Chronology of the Universe

At Home In The Universe Science, IT, Nature

Part 6: From a few millionths of a second after the Big Bang onwards, the chronology of the development of the universe is being studied, understood and mapped by modern physics.

It is convenient to divide the evolution of the universe into three phases.

Artists illustration of the expansion of the Universe. Credit: NASA, Goddard Space Flight Center
Artist’s illustration of the expansion of the Universe. Credit: NASA, Goddard Space Flight Center

In the first phase, the very earliest universe is so hot or energetic that initially no matter particles exist, or can exist perhaps only fleetingly. Space-time itself expands during an inflationary epoch, due to the immensity of the energies involved. This inflationary epoch is the period in the evolution of the early universe when, according to the inflation theory, the universe undergoes an extremely rapid exponential expansion. The inflationary epoch lasts from 10−36 seconds after the Big Bang to sometime between 10−33 and 10−32 seconds.

Gradually the immense energies cool, leading finally to the first elementary particles of matter (quarks, gluons, electrons).

In the second phase, after the cosmic inflation ended, the early universe is filled with a quark-gluon plasma. From this point onwards the physics of the early universe is studied, better understood and less speculative.

For a few millionths of a second after the Big Bang, the universe consists of a hot soup of elementary particles, called quarks and gluons. A few microseconds later, those particles begin cooling to form protons and neutrons, the building blocks of matter. Over the past decade, physicists around the world have been trying to re-create that soup, known as quark- gluon plasma (QGP), by slamming together nuclei of atoms with enough energy to produce trillion-degree temperatures.

“If you’re interested in the properties of the microseconds-old universe, the best way to study it is not by building a telescope, it’s by building an accelerator,” says Krishna Rajagopal, an MIT theoretical physicist who studies QGP.

Quarks and gluons, though they make up protons and neutrons, behave very differently from these heavier particles. Their interactions are governed by a theory known as quantum chromodynamics, developed in part by MIT professors Jerome Friedman and Frank Wilczek, who both won Nobel prizes (respectively 1980 and 2004) for their work. However, the actual behavior of quarks and gluons is difficult to study, because they are confined within heavier particles. The only place in the universe where QGP exists is inside high-speed accelerators, for the briefest flashes of time.

In 2005, scientists at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, reported creating QGP by smashing gold atoms together at nearly the speed of light. These collisions can produce temperatures up to 4 trillion degrees — 250,000 times warmer than the Sun’s interior and hot enough to melt protons and neutrons into quarks and gluons. The resulting super-hot, super-dense blob of matter, about a trillionth of a centimeter across, could give scientists new insights into the properties of the very early universe. So far, they have already made the surprising discovery that QGP is a nearly frictionless liquid, not the gas that physicists had expected. By doing higher-energy collisions, scientists now hope to find out more about the properties of quark gluon plasma and whether it becomes gas-like at higher temperatures. They also want to delve further into the very surprising similarities that have been seen between QGP and ultra-cold gases (near absolute zero) that MIT’s Martin Zwierlein and others have created in the laboratory. Both substances are nearly frictionless and theoretical physicists suspect that string theory may explain both phenomena, says Rajagopal. At the Large Hadron Collider in Geneva, MIT faculty Gunther Roland, Wit Busza and Boleslaw Wyslouch are among the physicists planning to double the temperature achieved at Brookhaven, offering a glimpse of an even-earlier stage of the universe’s formation.

Continuing our story, the quark–gluon plasma that composes the universe cools, until hadrons, including baryons such as protons and neutrons, can form. The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe.

After most leptons and anti-leptons are annihilated at the end of the lepton epoch, the energy of the universe is dominated by photons. During the photon epoch the temperature of the universe falls to the point where atomic nuclei can begin to form.

Gradually the current fundamental forces we know take their present forms and the full range of complex and composite particles we see around us today becomes possible, leading to a gravitationally dominated universe, the formation of stable atoms and “the afterglow of creation”, the cosmic microwave background radiation we can detect today, called the oldest fossil in creation.

Tune your TV between the stations and watch the static or “snow” on your screen: you are watching the CMBR, a leftover of the Big Bang!


Hydrogen and helium atoms begin to form as the density of the universe falls. This is thought to have occurred about 377,000 years after the Big Bang.

The third phase starts after a ‘short’ dark age (from 300,000 to 150 million years) with a universe whose fundamental particles and forces are as we know them and witnesses the emergence of large scale stable structures, such as the earliest stars, quasars, galaxies, clusters of galaxies and superclusters and the development of these to create the kind of universe we see today.


How do such structures arise? Gravity amplifies slight irregularities in the density of the primordial gas and pockets of gas become more and more dense, even as the universe continues to expand rapidly.

These small, dense clouds of cosmic gas start to collapse under their own gravity, becoming hot enough to trigger nuclear fusion reactions between hydrogen atoms, creating the very first stars.

Large volumes of matter collapse to form galaxies and gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters.

The first stars are short-lived supermassive stars, a hundred or so times the mass of our Sun, known as Population III (or metal-free) stars. These first stars form and start the process of transforming the light elements, that were formed in the Big Bang (hydrogen, helium and lithium), into heavier elements. However, as yet there have been no observed Population III stars and understanding of them is currently based on computational models of their formation and evolution.

Fortunately, observations of the Cosmic Microwave Background Radiation can be used to date when star formation began in earnest.


Analysis of such observations, made by the European Space Agency’s Planck telescope, as reported by BBC News in early February 2015, concludes that the first generation of stars lit up 560 million years after the Big Bang.

On July 11, 2007, using the 10-meter Keck II telescope on Mauna Kea, Richard Ellis of the California Institute of Technology at Pasadena and his team found six star forming galaxies about 13.2 billion light years away and therefore created when the universe was only 500 million years old.


Eventually, Population II and then Population I stars also begin to form, from the material from previous rounds of star-making. Larger stars burn out quickly and explode in massive supernova events, their ashes going to form subsequent generations of stars.

On a far, far longer timescale, the present Stelliferous Era or the Era of Stars will end, as stars eventually die and fewer are born to replace them. As with interpretations of what happened in the very early universe, advances in fundamental physics are required before it will be possible to know the ultimate fate of the universe with any certainty.

Various theories suggest a number of subsequent possibilities, like Big Rip, Big Crunch and Big Freeze and Ages gloomily called the Degenerate Era, the Black Hole Era and the Dark Era.

Thanks to Wikipedia for the Chronology of the universe and to MIT News

ShantiShanti is a regular contributor to Osho News

All articles of this series can be found in: At Home in the Universe

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