Observerspace and special relativity

From Relativity
Revision as of 14:52, 4 July 2016 by Eric Baird (Talk | contribs) (1 revision imported)

(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff)
Jump to: navigation, search
OBSERVERSPACE

Observerspace and special relativity

link=MEDIA:Grid_Doppler_05.jpg


Einstein's special theory has many of the trappings of an observerspace theory – it wears "observerspace clothes" in that it appears to make the logic what observers must experience in a given situation central to its derivations. However, it departs from a strict observerspace approach in its definition of what constitutes an "observer" or an "observation".

Social background

At around the turn of the 19th/20th Century, scientists were using "logical positivist" arguments to try to distinguish between "proper" scientific models and other models that might appear, in, say, psychology, where a theory's adherents might believe that the evidence supported their system, but where there were no clear unambiguous evidence or verification procedures in place to allow people to test whether this was the result of wishful thinking, or whether there was a real connection between beliefs and reality. The resulting enthusiasm for strict scientific testability led in some areas to an almost fetishistic obsession with operational and experimental procedural definition, and some of this enthusiasm can be seen in Einstein's 1905 paper. If one was presenting a paper that could be criticised for being overly philosophical, one way of silencing critics would be to overload the theory with operational definitions of concepts.

Observerspace and non-observerspace aspects of the 1905 theory

Einstein legitimises his 1905 reworking of 1904 Lorentzian electrodynamics by applying what seems to be the "logical positivist" approach – rather than impose assumptions about what length and distance "really" are, he specifies a way of defining lengths and distances using lightbeams, and goes on to extend the method to create definitions of more abstract concepts such as distant simultaneity. Operating in flat spacetime, with complicating gravitational and acceleration effects assumed to be absent or small enough to be ignored, special relativity also assumes that no information is concealed from the observer, who is then in possession of "the full set of cards" regarding the physics that then plays out.


The "instrumentational" and "operational" definitions of special relativity mean that the theory is appears logically positivist – for instance, it rejects the interpretation of the SR/LET math as being due to an assumed aether, because the presence of such an aether cannot be directly measured, and is not required for deriving the mathematical relationships.

However, the 1905 paper is not quite as positivist as it appears, as it replaces the assumption of an absolute aether (whose state of motion then cannot be identified), with the core assumption that spacetime must be flat.*

In Einstein's special theory, observers are not "perfect observers" - they do not report what they see, but what they interpret to be happening based on the assumption of global c – in more general terms we would tend not to refer to these entities as true observers, as their reported lengths and times are not the uninterpreted lengths and times that they see or photograph, but are the calculated results of processes that involve measuring space with lightbeams whose assumed behaviour seems to be designed to allow Einstein to end up with the 1904 Lorentz equations (Lorentz's undistorted aether becomes Einstein's flat spacetime).

Under special relativity, we certainly end up with an unambiguous set of predictions for what observers do see (which some contemporary physicists then got wrong*), but these predictions of visible behaviour result from calculations based on the relativity of measurement (in flat spacetime). The theory was not derived from the need for the principle of relativity to apply to what we see, but to what we measure, with the measurement process then necessarily involving additional interpretations and assumptions.

More "fundamentalist" observerspace approaches

A "purist" observerspace critique of special relativity would tend to seize on the 1905 derivation's use of interpreted length (rather than apparent or photographable length) as a fundamental property. The concept of "observed" length under special relativity is not an observerspace property, in that it doesn't relate to the "raw" data collected by a recorder. A more extreme observerspace approach would reject "calibrated length" as a property, as it cannot be directly experienced - a purist observer cannot judge the "real" length of a ruler without either the use of instantaneous signalling or by being in two places at once, neither of which are obviously options. However relativising seen behaviour would probably focus instead on the observers' measurements of frequency, which only require the observer to be in one place at two times, and count the number of incoming ticks per second, as judged by their own personal sense of time. Visible length is also an unambiguous observerspace property judged by the content of a photograph taken at an observer's location.


While special relativity produces unambiguous predictions for what can be seen, the relativity of visible physics is not the basis of SR's derivations - applying the PoR to more literal observerspace descriptions tends to produce a different type of relativistic solution.