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Our future, our universe, and other weighty topics

Sunday, August 13, 2017

Shocking CMB Anomalies Contradict Guth's “Empirical Success” Claims

Earlier this year, Scientific American published a blistering critique of the theory of cosmic inflation originally advanced by Alan Guth (not to be confused with the more general Big Bang theory). The theory of cosmic inflation (which arose in 1980) is a kind of baroque add-on to the Big Bang theory that arose decades earlier. The Big Bang theory asserts the very general idea that the universe began suddenly in a state of incredible density, perhaps the infinite density called a singularity; and that the universe has been expanding ever since. The cosmic inflation theory makes a claim about less than one second of this expansion – that during only the first second of the expansion, there was a special super-fast type of expansion called exponential expansion.

The article in Scientific American criticizing the theory of cosmic inflation was by three scientists (Anna Ijjas, Paul J. Steinhardt, Abraham Loeb), one a Harvard professor and another a Princeton professor. It was filled with very good points that should be read by anyone curious about the claims of the cosmic inflation theory. But now the article has been half-censored, for Scientific American has put the article behind a paywall. But don't worry, you can still read the article on a Harvard web site here. Or you can go to this site by the article's authors, summarizing their critique of the cosmic inflation theory.

The Scientific American article by the three scientists provoked an unusual response. The main supporters of cosmic inflation theory (including Alan Guth and Andrei Linde) along with about 30 other cosmologists have published a rebuttal article called “A Cosmic Controversy.” It is kind of an authoritarian power play, designed to impress the reader by listing authorship by some of the top names in cosmology. The list of authors is very impressive, but there are some factually inaccurate claims in the article.

The article claims that the cosmic inflation theory has been empirically successful. Referring to variations of the theory called slow-roll models, Guth claims that “many models in this class continue to be very successful empirically,” and later refers to “the dramatic observational successes of inflation.” These claims are not accurate.

The cosmic inflation theory makes two main claims: (1) that there is or was something called an inflaton field; (2) that the universe underwent a period of exponential expansion during part of its first second. Various versions of the cosmic inflation theory have also claimed that there exist or once existed other universes (sometimes called “bubble universes”), or that something called grand unification theories (GUT theories) are in some sense correct. We have not a single observation verifying any of these claims.

The claim that the universe underwent an exponential expansion during part of its first second is one that can never be confirmed, because of physical limitations (the recombination era issue) that will always prevent us from looking back to the universe’s first second with our telescopes. No evidence has been produced for this so-called inflaton field, and it has not been detected by the Large Hadron Collider. No evidence has been produced that there is any universe other than our own, and there are very strong reasons for thinking that no such evidence ever could be produced (anything that we might observe would always be an observation of our universe, not some other universe). No evidence has turned up for the idea of grand unification theories (GUTs), which have been one of the more embarrassing failures of modern physics.

Given this situation, in which not a single one of its key claims has been backed up by observations, it is pure baloney for Guth and his allies to be calling their theory an empirical success. Their claim is based on the very shaky idea that various versions of cosmic inflation theory have made some predictions about a few things that have been consistent with observed reality. In my post here I give several paragraphs explaining why this type of claiming success based on imprecise general predictions is fallacious. Among the reasons I gave is that there are very many versions of the cosmic inflation theory (each predicting a wide range of things, as each version allows a range of input parameters); so even if the theory is bunk we should not be surprised if some of the resulting predictions matched reality.

Let us suppose that some theory claimed that green monsters from Alpha Centauri have landed on our planet and invested in the bond market; consequently next year the bond market will go up and the stock market will go down. If next year the bond market did go up and the stock market did go down, it would still not at all be accurate to claim that this weird theory was empirically successful. It would only be correct to say that if the green monsters were actually observed. Similarly, no theory of cosmic inflation can be called empirically successful until one of its core central claims (unique to the theory) has been observed. No such thing has happened.

theory predictions

There is another huge reason why the cosmic inflation theory cannot be called empirically successful. The reason is that the theory is inconsistent with observations of anomalies in the cosmic background radiation (also called the cosmic microwave background, or CMB). 

Believed to date from early in the universe, the cosmic background radiation is a type of radiation pervading all of space. The cosmic inflation theory predicts that this radiation should be very smooth and isotropic (just as the theory that your friend spent 20 minutes stirring his bowl of pancake batter predicts that the pancake batter should be very smooth, and without lumps).

The first satellite to observe in detail the cosmic background radiation was the WMAP satellite launched in 2001. This satellite detected some very strange anomalies in the cosmic background radiation, anomalies that came as a surprise to scientists. One was an anomaly called the cosmic cold spot. Another was an anomaly that is technically known as the hemispherical variance asymmetry. Then there is an anomaly called the quadrupole-octopole alignment. There are nine other anomalies in the cosmic background radiation that are summarized in a table in this scientific paper. The table is below:

The p-values here give us a rough idea of the probability of finding such anomalies if standard ideas of cosmology (including cosmic inflation and dark matter) are correct. This all presents a huge problem for cosmic inflation theorists such as Guth. These are all things that we should not expect to be finding in the cosmic background radiation if the cosmic inflation theory is correct.

Years after the WMAP satellite was launched, scientists launched another satellite called the Planck satellite. It was predicted that the troubling anomalies in the cosmic background radiation would go away after the more powerful Planck satellite did its work. But that did not happen. The Planck team reported the same anomalies. The table above is from a paper entitled, “CMB Anomalies After Planck.” When the Planck team reported its results on these anomalies, they buried their findings in a dense technical document, as if they were trying to make it as hard as possible for anyone to discover the truth about this matter. But the “CMB Anomalies After Planck” paper gives us some of the straight talk that the Planck paper lacked.

Referring to the hemispherical asymmetry it reported, the paper says, “An inflationary theory could, in principle, accommodate models that produce hemispherical asymmetry, but such a model would have to be multi-field and involve, for example, a large-amplitude superhorizon perturbation to the curvaton field.” Which is a fancy say of saying the simpler versions of the cosmic inflation theory are not compatible with this CMB anomaly – only more baroque and implausible versions are compatible with it. Requiring a multi-field cosmic inflation theory (imagining not just one but more than one undiscovered fundamental field involved in primordial cosmic inflation) is kind of like it being that your theory of crop circles requires not just UFO's but also cooperation by Bigfoot creatures.  In a similar vein, this paper states that the most popular version of the cosmic inflation theory (called slow-roll inflation) is not compatible with the CMB anomalies:

Measurements of CMB temperature fluctuations by the Wilkinson Microwave Anisotropy Probe (WMAP) indicate that the fluctuation amplitude in one half of the sky differs from the amplitude in the other half. We show that such an asymmetry cannot be generated during single-field slow-roll inflation without violating constraints to the homogeneity of the Universe.

But this “slow-roll” version of the inflation theory is the very one that Guth called “very successful empirically” in his Scientific American article. Apparently it is no such thing.

A 2010 paper states the following about the anomalies in the cosmic background radiation:

While not all of these alignments are statistically independent, their combined statistical significance is certainly greater than their individual significances. For example, given their mutual alignments, the conditional probability of the four normals lying so close to the ecliptic, is less than 2%; the combined probability of the four normals being both so aligned with each other and so close to the ecliptic is less than 0.4% × 2% = 0.008%. These are therefore clearly surprising, highly statistically significant anomalies — unexpected in the standard inflationary theory and the accepted cosmological model.

This is a probability of less than 1 in 10,000 under the assumptions of the cosmic inflation theory and the accepted cosmological model. That's hardly what we would find if the cosmic inflation theory really was “empirically successful” as Guth claims.

Using the phrase “in tension” to mean “conflict with,” Stephon H. Alexander (a professor of physics at Brown University) writes the following about these anomalies in the cosmic background radiation, and their relation to the cosmic inflation theory:

During the epoch that the CMB anisotropies were formed, they too are supposed to, on average look the same in every direction. The theory of cosmic inflation generically predicts this feature. This means that if one divides the sky into two arbitrary hemispheres, we should see the same statistical features of the anisotropies in both hemispheres. However, both WMAP and Planck see a difference in the amount of anisotropies in different hemispheres in the sky. This feature is in tension [with] one of the most powerful attributes of inflation, whose rapid expansion of space-time smooths out any large-scale directional preference, while democratically sprinkling the space-time fabric with the same amount of ripples in every direction. With some decorative tweaking, it is possible to modify inflation to account for the anomaly, but this seems to be at odds with what inflation was invented for-to make the early universe smooth enough and see the tiny anisotropies that later become galaxies. One might think that this would be a great opportunity for alternative theories of the early universe, such as bouncing/cyclic cosmologies to rise to the occasion and explain the anomalies, but so far, there is no compelling alternative.

By suggesting that it may be time for “alternative theories of the early universe,” Alexander is clearly suggesting these CMB anomalies are in conflict with the cosmic inflation theory.

Contrary to the claims of Guth and his clique, the cosmic inflation theory is not empirically successful. It has enjoyed another type of success: sociological success. The history of modern science culture shows repeatedly that a theory that is not empirically successful may become sociologically successful and become popular due to a bandwagon effect and groupthink. Once this snowball effect gets rolling, the theory may become a speech custom of an insular academic subculture, and a little piece of tribal folklore has been born. The adherents of the theory will in effect place gold medals around their own necks, congratulating themselves on what they think is their brilliant explanatory triumph. But such gold medals may be very undeserved.

But why did I use the term “shocking” in this blog post's title to refer to these anomalies in the cosmic background radiation? There's one CMB anomaly that is quite shocking. It seems that something called the quadrupole – octopole alignment aligns with the plane of our solar system. Since the cosmic background radiation has often been described as something that looks the same everywhere in the universe, we should not expect to find any such correlation involving our solar system. One paper states the following:

Particularly puzzling are the alignments with solar system features. CMB anisotropy should clearly not be correlated with our local habitat. While the observed correlations seem to hint that there is contamination by a foreground or perhaps by the scanning strategy of the telescope, closer inspection reveals that there is no obvious way to explain the observed correlations. 

Physicist Lawrence Krauss has this to say about this topic:

 But when you look at CMB map, you also see that the structure that is observed, is in fact, in a weird way, correlated with the plane of the earth around the sun. Is this Copernicus coming back to haunt us? That's crazy. We're looking out at the whole universe. There's no way there should be a correlation of structure with our motion of the earth around the sun — the plane of the earth around the sun — the ecliptic. That would say we are truly the center of the universe. The new results are either telling us that all of science is wrong and we're the center of the universe, or maybe the data is simply incorrect, or maybe it's telling us there's something weird about the microwave background results and that maybe, maybe there's something wrong with our theories on the larger scales. 

There is a small band of cosmology-following geocentrists who believe that the Earth is the center of the universe, and that this quadrupole – octopole alignment supports their claim. But we know the earth revolves around the sun. A less outrageous claim would be that the solar system may be somehow in some kind of privileged position, and that the quadrupole – octopole alignment supports this claim. It would be premature to make even this less outrageous claim based on this limited evidence. But it is interesting that this quadrupole – octopole alignment may suggest one of the key assumptions of modern cosmology (the Copernican principle, that there is nothing special about the position of the solar system) may be wrong. 

Postscript: For more information on this topic, do a Google search for "lopsided universe," "axis of evil (cosmology)", "CMB cold spot," and "CMB anomalies." In a previous post I  had mentioned the cold spot as a thorn in the side of cosmic inflation theory, but from the table above it is clear that the hemispherical variance asymmetry is a ten times bigger problem for that theory. 

Postscript: Theoretical physicist Sabine Hossenfelder has a post entitled "Is the Inflationary Universe a Scientific Theory? Not Anymore."  After belittling some of the reasons given for the theory, she states this:

It is this abundance of useless models that gives rise to the criticism that inflation is not a scientific theory. And on that account, the criticism is justified. It’s not good scientific practice. It is a practice that, to say it bluntly, has become commonplace because it results in papers, not because it advances science.