What makes this so interesting is that from Atama Cosmology Telescope (ACT) collaboration, a new set of analyses has arrived (see this). From ACT alone, the significance rules out zero rotation angle (β=0°) at 2.9σ, and by jointly combining WMAP, Planck, and ACT data together, a new paper accepted in Physical Review D in August of 2026 claims to see β=0.277° +/- 0.057°, which is non-zero at 4.8σ significance.
Ordinary birefringence in condensed matter occurs because orthogonal linear polarizations travel with different velocities. This causes phase difference between polarizations visible as a rotation of the polarization plane.
Cosmic birefringence occurs because circular polarizations travel with different velocities.
- The reason why for circular polarizations is that initial polarizations are linear with a fixed direction caused by the density perturbations (E-mode) with quadrupole character.
E-mode polarization is generated by density perturbations such as sound waves, which are scalars. Quadrupole (4 poles) is realized as two pairs of sources of radiation in orthogonal directions and photons coming from these sources experience Thomson scattering from charged particles such as electrons. The scattering is dominantly in right angles. If the other source is more intense (hotter) the polarization (as statistical parameter) is linear and along the axis connecting the more intense source pair.
- Also B-mode polarization is in principle possible and would be created by gravitational waves interacting with matter and inducing to the energy momentum tensor non-diagonal components. This would cause B-modes for which the distribution of scattering angles are characterized by spherical harmonics Y2+/-2 rather than Y2+/-1,0 as for E-modes. Y2+/-2 has characteristic sin(2φ) or cos(2φ) dependence implying cross-shaped polarization pattern with 4 angle maxima.
- Cosmic birefringence would emerge in the following way. The original linear polarization can be expressed as the sum of circular polarizations. These travel with different velocities and this causes a phase shift. When the polarizations combine in a telescope, the resulting linear polarization is rotated by some angle by interference. Quantum effect in cosmic scales is in question and would require a revolution in cosmology and entire quantum physics.
- Quantum coherence is required in arbitrarily long, perhaps even cosmological length scales. The hierarchy of Planck constants, which includes gravitational Planck constant, makes this possible. So called massless extremals (MEs) as geometric counterparts of massless radiation realize precisely targeted propagation of photons along MEs as dark photons. Darkness means a very large value of gravitational Planck constant making possible very long quantum coherence length. The MEs can be also associated with the monopole flux tubes arriving from distant sources.
- Also a polarization dependent light-velocityd ue to interactions with environment is required.
The possibility of warping is one of the basic differences between GRT and TGD. It makes possible reduced light velocity and the polarization dependence of the light velocity.
- Warped space-time surfaces are flat like Minkowski space but the light-velocity is reduced because 3-space can be said to rotate along CP2 geodesic. This notion emerged already during the first years of TGD but are only during last year (see this and this)). I have started to realize how deep its implications are. Warping effect occurs also for the fermion lines associated with the 3-D light-like parton orbits containing them.
- Fermion line is a light-like geodesic of H = M4×CP2 and also of space-time surface but its M4 projection is time-like geodesic of M4 and characterized by mass. Therefore warping gives rise to a space-time description of particle massivation.
- Also Allais anomaly and the variation of gravitational constant could be understood (see this). In condensed matter physics refraction and reflection of light would involve change of the reduced light-velocity at the boundary between differently warped space-time regions.
- Space-time surfaces are small deformations of these warped gravitational vacua (for warped gravitational vacua the gtt component of the induced metric is constant deviating from unity and defines constant gravitational potential as analog of constant electric potential). Warping can be generalized to the level of Hamilton-Jacobi structure (see this).
- The MEs assigned to the photons arriving from a distant source are different from opposite circular polarizations because ME allows only single polarization which can be local. The linear polarized ME can be decomposed to a superposition of MEs with circular polarizations and the photons associated with these MEs propagate with different velocity and cause the rotation of the polarization plane observed in the measurement in which linear polarization is the outcome.
- Cosmic birefrience also implies parity violation in cosmic scales. The hierarchy of effective Planck constants allows the weak parity violation to occur in arbitray long scales.
TGD is strongly non-linear and linear superposition for the induced gauge potentials fails in the general case. Massless extremals (MEs) are however an exception.
- MEs are characterized by two parameters: light-like wave vector k satisfying k· k=0 and polarization vector ε orthogonal to it satisfying k· ε=0. For the simplest MEs k and ε are constant. The inner product u=k·m of k with the vector m defined by linear Minkowski coordinates appears in the plane phase factor exp(ik·m).
- This picture generalizes. One can assume a local light-like vector k(m) expressible as a gradient k(m)= ∇ u and thus defining tangents for coordinate curves of u. k· m→ u= ∫ m k(m)dm. Also ε can be made local polarization vector ε (m) as tangent vector to coordinate curves orthogonal to the local plane M2 defined by light-like vector u.
In the same way, the coordinate line parallel to ε (m) corresponds to v= ∫ m ε(m)dm. This would make possible local variants of polarization and light-like vector and make possible curvilinear photons.
This picture was one motivation for introducing the notion of Hamilton-Jacobi (H-J)structure (see this) as a generalization of complex structure to M4. H-J structure involves a integrable distribution of hypercomplex planes defined by the local light-like vector and its dual and orthogonal complex planes defined by a complex local polarization vector and its conjugate.
- For MEs, the superposition for waves propagating along ME in the same direction holds true and is only restricted by the condition that the amplitudes are small so that the CP2 characterizing the induced fields are in the allowed range (say angle variable cos(θ) for geodesic sphere of CP2. This restriction can be removed by using complex coordinates for CP2. These coordinates are always possible and especially natural for CP2 if holography = holomorphy hypothesis is satisfied (see this and this). Also waves with the same fixed local linear polarization can be superposed.
- What about circular (elliptic) polarizations, which are superpositions of two linear polarizations which are not parallel? Are these possible?
- They could correspond to superpositions of solutions corresponding to two different polarization vectors ε1(w) and ε2(w) giving rise to complex polarization vectors ∫ mε1(w)dw and ∫ mε2(w)dw. Can these polarization vectors have phase difference?
- The second way to obtain circular polarization is as a rotating linear polarization. Could one assume that the local polarization ε depends on both w and u: ε ε(w,u)?
- The linear polarization can be expressed for ME with standard light velocity as a superposition of two circular polarizations with phase difference. The interaction with the environment must distinguish between these polarizations so that they must correspond to different MEs with different warping and reduced light-velocity.
- This interaction must induce the entanglement of the circular polarization states with the environment. Entanglement must induce the warping of MEs and reduce the maximal signal velocity by giving to the photon a very small mass (see this). p-Adic thermodynamics indeed predicts this possibility (see this and this. The opposite circular polarizations would propagate with slightly different velocities so that the MEs must be different.
- Gravitational Planck constant characterizes a pair M,m of masses. The associated Compton length is proportional to the Schwartschild radius of the larger mass M associated with the pair of masses. For the Milky Way it is .47 ly and much shorter than the path travelled by photon in the case of cosmic birefringence. Therefore it seems that entanglement cannot be preserved during the entire trip. Quantum measurements during the travel can destroy it and interaction with the environment can transform it to superposition of circular polarizations re-entangling with the environment.
- Zero energy ontology (ZEO) is forced by the slight non-determinism of the classical time evolution in TGD. ZEO solves the basic paradox of quantum measurement theory. In ZEO one can distinguish between two kinds of state function reductions (SFRs). The "small" ones (SSFRs) generalize the Zeno effect so that repeated quantum measurements do not leave the state invariant anymore. SSFRs are crucial for TGD inspired theory of consciousness and cognition and, somewhat surprisingly, also for the TGD description of fundamental interaction. The "big" SFRs (BSFRs) correspond to ordinary quantum measurements and they change the arrow of time. Either SSFRs or pairs of BSFRs changing the arrow of time temporarily could occur during the travel.
For a summary of earlier postings see Latest progress in TGD.
For the lists of articles (most of them published in journals founded by Huping Hu) and books about TGD see this.