the Atemporal Universe - Resolving the Problem of Time [in physics]

I just started a post on this topic in the Physics and Chemistry section because I hadn't gotten a response here. Not sure if they need to be merged or what is the policy on that? I will answer your post here anyway.

Black Swan wrote: »

I am familiar with this thought experiment. Although not in depth. It's a grand analogy.

I'll outline it below, as it forms part of the argument, so hopefully it will be clear afterward.

Black Swan wrote: »

I also like this discussion by you. Can you expand upon it, and in terms that most of our philosophy readers may understand, who may not be as versed in physics?

Hopefully the below is clear enough, but anything that isn't can be fleshed out.

The Galilean principle of relativity can be expressed as there is no experiment that can determine whether an object is in motion or at rest - Gallileo's Ship illustrates this point. We can extend this princile to the notions of simultaneity and synchronisation, in Einsteinian Relativity and state that there is no experiment which can determine the simultaneity of events and, by extension, the synchronisation of two spatially separated clocks. In extending this principle, we will see that the notion of Relativity of Simultaneity - events which are simultaneous in one reference frame are not simultaneous in a relatively moving frame - is unjustified/unjustifiable.

In his 1905 paper Einstein effectively states that the simultaneity of events in the "stationary" frame must be assumed - this follows from the fact that his synchronisation convention is established "by definition".
If we consider the clock synchronisation thought experiment:

The observer in the "stationary" frame is located at the mid-point between 2 clocks. A co-located emitter sends a light pulse to each clock (to start them ticking). The light pulses travel in opposite directions to each clock, start the clock ticking and are reflected to the observer at the mid-point, where they arrive simultaneously. The observer concludes that their clocks are synchronised because they know the speed of light and the distance to the clocks, and because the light pulses returned simultaneously.

While the observer in the "stationary" frame is performing this clock synchronisation, they observe a relatively moving observer perform the exact same synchronisation process. They are also located midway between 2 clocks. The light pulses are sent to each clock and reflected; crucially, the "stationary" observer sees the light pulses hit each clock not-simultaneously, get reflected, and arrive back to the "moving" observer simultaneously. The "moving" observer concludes that their clocks are synchronised. The "stationary" observer has observed that the clocks are not synchronised.

Here, in the original thought experiment, we are provided with a clear case of why the assumption of synchronisation/simultaneity is unjustified. The oberver in the "stationary" frame observes the "moving" observer perform the exact same synchronisation procedure, with the light pulses simultaneously returning to the mid-point, yet, the clocks are not synchronised. This should, at the very least, cause the 'stationary" observer to question their [i/]assumpion[/i] that their clocks are in fact synchronised.

Imagine, on top of this, both observers are wearing body cameras and record footage of their counterparts synchronisation attempts. They then send the footage to each other - by light signal. Each observer will be presented with observational evidence that their clocks are not synchronised.

The reasonable conclusion in this scenario would be to accept that each was mistaken in their assumption about the simultaneity of the clock synchronisation events, give the observational evidence to the contrary.

Constant Speed of Light
The tendency might be to refer back to Einstein's 2nd postulate about the constancy of the speed of light, as justification for maintaing the assumption of simultaneity/synchronisation - in spite of the observational evidence; but here too we can offer a more parsimonious interpretation.

Light Clock Thought Experiment
For this, we need only consider the thought experiment involving each observer carrying a single light clock - a photon bouncing between mirrors. The "stationary" assumes thata their clock is ticking normally, while they observe the "moving" clock as ticking slowly, as the photon travels a longer, diagonal path between the 2 mirrors.

Again, imagine each exchanging bodycam footage and being presented with evidence that their own clock is also ticking slowly. It makes sense to both observers. They only ever observe the vertical velocity component of the photon. This would be true whether they are "stationary" or ""moving" and whether the photon traced the longer diagonal path, or not.

What about the speed of light? If they measure the speed of light in the light clock, will they not measure it as having a slower speed, if they can only detect the vertical velocity component?

To answer this imagine that each tries to measure the speed of light. How will they perform the measurement only by using their trusty light clock to count the time. The issue should be apparent. Any attempt to measure the speed of light will always yield the same value because their clock will be biased by the same factor.

Conclusion
The above highlights the circular reasoning in the Einsteinian interpretation. It is the assumption of the simultaneity of events in the "stationary" frame which leads to the conclusion of the Reativity of Simultaneity. As has been illustrated, the simultaneity of events in the "stationary" frame is an assumption; an unjustified (dare I say unjustifiable) assumption, which leads to the conclusion of RoS, thereby assuming the conclusion.

Introducing bodycam footage leaves with the assumption of simultaneity in "stationary" frames vs observational evidence to the contrary. This represents a class of evidence that cannot be explained under the Einsteinian interpretation.

Consequences
This restores absolute time and simultaneity to relativity, aligning the conceptualisations of time in QM and GR.

Absolute time is indistinguishable from a timeless universe. Clocks provide units of comparison - they don't measure a background phenomenon called "time". "Time" then is a system of measurement, much like the metric system, neither of which are fundamental or emergent. In this way, time cannot be said to form part of a background structure. This removes the issue of background dependence in Quantum Mechanics which is one of the issues in unifying QM and GR.