Version History and Errata

May 2023

• Use plainer language in a number of places.

April 2023

• In Part I, use the rel- prefix for physical quantities that are relative to a grid, not absolute. Part II does not use this convention.
• Add the Questions To Ask Of An Author section.
• Add the Aberration Preserves Angles section.
• Reference Newton instead of Galileo. Galileo believed in the natural circularity of motion of celestial objects. Many authors refer to Galilean relativity, but this seems inappropriate given that belief.
• Add a reference to Minkowski's 1908 article Space and Time, which is surprisingly modern.
• Add examples of the jargon used by various authors for the space-time interval.
• Add the Four Time Dimensions section.
• Add some informal Notes on Groups, outside of the main text.

March 2023

• Add the Introduction section.
• Add the The Problem Of Language section.
• Add the Standard Configuration Of Two Grids section.
• Stop using the Zoomer and Home Base jargon. Replace with boosted grid and unboosted grid, respectively.
• Various small edits.

October 2022

• Replace the word parochial with specific to or relative.
• Use the term wristwatch-time whenever possible.
• Use the term pancake effect whenever possible. The term length contraction seems inadequate to describe all of the geometrical distortions. The term pancake effect seems to have better connotations.
• Replace the unconventional term photon vector with the conventional term wave vector.
• Note that s² (as the square of something) is an artifact of trying to match spatial metrics.
• Stop referring to the concept of relativistic mass as an outright error. That's going too far. It shouldn't be so strongly worded.
• Add a section called What does relative mean? Add a table showing relative/invariant items.
• Emphasize that the pancake effect flattens out angles as well.
• Suggest that it's useful to think of the Doppler effect and aberration as prototype effects, to better understand time dilation and the pancake effect, and to put them all in the same category of phenomena.
• Mention the radar station model for measurements in a frame of reference.
• Mention that grids aren't rigid objects. SR disallows strictly rigid bodies, because they require instantaneous interactions.
• Mention that the boosted versions of the events (1,0) and (0,1) are just the columns of the boost matrix.
• State that the clocks in a grid are identical, and the meter sticks are identical.
• Remove the part about using your hands to infer the direction of "event flow".
• For a boost, use G and G' as standard names of the grids.
• Note the distinction between the active and passive ways of looking at a boost transformations.
• Clarify the remarks on aberration.
• Add a small section on light-slice and time-slice.
• Change capital gamma Γ to small gamma γ, to match the conventional name. This was an issue because the letter renders poorly when a sans-serif font is used. A custom CSS class is now used to render that letter in an improved manner.
• Add the coefficients of the boost transformation to the list of dimensionless items.
• Re-do all formulas with a new latex image generator. (Use resolution 150, scale 100%.)
• Left as is: there's an angle θ in both the aberration formula and the Doppler effect formula. At present, the definitions of θ in those two formulas don't match. One formula uses the complement of the other, 180 - θ. I'm going to keep that as is, because in each case I'm using the angle that seems most natural to me.
• Link to the github repository for this site.
• Explain variations in formulas coming from variations in how an angle θ is defined: θ versus (180 - θ).
• Add more remarks on the relativity of simultaneity.
• Add remark on using a flash of light for synchronizing clocks.
• Add the matrix form of the boost transformation, as an aside.
• Add a chart of how SR relates to to the other parts of physics.
• Remove the section on Dilation Versus Contraction. It had an error for the pancake effect, and is better illustrated elsewhere.
• Use a space-time diagram to explain why the pancake effect decreases the size.
• Add graphs of the aberration formula.
• Improve the description of the wave vector for photons.
• Various small edits, meant to increase the clarity of the text.

May 22, 2020

May 15, 2020

May 8, 2017

February 27, 2014

January 28, 2014

January 25, 2014