Speed of Light

What radial velocity? Stars do not not have a radial velocity component in their motion around their galactic host (other than that caused by individual local proper motion that will be inward and outward) - there is no evidence to the contrary in any galaxy where we can monitor the individual motion of the constituent stars, and the Earth is certainly not falling towards the centre of the MMilky Way. Similarly, and rather fortunately, the Shuttle does not have a inward radial velocity component in its orbit around the Earth.

Funny, I was driving past Keele University on Sunday. Given the complete lack of understanding, almost total miscomprehension, and uttermost confusion in the above two posts, it would sadly appear that Keele is not what it once was...

You say you are 79 - that means that when you were born, most of your questions had already been answered 25 years earlier with Special Relativity, and the rest would take just another 15 years with Quantum ElectroDynamics. So at best, you are 64 years too late.Of course, you are free to disagree with SR and QED, but I should point out that they are the most successfully tested theories ever constructed by mankind, and are tested every second of every day to extraordinary precision by processes such as the GPS system and every particle accelerator in use around the world, not least the new LHC at Cern. Every particle physicist involved in the experiments at these particle accelerators knows the answers to your questions as basic graduate introductory material.Just to give a little active content to this post, let me briefly address question 8:Can light be scattered by light, as some experimenters have claimed?Yes, it can, but it is a second order effect and so is exceptionally hard to detect. As you infer, it is a very good job it is a second order effect as otherwise light would be useless for sight!!Photons are excitation of an abelian quantum field, which in simple terms means that the excitations do not self-interact. This is in contrast to the non-abelian fields of the gluons, and the W,Z bosons, which do self-interact:

/ Ph
        /
Ph     /
  ~~~~~    Doesn't Happen !!!!
       \
        \
         \ Ph

Ph \    / Ph
    \  /
     \/   Doesn't Happen !!!!
     /\
    /  \
Ph /    \ Ph

However, a pair of photons can produce an electron/positron pair (pair creation):

/e+
        /
Ph     /
~~~~~~|
      |
      |
Ph    |
~~~~~~|
       \
        \
         \ e-

This interaction can be used to build a second order photon-scattering interaction:

Ph \          / Ph
    \        /
     \___e__/
     |      |
     |e     |e
     |______|
     /   e  \
    /        \
Ph /          \ Ph

This is the famous box diagram of QED.Edited by cavediver, : No reason given.Edited by cavediver, : No reason given.

The key statement from his bio is as follows:

quote:

---

His aim is, by this means, to seek out and remove from theoretical physics its traditional accumulation of sheer conceptual clutter and to discourage the associated misuses of language which generate what the philosopher Wittgenstein called Scheinprobleme, a prime example of which, as Pope sees it, is the notorious, so-called 'EPR paradox'.

---

This is probably the one guiding principle behind every armchair-physicist - they read all of the layman-ese regarding theoretical physics, and unsurprisingly it seems confused and makes little sense to them - this is because it is usually complete crap! But they mistake these layman descriptions for the real physics/mathematics, and so completely miss the point. The only words we use in real theoretical physics are to connect the mathematics to the real world. The content is all in the mathematics, and that is never seen by the likes of Mr Pope.Even the Feynman diagrams in my previous post are simply graphical representations of the perturbative interaction expressions...

No need to apologise, I wasn't in the slightest disconcerted; for the simple reason that I didn't doubt your status in the slightest. I took what I read as read, and replied accordingly. Hostile? Really? If I was ageist at all, it was in my lack of hostility, compared to the usual verbal beating I dole out to those at EvC peddling nonsense. For that slight of ageism, I apologise and promise not to trim my hostility any further.However, my actual reference to your age was simply to put into context various dates, and had no implications of ageism whatsoever. No mistake was made, so no concession was necessary. Minkowski gave us this in 1907, and we use it to this day. You could have saved yourself much work.I'm sorry, but the staggering lack of understanding manifest in your "arguments" is sufficient to dismiss anything you have to say. You obviously have no awareness of something as simple as the relativistic composition of velocities, something I would teach to first year undergrads. And to suggest that when I am describing Quantum ElectroDynamics, THE MOST SUCCESSFUL THEORY KNOWN TO MAN, is simply staggering. The fact that you show zero knowledge of this, and claim that it is "thin", firmly removes any residual credibility.

Ah, I see - I take then that you are of similar opinion to Viv Pope that my response in message 38 copied below was a bit thin?Good to see I'm completely wasting my time - FFS Can light be scattered by light, as some experimenters have claimed?Yes, it can, but it is a second order effect and so is exceptionally hard to detect. As you infer, it is a very good job it is a second order effect as otherwise light would be useless for sight!!Photons are excitation of an abelian quantum field, which in simple terms means that the excitations do not self-interact. This is in contrast to the non-abelian fields of the gluons, and the W,Z bosons, which do self-interact:

/ Ph
        /
Ph     /
  ~~~~~    Doesn't Happen !!!!
       \
        \
         \ Ph

Ph \    / Ph
    \  /
     \/   Doesn't Happen !!!!
     /\
    /  \
Ph /    \ Ph

However, a pair of photons can produce an electron/positron pair (pair creation):

/e+
        /
Ph     /
~~~~~~|
      |
      |
Ph    |
~~~~~~|
       \
        \
         \ e-

This interaction can be used to build a second order photon-scattering interaction:

Ph \          / Ph
    \        /
     \___e__/
     |      |
     |e     |e
     |______|
     /   e  \
    /        \
Ph /          \ Ph

This is the famous box diagram of QED.Edited by cavediver, : No reason given.

Well, neither do I really. He claims that c is not a velocity. I would initially agree, because in the knowledge of Special Relativity, the concept of velocity becomes suffciently warped at a large fraction of c that it bears little resemblence to the everyday concept. However, he seems to want to cling to the Gallilean concept of velocity and simply redefine c.This is revealed in his confusion regarding velocity composition, seemingly unaware of the relativistic version of the classical Gallilean , which is . As you can see, if either of V₁=c or V₂=c, then V=c.This also answers his claim 5 - light has the same velocity in ALL frames. The rest of it is just so much confusion and nonsense, that do I really have to pull it all apart? He just cannot accept the bizarre consequences of SR and feels that applications of "common senes" will rescue his sensibilities. Ok, first two figures represent two photons colliding (from the right in the first diagram, confusingly) and joining in the first digram, and scattering in the second. This does not happen in nature - if it did, we could not see because photons would be bouncing off each other all the time, and there would be no free path for photons from object to eye. The third diagram shows how two photons can combine to create a positron and an electron, and the final diagram shows how to photons can come in from the left, then by clever creation and annihilation of the eletrcons and positrons, make it seem if the two photons scatter off each other, as they leave on the right.So photons do scatter off each other, but only by this clever electron-positron trick, and that makes it quite rare. Back in the OP, HH stated As we can see from the above, even in complete vacuum, there is some (exceptionally damped) scattering, just as in a non-vacuum.Edited by cavediver, : No reason given.Edited by Admin, : Fix Latex images - my bad.

Of course they are just diagrams. Obviously they constitute no proof by themselves. But they are the prediction of QED. And these same diagrams from QED, when summed to fourth order, calculate the eletcron g-factor to within 1 part in a trillion of the observed value, thus mkaing QED the most accurately tested theory ever. So if QED shows us that there is heavily damped photon-photon scattering, you had better have a much better reply than "they are just diagrams". Oh, and of course it has been indirectly experimentally observed. It is hoped that new more powerful laser laboratories will be able to make direct observation of this.May I ask what numerical predictions your theory has made, and how well do they match observations?Edited by cavediver, : No reason given.

It doesn't Not anymore. You are too used to talk of space-time, and space-time diagrams. But 100 years ago, this was not the case. You'll remember that in E/M theory, we have two constants appearing in Maxwell's equations: permitivity of free-space, and permeability of free-space, . When Maxwell constructed the electromagnetic wave-equation from the Maxwell equations, the velocity of the waves is given by which he called 'c'. So c is simply the velocity of the waves in the Maxwell wave-equation. But then when we realise that light is an electromagnetic wave, we see that 'c' is thus the speed-of-light.Later it was realised with some worry that the velocity of the e/m wave was independent of the velocity of the source! This made no sense whatsoever. Lorentz even went so far to suggest that physical matter would contract at velocity, so to counteract this bizarre effect. Out of all this confusion, Einstein managed to build a coherent picture of what was going on, and thus was born Special Relativity.But it was Minkowki that went the step further to show that all of Special Relativity could be understood as the geometry of a 4d space-time, where c is now simply the conversion factor between spatial and temporal units. This can be seen no clearer than in the wave equation, when we expand out: to and minimally rearrange to: which shows x, y, z, and t all on the same footing apart from the sign change and c factor with the t term.We then write this rather minimally as:

Well, you'll have heard this from me several times at EvC And yes, I think it's a great way of looking at it. But this is from your own POV as the traveller. An observer doesn't see it this way (unless he can observe a clock travelling with you and can deduce this)

sorry for the long wait - Ok, last first: E is simply electric field strength - it's a vector field, so it shows you the magnitude and direction of the elctric field at each point in space. Likewise, we have B, the magnetic field strength. We saw the wave equation for E but there is an idenitcal one for B, and we further find that in an electromagnetic wave, E at a point is always perpendicular to B at a point, and the direction of travel is perpendicular to the plane defined by E and B.The electric constant (permitivity of free space) turns up when we look at the force between two forces: It is just the dimensionful proportionality constant - a result of our definitions of meters, seconds, and kilograms - and that our definition of charge doesn't have an expression in terms of meters, seconds, and kilograms.Likewsie, the magnetic constant (permeability of free space) is the proportionality constant when we look at the magnetic force between two wires when a current is flowing in them: So, the two constants simply express the fact that we're not measuring the world around us in the right units! And not surprisingly, this is the case for 'c' as well.

...that Viv is actually correct when he says that light does not travel.Hopefully, the EvC regulars here should know by now that the space-time distance or time (interval) along a light path is zero. This is simultaneously the extreme of Lorentz contraction and time dilation which we get for v=c. So photons do not travel, nor do they age - as far as the photon is concerned, its point of emission and point of absorption are the same. This is true for light bulb to eye, or distant quasar to eye.For us, the observers, we can measure what we think of as the velocity of the photon, and we get the answer 'c'. But if it were a spacecraft travelling at 'c', if we looke closely, we would see that the clocks on board the ship are frozen - no time is passing at all.So, Viv is essentially correct But this is Special Relativity at its most basic, has been known since the earliest days of relativity, and certainly does not require his ten rather-dubious 'proofs'.Edited by cavediver, : No reason given.

Yes, that's rght. I've noticed And you're doing a good job - just keep pushing and demanding evidence, or at a minimum, predictions. I'm sorry, but I'm way over my crank quota for 2009 and aleady subject to heavy fines. Perhaps come the New Year... (but don't hold your breath)Edited by cavediver, : No reason given.

Now, this looks rather dishonest, Viv. I'm surprised at you. I have explained how QED, the most successful theory ever devised by man, demonstrates quite blatently how we get photon-photon scattering. Indirect evidence for this process is seen daily at particle accelerators around the world, and we hope to see direct evidence as soon as we have sufficient (laser) apparatus.Your defense to this has been to describe my explanation as 'thin' and to suggest that some unnamed individuals at the IC gathering of PIRT found this to be on 'dodgy ground' - I'm sorry, but around here, that does not count as a refutation.Please explain why QED is wrong in its prediction, whilst managing to predict the electron g-factor correctly to 12 decimal places - a prediction that involves summing over the very process that you are claiming does not exist!Once you have answered this, we can go on to your comments regarding velocity composition.Edited by cavediver, : No reason given.

Why should being massless mean that something is not a particle? Are you also suggesting that gluons do not exist?I also have to ask - if photons do not exist, then what causes electron positron pair creation, and how is energy conserved? As seen here: Edited by cavediver, : No reason given.