Other things not clearly acknowledged in relativity textbooks
ROGER ANDERTON
besides what has happened to one-way lightspeed, AI points out the following is not clearly acknowledged in relativity text books -
1. The Role of Convention in Simultaneity
Einstein's synchronization method using light signals assumes the speed of light is the same in both directions (one-way speed).
This cannot be empirically verified without already synchronized clocks—so it's a convention, not a measurement.
Many textbooks don't stress that simultaneity is defined by convention, not discovered by experiment.
🌬️ 2. Lorentz Ether Theory is Empirically Equivalent
Lorentz Ether Theory (LET) makes the same predictions as Special Relativity for all current experiments.
The distinction is philosophical: LET retains an absolute space/time framework, while SR redefines space and time.
Textbooks rarely discuss LET, or mention it only in passing as “historically obsolete,” despite its continued relevance to foundations.
🧮 3. Dependence on Coordinate Choice
Time dilation, length contraction, and relativity of simultaneity are coordinate-dependent effects.
They are not directly observable in an absolute sense but appear due to the way events are described in different frames.
Textbooks often present them as “real” effects without emphasizing that they depend on the observer's coordinate system.
🛰️ 4. Relativity and GPS: Subtle Interpretations
Textbooks use GPS as a successful application of relativity but often don’t mention:
GPS uses a preferred Earth-Centered Inertial (ECI) frame.
Synchronization and clock corrections are implemented in ways consistent with a global reference frame.
This hints at something akin to a practical “preferred frame,” which contradicts the spirit of full frame symmetry in SR.
⌛ 5. Time Dilation ≠ Clocks Running Slower per se
A moving clock “runs slow” relative to a specific observer—but in its own frame, it ticks normally.
Time dilation is reciprocal: each sees the other’s clock as slow.
Some textbooks give the impression that a moving clock just “slows down” in an absolute sense, which is misleading.
🔄 6. The Twin Paradox Often Glosses Over Asymmetry
The resolution often appeals to acceleration, curved worldlines, or spacetime diagrams, but:
It doesn’t always explain clearly why one twin ages less, given both experience the other as moving.
The reliance on switching inertial frames is not always thoroughly examined.
📉 7. Relativity May Be Incomplete or Approximate
General Relativity breaks down at singularities and is incompatible with quantum theory.
There is no definitive experimental proof that spacetime is curved in the ontological sense—it’s a model.
Some physicists explore alternatives (e.g., emergent gravity, ether-like models), but textbooks often present GR as the final word.
🧵 8. Historical Misrepresentations
Many texts simplify the history, e.g., portraying Michelson–Morley as “disproving” ether (it didn’t), or suggesting Einstein was unaware of Lorentz’s and Poincaré’s work (he likely was).
These simplifications create the false impression of a sudden clean break, rather than a more gradual evolution.
🧩 9. Conceptual Ambiguities Are Still Debated
Textbooks usually don't mention that philosophers of physics still debate:
What “space” and “time” really are.
Whether spacetime is physically real or just a useful model.
How causality and locality work in quantum+relativistic contexts.
🔍 10. Alternative Interpretations Are Underrepresented
Interpretations like:
Lorentz Ether Theory
Neo-Lorentzian interpretations
Process theory
Emergent spacetime
Shape dynamics
Preferred-frame quantum theories (e.g., Bohmian mechanics)
These are rarely discussed, even though they challenge the orthodoxy in subtle ways.