Today’s article comes courtesy of Sabine Hossenfelder. Sabine is an assistant professor for high energy physics at Nordita, Stockholm. She writes a blog called Backreaction and tweets as @skdh.

Dark matter is one of the most elusive and puzzling entities in our Universe today. We have plenty of indirect evidence for it, but one of the the “holy grail” questions in physics right now is to figure out exactly what its particle nature truly is.

Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

Image credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI).

It ought to exist in a halo around our galaxy, and if it interacts with normal matter at all — even weakly — it should leave a signal that changes slightly over the course of the year. So what to make of the DAMA results, which has seen exactly that for more than a decade now?

Images credit: DAMA collaboration, from Eur.Phys.J. C56 (2008) 333-355 (top) and DAMA/LIBRA collaboration from Eur.Phys.J. C67 (2010) 39-49 (bottom). The annual modulation is real and robust, but its cause is unknown.

Images credit: DAMA collaboration, from Eur.Phys.J. C56 (2008) 333-355 (top) and DAMA/LIBRA collaboration from Eur.Phys.J. C67 (2010) 39-49 (bottom). The annual modulation is real and robust, but its cause is unknown.

Believe it or not, we may have finally explained these results without the need for dark matter at all! Go read the whole thing.

Comments

  1. #1 John Duffield
    July 18, 2014

    This raised a flag: “Few physicists today doubt that dark matter exists, and the vast majority presume it to be some type of particle…” Yes, presume. And whilst Sabine mentioned modifying gravity, she missed out bog-standard general relativity. In the Foundation of the General Theory of Relativity Einstein said “the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy”. Space has its vacuum energy, this energy has a mass equivalence and a gravitational effect when inhomogeneous, but it isn’t comprised of particles. See http://arxiv.org/abs/1209.0563 and note that space expands between the galaxies but not within. Conservation of energy applies, so you’re left with inhomogeneous vacuum, which is what curved spacetime is. See http://iopscience.iop.org/0256-307X/25/5/014 and Einstein’s Leyden Address where he described a gravitational field as inhomogeneous space. Also note that “the FLRW metric starts with the assumption of homogeneity and isotropy of space”. That’s an assumption that spatial energy is uniform which leads to the particle presumption for dark matter.

  2. #2 Sinisa Lazarek
    July 18, 2014

    @ John

    you’re becoming pretty boring with your views of gravity is, what relativity is and what relativity in curved spacetime is. You’re like those bible preachers, there’s only one book and one sentence that you keep posting and on and on… And it’s getting old quick. Not to mention is very wrong and you completely miss a point.

  3. #3 David Brown
    July 21, 2014

    “Dark matter … It ought to exist in a halo around our galaxy.” More precisely, it ought to exist in a halo around our galaxy if MOND is wrong.
    Lambda-VDM Model: a Testable Modification of Lambda-CDM
    http://www.astro.umd.edu/~ssm/mond/moti_bullet.html The Bullet Cluster (Milgrom)
    http://www.scilogs.com/the-dark-matter-crisis/2013/11/22/pavel-kroupa-on-the-vast-polar-structures-around-the-milky-way-and-andromeda/

  4. #4 Robert Hudgins
    Lake Linganore, New Market MD (Science for Humanity Trust)
    July 22, 2014

    Concerning dark energy’s relation to expansion of the Universe. Assuming the Holographic Principle and the validity of the Bekenstein Bound for information/entropy, then expansion of the Universe must occur as the free energy available after the Big Bang converts to information/entropy (heat).

  5. #5 nemo
    Padova, Italy
    August 14, 2014
  6. #6 Francis
    September 11, 2014