Read Cosmological Conundrums: A Conversation with Justin Khoury by Howard Burton Free Online
Book Title: Cosmological Conundrums: A Conversation with Justin Khoury|
The author of the book: Howard Burton
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Edition: Ideas Roadshow
Date of issue: June 9th 2015
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Format files: PDF
The size of the: 38.28 MB
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I actually read this in conjunction with Justin Khoury's MasterClass on the WorldScienceU website.
It's a remarkable and surprising idea that dark matter may form a superfluid in galaxies. This was proposed as a sort of unification of two opposing ideas about the nature of dark matter:
1. Dark matter is composed of an as-yet-unknown kind of particle.
2. Dark matter doesn't exist. Rather, Newton's laws and general relativity must be modified at the scale of galaxies. This is called Modified Newtonian Dynamics (MOND).
The problem is that MOND works perfectly at the scale of galaxies but fails at the scale of galaxy clusters, whereas the converse is true for the hypothesis that DM is composed of some kind of particle.
Khoury's hypothesis tries to unify these two perspectives by postulating that at the scale of galaxies, DM forms a superfluid, giving rise to MOND, whereas at the scale of galaxy clusters, such a superfluid doesn't form, which is why we don't see MOND at these scales.
To test this theory, we must verify the predictions it makes. For one, it predicts that certain kinds of dark matter vortices must be seen inside galaxies, arising due to the superfluid nature of DM in these regions. But these vortices are extremely small (on the order of millimeters), so detecting them is a huge challenge.
I peronally think this idea, though beautiful, is highly speculative. There are stronger reasons to believe DM is composed of WIMPs instead. But WIMPs (or axions for that matter) don't satisfactorily explain the existence of MOND or how the Tully-Fisher relation arises.
Only time and continued research will settle the debate. It's clear though that the answer will be far from simple.
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