The beginning point of the known universe is called the big bang. It is a well-studied phenomenon. Much is known about the early timeline of the universe, going back even to a split second after the very moment of creation. The universe at that time bore no resemblance to anything we can even imagine today. This is an important issue. Some people doubt the big bang on the basis of a misplaced criticism – that the universe is too complex to have emerged spontaneously. But the big bang was not a colossal spewing forth of stars, galaxies, planets, and dinosaurs, as often shown in cartoon representations. The universe that emerged from the big bang was simple in the extreme. In the very moment of creation, there was no “stuff” as we know it, not even gas, dust, fire, or light. All that existed were space-time, forces, and fundamental particles of matter and energy. These are the subject matter of physics.
Many physics laymen are unclear about the difference between energy and forces. The clearest example of a force is gravity. It is a cause that pushes or pulls nearby matter. You are constantly in Earth’s gravitational field. If you stepped off a tall building, that field would cause you to fall and gain speed. Then you’d have energy. Thus, matter has potential energy simply by virtue of being in a force field.
Energy is actually the ultimate substance of the universe, because matter is simply a concentrated form of energy. Movement and heat are other manifestations of energy. Potential energy is stored in chemical bonds and planetary orbits. When it is free, energy is radiated in light or similar rays.
Space-time is the framework of the universe, the stage on which everything is played out. Physicists think of space-time as a unified four-dimensional reference system. It is not just an inert background, either. The big bang actually caused space itself to expand, an expansion that continues to this day.
Most people today know that matter is made of atoms. An atom consists of protons, neutrons, and electrons, and the protons and neutrons are themselves formed from quarks. Quarks and electrons are examples of fundamental particles. They are not made of smaller sub-units. These are the particles that came immediately out of the big bang. Ultimately, each fundamental particle is a tiny, standardized little knot of energy.
The standard model describes the dozens of fundamental particles in an organized scheme, something like the periodic table of chemistry. (See table). It is an incredibly interesting and important model because it describes matter, energy, and most forces all at the same time.
One of the simplest but most profound facts of nature is that fundamental particles are identical everywhere. All of the electrons flowing through your brain and your computer right now are perfect copies of one another. These electrons have remained constant in the 14 billion years since they formed. The electrons in distant galaxies are identical to the ones on Earth. This is an important consideration for the consistent development of the universe. The universe is made out of interchangeable fundamental particles that always replace each other perfectly. That could be because they were all formed in identical circumstances at essentially the same place and time. It could also be a consequence of some inherent properties of space-time and the forces.
Understanding the big bang is one of the greatest questions at the frontiers of science. Other great frontier questions include the origin of life and the workings of consciousness. These are the fundamental questions that curious people can’t help be curious about. So far, these questions have not yet been fully answered in terms of known natural principles. That is why they are so subject to supernatural speculations. The frontier questions are in fact the doorways that lead out of the hall of science, into the hall of religion. Therefore, even though the big bang was very brief and is not entirely understood, it is one of the most important questions about our past, and one of the junctures between major belief systems. It demands a lot of attention in the history of the universe.
The big bang raises some fundamental questions. What was the first cause of matter, energy, and force fields? Why do forces and fundamental particles have the particular properties that they do? (for instance, why is the speed of light 300 million meters per second instead of 200 million?) The short but frustrating answer is — “Nobody knows!” At this point, then, we have a choice. We can study the big bang as far as possible in terms of what we do know about natural principles. Alternatively, we can simply assume that the big bang required supernatural forces that we’ll never be able to observe (such as God). The latter option is for the religious. This book will follow the former, scientific path.
Throughout most of history, the creation of the universe was beyond any scientific understanding, so it was completely open to religious speculation. It got wrapped up in many cultural traditions, which are still widely taught today. Although most of us were taught creation mythology as children, there is no particular reason to believe in it. The objective thinkers of today understand that religious questions like the existence of God are matters of cultural and personal belief. Science is the realm of facts that everyone could, in principle, come to agree on. Religion is for beliefs that people can disagree about. The presentation in this book is fully scientific. If you prefer to interpret these events with some religious context (e.g. “God made that happen”) you are free to do so.
The question of how so much energy could come from empty space might seem intractable. Actually, physics offers many insights and clues. Unlocking the key to the universe’s first moments requires a synthesis of two powerful but disparate 20th century theories: quantum physics and general relativity. Quantum physics is the study of matter and energy on a very small scale, at the atomic and sub-atomic levels. It is the realm of the Standard Model discussed above. General relativity (GR) is the description of gravity as the interaction between matter-energy and space-time. Note that the Standard Model says nothing about gravity. Likewise, Einstein’s GR is a model that does not extend to the microscopic scale. To fully understand an early universe when a great deal of matter, energy, and gravity was all crammed into a microscopic space, scientists need to make a connection between quantum physics and GR. If these two theories are ever successfully unified into what physicists call the “Theory of Everything,” it could help us understand matter / energy, space-time, and forces under all possible conditions, including black holes and even the big bang.
A crucial discovery of recent times is that space naturally seethes with energy. If you zoomed in closely on a point in empty space, you would find space twisting itself into fundamental particles, which decay back into space. These interactions are called vacuum fluctuations. They have actually been indirectly observed: “Something” arising out of “nothing”! Many of the fluctuations cancel each other out: a particle with positive charge and an anti-particle with negative charge will pop into existence as twins. Added together, their total charge is zero, just like the empty space from which they were born.
Ordinary vacuum fluctuations are very small and limited to very short durations of time. According to inflation theory, a particularly large vacuum fluctuation could have gravitational consequences that make it blow up. Inflation theory does a very impressive job of explaining how the big bang could have been a gravity-assisted vacuum fluctuation. Interestingly, gravitational energy is considered negative, 1 so it cancels the positive energy of matter. All told, the total amount of energy in the universe could very well be zero! “Because there is a law such as gravity, the universe can and will create itself from nothing,” concluded Stephen Hawking and Leonard Mlodinow in their recent book “The Grand Design.” 1
Even though the mechanics of the genesis moment itself cannot yet be fully explained, it is important to note that the rest of the big bang is understood pretty well. Current 21st-century physics has done an incredible job of retracing the early universe as far back as seconds after the big bang (a trillionth of a trillionth of a trillionth of a second.)
A popular description of the ultra-early universe is a “sizzling sea of quarks” 2 at unimaginable temperature and density. As the universe expanded, it thinned out and cooled down over time. Only as the universe got sparser and cooler did it resemble what we see today. Along the way, it went through some strange phases that are almost impossible to describe in terms of human understanding. When the universe was packed into a volume the size of a planet or a lake or a suitcase, it behaved in ways that we cannot begin to visualize. The rules of physics as we know them literally could not operate in those conditions. All notions of what “stuff” is and what it “looks like” didn’t even apply.
Once matter was created and had some space to work in, forces immediately went to work combining the fundamental particles into more complex, coherent structures. The “sizzling sea of quarks” of the early universe did not survive the big bang for long. All quarks generate the strong nuclear force, which causes them to attract each other. In an instant, quarks all clumped together in triplets to form protons and neutrons. Those very same protons and neutrons still exist today, all identical and unchanged for 14 billion years. One proton by itself is also called a hydrogen nucleus because, in today’s world, a proton now forms the small central core of a hydrogen atom. Complete atoms did not exist yet in the big bang environment. Temperatures were too high for atoms to hold themselves together.
Protons also generate the electromagnetic force, which makes them repel each other. The strong nuclear force is much stronger than the electromagnetic force, but it has a much shorter reach. If two protons are placed very close together, the strong nuclear force will fuse them together. Before they can get that close, though, the protons must overcome their electromagnetic repulsion to each other. That only happens if they are smashed together at incredible speeds. In the high-energy conditions of the big bang, protons routinely fused together, in a process called big bang nucleosynthesis.
Neutrons have the strong nuclear force too. If a neutron is fused to a proton, it forms a nucleus of heavy hydrogen or deuterium. Deuterium is represented as , meaning that it has 1 proton (nuclear number, lower left) and a total of 2 protons and neutrons (nuclear mass, upper left). Two protons and two neutrons fused together form a helium nucleus, . Three protons fused with three or four neutrons form a lithium nucleus. Four protons fused with five neutrons form a beryllium nucleus. Hydrogen, helium, lithium, and beryllium are the four lightest chemical elements, numbers 1, 2, 3, and 4 on the periodic table. Note that atoms are called “elements” because at one time in history they were believed to be the indivisible, elementary particles of matter! Only since the 19th century have scientists understood that atoms are composed of smaller parts.
After the light nuclei were formed, the universe cooled down too much for protons and neutrons to continue fusing together. Therefore, for hundreds of millions of years afterward, the chemical composition of the universe was fixed at 75% hydrogen and 25% helium by mass, or 93% hydrogen and 7% helium by the actual number of nuclei. Only trace amounts of deuterium, lithium, and beryllium were created. All of these nuclei are very stable and have not changed since their formation. That allows scientists to study their relative abundance, to test hypotheses about how they were formed. The study of hydrogen, heavy hydrogen, helium, and lithium throughout outer space has been valuable in corroborating the big bang theory and understanding the conditions of the very early universe. Other various combinations of 3 – 8 protons and neutrons were momentarily created in big bang nucleosynthesis. These variations are unstable; they cannot hold themselves together for very long.
When the universe was young and dense enough, all of the particles were clumped together like a big soup, or what is more technically termed a plasma. The particles regularly interacted with each other and changed from one form to another, in a state called thermodynamic equilibrium. As the “soup” expanded, neutrinos came free and started to move freely through the smallest of pores in the soup. Neutrinos are ghostly little particles because they do not interact with “solid” matter. They can travel through the entire Earth as if the planet were not there. Therefore, they were the first particles to separate themselves from the plasma and flow freely. Otherwise, though, the universe remained a gigantic soup of light nuclei, electrons, and photons all stirred together in thermodynamic equilibrium. What this stage of the universe “looked” like is beyond human imagination.
You might be surprised to hear that everything described so far happened within the first few minutes of the universe. In fact, the protons, neutrons, and deuterium nuclei were all formed within the first split second after the big bang. Neutrinos broke free after about one second. It took roughly three minutes for helium to come onto the scene. By 20 minutes after the big bang, the universe was already too cool to fuse nuclei together into heavier elements. After those first 20 minutes, the universe didn’t change much for a few hundred thousand years! That particle soup just kept expanding and cooling.
After about 400,000 years, the universe had expanded and cooled enough so that a couple of major, related events occurred. Nuclei and electrons, which are electromagnetically attracted to each other, finally cooled down enough to start settling down together and forming complete atoms of hydrogen, helium, lithium, and beryllium. With an equal number of protons and electrons, each atom was electrically neutral. (Atoms will be discussed further below).
When neutral atoms formed, the photons (particles of light) that had been sticking to matter were finally released, like the neutrinos had been earlier. For the first time, light traveled freely through space. The universe became transparent! The photons that were released at this time are the earliest phenomenon in the universe that an observer would be able to see. Actually, they can still be easily detected! They are weaker now, but they still fill all of space and are therefore referred to as the cosmic background radiation of the universe.
The background radiation is not visible to the naked eye. Originally, these photons were released as very energetic gamma rays. Now that they have been stretched out by the expansion of space, they are in the microwave (medium-low energy) portion of the spectrum. Modern scientists have very good microwave telescopes, and have actually mapped out the microwave background radiation throughout the entire universe. (See image). In the image, red zones are the hottest and blue zones are the coolest. The temperature differences are only a matter of thousandths of a degree, so actually the distribution of energy is very uniform. This uniformity provides evidence of the inflationary period; when the universe was expanded hyper-rapidly, it was almost perfectly smoothed out. We can be glad that some lumpiness remained, though, because that allowed the universe to develop some complex structure later on, as we will discuss below.
The discovery of the cosmic background radiation in 1965 was an astonishingly compelling piece of evidence leading to widespread acceptance of the big bang theory. The radiation that you see on the skymap is not coming from any particular source. It is not like a telescope image of stars and galaxies shining their light at us. This radiation simply fills empty space. Without the big bang, it would be very difficult to explain why all that background radiation fills the universe. Most strikingly of all, big bang physicists accurately predicted the cosmic background radiation before it was ever observed. It was discovered accidentally, by antenna engineers who were not looking for it and had never heard of it. Even the radiation’s temperature and wavelength matched the predictions. The search for the cosmic background neutrinos (the ones that broke free one second after the big bang) is now on as well, though neutrinos are much more difficult to detect than photons.
After light was “released” from matter, the universe finally assumed a form that humans can begin to visualize. It was a very dark and empty universe compared to what we know today. It consisted primarily of very hot gas, hydrogen and helium atoms flying quickly through space. There were no galaxies, stars, or planets, no starlight or solid matter at all. Light and similar radiation was free to travel through space, but it was emitted randomly and did not reveal any meaningful features. (Yes, it’s still very hard to visualize!)
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