10.III: Early Outer Space

galaxies universe outer space big history

Hydrogen gas clumped into galaxies and then stars, where it got assembled into the variety of elements that we know today.  1

A.  The Gravitational Clumping of Stars and Galaxies

B. Stellar Nucleosynthesis and the Heavier Elements

C. Atoms: From Physics to Chemistry

D. Complexity and Stability

E.  Citations

A. The Gravitational Clumping of Stars and Galaxies

 

Over the next several hundred million years, gravity became the dominant force in shaping the universe.  Remember again that matter generates forces.  Atoms, as small as they are, all generate a gravitational force that attracts other atoms.  Gravity is different from the other three forces.  It involves the warping of space-time, and might not require the exchange of force carrier particles.  Thus, it can act on all matter, and across very large distances.

Also recall the “lumps” that remained in the universe after inflation, visible in the map of cosmic background radiation. In a cloud of atoms that are spread apart perfectly evenly, each atom would be gravitationally pulled “this way” just as much as it is pulled “that way,” so it would end up static and not moving at all. If the atoms in the universe had been dispersed perfectly homogeneously, they never would have coalesced together, and the universe would still be a featureless cloud of gas today! However, atoms were randomly concentrated a little more heavily in some regions of space than other regions. This is referred to as the heterogeneity of matter. The heavily concentrated atoms eventually started to clump together into giant molecular clouds (GMCs) due to gravity. Initially, these GMC’s were very large, hundreds of light-years across. Because a GMC is itself heterogeneous, when it contracts it breaks up into several smaller clouds. After millions of years of gravitational clumping, the universe got populated by ever-denser clumps of atoms, separated by ever-sparser regions of empty space. The slight heterogeneities that existed when the universe was a split-second old served as the “seeds” that eventually got exaggerated into the galaxies and galaxy clusters that formed millions of years later!

When a critical mass of hydrogen atoms gets together, the force of gravity shapes the cluster into a coherent sphere. This is the beginning of a star. The atoms pull each other downward into the center of the sphere. Eventually, the matter at the center of that sphere becomes subject to immense gravitational pressure. The weight pressing down on it makes it denser and hotter – and as you know from watching a stovetop, hot things begin to glow in certain colors. Protons and electrons become too energetic to hold on to each other anymore, so the ball of gas becomes a hot plasma of positive protons and negative electrons flying around furiously.

At around the same time that they were igniting, stars were grouping themselves into galaxies, including our own “Milky Way” galaxy. A galaxy is a large collective of stars surrounded by gas. Most galaxies, again including the Milky Way, become so dense at the center as to form a supermassive black hole, millions of times more massive than the sun. Recent discoveries suggest that galaxies also contain a large amount of dark matter, the mysterious form of mass that is not accounted for in the Standard Model. The evidence for dark matter’s existence is the fact that galaxies exert more gravitational influence on each other than could be accounted for by the stars and gas within them.

B. Stellar nucleosynthesis and the heavier elements

The big bang synthesized the four lightest elements of matter – combinations of up to four protons fused together. If those were still the only elements available, the universe would be very dull and lifeless! Life requires slightly heavier elements such as carbon, nitrogen, and oxygen. The planet Earth contains large amounts of even heavier elements such as silicon, iron, and nickel. Where did these elements come from? They were created in stars!

The earliest stars, like the gas that formed them, were about 75% hydrogen by mass. In the first few hundred-million years after the Big Bang, many proto-stars became massive enough so that gravitational pressure heated their cores to over 3,000,000 K. At this critical temperature, the protons in a star’s core become hot enough to fuse together into helium nuclei. This is the first, main sequence stage of stellar nucleosynthesis, the creation of new atomic nuclei inside of stars. Each time two nuclei fuse together to create a larger one, a small fraction of the mass is “lost” and converted to energy. The cumulative energy of all those nuclear reactions emanates in the starlight. Positrons and neutrinos are also released during stellar nucleosynthesis. The weak nuclear interaction, not a part of our ordinary macroscopic lives, is the most important force for governing the workings of starlight.

The heat and radiation that come from within a star’s core actually create a great deal of outward pressure. When a star first starts to shine, the radiation that comes pouring out of it blows the star’s thin outer layers into the interstellar medium. Only the hot, dense center remains. The duration of a star’s lifetime is a state of equilibrium between gravity, which wants to crush the star, and radiation, which wants to blow it away. A light but persistent solar wind of protons and electrons continues to stream out of a star as long as it shines. We see clear evidence of solar wind today in the Northern Lights and the tails of comets as they approach the sun.

stellar nucleosynthesis elements stars big history

The depths of a star’s core synthesize increasingly heavier elements, normally culminating in iron.

Helium is denser than hydrogen. It sinks to the star’s core. As more helium is created by fusion, the new helium sinks to the core as well. Eventually, the helium core becomes so dense and hot (over 100,000,000 K!) that the star begins a whole new phase. Helium nuclei get fused together three at a time to create carbon, {_6^{12}}C. The new carbon sinks into a smaller core, until it is hot and dense enough to fuse with helium to create oxygen, {_8^{16}}O. This process can continue for quite a few steps, until the star’s deepest core is synthesizing iron, {_{26}^{52}}Fe, and nickel, {_{28}^{56}}Ni. Some stars are able to synthesize elements as heavy as bismuth, the heaviest stable element, {_{83}^{209}}Bi. 2

A small – medium star, about the size of the sun, ends its life in a whisper, as its outer layers gradually dissipate into space, blown away by a super-hot core. This allows a rich mixture of elements to be made available for the next generation of stars and planets. A more massive star dies a more spectacular death, in the form of a supernova explosion (remember that this is expected to be Betelgeuse’s fate and could happen in the near future). Supernovae are relatively common, occurring once or twice per century in a galaxy. Astronomers routinely observe supernovae every day in remote galaxies. A supernova is the third major natural source of new elements. It produces enough energy to fuse heavy nuclei together, even if only for a few seconds. Supernova nucleosynthesis is the only source for very heavy elements such as uranium.

C. Atoms: From Physics to Chemistry

In a theme that was to be repeated many times throughout natural history and religion alike, the first stars had to die in order to give life to the modern universe. After synthesizing almost 100 new kinds of atomic nuclei, the first generation of stars exploded or dissipated, releasing their new nuclei into the molecular gas clouds of outer space. When they cooled down, these nuclei captured negatively charged electrons to form complete atoms. As we have discussed, quantum physics is the science of fundamental particles and how they combine to form atoms. Chemistry picks up from there, describing the interactions of atoms to create new, more complex forms of matter. Atoms cannot exist in the super-high-temperature environment of stars. Therefore, chemistry itself had to wait until the first stars completed their life cycles.

A nucleus captures as many electrons as it has protons, creating an atom with no net electric charge. For example, a hydrogen atom comprises one proton and one electron. A helium atom has two protons and two electrons. A carbon atom has six protons and six electrons, and so forth. There are almost always some neutrons bound to the protons within the nucleus. Protons are important for determining how many electrons an atom will have. Neutrons are important contributors of the strong nuclear force, which holds the protons together. But when it comes to the actual chemistry of atoms, all of the action is in the electrons. In fact, only an atom’s outermost layer of electrons is pertinent in determining its chemical properties. This “skin” of the atom is the layer that chemists call the valence electrons.

Earth (above) and Jupiter as seen from Mars. The solar system is mostly empty space. Proportionally, each atom is much, much emptier still. 3

The electrons and the nucleus do not touch each other. Rather, the electrons situate themselves in orbitals around the nucleus of the atom, somewhat analogous to planets orbiting the sun. Like the solar system, almost all of an atom’s mass is concentrated in the nucleus. The solar system analogy is incomplete in other important ways, though. For example, electrons do not follow well-defined paths, but wander around randomly (and very quickly) within their three-dimensional orbitals. Orbitals can have extremely complex shapes, determined by the electromagnetic force. Another failure of the solar system model is the sense of scale. The average distance between the nucleus and the electrons in an atom is about 100,000 times the size of the nucleus itself. Compare this to the radius of Earth’s orbit, which is only about 100 times the size of the sun. Thus, relative to the space that it occupies, each atom is much emptier than the solar system! As you can see then, even such seemingly “solid” matter as steel and concrete is almost completely porous. It is not the protons and electrons themselves that create the appearance of solidity, but their electromagnetic force fields. When you “knock on wood,” the negative force fields of electrons on the tabletop are repelling the negative force fields of electrons in your knuckles. That’s all the more solid we really are! 1

Atoms were a major step forward in the early universe. They make incredibly good building blocks for matter. Atoms are complex enough to provide an endless variety of combinations. They have a natural tendency to bond together to form larger units such as molecules, liquids, and crystals. Atoms and their bonds provide the tangible structure of matter, and determine intangible physical characteristics from color to hardness. Just as importantly, atomic bonds store energy, in a manner that is easy to form, stable, and easy to access. The energy that powers our homes, cars, and bodies all comes from making and breaking bonds between atoms! The energy stored within the nucleus of an atom is about 1,000,000 times greater than the energy in chemical bonds. However, that energy is notoriously difficult to store or access. It takes stars and specialized power plants to harness nuclear energy. You can access chemical energy just by eating a sandwich. 

A substance made out of identical molecules is a compound. Water is a well-known compound, which is common in outer space as well as on Earth. Water’s chemical notation H_2O indicates that each molecule of water is formed from two hydrogen atoms bonded to one oxygen atom. We can discuss this molecule as a simple example of bonding.

water molecule chemistry big history

Atoms form a covalent bond by sharing outer electrons. The X’s represent electrons contributed by each hydrogen atom. The dots represent electrons contributed by the oxygen atom. This water molecule is very stable because it is electrically neutral, and because each atom has a full valence orbital. Note that oxygen’s two “inner” electrons play no part in the chemistry.

By itself, each atom is most stable when it is electrically neutral, meaning that it has exactly as many protons as electrons. In combination with each other, atoms are more stable yet when they can share electrons in such a way that each atom has a full valence orbital. The very first orbital around a nucleus can hold only two electrons. The next few orbitals can each hold up to eight electrons. Each hydrogen atom carries only one electron with it. The oxygen atom has eight – two inner and six valence electrons. When two hydrogen atoms and an oxygen atom come into close contact, the oxygen atom shares one pair of valence electrons with each hydrogen atom, as shown in the figure. Each hydrogen atom now effectively has a full valence orbital of two electrons, while the oxygen atom has a full valence orbital of eight electrons. Altogether, these three atoms have ten protons and ten electrons, so the entire water molecule is electrically neutral and stable. It’s perfect chemistry! Because the oxygen and hydrogen atoms share their outermost valence electrons, this arrangement is called a covalent bond.

Many molecules form in outer space, ranging from hydrogen’s stable form as a diatomic compound (H2) to massive balls of carbon atoms as large as fullerene (C70). Molecules formed from carbon, especially chains of carbon, are called organic compounds because they are essential for life.

D. Complexity and Stability 

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We are beginning to see a theme that is constant throughout natural history and human history alike – the progression toward complexity and stability. 4 The beginning of the universe was a time of complete simplicity. The material world had virtually no structure to it at all. It was a symmetric universe consisting of only the most fundamental particles of existence. By themselves, particles such as quarks were fleeting. As time went on, fundamental particles joined together to form protons and neutrons, which are exceedingly stable. With more time, gravity exaggerated the universe’s slight asymmetries into clumps and structures. After hundreds of millions of years, stars led to the creation of atoms, and then to molecules. Molecules are much more complex than fundamental particles. Molecules have structure and asymmetries. This allows them to be differentiated and to relate to each other in different ways, which we can think of as bearing “information.” As we will see in the following chapters, the complexities of chemistry developed into even further complexities of biology and then human nature.

To some people, the developing complexity and stability of nature points to a “plan.” To paraphrase another common religious conclusion, “Human beings are dependent on nature, so nature must have been pre-programmed with us in mind.” This is circular reasoning. We don’t depend on nature. We are nature, because there is nothing else that we could be. If physics had been differently complex and stable, “we” would have been different. And if complex or stable structures had never come to be, then neither would we!

When simple units come together to form larger or more complex structures, very often these new structures have completely new and unpredictable characteristics. They are called emergent properties. For example, hydrogen and oxygen are two flammable gases. When chemically combined, they create water. The properties of clouds, oceans, waterfalls, and ice crystals could not be predicted by a space alien who only knew about elemental hydrogen and oxygen. These properties emerge only after the water is formed. This is only the most basic of examples. Chemicals combine to produce life. When people come together into cities, they are able to invent technology that seems downright miraculous – well beyond any one person’s skill set. Yet from the bottom to the very top of the organizational pyramid, none of this requires magic potions or spells. Everything is made of the same fundamental particles. The amazing properties of living things do not come from any special life ether or divine forces, but from the ways they are organized. This is why complexity and stability are such central concepts.

Religious arguments often rely on complexity as evidence for God. “Nature and humans are too complex to have evolved without guidance,” they say. “Therefore, they must have been designed.” That is a very interesting argument, because it is based on a glaring logical fallacy. If there is a God, then he must be even more complex than man. Therefore, he is all the more unlikely than man to have formed without guidance!

In response, we have to understand the principles of complexity discussed above. Complex things are just combinations of older, simpler things. They evolved over vast periods of time, necessitating stability. The simplest ingredients, the fundamental particles, have been around since the beginning of the universe. Sometimes, nature seems to make a quantum leap when simple things come together to make something new with emergent properties. That doesn’t imply that the emergent properties were planned.

There may be many different alternatives to nature’s fundamentals that could have led to complexity / stability, and thus to life. Life as we know it depends on seemingly random things such as carbon chains, water molecules, sodium ions, DNA, and electromagnetic radiation within a particular band of frequencies. If the universe had developed differently with none of those ingredients available, life would make do with what it had. It simply wouldn’t be life as we know it.

That being said, atoms do make excellent building blocks for matter. As has been discussed, they are extremely small. This allows a lot of complexity to be jam-packed into a small amount of space. Even a small animal such as a mouse requires billions of trillions of atoms. Furthermore, all atoms of an element are identical. This makes them completely interchangeable. The fact that atomic bonds can store energy is just another amazing property of these tiny building blocks.

This discussion is related to the anthropic principle, which is not meant to “explain” anything but merely to make a point: The properties of the universe must be conducive to life as we know it, whether there is a reason for it or not. We know this, not because of any great theory, but based on one simple, undeniable, empirical observation: life exists. The anthropic principle does actually have good predictive power. In fact, I have already alluded to it once. If the universe began in a particular incident, then we know that it must be expanding. How do we know that? Because if it didn’t expand, it would never cool off and thin out enough for life to evolve. Mind you, that doesn’t explain how the universe is expanding. It just gives us insight and corroborates the evidence that the universe does seem to be expanding. As another example, when scientists debate what the early Earth was like, they know that at some point in time it must have had the right kind of chemistry to support the origin of life, simply because we know that life originated here!

  1. Image NASA / ESA, public domain
  2. Image: By R. J. Hall (Contributor) {GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY 2.5 (http://creativecommons.org/licenses/by/2.5)}, via Wikimedia Commons
  3. Image NASA / JPL / Malin Space Science Systems, www.MSSS.com/mars_images/MOC/2003/05/22/ (accessed 5/01/15)
  4. Image © Loopall | Dreamstime.comColor Paint Pouring From Buckets And Mixing Photo , licensed to author.
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