Also see: Evidence for the Big Bang FAQs
This essay is by Richard Carrier.
For years I argued that there might not have been a Big Bang, since the evidence for it was rather poor. I encountered as a result a sea of snobbery and condescension from physicists. I encountered bias and closed-mindedness, and this was all the more reason to go on record against it. I found my experience was not unique: even some professional astronomers had been pressured to advocate the Big Bang in order to get telescope time, which makes or breaks every astronomer’s career.. This kind of arrogance was appalling.
…. I always kept an open mind and continued my investigations. And over the past two years enough evidence has arisen, and two physicists (Victor Stenger and Bjoern Feuerbacher) took enough trouble to patiently persuade me with genuine facts and argument, that I have “seen the light” so to speak, and changed my mind. Equally important was my careful reading of the works of Barry Parker and Joseph Silk. I now conclude that the Big Bang Theory, in some formulation, is probably true. The odds are well in its favor. Why and how this is so I explain in this essay.
My Position Now
The current Big Bang Theory should be thought of as having two distinct elements.
The first part is a theory about the origin (or at least the early evolution) of the observed universe.
The second part is a theory about how that came about.
By confusing these two aspects of the theory I and others were easily led astray in our assessments of the evidence. The first element of the Big Bang theory now has about as firm an evidential foundation as anyone could reasonably expect of it. There is no good reason to doubt that the observable universe had its origin in a small, superheated state about 14 billion years ago, from which it expanded and cooled, condensing into the cosmos we now see.
The second element of the Big Bang Theory is another story. Hardly anyone can agree on the details, and evidence for or against any particular position is scarce and indecisive. But even if we had no clue at all as to why the universe began in a small, superheated state, this would not detract from the evidence that it did. And as it happens, we have more than a clue about the why. The basic outlines of Inflation theory account for the Big Bang and other observations fairly well. They do not have enough specifics to fit or explain all the facts that we observe, and both are largely undetailed and untested as far as theories go. So this element remains highly contentious and speculative, and much in need of more fact-finding. But it is the best game in town, and it makes a lot of sense.
(1) General Relativity and Vacuum Energy Imply a Big Bang Inflation Event
When Einstein applied the equations of General Relativity to the entire universe, rather than just the solar system, he found they predicted either that the universe must expand from or collapse to a singularity. Einstein eliminated this result by arbitrarily adding a “cosmological constant” that balanced everything out. As Parker notes, “Einstein was reluctant to add the term. It destroyed the simplicity and beauty of his equations” (p. 51). As Einstein himself said, “If Hubble’s expansion had been discovered at the time of the creation of the general theory of relativity, the cosmological member would never have been introduced. It seems now so much less justified to introduce such a member into the field equations” (Letter of 1932, quoted by Parker, p. 59).
When later scientists worked out all the possible solutions to this problem, it was found that the entire universe would inevitably have one of several particular shapes. Some of those shapes included a singularity at the beginning of time followed by an expansion: a Big Bang. As it happens, the known properties of the universe as presently observed entail that only one of those descriptions can be correct. So the universe had to have begun as a singularity. The only way this could not be correct is if General Relativity is false (and that is unlikely: it is very well corroborated) or if some as-yet unknown force or factor prevented it. As it happens, Stephen Hawking proved quantum mechanics is such a factor, since quantum uncertainty makes a singularity impossible (see “The Truth about Singularities“). So contemporary Big Bang theory no longer involves a singularity at all. Instead, scientists do not yet know what the shape and content of the universe was prior to the Planck time, a tiny fraction of a second. But on present theory the observable universe still begins very, very small.
Much later it was noticed that such a Big Bang event would experience a very brief period of “supercooling” which would cause a rapid but brief period of “inflation,” at least if we are right about currently-accepted physics. This in turn predicts many peculiar observations, like the near-perfect density, smootheness and flatness of the universe. Though Inflation Theory does not explain everything or fit all the facts, it has two things going for it: it appears to be independently predicted by other physical laws, and it explains a lot that otherwise would remain a mystery. Still, many physicists remain skeptical of Inflation Theory, even as they agree that the Big Bang theory is probably true.
(2) Expansion is Confirmed by Multiple Lines of Evidence.
There are five independent lines of evidence that all converge on a common conclusion: the universe began between 14 and 15 billion years ago in a superheated state where even atoms could not form, and has rapidly expanded and cooled ever since.
The first and most important piece of evidence is the observation of redshifts, which can only be explained by assuming that every galaxy cluster in the universe is moving away from every other: the more distant, the greater the speed. Though many scientists have shown or argued that some redshift has other causes, these explanations do not account for even a significant fraction of the observed objects, or of the observed redshift overall, which is simply too enormous to be accounted for by any other known means. The most obvious contrary explanation is that something to do with the space the light passes through causes the frequency to decay, but this has been soundly refuted by two observations. First, the expansion rate is accelerating, which only a change in velocity can explain (since the rate of a space-caused decay could not change but would have to be constant). Second, many observations of redshifted objects have been made whose light is split by a gravitational lens. These studies show that even when light coming from the same object traverses different distances, the redshift remains the same. So light is not decaying as it passes through space. The redshift must originate with the object, and only velocity can explain that.
The five independent lines of evidence for the universe’s age are as follows:
- First, taking into account all known factors, including the recently-confirmed acceleration of the cosmic expansion rate, scientists have shown that if you rewind the observed behavior of the known universe, it all comes together in a tiny, superheated state about 14.5 billion years ago.
- Second, we have confirmed that the oldest stars in our own galaxy are between 12 and 13 billion years old. Though Pickrell (cf. n. 5) notes that these “were probably not among the universe’s very first stars,” they would have formed no more than a billion years after the cosmos itself began to form. Though this only proves an age for our galaxy, not necessarily the universe, the result of 14 billion years perfectly matches the most recent calculation of the projected start-point for the universe’s observed expansion.
- Third, the most distant galaxy yet observed, based on the most precise and accurate observations to date, lies between 12 and 13 billion lightyears away, and thus is just as old as ours.
- Fourth, the observed interstellar abundance of certain radioactive elements, calculating backwards from their known rate of decay, entails that they must have been produced at least 12 to 13 billion years ago, about the time we would expect them to have formed if the universe began about 15 billion years ago.
- Fifth, the current calculated age of various globular clusters beyond our galaxy is no more than 15 billion years. This corroborates an age of the universe of about 15 billion years.
These five facts, especially in combination with all the other “evidences” ennumerated in this essay, would be a remarkable coincidence if the universe didn’t in fact originate between 14 and 15 billion years ago. So it probably did.
It must be noted that Lerner discusses experimental evidence that the pressure-action of light itself, upon galactic or stellar magnetic fields, would inevitably accelerate all objects away from each other: in other words, there is a possible explanation of expansion other than a Big Bang, indeed, an explanation of accelerating expansion. And despite critics who originally attacked this suggestion, intergalactic magnetic fields have recently been demonstrated to exist on a vast scale. Many other theories could perhaps account for it, too. However, all the other evidence concurs with a Big Bang event, not any of these other theories.
Likewise, M-Theory has recently provided an alternative that is just as successful as Inflation Theory without any Big Bang as ordinarily conceived. Called the ekpyriotic or “brane” theory, developed by Dr. Paul Steinhardt and others, this theorizes a “Big Collision” instead of a Big Bang. Or, as Boslough puts it, “Maybe the big bang was just a big bang, an explosion in our little neighborhood of the universe that was neither the beginning of time nor the creation of the cosmos. Nobody knows.” This fact should be kept in mind throughout this paper: Big Bang theory is consistent with many different interpretations of the originating event. It is no longer tied to Singularity Theory nor does it logically require Inflation Theory, nor does it entail that nothing else exists apart from what we observe: there may be other universes, and even this universe is probably much larger than we will ever see.
(3) The Microwave Background Radiation is Consistent with a Big Bang Event
Not only did Big Bang Theory predict a microwave background glow, it exactly predicted its temperature. Though there are problems with the exact pattern of that radiation, and though there may yet be other causes for it, no one has demonstrated any better explanation to be correct.
In contrast, analysis of the microwave background as observed by numerous independent instruments confirms certain features that suggest the universe was indeed in a superheated state (indeed, the very state that “Inflation” would have ended with) about 14 billion years ago.
The evidence is of sound waves that passed through the early superheated universe, in such a way that predicts the current existence of roughly 4.5% “baryonic matter,” based on experimentally proven ratios in particle accelerators, which is almost exactly what we observe. This is not a slam dunk proof, but it is very strong evidence that the universe was once in a superheated state 14 billion years ago, again corroborating the basic elements of the Big Bang Theory.
No other theory can explain this acoustic peak, except theories already resembling the Big Bang, like Brane Theory.
I originally saw this as a failed evidence because we know too little to get anything like a precise ratio of light to heavy elements and thus could not base any argument on what that ratio was. However, on closer examination I found that this ambiguity does not matter so much.
Even though a lot of matter remains unobserved, and the time and rate of star formation is not securely known so the actual ratio today is not securely known, the vast quantity of key light elements that we do observe is far too great to be accounted for in any other way than by something like a Big Bang. Alternative theories are at present entirely speculative, while Big Bang theory has experimental basis in particle physics.
This is most clear in the case of the verified presence of natural deuterium. Its quantity is not even important: its mere existence is inexplicable–except, so far, by the Big Bang theory. There is no other natural process known that can create stable deuterium. In fact, stars destroy this element.
But the evidence doesn’t end there: beginning at a superheated state entails a vast abundance of light elements over heavy, with more light elements in older epochs. Both observations are confirmed. The exact ratios are unknown, but everywhere (even in our own galaxy) older stars are comprised of more light elements than newer stars, and the vast scale of light elements is undeniable. There is simply way too much helium, for example, to explain by any other means.
And no other theory can account for the precise kinds of light elements we observe in superabundance: not just any helium, for example, but only helium-3 and helium-4; not just any lithium, but lithium-7; and so on. Other light elements exist in only trace amounts. This is exactly what would be predicted if the universe began as a superheated mass of superhot protons and neutrons which then cooled, according to the experimental results of atomic physics.
Those are the four lines of evidence for the Big Bang that carry convincing weight. Other evidence might be uncertain (such as that for epochal change on a galactic scale, cf. n. 13), or equally predicted by other theories (such as that the universe is very nearly flat, a finding now well confirmed ).
But when we examine the evidence above, there really is no better theory than the Big Bang: all lines of evidence point there. Inflation Theory could be false, yet even then some form of the original Big Bang theory might still be true (i.e. Lamaître’s theory that the cosmos began as a spherical superheated mass a few lightyears across). However, Inflation explains, even predicts, so much of the evidence we do have, and is predicted by well-tested theories like the Standard Model of Particle Physics, Quantum Mechanics, and General Relativity, that it is probably approximately true, at least in some fashion. But even if that is false, the Big Bang theory in some form is still probably true.
This remains so even despite problems. Indeed, some problems have been removed: for instance, more accurate measurements with higher resolution have resolved any doubts about the existence of observable objects more distant than 13 or 14 billion lightyears. None have been observed. Though some still might, current observation remains consistent with the Big Bang.
Note that it is only the observable objects that matter–the universe may easily be larger than 14 billion lightyears on any Big Bang theory, we just shouldn’t yet be able to see farther than that if the theory is true, and so far it seems we can’t. Likewise, though a value for the Hubble Constant had been confirmed that caused problems with earlier theories, the discovery of accelerating expansion has resolved that issue.
Likewise, while there has been trepidation over inconsistencies in observed vs. required mass, gravity observations have confirmed the existence of 30% of this missing mass (in some form as yet unobservable to current instruments), and much has been accounted for by the expected volume of neutrinos in the universe, according to the recently-confirmed neutrino mass. The number of observed kinds of neutrinos is also partly predicted by the Big Bang theory, so neutrinos are starting to provide an additional line of evidence for the Big Bang. Though this proof is less secure than the others, it is impressive that it happens to match and corroborate the same result as the stronger proofs (cf. Parker, pp. 105-111).
But some problems remain. Primarily, no version of the Big Bang theory yet explains supercosmic structure. As Peter Coles puts it, some scientists “argue, controversially, that the Universe is not uniform at all, but has a never-ending hierarchical structure in which galaxies group together in clusters which, in turn, group together in superclusters, and so on. These claims are completely at odds with the Cosmological Principle and therefore with the Friedmann models and the entire Big Bang theory.”
Certainly, the observation of very large-scale structure going very far back in time is as yet not entirely explained. Yet Wane Hu notes that evidence of supercosmic structure in the most accurate microwave background data so far (retrieved by BOOMERANG) shows such structure “on the largest scales at the earliest times.” But the incorporation of heavy neutrinos into cosmological models may be changing that.
Still, this is simply a mystery that remains to be solved. The evidence for the Big Bang theory is simply too strong to dismiss on this account. All we can be sure of is that we don’t know exactly how or why the universe existed in a superheated state about 14 billion years ago, though it seems to have had something to do with singularities and inflation. But the basic fact, that the universe existed in a superheated state about 14 billion years ago, now seems hard to dispute. I, for one, believe it.
Copyright 2002 by Richard Carrier. Copying of this material is permitted provided credit is given to the author and no material herein is sold for profit.
 Barry Parker, The Vindication of the Big Bang: Breakthroughs and Barriers, 1993. This is out of print, but I found it an excellent lay summary of the evidence by a bona fide expert and well worth acquiring. Though some of his facts (particularly concerning chronology) are out of date, recent advancements have made his case stronger, not weaker. He also summarizes quite fairly many problems with the Big Bang theory (pp. 159-208, 231-2, 281-300; but compare pp. 233-57 and 305-12), and several alternatives to it that were proposed before 1993 (pp. 302-04, 313-36). All the same is true of the very up-to-date work of Joseph Silk, The Big Bang, 3rd ed., 2000. Far less useful but still in the same genre lies the relevant chapter in Robert Ehrlich’s Nine Crazy Ideas in Science (2001) and of course Fox, op. cit. n. 9.
 The first three “proofs” are reported by J. Pickrell, “Faded Stars Get New Role: Hubble Takes a Long Look” and R. Cowen, “Sharper Images: New Hubble Camera Goes the Distance,” Science News 161 (May 4, 2002), pp. 277-78. The other facts are described by Parker, op. cit., n. 2, pp. 96-101.
 e.g. G. Goldhaber, et al. Timescale Stretch Parameterization of Type Ia Supernova B-band Light Curves (2001).
 See Karen Fox, The Big Bang Theory: What It Is, Where It Came From, and Why it Works, 2002, pp. 152-7. Brane theory fits superstring theory better than Inflation, and makes all the same predictions but one: different features in the gravity wave background, which we will probably not be able to measure for decades. See: J.R. Minkel & George Musser, “A Recycled Universe: Crashing branes and cosmic acceleration may power an infinite cycle in which our universe is but a phase,” Scientific American (March 2002), pp. 25-26. See also: “When Branes Collide: Stringing together a new theory for the origin of the universe,” Science News 160:12 (Sept. 22, 2001), pp. 184-5.
 e.g. Hoyle and Burbidge, “A Different Approach to Cosmology,” Physics Today, April 1999, pp. 38, 41. Their theory predicts a blackbody metallic dust as the source of the microwave background, and unexpected metallic dust has indeed been found in intergalactic voids (J. Michael Shull, “Intergalactic Pollution,” Nature, 2 July, 1998, p.17-19; Lennox Cowie and Antoinette Songaila, “Heavy-element enrichment in low-density regions of the intergalactic medium,” ibid., pp. 44-6). Another theory is Hannes Alfvén’s “plasma theory,” which is given at least a nod of respect by the science community: cf. Boslough, op. cit., n. 10, and Anthony Peratt, “Not with a Bang,” The Sciences, January/February, 1990. Fox also agrees that this makes all the same predictions as Big Bang theory with fewer difficulties, and has yet to be falsified by experiment or observation (op. cit., n. 9, pp. 133-4). Her one objection (“we must be at the very center of a matter…region of the universe”) operates on the mistaken assumption that such a region would be exactly as small as the visible universe: if these regions are trillions of lightyears across, we need be nowhere near the center of ours. It is also a known fact that such a glow would be created by, as Boslough puts it, “the continuous emission and absorption of electrons by the strong magnetic fields” of galaxies and their intergalactic filaments–fields and filaments recently proved to exist. However, as intriguing as these theories are, all the evidence taken together still more strongly supports the Big Bang interpretation.
 cf. Fox, op. cit., n. 9, pp. 150-2.
 Science News, July 25, 1998, p. 55 (cf. also January 10, 1998, p. 20): “maps of the far-infrared background glow had already demonstrated that visible-light images drastically underestimate the amount of star formation,” and based on submillimeter photography, “at early times in the universe, stars were born at a rate five times higher than visible-light studies have indicated,” etc. Also: J.K Webb, et al., “A High Deuterium Abundance at Redshift z=0.7,” Nature, 17 July, 1997, pp. 250-2: finds far more hydrogen isotopes than there should be; and J. Michael Shull, Lennox Cowie and Antoinette Songaila show there are far more heavy elements strewn throughout the intergalactic voids than anyone thought (Shull, op. cit. n. 11); and Ron Cowen, “All Aglow in the Early Universe,” Science News, May 27, 2000, pp. 348-50: “most of the light emitted by the very first galaxies in the cosmos is much too dim to be seen today. Objects that were bright long ago appear faint now, and less brilliant objects are entirely invisible,” p. 349.
 P. de Bernardis, et al., “A Flat Universe from High-Resolution Maps of the Cosmic Microwave Background Radiation,” Nature, 27 April, 2000, pp. 955-9. These results (from BOOMERANG) have been confirmed by a second balloon probe (MAXIMA), cf. Science News, June 3, 2000, p. 363.
 Riccardo Giovanelli, “Less Expansion, More Agreement,” Nature, 8 July, 1999, pp. 111-2. The “constant” lies in the range of 66-70 km/sMpc, which was not good news, for “values…above 60 have the embarrassing feature of yielding an age for the Universe since the Big Bang that is exceeded by the oldest stars in our Galaxy” unless the expansion is accelerating, and as it happens, it is. Further research has made both observations indisputable: cf. “Age of the Universe: A New Determination” Science News 160:17 (October 27, 2001), p. 261. It is 95% certain that the universe cannot be more than 14.5 billion years old (and that is the uppermost limit–its probable age is only 14 billion). This research also demonstrated that the hubble constant cannot be less than 55 and is probably around 72. See L. Knox, N. Christensen, & C. Skordis, “The Age of the Universe and the Cosmological Constant Determined from Cosmic Microwave Background Anisotropy Measurements,” updated Feb. 2002.
 “Physics Bedrock Cracks, Sun Shines In,” Science News 159:25 (23 June 2001). See also n. 21 and: “Laboratory measurements and limits for neutrino properties“; Super-Kamiokande at UC Irvine and New Results from Neutrino Oscillations Experiment.
 Wane Hu, Nature, 17 April, 2000, pp. 939-40. Cf. also, Ron Cowen, “A Cosmic Crisis? Dark Doings in the Universe,” Science News 160:15 (Oct. 13, 2001), pp. 234-6). Cf. also Science News, June 7, 1997, pp. 354-5.
originally found at https://infidels.org/library/modern/richard_carrier/bigbangredux.html