Wednesday, March 25, 2015

Absolute simultaneity and common sense

It's common sense that there is absolute simultaneity, whether directly so or because it's common sense that there is an objective present. It is sensible for philosophers to want to hold on to what is common sense. But here we should not be so quick. For consider some common sense claims:

  1. There is absolute simultaneity.
  2. If A and B are absolutely simultaneous and C and D happen t units of time after A and B respectively, then C and D are absolutely simultaneous.
  3. Properly functioning clocks correctly measure lengths of time.
  4. Clocks continue to properly function when moving, as long as they are not accelerated so quickly as to damage them.
But while (1)-(4) are all common sense, we have empirical data (assuming some uncontroversial claims of how to determine cases of absolute simultaneity for side-by-side events) that they are not all true, namely the data confirming the Twin Paradox.

Now when a number of common sense claims cannot all be held together, it is not responsible simply to say that one of them is common sense and therefore true. For the same thing could be said about the others. One would need to say something about how one's preferred claim is more commonsensical than the others, and that's a judgment that may well go beyond common sense.

I think most defenders of absolute simultaneity will reject (3) or (4). But if we look at how we actually acquire our concepts of durations of time by using clocks, watches and internal timers, it's plausible that we are committed to (3). And our practices of blithely using clocks even after coming to think that the earth is rapidly moving around the sun suggest (4).

I actually think that an interesting strategy for defending absolute simultaneity is to deny (2). This would lead to a view with absolute simultaneity but purely relative temporal durations.

That said, I am happy to deny (1).


Eugene Curry said...
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Eugene Curry said...

I think I would reject (4), and I don't think that doing so goes against common sense. We have mundane experiences all the time in which the proper functioning of mechanisms is frustrated by acceleration--even when the ill effects in view don't rise to the level of actual *damage* to the mechanism. Clocks that depend on the unwinding of coiled springs to keep time, for example, find the rate of their unwinding altered by the act of acceleration--the act of overcoming inertia itself serving partially to compress the spring. This takes place at even non-relativistically significant rates of acceleration. So if we have common experiences (and common sense built on those experiences) of acceleration interfering with the proper functioning of watches in even very mundane circumstances, I don't see how broadening that awareness to include relativistic interference predicated on acceleration involves violating that common-sense understanding. It would seem to represent an expansion, not a contradiction, of common sense

Alexander R Pruss said...

That's a good point. Note, though, that the amount of acceleration might be minuscule (though it would take longer to get up to near-light speed).


If you examine the consequences of there being "absolute motion" taking place within an "absolute 4 dimensional environment" known as Space-Time, these consequences lead to the creation of the very same bizarre outcomes that are described under the title of Special Relativity.

This examination also leads to the creation of all of the SR equations, meaning the Lorentz-Fitzgerald Length Contraction equation, the Time Dilation equation, the Velocity Addition equation, and the Lorentz Transformation equations.

Meanwhile however, Special Relativity itself can not lead you to the "absolute motion" that is taking place within the "absolute 4 dimensional environment" known as Space-Time. As a consequence, both are ignored or are often assumed to simply not exist.

This also applies to simultaneous events. You may witness absolute simultaneous events, but there is no in which you can verify if this is true or not.

I also discuss simultaneous events in my Youtube videos.