A Contrafactual History of Modern Physics

An early Rangefinder from 1900.

This connects to the recent posts on the 2019 SI unit standard of second and meter.

Suppose the 2019 SI standard had been implemented already say in 1900. This means that from 1900 on length was measured in terms of travel time of light assuming a speed of light of exactly 299792458 meter per second. 

This is how a rangefinder of today works: Send a signal towards an object and measure the time for the reflected signal to come back, assuming a certain speed of light. This would have been possible in 1900. 

Using the SI standard a null result from the Michelson-Morley experiment is to be expected. Each observer "drags along an aether" linked to the observer and defines length from travel time of light under the assumption that light propagates with exactly 299792458 meter per second. 

With an expected MM null result using the SI standard, there would be no reason to invent the new physics of Einstein's Special Relativity SR, because it was motivated by the MM null result seeming to be  inexplicable using the meter sticks/measuring rods envisioned by Einstein. More precisely, what motivated Lorentz to introduce the Lorentz transformation in 1904 (first formulated by Voigt in 1887), was to explain the MM null result as an effect of space contraction in the direction of motion. Einstein picked up the Lorentz transformation in 1905, without reference to Lorentz or Voigt. 

Modern physics as a physics under a SI standard adopted in 1900, would thus be free of SR. Modern physics would thus consist of quantum mechanics added to Newton's mechanics and Maxwell's electromagnetics as a fully compatible combination. This would be a modern physics without the incompatibility of relativity theory and quantum mechanics, as a main trouble behind the present crisis of modern physics.