News: International Astronomical Union has no Definition for Big Bang

IAU has no Definition for Big Bang

(c) copyright 2011 David Dilworth

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“…the [Big Bang] definition is a mess.” – Prof. P. James E. Peebles, Princeton University, Feb. 2011

News: (Carmel, California) The world’s most widely respected astrophysics organization, the International Astronomical Union (or IAU), has affirmed that it has no definition for any Big Bang model.


At the same time the world’s most cited cosmologist, Princeton’s Professor P. James E. Peebles, says that the Standard Cosmology Model’s “definition is a mess.”

Prof P.J.E. Peebles

Prof P.J.E. Peebles

Prof. P. James E. Peebles, Princeton University, recently wrote (1) —

The name Big Bang is a very poor choice because it suggests a moment of time — a bang — and maybe also a place — where the bang occurred. Neither is part of the reasonably well tested theory of the evolution of the universe from a hot dense state to what we see around us. But the name has stuck, so I have stopped boycotting it.”

As you see the definition is a mess. The connotation to me is the relativistic theory of the expansion of the universe.

Big Bang was chastised recently for its lack of a complete unambiguous definition by my paper “Ground Rules for Cosmological Physics” (

(Lack of an adequate definition is a logical fallacy called an Exclusion or Ambiguity Fallacy when the definition can have multiple meanings. “Equivocation / Ambiguity: The fallacy of failing to define one’s terms.“)

“As of 2009 we have no agreed upon unambiguous, testable definition of Big Bang or Inflation models.”

“A related serious problem with the “Big Bang” claim is that there is no . . . one central repository for its definition.”

“It would be a big improvement to Big Bang’s credibility to have one official place where its definition is kept, similar to how NIST (National Institute of Standards and Technology) is used for measurements.”

So in search of a definitive definition of Big Bang (2) and inspired by the thoughtful suggestion of San Diego State’s Andrew Young that IAU is a reasonable place to maintain such a definition, I wrote to IAU’s Cosmology Commission asking that they consider providing one. IAU confirmed that as of February 2011 they have no definition for Big Bang.

“. . . the IAU has not provided a definition of the Big Bang.”

IAU’s Cosmology Commission VP, Brian Schmidt, added his personal opinion that it might stretch the Commission’s mission more than a bit to do so. He suggested that —

“Big Bang is a broad concept under which many different ideas of the early Universe reside. It is not a physical object like a Planet, nor is it a constant of Nature”

and that

“there is no precedent for our commission defining broad theoretical concepts such as the Big Bang.”


I find IAU’s position eminently reasonable. It indicates, perhaps dramatizes, a fundamental problem Big Bang models have with basic astrophysics science; that currently Big Bang is too ambiguous to be a scientific hypothesis.

This does not necessarily mean that individual components of the standard model are inadequately defined. For example, the Spectral line Redshift-to-Distance correlation claim does adequately meet all the criteria or conditions for a valid hypothesis. However, it does mean that the overall “Big Bang” concept does not yet meet scientific muster.

An analogy I use is how getting a Driver’s License requires you to complete an application form – before you can take the driving test.

In my view, Big Bang is just like an incomplete application — until the idea is adequately defined (until the form is filled in), meeting the minimum for a scientific claim, it simply cannot claim to hold the status of a scientific hypothesis or theory.

Cart Before Horse

Cart Before Horse

To debate evidence before a scientific concept has a clear, meaningful, unambiguous definition — is the equivalent of “putting the cart before the horse.”

Burden on Inventor – Not on Skeptic

As I also try to point out in the paper — the responsibility of defining a scientific claim is on the proponent – not on the skeptics. This means the burden of defining Big Bang is on its supporters. Once a scientific hypothesis is adequately defined, then the burden of dispute is properly placed on a skeptic.

Reversing the burden to a skeptic without a complete definition is another logical fallacy called Shifting the Burden of Proof. “A fallacy that challenges opponents to disprove a claim, rather than asking the person making the claim to defend his/her own argument.

Hypothesis and Definitions Needed – Not History

A simple web search echoes the inescapable notion reached by my years of reviewing more than a hundred Cosmology books and hundreds of cosmology papers — that most Big Bang “definitions” are in reality almost exclusively a history of the idea rather than a scientific definition for a hypothesis; the Wikipedia entry is an example.

So, until a credible body or a paper provides a complete definitive definition of Big Bang — here are some resources that could help. Yet even when combined these remain incomplete as a scientific hypothesis:

1. Prof. P. James E. Peebles provides what is probably considered the best available narrative description of the science of facets of the standard model in his 1993 book “Principles of Physical Cosmology.” It provides a coherent, internally consistent description with abundant detail (and all the necessary math), but does not include a complete concise high level definition.

2. “The Standard Model” also by Prof. Peebles (1998)

3. “The Future of the Universe” by Fred Adams and Gregory Laughlin (Sky and Telescope Oct., 2000) is an excellent timeline of one of the many Big Bang models, but it is not really a definition.

4. I provide an overview (math-free) definition of the many Big Bang models here — Big Bang definition, but it is also incomplete – because I can’t find the needed answers for all the parameters – and I’ve looked hard and long.

Mistaken for Hypothesis: While some have suggested LCDM models (Lambda Cold Dark Matter models – adjustable versions of Big Bang) are complete scientific hypotheses, even if they were, those same advocates acknowledge that no LCDM model is a complete definition for Big Bang.

However, LCDM models have fundamental definition problems of their own, explained in my paper “Ground Rules for Cosmological Physics” and the article “Physical Cosmology Hypothesis Application Form.”

LCDM model problems include a failure to define “space” or even estimate the number of intergalactic photon-matter interactions per year (PMIY).

Part 2 of this article is the new (Feb 24, 2011) “Physical Cosmology Hypothesis Application Form“.

I welcome your suggestions for how to come up with a definitive definition of Big Bang.

Best wishes,
-David Dilworth

Notes and References:

1. Personal communication (Feb 2011)
2. “Definitive Definition for Big Bang” could be abbreviated to D2B2.
3. “Poof, There It Is Theory

Further reading:

The Burden of Skepticism by Carl Sagan

The Scientific Method, A helpful guide by Science Made Simple

How to Write a Science Fair Hypothesis


Learn More About the Scientific Method

Update 1 (June 2011): This article was just nominated for the “3 Quarks Daily 2011 Science Article Prize” ! (What an honor – because there are some really fascinating articles nominated.) If you would like to review the whole set of nominated articles click here :

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Update 2 (June 10, 2011): I am delighted and honored to report that this article was voted the 3rd most popular science article making it a semi-finalist in the “3 Quarks Daily Prize” contest on June 10, 2011. Only three of the 87 (fabulous) science articles received 100 or more votes. Thanks to you readers, colleagues and friends this article was one of those three.

Update 3 (June 10, 2011): Due to another article incorrectly describing and disputing this one I’m providing “Article on Big Bang’s Inadequate Definition Disputed – But Article Emerges Unscathed” to correct that other article’s errors.


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