Questioning Relativity 12: Simultaneity

· physics, theory of relativity

Modern physics, both quantum mechanics and relativity theory, is obsessed with a narcissistic observer perspective in which the World only goes around when observed by human observers.

The upshot of special relativity was a perceived difficulty for different observers moving with a speed close to the speed of light with respect to each other, to agree on simultaneity of events separated in space, that is, whether two events at different locations in space take place at the same time.

Observers tied to coordinate systems moving very quickly with respect to each other, would be reached in different ways by light signals from events separated in space and would then get different perceptions of simultaneity.

This is illustrated in the above picture typical of presentations of special relativity with the observer on ground and the observer in the bus being reached by light signals from two lightening events in different ways, who may not both say that the events happened at the same time.

This is one of Einstein’s famous “Gedankenexperiments” or “thought experiments” supposedly forcing all of us to change our concepts of space and time into a new mixture of space-time prescribed by relativity theory.

But the “thought experiment” has no connection to reality whatsoever, since a bus moving at 4/5 of the speed of light is pure fiction. It is unthinkable that human observers can be moving with respect to each other with a speed comparable to the speed of light. The “thought experiment” is thus similar to the “thought experiments” of the scholastics about e.g. the number of angels which can dance on the head of a pin.

Upon this criticism a physicist would argue that electrons can be accelerated to nearly the speed of light and and so the perception of simultaneity by electrons would meet the difficulties illustrated in the above thought experiment. But electrons do not care about simultaneity, they just speed around without any such perceptions, at least as far as we know.

The very concept of simultaneity is non-physical and only a construction by humans invented to coordinate human observations according to Coordinated Universal Time UTC used in e.g. GPS.

But physics is not controlled by UTC, physical events take place locally in space and time and there is no need nor any means for electrons to coordinate there actions in time.

The non-physical nature of simultaneity is one aspect of the non-physical nature of relativity theory.

5 Comments

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  1. David Philip

    Do you differentiate between “event simultaneity” and “observer simultaneity”? The GPS system effectively creates “event simultaneity” and has some real practical usefulness in enabling accurate navigation and positioning by one-way psuedo-range measurements using synchronised clocks.

    I am not convinced that “observer simultaneity” has any real usefulness as demonstrated by the continuing dominance of Newton’s theories and the very limited take up of Einstein’s Theories which are a mathematical aberration and quite unreal to the science of physics.

  2. claesjohnson

    Physics does not care about simultaneity, since events happen when they happen and when two particles meet they do it at the same time. The notion of simultaneity is thus either artificial/non-physical or trivial/physical. GPS measures distance by time lag but GPS is man-made artificial. We seem to agree.

    • David Philip

      Yes but I wondered if “event simultaneity” was an absolute concept rather than “observer simultaneity” which is a relative concept. The key problem as I see it with Einstein’s Theories is the confused ideas of “time” which seem to be assigned quite unreal properties. How would a true physicist define time? Can time really be linked with space or is this an artificial illusion a mathematical numerical artifact? If I try an picture a man sitting on the top of a high mountain and another nearby in a deep valley is time really different at the two locations or is it really just gravity that is different? Clocks behave differently but time does not.

  3. claesjohnson

    I agree, time cannot be mixed with space, and clock rate cannot change by inertial motion. If it does it is not a clock.

  4. SuperNova

    This might help your confusion.

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