AOTD #1 – new physics on top of new physics

The article of the day is by Stacy McGaugh, an astronomer that works on both sides of a debate, namely that of (particle) dark matter versus modified gravity.

As sort of a companion to a recent article of his ( https://arxiv.org/abs/1808.02532 ) he wrote this wonderful blogpost:

https://tritonstation.wordpress.com/2018/08/09/the-next-cosmic-frontier-21cm-absorption-at-high-redshift/

It’s a lucid account of a bird’s eye view of cosmology, the history of the universe, the dark matter debate and the recent data by the EDGES experiment, all mixed together!

The EDGES experiment recorded data about the Hydrogen 21cm line from the cosmic dawn, that is (as I understand it) a portion of the electromagnetic spectrum from when the universe was 200-250 million years old.

The strength of the signal came out much stronger than expected. Interestingly it seems that you have a hard time explaining that with dark matter while he shows that if you assume a universe without dark matter you predict such a strong signal.

Furthermore, such a signal is unexpected in the ‘standard model’ of cosmology, LCDM. One of my favourite punchlines from the post is

“Many of these ideas also strike me as a form of magical thinking that stems from ΛCDM groupthink. After all, ΛCDM is so well established, any unexpected signal must be a sign of exciting new physics (on top of the new physics of dark matter and dark energy) rather than an underlying problem with ΛCDM itself”

Go read that article and have fun!

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