"For every one billion particles of antimatter there were one billion and one particles of matter. And when the mutual annihilation was complete, one billionth remained—and that’s our present universe." -Albert Einstein (1879-1955)
An interesting aspect of science is that you never end up with all the answers. Every discovery and every advance brings with it new questions, so there is always another problem to attack.
Some of the unanswered questions are universal in scale. For example: What is the universe made of? Others are smaller in scale but more important in our daily lives: How do we think?
What is the universe made of?
This is one of the questions that seems like it should have an obvious answer, but it doesn’t. We know that there are about 100 elements and that any other elements that might exist are very unstable. Elements themselves are made up of electrons, neutrons, and protons, which together form atoms. And while neutrons and protons form the nucleus around which electrons spin, both neutrons and protons are composed of subatomic particles called quarks. It takes three quarks to make up either a neutron or a proton.
When we look at stars and galaxies we can detect many of the elements, but almost everything that we see is hydrogen or helium. So the universe is made of the elements that we know about, primarily hydrogen and helium, right? Wrong.
The problem is that there has to be more to the universe than what we can see. In the 1960s, astronomers discovered that galaxies would fly apart unless they had more mass than what we can measure in their stars. They proposed the existence of dark matter, which we cannot see but which exerts a pull of gravity. There is also not enough known matter to account for the distribution of galaxies in the universe. Cos-mologists have concluded that the gravitational forces that shape the universe must come from another, so far undiscovered type of matter. They estimate that this exotic dark matter accounts for about one-fourth of the universe—and we really don’t know anything about it other than its effects on the matter we see.
The most recent data we have about the composition of the universe comes to us via the Wilkinson Microwave Anisotropy Probe (WMAP), an Explorer mission from the National Aeronautics and Space Administration. In 2008, after studying cosmic microwave background (CMB) radiation—the "afterglow" light left over from the big bang—the WMAP revealed that the oldest light has been traveling across the universe for about 13.7 billion years. Data from the WMAP project also demonstrated that the entire mass density of the universe is equivalent to 5.9 protons per cubic meter. However, the density of the atom itself is roughly one proton per 4 cubic meters. Calculations show that atoms make up only 4.6 percent of the density of the universe.
Now let’s add another complication. We know from observations of distant galaxies that the universe is expanding. We also know that the force of gravity between any two chunks of matter in the universe should slow the rate of that expansion as galaxies pull on one another. For decades, scientists have been working to determine the rate at which the expansion of the universe is decelerating. That would give us a good handle on the amount of matter that is trying to pull itself together. WMAP has provided data to help answer that question. There are never easy answers, though. We find that the rate of expansion is actually accelerating. That means there is something working against gravity to push the universe apart—not at all what was expected. Cosmologists now theorize that there is a form of energy, which they call dark energy, that is pushing on the universe. No one knows what it is but only that its effects appear when we measure the universe. Ordinary matter and dark matter combined account for only about 30 percent of everything. The rest is dark energy (remember, E = mc2—matter and energy are two faces of the same thing).
So, to answer the question "What is the universe made of?" we will first have to answer other questions:
1. What is dark matter (and where is it)?
2. Is there more than one kind of dark matter?
3. What is dark energy?
Does anything exist outside the universe?
The short answer to this question is, "Nobody knows." So let’s start with the anthropic principle, a physics term that states human existence has built-in observational constraints based on our human condition. In short, the only universe humans will see is one that supports life, because if it did not support life, we could not exist to observe that universe. The term was coined in 1973 when theoretical astrophysicist Brandon Carter proposed it to a Krakow, Poland, symposium honoring the 500th birthday of Copernicus.
This is the kind of question that is hard to test. The first hurdle is to define the "universe." If you go with the original meaning of universe, that is, everything that exists, then by definition nothing exists outside the universe. That of course is much too simple a way to answer the question.
What if you define the universe as everything that we can possibly observe? Now you have a more interesting question. If it is outside the universe, we can’t observe it, so theories have to be based on indirect evidence and even some philosophical arguments. We know that the universe is expanding, so it is natural to wonder what it is expanding into.
One way of looking at that is that the universe defines time and space, so it is not expanding into anything because time and space do not exist outside the universe.
Another theory proposes the idea of a multiverse—multiple universes existing with varying characteristics, shifting and reforming like the baubles inside a kaleidoscope. Expanding on that is the idea of fecund universes that "give birth" to other universes.
On the whole this question may be more philosophical than scientific because it is not based on evidence. Some researchers, though, are looking at the big bang and trying to find evidence to show that something existed before it occurred and that we may be able to learn about things outside our universe based on the interactions of its material before the big bang. In the meantime, this may be the hardest question of all to answer.
Is there anyone else out there?
The question of whether intelligent life exists elsewhere in the universe has been around for a long time. Hindu scriptures speak of innumerable universes created by the Supreme Personality of Godhead, while the Jewish Talmud states that there are at least 18,000 other worlds. To examine the question in nonreligious terms, we should keep in mind that the human body is made up of 95 percent hydrogen, oxygen, and carbon atoms. So to find life like our own, we would probably need to find planets where similar molecular configurations could exist. However, the possibility of silicon-based life forms has been proposed, and some scientists think ammonia could do for other life forms what water does for life on Earth.
"What a splendid perspective contact with a different civilization might provide! In a cosmic setting vast and old beyond ordinary human understanding we are a little lonely, and we ponder the ultimate significance, if any, of our tiny but exquisite blue planet, the Earth … In the deepest sense the search for extraterrestrial intelligence is a search for ourselves." -Carl Sagan (1934-1996)
Most scientists involved in biology beyond Earth think that complex multicellular life, as found on Earth, would be a highly improbable circumstance on most planets. On the other hand, in a universe of hundreds of billions of galaxies, each made of hundreds of billions of stars, the highly improbable could happen many times. However, calculating the possibilities and finding evidence are two very different things.
The Search for Extra-Terrestrial Intelligence (SETI) program has existed for four decades and so far it has not turned up a radio signal from another world. Nevertheless, interest is not waning. The European Space Agency launched the Darwin mission designed to find Earth-like planets, and the French Space Agency’s COROT mission was launched in 2006 with a similar mandate. At the time of this writing the Kepler mission is scheduled for launch by NASA in November 2008.
To date, however, scientists have only identified a few dozen exosolar planetary bodies. Exosolar means planets circling stars, not necessarily planets that might support living beings. So for now, the answer to the question of "other life out there" remains "there is no evidence for it."
Fast Facts
On April 24, 2007 Chilean scientists at the European Southern Observatory announced they had discovered Gliese 581 c, the first Earth-like planet orbiting within the habitable zone of its star (in this case, Gliese 581, a red dwarf). It was initially thought that this planet could contain liquid water. Subsequent computer simulations by a team in Germany’s Institute for Climate Impact Research have suggested that gases in that planet’s atmosphere raised the surface temperature above the boiling point of water. It was a nice idea while it lasted.
How do we think?
Using functional magnetic resonance imaging (fMRI), scientists can see what happens inside the brain while thought is taking place. fMRI is a neurological imaging technique that uses the level of oxygen in the blood to show what structures of the brain are active during given mental operations. By studying activity in the visual and intraparietal cortexes (the sensory processors in the brain), they have discovered that the way people think may be shaped by the evolutionary history of the species and the way our brains developed. Even our moral outlook, some scientists now feel, might have something to do with how we are "wired."
Our brains are composed of nerve cells known as neurons that connect through signal-receiving dendrites and signal-transmitting axons. Imagine a leafless tree during winter and you have an idea of these branchlike projections. When dendrites and axons connect they do not touch. Rather, a gap called a synapse fires and an electrical impulse is sent. Each neuron has thousands of synapses, and each transmission takes place at lightning speed (about 300 milliseconds), so with the billions of neurons in the brain operating at such a clip, there is an infinite capacity for storing information, and endless neuron pathways.
Apparently, we can only think so fast. In 2004, three theoretical neurophysicists from the Max Planck Institute for Flow Research in Gottingen, Germany, discovered an upper limit on the speed of thought. The researchers used a mathematical model to show that due to the mechanical limitations of neural connections, the switching has an upper limit. The only way to beat this "speed limit" would be if every neuron in the brain could manage to be connected to every other single neuron.
Does this capacity diminish with age? The good news is that the brain can change. Thomas Elbert, a professor of psychology at the University of Konstanz in Germany, who has published extensively on brain activity, has demonstrated that the adult brain has malleable plasticity rivaling that of a child. This means that if we keep our brains healthy and active they will remain flexible, and our capacity for learning can last as long as we are living.
Neurogenesis is the process by which neurons are born, and now it may be possible to grow new cells in the adult brain. In 2000, a Stanford study revealed in the magazine Science that transplanted bone marrow cells can migrate to the brain and turn into neurons. Better yet, in November 2006, Fulton Crews, a professor of pharmacology and psychiatry and director of the Bowles Center for Alcohol Studies at the University of North Carolina at Chapel Hill, spoke at the National Institute on Alcohol Abuse and Alcoholism and described how heavy physical exercise increased neurogenesis in rats. Since humans have a similar brain structure, it follows that new brain cells can literally be exercised into existence.
However, understanding the processes of neurons does not answer another important question: What is the mind and how does it relate to the brain? The description of brain processes sounds remarkably like that of computer processing. There is a big difference between a computer and a human, though. No one has ever built a computer that is self-aware and makes decisions by its own will. Why are people able to think rather than just process information? That question remains unanswered.
How can we make replacement cells for body parts?
Can we make body parts to replace those that wear out during the course of living? This is a popular technique in science fiction to prolong life. But how can it be done—or can it be done at all?
Some researchers think that blueprints for new body parts can be printed out. A process called bio-printing was developed in 2006 by a research team lead by Julie Jadlowiec-Phillippi, a bioengineer at Carnegie Mellon University and Children’s Hospital of Pittsburgh. In a meeting of the American Society for Cell Biology in San Diego, she explained that her team had, in conjunction with the university’s Robotics Institute, created an inkjet printer to spray a chemical mix onto protein-coated slides, allowing them to manufacture bone and muscle cells in a petri dish. Within the dish were stem cells taken from the muscles of adult mice. While the team did not believe a method for growing body parts was imminent, their "bio-ink" method offered great promise and another method for studying how stem cells mutate into other specialized cell types.
"Every cell in your body is programmed to do a job, and our job is to put these cells in the right environment in the lab so they know what to do. To us, it doesn’t matter where the cell comes from—whether it’s a bladder cell or a blood cell or an adult stem cell—we use whatever cell gets the job done."
Two years later, a team led by Dr. Anthony Atala at Wake Forest University was manufacturing body parts. When interviewed by CBS News in February of 2008 in a segment called "Growing Miracles," Atala revealed that they had made 18 different types of tissue. Viewers were shown a functioning, engineered heart valve that was to be transplanted into a sheep. Their method sounded simple; they isolated cells capable of regeneration and coaxed them to grow. Like the Carnegie-Mellon team, the Wake Forest team’s heart cell regeneration began with the use of an inkjet printer. As the camera rolled, a mouse heart was revealed that was being grown, the cells sprayed on layer by layer.
It wasn’t only for animals, however. In an experimental procedure at Thomas Jefferson Hospital in Philadelphia, a patient received a bladder transplant of a bladder grown from her own isolated bladder cells!
At this time, it appears that there may be an answer to this question, although the idea of racks of spare parts is still in the science fiction realm. Will it be possible to someday produce whole organs? That remains a "maybe."
How did life begin?
Inside all living organisms, proteins and nucleic acids interact, causing structures to grow and reproduce. Life produces life in a constant chain of growth. But how did it all begin? When did the first living thing appear on Earth and how did it form since it was not the result of reproduction?
Charles Darwin’s The Origin of the Species was the landmark book about evolution, but he did not arrive at his i deas all on his own. French biologist Jean-Baptiste Lamarck (1744-1829) had evolutionary theories that were acknowledged in Darwin’s book. Lamarck believed that biological lessons learned by organisms during their lives were the reason species adapted, so that necessary changes would be passed on to offspring. While many people still believe that learned traits can be passed from one generation to the next, genetic study has shown otherwise.
While this is another unanswered question, there are some hints. In 1828, German chemist Friedrich Wohler synthesized urea, an organic molecule that most thought could only be made by living organisms. This demonstrated that there is no difference between physically produced and organically produced molecules. Prior to this accomplishment, it was generally believed that organic (living) compounds were fundamentally different material from inorganic compounds.
In 1953, Stanley, one of the pioneers of exobiology (which preceded astro-biology, the study of life in the universe) and Harold C. Urey conducted an experiment on the origin of life at the University of Chicago. The experiment simulated hypothetical conditions Urey assumed were present on the early Earth and tested the hypothesis that such conditions favored chemical reactions that would synthesize organic compounds from inorganic elements.
Ammonia, hydrogen, methane, and water were sealed in a sterile array of glass tubes and flasks connected to each other. The water was heated to evaporate it, with sparks fired between electrodes to simulate lightning through an atmosphere. After one week, 2 percent of the carbon had formed amino acids, with over half the amount necessary to make proteins in living cells. DNA and RNA were not formed, but the goo that remained was similar to organic material that can be found on a meteorite— meaning this could be a universal process.
In 1961, Juan Oro, a professor of biochemical and biophysical sciences at the University of Houston, discovered that amino acids could be synthesized via hydrogen cyanide and ammonia in an aqueous solution. His experiment produced a great deal of adenine, which was highly significant because adenine is an organic compound that is one of the four bases in RNA and DNA. Later experiments revealed that the other RNA and DNA bases could arise through simulated prebiotic chemistry with a reducing atmosphere.
These experiments have provided a foundation for a theory of the origins of life. However, the production of the molecules on which life is based is a very different thing from producing life itself. Beyond that, even if life were to be produced in a laboratory, more evidence would be needed to show that it had actually happened that way in nature. As of today, questions about how life began remain unanswered.
