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Missing matter of the universe FOUND? Rob Sheldon says, hold on a minute…


The hype detector got a good workout with this one:

After an intergalactic search lasting more than two decades, an Australian-led team of scientists say they have finally found the universe’s “missing matter”, solving a mystery that has long stumped astronomers…

Astronomers had been looking at the universe using all sorts of different forms of light — from radio waves through to x-rays and visible light. None revealed the missing matter.

That was until they started to measure fast radio bursts — brief flashes of intense energy found racing across the universe — and discovered the missing matter hiding in the cold dispersed gas between galaxies…

Repeating the process with six different FRBs coming from different parts of the universe, the team was able to figure out how — and where — the missing matter was. The results were published today in the top scientific journal Nature.

Michael Slezak and Penny Timms, “Astronomers find ‘missing matter’, solving decades-long mystery of outer space” at ABC Australia

Paper. (paywall)

Our physics color commentator Rob Sheldon suggests a timeout:

Well, like most astronomy press releases in the past decade, it is 3/4 hype, and 1/4 data, and it has nothing to do with dark matter. Since many people never read beyond the headline, the title is written to be as provocative as possible without outright lying.

The story starts in 2007 with the discovery of a narrow “whistle” in the archived Parkes Radio Telescope data, only a few milliseconds wide, that is, if our ears could hear radio waves.

In fact it would have been discarded as noise, except the grad student looking at the data had stacked the channels above each other, and watched how this narrow pulse went sliding down in frequency as it got later in time—like the back half of a “wolf whistle,” or an Irish slide-whistle.

At first it was thought to be contamination, like the 2010 “perytons” traced to the microwave oven at Parkes Observatory in Australia. But several more were found in archived data, and then in 2012, one repeated, and was linked to a distant galaxy.

They even got a name, “Fast Radio Bursts.” Theorists still had no idea what they were, with Harvard astronomer Abraham Loeb even publishing a paper to the effect that it was an alien microwave propulsion system.

Loeb likes to burnish his reputation as astronomy’s resident jester.

The Australian Parkes telescope, like the US Greenbank radio telescope, is a single steerable dish, which doesn’t have the resolution of the multiple radio telescopes like the VLBA in New Mexico. There didn’t seem to be a future for these dinosaurs, so the Fast Radio Burst was like fresh blood, or at least, fresh funding. In 2012 a new site in the central desert was dedicated for a “square kilometer array” like the VLBA called ASKAP. And U of Sidney was funded to upgrade an abandoned radio telescope MOST, and make it an FRB antenna just for this search, renamed UTMOST.

Australia really is perfect for radio telescopes, with miles of nothing but empty skies.

But by now it was a Gold Rush for radio telescopes, with new results coming in almost monthly. Just a month ago in April, CalTech astronomers made a claim that an FRB had been detected inside our own galaxy.

That would help the search for the source, but as of yet, no one knows what it is.

So that is the background for this paper on FRB studies. Without being able to crack the mystery of what an FRB is, the authors have decided to tackle the more mundane question, what does it do? FRB’s are thought to be created in unknown stellar upheavals, with highly polarized light that then passes through billions of lightyears on its way to us. This long journey permits the “shorter” or higher-pitched waves to travel faster than the longer, lower-pitched waves, which is why it sounds like a slide whistle when it arrives. And the reason the waves “disperse,” travelling different speeds, is that the ion and electron “plasma” that inhabits interstellar or intergalactic space, acts as a viscous “molasses” for radio waves.

So by locating the galaxy it came from, knowing how far away it is, and then calculating how far apart the high/low frequencies are, we get an estimate of the density or depth of the plasma between here and there. Then if you say, “Well everywhere in the universe has this plasma density,” then you can add it all up and weigh it to find out how much of the Big Bang was due to stars, and how much was due to plasma.

Now when people had done these calculations in the past, they knew how much matter “stuff” they had to put into the Big Bang simulation to get the right “Bang,” but they never actually saw more than 25% of that amount in the universe. (Mind you, this is ordinary matter, the stuff cosmologists call “baryonic matter,” not the mysterious “dark matter” you’ve heard so much about, which by definition, is non-baryonic.)

Well, when they finished their calculations, they got another 25% of the baryonic “stuff,” and were ready to call the press corps. For new investments like ASKAP, it is important that they get in the news early and often to justify their expense, and this is why the press release is both ambiguous and hyperbolic.

Is the hype justified?

Well, I would have to say not. Plasma is important, but it is by no means the only form of matter. Both dust and neutral hydrogen gas fill galaxies and to some extent, inter-galactic voids, and neither of these components can be measured with FRB dispersion. Further, the jump from 25% to 50% is big, but it still doesn’t account for the other half of the missing baryons.

First, we don’t know what a FRB really is. That means it could have been emitted by a giant slide whistle in a distant galaxy, (which is what Abraham Loeb is suggesting), so most of the dispersion was there from the very beginning. If so, then the entire calculation is wrong, and much less plasma exists between here and there. Most of the time, when we can’t solve a puzzle but desperately want to get something useful out of the data, we apply assumptions that are often later found to be wrong.

This paper relies on two or three unjustified assumptions: (1) FRBs start life as an instantaneous pulse over all wavelengths; (2) plasma is the most common form of matter in intergalactic space; and (3) The Big Bang model accurately predicts the baryonic density.

And second, I’ve mentioned before how the Hubble tension (discrepant H0 numbers) are causing people to revisit the BB model. There’s another half-dozen BB problems that have never been solved either, including 7Li abundances, D/H ratios, CMBR smoothness, early galactic formation, dark matter halos, Pop III halo stars, etc. So it is pretty clear that the Big Bang model is going to get a major overhaul in the near future, and who knows whether this 25% baryonic matter will turn into 75% or 5%, so hyping it as “solving the missing matter” is a bit premature.

But the unresolved problem is this: What process makes an FRB, and whether it is born with or without dispersion. That will be the judge of whether this paper is worthless or redeemable. And even Abraham Loeb doesn’t know the answer to that.

Rob Sheldon is the author of Genesis: The Long Ascent and The Long Ascent, Volume II

This whole cosmology thing is so confusing at this point... Definitely the real deal is in biology research these days... where discoveries are increasingly being made in multi-level control issues within the biological systems. Lots of complex functionally specified information-processing scenarios popping up all over the map. Regulatory issues galore. What do we get from cosmology-related literature today? Just confusing reports: A year ago the 13.8 billion year universe is corrected to 12.5 billion years in an article. Then recently another article corrects it to 11.4 billion years. That's just 17% difference. New measures to test modified gravity cosmologies
The observed accelerated expansion of the Universe may be explained by dark energy or the breakdown of general relativity (GR) on cosmological scales.
A measurement of the Hubble constant from angular diameter distances to two gravitational lenses
Science  13 Sep 2019: Vol. 365, Issue 6458, pp. 1134-1138 DOI: 10.1126/science.aat7371 The local expansion rate of the Universe is parametrized by the Hubble constant, H0, the ratio between recession velocity and distance. Different techniques lead to inconsistent estimates of H0.
ResearchGate 10 citations   The universe may be billions of years younger than we thought
New calculations point to an age of 11.4 billion years rather than the generally accepted number of 13.7 billion years.
Study finds the universe might be 2 billion years younger
The universe is looking younger every day, it seems. New calculations suggest the universe could be a couple billion years younger than scientists now estimate and even younger than suggested by two other calculations published this year that trimmed hundreds of millions of years from the age of the cosmos. The huge swings in scientists’ estimates — even this new calculation could be off by billions of years — reflect different approaches to the tricky problem of figuring the universe’s real age.
How fast is the universe expanding? The mystery endures
Scientists have known for decades that the universe is expanding, but research in the past few years has shaken up calculations on the speed of growth—raising tricky questions about theories of the cosmos.
An expanding controversy (2019)
One of the most fundamental and controversial measurements in cosmology, Hubble's constant (H0), informs scientists about how rapidly the Universe is expanding. The debate about the value of H0 has heated up recently as increasingly precise measurements from different techniques are converging on different values for H0. This discrepancy either means that the H0 measurements have systematic errors larger than astrophysicists can explain, or it reveals something profound about the physics underlying our universe. On page 1134 of this issue, Jee et al. (1) present a new way to measure H0, by combining information from strong gravitational lensing and the motion of stars within the lens galaxy, to calibrate supernova luminosities.
Universe is Not Expanding After All, Controversial Study Suggests (2014) Really?   :) Let's see what's going on: the above Pop-Sci article is a review of the following paper: UV surface brightness of galaxies from the local Universe to z ~ 5 which is cited by: A framework for the next generation of stationary cosmological models (PDF 2020) OLV
Hi Luke, Glad to see a real Aussie commenting on this post! Apologies for mispellings, its all Mycrosoft's fault--they didn't put a wiggly red line under it ;) And no disrespect for Australian radio astronomy, it's a testimony to inventiveness and pluck. As for not being deceptive, it depends on who reads the presser title. Ask your liberal arts friends to read the title and then tell you what they think the paper is about. Chances are over 50% that they use the word "dark matter" in their answer. Like I said, press releases today are as close to deceptive as possible to gain viral status. Here's another test for you, ask your nerdy non-astronomy friends if they think missing baryonic matter in the universe should be called "dark matter" or not. No excuses, just do it. Yeah, that was a trick question--the answer is a resounding Yes!! Why? Because Astronomers named it, not cosmologists, and no astronomer has ever ruled out dark baryonic matter. Which brings us to the main reason for our little disagreement. You trust the Big Bang models. I don't. You operate with "plausibility" as in "dispersion plausibly decreases toward zero". But the very word is charged with interpretation, like the BB models. Unless we know what an FRB is (and I think Loeb is on my side here), plausibility is a relatively meaningless word that equates to "scientific consensus" or suchlike weasel words. Why are alien microwave propulsion dispersions NOT plausible? And this is where we all say one thing in private and another in public. What makes Loeb unusual is he will say whatever he likes. The rest of us worry about tenure and proposal funding too much. Okay, the point about #2, is that if interstellar space were filled with, oh let's say, salty comets, then the dispersion would not be due to low density plasma, and the calculation would be entirely wrong. Saying that dispersion "must be due to plasma" is an assumption that comes out of your favorite BB model, so plugging it back into the model might be consistent, but it is definitely circular. I can think of 2 or 3 more things that generate dispersion, so I find this to be a question worth asking, rather than an assumption needing no explanation. Finally #3. Free parameters. Odd that you insist that baryonic density is a BB free parameter. I've got drawer-full of papers from PLANCK saying that it is a parameter-free model. (Again, ask your liberal arts friends to explain the difference between a free parameter and parameter-free.) This defense of BB is sounding like the defense of Darwinism--convergence is evolution, divergence is evolution, stasis is evolution! If baryonic density is a free parameter, then why does this paper know what proportion the plasma is contributing to the baryonic density? But really, all that is beside the point, you can't nail jello to the wall, and the BB model is bowl of jello right now. Why not make the title "FRB observations overturn the BB"--it would be just as eye-catching and even more accurate. -indefatigably yours, Robert Sheldon
1. The amount of "slide whistle" (dispersion measure - DM) from FRBs plausibly decreases toward zero with decreasing redshift, supporting the hypothesis that FRB's have no intrinsic DM. It's not certain, but it is hardly an "unjustified assumption". 2. There no assumption that "plasma is the most common form of matter in intergalactic space". This method measures the amount to plasma that is there. That's the whole point. 3. There is no assumption that "The Big Bang model accurately predicts the baryonic density." The Big Bang model leaves the baryonic density as a free parameter. This is part of an internal consistency check on the model - it neither confirms nor disconfirms it. There is nothing at all deceptive about the article. The second sentence says that it is about "ordinary matter", not dark matter. It is not remotely inappropriate to call matter that is missing, "missing matter". Also, it's spelled "Sydney". MOST was never abandoned - it was upgraded, because it continues to do solid scientific work. The dedication of the scientists and engineers who maintain and improve MOST on a tight budget is frankly heroic. lukebarnes

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