Big Bang cosmology arguably started in 1917. Vesto Slipher had measured 21 galactic redshifts by 1917. That’s when Albert Einstein wrote his cosmological considerations paper and Willem de Sitter came up with the de Sitter universe. The next year in 1918 Erwin Schrödinger came up with his cosmic pressure. In 1922 Alexander Friedmann came up with a non-static universe. In 1924 he came up with negative and positive curvature, and Knut Lundmark came up with an expansion rate within 1% of measurements today. In 1927 Georges Lemaître wrote his French paper. In 1928 Howard Robertson wrote his paper On Relativistic Cosmology. In 1929 Edwin Hubble came up with a relation between distance and radial velocity among extra-galactic nebulae. In 1931 Einstein conceded that the universe wasn’t static, and Lemaître proposed a primitive atom. Soon Lemaître was talking about the disintegration of the primeval atom and the exploding cosmic egg, suggesting that cosmic rays were the result. The Big Bang was born.
Big Bang image from the Open University, see physics and astronomy – The Big Bang
Oddly enough, not much happened for a while, even though Einstein gave his endorsement. He attended Lemaître‘s presentation in Pasadena in 1933 and said it was “the most beautiful and satisfactory explanation of the creation that I have ever heard”. Perhaps the hiatus was because Lemaître was a priest. Perhaps his exploding cosmic egg sounded too much like Genesis. Perhaps it suffered from a Chicken and Egg problem. Where did this cosmic egg come from?
Gamow takes up the baton
It wasn’t until 1946 and George Gamow that things moved on. Gamow had been a student of Friedmann’s. He wrote a one-page paper on the Expanding Universe and the Origin of Elements. He said abundance should decrease with atomic weight, but that this doesn’t happen in the second half of the periodic table. He also said the expansion must have been fast enough to reduce the initial high density by an order of magnitude in about a second, and that the conditions necessary for nuclear reactions existed for a very short time – less than the beta-decay period of free neutrons. He said “We can anticipate that neutrons forming this comparatively cold cloud were gradually coagulating into larger and larger neutral complexes which later turned into various atomic species by subsequent processes of β-emission”. He finished by saying the high abundance of hydrogen must have resulted from the competition between neutron decay and the “coagulation process through which these neutrons were being incorporated into heavier nuclear units”.
Alpher Bethe Gamow
Gamow wrote another one-page paper in 1948 with Ralph Alpher and Hans Bethe. It was called The Origin of Chemical Elements. They said the elements must have originated “as a consequence of a continuous building-up process arrested by a rapid expansion and cooling of the primordial matter”. They talked of compressed neutron gas decaying into protons and electrons with capture of the remaining neutrons by protons to form deuterium nuclei, then subsequent neutron captures resulting in heavier and heavier nuclei. They said the observed slope of the abundance curve must be related to the time period permitted by the expansion process rather than the temperature of the neutron gas. And that individual abundances must depend not so much on their intrinsic stabilities as on the values of their neutron-capture cross-sections. They gave an equation governing the process along with a relative abundance chart, and said the process must have been completed when the temperature of the neutron gas was still high, otherwise the observed abundances would have been strongly affected by slow neutrons. This was the famous Alpher Bethe Gamow paper, and it was wrong. That’s because of the mass-5 roadblock. No element has a stable isotope with an atomic mass of five, so the continuous buildup idea just didn’t work. Furthermore it starts with a neutron gas. Where did this neutron gas come from?
Alpher Herman Gamow
Philip “Jim” Peebles gives a wealth of detail in his 2013 paper Discovery of the Hot Big Bang: What happened in 1948. He says the Alpher Bethe Gamow paper assumes cold Big Bang cosmology and makes no mention of thermal radiation. But he also tells us of no less than ten papers in 1948 by Alpher, Bethe, Gamow, and Robert Herman:
Image from Jim Peebles’ Discovery of the Hot Big Bang: What happened in 1948
They include Evolution of the Universe where Alpher and Herman said “the temperature in the universe at the present time is found to be 5°K”. This is taken to be the first prediction of the cosmic microwave background radiation or CMBR, which has been measured at 2.725°K. Peebles however says there are issues: “Their numerical value is not significant because it depends on the present baryon density, which was very uncertain, and they compute element buildup along the wrong path”. He also quotes Fred Hoyle saying “the age of the universe in this model is appreciably less than the agreed age of the Galaxy. Moreover it would lead to a temperature of the radiation at present maintained throughout the whole of space much greater than McKellar’s”.
The temperature of space
For more information see the Jodrell Bank introduction to cosmology article where you can read about the temperature of space. It starts with Charles Fabry in 1917: “For interstellar space in our Galaxy he calculated this to be 3° absolute, or 3 K in modern notation”. You can also read about a temperature with a very restricted meaning and about Andrew McKellar. He wrote a paper in 1940 on the Evidence for the Molecular Origin of Some Hitherto Unidentified Interstellar Lines. On page 6 he talked about spectral lines R(0) and R(1) and said “if R(1) is not more than one-third, one fifth, or one-twentieth as intense as R(0), the maximum ‘effective’ temperature of interstellar space would be 2.7° K, 2.1° K, and 0.8° K, respectively”. The Jodrell Bank article also talks about ylem and after. It says as Gamow’s team studied the big bang they realised that the ylem could not have been pure neutrons, and in fact mostly consisted of gamma-ray photons. It also says they “never proposed an experimental search for these photons. One reason was that Gamow had heard about Eddington’s ‘temperature of space’ and thought that this would be difficult to disentangle from the relic photons from primordial nucleosynthesis”. The article also says that Gamow, like McKellar, “failed to spot the enormous difference between starlight with energy density equivalent to a 3 K blackbody, and a genuine blackbody spectrum”. And that “Alpher and Hermann had privately consulted radio astronomers and experimental physicists, and were told that the measurement was impossible”. The article goes on to say the general attitude of astronomers and physicists at the time was that a highly speculative theory of “creation” had failed.
Fred Hoyle and the steady state
That was perhaps in part due to the competition from Fred Hoyle and others. Hoyle was into stellar nucleosynthesis, and wrote a paper in 1946 on The Synthesis of the Elements from Hydrogen. He was deeply involved in the field and a co-author of the famous B²FH paper. The bottom line is that stellar nucleosynthesis trumped Big Bang nucleosynthesis because the latter more or less stops with helium. That’s perhaps why Hoyle was so critical of the Big Bang. And perhaps why in 1948 he came up with a steady state theory. The irony of course is that in 1949 he used the phrase “Big Bang” in a disparaging fashion on BBC radio, and the name stuck. He was happy enough with the expanding universe, but he didn’t like the idea that the universe had a beginning. I can empathize with that. He was also skeptical of the way the CMBR was presented as proof of the Big Bang. He said it could have been caused by something else. I have some sympathy for that too, because as they say, you can’t prove a theory right, you can only prove it wrong. All the more so because in 1940 McKellar had said the maximum effective temperature of interstellar space would be 2.7° K. However I have no sympathy for Hoyle’s “creation field” where matter pops into existence spontaneously, like worms from mud. Or for Bondi and Gold’s “perfect cosmological principle”. Because as per Sandra Faber’s counterbalance article about the steady state universe, quasars and radio galaxies are more frequent at large distances and so earlier times. So we have good evidence that the universe has changed, and thus is not a steady-state universe.
Discovery of the CMBR
That’s perhaps why the discovery of the cosmic microwave background radiation is generally accepted as good evidence for Big Bang cosmology. Alan Guth gives an account in his 1997 book The Inflationary Universe. On page 58 he tells us how Arno Penzias and Robert Woodrow Wilson were refurbishing Bell Labs’ 20-foot Holmdel Horn antenna at Crawford Hill in New Jersey for use in astronomy. They converted it into a Dicke radiometer using a “cold load” dewar of liquid helium at 4.2° K. By switching the receiver from the cold load to the antenna they could determine the true signal from the antenna. They ran a test tuned to a wavelength of 7.35cm, expecting their background subtraction to leave a zero signal. However the system “seemed to be picking up some unforeseen source of microwave signal”. It was the same in all directions and it didn’t vary with the time of day or season. Guth tells how 30 miles away in Princeton a group of physicists spearheaded by Robert Dicke himself had regular Friday-night discussions followed by beer and pizza. Dicke favoured a cyclical cosmology, whereby at the time of the bounce the universe must have been so hot that atomic nuclei were shattered into protons and neutrons. Hence “there must be a radiation background – an afterglow of this intense heat – that would continue to permeate the universe”.
Big bounce image from New Scientist article From big bang to a big bounce by Anil Ananthaswamy. also see Baez
Dicke got two young researchers Peter Roll and David Wilkinson to look for the background radiation using a 1ft horn antenna on the roof, and asked Jim Peebles to “think about the theoretical consequences”. The result was a 1965 paper Cosmology, Cosmic Blackbody Radiation and the Cosmic Helium Abundance which predicted a blackbody spectrum. Unfortunately Peebles couldn’t get it published because of an issue with credit given to prior work. However he gave a talk in Baltimore, and in the audience was his old friend Kenneth Turner. Turner later mentioned it to a fellow radio astronomer Bernard Burke, who told his friend Arno Penzias. Then “Dicke received a phone call from Penzias, and the Princeton crew was soon on the road to Crawford Hill. When Dicke and his collaborators saw the results Penzias and Wilson were obtaining, they were quickly convinced that the Bell Labs team had made the crucial discovery”. The two groups decided to submit back-to-back papers to the Astrophysical Journal. The papers appeared in July 1965. They were A Measurement of Excess Antenna Temperature at 4080 Mc/s by Penzias and Wilson, and Cosmic Black-Body Radiation by Dicke, Peebles, Roll, and Wilkinson. Guth says “the echo of the Big Bang had been found”.
It might have been found previously. In the 1965 NASA cosmic hiss article you can read how Andrei Doroshkevic and Igor Novikov published a Big Bang study saying the remaining heat would now be between 1 and 10 degrees Kelvin. They even proposed the use of the Holmdel horn measurements made in 1961 by Edward Ohm, who “had already identified in his data what seemed to be a 3.3 degrees Kelvin background radiation”. There are conflicting reports about that, but such is life. The article also says “Ten years ago Émile Le Roux reported a microwave background radiation of 3 degrees Kelvin, plus or minus 2 degrees at the Nançay Radio Observatory”. And that “In 1957 it was Tigran Shmaonov who nearly made the discovery. He reported measuring background temperature of 4 degrees Kelvin, give or take 3 degrees”. Ned Wright says that the claims that Le Roux measured the CMB in the 1950’s are incorrect. Whatever the truth of it all, something that is true is that the paper by Dicke et al talked about an oscillating universe. So according to them the evidence for the Big Bounce had been found. However they covered the bases by saying that even if the universe had a singular origin it might have been extremely hot in the early stages. But they didn’t say much about previous work by Gamow and his collaborators.
In a 1984 oral history interview with Martin Hewitt, Peebles wondered if the referee who rejected his 1965 paper was Gamow himself, but Hewitt said it wasn’t. Hewitt had previously interviewed Ralph Alpher and Robert Herman who said they reviewed Peebles’ paper and were appalled “because there was absolutely no indication that he had read any of our early work”. They were still unhappy with the references to their work in 1965 paper by Dicke et al. Alpher said “he did refer to the fact that you, Gamow and I had discussed an early hot, dense universe, but that was about it. There was no reference at all to any of the other stuff that we had published”. The interview makes it clear that they were bitter. The irony is that in Jean-Pierre Luminet’s rise of big bang models (5): from Gamow to today you can read that whilst Penzias and Wilson were awarded a Nobel prize in 1978, “at the moment of their discovery, they believed instead in the theory of continuous creation”. See PBS for a mention of that. Or the 2005 John Oakes interview with Penzias and Wilson where they say “along came this wacky idea from Princeton. They were actually thinking about multiple big bangs”. That’s where Wilson said cleaning up after the birds “did knock a little bit off our measured temperature. There was some radiation from the bird droppings”. Genesis and Hebrew revelations were also mentioned. For some more irony see Penzias’ Nobel lecture, where he said “Hoyle concluded that about ninety percent of the helium found in stars must have been made before the birth of the galaxy”. And that “attention was turned to helium formation in the early stages of an expanding universe, reviving work begun by George Gamow some sixteen years earlier”. Because of Hoyle’s helium problem, the Big Bang was born again.
The Big Bang was born again
The Big Bang was born yet again with COBE in 1992, which measured the CMBR black-body curve and the anisotropy that was said to be essential for structure formation. It was accompanied by a great deal of media coverage including pronouncements such as “the discovery of the century” and “seeing the face of God”. It led to Nobel prizes in 2006, to WMAP operating up to 2010, and to Planck operating up to 2013. Nowadays there’s plenty of articles about the Big Bang. Such as The Big Bang article on the NASA astrophysics website. Or the DAMTP Hot Big Bang article. Or the Scholarpedia modern cosmology article by George Ellis and Jean-Philippe Uzan. However the various articles sometimes cause confusion. The NASA article says one problem that arose from the original COBE results and persisted with WMAP was that the universe was too homogeneous. That comes as a surprise. The DAMTP article says “about ten billion years ago, the Universe began in a gigantic explosion”. Ten billion years ago? That doesn’t sound right. The Scholarpedia article has Hot Big Bang down as the third epoch, after Start and Inflation. That doesn’t sound right either, because in most articles the Big Bang is the thing that came first, before inflation:
Image by NASA, see NASA’s space place
There’s arguably more confusion in the NASA WMAP foundations of Big Bang cosmology article. It says “it is beyond the realm of the Big Bang Model to say what gave rise to the Big Bang”. But surely that’s what the Big Bang is all about? It’s the $64,000 dollar question. How did the universe begin? Or not, as the case may be. I think it’s the biggest mystery of them all. Particularly because of the supernovae observations that provided evidence of the accelerating expansion of the universe. If the expansion is speeding up, was it slower in the past? And was there a time when it was very slow?
God did it
See for example The 5 Biggest Questions About the Universe written by Dan Falk for NBC News. He asks questions such as What is Dark Matter? along with What is Dark Energy? and What’s Inside a Black Hole? I think we can get somewhere with such questions, in that when you read enough you can come up with some answers that make sense. Falk also asks What Came Before the Big Bang? and I think you can get somewhere with that too. Not however by saying things like God did it, which is a turtles-all-the-way-down non-answer pretending to be an answer. I say that because the word universe is derived from “uni” as in unicycle, and “verse” as in vice versa. It means turned into one. It means everything. Not just that part of everything that was created by some other part of everything. Hence God did it just doesn’t cut it.
A quantum fluctuation did it
Nor did Stephen Hawking’s 2010 book The Grand Design co-authored with Leonard Mlodinow. It caused a rumpus. See Hamish Johnston’s Physicsworld blog for M-theory, religion and science funding on the BBC. The crux of it is that Hawking said a quantum fluctuation did it, and it was still a turtles-all-the-way-down non-answer pretending to be an answer. But somehow it was worse, because it didn’t come from a bishop in a palace thumping his bible. It came from a scientist in a wheelchair plugging his popscience book. All the more so because in his 1974 Hawking radiation paper, Hawking talked of negative frequency waves propagating backwards to past null infinity. All the more so because he’d previously said the universe can be likened to a black hole in reverse, but he didn’t talk about the infinite gravitational time dilation and the zero “coordinate” speed of light at the event horizon. He didn’t talk about the very reason the black hole is black. Or about the upshot: moving away from a black hole across space can be likened to being in a universe expanding over time. Then when you play it backwards, as you move towards the black hole, you suffer ever-increasing gravitational time dilation, in line with the reducing speed of light. GRBs and firewalls apart, you end up with the frozen-star black hole, wherein it takes an infinite time to cross the event horizon, so you never ever do. And yet people say you do. They say you do a hop skippity jump over the end of time, and then you meet the point singularity in finite proper time. All this reminds me of a picture I saw. A picture where, if the black hole parallel is correct, something is missing:
Expansion of the universe image by NASA/WMAP, see Foundations of Big Bang Cosmology
What’s missing is the curve that gets flatter as it approaches the origin. The curve that describes a universe where the expansion was slower in the past. Like the M2 curve on page 9 of Ari Belenkiy’s 2013 paper about Friedmann. Or the static coasting universe in Jim Brau’s astronomy 123 course:
The image also shows a curve labelled “No Big Bang” which is associated with the big bounce. I don’t favour the big bounce because I can’t conceive of any way by which space might contract. Space is like some gin-clear ghostly elastic solid. It has its stress-energy, stress is directional pressure, and a stress ball expands when you open your fist. It doesn’t contract, no matter what the energy density. Because a gravitational field is a place where space is neither homogeneous nor isotropic. On the largest scale the universe is both, and always was. Because there once was a time when the speed of light was zero everywhere, and light can’t go slower than that. Nowadays the speed of light is not zero, and space expands. Not because of some kind of gravitational repulsion. But because at some fundamental level, space and energy are the same thing, like some kind of compressed gin-clear ghostly elastic solid. This doesn’t feature in the particle-physics Big Bang papers, nor does general relativistic time dilation, where the speed of light and the speed of all other processes depends on energy density. Yes Joao Magueijo and Andreas Albrecht came up with their VSL theory in 1998, but that gets it back to front. The speed of light in the early universe must have been slower, not faster.
The dawn of time
Come with me to the dawn of time. Outside our bubble of artistic licence the energy density is high. So very high that the outside environment is subject to infinite GR time dilation. It’s like the whole universe is like the frozen-star black hole. Note the word frozen. People tend to say the early universe was hot, but heat is an emergent property of motion. And in a frozen universe, there isn’t any motion. There is no heat. There is no radiation either, not when the speed of light is zero. This early universe where everything is frozen is a strange place. Motion is king, and if there is no motion there is no light. And if there is no light there are no photons, and no electrons too, because we make electrons out of photons in pair production. The same applies to protons and other particles, so there is no matter in the usual sense. Not only that, but clocks “clock up” regular cyclic motion, so without motion, there is no time. It’s hard to say what does exist. You can say energy exists, because that’s the one thing we can neither create nor destroy. But if nothing moves you can’t measure any distance, so does space exist? Maybe it’s space Jim, but not as we know it. It reminds me of the gravastar, where the central region is “a void in the fabric of space and time”. It’s like the early universe was like a black hole and nothing else. Like it was frozen space and a hole in space, with no space around it. Entropy is “sameness”, and everything is the same, so entropy is high. There’s no room for difference until the raum gets bigger. There’s no overall gravity either, because on the largest scale the energy density is homogeneous. And of course gravity doesn’t make space fall down. We do not live in some Chicken Little world. So the universe was never going to collapse.
Why is there something rather than nothing?
Yes, perhaps there was a phase change, like the way a block of C4 changes into a gas at 8000 feet per second. But as to why there was something that changed, I don’t know. I don’t know why there is something rather than nothing. I don’t know how the universe can be created from nothing. Ex-nihilo. Spontaneously, like worms from mud. But I suppose I know something happened to release the pressure, because here we are. Some say a quantum fluctuation did it, some say quantum tunnelling did it, and some say a phase change did it. I don’t know if any of them did it. But I can imagine an early universe expanding at some slow creeping pace. Like a pumpkin grows. If you were in that universe, you might be subject to what looked like infinite time dilation. So if you could make a claim, you might claim that this slow creeping pace was an infinite pace. After a while you might be subject to a huge but non-infinite time dilation. Then you might claim that the slow creeping pace was extremely rapid. And whatever you claim, later observers might claim the same, because they have no external yardstick. Then they might claim that the universe was created in finite proper time. Just as they might claim that it takes finite proper time to fall through the event horizon. When you never ever do. See the 1989 paper Did the big bang begin? by Jean-Marc Lévy-Leblond. Helge Kragh says the idea of two time scales was first discussed by Edward Arthur Milne, who distinguished between what he called kinematic and dynamic time.
It isn’t so cut and dried as people say
On page 10 of his 2013 paper Jim Peebles said singularity theorems “now convincingly argue against a bounce under standard general relativity theory”. I concur that we can argue against a bounce using standard general relativity. That’s because even if there was no measured redshift, I’d be saying the compressed gin-clear ghostly elastic solid just has to expand. But I do not buy singularity theorems, because I know light can’t go slower than stopped. So as for what banged? I’m not sure anything did. And as for how did the Universe begin? I’m not sure it ever did. So when it comes to the hot Big Bang theory, I’m not sure it’s as cut and dried as people say. Not when there’s stars that appear to be older than the universe. Not when there’s a lithium problem. Not when the doppler-shifted photon doesn’t lose any energy. Or the ascending photon. Or the CMBR photon:
Image by Tamara Davis and Scientific American, see Is the Universe leaking energy?
That’s because energy is conserved, because gravitational field energy is not negative, and because the universe is not some free lunch. But since I’m happy enough that it’s getting bigger and that old galaxies are different, I’m happy enough with the Big Bang. Even if it isn’t all cut and dried. Even if it didn’t bang, and was more of a whimper. All in all I’d say it’s the Big Bang Jim, but not as we know it.