical rather than just notional sense),

In what way do you think that dark matter is not falsifiable. Same
goes for Newtonian mechanics?

> not ad-hoc,

I'm sorry, we've not had this discussion, and I don't even know what
you mean by ad-hoc in this context.

> and
> predicting observations that are not already accounted for.

What? You're not aware of the predicted observations of dark matter
and Newtonian mechanics not already accounted for?

PD

From: PD on 1 Mar 2010 10:00

On Feb 27, 11:23 pm, Ste <ste_ro...(a)hotmail.com> wrote:
> On 27 Feb, 15:46, PD <thedraperfam...(a)gmail.com> wrote:
>
>
>
> > On Feb 26, 6:46 pm, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > On 26 Feb, 12:52, "Inertial" <relativ...(a)rest.com> wrote:
>
> > > > "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> > > > > Of course I'm not claiming to know anything profound about the solar
> > > > > system. The conceptual model has been accepted for centuries, and I'm
> > > > > not pretending to add anything new to it. The point I was making about
> > > > > it is that the conceptual model is required to give any real meaning
> > > > > to the equations.
>
> > > > We already have such model .. that's the whole POINT of physics .. it is
> > > > modeling reality. How reality behaves is the meaning to the equations ..
> > > > they describe what is going on.
>
> > > Then show the equations to a child. Ask him if he understands what is
> > > going on. And remember, you're not allowed to mention the conceptual
> > > aspect, or appeal to sensory perception. You must only use the
> > > equations. If these equations alone describe what is going on
> > > meaningfully, then the child ought to understand immediately.
>
> > I'm not sure I buy the argument that anything should be fundamentally
> > understandable to a child.
>
> The point was to explain the theory to someone who hasn't already
> implicitly internalised the conceptual model on which the equations
> rest. This is, after all, the test of whether the equations are a
> complete description of reality, as Paul contends.

In this case, then, I do agree that this is a good goal. And this is
in fact what physics students do all the time: get an explanation of
the theory prior to their internalizing the conceptual model on which
the equations rest.

I just don't get where you think this simply does not happen.

>
> You could substitute uneducated adults, or even foreign cultures, for
> the child, but that would probably attract the criticism that the
> problem is one of language, inherent (lack of) ability, or cultural
> incompatibility to account for the failure of those others to
> comprehend the meaning of the equations. Whereas, if we start with a
> child, we at least assume that they speak the same language, have a
> similar level of exposure to our culture (but are not yet educated in
> science), and have a reasonable amount of ability.

From: paparios on 1 Mar 2010 10:20

On 1 mar, 06:59, Ste <ste_ro...(a)hotmail.com> wrote:
> On 1 Mar, 06:48, "Inertial" <relativ...(a)rest.com> wrote:
>
> > "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> > > but in my scenario dealing with simply two specific
> > > events, both are simultaneous in both frames.
>
> > Yes .. it is possible to have some events simultaneous in multiple frames.
>
> > But that does not make simultaneity universal in any sense, as other pairs
> > of events that are simultaneous in on of those frames is not simultaneous in
> > another.
>
> Agreed. But what it does prove is that the lack of simultaneity is due
> to propagation delays. The effect you're describing is exactly the
> same for sound, and involves nothing physically profound.
>
> > So regarding "what is simultaneous in one frame is not simultaneous in
> > another" meaning "the set of all pairs of simultaneous events in one frame
> > is NOT identical to the set of pairs of simultaneous events in another
> > frame" is correct.
>
> > THAT is the relevant point.
>
> I'm not sure what the point is. My point is that the assertion that
> "no two events that are simultaneous in one frame can be simultaneous
> in another" is falsified. Yet that is precisely the assertion that has
> been made on a number of occasions now, liberally salted with
> allegations that I'm "an idiot", "need to learn physics", "don't know
> anything", etc.
>

The fact is that you don't have a point!!!
Even in Newtonian physics there are frame dependent quantities. For
instance, a car C1 in a highway going e-w at 60 miles/hour approaches
another car C2 moving w-e at 75 miles/hour. These figures are measured
with respect to the highway (for instance a cop is using a radar gun
to measure those speeds). For the driver of C1 he is moving with
respect to C1 at 0 miles/hour, while he measures C2 approaching at 135
miles/hour.

In SR, simultaneity measures differences are not due to propagation
delays as you so confident and ignorantly assert.

What SR says is the following:

If we consider the cop at location C0 at rest with respect to the
highway, and the car C1 is moving at a speed v=1 km/sec with respect
to the cop, then if a lightning strikes the highway at x=-10 km from
the cop location at x=0 and t=0 (as measured with the cop clock) the
cop will determine that the strike was at t=-10/300000 seconds (this
indeed is considering the propagation delay due to the finite speed of
the light signal).

However the driver of the car C1 will measure things quite
differently. He will determine that the strike, as measured by his own
clock, was at t'=(1/sqrt(1-v^2/c^2))(t-vx/c^2)=(1/
sqrt(1-10^2/300000^2))(-10/300000+10/300000^2) seconds
and at location x'=(1/sqrt(1-v^2/c^2))(x-vt)=(1/sqrt(1-10^2/300000^2))
(-10+10/300000) km.

Both x' and t' calculations have nothing to do with propagation delays
but they do have to do with spacetime rotation.

Miguel Rios

From: PD on 1 Mar 2010 10:48

On Feb 28, 12:54 am, Ste <ste_ro...(a)hotmail.com> wrote:
> On 27 Feb, 15:54, PD <thedraperfam...(a)gmail.com> wrote:
>
>
>
> > On Feb 26, 6:54 pm, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > On 26 Feb, 17:34, PD <thedraperfam...(a)gmail.com> wrote:
>
> > > > On Feb 25, 9:05 pm, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > > > I also doubt one exists at the moment, but I see that as a problem.
> > > > > It's utterly irreconcilable, within any conceptual framework that I
> > > > > know of, to have situations where, for example, a large ladder can end
> > > > > up in a smaller barn according to an observer stationary in the barn,
> > > > > but not according to an observer riding the ladder.
>
> > > > Why? And here we can systematically trace back to the assumptions you
> > > > are making and then question them. In this case, you have a firm
> > > > belief that length is definable in such a way that it is intrinsic to
> > > > the object and frame-independent, and that physical "fitting" is a
> > > > function of the *intrinsic* lengths of two objects (or an object and a
> > > > container).
>
> > > My only contention is that it is *not realistic* to say that from the
> > > barn frame frame the ladder contracts and fits inside, while saying
> > > that from the ladder frame it is the barn that contracts and the doors
> > > actually never shut simultaneously. It is simply not realistic.
>
> > I don't know what basis you have for judging whether something is
> > "realistic".
>
> I must admit I can't quite put my finger on it myself.

And this is precisely what I want to make sure you look at again and
again. Science DOES have a consistent and established way of judging
what is realistic.

>
> > I'm guessing that it means that it is consistent with
> > your intuition, and that your intuition tells you that something
> > cannot fit in one frame and not fit in another, or that two events are
> > simultaneous in one frame and not simultaneous in another. If this is
> > accurate, then I would ask on what basis you trust your intuition. Or,
> > even more aptly, why do you trust your intuition so much that you rule
> > out other possibilities as real if they conflict with your intuition?
>
> Because on the one hand my physical (i.e. practical-mechanical)
> intuitions are well-developed and highly consistent with my experience
> of reality,

Right, with YOUR experience of reality. This is the value of personal
contact with experimentation, so that you can see nature operate in
ways that are beyond your current experience of reality. It is my
contention (and my broader experimental experience supports this) that
nature behaves in ways that are quite surprising and different than
what is in most people's ordinary experience of reality, and thus it
is not surprising that those results would be in conflict with an
intuition honed on the everyday experience of reality.

There is no substitute of comparable efficacy for this step.

> and secondly it is not readily apparent that SR is
> inconsistent with these intuitions.

Well, I just stated in plain language what SR says is true of nature
in a particular case, and this DID come in conflict with your
intuitions, albeit in a vague and difficult-to-place way, as you
described yourself.

> In the face of people who suggest
> the two are inconsistent, obviously I've got to first consider whether
> there's a language difference between me and the opponent (i.e. no
> common apprehension of verbal meaning),

Yes, indeed!

> and secondly whether the
> opponent is confused or simply wrong (i.e. no common apprehension of
> the evidence).

Well, wait right there for a minute. Just because you're not exposed
to the evidence would not mean that I am wrong, would it?

>
> The ultimate resolution of this question seems to be confounded
> firstly by the degree to which there is no shared language,

I'd put it differently: that the statements in relativity, which you
are trying to understand, are expressed in a language that you don't
completely recognize. This is confounded by some lack of insight on
your part as to which parts of the language are the same and which are
different. This in turn is probably due to the fact that you have not
availed yourself of resources that are structured to make those
distinctions proactively.

> secondly
> the degree to which opponents seem to be unclear about the conceptual/
> qualitative basis of SR,

I'd be careful about this. It may be that they are clear on the
conceptual/qualitative basis, but are declining to present it to you,
out of a personal preference for using the clarity and condensed
efficiency of mathematics. This unwillingness to cater to your
pedagogical needs should not be construed as their being unclear.

> and thirdly the preconceptions and
> psychological style of many posters.

In other words, your basis for deciding what is correct depends on the
manners of the people you discuss it with?

>
> > > If
> > > such a thing appears to happen, then it is obviously an artefact of
> > > subjective observation.
>
> > I disagree. In science, if there is a conflict between experimental
> > observation and intuition, then it is *intuition* that becomes
> > suspect, not the experimental result, especially if the latter is
> > confirmed independently and by complementary means.
>
> I'm afraid there is no room for a discrepancy between intuition and
> observation.

I'm sorry, but I've got a lot of classroom experience that shows that
this is simply a bogus expectation. I can set up a series of simple
experiments on a daily basis in class where I can display all the
elements of the experiment and show them plainly how the simple set-up
is put together, and then I can ask everyone in the class what their
intuition tells them will happen, and at least have of them will get
it wrong, which the subsequent observation will show. This I can do
(and have done) on a DAILY basis, with ordinary phenomena. I do this
for a reason, to show that (1) nature is surprising, and (2) that
intuition is no replacement for observation and in fact often lies and
cheats, and (3) there is demonstrable reasons why we believe certain
laws hold, even if they seem to point to unusual conclusions.

> Intuition is supposed to account for observation, and
> there is no question of observation taking a back seat to intuition.
> So that in that way we agree.
>
> But this is not the same as crude observationalism.
>
>
>
> > > > > > Your disbelief of SR stems from the fact that you don't understand it.
>
> > > > > My disbelief, really, stems from the blatant lack of conceptual
> > > > > understanding of the theory. I mean, as I repeatedly point out, I
> > > > > don't know a single equation of relativity, and yet I can root out the
> > > > > conceptual contradictions immediately when people here have a crack at
> > > > > making meaningful qualitative statements in SR. The classic example,
> > > > > of course, was Paul's contention that "what is simultaneous in one
> > > > > frame can never be simultaneous in another", which of course isn't
> > > > > true according to SR.
>
> > > > I'm sorry? It is very much true in SR that two spatially separated
> > > > events that are simultaneous in one frame are not simultaneous in
> > > > another frame moving relative to the first.
>
> > > But I contradicted that when I pointed out that two observers can be
> > > moving relative to each other, and yet undoubtedly events can be
> > > simultaneous for both.
>
> > Not spatially separated ones, no.
>
> I'm confused, because I thought we previously agreed that two
> observers travelling along the same axis, maintaining equidistance
> from both events at all times, would both report each event as
> simultaneous with the other event.

Not quite. What we said was defined what it means for two spatially
separated events to be simultaneous, by a procedure. The same
procedure can similarly tell you when two events are not simultaneous.

Where we left off the discussion of the case I presented is that for
the same pair of events, one observer (which satisfies all the
criteria of being equidistant between the events and so on) concludes
correctly from his observations that the two events are simultaneous,
and the other observer (which also satisfies the same criteria)
concludes correctly that the two events are not simultaneous.

We were about to show how this is completely consistent with the laws
of physics.

> And moreover, if they not only both
> maintained equidistance from both events, but if they maintained a
> separation which was equal for both observers (which, if both
> observers are moving relative to each other, requires either a
> collision course between observers, or travel in diametrically
> opposite directions), then there is no question that the signals are
> received simultaneously.
>
> Illustration:
>
> E1
>
> --------
>
> E2
>
> The line represents the line between events E1 and E2, along which the
> observers may move while always reporting both events to be
> simultaneous.

Yes, I see what you are thinking of. And it is true that IN THIS CASE,
E1 and E2 will be viewed as simultaneous by both observers. I do
concede this.

This is not the situation we were discussing before, however.

PD