When man entered this world, his one natural tendency must have been to wonder. How to find his next meal, what to do with it, when to search for it. And after setting his evening meal alight in a fire, he might step into the dark and look at the majesties that adorned the sky, at the crisp white pearls that crystallized faint clouds of blue and gray. And then a new fire would be set ablaze, a new spark kindled. He might wonder what painted the skies, when it had arrived, and how it had come. He might wonder about his place in the midst of this overwhelming beauty, how he fit into the picture, what he was and how he had become what he was. Knowing these things would make meals no more abundant nor death any less prevalent, yet there was something about just pondering over them that set his mind into motion.
The grand scheme of the cosmos—the universe—is as elusive as it is exciting to imagine, and the volume of thought it has aroused since the dawn of humanity is almost as vast as space itself. No one subject can carry the breadth of cosmology because it is, after all, the study of everything (Narlikar, 2002). Everything that now exists, has ever existed, or will ever exist is inextricably tied to the origin and development of the universe. So how do we tame this beast? How do we begin our journey to understand the ultimate puzzle? Let us begin by going back to the first cosmologist, to the caveman who decided to contemplate the stars late one night two hundred thousand years ago (Hawking, 2010). What would be the first thing to cross his mind upon beholding the mysteries that adorned his sky? If your city suddenly fell victim to a massive power outage tonight, enabling you to gaze into the heavens with as unclouded a view as that of the caveman, and you looked up, what would your eyes feast on? It is likely that you would see something like this:
Now, what would you ask? Given that you knew absolutely nothing about the night sky, what would be the first thing to come whizzing through your mind? Ask anything; surely anything will ultimately bring you to the study of everything. One simple question might be
This is a star. A clear sky will allow your unaided eye to see around two thousand of these on average. They may seem small from Earth, but many of the stars we see at night are actually anywhere from a hundred to a thousand times larger than our sun, and they tend to cluster into massive regions called galaxies, each containing billions upon billions of stars (Cornell University). But just what is a star? To understand this, we first need to understand gravity.
Gravity is an interaction we encounter everywhere. It is simply a force of attraction between objects, meaning it pulls them closer together. There are three very important things to know about gravity:
1. It gets stronger the closer together two objects are.
2. It gets stronger the heavier the objects are.
3. It only becomes significant when the objects are extremely heavy and/or close together. This is why, for example, you feel an attraction toward the Earth, which is a million billion times heavier than you, but not to the objects around you.
Gravity has been at work from the beginning of time (Northwestern University). It is the fundamental force responsible for shaping the cosmos, and what it will do in the future could determine the ultimate fate of the universe. But to understand gravity, we must first understand a few fundamental things about the universe, and to begin, we need simply take a walk down the street.
If you stand still on a busy road and observe an ambulance rushing past you, you’ll notice that the pitch of its siren increases as it nears you and decreases as it passes away. You may have even noticed that the faster the ambulance passes you by, the more its siren’s pitch seems to peak. It turns out that this phenomenon, called the Doppler Effect, is not unique to sound. As a matter of fact, if you somehow had superhuman vision, you’d notice that not only the pitch, but also the color of the ambulance changes as it moves. As the ambulance moved toward you, it would appear slightly blue, and as it moved away from you, it would seem to be slightly red (Hawking, 2010). This is what you would see:
In the early 1900s, by taking samples of light from distant galaxies, we discovered that our view of the night sky was slightly red. We also learned that the reddest parts of the night sky were those furthest away from us. They had a higher redshift, as it came to be called. What, then, could we deduce from this? If the night sky has a redshift, then everything in it must be moving away from us, in all directions. This tells us something fundamental to cosmology: the universe is expanding, like a balloon being inflated, getting larger and larger (Coles, 2001).
Now, what if we stop the cosmic clock and run it in reverse? We can say that if the universe is larger now, and it is expanding, then it must have been smaller and denser in the past. Move the cosmic clock back far enough, and we find that at the very beginning, 13.7 billion years ago, the whole universe existed as a single point (Hawking, 2010).
Now, allow that idea to settle in your mind for a moment. Current estimates place the size of the observable universe—the part of the universe we’re actually able to see from Earth—at around one hundred billion light years (NASA). Traveling at the speed of light, 671 million miles per hour, the fastest anything can go, it would still take you a hundred billion years to get from one end to the other (Narlikar, 2002). Imagine taking something that large and squeezing it into a region of space smaller than a single atom. The universe, something regarded as almost infinitely large, came out of something almost infinitely small, out of nothing.
This singularity, a point of infinite density within zero volume, baffles physicists even today; it is a complete breakdown of our present ideas about matter and gravity (NASA). Many theories agree on the singularity having been nothing but a dense fog of energy, one to which we would not be able to apply our traditional definitions of space and time (after all, there was no space or time in the singularity).
What would the singularity look like? Well, attempting to figure this out presents a problem because we would not be able to see it; light did not yet exist and, perhaps even more importantly, nothing could exist outside of the singularity (Hawking, 2010). The universe is, after all, everything. Attempting to find anything outside of the singularity, outside of the universe, is a bit like trying to find a point north of the North Pole. It simply does not exist (Coles, 2001). The singularity is one of the true enigmas of cosmology: ever elusive, yet ever fascinating. Our theories about the universe regain their sense once we move to the moment the cosmic clock was set in motion, and we have reason to believe that it all began with an enormous flash, a Bang.
The Big Bang represents the beginning of space and time, the point at which the huge energy of the singularity burst outward, starting the expansion of the universe (Max Planck Institute for Gravitational Physics). One second later, a large portion of this energy had been converted into the first matter. This glorious moment, however, was no guarantee of the survival of the universe, for just as the Big Bang gave us matter, it also gave us its greatest enemy, antimatter (Hawking, 2010).
What is antimatter? To get into the proper mindset, first imagine taking a red-hot pan and dropping it into a bucket of cold water. What would you see? The instant the pan touched the water, you would begin to see a huge amount of steam—something indicative of the huge amount of energy given off from the contact of the very hot with the very cold—and, chances are, you would not want to stick your hand into the bucket! In the same way, any interaction between matter and its opposite, antimatter, is extremely dangerous business. When a particle of matter and a particle of antimatter come into contact, they instantaneously attack each other in a process called annihilation, which results in a colossal release of energy and radiation and the death of the two particles (Max Planck Institute for Gravitational Physics). This is where sheer cosmological luck comes into play, for if the Big Bang had churned out equal amounts of particles of matter and antimatter, the universe would not have continued to exist past its first second; everything would have annihilated itself in a vicious storm of energy. Our universe, then, must have survived because of one essential characteristic: it gave rise to more particles than antiparticles, just one in a billion more (CERN). While this seems a trivial difference, it was enough to ensure the continuity and evolution of matter and the cosmos.
We’ve now got what would appear to be a stable universe, or at least one that will not blow itself up. This is not, however, an end to intense chaos, for while the annihilation era had indeed ended, the immense radiation it released would linger for many many years to come. During this period, two of the first particles of matter, protons, which carry positive charge, and neutrons, particles of zero charge, began to combine to form the cores, or nuclei, of the first atoms (Max Planck Institute for Gravitational Physics). Note that a complete atom is actually made up of three kinds of particles: protons and neutrons at the nucleus with electrons, particles of negative charge, orbiting it. And during all this time, it is essential to recall, the universe was still expanding, and the intensity of the radiation was diminishing. Around the universe’s 300,000th birthday, the radiation weakened to the point where electrons could begin to orbit the nuclei (Case Western Reserve University). The first atom, the basic building block of matter, was born, and the universe evolved into a vast expanse of hydrogen gas made up of atoms (Hawking, 2010). Three hundred thousand years after the Big Bang, after the dark veil of radiation was lifted, the first light began its journey through space, enabling us to look back and see it today (Max Planck Institute for Gravitational Physics). This is a map of the universe as it was then:
The red and yellow spots indicate denser, hotter areas of the early universe, and it is precisely there that gravity began to work as the sculptor of the cosmos.
Over the next 400 million years, gravity drew these regions of hydrogen gas—those heaviest and already closest together—even closer together, compressing them into ultra-dense and ultra-hot spheres (Hawking, 2010). It is now that we can return to one of the first questions we asked: “What is a star?” Simply put, a star is a massive sphere of balance. This may not be how you were introduced to stars; perhaps you were told they were massive spheres of gas or fire, and these are all true statements, but it is essential to know that a star exists only because of a precisely balanced interaction between gravity and another vital force. Remember the super-dense and hot sphere we mentioned earlier? This is the heart of a star, its core. Temperatures in the core get so high that hydrogen atoms are welded together to form a heavier gas called helium, which gravity then sinks deeper into the core. This process, called nuclear fusion, releases an enormous amount of energy, creating a super-strong pressure that wants to push the star outward, to inflate it. However, gravity wants to do the opposite; its goal is to squeeze the gases tighter and tighter, to pull the star back into its center as it did when first creating it. In a main-sequence star like our sun, the forces of gravity and fusion are equal. What this means is that the pushes and pulls cancel each other out; the star doesn’t expand or shrink (Cornell University). Think of what happens when you shake an unopened can of soda. The movement makes the soda fizz and the bubbles of gas rising to the surface of the soda increase the pressure in the can. However, the can is strong enough to keep the expanding gases inside; nothing happens.
But what if the can isn’t strong enough? What happens when the core of a star runs out of hydrogen? Well, then the tug-of-war is decided. Gravity wins. All the material in the star is quickly compressed further and further. The core is forced to produce heavier and heavier elements: oxygen, carbon, silicon, and iron. The star then reaches its breaking point and explodes. This intense release of energy forges even heavier elements and creates a blast that shines across the universe, brighter than a billion suns. This is what cosmologists call a supernova (NASA).
The material from the supernova flies outward in all directions, just like the jet of energy emanating from the Big Bang, except that this time, gravity has not only gas to play with, but also metals, metals like silicon and iron, metals with which it can create large cosmic rocks, some of which become planets. This is precisely how the Earth came into existence 4.5 billion years ago. A billion years afterward, the first life on Earth evolved, building itself out of the elements expelled from a dying star. Then move ahead to the universe as it was two hundred thousand years ago, and the first human beings emerge as a clever rearrangement of those very elements. Every single atom in your body, every hair, every cell, even every thought, is a product of stellar evolution (Hawking, 2010).
Not all supernovae, however, turn out such beautiful results. Some, instead, create the monsters of the cosmos, black holes. When a very massive star, one many times heavier than our sun, exhausts its nuclear fuel, gravity again compresses the core and triggers the explosion we’ve just learned about. This time, however, because that core is so incredibly heavy, the gravity inside of it gets almost infinitely strong. The result is a black hole, a region of space from which nothing, no matter how massive or fast, can escape (Coles, 2001). Perhaps even more fascinating is the fact that at the center of a black hole lies a point of zero volume and infinite density, another singularity, a point at which time itself ceases to exist (Boston University). Does this sound familiar? Could the singularity of a black hole have anything to do with that of the Big Bang? Some say it does, that there is another side of a black hole called a white hole, a sort of exhaust pipe for our universe. According to the theory, if you fall down a black hole, you do not disappear permanently, but instead emerge as new matter in a new universe (Than, 2010). There has been no way to prove any of this, and many still hold that we will never know for certain what happens at the singularity, but it is among the most exciting trains of thought for a cosmologist to follow.
We have allowed cosmology to take us from the beginning of time, 13.7 billion years ago, to the present. We have witnessed the creation of the first matter, the outpour of the first light, and the origins of our own existence. We have watched the universe grow from nothing into everything. There remains one last thing for us to explore, and that is the ultimate fate of the universe. It’s been said that all great things must come to an end, and if the science is right, then the cosmos, too, must one day be extinguished.
The most accepted theory on the end of the universe describes an event known as the Big Chill, a point at which the universe will have expanded so much that everything in it will be very far apart (Hawking, 2010). Distances between things would become so great that gravity would no longer be able to play an active role. As interactions deaden and the cosmos expands further and further, temperatures would decline further and further (Leslie, 1998). Stars would gradually burn out, planets would freeze over, and the universe would very slowly approach the lowest possible temperature, absolute zero. During this time, atoms would begin to fall apart into individual particles, some of which would decay and become antiparticles. The resulting annihilation would wipe out almost all matter in the universe. Only black holes would remain, and after a very, very long time, even they would decay, leaving the universe as a vast expanse of cold nothingness, and because nothing would occur, there would be no time (Physics of the Universe). This point would mark the end of the glorious wonder that once was our universe, the end of the story of everything.
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