The universe continues to expand
.01 secs to a second after the bang (ATB) – matter triumphs over antimatter[1]
At about 0.01 s post BB, the temperature had dropped to about a trillion degrees, and quarks could bind together to form protons and neutrons[2] without instantly being ripped apart again. However, antiprotons and antineutrons were also being formed, and whenever a particle met an antiparticle, each having an opposite charge, they mutually annihilated, vanishing into a pair of photons. These photons then spontaneously converted their energy back into mass, producing a new proton/anti-proton pair, which sped away from each other. As the universe kept cooling, eventually the temperature dropped enough with the result that the photons didn’t have enough energy to make a new pair of particles. When that happened, the particles and antiparticles annihilated one last time[3].
For reasons we still don’t really understand, a tiny imbalance of matter over antimatter was the result. For every 30 million antiparticles there were 30 million and one particles. After the annihilation was complete, only this small amount of left-over matter remained. The rest had disappeared into radiation. About 99% of the photons in the universe are the result of these big bang annihilations[4]. About a second ATB, there was about one proton or neutron for every billion photons or electrons or neutrinos. If matter and antimatter were perfectly symmetrical, the cooling of the universe would have resulted in particle/antiparticle annihilation that would have left the universe filled only with photons. Accelerator experiments have revealed that the laws of physics are ever so slightly biased in favour of matter, and in a still to be understood series of particle interactions very early on, this slight bias led to the creation of the quark excess[5].
One hypothesis as to how this preponderance of matter over antimatter may have come about has to do with the rare nuclear physics phenomenon known as double beta decay. In single beta decay, when radioactive nuclei settle into more stable configurations by changing a neutron into a proton, an atom emits an electron along with an antineutrino.
However, if the neutrino is its own antiparticle, as is suggested may be the case, the same antiparticle emitted in the first decay can be absorbed in the second, the result being a double beta decay that does not emit any neutrinos or antineutrinos. This form of neutrinoless decay has not yet been convincingly observed. However, if one day it is demonstrated that within the realm of neutrinos, matter and antimatter are the same and neutrinos are their own antiparticles, the balance of matter and antimatter could be altered, potentially explaining why there is more matter than antimatter and how matter came to dominate the universe in the universe [6].
Experiments are under way to determine how long neutrons live before decaying into other particles [7]. Inside an atomic nucleus, a typical neutron can survive for a very long time and may never decay, but on its own it will transform into other particles within 14 minutes - more or less. Two main types of experiments are under way: bottle traps count the number of neutrons that survive after various intervals, and beam experiments look for the particles into which neutrons decay. However, the two experiments, conducted by different teams in different parts of the world, cannot agree as to a result. They come up with different outcomes as to the decay rate. They vary by up to eight seconds. Could the answer be that some neutrons may have metamorphosed into particles never before detected? This has important repercussions for the formation of the universe and the process of big bang nucleosynthesis, as discussed immediately below.
Two or three minutes ATB - the first nuclei[8]
Meanwhile, the standard and inflationary models are now at a point where they may be said to coalesce.
By the time the universe was a couple of minutes old it was filled with a nearly uniform hot gas composed of roughly 75% hydrogen, 23% helium and small amounts of deuterium and lithium[9]. When the temperature dropped to about 10 billion degrees, the strong nuclear force caused the protons and neutrons of these elements to fuse together to form the first atomic nuclei (hadrons). Protons and neutrons fused to form deuterium, then helium-3 and helium-4, but nothing else, there being no stable nucleus containing five particles, so when an unstable nucleus is struck by another particle, the whole lot was again split apart[10]. At this point in time, the rest of the plasma (about 75%) stayed in the form of protons that would eventually become hydrogen atoms. All the rest of the elements in the periodic table formed billions of years later in stars and stellar explosions[11]. This was the period known as primordial or big bang nucleosynthesis.
This is where the discussion on the proton’s decay rate alluded to above assumes peculiar importance[12]. At this early stage when the universe was in the process of formation, had neutrinos decayed at a rate faster than the universe cooled, there would have been no neutrons left when the universe reached the right temperature to form nuclei. Only the protons would have remained and the cosmos would be composed almost entirely of hydrogen. But if the neutron lifetime were much longer than the time required to cool sufficiently for big bang nucleosynthesis, the universe would have an overabundance of helium, which in turn would have affected the formation of the heavier elements involved in the evolution of stars and ultimately life. So the issue as to the neutron’s decay rate is far from being academic. It is of critical importance to the understanding as to how the universe came into being.
A dense fog of radiation
The universe continued to expand and cool giving rise to longer and longer wavelengths corresponding to cooler and cooler radiation in accordance with the Planck formula, which holds that a wave’s frequency is proportional to the intensity of the minimum amount of energy it can have. By the time the universe was three minutes old, nearly all the neutrons were combined into nuclei while most of the protons were still free. The universe consisting of hydrogen and helium continued to expand in a fog of radiation that continued to cool, but it was still too hot for electrons to combine with the protons and nuclei to form atoms, so the whole universe was filled with a glowing, blindingly bright, plasma of particles, mostly protons and electrons. Because electrically charged particles have the ability to jostle photons – particles of light – this plasma would have appeared opaque, or to borrow Greene’s descriptive terminology, would have provided a diffuse glow similar to a car’s high beams cloaked by a dense fog. The universe continued to grow and cool in this manner for the next few hundred thousand years[13].
Big bang plus 380,000 years - atoms formed, photons as radiation released, but cooling temperatures bring on a Cosmic Dark Age
When the temperature had cooled to about 3,000 degrees some 380,000 years after the bang, the swarming electrons slowed down enabling them to be captured by the atomic nuclei, mostly the lighter elements: hydrogen and helium. This event (known as recombination) was a key transformation. Because protons and neutrons have equal but opposite charges, their atomic unions are electrically neutral[14]. The formation of atoms meant that the charged obstructions disappeared and the universe changed from being opaque to being largely transparent. The formation of atoms enabled the cosmic fog to clear and the heat of the big bang known as the Cosmic Microwave Background Radiation (CMBR), the product of so many matter-antimatter annihilations, to be released as a “luminous echo of the big bang”.
"The most accurate picture yet on the Universe’s Dark Age"
If you are one for oxymorons, imagine if you can a burst of energy unimaginably small about the size of a single atom “flipping over”, the first flash of energy after the big bang, travelling for 12 billion years through stars and plates, galaxies and black holes until it reaches earth. The search is now on to find that extremely faint energy emitted just before the moment of first ignition.
Radiation from the first stars killed the signal’s source, contributing to the cosmic Dark Age, and looking for areas where the signal stopped, one should be able to spot the first stars in the universe. An Australian team including scientists from America, Japan and India, is using data from the Murchison Widefield Array, a collection of small antennas in the West Australian Desert in an effort to locate it, and in the process building the most accurate picture yet on the Universe’s Dark Age.
The universe's very first molecule discovered
In May 2016 scientists in fact achieved verification of the first molecule that formed minutes after the Big Bang. The helium hydride ion (HeH+) the scientists detected wasn't the original one created just after the Big Bang, but has the same molecular structure - helium combined with hydrogen - they theorised formed at the time..
As temperatures cooled and the first atoms helium, hydrogen and lithium, formed, they existed separately, but scientists knew that, in order to create the elements we see today, there had to be a bonding of elements. They theorised that the first would be a joining of helium and hydrogen. But they couldn't find any trace of this anywhere in space. Scientists knew they had to look for it somewhere where conditions mimicked the early universe, and one of the best candidates was NGC 7027.
The formation of HeH+ was the universe's first molecular bond, and paved the way for the creation of other molecules. When it reacted with a hydrogen atom, for example, it created H2, or molecular hydrogen - marking the beginning of the modern universe. It kicked started things, as it were.
After looking for many years, they finally found this molecule in NGC 7027, a planetary nebula (so-named because the star at the centre looks like a planet) that lies 3,000 light years from Earth in the constellation Cygnus. The nebula is only 600 years old, but has some of the best conditions where HeH+ might be found. The researchers plan to search for more HeH+, which could exist in the heart of our galaxy.
This is credited as being the first step on a path of increasing complexity that ends up with very complicated things in the universe, like very complicated molecules, like DNA, not that the helium hydride led directly to DNA, but it basically shows that what started out as “a very boring, smooth universe just containing atoms” can end up with more complicated structures, molecules, and ultimately, as we know, life.[15]
Photons released to travel freely
In any event, following recombination and the consequent formation of atoms, radiation in the form of photons was released to travel freely through space and has been doing so ever since. It is isotropic in the sense that it strikes the earth uniformly from all directions with its Planck curve corresponding to cooler and cooler temperatures. The hot soup of subatomic particles which hitherto existed is one reason why we will probably never be able to “see” right back to the bang, because until this time photons were not free to travel freely across space. Until this happened, we would see nothing but an opaque wall when the first atoms were made[16]. The microwave photons are in fact the oldest we can ever hope to see, because their elder brethren were trapped by the foggy conditions that prevailed during earlier epochs.
When particles of light (photons) cool, their vibrational frequencies decrease which means they change colour: violet photons shift to blue, then to green, yellow, red and then into the infrared, the microwave and finally into radio frequencies[17], and once the temperature fell below a few thousand degrees, the radiation shifted into the infrared, and nothing in the universe was hot enough to produce visible light. The universe was completely dark. This cosmic Dark Age lasted for perhaps a hundred million years.
The disparity in time between the binding together of the particles forming nuclei (approximately one minute ATB) and atoms (380,000 years ATB) is due to the huge difference between the force that binds nuclei and that which binds atoms together. In nuclei, protons and neutrons are attracted to each other via the strong nuclear force, which is about 100 times stronger than the electro-magnetic force, which binds atoms together, electrons being electrically attracted to protons[18].
[1] I acknowledge my indebtedness to Helen Johnston's CCE course Origins: From the Big Bang to Life, March 2011 in the formulation of this page.
[2] These composite particles are known as hadrons.
[3] Helen Johnston, CCE Course, From the Big Bang to Life, March 2011.
[4] Best, op cit, p 8. See also Michael S Turner, op cit, 41
[5] Turner, Ibid
[6] Martin Hirsch et al, “Ghostly beacons of new physics”, Scientific American, Special Collector’s Edition, August 2013, 20-27.
[7] See Geoffrey L Greene and Peter Geltenbort, “The neutron enigma”, Scientific American, April 2016, 28-33.
[8] On the first three minutes, see also Brian Greene, The Hidden Reality – Parallel Universes and the Deep Laws of the Cosmos, Alfred A Knopf, New York (2011), 38 ff. The First Three Minutes is an evocative phrase in any account of cosmic origins and also the title of a book on the subject by the Nobel laureate Steven Weinberg. Flamingo, Cambridge, Mass 1976, and is also available in PDF form on the internet (URL too long to reproduce here).
[9] Greene (2005), 171.
[10] Helen Johnston, CCE Course, From the Big Bang to Life, March 2011.
[11] Michael S Turner, op cit, 40.
[12] As also discussed in Greene and Geltenbort, “The neutron enigma”, Scientific American, op cit, 28 at 33.33.
[13] Greene (2011), 38-39.
[14] Greene (2011), 39.
[15] Nicole Mortillaro, "Astrophysicists find elusive molecule that 'kick-started' the universe": https://www.msn.com/en-au/news/techandscience/astrophysicists-find-elusive-molecule-that-kick-started-the-universe/ar-BBW4ghv?ocid=spartandhp
It took about 3 years for the discovery to be verified and reported. A helpful explanatory video appears on the website.
[16] Gleiser, 73.
[17] Ibid, 39.
[18] Greene (2011), 65.