Friday, April 22, 2011

4d/3d controversy in objects

There is a familiar controversy in the philosophy of time. It has to do with whether objects are 3 dimensional (3d) and "persists" through time or 4 dimensional (4d) spacetime "worms" (or as Ted Sider claims in his Four Dimensionalism, 4d stages). 3ders think that objects do not have temporal parts analogous to the object's spatial parts while 4ders think that the object at any time is just a part of the object at all times (its a segment or slice of the whole worm).

I realized that modern physics might say a thing or two about this. More specifically, quantum mechanics and especially quantum field theory. It could be that both the 3ders and the 4ders are right.

Consider particles in space. In classical physics such as relativity and Newtonian mechanics, objects have a definite position (the classic billiard ball analogy). In quantum mechanics, they do not; rather they have a "quantum superposition" or are "field quanta." They are neither specifically here nor there but their position is kind of spreading out in space. Quantum field theory has it that objects, even large objects, are mere properties of spacetime itself; just ripples or disturbances smeared in that spacetime manifold. Everything can be described by force differentials at any set of localized points in spacetime.

Objects are not only neither here nor there but neither now nor then. But particles do have definite positions once they are being measured or observed in some way. When the wave function collapses under observation and the scope of the scientists' equipment, they will have a definite positions.

I wonder if this can be used as an argument that in some sense, both the 3ders and the 4ders are right much as the corpuscular theory of light and the wave theory of light are both partially right even though they seemed contradictory when they were first proposed but quantum theory eventually resolved the issue in its familiar unforeseen way. Because objects are located in spacetime in quantum field theory, they are more like worms (or fuzzy worms, perhaps caterpillars, as they are smeared in that spacetime) as the 4der claims but may have specific spacetime locations once they are under the purview of observation and common discourse as the 3der claims.

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