Sunday, September 14, 2008

Definition of Scientific Cosmology

(Update: minor corrections and additional questions at the end)

SAGREDO: Scientific cosmology is a branch of physics that studies the structure of the universe as a whole, its origin, dynamics and composition based on the fundamental laws of physics and following an empirical method of testing hypothesis with observations. As such it excludes a large number of alternative models and explanations of the universe not based on testable hypothesis, such as philosophical speculation, creation myths and the biblical narrative of creation. A representative example of the standard definition of scientific cosmology found in most textbooks and popularization of science books is that given by Primack and Abrams [1]: "Cosmology is a branch of astrophysics that studies the origin and nature of the universe as a whole by developing theories and testing them against observational evidence to support or rule them out... Modern scientific cosmology says nothing about human beings or how we should live. It aims to provide scientific accuracy, not meaning." George Gamow, one of the originators of the big bang model in his popular book of 1952 "The Creation of the Universe" [2] calls it "cosmogony" and defines it simply as the theory of the origin of the world.

The models of the universe developed by the ancient Greeks, such as the heliocentric cosmos of Aristarchus of Samos (third century BC), the geocentric models of Aristotle and Ptolemy were based on logic, observations and solid geometric concepts. The same applies to Newton’s notion of an infinite universe. Modern scientific cosmology began with Einstein’s theory of gravity (1917) and later married with nuclear physics to explain the observed abundance of the elements (Gamow, 1948). The establishment of the widely accepted standard cosmological model is marked by the publication of Peebles’s book "Physical Cosmology" [3] (1971) after independent confirmation of the discovery of the cosmic background radiation. The model consists of the idea that the universe is expanding and in the past the temperature of the universe was higher and therefore provided the conditions to produce the nucleo-synthesis of the light elements. The model is supported by a web of interrelated observations that are consistent with the predictions of the model and with general relativity and the standard model of particles and fields: abundance of nuclear elements, expansion of space, the universe is denser and hotter in the past, and detection of the cosmic background radiation its temperature, polarization, spectrum and anisotropies. The big bang model however introduces two constituents that make up most of the universe, 25% of the mass/energy in the universe is dark matter and 70% is dark energy. This is problematic because the evidence currently available for dark matter and dark energy is weak and the nature of these components is unknown. Dark energy and dark matter are seen by the critics as ad hoc elements added to the theory so that it fits the data.

Cosmology is an experimental science in the full sense. While it is not possible to recreate the explosion of a supernova in the laboratory the supernova ‘experiment’ is played out by nature and astronomers make observations to collect data from these experiments. With the advent of satellite-based missions making observations from outer space, unperturbed by atmospheric effects, extensive amounts of new data covering a wide range of the electromagnetic spectrum (from microwaves to gamma rays) has been made available, ushering the emergence of the so called age of "precision cosmology". The recently analyzed data of NASA’s WMAP mission [4], for example, provides the parameters of the standard cosmological model with an unprecedented level of accuracy and coherence.

The actual domain of scales studied in cosmology range from galaxies and galaxy clusters and their distributions to the whole "visible" universe. In the theoretical side they range from quantum mechanics to general relativity. The earliest that we have been able to observe in the past is few minutes (~3) after the big bang by looking at the relative abundances of light elements (hydrogen, helium, deuterium, and lithium). To understand what happened before the first 3 minutes theorists have used the standard model of particles and fields and pushed the boundaries to where relativity and quantum mechanics leads them, but because of the lack of observational support this effort has been criticized as speculative. A favorite explanation for the initial state of the big bang is the mechanism of inflation (Guth 1981) but it has not been tested and therefore it is not part of the standard model. Grujic [5] summarizes this situation as follows: "As a research field cosmology covers a broad range of physical conditions (ontological aspect) and wide spectra of methodological approaches (epistemological aspects). The former go from the visually accessible parts of the cosmos we live in, to the remote parts whose nature we may only speculate about. It is these inaccessible regions that force us to resort to (often wild) speculations that go beyond the positive science. These speculations, though dressed in mathematical clothes, have provoked a number of astrophysicists, including cosmologists, to compare modern cosmology with traditional mythological representations of the universe." Theoretical speculation, as long as it is not teleological, eschatological or in search for purpose, has been a healthy activity in physics. Important contributions (relativity, prediction of antimatter, prediction of black holes, quarks, etc) have resulted from speculation founded on a sound theoretical framework and accompanied with testable predictions. The speculation that Grujic refers to has to do with theories that loose contact with the observable world, such as theories that predict multi-universes to which we cannot have causal contact, or "curled" extra- dimensions that have no "visible" manifestation.

Cosmology is different than other areas of scientific inquiry in that it touches fundamental questions about our origins encroaching fields of study traditionally claimed by philosophy, anthropology and theology and at times conflating with religious ideas. For this reason the work of cosmologists has been intensively attacked from all camps of humanities, philosophy, obviously theology, and even physics. The most important non- frivolous critiques are that 1. Modern scientific cosmology rests on monumental assumptions of homogeneity and isotropy (which are not firmly confirmed); 2. Astrophysicists are gratuitously extrapolating to the scales of the whole universe the theories and laws of nature that were developed to explain the local world. These are valid critiques. The homogeneity and isotropy assumption is a simplification to help work out the solutions to the equations of general relativity and is part of the scientific practice. Just as planetary orbits can be explained and studied in great detail by assuming that the planets are just simple points (a gross simplification indeed!) the large scale structures in the universe is deemed homogeneous because on average it exhibits a uniform distribution (with deviations from the mean of the order of 1% of the size of the universe) that justifies the simplification. No astrophysicist with full command of his/her senses is claiming recklessly that scientific cosmology is ‘final’ and complete. Most likely few decades from now there will be a better model of the universe with the big bang subsumed into it. As for the problem of scales, all of the observations rely on collecting electromagnetic radiation emitted far away. The mechanisms of radiation are the same (atomic transitions or accelerating charged particles) here or there, the characteristics of this radiation (spectrum) have been observed to follow the same properties regardless of the location the emission took place, near or far.

Can there be an exchange between scientific cosmology and the wider cosmology of past and present cultures? The definition of scientific cosmology with the necessary condition of adhering to scientific practice and method strongly suggests that these are two approaches whose relationship is appropriately characterized by Stephen Jay Goul’d dictum of "non overlapping magisteria" that he suggested for science and religion.

Nota Bene

An attempt was made to provide a definition of "scientific cosmology", but another question that arises in this context is: what makes a cosmology scientific? Mention was made of the requirement for testability and adherence to scientific practice and method; however a proper treatment of the subject would mean that we need to define what science is. I will not attempt that. After 800 years of trying, since Roger Bacon in the 1200s, it seems like there is no consensus and all we have to show after all this time is the "science wars" [6] and Feyerabend’s "anything goes". As an alternative let me offer a subjective criterion: "I know it when I see it". That is, if you show a purported scientific theory to a group of reputed scientists, once they see it most likely they can reach a consensus as to whether that can be accepted as scientific or not. This criterion is practical but I do not entirely like it because it has all the marks of accepting the putative and menacing "orthodoxy" (i.e. the group of scientist judges) that so insistently the sociologists of science of postmodern tendencies are pushing. The "I know it when I see it" criteria has origins in deliberations by the U.S. Supreme Court confronted with the need to define what is "obscene" under U.S. law. A task of immense ramifications as it impinges on the freedom of speech guaranteed by the First Amendment. The Supreme Court found huge difficulties when trying to define what pornography is. If you place the line a bit to one side, the whole Sistine Chapel falls in the pornographic side, if a bit to the other side the Pompeii orgy frescoes fall in the side of art. In 1964, Justice Potter Stewart tried to explain pornography by saying "I shall not today attempt further to define the kinds of material I understand to be embraced... but I know it when I see it" (Jacobellis v. Ohio, 378 U.S. 184, 197) [7]. So, the same with science: I know if it is science when I see it. Hoyle’s steady state cosmology was scientific but his theory that viruses that cause flu epidemics come from outer space is not scientific.


1. Why virtually every human society has developed models of the universe and explanations of how it came into being? Does developing a cosmology provide an evolutionary advantage?

2. Can the scientific approach to cosmology claim epistemic advantages?

3. Are sociological studies about how cosmological models are developed relevant?

4. Is the principle of symmetry an honest an ethical approach in the face of anti-science pronouncements based on ideological dealership? (i.e. global warming denial, evolution denial, etc -- see for instance the Kitzmiller vs Dover case)

5. Is sociology of science a science? If so, can it produce legitimate attacks on science while at the same time using a scientific approach? If not, what guarantees that the theses put forward by sociologists have any value beyond subjective utterances?

6. Do people (i.e. the layperson) in a modern society need to be educated about scientific knowledge about the universe? How about the leaders and decision makers?

7. Should/can scientific cosmology be reconciled with the wider cosmologies studied by anthropologists?

8. From the epistemic point of view should scientific cosmology receive the same treatment as any other creation myth and world view? What is a myth? And what is a worldview?

9. Are the claims leveled against scientific cosmology of being a dogmatic and inquisitorial sustainable? Is there a scientific "orthodoxy"? (see for instance


[1] J. R. Primack, N. E. Abrams, "The View from the Center of the Universe" (Riverhead: New York, 2006), p.16

[2] G. Gamow, "The Creation of the Universe", Bantam: New York, 1952.

[3] P. J. E. Peebles, "Physical Cosmology", Princeton University Press: New Jersey, 1971.

[4] J. Dunkley, et. al., "Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Likelihoods and Parameters from the WMAP data", 2008,

[5] P. V. Grujic, "Some Epistemic Questions of Cosmology", 2007,

[6] "The Science Wars Homepage",

[7] J. A. Silver, "Movie Day at the Supreme Court or ‘I know it when I see it’: A history of the Definition of Obscenity",