Not always is a dynamical property produced in an experiment


Half-silvered mirror (beam splitter)

Not alway is a dynamical property prepared in an experiments, even if it looks so at first sight. This can be seen in the following experiment:
Experiment: Light is incident on a beam splitter (a half-silvered mirror) with an angle of 45 degrees (Fig.). The light is partly transmitted and partly reflected. Transmitted and reflected beam have the same intensity.

Does the transmitted part of the light possess a certain property that leads to being transmitted? Has the beam splitter prepared light with the property "is being transmitted"? The question can be answered using the general scheme of preparation and test. To this end, a second beam splitter is set in the way of the transmitted beam. This second beam splitter performs the test measurement. If the light in the transmitted beam has the property "is being transmitted" it must show in the test measurement. Thus at the second beam splitter, all the light would pass through, nothing would be reflected.

Experiment: The transmitted beam is sent through a second beam splitter (Fig.). Again, it is split up into a transmitted and a reflected part.

The result of the experiment shows that the transmitted beam did not possess the property "is being transmitted". A beam splitter does not perform such a preparation. In fact, it is not possible at all to prepare a beam of light in such a way that it totally passes through a half-silvered mirror.

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