Let's answer Motl's post on VSL point by point: The Reference Frame: Varying Speed of Light (VSL) theories: crackpots par excellence

The archives and sometimes even journals are continuously flooded with new articles about a theory that was originally invented by young Earth creationists to reconcile the Bible with the Big Bang and that was later adopted by non-Christian crackpots, too. It is called Vary Speed of Light (VSL) theory.

What's the argument here? The concept of "atoms" was invented by a pre-Christian pagans. So what? Furthermore, when I do a search for "VSL" on arxiv, I get a total of 233 hits, that's a trickle, not a "flood".

George Ellis has decided that there should exist an authoritative, published article explaining why all this VSL industry is complete crap. I fully agree. If this nonsense keeps on appearing all the time, there should exist some reactions that can be referred to. He mentions virtually identical arguments that I always say about these VSL theories:

Their authors don't understand that one can always change her units.

Changing units has nothing to do with VSL theories. Perhaps Motl means to say that one can always change ones coordinate system. This is true in general relativity, but it need not be the case for a succeeding theory.

Furthermore, I would suggest that it is quite impossible to get a PhD in physics without understanding that one can change units. Claiming that the authors do not understand this is an ad hominem attack that one can safely reject.

They don't know what's the difference between dimensionless and dimensionful quantities.

Oh come on. There's something like 30 authors who've written papers with VSL in their abstract. They are employed by the usual physics institutions. Is it really possible to get a position in physics at Cambridge without knowing the difference between dimensionful and dimensionless quantities?

The meter is moreover defined as 1/299,792,458 of a light second, so according to current definitions, a varying speed of light is simply a contradiction.

The current definition of the meter assumes that the speed of light is constant. To use this as evidence that the speed of light is constant is hardly proof that the speed of light is constant. If a VSL theories wins out, it's likely that the definition of the meter will not need changing in its usual context. Eventually, some corrections might be needed.

One doesn't gain anything whatsoever by redefining the speed of light in a time-dependent fashion because it is just a time-dependent change of units (or coordinates in GR).

It's not possible to get a PhD in physics without knowing this and of course the authors of VSL papers know this as well. The statement is true under the assumption that GR is the final theory of gravity, but VSL papers do not, or should not assume GR.

When the speed of light is allowed to be different for various phenomena, we need to determine the right modifications in all equations of physics, including Maxwell's equations and others. No VSL paper is doing anything like that.

I agree that a VSL paper that proposes to define a complete description of physics needs to do this. However, physics is a big thing, and one really can't expect every single VSL paper to completely redefine all of physics. One might as well require that every string theory papers include a complete derivation of Maxwell's equations.

Furthermore, it is not the case that "no VSL paper" has an explanation for how Maxwell's equations work in their theory. In particular, the Cambridge geometry group's "Gauge Gravity" includes Maxwell's equations. For instance, Hestenes' paper on a flat space version of gravity (which must needs be a VSL theory) includes extensive discussion of Maxwell's equations:

Gauge Theory Gravity with Geometric Calculus
David Hestenes
A new gauge theory of gravity on flat spacetime has recently been developed by Lasenby, Doran, and Gull. Einstein's principles of equivalence and general relativity are replaced by gauge principles asserting, respectively, local rotation and global displacement gauge invariance. ...
GTG.w.GC.FP.pdf

Moreover, one expects to end up with a generic non-relativistic theory with infinitely many parameters. The VSL papers never offer any principle that would replace the broken Lorentz symmetry and determine these parameters. They don't even acknowledge this problem.

The above referenced paper by Hestenes is based on geometric calculus. It is inherently Lorentz symmetric and one will find that the above paper discusses the subject at great length.

In other words, VSL theories are 100% vacuous and stupid crap. Tonight, Magueijo and Moffat have submitted an answer that have made me so upset by its breathtaking stupidity that I simply had to write this text to calm down. ;-) They don't understand a single one among Ellis' obvious complaints. Instead, they paint themselves as new Galileos because they are ready to make a constant variable.

One of the things I've noticed about physicists is that they tend to get quite emotional when relativity is discussed. Here Motl mentions that he had to write in order to calm down. Perhaps this is an excuse for the poor arguments.

Important physics has never worked like that. Quite on the contrary. Every new major revolution in physics has shown that a certain conversion parameter was not only constant but it was meaningful to set it equal to one.

If one defines a "major revolution" to be the situations where a certain conversion parameter turned out not only to be constant, but was set equal to one, then the above vacuous statement is true. But even if one were to do this, the fact that physics has advanced in this manner is not proof that it will continue to advance this way.

A clear lesson from the history of physics is that revolutionary advances tend to reject certain very well established ideas. In fact, one might say that in order to be a revolutionary physics theory it has to be this way. Otherwise it's just adding more knowledge to the heap, rather than "revolting".

Richard Feynman said that correct theories of physics are perfect things, and a replacement theory must be a new perfect thing, not an imperfection added onto an old perfect thing. This is the essence of "revolution", the replacement of the old with a new, not the adding of more crap on to the old.

And the replacement theory replaces the old, just as Einstein's gravitation replaced Newton's. The old theory can stick around for computational convenience, but the new theory does not need to obey the restrictions and assumptions of the old theory. One cannot reject possible new theories of physics by their failure to hew to established principles. One can reject them only for failing to match experiment. All that a new theory of gravity HAS to do is to provide calculations that match the known experimental results. It does not have to have the speed of light as a constant, and it does not have to treat coordinates the same way as general relativity does.

Joule has figured out ... ... The number of constants we need to write into our equations decreases. Making constants variable is going exactly in the opposite direction than what progress in \theoretical physics has always been doing.

This is all true, and ancient history. And I have no doubt that the next revolution in physics will involve a reduction in the number of constants. In fact, the biggest problem with the standard model today is the fabulous number of arbitrary constants it possesses. But that in itself is not proof, or even much in the way of evidence, that our current choice of constants will stand the test of eternity.

While physics does involve a slow reduction in the number of constants, this is not the same as saying that the things that physics describe become simpler with time. In fact, just the opposite occurs. Matter was once described as a mixture of fire, earth, air and water. Now we know that it is far more complicated than that.

It is in the nature of man to look for the simplest explanation for those things he does not understand. It is almost inevitable that his explanations are too simple. Repeatedly, time and time again, we have had to replace simple explanations with more complicated ones.

For example, Maxwell's equations as they were known in the 19th century are now replaced with field theory. It turns out that the continuous electric and magneic fields do not exist except as an approximation to a quantum reality that is far more complicated to model classical phenomena, (for example, a lightning bolt), than the classical model of electricity and magnetism. The fact that Maxwell's equations were simple and elegant did not help them when it was time for the E&M theory to be replaced by a deeper, more fundamental theory. Similarly, the simplicity and beauty of Lorentz' equation is not evidence that it will stand forever as an exact description of reality.

The only "constants" that should be variable are those that depend on some parameters of the environment. But such a declaration of their variability is only interesting once we understand how the environment actually works.

It's quite natural that a physicist pursuing his own dreams of revolution is uninterested in the papers of others. But this is sociology, not physics. And of course no one knows how quantum mechanics or relativity really work. What's more, a lack of interest is not the best evidence that Motl can write a critique that understands the ideas presented.

Saying that quantities should become variable without understanding how they vary is a meaningless sleight of hand ...

As shown above, this is not necessarily the case.

... but certainly not a complete theory of anything.

To criticize someone for their failure to publish a complete theory of everything is a bit much.

A very similar criticism applies, to a lesser extent, to doubly special relativity etc.

I will let DSR defend itself.

The people who work on all these stupid things have a tremendous problem to distinguish physics from conventions, predictions from ways of writing things, deep insights from vacuous sequences of mathematical symbols.

This is probably true of all physicists. At the present moment, string theory has made no predictions whatsoever. If the VSL papers are to be described as a "flood", what is the term for the string theory papers?

They don't understand what a choice of units and field redefinitions means and why they're unphysical.

Gauge Gravity is a flat space gravity theory, where "flat" means Minkowski space. The advantage of the theory over Einstein's GR is that it is simpler and easier to calculate with.

A well loved principle in physics is that if there is a very complicated way of describing physics, and a very simple way, and the simple way gives the same predictions as the complicated way, then the simple way is the correct theory to use. Making a simple theory complicated is not "physical" or "unphysical", it is "mathematical", and if it gives no advantage, it is useless.

Despite all of their profound ignorance about basics of physics, these crackpots are extremely arrogant (Magueijo is the #1 example, of course) - they view themselves as competitors of inflationary cosmology and many other key segments of science - which makes me quite upset. ;-) And that's the memo.

Magueijo took his PhD in physics at Cambridge. It's silly to claim that he is profoundly ignorant of the basics of physics. As for their being competitors to inflationary cosmology, none of these theories has much in the way of predictions at this time. I don't hold any of them to be true. But I think that Motl's arguments against them have been quite weak. And of course arrogance is hardly an indication of stupidity.