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

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From: Ste on 17 Feb 2010 09:19

On 16 Feb, 13:54, mpalenik <markpale...(a)gmail.com> wrote:
> On Feb 16, 7:59 am, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > > You seem to insist that 4 dimensional spacetime is some abstract
> > > philosophical thing when really, it's nothing of the sort. The real
> > > world exists as a 4 dimensional manifold. That's not dependent on
> > > mathematical tricks. You have a four dimensional space. We call one
> > > of those dimensions time.
>
> > > You percieve a 3 dimensional world. But you have to realize that's
> > > only your perception and that the universe exists outside of your
> > > perception.
>
> > No we don't perceive a 3D world. We perceive a 4D world, and have done
> > since the beginning of time (as it were).
>
> Which also exists independently of our perceptions.

Yes I certainly agree that the world exists independently of our
consciousness or our interpretation of it.

> >That's what I'm saying to
> > you: the real world existed long before geometry. And geometry is just
> > a mathematical formalisation of basic concepts that were already
> > physically obvious to anyone who ever considered the issue.
>
> This has nothing to do with rotation, which also exists independent of
> human mathematics. Rotation and orientation are physical things with
> physical consequences.
>
> I also think you might be confusing geometry with coordinate dependent
> descriptions of geometry. For example, length is a geometric
> property, which is independent of coordinate descriptions. Length is
> a property that an object has--i.e. the rod is longer than this other
> rod. It's not an algebraic or coordinate dependent property.

Perhaps. I don't really understand the distinction that you're
describing.

> > > I understand relativity in the actual terms of the way the universe
> > > really works. You're looking for something that conforms to your
> > > specific desires, which relativity does not.
>
> > > Let's try it this way: what about the picture I drew for you do you
> > > not think could represent physical reality?
>
> > I never said it didn't *represent* physical reality, at least in some
> > way. But my ability to understand requires me to translate that
> > representation into something physical and concrete. The idea that the
> > representation means anything in itself is just absurd to me.
>
> So, the problem is actually that you find what the picture describes
> absurd so you reject it off hand, despite the fact that it can be used
> to recreate every prediction of relativity.

I didn't say that the picture was absurd, and nor have I rejected it
out of hand.

It seems to me that one of the essential features of the theory is the
need to account for propagation delays, but I keep getting told that
it isn't, yet the only alternative explanation I'm given is that
relativity reflects something "more real" than "mere propagation
delays". So I've really just put the question into abeyance for now
while I try to build some sort of consistent picture of how light
behaves (which of course is what I'm doing on the thread "Known
physics defeated..."), and I'm hoping that the pieces will eventually
fall into place.

> There's not that much
> that needs to be interpreted in that picture. it means exactly what
> it says it means, literaly--not in some abstract sense. Literally
> think of a 4 dimensional space with that rotated rod in it. It was
> not meant as a metaphor.

As I say, it's something that I'll just have to put in abeyance for
now.

> > > It represents rotation, just like when I tell you that I rotated a
> > > pole, that also represents a rotation. You just don't understand that
> > > the two things are the same. You insist that they must be different
> > > but in reality, they are not. They don't look quite the same to you
> > > because of your perspective. It's exactly like the flatland example I
> > > gave before. If you have people that live on a little, flat world
> > > sitting in our 3 dimensional space, who can only percieve the things
> > > that exist inside of their little 2 dimensional world, when something
> > > rotates into that third dimension, they'll go "what the heck just
> > > happened? That doesn't look like any rotation I've ever seen."
>
> > But there is no such thing as a two-dimensional "flatland" in reality.
> > This is much like saying "imagine a place that is not real with people
> > who are not real, and imagine what reality would look like to those
> > people" (which I can only say is unimaginable), and then using this as
> > some sort of proof of a "hidden reality" that is not apparent to
> > people who *are* real. As I say, the four dimensions have been with us
> > since the beginning of time, and people have in one way or another
> > recognised their physical existence since the beginning of time.
>
> I don't think I can get you to visualize a 4 dimensional space, so I
> took a 3 dimensional slice of 4 dimensions.

I visualise 4D simply as 3D but with change - a bit like an animation,
I suppose. But information also travels instantly in this
visualisation, because I play the part of God, not of the human
observer.

> There's nothing invalid
> about that. It's like looking at a building from the side and drawing
> a 2 dimensional profile.

But again, the 2D representation only means something because it can
be translated into a 3D object. That's why every now and again you
look at something and can't make sense of it until you identify the
perspective and the nature of the objects depicted. 2D makes sense
*precisely because* it can be translated into meaningful 3D objects.

> In this case, we're looking at the universe
> by taking a 3 dimensional slice--just a different 3 dimensional slice
> than the one we're used to looking at.

As I say, I can do 2D with time in my head. It just acts like a piece
of paper, with the shapes moving. Or, if you wanted extra realism, you
can build the pages up into a block of paper, and each level of the
block represents a point in time, and if you remove/dissolve/make the
paper transparent, then the 2D shapes build into 3D shapes. And if,
for example, you had a 2D square moving spatially at a constant speed,
then from a certain perspective it would make a trapezoid shape when
formed into 3D.

Of course, I can then understand this in terms of the shape becoming
"shorter in space and longer in time", if we take that trapezoid and
rotate it in time, so that the "points" of the trapezoid extend
further into time, and the length of the shape contracts.

But then I think to myself, space isn't 2D. But what sees only in 2D?
The eye (or the camera, or whatever). And it becomes very convenient
to view each "timeslice" as representing "what is visually observed".
And believe it or not everything falls into place - relativity
describes what is observed.

> > > > > The picture I made for you wasn't supposed to represent an analogy--it
> > > > > was supposed to represent physical reality (except with a slightly
> > > > > different metric--but we don't need to worry about that just yet)..
>
> > > > If you don't recognise geometry as being an abstract *representation*
> > > > of the physical world, as opposed to the physical world itself, then
> > > > that is a clear difference in our understandings - and it's a
> > > > philosophical difference which will not be reconcilable.
>
> > > It's no more or less geometry that showing you a picture of a pole
> > > that's rotated in our regular 3 dimensional space. It's no more
> > > abstract than that. Why do you insist on calling it something more
> > > abstract than that? The picture I showed you is exactly the same
> > > thing.
>
> > > Relable the axes x and y, instead of x and t. Now can you agree that
> > > it's simply a picture of a rotated pole? Now, suddenly if I switch
> > > the axes back to x and t, does it magically become more abstract just
> > > because I changed the labels?
>
> > No, both are abstract. The difference is that a rotation in the y-axis
> > translates into something quite physically different than a rotation
> > in the t-axis.
>
> No, it doesn't. Take the picture exactly at face value. There is no
> metaphor involved--it doesn't translate into anything other than what
> the picture shows. Your problem is you're looking at the picture and
> saying, "ok, on x and y, this is a rotation--exactly what it shows in
> the picture," and then saying "ok, x and t, what does this mean in the
> real world?" instead of saying, "ok, x and t, this is a rotation--
> exactly what it shows in the picture." Do not try to find some hidden
> layer of interpretation. It is simply a "snapshot" of a 2 dimensional
> slice of the universe. It doesn't matter what axis we take this slice
> along. It does not represent anything different.

I'm afraid we'll have to disagree. There is no argument that you make
which will convince me that it is not necessary to ask "what does this
mean in the real world".

From: kenseto on 17 Feb 2010 10:03

On Feb 16, 6:42 pm, "Inertial" <relativ...(a)rest.com> wrote:
> "PD" <thedraperfam...(a)gmail.com> wrote in message
>
> news:da09c070-e346-42f6-a55f-cabf519d20dc(a)k36g2000prb.googlegroups.com...
>
>
>
>
>
> > On Feb 16, 5:17 pm, "Inertial" <relativ...(a)rest.com> wrote:
> >> "PD" <thedraperfam...(a)gmail.com> wrote in message
>
> >>news:995b34f4-be02-48bb-b9db-463e3437283a(a)j27g2000yqn.googlegroups.com....
>
> >> > On Feb 16, 12:57 pm, kenseto <kens...(a)erinet.com> wrote:
> >> >> On Feb 16, 1:46 pm, PD <thedraperfam...(a)gmail.com> wrote:
>
> >> >> > Picking and choosing your definitions, Ken?
> >> >> > Look at the definitions I highlighted for you.
> >> >> > Look at your freshman physics textbook. Does it tell you that the
> >> >> > electric field is not physical?
>
> >> >> In the past you insisted that length contraction in SR is physical and
> >> >> at that time you think that physical means material.
>
> >> > No, sir, I *never* said length contraction was material. I said it was
> >> > PHYSICAL.
>
> >> >> You even
> >> >> suggested that length contraction can be measured directly by shooting
> >> >> lasers from the ends of a moving ruler to the rest frame of the
> >> >> observer.
>
> >> > Yes, it is MEASURABLE. Physical things are measurable.
> >> > Energy is MEASURABLE, it is not material.
> >> > Magnetic fields are MEASURABLE, they are not material.
> >> > Radio waves are MEASURABLE, they are not material.
>
> >> >> So you see you think that length contraction in SR is
> >> >> material.
>
> >> > No, it is MEASURABLE. It is not material.
>
> >> >> Also your SR brother Inertial said in this thread that contraction in
> >> >> SR means that the atoms get closer....this means material contraction.
>
> >> > Ken, rather than desperately trying to gather excuses to support your
> >> > mistaken impression, why don't you just take another look at the
> >> > correct definitions for physical that I've already shown you? Why
> >> > don't you reread your freshman physics text again, and check whether
> >> > it says the electric field is not physical? If you've made a small
> >> > mistake, then CORRECT IT and move on. If you cannot ever correct a
> >> > small mistake, you'll never get out of square one. You'll spend all
> >> > your time searching newsgroups for support for your mistake.
>
> >> Note that the atoms in a length-contracted rod are physically closer
> >> together, as measured in the relatively moving inertial frame. In that
> >> frame the material that makes up the rod is fitting within a shorter
> >> distance (ie compressed).
>
> > Well, I know what you're saying, but I'd be very careful about
> > terminology here to avoid confusion. Seto thinks of compression as
> > being solely the effect of a material interaction, such as a
> > compressive *force* or perhaps a low temperature bath. That's not
> > what's going on here. So yes, the pole is shorter and since no atoms
> > have been lost, then the atoms have a different length, but this does
> > not imply anything squeezing on them (even if Seto can't imagine it
> > happening any other way).
>
> I didn't say they were squeezed .. I said they were closer together.

You didn't say that they were squeezed and I didn't interpret that
they were squeezed. But when you said that the atoms are closer
together I interpreted that the pole is materially really gotten
shorter...iow it is not just a geometic projection effect.

Ken Seto

>
> But yes .. it depends on whether one assumes something being compressed
> implies that there is some external agent compressing it or not. In this
> case there isn't an agent .. its just a result of the rotation. Just like a
> tilted ladder has a shorter height even though nothing has squeezed it.
>
> >> However, the intrinsic/proper/rest length of the rod is unchanged, and
> >> the
> >> intrinsic/proper/rest distance between the atoms of its material are
> >> unchanged.
>
> > The rest length of the rod is unchanged. Since this rest length is the
> > length measured in only one frame (the rest frame), I'm reticent to
> > call it an intrinsic property.
>
> Perhaps more to the point, the frame-dependent length (spatial distance
> betwen end points at a given time) and the invariant length both correspond
> in the frame when the object is at rest. So the invariant length and rest
> length are always the same value.
>
>
>
>
>
> >> So whether of not it's 'materially' compressed (meaning the atoms of the
> >> material of which it is made are closer together) depends on whether you
> >> are
> >> talking about the frame dependent view of the material or the invariant
> >> view. Which, when you say it, is bleedingly obvious.
>
> >> Also note that just because the contraction is MODELLED by a geometrical
> >> rotation does not mean it there is nothing 'physical' going on wrt
> >> frame-dependent measurement (which is the sort of measurement we work
> >> with
> >> every day, and that makes sense).
>
> >> It all comes down to whether you are referring to frame dependent or
> >> invariant measures. In the pole and barn scenario, when one says "in the
> >> frame of the barn", that implies we are talking about frame-dependant
> >> values
> >> .. and 'length contraction' means the frame-dependent length of the pole
> >> is
> >> shorter, and in a frame-dependent view of the pole, the atoms that make
> >> up
> >> its material are closer together.-
>
> > Yes,
>
> > Seto suffers from a false dichotomy.
>
> Indeed .. among other things.
>
> > If there is a change in length,
> > he believes this can be the result of only two possibilities: a
> > material interaction that causes a stress in the body; or an optical
> > illusion.
>
> > It is neither. He doesn't understand the third possibility.
>
> Indeed again :):)- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -

From: Ste on 17 Feb 2010 10:04

On 16 Feb, 15:53, PD <thedraperfam...(a)gmail.com> wrote:
> On Feb 16, 6:59 am, Ste <ste_ro...(a)hotmail.com> wrote:
>
> > No we don't perceive a 3D world. We perceive a 4D world, and have done
> > since the beginning of time (as it were). That's what I'm saying to
> > you: the real world existed long before geometry. And geometry is just
> > a mathematical formalisation of basic concepts that were already
> > physically obvious to anyone who ever considered the issue.
>
> You are quite right! But it turns out we've made some erroneous
> presuppositions about that 4D world. In fact, the presupposition we
> had has a fairly tight specification. We had the notion that the
> universe was structured as what's called a "fiber bundle" (it's a
> mathematical term), with 3 spatial dimensions and an *independent*
> time dimension. This expresses itself in certain ways. For example,
> two observers in relative motion can label coordinates in 3 spatial
> and 1 time dimensions in several possible ways, and it's possible to
> make diagrams that show those relationships. One possible way is the
> "fiber bundle" way that says that the distance between two events in
> space and time (x^2 + y^2 + z^2) will be the same for both observers,
> and this can be traced to the *independence* of the time dimension.

Has time ever really been considered "independent"? It seems to me
that much of this "relativity of simultaneity" can be constructed with
reference only to acoustic phenomena.

> > > Let's try it this way: what about the picture I drew for you do you
> > > not think could represent physical reality?
>
> > I never said it didn't *represent* physical reality, at least in some
> > way. But my ability to understand requires me to translate that
> > representation into something physical and concrete.
>
> You'll find that this chaining of representations to objects that you
> are already familiar with prevents you from discovering much that is
> wholly new and unfamiliar.

As I've said before, I disagree that we ever see anything that is
totally "new and unfamiliar".

> > But there is no such thing as a two-dimensional "flatland" in reality.
> > This is much like saying "imagine a place that is not real with people
> > who are not real, and imagine what reality would look like to those
> > people" (which I can only say is unimaginable), and then using this as
> > some sort of proof of a "hidden reality" that is not apparent to
> > people who *are* real. As I say, the four dimensions have been with us
> > since the beginning of time, and people have in one way or another
> > recognised their physical existence since the beginning of time.
>
> As we discussed earlier, it may be that we are only AWARE of four
> dimensions. It may well be that there are more. Then the way to
> entertain this notion is to ask the question, how would something that
> is only AWARE of two dimensions become convinced that there is a third
> dimension? This turns out to be very answerable.

I'm afraid that was not my conclusion. As I've said, these
possibilities only seem credible to those who already hold them to be
credible.

From: Ste on 17 Feb 2010 10:19

On 17 Feb, 13:25, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
wrote:
> "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> news:9b31d2c9-e699-41a8-a366-bc2f407ad017(a)o30g2000yqb.googlegroups.com...
>
>
>
>
>
> > On 16 Feb, 13:53, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> > wrote:
> >> I never said it didn't *represent* physical reality, at least in some
> >> way. But my ability to understand requires me to translate that
> >> representation into something physical and concrete.
> >> ___________________________
> >> A lot of people have trouble understanding abstract concepts. You
> >> shouldn't
> >> feel shy about this, but you may take it as a sign that possibly physics
> >> is
> >> not for you.
>
> > I don't have too much trouble understanding abstract concepts within
> > their own terms, if I'm inclined to familiarise myself with them. But
> > if the abstract concept is supposed to describe something physical,
> > then I wouldn't claim to "understand" unless I could indeed translate
> > it into something concrete.
>
> > Indeed when I say "I don't understand", I may sometimes be using it as
> > a polite synonym for having actually made a judgment that "this theory
> > is obviously ludicrous and unworkable as an explanation for the
> > phenomenon that was to be explained".
>
> Well, its obviously not ludicrous, because it works. The experimental
> evidence is overwhelming. That is seems ludicrous to you is because you
> don't understand some key concepts; one is the mathematics, and the other
> relates to the philosophy of science.
>
> I might add that I have never heard of anybody who understood the
> mathematics but thought SR (or GR for that matter) as being "ludicrous"; if
> you were somewhat less lazy or considerably brighter (or perhaps both) you
> could learn the maths as well and by the time you have learned Maxwell and
> Minkowski you won't think its ludicrous, you will think SR (at least) is
> obvious.
>
> But alas, lazy and stupid, that is a recipe for being a crank, not
> understanding science.

Just to remind you, I don't necessarily think relativity is ludicrous.
Only the explanations here for why it works.

From: mpalenik on 17 Feb 2010 10:41

On Feb 17, 10:19 am, Ste <ste_ro...(a)hotmail.com> wrote:
> On 17 Feb, 13:25, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> wrote:
>
>
>
> > "Ste" <ste_ro...(a)hotmail.com> wrote in message
>
> >news:9b31d2c9-e699-41a8-a366-bc2f407ad017(a)o30g2000yqb.googlegroups.com....
>
> > > On 16 Feb, 13:53, "Peter Webb" <webbfam...(a)DIESPAMDIEoptusnet.com.au>
> > > wrote:
> > >> I never said it didn't *represent* physical reality, at least in some
> > >> way. But my ability to understand requires me to translate that
> > >> representation into something physical and concrete.
> > >> ___________________________
> > >> A lot of people have trouble understanding abstract concepts. You
> > >> shouldn't
> > >> feel shy about this, but you may take it as a sign that possibly physics
> > >> is
> > >> not for you.
>
> > > I don't have too much trouble understanding abstract concepts within
> > > their own terms, if I'm inclined to familiarise myself with them. But
> > > if the abstract concept is supposed to describe something physical,
> > > then I wouldn't claim to "understand" unless I could indeed translate
> > > it into something concrete.
>
> > > Indeed when I say "I don't understand", I may sometimes be using it as
> > > a polite synonym for having actually made a judgment that "this theory
> > > is obviously ludicrous and unworkable as an explanation for the
> > > phenomenon that was to be explained".
>
> > Well, its obviously not ludicrous, because it works. The experimental
> > evidence is overwhelming. That is seems ludicrous to you is because you
> > don't understand some key concepts; one is the mathematics, and the other
> > relates to the philosophy of science.
>
> > I might add that I have never heard of anybody who understood the
> > mathematics but thought SR (or GR for that matter) as being "ludicrous"; if
> > you were somewhat less lazy or considerably brighter (or perhaps both) you
> > could learn the maths as well and by the time you have learned Maxwell and
> > Minkowski you won't think its ludicrous, you will think SR (at least) is
> > obvious.
>
> > But alas, lazy and stupid, that is a recipe for being a crank, not
> > understanding science.
>
> Just to remind you, I don't necessarily think relativity is ludicrous.
> Only the explanations here for why it works.

Then you *really* won't like general relativity.