A world without WIMPs

There was talk over lunch and coffee of dark forces, dark photons, and dark neutrons.1 (emphasis added)

This is the extent of what is actually known about dark matter and any other entities from the dark sector of particle physics.  At a workshop where more than 100 physicists took over the University of Maryland, titled “US Cosmic Visions: New Ideas in Dark Matter,” attendees were encouraged to think more broadly to solve the vexing problem of the non-detection of dark matter particles in all experiments that have ever been tried for the last 40 years, at least.

They spoke of axions and other dark-matter candidates so lightweight that they would be detected as waves, and of particles so heavy that they would clump together and encounter Earth only occasionally as a vast invisible glob.1

Despite impressive sensitivity, dark-matter detection experiments such as Large Underground Xenon (detector array above) have not found any evidence of WIMPs. Credit: C. H. Faham/LUX

A recalibration for the dark-matter community

For decades physicists have been fixated on the putative WIMP, a Weakly Interacting Massive Particle, which allegedly has a tendency to intermittently mingle with ordinary matter via the weak force. WIMPs have been alleged to inhabit our part of the Galaxy but all experiments, like the Large Underground Xenon (LUX) detector array, have failed to find any trace of their existence.  Theorists developed ideas that WIMPs might be the lowest mass yet stable supersymmetric particle, called the neutralino but experimentalists with vast, exquisitely sensitive underground detectors such as the LUX array or using the powerful particle accelerator the Large Hadron Collider (LHC) found no such particles though they were meant to be constantly streaming stealthily through our planet. Now, Continue reading

Has the dark matter mystery been solved?

Unseen dark matter has been invoked several times to solve problems in astrophysics and cosmology. Historically the most significant problem has been the rotation curves of galaxies, particularly spiral galaxies. Using the Doppler Effect the speeds of the stars and gases in the disk regions of spiral galaxies can be measured. See Fig. 1.

By now hundreds of thousands of galaxies have been measured this way. What is observed is that the speeds of the stars, and the gases beyond where the stars are observed, are much greater than it would appear Newtonian physics allows for.

Figure 1: Edge on spiral galaxy and a rotation curve. Speeds of stars measured from the centre of a galaxy like this, as a function of distance in light-years. Using carbon-monoxide (CO) as a tracer gas the speeds of gas in the rotating disk can be also measured where there are no visible stars (labelled “No Stars”).

As a result it has been suggested that there is an invisible halo of cold non-interacting matter. This putative invisible halo has the needed gravitational effect on the stars and gases but it cannot be seen, hence it is called dark matter. Dark matter is alleged not to be normal atomic matter, made from protons and neutrons (which are known as baryons), but some sort of slowly moving (cold) exotic non-baryonic matter. Weakly Interacting Massive Particles (WIMPs) were suggested. Continue reading

Materialists believe in dark unseen life

Awhile ago I wrote about Lisa Randall, Professor of Science at Harvard University, a theoretical physicist and cosmologist, who proposed that the dinosaurs went extinct due to the actions of unseen dark matter.¹ There now appears again an article in the popular science magazine Nautilus with the title “Does Dark Matter Harbor Life? An invisible civilization could be living right under your nose.”² It would appear to be excerpted from Randall’s book Dark Matter and the Dinosaurs. In the article Randall asserts that we may, in fact, be kind of racist against dark matter, well, at least, we are biased towards ordinary matter, where, she claims, in fact, that dark matter is the stuff that holds galaxies together so it is really important stuff.

The common assumption is that dark matter is the “glue” that holds together galaxies and galaxy clusters, but resides only in amorphous clouds around them. But what if this assumption isn’t true and it is only our prejudice—and ignorance, which is after all the root of most prejudice—that led us down this potentially misleading path?

People in foreign relations make a mistake when they lump together another country’s cultures—assuming they don’t exhibit the diversity of societies that is evident in our own. Just as a good negotiator doesn’t assume the primacy of one sector of society over another when attempting to place the different cultures on equal footing, an unbiased scientist shouldn’t assume that dark matter isn’t as interesting as ordinary matter and necessarily lacks a diversity of matter similar to our own.² (emphasis added)

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Illustration by Jackie Ferrentino from Nautilus article, representing (I assume) dark life.

She goes on to promote the possibility of dark life, invisible creatures living on dark planets around dark stars in dark parts of galaxies. She suggests dark matter may be much more than just amorphous matter, but have a rich life with dark forces and therefore this implies a dark invisible universe of creatures we cannot detect. Sure sounds like good material for a sci-fi story.

Partially interacting dark matter certainly makes for fertile ground for speculation and encourages us to consider possibilities we otherwise might not have. Writers and moviegoers especially would find a scenario with such additional forces and consequences in the dark sector very enticing. They would probably even suggest dark life coexisting with our own. In this scenario, rather than the usual animated creatures fighting other animated creatures or on rare occasions cooperating with them, armies of dark matter creatures could march across the screen and monopolize all the action.

But this wouldn’t be too interesting to watch. The problem is that cinematographers would have trouble filming this dark life, which is of course invisible to us—and to them. Even if the dark creatures were there (and maybe they have been) we wouldn’t know. You have no idea how cute dark matter life could be—and you almost certainly never will.

Though it’s entertaining to speculate about the possibility of dark life, it’s a lot harder to figure out a way to observe it—or even detect its existence in more indirect ways. It’s challenging enough to find life made up of the same stuff we are, though extrasolar planet searches are under way and trying hard. But the evidence for dark life, should it exist, would be far more elusive even than the evidence for ordinary life in distant realms.

Dark objects or dark life could be very close—but if the dark stuff’s net mass isn’t very big, we wouldn’t have any way to know. Even with the most current technology, or any technology that we can currently imagine, only some very specialized possibilities might be testable. “Shadow life,” exciting as that would be, won’t necessarily have any visible consequences that we would notice, making it a tantalizing possibility but one immune to observations. In fairness, dark life is a tall order. Science-fiction writers may have no problem creating it, but the universe has a lot more obstacles to overcome. Out of all possible chemistries, it’s very unclear how many could sustain life, and even among those that could, we don’t know the type of environments that would be necessary.² (emphasis added)

Continue reading

Why look for a new theory of gravity if the big bang cosmology is correct?

Occasionally we read in the popular press, especially online, that someone has come up with a new theory of gravity. Why is that even necessary if the current theory describing the evolution of the universe is so correct?

The standard ΛCDM big bang cosmology is derived from an application of certain non-biblical boundary conditions to the physics of Einstein’s general relativity theory. But when that was applied to the universe as a whole, two problems developed for the secular model. One is the need to add in dark energy (or the cosmological constant, Λ (Lambda), to Einstein’s field equations) and the other is the need for a significant amount of invisible cold dark matter (CDM).

On the scale of galaxies and even clusters of galaxies Newtonian physics is used as it is the low gravity limit of general relativity. But without the addition of dark matter the resulting theory, using the known density of visible matter in galaxies (see Fig. 1) and clusters, does not match observations. But for more than 40 years now dark matter has been sought in various lab experiments with consistently negative results. This has developed into what is called the dark matter crisis.1

galaxy-rotation-curve

Figure 1: Typical rotation curve of a spiral galaxy: Speeds (V) in km/s units as a function of distance from the centre of the galaxy (R) in 1000 light-year (ly) units. The upper curve shows the speeds of the stars in disk region determined from their visible light and the gasses beyond that determined from radio frequency emissions. The lower curve shows what standard Newtonian physics predicts should be observed. The discrepancy is made up by positing the existence of invisible dark matter. Credit: Wikipedia

Occasionally a claim is made that a theorist has some inkling of what dark matter particles might be but the crisis remains.2 Dark matter particles have been sought without success in the Galaxy using very sensitive detectors deep in underground mines,3 or with the Large Hadron Collider (LHC) over 10 years of experiments looking for the lowest mass stable particle in a theorised class of as-yet-undiscovered supersymmetric particles.4

The observational data from thousands of galaxies together with the negative outcome of all the experiments searching for Dark Matter particles indicate that either something is wrong with the physics we use or that the expected dark matter is much more elusive than supposed, or, indeed, does not, in fact, exist—which gets us back to something being wrong with the physics. Continue reading

Dark matter caused the demise of the dinosaurs?

Dark matter has been invoked to solve many vexing problems in astrophysics and cosmology.1 Now it seems it has been invoked to solve the evolutionists’ problem of extinction of the dinosaurs.2

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Lisa Randall Credit: Wikipedia Public Domain

American theoretical physicist and cosmologist Dr Lisa Randall has developed a breakthrough five dimensional warped geometry theory. About two years ago she proposed a new hypothesis on dark matter which suggests the mysterious invisible substance that allegedly dominates the universe played a role in killing the dinosaurs.3 She even has written a book on it—Dark Matter and the Dinosaurs. In the book her new theory is summarised as follows.

[A]bout 66 million years ago, gravitational perturbations caused by a thin pancake-shaped disc of dark matter in the Milky Way galaxy dislodged icy comets in the Oort cloud at the very edge of the known solar system, resulting in the fiery meteoroid that eventually crash-landed in the Yucatan, leading to the mass extinction of more than 75 per cent of life on the planet in the process.3

Her radical new theory even posits mass extinctions every 35 million years or so.

“I am fully aware that it is speculative,” she says.4

Dinosaurs sell books and she has written a book that needs to be sold.

I’d call it a fairytale, except that might be insulting to fairies. To believe that it could even be true takes a lot of faith, which apparently describes Randall. She is reported to be unfazed by the panoply of uncertainties that her new theory incorporates.4 Continue reading

Why should baryons define where the dark matter is? Another dark matter problem

A research paper1 recently accepted for publication in Physical Review Letters titled “The radial acceleration relation in rotationally supported galaxies”2 highlights a discovery that is bad news for dark matter. It certainly does not strengthen the case for halo dark matter around spiral galaxies.

The research team, McGaugh et al, took data for 153 spiral disk galaxies from the Spitzer Photometry and Accurate Rotation Curves (SPARC) database that represents spiral galaxies of all types and morphologies, from very bright to very low surface brightness disks. It included representative spiral galaxies that would be assumed to contain a very high fraction of dark matter at very low orbital accelerations to those with very little dark matter at high orbital accelerations. These galaxies are all assumed to be rotationally supported, which means their disks are assumed to be gravitationally bound by the included matter inside any radial distance (R) from the centre of the galaxy. The speeds of the stars and gases (V) as a function of their measured radial distance (R) determines what is known as a rotation curve V(R). See Fig. 1.

In this paper the observed acceleration, gobs, at each radial distance R from the centre of the chosen galaxies, was calculated from the measured values of V(R) and R for each galaxy, totalling 2693 data points over the 153 galaxies. Also using infrared data the mass density was accurately measured at these same radial points, which permitted, via the Poisson equation, a direct calculation of the expected acceleration, gbar, due to the baryonic matter (protons and neutrons, i.e. normal matter) content within the same galaxies. No free fit parameters were used in these estimations, except a single fixed Mass-to-Light ratio of 0.5 was used across all galaxies.

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Figure 1: Examples of mass models and rotation curves for individual galaxies. The points with error bars in the upper panels are the observed rotation curves V (R). The errors represent both random errors and systematic uncertainty in the circular velocity due to asymmetry in the velocity field. Each baryonic component is represented: dotted lines for the gas, dashed lines for the stellar disk, and dash-dotted lines for the bulge, when present. The sum of these components is the baryonic mass model (solid line). The lower panels illustrate the run of gbar and gobs for each galaxy, with the dashed line being the line of unity. Note that higher accelerations occur at smaller radii. From left to right each line is replotted in gray to illustrate how progressively fainter galaxies probe progressively lower regimes of acceleration.

Assuming standard Newtonian (or Keplerian) physics the acceleration due to the baryonic matter, gbar, is all we should need to correctly calculate the rotation curve of any galaxy. See Fig. 1 (which reproduces their Fig. 2). Some representative rotation curves are shown by the upper-most black circles with error bars. Quite obviously the solid blue lines—the expect rotation velocities due to the observed baryonic matter—do not follow the observed rotation curves, but fall well below, in most galaxies. This is the reason halo dark matter is invoked. See Fig. 2. Continue reading

Now the expansion of the universe is not accelerating

In 2011 the Nobel Prize in Physics was awarded to three astronomers for their discovery, as part of two separate teams which published their results around 1998 that they claimed showed that the Universe is expanding at an accelerating rate. Also they claimed the existence of some sort of mysterious ‘dark energy’ that was driving the expansion at a faster and faster rate.

Hubble image of supernova remnant N 49 in the Large Magellanic Cloud. Credit: NASA and The Hubble Heritage Team (STScI/AURA)

Hubble image of supernova remnant N 49 in the Large Magellanic Cloud. Credit: NASA and The Hubble Heritage Team (STScI/AURA)

The interpretation of the 1998 data depended heavily on the big bang cosmological theory they applied and the assumption that it was the correct theory to describe the structure and time evolution of the Universe. It also depended heavily on the assumption that the type Ia supernova explosions that they used are reliable standard “light bulbs”, i.e. that those stellar explosions all were accurately chosen to have the same characteristic intrinsic absolute brightness.1 The latter, however, we now know is not the case.2

It has been shown that the stellar masses of the stars that result in the type Ia class of supernova are not so well-defined that they all fall within a narrow range as to give a clear standard in terms of the intrinsic brightness of the resulting explosions and hence the type Ia are not a uniform reference. Also as I have previously indicated circular reasoning was employed in the choice of the candidate supernova to be considered.2,3 The cosmology under test was used to choose the candidate Ia supernovae and then those chosen were used to test the same cosmology.

A new study, published in the Nature journal Scientific Reports, on a data set ten times larger than the original studies used (5 years ago) has been carried out.4

Now, a team of scientists led by Professor Subir Sarkar of Oxford University’s Department of Physics has cast doubt on this standard cosmological concept. Making use of a vastly increased data set – a catalogue of 740 Type Ia supernovae, more than ten times the original sample size – the researchers have found that the evidence for acceleration may be flimsier than previously thought, with the data being consistent with a constant rate of expansion. (emphasis added)

Continue reading