Current Theme: A History of the Universe

Given the deep connection between the physics at the CERN Large Hadron Collider (LHC) and cosmology, a natural sequence of sub-themes emerges for the proposed Science-Art-Education (SciArtEd) Trail: each stop along the trail would correspond to one of the pivotal epochs in the history of the universe as we currently understand it.

 

The possible epochs, and brief descriptions of each, are:

The Big Bang                The origin of the universe

The universe begins in an enormously dense, extremely hot, extremely luminous, state.  Saying the universe was once very dense is to understate an understatement. There was a time in the early universe when one cup of the dense, bright, hot fluid of light and particles had as much mass as the Earth!

The rate of expansion of space far exceeds the speed of light, but rapidly decreases. Cosmic sized sound waves traverse the universe and leave an imprint in the distribution of galaxies.

In the very early universe there are small changes in the density of the fluid from place to place that also leave an imprint of patches, which today are about 1 degree across on the sky. Some patches are slightly hotter (by one part in 100,000) than average and some are slightly colder. What is extraordinary is that these patches may have been the result of processes that once occurred on microscopic scales. In a literal sense, the sky is a cosmic-scale microscope that shows an image of the microscopic patches of varying fluid densities that were present in the very early universe.

It is ironic that for the first 350,000 years after the Big Bang the universe was so bright that light had great difficulty going through it; that is, a universe filled with light and charged particles was opaque to light. The same is true of our nearest star, Sol (the Sun), whose opacity to light is such that the light created in its core takes up to a million years to reach the Sun’s surface even though light travels at 300,000 km/s! It is an arresting thought that the sunlight now falling on your skin was created about a million years ago deep within the Sun.

 

Free at Last             Light from the Big Bang is able to stream freely throughout space

It was not until the temperature of the universe lowered sufficiently that the universe became transparent and the light from the Big Bang was finally able to travel freely throughout space – we are still receiving light from this epoch albeit now in the form of microwaves. These microwaves are called the Cosmic Microwave Background (CMB) and constitute the best evidence we have that the universe was once extremely hot and dense.

The universe became transparent because the temperature became low enough for atoms (mostly hydrogen) to form. Hydrogen is neutral and so light can stream past such atoms without a problem.

 

The Dark Ages             The time before the first stars

For about 100 million years after the light was freed the universe would have looked like a dark featureless void. There were no stars; only hydrogen (and helium) atoms and (according to current understanding) dark matter, a form of matter whose nature, even today, remains a mystery.

 

A Star is Born               The first stars are born in the universe

The trillions of regions that are slightly denser in the universe than average begin to collapse, that is, shrink, as gravity draws the hydrogen atoms together. The density of each region increases as more and more matter is drawn in. As matter gets squeezed by gravity, the temperature of each of these trillions of clumps of hydrogen rises. Eventually, the centers of these dense regions become so hot that self-sustaining nuclear fusion reactions begin in which hydrogen is fused into helium, releasing light, the first time new light has been created since the Big Bang; the light of the first stars.  The stars group into immense stellar structures called galaxies, some like the Milky Way containing 100 billion stars.

The largest stars live fast and die young in titanic explosions that scatter their ashes far and wide seeding galaxies with elements heavier than hydrogen and helium.

New generations of stars form from the ashes of the previous generations. The sun is a 2^nd or 3^rd generation star – formed from the ashes of previous generations of stars. The carbon and other elements in our bodies are the ashes from stars that exploded long before the Sun was formed. We are, therefore, the beneficiaries of recycling on a cosmic scale. We are literally made of stardust.

Many stars are born in clusters but our Sun is odd because it’s a lone star. Jupiter – if it was about 100 times larger could have ignited into a star and we would have been in a double-star solar system. There are many double-star solar systems in our galaxy.

 

The Dawn                     Life emerges on at least one planet

Something truly transcendent occurs about 11 billion years after the Big Bang: the first self-replicating molecule evolves on a small blue planet around an ordinary yellow star located in the suburbs of a large galaxy, one of about 30 in a group of galaxies, which are part of a vast empire of galaxies, one of thousands in the known universe.

One day, a curious biped on this blue planet stood upright, gazed upon the stars, and began contemplating her place within the glorious vista above. And the rest, as they say, is history.

 

The Sunset                   The Sun, now a Red Giant, engulfs the Earth

Six billion years from now, the Sun will swell into a Red Giant and engulf Mercury and Venus. For a while, the Earth shall be spared. Our descendants, or their AI avatars, if they are still around, will see a red star that occupies half the sky. Hundreds or thousands of millennia will elapse and gradually the red star will occupy more and more of the sky until it will be the sky. And one day, the blue planet, which long, long, ago lost its iridescent beauty will enter the star and its amazing history will end.

 

Worlds in Collision     The Milky Way and Andromeda galaxies collide and merge

The Milky Way, the galaxy we inhabit, is in a collision course with our sister galaxy Andromeda. At about the same time that the Earth is being threatened by the Sun during its Red Giant phase, the collision between the two galaxies will begin. Fast forward a few billion years and the galaxies will have merged into one super-galaxy at the center of which is likely to be a black hole with a mass perhaps a billion times that of the Sun.

https://apod.nasa.gov/apod/ap130825.html

 

To Infinity                     The universe enters another Dark Age as all the stars burn out

In 1998, a stunning discovery was made: the expansion of the universe is accelerating. No one knows why, but the best hypothesis is that the universe is filled with yet another mysterious “substance” or energy, which has been dubbed dark energy. If this acceleration continues far into the future, two profoundly sobering consequences follow. The first is that every second, thousands of the most distant galaxies slip beyond our horizon because the light from them will never reach us. Why? Because the light, fast as it is, cannot outpace the expansion of the universe. Consequently, whatever the longevity of our species there is a finite amount of information we can learn about the universe; indeed, second by second there is less and less of the universe available for us to explore. We must learn as much as we can because one day the curtain will fall.

The second consequence of the accelerating expansion is that we shall enter an era in which each galaxy will be surrounded by a vast void of empty space as all the other galaxies are pushed far beyond our horizon. Future cosmologists, if they exist, will build theories that mistakenly view the universe as a place containing a single galaxy surrounded by what seems like never-ending darkness. They will never know the awe-inspiring majesty of a universe filled with galaxies both great and small. And then, slowly but surely,  the stars in each galaxy will burn out and a Second Dark Age will begin.