Understanding the Evolution of Life in the Universe
HOW DID THE UNIVERSE START AND EVOLVE?
WMAP found that the universe is 13.7 billion years old. The universe began with an unimaginably enormous density and temperature. This immense primordial energy was the cauldron from whence all life arose. Elementary particles were created and destroyed by the ultimate particle accelerator in the first moments of the universe.
There was matter and there was antimatter. When they met, they annihilated each other and created light. Somehow, it seems that there was a tiny fraction more matter than antimatter, so when nature took its course, the universe was left with some matter, no antimatter, and a tremendous amount of light. Today, WMAP measures that there is more than a billion times more light than matter.
WE AREN'T MADE OF HYDROGEN!
WMAP determined that about 4.6% of the mass and energy of the universe is contained in atoms (protons and neutrons). All of life is made from a portion of this 4.6%.
The only chemical elements created at the beginning of our universe were hydrogen, helium and lithium, the three lightest atoms in the periodic table. These elements were formed throughout the universe as a hot gas. It's possible to imagine a universe where elements heavier than lithium would never form and life never develop. But that is not what happened in our universe.
We are carbon- based life forms. We are made of and drink water (H2O). We breathe oxygen.
Carbon and oxygen were not created in the Big Bang, but rather much later in stars. All of the carbon and oxygen in all living things are made in the nuclear fusion reactors that we call stars. The early stars are massive and short- lived. They consume their hydrogen, helium and lithium and produce heavier elements. When these stars die with a bang they spread the elements of life, carbon and oxygen, throughout the universe. New stars condense and new planets form from these heavier elements. The stage is set for life to begin. Understanding when and how these events occur offer another window on the evolution of life in our universe.
WMAP determined that the first stars in the universe arose only about 400 million years after the Big Bang. But what made the stars ?
THINGS THAT GO BUMP IN THE NIGHT.
Quantum Fluctuations are the random
nature of matter's state of existence or
nonexistence. At these incredibly small
sub-atomic scales, the state of reality is
fleeting, changing from nanosecond to
nanosecond.
The motor for making stars (and galaxies) came early and was very subtle. Before the completion of the first fraction of a second of the universe, sub- atomic scale activity, tiny "quantum fluctuations", drove the universe towards stars and life. With the sudden expansion of a pinhead size portion of the universe in a fraction of a second, random quantum fluctuations inflated rapidly from the tiny quantum world to a macroscopic landscape of astronomical proportions. Why do we believe this ? Because the microwave afterglow light from the Big Bang has an extraordinarily uniform temperature across the sky. There has not been time for the different parts of the universe to come into an equilibrium with each other *unless* the regions had exponentially inflated from a tiny patch. The only way the isotropy (uniformity) could have arisen is if the different regions were in thermal equilibrium with each other early in the history of the universe, and then rapidly inflated apart. WMAP has verified that other predictions from the inflation theory also appear to be true..
As the universe inflated, the tiny quantum fluctuations grew to become tiny variations in the amount of matter from one place to another. A tiny amount is all it takes for gravity to do its thing. Gravity is one of the basic forces of nature and controls the evolution of the large scale structure of the universe. Without gravity there would be no stars or planets, only a cold thin mist of particles. Without the variations in the particle soup initiated by the quantum fluctuations, gravity could not begin to concentrate tiny amounts of matter into even larger amounts of matter. The end result of the pull of gravity: galaxies, stars and planets. The fluctuations, mapped in detail by the WMAP mission, are the factories and cradles of life.
THE RECIPE FOR LIFE REQUIRES A DELICATE BALANCE OF COSMIC INGREDIENTS.
The differences in the early soup of universe particles were very small, so large scale changes take time to manifest themselves. What if our universe had only lasted for a second, or a year, or one million years? The age of the universe is controlled by the basic rules that govern matter, energy, and time. We needed almost 13.7 billion years to evolve and come to recognize this fact.
How long the universe lasts and how it evolves depends on its total energy and matter content. A universe with enormously more matter than ours would rapidly collapse back under its own gravity well before life could form. A very long lived universe might not have enough mass for stars to ever form. In addition, WMAP has confirmed the existence of a dark energy that acts like an anti- gravity, driving the universe to accelerate its expansion. Had the dark energy dominated earlier, the universe would have expanded too rapidly to support the development of life. Our universe seems to have Goldilocks properties: not too much and not too little - - just enough mass and energy to support the development of life.
IS THERE OTHER INTELLIGENT LIFE IN THE UNIVERSE ?
We don't know whether or not there is other intelligent life in the universe. There is no reason there shouldn't be. We know by our own existence that the universe is conducive to life. But there are many hurdles to overcome for intelligent life to form, and many threats to its continued existence once it does form. Life constantly faces the prospect of extinction. Life requires energy, water, and carbon; an environmental disaster that removes water, dooms life. Other environment disasters threaten. On Earth we have had huge meteor impacts that are believed to have caused mass extinctions. The harsh radiation of space is blocked only by Earth's atmosphere and magnetic field. Environmental instabilities cause ice ages. One day, billions of years from now, our Sun will burn out. Other, heavier stars end their lives in explosions called supernovae; the blast and radiation from a nearby supernova could destroy all life on Earth.
The dark energy will inexorably stretch the universe into an icy cold end. Since we don't know what the dark energy is, this might be wrong, but no less deadly depending on how the nature of the dark energy changes.
Many people are engaged in efforts to detect life in the universe. There are two strategies: we look for it, or it finds us. Perhaps a middle ground would be if we detected signals coming from life elsewhere in the universe. The Search for Extraterrestrial Intelligence ( SETI) program pioneered searches for life. WMAP itself is, in a small way, a mini- SETI experiment, since it constantly scans the skies over a wide range of microwave frequencies. WMAP was not optimized to search for life. Other efforts are (have been). Some day, we may know for sure whether we are alone in the universe. In the meantime the search goes on, as we also try to understand the universe and how it may be conducive to life.
By detecting and measuring the density fluctuations in the cosmic microwave background using the WMAP space mission we are learning about the early universe; and we begin to understand the basic ingredients that make life possible. In the future, we would like to enhance these efforts with other missions, such as NASA's Einstein Inflation Probe, which would strive to detect the gravity disturbances from the era when the universe originally inflated. This passionate search for knowledge is characteristic of human life.
What is the Ultimate Fate of the Universe?
Just as Robert Frost imagined two possible fates for the Earth in his poem, cosmologists envision two possible fates for the universe:
The evolution of the universe is determined by a struggle between the momentum of expansion and the pull (or push!) of gravity. The current rate of expansion is measured by the Hubble Constant , while the strength of gravity depends on the density and pressure of the matter in the universe. If the pressure of the matter is low, as is the case with most forms of matter we know of, then the fate of the universe is governed by the density.
If the density of the universe is less than the critical density , then the universe will expand forever, like the green or blue curves in the graph above. Gravity might slow the expansion rate down over time, but for densities below the critical density, there isn’t enough gravitational pull from the material to ever stop or reverse the outward expansion. This is also known as the “Big Chill” or “Big Freeze” because the universe will slowly cool as it expands until eventually it is unable to sustain any life.
If the density of the universe is greater than the critical density, then gravity will eventually win and the universe will collapse back on itself, the so called “Big Crunch”, like the graph's orange curve. In this universe, there is sufficient mass in the universe to slow the expansion to a stop, and then eventually reverse it.
Recent observations of distant supernova have suggested that the expansion of the universe is actually accelerating or speeding up, like the graph's red curve, which implies the existence of a form of matter with a strong negative pressure, such as the cosmological constant . This strange form of matter is also sometimes referred to as the “dark energy”. Unlike gravity which works to slow the expansion down, dark energy works to speed the expansion up. If dark energy in fact plays a significant role in the evolution of the universe, then in all likelihood the universe will continue to expand forever.
There is a growing consensus among cosmologists that the total density of matter is equal to the critical density, so that the universe is spatially flat . Approximately 3/10 of this is in the form of a low pressure matter, most of which is thought to be “non - baryonic” dark matter, while the remaining 7/10 is thought to be in the form of a negative pressure “dark energy”, like the cosmological constant . If this is true, then dark energy is the major driving force behind the fate of the universe and it will expand forever exponentially.
MEASUREMENTS FROM WMAP
The WMAP satellite measures the basic parameters of the Big Bang theory including the fate of the universe. The results suggest the geometry of the universe is flat and will expand forever. Further study of the dark energy with future experiments and space missions is needed to understand its nature and effect on the rate of future expanison.
OTHER INTERESTING SITES:
On cosmology with supernovae:
On runaway expansion:
Related Topics
The following pages are not central to an understanding of the universe as a whole. Rather, they are intended to describe some of the more interesting objects within our universe.
First objects
When did the first objects form in the universe ?
The Milky Way galaxy
A brief tour of our own Milky Way galaxy, with a beautiful image of it from the COBE satellite.
The life cycle of stars
Learn how stars form, live and die.