[Paper Review] Search for anisotropic light propagation as a function of laser beam alignment relative to the Earth's velocity vector

C. E. Navia, C. R. A. Augusto+3 more|arXiv (Cornell University)|Aug 10, 2006

Experimental and Theoretical Physics Studies6 citations

TL;DR

This study investigates anisotropic light propagation using a laser diffraction setup with segmented photodiodes to measure sub-micron spot positions. It finds a 18% deviation from Special Relativity's prediction of isotropy, yielding a parameter $ a = -0.4106 \pm 0.0225 $, suggesting a preferred frame tied to the cosmic microwave background rest frame.

ABSTRACT

A laser diffraction experiment was conducted to study light propagation in air. The experiment is easy to reproduce and it is based on simple optical principles. Two optical sensors (segmented photo-diodes) are used for measuring the position of diffracted light spots with a precision better than $0.1 μm$. The goal is to look for signals of anisotropic light propagation as function of the laser beam alignment to the Earth's motion (solar barycenter motion) obtained by COBE. Two raster search techniques have been used. First, a fixed laser beam in the laboratory frame that scans due to Earth's rotation. Second, an active rotation of the laser beam on a turntable system. The results obtained with both methods show that the course of the light rays are affected by the motion of the Earth, and a predominant quantity of first order with a $Δc/c=-β(1+2a)\cos θ$ signature with $a=-0.4106\pm 0.0225$ describes well the experimental results. This result differs in a amount of 18% from the Special Relativity Theory prediction and that supplies the value of $a=-1/2$ (isotropy).

Motivation & Objective

• To test for anisotropic light propagation as a function of laser beam alignment relative to Earth’s velocity vector relative to the CMBR.
• To investigate potential deviations from Lorentz invariance and Special Relativity by measuring one-way light speed variations.
• To explore the existence of a preferred inertial frame, possibly linked to the cosmic microwave background rest frame.
• To provide a reproducible, high-precision optical experiment using segmented photodiodes to detect minute angular shifts in diffracted light spots.
• To compare experimental results with test theories of relativity, particularly Mansouri-Sexl and Lorentz-Poincaré frameworks.

Proposed method

• Employed a laser diffraction setup with a transmission grating to produce diffracted light spots on two segmented photodiodes.
• Used high-precision segmented photodiodes to measure spot positions with sub-0.1 μm resolution.
• Conducted two scanning techniques: (1) fixed laser beam scanning via Earth's rotation, and (2) active beam rotation on a turntable.
• Analyzed data using a model predicting one-way light speed anisotropy: $ c(\theta) = c - v(1 + 2a)\cos\theta $, where $ \theta $ is the angle relative to Earth's velocity vector.
• Fitted experimental data to extract the parameter $ a $, comparing it to the SRT prediction of $ a = -0.5 $.
• Used COBE-derived Earth velocity vector (relative to CMBR) as the reference direction for alignment.

Experimental results

Research questions

• RQ1 Does the one-way speed of light exhibit anisotropy as a function of the laser beam's orientation relative to Earth's motion through the CMBR rest frame?
• RQ2 Can experimental evidence for a preferred inertial frame be detected using a simple optical diffraction setup with high-resolution position sensing?
• RQ3 To what extent do the experimental results deviate from the isotropy predicted by Special Relativity?
• RQ4 How do the results compare with the Mansouri-Sexl test theory of relativity and the Lorentz-Poincaré framework?
• RQ5 Is the observed anisotropy consistent with the CMBR dipole direction, suggesting a cosmologically preferred frame?

Key findings

• The experiment detected a significant anisotropy in light propagation, with a measured parameter $ a = -0.4106 \pm 0.0225 $, differing from the Special Relativity prediction of $ a = -0.5 $ by 18%.
• The anisotropy signature follows the form $ \Delta c/c = -\beta(1 + 2a)\cos\theta $, indicating a directional dependence on the beam's alignment relative to Earth's velocity vector.
• The results were consistent across two independent scanning methods: Earth's rotation and active beam rotation, reducing systematic drift errors.
• The data strongly support a preferred frame of reference, with the dipole direction of the CMBR serving as the reference, implying a cosmologically defined rest frame.
• The observed deviation from isotropy is incompatible with standard Special Relativity but aligns with certain extended or alternative theories of relativity that allow for anisotropic light speed.
• The experiment demonstrates that high-precision optical measurements using segmented photodiodes can detect minute directional effects in light propagation, even at the sub-micron level.