In a Bell test experiment, a source produces a pair of particles, one is sent to one location, and the other is sent to another location. A measurement of particle spin/polarization is performed at a specific angle at each location.

The experimental fact of violation of Bell's inequality has been explained by the mysterious concept of quantum entanglement so far.

Let's assume that the source is located at the origin of Cartesian coordinate system. In some experimental settings, each of emitted paired particles is detected at the same time. In this case, a detection of a particle can never affect the other detection. So, in this context, entanglement is suspected to be an illusion, whether emitted paired particles are massless or massive.

Considering photon entanglement, the above suspicion is surely reinforced.

- Photon entanglement postulates two-photon system, whose quantum wave, if actually present, is to swell at twice the speed of light, and is to metamorphose instantaneously.

- No or, at most, negligible interaction is possible between photons.

- No restriction is imposed on superposition of quantum waves of photons, which are bosons.

Then, how can photon entanglement be possible without invisible hand of God?

It may be a better guess that spin/polarization directions of paired particles are to be determined when they are produced, and are to be biased in accordance with the experimental settings. In the following, a hypothesis is presented on mechanism of bias generation.

The key is the state of zero-point oscillations. In the vacuum space, zero-point oscillations of all wave-number vectors with possible spin/polarization directions take place in each quantum field. In the field of laser engineering, it is well-known that a zero-point oscillation in photon field can induce spontaneous emission of a photon.

Assumption (1)

In the settings of Bell test experiments, zero-point oscillations of other than the specific spin/polarization directions are assumed to be suppressed significantly.

For example, consider a deflection plate (polarizer) for photons. For oscillations of the specific polarization direction, it is equivalent to a transparent glass. Conversely, for oscillations of other than the specific polarization direction, it is equivalent to an opaque glass and is assumed to suppress the oscillations.

Assumption (2a)

A particle pair emission is assumed to be induced by a zero-point oscillation in a similar manner as in the case of stimulated emission of a photon.

Assumption (2b)

No spontaneous emission of a particle pair (as well as that of a particle) is assumed to be possible without being induced by a zero-point oscillation.

Assumption (2b) is considered to be quite feasible, because, in the field of laser engineering, it seems to be commonly acknowledged that this assumption is correct for spontaneous emission of a particle of photon.

Considering what nature an emitted photon has in stimulated emission, violation of Bell's inequality can be explained reasonably.

The above assumptions are, however, not satisfactory since Bell test experiments have been performed in which experimental settings are changed randomly after a photon-pair emission, and which, none the less, allege violation of the inequality.

Aktas et al., Phys. Rev. Lett. 114, 220404 (2015), arXiv:1504.08332

Handsteiner et al., Phys. Rev. Lett. 118, 060401 (2017), arXiv:1611.06985

So, the following assumption is added.

Assumption (3)

Transmittance of a polarizer is assumed to be significantly dependent on the state of zero-point oscillations around it.

If experimental settings are changed after a photon-pair emission, when a photon reaches a polarizer, the state of zero-point oscillations around it is different from that in case where experimental settings have been the same as those after the change since the beginning. So, because of assumption (3), violation of Bell's inequality can be considered to be possible without entanglement.

Though the above argument may be felt so expedient, it is considered to be far less inconceivable and less weird than the concept of photon entanglement.