In the February 2017 issue of Scientific American, 32, in an article entitled POP goes the universe, authors Ann Iijas, Paul J. Steinhardt and Abraham Loeb (ISL) write a summary of a more detailed paper they wrote, describing problems that they see in the generally accepted paradigm of physics called Inflation. While this article is interesting in its own right, what is even more interesting to me is that the article in a general readership magazine on science provoked a response letter to Scientific American cosigned by 33 of some of the most prominent physicists in particle physics and cosmology.
The authors of POP provide cogent arguments against the standard inflation models based on the latest data (at that time) from Planck (2013). As well they point out logical problems in the basic concept of inflation that have been with the theory from the outset.
They point to an alternative theory that they have apparently espoused involving a bounce rather than a Big Bang with Inflation. It is beyond the scope of a single blog to go into much detail on either approach, but I found the controversy they generated and the response worth looking at and discussing.
(ISL) have written a more in-depth scientific paper than the Scientific American paper which was challenged by several of the “group of 33” in separate academic papers. In a paper entitled, Inflationary schism after Planck2013, (arxiv.org: 1402.6980v2), (ISL) give even more detail for their arguments that the inflation paradigm is in trouble. In particular they give some very concise comparisons of the various problems in tabular form which makes it very easy to follow their arguments and compare them to contrary points. In this paper (ISL) focus on a paper by Guth, Kaiser and Nomura (GKN) Inflationary paradigm after Planck2013,
(arxiv.org: 1312.7619) which was written in response to their criticisms of the current inflation paradigm. After all this dust up the authors (ISL) remain committed to their stance and the group of 33 apparently are not swayed from their reaction.
The Standard Model of Cosmology, as noted in earlier blogs, has come to be called the
/\CDM model and has for decades now, assumed as a foundation, that the Universe we inhabit started with a Big Bang (details to be worked out) followed by a period of inflation, with the original inflation concept and model usually attributed to Guth, one of the group of 33. What (ISL) point out is that the original simple models of inflation have been ruled out by the data – a vast array of data that has accumulated over the years and usually summarized in the Physics literature by a variety of acronyms – Planck2013, more recently Planck2015, WMAP, etc.
(ISL) further state that the current inflationary theories that have arisen to replace the original simpler models have changed in major ways and have become “highly tuned” to fit the data – losing their ability to be falsified, i.e. to make testable predictions.
These authors go so far as to state that some scientists accept that the theory of inflation (in its current form), “ is untestable, but refuse to abandon it”. No references are given for these views and no scientists are named who support such a view. I find it unfortunate that (ISL) are not more specific in naming names and identifying sources for these claims. It certainly weakens their case somewhat.
This lack of specifics was also picked up in the response from the group of 33, which was printed in the Scientific American Blog Network and is entitled A Cosmic Controversy. The 33 authors include many of the “Biggies” of theoretical physics and cosmology, including Alan Guth (usually credited with initiating the concept of inflation), Andrei Linde, Sean Carroll, Stephen Hawking, Juan Maldecena, Lisa Randall, Leonard Susskind, Steven Weinberg, Edward Witten, Alexander Vilenkin, Frank Wiliczek – to name just some of the names I am familiar with.
My first response to such a reaction by 33 named authors is that it amounts to a stomping exercise – an almost mob-like response to what is surely an appropriate academic exercise – contesting an orthodoxy and asserting a contrary view, with rationale supported by data.
That 33 prominent scientists have felt moved to sign their names to a rebuttal at least hints that (ISL) have hit a nerve. (ISL) are themselves accomplished academics, that is to say, not in the same class as flat-earthers, for example. For them to question an accepted paradigm strongly suggests there is valid reason for such questioning.
As mentioned, the rebuttal to (ISL), A Cosmic Controversy,) (CC), refers to the point made by (ISL) that some scientists are “promoting the idea of some kind of non-empirical science.” The authors to (CC) state: “ We have no idea what scientists they are referring to.” It is too bad – and odd – that (ISL) were not more specific in stating who or what proposals of inflation were accepting unscientific principals .
However the (CC) paper makes a few (il)logical leaps of its own. For example, on p. 5 of their rebuttal the group of 33 state: “Inflation is not only testable, but it has been subject to a significant number of tests and so far has passed every one.”
They then go on to assert: “Inflation is not a unique theory but rather a class of models based on similar principles.”
That is they are conceding that inflation is a phenomenological (curve fitting) paradigm that has been adjusted as needed to fit the data – the very point being made by (ISL)! They also in effect confirm (ISL)’s contention that the original models of inflation have had to be abandoned.
The (CC) authors stand by the success of the inflationary concept and compare it to the evolution of the Standard Model of Particle Physics which has evolved over the years while staying rooted in fundamental principles.
The concept of inflation was introduced to try and explain some of the remarkable features observed in our universe which are inconsistent with a simple Big Bang model. Some of these conceptual problems are examined and compared to present day inflation models in tabular form by (ISL). For example, the vast size of our universe, along with the observed similarity in the physics of what we observe at all scales, directions and distances is hard to explain. In our universe most regions would not have had time to interact and mix to produce the level of homogeneity and isotropy that is observed in the distribution of matter and energy.
The theory of inflation provides an opportunity for all parts of the observed universe to interact before a period of exponential expansion (inflation) begins, thus, supposedly solving the bigness problem along with why the disparate parts of the universe appear so similar in structure and underlying physics.
The problem, however, is that workable models of inflation require a very fine tuning of the parameters – the numbers that have to be put into the equations – to have inflation start under the right conditions and to stop at a time and under conditions consistent with the universe we observe. To put it simply, inflation was an attempt to explain certain conditions of the universe, but the conditions required for inflation are as hard to explain as the original conditions without inflation. Inflation was supposed to be the answer to a number of questions, but instead has generated a whole set of equally not understood questions of its own.
Conceptual problems of this kind have been part of the inflationary paradigm since its inception as (ISL) point out, but they make the case that continued refinements and fine tuning of inflationary models in order to fit new data has rendered the concept untestable as a fundamental theory.
Obviously, a large body of physicists do not agree with these authors and it could be argued that (ISL) are just promoting their own alternative models to inflation. However, it could equally be argued that the majority of physicists who have invested large parts of their years of study as well as their reputations supporting and accepting the inflation paradigm also have a vested interest in the concept. Furthermore, it could all be seen as an academic tempest in a teapot – like, who cares???
Well, for one thing, as pointed out in an earlier blog on the alternatives to Dark Matter, scientists who hold to an unorthodox view on any paradigm risk not being funded for their research – having a theory that is accepted without questioning produces a bias in the funding and research in the whole hierarchical structure of academic studies.
However there is always merit, in my opinion, in allowing and even nurturing contrary views to what is generally accepted by the majority, especially in disciplines in science. Gadflies like Iijas, Steinhardt and Loeb force everyone to rethink fundamental questions about what they are doing and also provide avenues for really new ideas to be developed. The response of the “group of 33” seems a bit overwrought – to paraphrase Shakespeare: they doth protest too much, methinks.