I've spent three days now making a plot that would summarize the past 10 years of cosmic birefringence research Different datasets with widely different systematics (astrophysical + instrumental) favor a positive and non-zero cosmic birefringence angle! Excited to fill in more colors in the future!

In 2022, we were very excited to see 3.6sigma evidence of Cosmic Birefringence in Planck+WMAP. We've been waiting for confirmation from other experiments since, and now we are slowly getting it! New paper is finding 2.9sigma evidence in ACT DR6. This is getting serious! arxiv.org/abs/2509.13654

ACT's 2.5sigma cosmic birefringence measurement should not be viewed in isolation. Combining their measurement with previous WMAP+Planck result increases the significance to 4+ sigma (assuming Gaussian dist+independent measurements). Graph credit: E. Komatsu

Although #ACT DR6s headline is that LCDM is still king, they do find a 2.5 sigma of an unexplained polarization angle (aka cosmic birefringence)! I am amazed that people are not more excited by this! Their beta = 0.20 \pm 0.08 is very consistent with our Planck+WMAP results! arxiv.org/abs/2205.13962