Sunday, October 26, 2014

News from Other Fronts

Since so many alternative cosmologies get discussed on this site, here's a good summary of how the current model came to dominate the field from Ethan Siegel at "Starts with a Bang": 
- How the Big Bang's alternatives died.
- 10 Things You Didn't Know About the Anthropic Principle

I've been busy preparing my own response to the Geocentrists' sad attempt at meeting the Lagrange Point Challenge, which I heard about from Geocentrism Debunked: Geocentric Physics: Is That All You've Got?

They also have another good article on Geocentrists' claims about the Cosmic Microwave Background: The CMB and Geocentrism"

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.