Friday, June 30, 2017

Away Note

I’ll be traveling the next two weeks. First to Cambridge to celebrate Stephen Hawking’s 75th birthday (which was in January), then in Trieste for a conference on “Probing the spacetime fabric: from concepts to phenomenology.”  Rant coming up later today, but after that please prepare for a slow time.


  1. Isn't it possible that Universe has a high but uniform curvature but it is not directly measurable to observers inside of it?

    Can people of Flatland really measure the curvature of the sphere surface they were living on?

    Even though sum of the internal angles of a triangle on a spherical surface, would be greater than 180 degrees, are we sure that flatland people could really measure and find that?

  2. A new paper purports to rule out all forms of collisionless dark matter in a general fashion.

    Taken together with exclusions for self-interacting dark matter, MACHOs, WIMPs, Cold Dark Matter (as opposed to Warm Dark Matter) generally, and strict limitations from accelerators and annihilation searches on Warm Dark Matter parameter space (which pretty much requires it to have no EM, strong or weak interactions), this strongly favors modified gravity solutions as the only viable solutions.

    This echoes another recent paper discounting baryon effects as a way to save Cold Dark Matter models.

  3. What about primordial black holes? A recent paper by Carr and others shows that not all mass ranges are ruled out.


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