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Cosmic Calendar: Galaxies and Stars

And the earth was without form, and void; and darkness was upon the face of the deep. (Genesis 1:2)

One billion years have passed on the Cosmic Calendar since the Big Bang. Much of that time has been spent in the darkness known as the Dark Ages. The universe created no new light since the time that the photons that were released during Recombination, the time when the primordial plasma of electrons and atomic nuclei coalesced into a sea of hydrogen and helium atoms. The universe continued to expand and cool. From this beginning, we might expect the universe to end in frozen darkness, yet when we look to the heavens we see myriad stars, blazing stellar furnaces.

What happened to change the cold, dark fate of the universe?

The early universe was also very homogeneous. The matter and energy in the universe was spread out smoothly, almost perfectly so. Small fluctuations did exist,1 yet the universe was so smooth—How smooth was it?—it would be like hiking the 4,500 kilometers2 from Los Angeles to New York in an alternate universe where the terrain was flatter than Kansas, like glass. The only landmark to relieve the monotony of the months of hiking across glassy plains would be a single blip of a hill perhaps seven stories tall.3

Yet the universe isn’t so plain and boring now. Everywhere we look we see a riot of diversity and complexity. How did unrelenting plainness become practically infinite diversity?

The Dark Ages weren’t an uneventful chapter in our story. Things were taking shape in the darkness.

Some of the answers to our questions may lie in the colossal inflation of the universe that happened during the Electroweak Epoch. If inflationary theory is correct, those tiny fluctuations in the early universe became the seeds for the structure that we see today. When the universe began to inflate to about 1026 times its size, these quantum fluctuations smaller than atoms got caught up in inflation. They grew to galactic proportions and started in motion the formation of structure.

In its early history, the universe was dominated by the expansion of the Big Bang. As time went on, another force began to assert itself at large scales: gravitation, the force that attracts all particles of matter to each other.4 Inflated quantum fluctuations created some places of greater density where more matter was packed into a small space. Because these places of greater density had more matter, they had greater gravity. Because they had greater gravity, they could attract even more matter. An so on.

In the inky darkness, the first structures began to take shape.

The first structures to form were what we see today as galaxy clusters. Dense clouds of hydrogen and helium gas and dark matter collapsed in on themselves due to the force of their own gravity. Like a runaway train, nothing was yet able to stop this collapse.

Galaxies and Quasars

Smaller parts of these huge clouds were denser than others and began the process of gravitational collapse at a smaller scale. As the clouds of atoms and dark matter collapsed, they began to spin, forming the first nascent galaxies, including our own Milky Way. As atoms fell into these swirling vortices, they collided with each other. These collisions created heat. The universe began to warm up again.

At the heart of most large galaxies is a supermassive black hole 105 to 1010 times as massive as the sun.5 A black hole is a region of space that is so dense that its tremendous gravity captures everything that comes too close. Even light is unable to escape its gravity once it gets too close.

These monsters had a voracious appetite, consuming tremendous amounts of matter in the early universe. As the black hole eats, it is thought to create very dense regions where the infalling matter has been packed together very tightly. This somehow releases tremendous energy and light. These bright phenomena are known as quasars, the brightest objects in the visible universe. The brightest quasar in our sky would be as bright as the sun if it were 33 light years away, almost 2 million times as far away as the sun. This particular quasar is therefore about 2 trillion times as bright as the sun or 100 times as bright as the average galaxy!

Of the 100,000 known quasars, the nearest to us is 780 million light years away. Most of them are much farther. Quasars were therefore more common in the early universe. Once they run out of matter to consume, quasars turn off. It seems that the age of quasars is over.


Parts of these galaxies were denser than others, so the process of collapse repeated itself yet again at smaller scales. Clouds of gas inside galaxies began to collapse in on themselves and spin just like their parent galaxies had. These spinning clouds of gas were the beginnings of the first stars. As they collapsed, they generated even more heat, enough to strip the electrons from the nuclei of atoms. These proto-stars eventually got dense and hot enough that the bare atomic nuclei began to fuse together to form heavier elements when they collided. When nuclei fuse together, some of their mass is lost and is converted directly into energy and light. Nuclear fusion is what lights the stars.

The stellar furnaces had been lit.

Nuclear fusion is also what finally stops the progress of gravitational collapse. Stellar radiation and heat exerts an outward pressure that balances against the inward pull of gravity. This dynamic equilibrium holds stars together and prevents them from collapsing altogether.

The radiation from newly formed stars began to heat up the gas between the stars. These gaseous atoms also lost their electrons and became ions again. The atoms were ions when they first formed, before they trapped electrons during Recombination. Today, almost all of the visible matter in the universe is ionized. For this reason, this period of reheating is known as Reionization, the time when the universe lit itself again and came out of the Dark Ages. On the Cosmic Calendar, this period began on January 5th and lasted until about today, the 27th (13,550–12,700 million years ago).

That is how the cosmos came to have the shape and light that we see.

As I began with a biblical passage, I must end with the Galaxy Song. How amazingly unlikely is our birth indeed!

We will continue our story at the end of August.

Observance Ideas

  1. These were on the order of 1 part in 100,000. []
  2. 2,800 miles []
  3. Depending on how wide it is, no taller than 40 meters. []
  4. Gravitation is commonly called gravity. []
  5. That is 100,000 to 100,000,000,000 times as massive as the sun. The sun is 332,950 times as massive as the Earth. []

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Cosmic Calendar: Delay

I planned to post today about the birth of stars and galaxies. It’s taking longer than expected. Rather than put out something rushed, I’ll wait until it’s ready. I have reason to believe that this won’t be a recurring problem.

In the meantime, check out the spectacular pictures of the Hubble Space Telescope Advent Calendar over at the best new blog of 2008, The Big Picture.


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Cosmic Calendar: Big Bang

Big Bang—1 January, 12:00 midnight

In its beginning, everything was a single point. This cosmic womb nurtured everything before it came to be. Every star; every planet; every flower; every lion, tiger, or bear; every Mozart, Einstein, or Madonna; every banana split, parfait, or brownie à la mode; every Illiad, I-Ching, or Bible; every hatred, joy, or love; every thing lay dormant within this primordial point. This is the story of how that point became our world, became us. This is our story.

According to current theory, all of what currently makes up the universe was packed into a space no larger than an atom. It doesn’t make sense to ask what was outside that point because even space was curled up inside this cosmic egg. It’s kind of like asking what’s north of the North Pole. Nor does it make sense to ask what happened before the point began to expand billions of years ago because time began its flow with the expansion. Our universe began in the in what is known as the Big Bang.

There was neither non-existence nor existence then. There was neither the realm of space nor the sky which is beyond. What stirred? Where? In whose protection? Was there water, bottlemlessly deep?

There was neither death nor immortality then. There was no distinguishing sign of night nor of day. That One breathed, windless, by its own impulse. Other than that there was nothing beyond.

Darkness was hidden by darkness in the beginning, with no distinguishing sign, all this was water. The life force that was covered with emptiness, that One arose through the power of heat.

Desire came upon that One in the beginning, that was the first seed of mind. Poets seeking in their heart with wisdom found the bond of existence and non-existence.

Their cord was extended across. Was there below? Was there above? There were seed-placers, there were powers. There was impulse beneath, there was giving forth above.

Who really knows? Who will here proclaim it? Whence was it produced? Whence is this creation? The gods came afterwards, with the creation of this universe. Who then knows whence it has arisen?

Whence this creation has arisen—perhaps it formed itself, or perhaps it did not – the One who looks down on it, in the highest heaven, only He knows or perhaps He does not know. (Nāsadīya Sukta, Rigveda)

Planck Epoch: We really don’t know what was happening in the first instant of the Big Bang 13,700 million years ago (Mya). The laws of physics as we know them break down during the Planck Epoch, the first 10-43 seconds after the Big Bang.1 This notation means one tenth multiplied by itself 43 times, or put another way, 0.000 000 000 000 000 000 000 000 000 000 000 000 000 000 1, an extremely, extremely small number. According to one theory, the universe was about 10-35 meters across.2 Because all of the matter and energy of the universe were packed into such a small space, it was also ludicrously hot: 1032 degrees Celsius. This notation means 10 multiplied by itself 32 times, or 100 000 000 000 000 000 000 000 000 000 000.3

It is impossible to fully comprehend how extremely small the universe was. To try, imagine a young child about one meter tall who holds in their cupped hand a sphere that is 10-35 meters across. Actually, the sphere is so small that the child’s hand would appear empty. Now, stretch the child and the sphere until the child is as tall as the diameter of the universe that we can currently see. Light travels very fast—186,000 miles per second—but it would take 93 billion years for light to travel from the child’s head to its foot. The sphere has stretched too, but if we were cradled in the child’s gigantic hand, the expanded sphere would still be too small for us to see. It would still only be a few atoms wide. This is unimaginably small.

Just as the universe was incomprehensibly small, the temperature was incomprehensibly large. For comparison, the core of our sun is only 107 degrees Celsius (i.e. 10,000,000 degrees). Multiply the heat of the sun by ten million. Hellish, we might be tempted to call it. Now multiply that hellish temperature by another million. And do it again. And again. And again. That is wicked hot!

All of the fundamental forces which govern our universe—gravity, electromagnetism, and the strong and weak nuclear forces—were equally strong and acted as one during the Planck Epoch. Today, gravity attracts all matter together and is the force that keeps the Earth circling the Sun and our feet firmly planted on the ground. The electromagnetic force governs light and magnetism. It makes radio, television, and cell phones possible and it holds our atoms together. The nuclear forces govern interactions within the nucleus of atoms. In the beginning, they were a single force.

Grand Unification Epoch: At the end of the Planck Epoch, an unimaginably small moment in time, this symmetry broke and gravity became weaker, separating itself from the other forces. (Please refer to the time line.)

As the universe expanded, it cooled down. But at this early stage immediately after the symmetry of universal forces was broken, the universe was still incredibly hot: 1027 degrees Celsius.

The Grand Unification Epoch is so named because the nuclear forces and the electromagnetic force were still unified in a single force called the electronuclear force. This epoch ended 10-36 seconds after the Big Bang when the strong force broke away from the others.

Electroweak Epoch: When the strong force separated from the others, the universe had cooled to about 1015 degrees Celsius and began a period of incredible expansion known as cosmic inflation. Its diameter increased in size by a factor of about 1026 in a small fraction of a second: by the end of this epoch something that had been the size of a millimeter grew to dwarf the Milky Way galaxy. Elementary particles were stretched to cosmic sizes, all within 10-32 seconds. Big Bang indeed.

Quark Epoch: This period began 10-12 seconds after the Big Bang when the electromagnetic and weak forces separated themselves and the four fundamental forces took their present form. The universe had cooled enough that subatomic quarks and gluons—the basic building blocks of matter—could condense out of its roiling energy. The universe was still too hot, however, for quarks to bind to each other to form neutrons and protons.

Hadron Epoch: One microsecond after the Big Bang, the universe had cooled enough to allow quarks to form hadrons such as protons and neutrons, the building blocks of the nuclei of all atoms. A nearly equal number of particles and anti-particles were forged from quarks in the primordial furnace. Particles and anti-particles have an explosive relationship. When they collide, both are annihilated in an explosion that releases tremendous energy. At this point, any hadrons that were destroyed in this way were replaced by others that were created in the heat of the early universe.

The universe continued to cool, reaching the point where hadrons were no longer being created. Most of the particles and anti-particles soon destroyed each other. When the figurative smoke cleared, all of the anti-hadrons were destroyed, but a small number of hadrons were left over. You and I and everything we see are partly made of those leftover hadrons. We exist because of an imbalance in particle/anti-particle destruction.

Lepton Epoch: One second after the Big Bang when most of the hadrons and anti-hadrons had destroyed each other, leptons (such as the familiar electrons) dominated the mass of the universe. The universe was still creating pairs of leptons and anti-leptons until three seconds after the Big Bang. In a now familiar story, most of the leptons and anti-leptons destroyed each other, but a small residue of leptons survived (to later create atoms later in the story).

Photon Epoch: After most of the pairs of leptons and anti-leptons had destroyed each other, photons—particles of light—made up most of the energy in the universe. Photons were still being scattered by electrons. The universe was therefore opaque: light couldn’t shine through the thick soup of scattering particles. Protons and neutrons began to form small atomic nuclei (e.g. helium, lithium, and beryllium).

Matter Domination—1 January, 12:03 AM

70,000 years after the Big Bang (3 minutes at the scale of the Cosmic Calendar), the amount of what we would call matter had grown to become equal to the amount of radiation (e.g. light) in the universe.

Recombination and Dark Ages—1 January 12:16 AM

Up to about 379,000 years after the Big Bang, the universe was filled with a plasma. In other words, the electrons were racing around unattached to atomic nuclei (contrary to our normal experience). It was just too hot for electrons to settle down. Lightning and the sun are two common examples of plasmas. Light is scattered by plasma, so light couldn’t travel very far in a straight line in the early universe. You could say that visibility was practically zero. If you were alive then (and could manage to stay alive), you wouldn’t be able to see the end of your nose.

After 379,000 years, the universe had cooled enough to allow atomic nuclei to capture electrons and form true atoms such as hydrogen and helium. The fancy name for this is recombination. This freed the light that had been held captive by the universal plasma. The universe became transparent; visibility was no longer zero. The consequent burst of light as the universe became transparent is known as the cosmic microwave background.

After the release of photons, the universe was plunged into darkness. No new light was being generated. This was the beginning of the Dark Ages.

Observance Ideas

  • Watch a fireworks show at the stroke of midnight and think about cosmology.
  • Make your own big bang (wink wink) at midnight… while thinking about cosmology.

Further Study

A Brief History of Time by Stephen W. Hawking

The Universe in a Nutshell by Stephen W. Hawking

Born With a Bang by Jennifer Morgan

Character of Physical Law by Richard Feynman

QED by RichardFeynman

  1. This unit period of time is known as a Planck time after Max Planck, the founder of quantum theory. []
  2. A unit of length known as the Planck length. []
  3. A unit of temperature known as the Planck temperature. Note that I use the Celsius scale because it is more familiar than the Kelvin scale to most readers. Even though the Kelvin scale is technically more correct, at these temperatures the difference is negligible anyway. []

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Cosmic Calendar: Introduction

I’m a sucker for a good story, and modern science has a fascinating story to tell. Only recently have I begun to wholeheartedly listen to its story. And call me self-centered, but I love stories about me. I love to hear about my past and how I came into the world. Further, a childlike curiosity drives me to understand why the world is the way it is. Science has a barn burner of a story.

The effort to understand the universe is one of the very few things that lifts human life a little above the level of farce, and gives it some of the grace of tragedy.—Steven Weinberg

In recent centuries, we have teased out fragments of our origin story, a tale strange and vast. It is inextricably bound to the story of the origin of the universe, for the universe gave birth to us. If its story had been different, we would be different—if we existed at all. The story occurs on a timescale that is almost beyond human comprehension. We have become accustomed to think of history as a few thousand years after we learned to write, or perhaps a few million years beyond that. Perhaps the dinosaurs seem like deep history. This utterly pales in comparison to the real story. Human history is only the smallest part of the story. Even dinosaurs or callow newcomers on the universal stage. Words fail (as they often do) to convey understanding. I want to experience this story for myself, to get a small taste of the true proportions of history.

One way we have experienced our stories in the past is through rituals and festivals marked out on a calendar. Early calendars made sense of the yearly rhyme of season and flood. Within the yearly cycle, we placed holy days commemorating important events, important gods, rites of initiation, and the world’s mythic creation. The yearly repetition increased our connection to our world and imparted a sense of continuity to our lives.

Someone’s genius guided them to combine the great story of science with the calendar. The premise of the remix is simple: take the history of the universe from its beginning to the present day and condense it to the span of a single year. Mark milestones in the history of the universe on the calendar as they happen at that reduced scale.

I first saw Carl Sagan present the Cosmic Calendar as part of his wonderful Cosmos series.1 I loved flying with him as a child in his ship of the imagination. He introduced me to the beautiful and fascinating world around me as seen through the curious, playful, shrewd eyes of scientific inquiry. His Cosmic Calendar is an excellent example of how thought provoking he was as a educator. He is missed.

He presents the Cosmic Calendar masterfully and humanely, and it still inspires me. Scientific understanding has progressed since he recorded that program. For example, scientific consensus tells us that the universe is most likely to be about 13.7 billion years old rather than 15 billion, and the Milky Way is thought to have formed much earlier than Sagan stated.

I have decided to update and extend the original Cosmic Calendar and to to follow the Cosmic Calendar for a year. Rather than just reading about our history, I wanted to experience it in a modern ritual. It’s one thing to read about something or see it illustrated in a diagram; it’s another thing entirely to experience the long year and watch as milestones pass by. When something happens on the Cosmic Calendar, I’ll post about it and give some background, maybe suggesting some places to investigate further or ways to observe the holiday.

At the time scale of a revised Cosmic Calendar:

1 year = 13.7 billion years
1 month ≈ 1.1 billion years
1 day = 37.5 million years
1 hour = 1.5 million years
1 minute = 26,000 years
1 second = 434 years
0.16 seconds ≈ 1 modern human lifetime

I can’t get over the fact that my life is literally less than a blink of the eye on the Cosmic Calendar. How ephemeral am I! While I am saddened by the relatively short duration of my life, I am awestruck by the vastness of time.

If you would like to follow along, it may help to subscribe to my version of the Cosmic Calendar (XML or iCal).2

Caveat lector

I am not an expert on any of the materials included in the calendar, only an interested layman. It is highly likely that I will make mistakes in compiling the calendar. I will cite my sources—too many from Wikipedia I suspect—and endeavor to improve the calendar as time goes on.

Also note that science operates on consensus. The corollary to that is there will always be disagreement at the limits of science. I have tried to harmonize any conflicting information that I have found, but in the hands of a hobbyist, the nuances of the scientific debate is sure to get mangled.

I could have renamed this the Human Advent Calendar because this is the story of our coming into the world. It begins to answer the questions “Who am I?” and “Where did I come from?” from a human perspective. It may be self-centered, but as I said, I like stories about me. However, this shouldn’t be taken as an endorsement of the idea that homo sapiens is the culmination of creation. It seems perfectly clear that we are just another wayfarer in the epic tale of this universe. The rest of the universe has just as much claim as we to the title of center of the universe.

As a last warning, science moves on. This calendar, even where it fairly represents current scientific understanding, should not be taken as dogma. If new data come in that conflict with the calendar, out with the old, in with the new; no regrets.

Further Study

Maps of Time: An Introduction to Big History by David Christian

The Structure of Big History: From the Big Bang until Today by Fred Spier

Big History: From the Big Bang to the Present by Cynthia Stokes Brown

Big History: The Big Bang, Life on Earth, and the Rise of Humanity (lectures) by David Christian

  1. It was also published in his book The Dragons of Eden. []
  2. Anyone who wants to verify my dates can check the source code for the script I wrote just for this purpose. I sometimes used a calculator and a day-of-year table as a sanity check. []

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