In the last two installments of the Universe Synthesis series, I explained in relatively simple terms what happened during the first 380,000 years of the life of the universe. In the first trillionth of a second or so, the four major forces that we know today split from the single force that they started out as, and then the first inklings of matter formed. We left off with the creation of hydrogen and helium.
The problem with an expanding universe is that as is expands, it loses kinetic energy. Imagine two pots of boiling water (each with an equal amount of water in them). If you set one on the stove and dump the other one on the floor, which will cool down faster? Clearly, the water, as it expands, radiates (and conducts) more heat away from it at a faster rate. In the same sort of way—as the universe expands—it cools down. Unfortunately, it takes energy to force atoms together to make heavier atoms. At 380,000 years after the Big Bang, the universe is overwhelmingly (if not completely) devoid of any element heavier than helium. With the matter in the universe cooling and spreading out at an alarming rate, how did the rest of the periodic table form? Where do we get carbon, oxygen, nitrogen, iron, and gold?
The answer is—in the simplest form—gravity. The fast expanding space is filled, intermittently with enormous clouds of hydrogen (mixed with a very little helium). But the clouds aren't homogeneous; they're clumpy. In some places there are a few more atoms per cubic centimeter, making the region very slightly more massive than the areas around it. Believe it or not, this is the beginning of a star.
The slightly-more-massive clump has just a little stronger gravity than the other slightly less dense regions. As a result, other hydrogen atoms are statistically more likely to fall into the clump and join it. Over a very long time, the clump gets larger and larger, becoming more dense and more compact. As it gains matter (again, only hydrogen), the matter tends to fall towards the center of gravity, causing a particularly large mass of hydrogen gas to start forming there. The gas pushes on itself, or rather, it pulls it self together by its own gravity until the pressure is so great that it ignites.
Ignition, here, does not have the same meaning as it does on earth. The hydrogen is not burning, per se, it's fusing. The pressure is so great that the atoms are fused together. Two protons (which is just a hydrogen atom without its electrons) are fused into deuterium (still hydrogen, but with an extra neutron), deuterium and another proton make helium. Helium fuses into lithium, which fuses into beryllium. This is called the proton-proton chain. In heavier stars, there's enough thermal energy to initiate the CNO cycle, which creates primarily carbon, nitrogen, and oxygen. With each fusion reaction, a little bit of energy is released as light. The light you see when you look at the sun (note: don't look at the sun) is the byproduct of the proton-proton chain.
Atoms continue to fall toward the center of gravity. As they do, and because they do not fall uniformly in every direction, the whole mass begins to spin. As it does, a disc that is perpendicular to the axis of rotation begins to form around the newly formed star. Matter begins to collect into the disc. Soon a star is happily burning. Around it, other pockets of dense hydrogen have started to burn. The whole collection of them is now a galaxy.
In course of time, the star runs out of material to burn. Heavy stars can get big and hot enough to force helium, carbon, and other heavier elements to burn, but eventually the matter in the star ceases to fuse. Either gently, bit by bit, or in a violent explosion, the layers of new elements are ejected into the interstellar medium (left-over hydrogen), enriching the surrounding area with new elements. In the particularly large explosions, the atoms gain enough energy to fuse into extremely heavy elements such as gold, copper, tungsten, or mercury. Since the interstellar medium is still, even after all that, predominantly hydrogen, the whole process stars again. Only this time, the conglomerating gas is enriched.
When the disc forms around this new star, the heavier elements stay behind as the hydrogen and helium fall towards the center. Close to the star, almost all of the hydrogen falls into the giant fusion reactor leaving behind rocky clumps of carbon. These clumps eventually collide and conglomerate themselves, forming huge spinning rocks that eventually form terrestrial planets. Further out, lots of hydrogen and helium remains to collect into large, dense clouds not big enough to become stars; they become gas giants. The further away a gas giant is from the star, the more molecules are able to form in its atmosphere (being cool enough to form them without immediately breaking them apart again) such as methane (which is what give Neptune and Uranus that nice, blue color).
Lest you think that we'll one day run out of building materials, consider that after 14 billion years of element synthesis, the detectable matter in the universe is still 75% hydrogen and a little less than 25% helium. That is, everything else that is not those two elements comprises much less than 1% of the total matter in the universe. Even then, consider your car, your kitchen appliances, a gold deposit in a mountain, or the circuitry in your computer. A long time ago, in a galaxy far away (I couldn't resist, but seriously...) every single one of those atoms was being shoved together in the first few seconds after a violent supernova explosion. And every single breath of air you take is filled with atoms that were fused inside a star millions of years ago. We live and breathe stardust.
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So, that's how it happened. Or, at least, that's the best we can do at explaining it right now. This model is constantly being reformed and reworked, and new processed are constantly being discovered. One of the most amazing things to me is that almost all of this information was deduced by astronomers looking at the sun and other stars (note: do not look at the sun unless you are a trained professional). The only information from those sources that we can get is the light that they give off. In other words, astronomers found a way to deduce all of this just by looking at patterns of light given off by stars and combining it with what we already know about physics on earth. That, to me, is an amazing accomplishment.
Showing posts with label Universe Synthesis Series. Show all posts
Showing posts with label Universe Synthesis Series. Show all posts
Wednesday, October 21, 2009
Tuesday, June 30, 2009
Universe Synthesis: Part II
Previously, we explored the first three epochs of the synthesis of the universe from the beginning of the Big Bang until 10-12 seconds after it. Remembering that the longer time is around, the more time it takes to make something interesting happen, let's explore the next several epochs.
The Quark Epoch
10-12 to 10-6 seconds
As the universe continued to cool, fundamental particles finally started to emerge. The first of these are known as quarks. These are the building blocks of subatomic particles and certain kinds of quarks are even associated with each of the four fundamental forces. That is to say, at the formation of quarks, the fundamental forces began to be distinctly separated where before they were unified.
The Hadron Epoch
10-6 to 1 second
The next three epochs are characterized by which kind of particle dominated the rest (in number) at the time considered. The first kind of dominant particle formed due to the continuing cooling of the universe. Quarks started to combine to form multi-quark particles known as hadrons. At the same time, antimatter formed (I know that sounds terribly complicated, but we only use the term to describe a certain kind of matter that, when it reacts with the stuff that's currently in our universe, turns into energy in a process called annihilation. That's not so scary, is it?). Further cooling caused anti-hadrons to collide with the hadrons, eliminating most of them. However, since the number of particles was not exactly equal to antiparticles, a residue of what we now call matter stayed behind in the form of hadrons (i.e. if the other kind of matter had been more numerous, we would have called that matter, and the stuff that's in our universe now would be antimatter). Another noteworthy fact -- of course -- is the fact that now a single second has elapsed in the life of the universe.
The Lepton Epoch
1 to 10 seconds
After the hadron/anti-hadron annihilation period, leptons dominated the particle population in the universe. Leptons are also elementary particles (which come in six flavors), but are not quarks. Your favorite lepton is the electron, which is largely responsible for every electrical device that you've ever heard of. Similar to the Hadron Epoch, the Lepton Epoch ends with a large scale annihilation due to interaction between lepton/anti-lepton pairs.
The Photon Epoch
10 seconds to 380,000 years
Well, now you're thinking, "So everything annihilated everything else? What is left?" We need to get a few things straight. The term annihilation refers only to the annihilation of mass. But nothing can simply disappear. When mass is annihilated, it turns into energy. That's what all that E=mc2 business is about, anyways. Annihilated mass turning into pure energy yields an amount of energy equivalent to its mass times the speed of light squared (9*1016, or a whole bunch). That energy is expressed in little packets of energy called photons, which we more commonly call light. Also worth mentioning is that each of the two previous epochs left behind a substantial amount of matter (from which is formed every planet, star, and galaxy in the universe. So there's still stuff out there.
During this epoch, however, light rules the universe. We have an extremely dense concentration of photons that is rapidly (at the speed of light, no less) expanding. Minutes into the epoch (between 3 and 20) is a period known as nucleosynthesis, during which hadrons and leptons start to combine to form tiny pairs. The most common hadron-lepton pair is the friendly little proton-electron system that we call Hydrogen. Close behind it is a double pair (two protons, two electrons) known more commonly as Helium (finally, something we've heard about before).
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We are now hundreds of thousands of years into the history of the universe and we are just getting ready to make life sustaining planets (in just a few hundred million years!). The third Universe Synthesis post will talk about how stars and planets are formed and how the universe came to look like it does today (i.e. no more particle physics).
The Quark Epoch
10-12 to 10-6 seconds
As the universe continued to cool, fundamental particles finally started to emerge. The first of these are known as quarks. These are the building blocks of subatomic particles and certain kinds of quarks are even associated with each of the four fundamental forces. That is to say, at the formation of quarks, the fundamental forces began to be distinctly separated where before they were unified.
The Hadron Epoch
10-6 to 1 second
The next three epochs are characterized by which kind of particle dominated the rest (in number) at the time considered. The first kind of dominant particle formed due to the continuing cooling of the universe. Quarks started to combine to form multi-quark particles known as hadrons. At the same time, antimatter formed (I know that sounds terribly complicated, but we only use the term to describe a certain kind of matter that, when it reacts with the stuff that's currently in our universe, turns into energy in a process called annihilation. That's not so scary, is it?). Further cooling caused anti-hadrons to collide with the hadrons, eliminating most of them. However, since the number of particles was not exactly equal to antiparticles, a residue of what we now call matter stayed behind in the form of hadrons (i.e. if the other kind of matter had been more numerous, we would have called that matter, and the stuff that's in our universe now would be antimatter). Another noteworthy fact -- of course -- is the fact that now a single second has elapsed in the life of the universe.
The Lepton Epoch
1 to 10 seconds
After the hadron/anti-hadron annihilation period, leptons dominated the particle population in the universe. Leptons are also elementary particles (which come in six flavors), but are not quarks. Your favorite lepton is the electron, which is largely responsible for every electrical device that you've ever heard of. Similar to the Hadron Epoch, the Lepton Epoch ends with a large scale annihilation due to interaction between lepton/anti-lepton pairs.
The Photon Epoch
10 seconds to 380,000 years
Well, now you're thinking, "So everything annihilated everything else? What is left?" We need to get a few things straight. The term annihilation refers only to the annihilation of mass. But nothing can simply disappear. When mass is annihilated, it turns into energy. That's what all that E=mc2 business is about, anyways. Annihilated mass turning into pure energy yields an amount of energy equivalent to its mass times the speed of light squared (9*1016, or a whole bunch). That energy is expressed in little packets of energy called photons, which we more commonly call light. Also worth mentioning is that each of the two previous epochs left behind a substantial amount of matter (from which is formed every planet, star, and galaxy in the universe. So there's still stuff out there.
During this epoch, however, light rules the universe. We have an extremely dense concentration of photons that is rapidly (at the speed of light, no less) expanding. Minutes into the epoch (between 3 and 20) is a period known as nucleosynthesis, during which hadrons and leptons start to combine to form tiny pairs. The most common hadron-lepton pair is the friendly little proton-electron system that we call Hydrogen. Close behind it is a double pair (two protons, two electrons) known more commonly as Helium (finally, something we've heard about before).
--
We are now hundreds of thousands of years into the history of the universe and we are just getting ready to make life sustaining planets (in just a few hundred million years!). The third Universe Synthesis post will talk about how stars and planets are formed and how the universe came to look like it does today (i.e. no more particle physics).
Friday, May 15, 2009
Universe Synthesis: Part I
Lifetimes of research have been dedicated to discovering how the universe was formed, and what it looked like and how it behaved during its stages of development. The topic is a little lengthy, so it will be divided into several independent posts. But first (as usual) we need to address a critical concept: time.
Astronomers estimate that the age of the universe is something like 14 billion years. Imagine what it will look like in twice that time, another 14 billion years from today. Do you expect it to look the same? Clearly not. Most of the stars currently in the universe will have extinguished and exploded and new ones (made up of the less pure remnants of the recently departed stars) will have taken their place. With these new stars (known as population III stars), it is entirely possible that everything we currently know about the behavior and interactions between stars will have changed. Their compositions, lifetimes, and nuclear reactions will be different. With that established, it doesn't seem like a stretch to say that doubling the age of the universe changes it significantly.
Keep that in mind as we explore the first few epochs of the existence of the universe. They take place fractions of seconds after each other in what would today be termed rapid succession. Remember, however, that when the universe was 10-30 seconds old (a trillionth of a trillionth of a millionth of a second or so), it was millions of times older than it was when it was 10-40 seconds old. Back then, time wasn't very old. The age of the universe doubled in units of time too small to think about. So, at that time, fractions of a second were as significant as billions and billions of years would be today. Let's take a look at the earliest stages of the life of our home.
The universe started as an immensely massive, yet infinitely tiny point. At some point in time, something caused it to expand at an astounding rate.
The Planck Epoch
0 to 10-43 seconds
Light and heat are the only two things able to exist. Due to an extremely high temperature (~1032 °C), nothing solid can form and remain formed. Much in the same way that ice can't remain ice at high temperatures, any energy trying to form itself into matter disassociated (broke apart) immediately due to high energy light and became energy again. During this time, it seems that all of the forces that we are familiar with (gravitational, electromagnetic, and nuclear forces) were combined into one unified force that governed all things.
The Grand Unification Epoch
10-43 to 10-36 seconds
As the universe expands, it cools (the same amount of energy is distributed over a larger space), causing gravity to establish itself as a unique, fundamental force. The smallest and most fundamental particles (Higgs Bosons) also form.
The Electroweak Epoch
10-36 to 10-12 seconds
At a whopping 1028 °C, the universe separates the nuclear strong force into a unique and fundamental force (the word fundamental here is not a contradiction even though the force came from something else. I only mean that in these conditions, the force becomes fundamental). During this epoch, we suspect that a rapid expansion period took place known as the cosmic inflationary period. The volume of the universe expanded enormously for several thousand trillionths of trillionths of seconds (during which the total age of the universe doubled about 5000 times). The temperature dropped significantly and quarks (the building blocks of protons and neutrons) formed out of the now cooler energy.
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We're still a trillionth of a second away from the first whole second of the universe's life, but we have already traversed three major epochs in the formation of the universe in which we live. Stay tuned for the next major age of synthesis.
Astronomers estimate that the age of the universe is something like 14 billion years. Imagine what it will look like in twice that time, another 14 billion years from today. Do you expect it to look the same? Clearly not. Most of the stars currently in the universe will have extinguished and exploded and new ones (made up of the less pure remnants of the recently departed stars) will have taken their place. With these new stars (known as population III stars), it is entirely possible that everything we currently know about the behavior and interactions between stars will have changed. Their compositions, lifetimes, and nuclear reactions will be different. With that established, it doesn't seem like a stretch to say that doubling the age of the universe changes it significantly.
Keep that in mind as we explore the first few epochs of the existence of the universe. They take place fractions of seconds after each other in what would today be termed rapid succession. Remember, however, that when the universe was 10-30 seconds old (a trillionth of a trillionth of a millionth of a second or so), it was millions of times older than it was when it was 10-40 seconds old. Back then, time wasn't very old. The age of the universe doubled in units of time too small to think about. So, at that time, fractions of a second were as significant as billions and billions of years would be today. Let's take a look at the earliest stages of the life of our home.
The universe started as an immensely massive, yet infinitely tiny point. At some point in time, something caused it to expand at an astounding rate.
The Planck Epoch
0 to 10-43 seconds
Light and heat are the only two things able to exist. Due to an extremely high temperature (~1032 °C), nothing solid can form and remain formed. Much in the same way that ice can't remain ice at high temperatures, any energy trying to form itself into matter disassociated (broke apart) immediately due to high energy light and became energy again. During this time, it seems that all of the forces that we are familiar with (gravitational, electromagnetic, and nuclear forces) were combined into one unified force that governed all things.
The Grand Unification Epoch
10-43 to 10-36 seconds
As the universe expands, it cools (the same amount of energy is distributed over a larger space), causing gravity to establish itself as a unique, fundamental force. The smallest and most fundamental particles (Higgs Bosons) also form.
The Electroweak Epoch
10-36 to 10-12 seconds
At a whopping 1028 °C, the universe separates the nuclear strong force into a unique and fundamental force (the word fundamental here is not a contradiction even though the force came from something else. I only mean that in these conditions, the force becomes fundamental). During this epoch, we suspect that a rapid expansion period took place known as the cosmic inflationary period. The volume of the universe expanded enormously for several thousand trillionths of trillionths of seconds (during which the total age of the universe doubled about 5000 times). The temperature dropped significantly and quarks (the building blocks of protons and neutrons) formed out of the now cooler energy.
--
We're still a trillionth of a second away from the first whole second of the universe's life, but we have already traversed three major epochs in the formation of the universe in which we live. Stay tuned for the next major age of synthesis.
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