Simultaneous events and Einstein's absolute time
in [Relativity]
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From: artful on 3 Feb 2010 07:04 On Feb 3, 10:31 pm, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > On Feb 3, 3:35 am, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > > > > > > > On Feb 2, 9:51 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 2 Feb, 22:08, Igor <thoov...(a)excite.com> wrote: > > > > No, relativity is based on a constant c which may or may not represent > > > > the speed of actual radiation in vacuum. All that's sufficient to > > > > state is that c is the maximal attainable speed possible. That's what > > > > leads to the predictions of SR, not necessarily that c must be the > > > > actual speed of electromagnetic radiation in vacuum, although for the > > > > most part, it still holds up. But it really doesn't have to. They're > > > > two entirely different issues. > > > > Then how could you possibly establish a value for 'c', if not by > > > measuring the speed of light? > > > The point is, that EVERYTHING has the same limit. Whether you are > > accelerating charged protons or electrons in an accelerator, or > > estimating the dispersion of uncharged neutrinos from SN1987a, or > > directly measuring the speed of light, or measuring anisotropies > > in the two-way or one-way speed of light in the direction of the > > earth or perpendicular to the direction of the earth, it's the > > same limit. > > > There is a fundamental quality about the value of "c" that other > > speeds, such as the speed of sound, do not share. All experiments > > point to this value being a constant, whether measured locally in > > direct fashion, or estimated indirectly at far reaches of space > > and time through the astronomical measurement of physical constants > > that are dependent on light speed. > > > The existence of such an upper limit is a trivial geometric > > property of Minkowski spacetime. It is for this and for many > > other experimental validations that we believe in the > > applicability of special relativity as a relevant description of > > the universe (in low gravity regions). > > Minkowski spacetime converts the issue of the existence of a > constant upper limit to the speed of communications from a deeply > mysterious question, to a "Duh, of course!" observation. > > Here is an analogy. Have you ever heard of the book Flatland, by > Edwin Abbott?http://en.wikipedia.org/wiki/Flatland > > Imagine that once upon a time, scientists at the Flatland > Institute of Technology (FIT) decide to investigate the question, > "Does the mathematical law, C = pi*D apply to real circles?" > By drawing precise circles and making careful measurements of > diameter and circumference, the scientists are delighted to find > that yes, indeed, the circumference of a physically drawn circle > has a length pi times the diameter, as theoretically predicted. > > But the relationship is not exact. Well, it's probably just a > matter of the measurements not being done precisely enough... > > Unfortunately, increasing the precision of the measurements does > not make the discrepancy go away. Furthermore, the larger you > draw the circles, the greater the discrepancy. Even more > shockingly, FIT scientists discover that there seems to be a > limit to the size of the circles that you can draw. > > This enigma deeply puzzles the greatest minds of the time. In > desperation, one of the greatest of their scientists proposes > a contraction hypothesis. Large circles are subject to forces > that shrink their circumferences relative to their diameter. > Totally ad hoc in nature, this proposal nevertheless fits with > the data... > > It takes an obscure young patent clerk to come up with the > correct answer to this great enigma. Perhaps, he suggests, we are > not living on a flat surface at all, but rather a sphere? > > Most readers of his paper do not get the point. His paper simply > does not read like anything else they are used to reading. Rather > than being a treatise with dozens of references to a plethora of > experimental results and filled with complex math, his paper > reads rather like a philosophical dissertation, starting with > simple premises, but ultimately ending up with conclusions that > violate all common sense. > > But a few readers do get the point. No special property of matter > is required to explain the experimental results. Large circles > are not subject to compressive forces that shrink their > circumference relative to their diameters. The explanation is > a simple matter of geometry. > > This geometry is completely outside the experience of most > Flatlanders, who have a strictly 2-D view of the world. But to > those few who studied the subject of 3-D geometry in their higher > math courses, the theory comes as a revelation. > > To the Flatland scientists, spherical geometry converted the > issue of the existence of a constant upper limit to the size > of a circle from a deeply mysterious question, to a "Duh, of > course!" observation. > > That is the same way with the geometry of Minkowski spacetime. > > Jerry A beautiful analogy. Very nicely put. Did you come up with it yourself, or was it something you read somewhere (just interested in the source).
From: Igor on 3 Feb 2010 09:50 On Feb 2, 5:16 pm, "Androcles" <Headmas...(a)Hogwarts.physics_u> wrote: > "Igor" <thoov...(a)excite.com> wrote in message > > news:b0bf0a4c-f6a1-48b8-90e1-c991abdf4846(a)b2g2000yqi.googlegroups.com... > > No, relativity is based on a constant c which may or may not represent > the speed of actual radiation in vacuum. > =============================================== > No, relativity is based on the absurd assertion that the ``time'' required > by light to travel from A to B equals the ``time'' it requires to travel > from B to A. > No, you have no what you are a babbling about. > No, you are an idiot. > No, you should learn to read. So now's your chance to provide us with your wisdom, Mr Parker. Please explain how vacuum spacetime becomes anisotropic.
From: Igor on 3 Feb 2010 10:08 On Feb 2, 10:51 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 2 Feb, 22:08, Igor <thoov...(a)excite.com> wrote: > > > > > > > On Feb 2, 12:08 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > Absolute time and a finite speed of light are contradictory concepts. > > > > > > Therefore, since it's easy to demonstrate that light has a finite > > > > > > speed, absolute time cannot exist. > > > > > > The same arguments (whether true or not) can also be made from the > > > > > existence of a finite speed of sound. > > > > > You are confused by a serious PUN. > > > > > There exists a demonstrable maximum possible speed of > > > > communications, designated "c". > > > > You mean the maximum speed of communications using matter? Somewhat > > > like how there is a maximum speed of communications using sound waves? > > > But there's not a maximum speed of communications using sound waves. > > Speed of sound is proportional to the density of the medium and has no > > theoretical upper bound. > > If you hold the expanding universe hypothesis to be true, then I > believe the same argument about density applies to light. Except that light travels perfectly well through regions of zero density. When it does travel through matter, it actually slows down. And I don't understand what the expanding universe has to do with any of this. > And in any event, the point is that if the density of the medium *is* > held constant, then the speed of propagation is constant and finite. That's true, but light and sound behave oppositely in regards to that. Sound speeds up in higher density media, whereas light slows down. So your analogy fails. > > > > > > > > Should the speed of light ever be discovered not to precisely > > > > equal "c" (and there is some controversial evidence that this > > > > may be the case for high energy gamma rays), this will have NO > > > > CONSEQUENCE WHATSOEVER in regards to the validity of relativity, > > > > since the "c" which is the speed of light is not the same "c" > > > > which determines the properties of spacetime. > > > > Which is the most absurd drivel I've ever heard. What you're basically > > > saying is that the validity of relativity is independent of any > > > measurement of the validity of its terms. > > > No, relativity is based on a constant c which may or may not represent > > the speed of actual radiation in vacuum. All that's sufficient to > > state is that c is the maximal attainable speed possible. That's what > > leads to the predictions of SR, not necessarily that c must be the > > actual speed of electromagnetic radiation in vacuum, although for the > > most part, it still holds up. But it really doesn't have to. They're > > two entirely different issues. > > Then how could you possibly establish a value for 'c', if not by > measuring the speed of light? There are many quantities in physics that depend on c. So determining c is not necessarily a question of measuring the actual speed of light. And so far, we have no reason to doubt that the vacuum speed of light is c, but it's not actually necessary. Maybe you need to research how physical constants are measured. > > > It's this arrogance and loss of touch with reality that explains why > > > we're up to 20-odd "hidden dimensions", because the loss of touch with > > > reality has left scientists out in the wilderness, with neither the > > > inspiration nor the intuitive guidance that comes with a connection to > > > the material world. > > > Well even Einstein said that our understanding of the universe should > > be "as simple as possible, but no simpler". If it requires 20 hidden > > curled up dimensions, so be it. But I think we've just begun to > > scratch the surface on this stuff. > > I agree, but whatever we find underneath, I don't expect it to be > additional dimensions. The main problem is that, without additional dimensions, whether they be metric spaces, fiber spaces, or whatever, GR is essentially a dead end in explaining the bases of the other forces of nature. But this is the conundrum we find ourselves in right now. Maybe there is another way to approach this, but I have no idea what it would be.
From: PD on 3 Feb 2010 12:03 On Feb 2, 9:31 pm, Ste <ste_ro...(a)hotmail.com> wrote: > On 2 Feb, 19:07, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Feb 2, 10:51 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > On 2 Feb, 13:15, Igor <thoov...(a)excite.com> wrote: > > > > > On Feb 1, 10:29 pm, artful <artful...(a)hotmail.com> wrote: > > > > > > On Feb 2, 10:44 am, Ste <ste_ro...(a)hotmail.com> wrote: > > > > > > > On 1 Feb, 18:27, Igor <thoov...(a)excite.com> wrote: > > > > > > > > Absolute time and a finite speed of light are contradictory concepts. > > > > > > > Therefore, since it's easy to demonstrate that light has a finite > > > > > > > speed, absolute time cannot exist. > > > > > > > The same arguments (whether true or not) can also be made from the > > > > > > existence of a finite speed of sound. > > > > > > Nope .. because the speed of sound is frame dependant > > > > > And sound requires a medium. > > > > And light requires a medium - we call it "empty space". > > > And if this is how you want to define "medium" -- anything that > > carries a transmission of any description -- then there is no > > argument. But once again, this is not the connotation that physicists > > had associated with "medium" when there was much fuss about whether > > light was carried in a medium. > > As far as I'm concerned, space is to light what air is to sound. In a very simplified and overly vague sense, this is certainly true. The problem then comes in assuming that because the statement is true in the vague sense, then it is true in the detailed sense. This is, of course, where it breaks down. The statement is similar to saying that mammals are just like reptiles. When asked to defend the statement, one could say "They are both vertebrates. They both are tetrapods." Those statements are undeniably true, and yet it is just as undeniably false that mammals are just like reptiles.
From: Ste on 3 Feb 2010 12:32
On 3 Feb, 09:35, Jerry <Cephalobus_alie...(a)comcast.net> wrote: > On Feb 2, 9:51 pm, Ste <ste_ro...(a)hotmail.com> wrote: > > > On 2 Feb, 22:08, Igor <thoov...(a)excite.com> wrote: > > > No, relativity is based on a constant c which may or may not represent > > > the speed of actual radiation in vacuum. All that's sufficient to > > > state is that c is the maximal attainable speed possible. That's what > > > leads to the predictions of SR, not necessarily that c must be the > > > actual speed of electromagnetic radiation in vacuum, although for the > > > most part, it still holds up. But it really doesn't have to. They're > > > two entirely different issues. > > > Then how could you possibly establish a value for 'c', if not by > > measuring the speed of light? > > The point is, that EVERYTHING has the same limit. Whether you are > accelerating charged protons or electrons in an accelerator, or > estimating the dispersion of uncharged neutrinos from SN1987a, or > directly measuring the speed of light, or measuring anisotropies > in the two-way or one-way speed of light in the direction of the > earth or perpendicular to the direction of the earth, it's the > same limit. But 'c' then becomes an arbitrary constant, and I have no idea how its value could be established if not from the speed of light. Personally I think it will be the death knell for relativity if the speed of light turns out not to be constant, not because relativity will suddenly become useless, but because it will undermine its virtually untouchable status as a "fundamental truth" in physics (which, really, is how many people treat it), and it will also undermine all the baggage in physics that is built on the assumption that relativity is true. |