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).
--
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).
Tuesday, June 30, 2009
Thursday, June 18, 2009
Newton's Laws
There has not been a more complete contribution to the field of mechanics since Sir Isaac Newton defined the basic laws of motion. The real beauty of these laws which now bear his name is that they can explain how an apple falls off a tree to the group as simply as they can describe how the moon moves around the earth. In fact, it was that very juxtaposition that got him thinking about it in the first place.
Before him, no one could understand what kept planets and moons in their orbits. They weren't connected to anything, so explaining why they didn't fly away was a difficult proposition. But watching the apple fall led him to understand the fundamental principles of forces. I'll define the laws and then use them to explain this phenomenon.
The First Law
The first law can be described in several different ways. We can say, as is often said, that objects at rest will stay at rest and objects in motion will stay in motion until acted upon by an outside force. Another way to say this is to say that something changes velocity only when another object is applying a force. Most simply, this law describes a characteristic of mass known as inertia (which is its propensity to stay in motion unless acted upon).
This law explains that the natural motion of an object with velocity is a straight line, which is not as obvious as one might think. Before forces were well understood (i.e. before Newton), it was easy to think that forces tended to travel in curves (just throw a ball in the air) and that straight line motion was anomalous. Thus, by logic we can assume that anything moving in anything other than a straight line has a force acting on it.
The Second Law
The second law describes the effect of forces on masses. Specifically, the amount force on an object can be quantified by multiplying its mass by its acceleration. Succinctly, we say that F = ma. Here we learn an important characteristic of mass: it resists change. The larger the mass, the larger the force required to cause it to accelerate as quickly as a smaller mass.
The first law is just a special case of the second law. That is, the first law is simply a description of what happens when F = 0. By the second law we know that ma = 0, and since we know the object has a non-zero mass (it being an object), we must conclude that there is no acceleration. In other words, something with no forces acting on it cannot change velocity (whether moving or not).
The Third Law
You know this one, too. In fact, I've never met a person to whom I could say the first half without having the second half repeated to me. For every action (applied force) there is an equal force applied in the opposite direction. We sometimes finish that sentence with "...there is an equal an opposite reaction," but I prefer to avoid the term reaction, as it can cause misconceptions.
To clarify the terms of the law, nothing can apply a force on another object without having that object exert an identical force on it. To prove this to yourself, stand facing a wall with your toes against it and push as hard as you can without moving your feet. Of course, you move backwards. Why? Because the wall pushed you with the force that you pushed it.
It's easy to over-think this law. If all forces are paired and equal, then how does anything move at all? Why don't all forces cancel out? The answer is contained in the second law. When you push against a train, the train pushes against you. The train having a huge mass (relatively) has an extremely small acceleration. You, on the other hand, have a very small mass and thus your acceleration is much greater. That is why -- as a general rule -- we try to avoid getting hit by trains.
An Application:
Suddenly, very complex situations are rather easy to describe qualitatively. We can see that the moon is not travelling in a straight line, but that it is travelling in a circular motion. By application of the first and second laws we can say that there is a non-zero force acting on the moon which causes its acceleration. By observing an apple fall (which moves toward the earth without being connected to it), we can assume that the moon is similarly falling toward the earth while moving linearly past it thus keeping it in orbit.
But how can we verify this unseen force? How do we know that it is the earth which exerts a force on the moon and not some other thing that we haven't yet discovered. Newton's third law tells us that if the earth exerts a force on the moon, then the moon must necessarily exert a force on the earth. This force is observed in the tides. The moon's gravitational force on the earth causes the envelope of water around the earth to be distorted, egg-shaped. As the earth rotates, the envelope stays oriented towards the moon and we observe varying depths of the ocean depending on the time of day.
This (long) explanation and application of the most basic laws of physics have set the stage for the explanation of every mechanical (moving) system that we have been able to describe. These laws provide the fundamentals of operations for -- off the top of my head -- space travel, jet engines, dishwashers, fork lifts, building construction, airplanes, cars, and many, many more situations.
Before him, no one could understand what kept planets and moons in their orbits. They weren't connected to anything, so explaining why they didn't fly away was a difficult proposition. But watching the apple fall led him to understand the fundamental principles of forces. I'll define the laws and then use them to explain this phenomenon.
The First Law
Corpus omne perseverare in statu suo quiescendi vel movendi uniformiter in directum, nisi quatenus a viribus impressis cogitur statum illum mutare.
The first law can be described in several different ways. We can say, as is often said, that objects at rest will stay at rest and objects in motion will stay in motion until acted upon by an outside force. Another way to say this is to say that something changes velocity only when another object is applying a force. Most simply, this law describes a characteristic of mass known as inertia (which is its propensity to stay in motion unless acted upon).
This law explains that the natural motion of an object with velocity is a straight line, which is not as obvious as one might think. Before forces were well understood (i.e. before Newton), it was easy to think that forces tended to travel in curves (just throw a ball in the air) and that straight line motion was anomalous. Thus, by logic we can assume that anything moving in anything other than a straight line has a force acting on it.
The Second Law
Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur.
The second law describes the effect of forces on masses. Specifically, the amount force on an object can be quantified by multiplying its mass by its acceleration. Succinctly, we say that F = ma. Here we learn an important characteristic of mass: it resists change. The larger the mass, the larger the force required to cause it to accelerate as quickly as a smaller mass.
The first law is just a special case of the second law. That is, the first law is simply a description of what happens when F = 0. By the second law we know that ma = 0, and since we know the object has a non-zero mass (it being an object), we must conclude that there is no acceleration. In other words, something with no forces acting on it cannot change velocity (whether moving or not).
The Third Law
Actioni contrariam semper et aequalem esse reactionem: sive corporum duorum actiones in se mutuo semper esse aequales et in partes contrarias dirigi.
You know this one, too. In fact, I've never met a person to whom I could say the first half without having the second half repeated to me. For every action (applied force) there is an equal force applied in the opposite direction. We sometimes finish that sentence with "...there is an equal an opposite reaction," but I prefer to avoid the term reaction, as it can cause misconceptions.
To clarify the terms of the law, nothing can apply a force on another object without having that object exert an identical force on it. To prove this to yourself, stand facing a wall with your toes against it and push as hard as you can without moving your feet. Of course, you move backwards. Why? Because the wall pushed you with the force that you pushed it.
It's easy to over-think this law. If all forces are paired and equal, then how does anything move at all? Why don't all forces cancel out? The answer is contained in the second law. When you push against a train, the train pushes against you. The train having a huge mass (relatively) has an extremely small acceleration. You, on the other hand, have a very small mass and thus your acceleration is much greater. That is why -- as a general rule -- we try to avoid getting hit by trains.
An Application:
Suddenly, very complex situations are rather easy to describe qualitatively. We can see that the moon is not travelling in a straight line, but that it is travelling in a circular motion. By application of the first and second laws we can say that there is a non-zero force acting on the moon which causes its acceleration. By observing an apple fall (which moves toward the earth without being connected to it), we can assume that the moon is similarly falling toward the earth while moving linearly past it thus keeping it in orbit.
But how can we verify this unseen force? How do we know that it is the earth which exerts a force on the moon and not some other thing that we haven't yet discovered. Newton's third law tells us that if the earth exerts a force on the moon, then the moon must necessarily exert a force on the earth. This force is observed in the tides. The moon's gravitational force on the earth causes the envelope of water around the earth to be distorted, egg-shaped. As the earth rotates, the envelope stays oriented towards the moon and we observe varying depths of the ocean depending on the time of day.
This (long) explanation and application of the most basic laws of physics have set the stage for the explanation of every mechanical (moving) system that we have been able to describe. These laws provide the fundamentals of operations for -- off the top of my head -- space travel, jet engines, dishwashers, fork lifts, building construction, airplanes, cars, and many, many more situations.
Saturday, June 13, 2009
Galileo Galilei
b. 15 February 1564
d. 8 January 1642
Noteworthies:
- Invented physics
Galileo was a student of observation. On top of that, he was sarcastic, confrontational, pugnacious, and brilliant. His mantra was the quest of observable truth and the rejection of "truth" declared in ignorance. His mission was to enlighten those ignorant who trusted their source of truth.
During his time, truth was whatever the Church declared it to be. The Earth was the center of the universe, all things in the heavens were perfectly spherical and traveled in perfect circles, and all unanswerable questions were answered by Church leaders. Galileo's life seems to have been dedicated to breaking the mindset that truth is what men of power think it should be. His methodology was flawless: experimentation and demonstration.
When told (by a Cardinal) that ice floats only because of its sheet-like shape, Galileo performed a public experiment in which he demonstrated that density rules buoyancy. The audience watched as thin sheets of ebony sunk while large blocks of ice remained at the surface. No one could refute the evidence before them.
He was challenged on basically every important discovery he made. When observing the moon through a telescope, he discovered mountains, ridges, and hills. Saturn had "ears" and the Sun had spots. All of these went against the common philosophy that the sky was filled with perfectly circular, perfectly formed bodies. His discoveries were uniformly pronounced untrue until he simply showed his accusers what he had seen with his own eyes.
Again, turning heavenward, Galileo discovered that Venus—like the Moon—displayed phases: crescent, half, full, and back to new. Such a thing could only be possible if it orbited the sun, sometimes lying between us and the Sun, and sometimes being on the other side of the Sun. The Church was scared and frustrated. If a layman could disprove "truths" that had been taught for years by the Church, their authority would be undermined. They arrested him, threatened him with his life, and eventually exiled him. But the damage was done. People started to see that physical truths needed to be observable. Simply declaring a geocentric universe could not make it true. Our declarations must be backed by confirmed fact.
Lest we erroneously think that Galileo's anti-Church stance was anti-religious, let us consider the counsel he gave to his accusers who argued their points from out-of-context Biblical references: "The task of wise interpreters is to find true meanings of scriptural passages that will agree with the evidence of sensory experience." Indeed, his stance was more religious than their own. He maintained that God created a physically explainable world and that part of our reason for being on it was to figure out how it worked. We do not have to deny that God held the Sun in the sky for Joshua, or that He parted the Red Sea just because we can't explain it. But we also do not have to assume that it will remain unexplainable forever.
From his example comes the scientific method. A scientific question asked can only be considered answered when it is backed by repeatable, concrete evidence. The answered question then remains to be further backed by experiment or else disproved by more detailed analysis. The quest is not to be personally right, but to find the truth behind the phenomena that we encounter each day.
Perhaps these stories of Galileo disproving the clergy by experimentation seem trivial. Surely they would have thought to test buoyancy by putting things in water. Isn't that the obvious solution? That sentiment, in and of itself, is a tribute to the great gift that Galileo gave us. We see the simplicity in his methods because we have adopted them through and through. You were raised to experiment, to test, to try, to guess and be wrong, and to reason in part because of the scientific contributions made by an Italian astronomer (of course) several hundred years ago. Someone else probably would have done it if he hadn't been so persistent, but his influence stands out as the catalyst for a reasoning, scientific community that seeks for physical truth by physical confirmation.
Subscribe to:
Posts (Atom)