Tuesday, October 10, 2017

Missing Baryonic Matter Found

Using a careful analysis of the Planck data, scientists have found that the roughly 50% of all baryonic (i.e. ordinary non-dark) matter in the universe that was previously unobserved is located in filaments of interstellar gas between galaxies.


Maju said...

Not sure if related but I wanted to ask you a question, Andrew: what do you think of Erik Verlinde theory of gravity being an emerging property of space-time and this one as made up (sorta, not sure if I understand well) of quantum information, of entangled photons, whose entropy is what causes gravity somehow? Have you written something about this?

andrew said...

I have blogged it at least five times and conceptually it would be awesome if it worked. I was rooting for it for quite a while. Alas, after he proposed a couple versions of this this theory, it didn't fit the data according to comparisons done by two independent teams of investigators looking at two different sets of predictions of the theory.

This is a huge problem, because Verlinde's theory is so elegant that there is very little wiggle room to adjust the theory by adjusting multiple parameters. In Verlinde's theory, the already known rules of quantum mechanics already fix most of the key moving parts and the only wiggle room available is in the known distribution of matter and energy in the universe. But, the actual distribution and the predicted one necessary to make it fit what we know about how gravity behaves don't add up. The first comparison concluded that:

We find that (i) EG is consistent with the observed RAR only if we substantially decrease the fiducial stellar mass-to-light ratios; the resulting values are in tension with other astronomical estimates; (ii) EG predicts that the residuals around the RAR should correlate with radius; such residual correlation is not observed.

The other comparison concluded that:

We conclude that the formula leads to marginally acceptable fits with strikingly low best-fit distances, low stellar mass-to-light ratios, and a low Hubble constant. In particular, some unobserved wiggles are produced in rotation curves because of the dependence of the transition on the derivative of the Newtonian acceleration, leading, even in the most favorable case, to systematically less good fits than MOND. Then, applying the predicted transition from emergent gravity in a regime where it should be fully applicable, i.e. in spherical symmetry and outside of the bulk of matter, we show that the predictions for the secular advances of Solar System planets' perihelia are discrepant with the data by seven orders of magnitude, ruling out the present emergent gravity formalism with high confidence.

Very sad. ;( It was a great idea and it wasn't wildly off. But, not all great ideas work and we can compare the predictions to the reality with enough precision to confidently rule out this theory.

andrew said...

If you want to know what someone who isn't me has to say about the topic (but why would you?), you can read what Sabine has to say at: http://backreaction.blogspot.com/2016/12/can-dark-energy-and-dark-matter-emerge.html

Here analysis pre-dated the February 14, 2017 rebuttal papers, but even so, I am aware that she is more upbeat about the possibility of a fix the Verlinde's theory than I am.

Maju said...

Alright, Andrew. Thank you very much. I happened to stumble on his conferences recently and, even he's not the best communicator quite obviously, I still found appealing that he acknowledges that no evidence exists for particle "dark matter" and that its alleged structure is very much puzzling, so he (and surely others, I guess) are trying to approach the issue of "extra gravity" or "gravity anomalies at large scales" from a different, more strictly theoretical point of view.

Arguing for particle "dark matter" without any evidence seems to me almost like arguing for "God", i.e. it's like Sagan's "dragon in my garage" parable. There should be some other answer, even if it's not Verlinde's.

Thanks again.

andrew said...

The evidence for a gravitational force solution over particle dark matter is definitely shifting towards gravity as I have been recounting at this blog, study by study, as the parameter space of possible particle dark matter theories has shrunk to almost nothing. I currently think that Deur is closest to the mark.