Sunday, October 19, 2014

Relativity Denial: The Importance of Dimensional Analysis

From the comment stream for the post Scott Rebuttal. I. GPS & Relativity this little goodie was flagged by the blogspot spam filter from an anonymous poster:
"The Engineering manager for GPS states that there are no corrections for relativity used in GPS, only a correction for gravitational potential (which has nothing at all to do with GR). If you want to discuss real errors with relativity you should check the mathematics of Einstein in GR for errors, because the whole lot is mathematically seriously flawed leading to all kinds of false conclusions!"
It also included a link to a site claiming relativity is flawed but not a link with documentation of the specific claim in the comment (and I already have plenty of links from this site to that site, so I don't need another).  I therefore regarded the comment as link-spam (Wikipedia) and have dumped it. 

However, it did make a couple of comments that I thought worthy of addressing and clarification.

The statement about the "Engineering manager for GPS" was made with no reference.  However, I have heard this term used to indicate the authors of the paper discussed in the main article, Scott Rebuttal. I. GPS & Relativity, "GPS and Relativity: An Engineering Overview".  Therefore I suspect the commenter actually mean the very same paper that was discussed in the main post.  One point of my original post was to point out that because of the "An Engineering Overview" paper, with the statement of no GPS effects, an additional experiment was actually conducted (again) and found the predicted relativistic effects.  Clearly the commenter either didn't read, or didn't understand the information.

Then there is this statement:
"there are no corrections for relativity used in GPS, only a correction for gravitational potential (which has nothing at all to do with GR)"
Let's see, Newtonian gravitation involves gravity, so we expect to see G.  It involves the mass of objects, so we expect to see M, and it involves positions, so we expect to see some representation of position, such as radial distance from a center, R.  Masses and positions are the main inputs for the theory.  This is true for Newtonian gravitation, as well as General Relativity. 

The gravitational potential for a point mass is G*M/R in Newtonian gravity.  The gravitational potential has units of energy per mass (joules/kilogram) which is dimensionally the same as velocity squared (meters/second)^2.

General relativity involves the very same quantities of G, mass, and position.  Being an extension of special relativity, the energy of the gravitational field must also be a component, since it also contributes to the mass of the system.  Therefore we expect a gravitational representation of energy in General Relativity.  With the quantities we have available, only one combination comes close to units of energy, and that is G*M/R, the same as the Newtonian gravitational potential.

Therefore basic dimensional analysis EXPECTS a quantity like the gravitational potential to appear in General Relativity in some form.  Very often, researchers will recast the full relativistic solution into a form using the classical gravitational potential to facilitate comparison of other derivations to the Newtonian solution.

So how can the commenter claim that the gravitational potential can have nothing to do with General Relativity?

The commenter's statement exhibits an incredible lack of understanding of not just general relativity, but basic physics and the importance of dimensional analysis.  These types of errors can be dangerous, expensive, or even fatal.  Dimensional analysis is a powerful tool that can often be used to find errors in analysis and is a vital tool in engineering.

Additional Resources on the Importance of Units and Dimensional Analysis

Sunday, October 12, 2014

Star Talk Radio Episode: Pseudoscience

Neil deGrasse Tyson's "Star Talk Radio" show recently conducted an episode on Pseudoscience.  Most of the topics discussed were rather 'garden-variety' pseudo-science, not much overlap with the topics discussed on this blog, but it might be of more general interest.

Star Talk Radio: Cosmic Queries, Pseudoscience

One of the topics discussed was an online list of cognitive biases or failures - a list of ways in which people fool themselves. 

Wikipedia: List of Cognitive Biases
RationalWiki: List of Cognitive Biases

The best scientists are pretty good about checking their ideas against such biases, which is why they often devote a large part of some of their potentially more controversial papers to checks on their methodology.

Meanwhile, pseudo-scientists usually just accuse mainstream scientists of group-think, and other items on this list, while never doing a serious check of their OWN biases. 



Sunday, October 5, 2014

Geocentrism: Mach, 'Aether Drag' and Aberration

I have received some email inquires requesting a follow-up on the geocentrism claims of John Martin (In Response to Dr Bridgman's "Geocentrism: Failing More Basic Physics").  These are followups to my original post, Geocentrism: Failing More Basic Physics...

Mr. Martin engages in the common practice of the "Gish Gallop" (RationalWiki), throwing out a plethora of claims most of which are nonsense, many are even contradictory, as we shall see below.  Mr. Martin has dumped a load of similar claims in the comment stream of my original post which I am holding until I complete addressing the individual entries.  I've been accumulating info on many of these earlier claims, each one of which would require an entire post to provide details and examples of why it's nonsense.  Since I have a number which are in various stages of completion, I thought I would write up a summary of some of the 'high points' where I have the most complete information.

Mr. Martin claims I have not provided specific examples of problems that cannot be addressed with a 'stationary earth'.  Yet I have not seen him or any of his supporters meet my Lagrange Point challenge.

I have also provided simulations of Newtonian gravitation operating on massive objects dealing with some of Mr. Martin's bizarre claims about how a center-of-mass of a system operates.
If the center of mass behaved the way Mr. Martin claims, then an automobile engine, consisting of many moving parts and many different centers-of-mass for any combination of the components, would be incapable of moving!

Mr. Martin continues by making ambiguous claims to various professional research papers which he claims have 'solved' these problems.  These are apparently used as a diversionary tactic so they don't have to do any actual work - just claim their theory gives the exact same predictions!  

Yet any example that can be placed into a form for a 'stationary Earth' can be placed in a form for a 'stationary Moon', a 'stationary Saturn', or any other place in the universe.  NASA routinely uses these types of transformations to send spacecraft to land and orbit other planets (see Geocentrism: Does NASA use Geocentrism?). 

Geocentrism and 'Machian' Models

Another funny, and again, contradictory, argument tactic by Geocentrists is to invoke Mach's principle (Wikipedia: Mach's Principle).

Machian ideas are actually the ultimate in relativistic thinking, as they try to define the inertial properties of any object in the universe based on the rest of the universe.  Taking this ideas to the ultimate extreme, some authors like to say these models can be viewed as a moving universe around a stationary Earth (a statement which makes them popular for use among the Geocentrists).  Some of these papers go so far as to use the example of if I spin around, I'm actually making the entire universe spin around me - I guess that would be an EGO-centric universe! 

But Geocentrists' professional references doing the 'Machian' calculation are simply generalizing the techniques I've outlined before - doing the computation in, say, a heliocentric frame, and then doing the conversion to the Earth frame - a trick that works identically for any other planet or any other location in the Universe!  Therefore their claimed proof fails to demonstrate the Earth more preferred than any other frame!  By relying on these references they are making MY point.  They do not show that the location of Earth is in any way a preferred frame beyond Mr. Martin's own personal prejudice.

Mr. Martin provides references to papers by Julian Barbour and various co-authors.  A number of these papers, and summaries, are available on Barbour's site.

Note that in one of the Machian papers, the first paragraph of "Relative-distance Machian theories" reference by Barbour:
"Mach's principle, in essence, requires that the dynamical law of the Universe be expressed ultimately in terms only of the relative distances between observable entities in the universe.  Here I propose a framework for constructing theories that satisfy this postulate automatically."
Note that he specifies RELATIVE DISTANCES between objects.  This is because Machian models have no absolute frame. 

Also note the mathematics in these papers.  The equations contain summations over objects in the universe, computing parameters based on the particle mass and velocity relative to each other.  Therefore, each entry in the sum treats all particles in the universe the same!  The very mathematical structure contains no preferred location or motion! 

The problem the Geocentrists don't acknowledge, is that these models also work having the entire universe rotate around Mars, or the Moon, or even a planet orbiting a star in a distant galaxy.

Planetary Aberration

In regards to planetary aberration, Mr. Martin had this to say:
"The above statement by Wicki doesn’t give us any calculated examples or any references to any journal articles. This is telling on wicki and shows the reader that planetary aberration is merely assumed, but no evidence is presented for its existence."
Planetary aberration is calculated as it is for stars, based on the RELATIVE velocity of the planet and spacecraft.  These corrections are installed in numerous software used for planetary navigation (see Geocentrism: Ubiquitous Aberrations).  The aberration calculation itself is trivial once the positions and velocities of the objects of interest are known.  The real work is computing the positions and velocities of the objects involved, be they planets or spacecraft, a task which geocentrists have demonstrated no competence.

"Aether Drag"

In the late-1800s as Maxwell completed the mathematical unification of electricity and magnetism with his equations and light was recognized as an electromagnetic phenomenon, the question arose "what is the medium that allows light to travel?"  Previous experience with sound suggested that a medium was required for the waves.  It seemed reasonable to researchers of the day that light would also need such a medium.  They called that hypothetical medium the aether or ether and proceeded to devise experiments in an attempt to determine its properties (much like today we adopted the name Dark Matter as the explanation for cosmological gravitational inconsistencies and proceed to determine its properties).

Experiments searching for the aether gave such contradictory and inconsistent results it was eventually suggested that light did not need an aether to propagate and the proposal of special relativity in 1905 provided a firm mathematical foundation.

Nonetheless, some try to hang onto the aether as a way to claim Earth is motionless.  Per Mr. Martin:
"Galileo’s theory of gravity is false. Things do not fall at the same acceleration. Newton’s theory of gravity is also false because the aether has been found. Finally Einstein’s theory is also false because of the constancy of c, time dilatation and length contraction have all been invalidated or are internally logically incoherent. All this is in an article dedicated to debunking crank science and all the time you are unaware of the findings of modern science which overturn you pet theories. Evidently your example is just as flawed as your understanding of science and gravity. Maybe it is you who has no operational experience other than deluding yourself into thinking you know more about gravity and science theory than what your erroneous posts are saying."
Things do not fall at the same acceleration?  Not sure where THAT comes from as Mr. Martin provides no reference.  I can take two ball-bearings of different masses and holding them the same height above the ground and releasing at the same time, they will hit the ground simultaneously.  If you want to use a hammer and a feather (which has much more drag from air resistance), you'll need a good vacuum for the experiment (see YouTube: Hammer vs Feather - Physics on the Moon).  No word yet if Mr. Martin will be claiming the Apollo lunar landings were faked (see Exposing PseudoAstronomy, Bad Astronomy: Moon Hoax).

Claims of Aether drag having been 'found' conveniently ignore the fact that it has been known since 1907 that the Einstein theory gives the same result as the Fresnel 'aether drag' equation.  This derivation is illustrated on the Wikipedia page (Aether drag hypothesis: Lorentz and Einstein)

Even funnier is that many of the mainstream papers which 'aether' supporters reference as evidence for the existence of an 'aether' often include the derivation of the 'aether drag' in the relativistic formulation.  A number of experiments in the 1970s were done by R.V. Jones:
Note that R. V. Jones would even write 'Fresnel Aether Drag' in quotes to emphasizes it is not to be taken literally!

Spurred on by Jones' research, M. Player (Dispersion and the Transverse Aether Drag) examined the problem in more detail, considering the optical dispersive properties of the medium.  Player also used the relativistic derivation, but now included how the Doppler effect would change the wavelength of the light and the refractive properties of the medium (Wikipedia: dispersion) under testing would change.

One of the most popularly cited papers by 'aether' supporters is by Aleksandar Gjurchinovski (Aberration of light in a uniformly moving optical medium").  However, if you actually READ the paper (and understand it), you'll notice that Gjurchinovski is explaining the Jones result in a relativistic framework.  Note in particular equation 3 which is the Lorentz transformation!  Pushing the parameters of the experiment with a very dispersive medium, Gjurchinovski gets a result that matches the derivation by Player (referenced above) including the effects of dispersion.  I have found some quotes from the Gjurchinovski papers where there is a discussion of how 'real' these effects are, but one must exercise care with the wording.

So it looks like the proponents of the claim that 'aether drag' is real and are using these papers never actually understood the papers!   They just blindly assumed they must back up their claims!

So what's the excuse for such blatant errors?
  1. Did Mr. Martin not bother to read the papers he is citing, or did he just blindly accept someone else's claims?
  2. Perhaps Mr. Martin read the papers, but did not understand them and decided to use them anyway?
  3. Or perhaps Mr. Martin read the papers, understood that they did not support his claim, but decided to use them anyway under the assumption that anyone following his claims would just blindly accept them?
Whatever the reason, these falsehoods are now exposed.

Note that Mr. Martin actually invokes CONTRADICTORY claims as his own evidence, invoking Machian models (the ultimate in relativity) simultaneously with 'aether' models (the ultimate in anti-relativity).  This is a popular tactic for those who have no evidence FOR their actual claims - they desperately throw out any claims they think might have any sticking power, and hope no one is the wiser.

Oh, and one entry in Mr. Martin's 'laundry list' invokes Halton Arp's discordant redshifts.  The final post I did on this topic from 2013,  summarizes the more detailed posts (and includes links to the details) at Discordant Redshifts: A Post-Mortem.

Update 2014-10-05: minor typo fixed.  Format problem fixed.