The Universe is
very large, and we are very small compared to it, not only in size. Creating a
cosmology that attempts to explain the whole existing Universe is an obsession
shared by all cultures. We think we now have the true cosmological model, like
many civilizations that have come before us. There are, however, reasonable
grounds for thinking that the total truth about the origin and evolution of the
Universe is beyond our reach. Nonetheless, there is widespread propaganda
claiming that absolute truth about the Universe has already been obtained, and,
like in any religion or ideology that constitutes the essence of our society,
there are shepherds or priests controlling the flow of ideas and guiding the
herds so they do not deviate from what they consider this absolute truth.
Photography credit: Hoyle, F., Burbidge, G. and Narlikar, J.V. (2000) A Different Approach to Cosmology: from a Static Universe through the Big Bang towards Reality, Cambridge University Press, Cambridge, p. 188.
Only the
standard model, usually known as the “Big Bang,” is considered by most
professional cosmologists, while the challenges of the most fundamental ideas
of modern cosmology are usually neglected, owing mainly to sociological
factors. Funding, research positions, prestige, telescope time, publication in
top journals, citations, conferences, and other resources are dedicated almost
exclusively to standard cosmology. Moreover, religious, philosophical,
economic, and political ideologies in a world dominated by anglophone culture
influence the contents of cosmological ideas.
The standard
cosmological model is a long list of speculative ideas to which many ad hoc elements
[e.g., charge conjugation parity symmetry violation (CP violation),
non-baryonic dark matter, and inflation] were added when the theory did not
reproduce observations. At the end of the 1990s, another patch was applied to
the theory in an effort to solve new inconsistencies with the data: “dark
energy,” which supposedly produced acceleration in the cosmic expansion. The
problems to be solved were basically the new Hubble-Lemaître diagrams with type
Ia supernovae (SNIa) as putative standard candles, the numbers obtained from
cosmic microwave background radiation (CMBR) anisotropies, and especially
estimates of the age of the Universe, which were inconsistent with the
calculated ages of the oldest stars. The renovated standard model including
these new elements added ad hoc would come to be called the ΛCDM cosmological
model, where Λ stands for dark energy and CDM stands for cold dark matter. Such
models became the favored subgroup of models of non-baryonic dark matter.
Some
cosmologists have referred to ΛCDM as “concordance cosmology” to emphasize that
this model agrees with all the known observations. Other authors were critical
of the standard model and preferred instead to call it “consensus cosmology.”
This term emphasizes that this new cosmology is, above all, a sociological
question of agreement among powerful scientific teams in order to establish the
orthodoxy of a fundamental dogma. This agreement was mainly between two
powerful cosmological groups, the teams dedicated to the analyses of SNIa
and CMBR,
who found a rough coincidence in the necessary amount of dark energy, albeit
with large error bars. This coincidence reinforced these groups’ belief that
they had discovered an absolute truth, thus compelling the rest of the
community to accept this truth as a solid standard. Meanwhile, they discarded
the results of other less powerful cosmological groups that presented different
values of the parameters or that could interpret the results of SNIa or CMBR
without needing to introduce an exotic element like dark energy. Talking about
consensus cosmology, Rudolph “Rudy” Schild (b. 1940) once queried, “Which
consensus? Do you know who consented? A bunch of guys at Princeton who drink
too much tea together.”
The last 25
years in the development of cosmology have been characterized by a lack of
discussion on its fundamental ideas. The belief that all the major problems
have been solved became a tenet. Minor subtleties (byzantine arguments) about,
for example, the equation of the state of dark energy and the types of
inflation or the coldness or hotness of dark matter, continued to be debated,
but the fundamental ideas did not. This is the epoch of the highest social
recognition of cosmology: Not only do schools, museums, and popular science
journals have described the Big Bang as well-established and as something to be
compared to Darwin’s evolution and natural selection theory, but cosmology have
occupied a privileged ranking among the most prestigious natural sciences. For
instance, researchers of cosmology and its dark were awarded Nobel Prizes in
Physics in 2011 and 2019, respectively, for the putative discovery of the dark
energy that produces the acceleration of the expansion and for the inclusion of
the dark components in our understanding of the Universe.
One may wonder
whether unconfirmed quasi-metaphysical speculations should form part of the body
of recognized knowledge of physics, leaving behind the conservative tradition
of Nobel committees not awarding prizes for speculative proposals. Einstein did
not receive either of his Nobel Prizes for his discovery of special and general
relativity. Moreover, Curtis did not receive a Nobel Prize for his definitive
recognition of the true nature of galaxies in the Great Debate of 1920. Neither
Lemaître nor Hubble received the Nobel Prize for their discoveries about the
expansion of the Universe, but we now have committees that give maximum awards
for the highly speculative proposal of the acceleration of the expansion, whose
reality has yet to be confirmed. We certainly live in a very special time for
cosmology.
This is also the
epoch in which the main enterprise of cosmology consists of spending big money
on megaprojects that achieve accurate measurements of the values of the
cosmological parameters and solve any small problems that remain to be
explained. However, this brand of epistemological optimism has declined over
time, and the expression “crisis in cosmology” is stubbornly reverberating in
the media. The initial expectation of the removal of the pending minor problems
arising from increased accuracy of measurements has backfired: the higher the
precision with which the standard cosmological model tries to fit the data, the
greater the number of tensions that arise. That is, the problems are
proliferating rather than diminishing.
The top
shepherds of the business of cosmology also pretend to be leaders of the crisis
and tell the herds which problems are relevant and require further attention.
In the last five years, no problem in cosmology has received as much attention
as what is called “Hubble tension.” Hundreds or perhaps even thousands of
papers have investigated the observations that originate the tension within the
standard cosmological model or proposed alternative scenarios. The tension was
mainly triggered by the claim made in 2019 of a Hubble-Lemaître constant, H0,
estimated from the local SNIa distance ladder, which is at odds with the value
extrapolated from CMBR data, per the standard ΛCDM cosmological model, which
gave an incompatibility
at the 4.4σ level. This tension was later increased up to 6σ depending on
the datasets considered.
This Hubble
tension is unsurprising, given the number of systematic errors that may arise
in the measurements. As a matter of fact, there have always been tensions
between different measurements of the values of H0, which
have not received much attention. Before the 1970s, due to different
corrections of errors in the calibration of standard candles, the value of the
parameter continuously decreased, leading to incompatible measurements of
different epochs. Even after the 1970s, some tension has always been present.
Statistical analyses of the measurements of H0 after the
1970s have also shown that the dispersion of its
value is much larger than would be expected in a Gaussian distribution,
given the published error bars. The only solutions to understand this
dispersion of values are to assume that most of the statistical error bars
associated with the observed parameter measurements have been underestimated or
to assume that the systematic errors were not properly taken into account.
The fact that
the error bars for H0 are so commonly underestimated might
explain the apparent discrepancy of values. Indeed, a recalibration of the
probabilities with this sample of measurements to make it compatible with a
Gaussian distribution of deviations indicates that a tension of 4.4σ would be
a tension of 2.1σ in equivalent terms of a Gaussian distribution of
frequencies. Meanwhile, a tension of 6.0σ would be a tension of 2.5σ in
equivalent terms of a Gaussian distribution of frequencies. That is, we should
not be surprised to find tensions of 4-6σ because they are much more frequent
than indicated by the Gaussian statistics, and they stem from underestimation
of errors, not from real tensions in the background physics or cosmology.
Values of H0
derived from CMBR are subject to errors in the cosmological
interpretation of CMBR with ΛCDM, and they are subject to the many anomalies
remaining to be solved in CMBR anisotropies. Moreover, Galactic foregrounds in
CMBR are not perfectly removed and are an important source of uncertainties.
Values of H0 derived from SNIa are affected (and not properly
corrected) by dust extinction in SNIa depending on the type of host galaxies,
variations of the intrinsic luminosity of SNIa with the age of the host
galaxies, etc. Ignoring all these latent variables can only lead to
underestimated errors and possible biases. We must also bear in mind that the
value of H0 is determined without knowing which scales of the
radial motion of galaxies and clusters of galaxies relative to us are
completely dominated by the Hubble-Lemaître flow. The homogeneity scale may be
much larger than expected, thus giving important net velocity flows on large
scales that are incorrectly attributed to cosmological redshifts.
Why, then, is
there so much noise and commotion surrounding Hubble tension? There are tens of tensions
and problems in the standard model that are more challenging than this, but
the cosmological herds are currently obsessed with solving the Hubble tension
as the key problem in cosmology. The answer to this problem has to do with the
fact that this tension has been promoted by the dominant groups that control
cosmology. These, again, are the SNIa and CMBR teams who promoted the idea of
concordance cosmology and dark energy. In the late 1990s, they told herds
something like, “Now we have a consensus. Everybody should go in this
direction,” and we saw thousands of cosmologists, almost the whole community,
moving in this direction like guided sheep. Now, one of the supreme leaders,
Adam Riess (who won a Nobel Prize in 2011), has said that there is an important
problem in cosmology. It is the problem derived from the analysis performed by
his own team on SNIa data in comparison with CMBR data, expressing something
like, “There is a tension in cosmology, and everybody should go in this
direction.” Again, we see the sheep-cosmologists struggling to understand this
tension and reinvent cosmology by adding new patches.
This is called
“groupthink,” a sociological phenomenon studied in depth, for instance, by
psychologist Irving Lester Janis (1918–1990). Orthodox cosmology has an
important element of groupthink, of following a leader’s opinion. Any opinion,
however outrageous, can be accepted if it is supported by the leading
cosmologist. In this way, the Big Bang theory, even if it is a very speculative
set of hypotheses, still finds a place in the psychology of the wider community
of scientists.
The analysis by
Cass R. Sunstein (b. 1954) in his book Conformity
applies to social dynamics in the sciences. Conformity dynamics are particularly
pronounced when dealing with very difficult problems. Social experiments in a
multitude of contexts clearly show that when a problem is hard to solve, as in
cosmology, people tend to follow the crowd, tending to defer to those who are
perceived as authorities on the matter. A key mechanism in this collective
effect is so-called informational cascades, by which people primarily rely on
the signals conveyed by others rather than on independent information. Once
this happens, the subsequent statements or actions of few or many others add no
new information. They are just following their predecessors. This cascade is
very hard to stop, as shown by social networks on the Internet. A reputational
cascade develops along with and reinforces an informational one. At this stage,
it simply becomes too risky to go against the core consensus.
As said in Novum
Organum by English philosopher Francis Bacon (1561–1626):
The human understanding when it has once adopted an opinion (either
as being the received opinion or as being agreeable to itself) draws all things
else to support and agree with it. And though there be a greater number and
weight of instances to be found on the other side, yet these it either neglects
and despises, or else by some distinction sets aside and rejects; in order that
by this great and pernicious predetermination the authority of its former
conclusions may remain inviolate. (Chapter XLVI)
Note: some parts of this article were taken from the book: López-Corredoira, M., Fundamental Ideas in Cosmology. Scientific, philosophical and sociological critical perspectives, IoP Science (2022).
