Consistency key to understanding of the universe

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The universe would seem incomprehensible if knowledge of matter and physical laws was contradictory on vary large and small scales. Hypotheses on the workings of the universe must demonstrate consistency across all scales of size.

Understanding the smallest subatomic phenomena has proven to be crucial to explaining the workings of the largest structures in the universe.

Contemplate for a moment that our most sensitive astronomical instruments, such as the Hubble Telescope, collect light that has been in transit across the universe for about 13 billion years. This light was emitted when the universe was less than a billion years old.

Deep space observatories are as close to time-machines as we will ever have. Light travels at a constant 186,000 miles per second. This leads to the amazing fact that ultrasensitive telescopes do not see the farthest reaches of the universe as they are today. Rather, they are seen as they were long ago when the light we see was emitted.

Deep space structures don’t look like our mature Milky Way galaxy or its sister, Andromeda galaxy. What is seen are stars and galaxies in the process of taking form. Those forms are very suggestive of their earlier history.

Analysis of this light shows the composition of the billion-year-old universe to have been predominately hydrogen and helium. These are the simplest of the atomic elements. More massive elements like carbon, oxygen, silicon and iron are absent.

What do we know about the development of the universe in the first billion years? What existed before hydrogen and helium came to dominate the material universe?

Since more distant objects are fainter, searching for older, more primitive objects becomes increasingly difficult. Currently, there are larger, more innovative telescopes being built that promise to show the universe in the later stages of the first billion years.

As telescopes reach the limit of their sensitivity, we rely increasingly on another giant tool of modern science. This is the high energy particle accelerator.

To make sense of the early development of universe, our explanations rely on data from particle accelerators. Within such accelerators, high energy beams of particles are made to collide.

Detectors discriminate the fragments of matter (particles) flying out from such collisions. The kinds of particles and their properties tell the story of the earliest moments of the universe.

Physicists are forever trying to build bigger, higher energy accelerators, creating conditions closer to those that existed at the beginning of the universe. The Large Hadron Collider beginning operations in Europe this month is the most powerful accelerator ever built.

Physicists and cosmologists are in general agreement about the timeline of what has come to be known as the "Big Bang." Not all of the physics is understood, but data from the LHC will help to resolve which of the competing ideas best conforms to reality.

In the earliest phase of formation the universe seemingly had no structure. It consisted of very high energy density, temperatures and pressures. Temperatures were so high matter as we know it did not exist.

From its beginnings, the universe underwent expansion and consequently began to cool. Only when the universe had cool sufficiently did matter take on forms we would recognize.

Along the way a series of phase transitions occurred. In a similar fashion, water undergoes a series of phase transitions as temperature decreases. Gaseous water vapor changes to liquid water, and, finally, to solid ice as temperature plummets.

The first phase transition occurred just a very small fraction of a second (a decimal point followed by 37 zeros) after formation of the universe had begun. What had been a uniform expansion abruptly accelerated, initiating a period of exponential growth. This is referred to as cosmic inflation.

The energies at this time were so large accelerators cannot replicate them. However, accelerators that have been operating at lower energies over the past several decades provide data that clarifies later events in the timeline. Those accelerators have created conditions that are thought to have existed just 0.00000000001th of a second after initiation of the Big Bang.

At the conclusion of inflationary grow the universe consisted of a quark-gluon plasma. Quarks and gluons are only familiar to us from experiments performed at the world’s most powerful accelerators.

Temperatures were still so high particles traveled at relativistic speeds (very near the speed of light). Collisions of particles at such speeds can create new particles along with their anti-matter antiparticle pair.

After just 0.000001 seconds the universe experienced another phase transition. It had cooled to the point quarks and gluons combined to form baryons. Baryons constitute a class of subatomic particles which includes the more familiar protons and neutrons.

The principle constituents of ordinary matter had arrived on the scene. This is the stuff at the nucleus of elemental atoms.

However, there were almost equal amounts of matter and antimatter. The universe was poised for another dramatic transformation.

For reasons not yet fully understood, there was a very small excess of matter over antimatter. When particles and antiparticles collide they annihilate each other releasing energy in the form of electromagnetic radiation.

Temperatures (energies) had dropped below the point where collisions could create new particle-antiparticle pairs. There were no longer mechanisms energetic enough to replace these two forms of matter once they annihilated each other.

The mysterious imbalance of matter over antimatter accounts for the material universe being composed almost exclusively of matter. In the end, only a very small fraction of the original protons and neutrons survived. However, they account for the bulk of the matter that currently exists.

The electromagnetic radiation released in the annihilation events comes in discrete packets of energy called photons. Astronomers have measured this relic radiation which is known as the cosmic background radiation.

After only a few minutes of expansion the temperature of the universe had dropped to about a billion degrees Kelvin. At this point, the density of all matter was about that of our atmosphere.

Most protons would remain uncombined. As such they existed as hydrogen nuclei. However, it was now possible for some protons and neutrons to combine to form deuterium and helium nuclei.

These are the simplest of the elements. They are the fuel that would ignite in the first stars in the first galaxies. Such objects are what Hubble telescope images suggest are just beyond our current reach.

The other important part of an atom, the electron, had a similar history to that of baryons. It wasn’t until the universe had cooled for about 379,000 years that electrons could be captured by atomic nuclei to form complete atoms.

Eventually, gravitational attraction concentrated the hydrogen, deuterium and helium gases. Nuclear reactions ignited once gas densities became sufficient and stars were born. I will explain in my next article how the heavier elements came about from these stellar furnaces.

Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at steveluckstead@charter.net.

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