Sunday, January 30, 2011

Our Universe Part 1: Water


Using water as a model, we can learn a lot about how atoms and subatomic particles behave under everyday conditions on Earth and under some extreme conditions elsewhere in universe.

If you have ever wondered about the world we live in - all the different objects we encounter every day and how they interact with each other and the changes that they undergo, then you have asked a fundamental question that scientists are still asking. Experts are still wondering what matter is ultimately made up of and we don't know the whole story of how matter and energy interact. We are living in a curious age filled with strange phenomena like black holes and magnetars. At the same time, ordinary things right under our nose, the atoms inside a water molecule, for example, defy our common sense and even appear to defy the laws of physics themselves!

Let's first get a feel for matter and energy and then we can explore their origins with the birth of the universe itself.


Water: Why start here? It's so mundane! Hold up a glass of pure water and you will see that it is nothing more than a transparent liquid, a collection of simple molecules lollygagging about amongst each other.

But even this very simple molecule has some bizarre secrets to share.

A water molecule is an oxygen atom covalently bonded to two hydrogen atoms.

Check out A Gentle Introduction to Water to see how a molecule of water is put together. This website also has a great introduction to water's various physical and chemical properties.

What is a covalent bond? Well first, every single interaction in our universe can be described as one of four fundamental forces, to which I will often be referring in these articles. Every force in our universe can be broken down into one or a combination of:

The covalent bonds that hold the atoms of water together to form a molecule are an example of the force of electromagnetism. In fact, every single chemical reaction relies on this fundamental force.

This force is based on the movement of electrically charged particles called electrons. Electrons, along with protons and neutrons, are part of the atoms that make up every molecule, including water. 

What is the stuff of these protons, neutrons and electrons and why do they interact with each other? This simple question gets to the heart of contemporary theoretical physics, and this is where water begins to get interesting.

The Nuts and Bolts of Water

Let's take water's oxygen atom for example. After hydrogen and helium, oxygen is the third most abundant element in the universe. It consists of eight protons and eight neutrons grouped together in a nucleus surrounded by two orbitals of electrons.  Protons are positively charged and therefore they naturally repel each other. The electromagnetic force is at work here. The strong fundamental force acts against this much weaker repulsive force and squeezes them together in the nucleus. The strong force, in fact, is much stronger than all the other forces. It is billions of times stronger than the force of gravity but it only acts over an extremely short distance, just a little beyond the diameter of the nucleus itself. The neutrons and protons are themselves made up of even tinier particles called quarks and these quarks are bound together by mass-less particles called gluons. You can think of gluons like photons. Photons carry light, or more precisely, electromagnetic radiation, whereas gluons carry the strong force. All the fundamental forces are carried out by tiny fundamental particles, except gravity. Physicists don't know how gravity works and that is a huge open question in physics.

A simple molecule like water is a whirring complex of tiny mysterious particles of matter being acted upon by a variety of forces. Below is a basic outline of what physicists presently know about matter and energy. Don't worry about unfamiliar words, we will explore them all in due time:


Electrons, as far as physicists know at present, cannot be broken down into anything smaller. An electron has a specific charge, energy and mass. But it is not a solid little sphere; it does not have a size and it cannot be located in any precise location around the atom's nucleus. It can only be narrowed down to a region of probability where it is most likely to be found. This is because the electron has a puzzling dual wave-particle nature, and in fact, all elemental particles have this nature. Some physicists believe that rather than thinking of quarks and electrons as zero-dimensional "objects", they can be thought of a one-dimensional "strings," labelled "6" in the diagram below of a carbon atom (4) in diamond (1). The specific vibration of a string is what makes it a quark or electron (matter), or even a photon or gluon (energy). It is as if each tiny bit that makes up an atom or a quantum of fundamental force is a musical note and the atoms and complex forces we experience are symphonies composed of these notes.


In the oxygen atom, the electrons and quarks, all of this, is packed into a sphere roughly 10-11 m wide. The nucleus is only 10-15 m wide within that. To put this in perspective, if the oxygen nucleus were the size of a golf ball, then the first shell of electrons would be 1 km away and the second electron shell would be 4 km away! The rest of the volume of the atom is absolutely nothing. It is a vacuum. Fundamental forces keep everything in place where it should be. But there are places in the universe where even these powerful forces can be overcome so that electrons get squeezed into the nucleus or they get sheared off. Ordinary matter starts to look and act very strange when that happens. 

Some Strange Characters

Let's get back to our glass of water. You know that you could freeze this water to form ice or boil it to form water vapour.  Water, in each of these three physical states or phases, can be found in any kitchen.

But this isn’t the whole story. Water can also exist as a supercritical fluid, a fourth state, in hydrothermal vents when it becomes hot enough (about 400oC) and dense enough (about 250 times higher than standard air pressure). The liquid and gas phases converge into a fluid that is both liquid and gas at the same time and which has unique properties all of its own.

There is also theoretical evidence that even more exotic phases of water may exist under more extreme pressure and temperature conditions inside ice giants such as Neptune and Uranus. Superionic water does not act like a solid or a liquid. It may be thought of as a frozen three-dimensional scaffold of oxygen atoms with hydrogen atoms whizzing around within it at very high speeds. Models suggest that this ice would be an iron-hard fluid so hot that it would glow bright yellow. If it were placed in a petri dish in a lab here on Earth, it would instantly explode. This ice has electrical insulating properties whereas another theoretical phase of water, called metallic ice, is thought to be solid and electrically conductive, like most metals. Under extreme pressure and temperature, water atoms become so disordered that multiple electrons states are simultaneously partially occupied. Orbitals of electrons overlap each other and this accounts for its conductivity because electrons can move around freely. Scientists have often wondered how the ice giant planets create their large magnetospheres when they have little or no electrically conductive metallic core, which Earth has. They now believe that these planets have fluid inner mantels composed of electrically conductive water and ammonia, and it is these mantels that create the magnetic fields surrounding the planets. This is what scientists think is inside Uranus:

So much for that deceptively simple-looking liquid in your glass.

A Connection to the Stars

Now where did the water molecules in your water come from? Most people believe that all the water on Earth has been here since early in its creation and that each molecule is simply cycled through what is called the hydrologic cycle, shown below . . .

. . . where water evaporates, rains down, is absorbed into soil or rained into lakes and oceans and then evaporates again. This is mostly true. The general volume of water changes very little on Earth over time.  However, individual molecules regularly come and go. Combustion reactions as well as many of the biochemical reactions in your body create "new" water all the time.

On the other hand, water molecules can be split apart through the process of electrolysis into hydrogen and oxygen. This happens naturally in our bodies and even during lightning storms to a small extent.

Now that we know that water is continually assembled and disassembled all the time, what about its constituent elements, oxygen and hydrogen? Where in the world do they come from? It turns out they don't come from this world at all.

Hydrogen and oxygen and in fact all elements are created during a process called nucleogenesis, and extreme energies are involved (I explore this process in my article How Atoms Are Made).

Hydrogen is the simplest of the elements and it accounts for over three quarters of the entire mass of the universe. Almost all of the universe's hydrogen was created after the universe exploded into existence in what is called the Big Bang. After the Big Bang, a pre-particle soup of quarks and gluons settled into protons and neutrons and a little later into electrons, all within about a second. It took about another 400,000 years for electrons and nuclei to combine into atoms, mostly hydrogen.

The process of fusion shut down soon after nuclei the size of lithium were made as much of the initial energy of the Big Bang was lost to expansion and cooling, about 20 minutes post-bang. Oxygen is too large an atom to have been created this way. It first showed up on the universal stage millions of years later when the first stars expanded into red giants toward the ends of their lifespan, blowing their outer layers rich in elements, including oxygen, away to be dispersed into space and carried on stellar winds. Below is an image of the evolution of our universe, starting with an unimaginably powerful explosion - the Big Bang, the bright white spot at the left, and ending up today almost 14 billion years later:

So the hydrogen in water can be traced back to the birth of our universe. Oxygen, fused in the bellies of stars, is still being formed as stars die.

On Earth, we and in fact all life exist because this planet resides just the right distance from the Sun to support liquid water in our oceans and water vapour in our atmosphere. The water on Earth is thought to have come from the release of gases from its interior rocky material as it was forming as a planet.  Later, impacts with icy comets contributed some water as well.

Water, one of the most abundant molecules in our universe, has been detected on the moon, on Mars and several other planets in the solar system as well as in the form of vapour on various planets outside our solar system. It has even been detected in massive high-energy jets streaming from black holes in the centers of very distant and very old galaxies. It is the molecular signature astronomers look for as they search for life in the universe.

How and why did water, and in fact all matter and energy, begin? For our answer we must look back to the beginning of the universe itself, the Big Bang, coming up next.

Saturday, January 29, 2011

Our Universe Part 2: The Big Bang

We begin with an utterly unfathomable newborn universe and probe the nature of the singularity it is. How does physics itself begin?


In 1929, Edwin Hubble noticed that distant stars are moving away from us in all directions and that the further away they are, the faster they are moving. He looked at the light spectra from various distant galaxies and compared them with the Sun's spectrum. He found that black lines, called absorption lines, shifted toward the red end of the spectrum in all of the distant galaxy spectra he looked at, as shown below.

(Georg Wiora; Wikipedia)

This red shift is a Doppler effect. It means that the galaxies are all moving away from us. He then compared the galaxies' brightness, an indication of its distance away, to how much its spectrum was redshifted and he discovered that the further away the galaxy was, the faster away it was moving.

This observation was the seed that brought the Big Bang theory to life. Later, using the theory of general relativity as a theoretical framework, scientists were able to extrapolate the expansion of the universe backwards to a point of infinite temperature and density about 14 billion years ago. This theory has been tested using a variety of data from both cosmology and particle physics and it has gained a great deal of scientific support. There is one catch though - the infinite values for temperature and density at the very beginning of the Big Bang. Singularities, as these are called in theoretical physics, are usually taken to be a sign that the there is something wrong with the calculations, and this point still bothers physicists. Either the theory is wrong or the laws of physics themselves break down at the exact point the universe began.  Most physicists today are willing to put their money on the latter being true, and this willingness to explore the unfathomable is bearing some very strange fruit.

The graphical timeline of the Big Bang below, part of the Wikipedia page of the same name, provides a theoretical timeline of the universe that will be very handy as we begin our exploration of its birth (the website has a clearer image).

The very beginning of the universe from zero to 10-43 seconds is called the Planck epoch. Scientists can't make any predictions about events that occurred in an interval shorter than Planck time (10-43 seconds). Planck time is the time it takes light to travel 1.6 x 10-35 meters (this length is called Planck length).

Check out this website Planck Scale to put this strange value into perspective and to find out how it is obtained. There are values for Planck energy, time, length, mass and temperature. These values are all derived from combinations of fundamental constants in physics and some of them represent the smallest (length and time) or largest (temperature) possible theoretical measurement.

Why is this Planck value so significant? When scientists explore intervals smaller than this, our current theories about gravity and space-time cease to be valid. No smaller division of length or time has any meaning according to our current theories and this is why:  Electrons and, in fact, all subatomic particles break down at this point into wave functions. A wave function is a function of a subatomic particle's spin and momentum, two characteristics that distinguish one subatomic particle from another. It is nothing more than a probability amplitude - all measurable certainty goes out the window. You can think of an electron's orbital inside an atom as an example. You cannot know its exact location; you can only know where it might be. Below is a diagram of an electron orbital in a hydrogen atom. The electron could be in any one of the three doughnut shapes. It is even accurate to say the electron is a wave function "smeared" over all three regions:

This is not an easy concept to grasp let alone accept. It feels so counter-intuitive. All quantum mechanical systems like this one break down into wave functions when we approach the Planck scale universe. That means all particles of mass and energy. It makes pinning down an exact point where the universe began impossible, and it leaves us stuck at the Planck-scale border of time and length, where the entire universe, as best as physicists can describe it, is a wave function.

You could think of Planck-scale as the ultimate limit of resolution, as in a photograph. Beyond a specific point (Planck time or length) our understanding of reality breaks down into nonsense (the picture is just a fuzzy grain).

So, we have established that we can only make sense of the universe at the baby age of 10-43 seconds and older. At zero seconds we just can't know or understand the universe. Extrapolating backward gives physicists infinite temperature and density values squished within an implied infinitely small volume: zero volume.

There is another example of a singularity in our universe - black holes. I explore them in Stellar Objects Part 5. Within a black hole, all matter and energy collapse into an infinitely dense and small space. And according to current theories, not just matter and energy disappear but information itself is obliterated. Some physicists speculate that the birth of the universe may have been a black hole operating in reverse, and they call it a white hole. This theory suggests that a big bang occurs at the core of a black hole, creating a new universe independent of its parent universe. Our universe is thought to contain countless black holes, each one potentially spawning a new universe on the other side, with its own physical laws that may be different from ours, an hypothesis called the fecund universes hypothesis.

Mother Force?

Back to our universe, what is happening at 10-43 seconds? Most physicists believe that all four of the fundamental forces are jumbled into one unified force in this ultra-energetic environment. This enormous energy, expressed as particle energy, is measured in gigaelectron volts (GeV). Researchers believe the maximum energy of the universe right after the Big Bang was about 1019 GeV. This is another example of a Planck value, a theoretical energy maximum. At this energy, all four fundamental forces are believed to unify into one "mother force."

Three researchers, Abdus Salam, Sheldon Glashow and Steven Weinberg, helped provide direct evidence that two fundamental forces, the weak force and electromagnetism, combine into one force, called the electroweak force, at energies higher than around 100 GeV, earning them a Nobel prize in 1979. The particle energy of our current universe is very low, in comparison, about 10-4 eV, or 3K above absolute zero.

The weak force, strong force, and the electromagnetic force can be theoretically unified in terms of the particles that mediate them. They are each mediated through the exchange of closely related virtual particles called gauge bosons. Quantum particles of matter, called fermions, attract or repel each other by exchanging bosons. Bosons carry energy and momentum between the fermions, changing their speed and direction. Examples of these gauge bosons are photons and gluons (remember them from the previous article?) However, no boson has yet been discovered for the fourth fundamental force, gravity, and no one has been able to fit gravity into the same theoretical framework as the other three fundamental forces.

Gravity: A Big Problem When Describing the Planck Universe

The fly in the ointment when trying to understand the Planck epoch universe is gravity. Gravity is so incredibly feeble compared to the other three forces that it is simply ignored when working on particle physics problems. Physicists don't yet have a quantum mechanical theory for gravity, as they do for the other three fundamental forces. This, at first thought, might not seem to be a huge problem, because gravity is so weak it can be ignored when describing physics at the scale of particles. Gravity is described very well, however, at the macroscopic level and especially at the cosmic scale, where its effects are significant, by using the framework of general relativity. But what about black holes and the Big Bang, where gravitational effects are enormous and take place in the super-squeezed down subatomic quantum realm? Here, both general relativity and quantum mechanics must be used to describe what is going on, and at least for now, the two theories cannot be made to work together.

What Scientists Know About Gravity

We know that gravity has some peculiar qualities:

It is the only force that acts on all particles having mass (and it has an infinite range of influence over them).
It cannot be absorbed or shielded against.
It always attracts and never repels (nothing "cancels" gravity).

Gravity was first scientifically described by Galileo Galilei and later refined by Isaac Newton. Newton's laws of gravitation work well for objects on Earth but Albert Einstein's general theory of relativity, on the other hand, is the gravitational theory we rely on today for all objects, both here on Earth and heavenly bodies. It describes gravity in terms of the geometry of space-time and it works perfectly for all macroscopic objects. Try Spacetime 101 for a very good tutorial on general relativity.

We know how gravity works on large objects but we don't know how it works at the quantum level. How do you pin down the gravitational field of a subatomic particle which is a wave function? 


Unlike the gauge boson, no mediator particle has been discovered for gravity, although physicists are currently in hot pursuit of a hypothetical massless spin-2 particle called a graviton that they believe might carry out this force.  Physicists want to come up with a unified theory that resolves quantum gravity, special relativity and general relativity to explain the bizarre behavior of this very early universe, as well as black holes. The theoretical graviton could bridge the gap between quantum mechanics and general relativity. Many of the unified theories in vogue right now such as string theory, superstring theory and M-theory all depend to some extent on this theoretical graviton.

Even though there is no evidence yet for it, many physicists hold to the idea that one primordial force operated in the Planck-time universe. It is possible, according to other theorists that gravity is different from the other three fundamental forces. Einstein describes gravity as the curvature of spacetime in his theory of general relativity. It is possible that gravity, therefore, has no particle associated with it.

The recent well-publicized discovery of the Higgs boson may play a role in understanding quantum gravity. Physicists do not know why some particles have mass and others do not and they believe this massive zero-spin boson may "give" mass to those particles. If so, there could be a connection between this particle and the graviton, if it exists.

There are more questions than answers when we explore the very mysterious Planck-epoch universe. The first entity to explode from absolute nothingness is believed to be some kind of primordial force from which the four fundamental forces will evolve. This primal unified force doesn't seem likely to ever be experimentally observed because scientists would need to recreate the unimaginable energy in which it existed in order to observe it. At this point, physicists cannot even put the Planck universe into a complete theoretical framework, with gravity being the problem. Without the four fundamental forces in place yet, it is reasonable to assume that the laws of physics themselves do not exist between zero and 10-43 second. No one knows if spacetime exists right from the very beginning, or if it appears with the appearance of gravity as it breaks away from the other three (still unified) fundamental forces. This is where we are in bullet-point form:

  • There is a fuzzy primal unimaginably enormous energy from which everything in our universe has yet to evolve.
  • There is no mass and there are no objects, not even a subatomic particle, with the possible exception of some very exotic particle that has burst into existence at this point to mediate the primal unified energy, or "mother force," from which the four fundamental forces will evolve.
  • Time begins, and it has jumped mysteriously from zero to 10-43 seconds for us observers because we cannot know any smaller time unit.
  • There is as yet no framework in which energy operates.  It is about to explode into being now. Is it space-time as we know it or something stranger yet . . . ?

Stay tuned. Next: The Planck Epoch.

Friday, January 28, 2011

Our Universe Part 3: Planck Epoch

The Planck epoch universe is a point of unimaginably immense energy confined in an incredibly tiny space. What space-time is made of, and how does a unified force "break" into the four fundamental forces of the universe today?

At 10-43 seconds, the universe is about 10-33 centimeters across with a temperature of 1032 K. It's an unimaginably tiny bubble of indescribably immense energy. This particular size is is Planck length, the smallest theoretical size possible, and in string theory, it is the size of one "string," about 10-33 centimeters long. It is 10-20 times smaller than a proton inside an atom. 

How hot is HOT?

The temperature, 1032 K, is also a theoretical limit, called Planck temperature. Above this temperature, calculations break down because particle energies become so large that gravitational forces between them become as strong as the other three fundamental forces. The forces essentially melt into one unified force and predictions about everything we know about the universe, including spacetime, break down into nonsense. A recent discovery may help put this bizarre temperature into scale. Physicists recently created the highest ever measured temperature, inside the Relativistic Heavy Ion Collider, about 4 trillion degrees Celsius (about 7 x 1012 K). At this temperature, they observed atoms "melting" into a gluon-quark plasma soup, all within a temporary bubble. In this bubble, there was evidence that some laws of physics began to break down - the electromagnetic force and the weak force began to combine into a unified electroweak force. At 1032 K, theoretically at least, quarks and gluons, and in fact all matter and energy simply melt together. You will find out what quarks and gluons are in a future article - these particles will make their first appearance in the Quark Epoch Universe. For now you can think of them as the building blocks of atomic nuclei.


What's really weird about this Planck universe is that there is absolutely nothing beyond it! There is not even a vacuum because even an absolute vacuum exists within the framework, or manifold as it is called, of spacetime. There is no space or time outside the tiny newborn universe, unless . . .

We start here with a Planck-time universe in which time is now beginning and the laws of physics are just shifting into place. There is a theory that the laws of physics may not be absolutely fixed. There could be many universes, each with its own physical laws, matter and force particles. Below, a ten minute interview with physicist Michio Kaku puts this multiverse concept into perspective, and he gives us an introduction to another strange concept, extra dimensions, as well:

Let's begin with what we think might be the birth of space-time, that is, the three dimensions of space and one dimension of time that exist throughout the universe today.

First we need to know what space and time are. Time seems simple until we examine it closely. We perceive time differently from spatial dimensions. Einstein's theories of relativity treat space and time as components of a four-dimensional manifold called spacetime. The quantum mechanical model treats time a little bit differently: the perception of time flowing forward in one direction is an artifact of the laws of thermodynamics. In the quantum realm there is no rule against a backward time arrow but in the macroscopic realm we live in, time reversal is forbidden. A spilled glass of milk cannot refill itself like a film being played backward. For a photon on the other hand, or any object traveling at light speed, time stops altogether. This is a consequence of relativity. It gives time a stretchiness that becomes apparent only near the speed of light or under extreme gravity. Time is not nearly as simple as it first seems and I explore the puzzle of time in the article, Time. This being said, we may be able to set aside any questions about multiple dimensions of time. There is no evidence for multiple time dimensions and adding time dimensions does not simplify the quantum mechanical equations or help marry them to general relativity.  Yet there is an interesting article by physicist Itzhak Bars that explores the possibility of two time dimensions.

If we try to dissect and examine space-time, it is impossible to know exactly what the components are made of, but when physicists attempt to consider the laws of quantum mechanics and general relativity together, spacetime can be divided up into chunks as small as Planck-length. When they get down to pieces this small, spacetime loses its smooth appearance; it "boils." It becomes what is called quantum foam. To explain quantum foam, let's begin with a larger piece of space-time. This piece of space-time fabric appears completely smooth at a scale of 10-12 cm and larger; some roughness shows up at 10-20 centimeters, and as we zoom in to 10-33 centimeter range, the Heisenberg uncertainty principle tells us that spacetime has a certain minimum energy. This energy, called vacuum energy, means that virtual particles randomly and continuously pop into and out of existence, without violating conservation laws. With this activity, spacetime resembles a three-dimensional frothing sea.

Enter Strings

As I have mentioned in an earlier article, we have a conundrum of two well-established theories that physicists have so far been unable to mesh together into a single theory of everything. General relativity accurately describes planetary motion, the evolution of galaxies and stars and even recently observed black holes and gravitational lenses - it describes gravity perfectly on the big scale. On the other hand, quantum mechanics describes the behaviour of atoms and subatomic particles wonderfully, but it neglects gravity. For most experiments this isn't a problem because at this scale gravity is monumentally weak, but a chasm forms when physicists try to describe particle behaviour under the extreme conditions of the very early universe, where gravitational force needs to be taken into account.

String theory is a developing theory that might close this gap.  It suggests that particles arise as vibrations of tiny one-dimensional Planck-length strings which themselves arise from the quantum foam I mentioned earlier. The graviton, the theoretical mediator particle of gravity, would for example be a closed string with a vibration frequency that translates into two units of spin. Likewise, electrons and quarks are one-dimensional strings with their own specific oscillations, which give them their momentums and spins. I explore string theory in the article, String Theory.

Travel to the Fourth Dimension and Beyond!

M-theory is an extension of string theory and for its equations to work, a string has to vibrate in 10 dimensions of space. Don't worry, no one can visualize what this might look like. 10 dimensions implies six extra dimensions to our four, which have not yet been experimentally verified. Also, according to the theory, these strings exist along with sheets called branes. Strings can be confined on branes like waves on the surface of a sea. Some strings may be able to move through them. According to Einstein's general relativity, the gravitational force that arises from mass tells space-time how to curve and the solutions to his equations allow for many different curvature geometries ranging from a circle, to very complex shapes. Working with a number of dimensions, the geometry will try to minimize the energy it builds up as a result of its curvature. As a result of the elegance of string theory, many physicists embrace the idea that we have three spatial dimensions with several hidden dimensions that do not change over time. Think of energy as a ball rolling down in a spiral toward the bottom of an inverted energy cone. Energy-wise, we are sitting at the bottom of that cone. More accurately we are sitting at the bottom of a three-dimensional curve, which is just one slice through a complex multidimensional mountain range. In this sense, our particular universe may be just one of many points where that ball could rest. In other words, according to string theory, there may be many stable multidimensional possibilities for a universe to adopt as it pops into being - we just happen to have three observable spatial dimensions. These dimensions determine not only which particles can exist but also which and in what form fundamental forces exist.

How do we reconcile the predicted 10 dimensions with our three observable spatial dimensions? One idea is to consider that the extra dimensions are very small. A common analogy for this multidimensional space is a garden hose. From far away it appears to have only one dimension, length. Now imagine getting closer to the hose and finding out that it contains a second dimension, its circumference. An ant crawling in one direction down the outside of it would move in two dimensions and a fly stuck inside flying around inside it would move in three dimensions. This new third dimension is only visible within very close range of the hose. If you extend this rationale to the theory of particle-wave duality, you will discover that as you experiment with particles of smaller and smaller wavelengths and you approach the radii of some of these smaller dimensions you run the chance of coming face to face with direct evidence for the existence of even more dimensions (it is hoped). In quantum mechanics, this means blasting particles with very high energies, and that is one reason why people are putting so much money and effort into building better particle accelerators.

Extrapolating from this idea, we will surmise that the universe began with 10 dimensions. What caused some to contract and others to expand into our current space-time geometry?

String theory tells us that, when a dimension is curled up like a circle, a closed string can wrap around it and keep it from expanding. All dimensions in the very early universe may have been wrapped up by string loops. Each string-looped dimension couldn't expand beyond one Planck-length in any direction. However, strings may wrap around a dimension in one of two directions. When two strings wrapped in opposite directions come into contact they should annihilate each other. If this process happens rapidly enough some strings should annihilate each other, allowing only some dimensions to expand, but why exactly three spatial dimensions and not four or two? Some theories suggest that this is simply because three unfurling dimensions present the right number of trajectories that are least likely to interfere with one another during a very rapid expansion. Other theories suggest that we just happen to have three expanded dimensions by chance but we could have had more (or maybe less like the 2-D world in which the Simpsons live). So, we have three dimensions growing and six dimensions settling into tiny but stable curled up shapes called Calabi-Yau shapes.

This might explain why gravity is so weak. Gravity might function in more than three spatial dimensions. The graviton string might be able to move through and across dimensions. In a three-dimensional world, the strength of gravitational attraction is squared when the distance between two masses is halved. But in four dimensions strength varies as a cube rather than a square, and in five dimensions as the fourth power and so on. It's possible that gravity isn't weak at all - it just seems that way in three spatial dimensions. The extra dimensions don't need to be large for this argument to work.  This website explores how this might be so, and also how both the graviton and extra dimensions might someday be experimentally proven.

Let's go back and reconsider the beginning of spacetime fabric. We will operate on the assumption that gravitons exist and that a gravitational field is composed of an enormous number of gravitons much like an electromagnetic field is composed of an enormous number of photons, and each of these gravitons is a string executing the graviton vibration. A gravitational field is encoded in the bending of spacetime, so imagine the fabric of space-time being composed of an orderly fabric of strings all vibrating in tune. This is called a coherent state. We could ask ourselves if there is a precursor to this orderly string state, a precursor of spacetime itself. We can think of each graviton string as an indivisible unit of space-time much like an atom is an indivisible unit of an element. Now we have a problem because the whole notion of string theory presupposes strings operating within a spacetime framework. And if we take this argument further, we begin to wonder if space, time and the dimensions that arise from them are not fundamental aspects of the universe but artifacts that emerge from a much more primitive state. This is a thought to consider and I have no good answer for you.


Let's get back to our Planck-time universe - we'll again assume that gravity is analogous to the other three fundamental forces; that it is carried out by gravitons. Physicists don't know for sure if this is a true picture of gravity.  It could be just the geometry of stretchy spacetime instead, rather than a true force like the other three fundamental forces. For now, we'll treat gravity as a "normal" force, so the universe begins with one unified force, from which four different forces will arise. Think of this state as being analogous to four metals melted together to form a smooth amalgam. This amalgam is perfectly symmetrical, that is, it contains no lumps or inconsistencies. Now look at our universe today: it is full of lumps and inconsistencies - all different kinds of matter and energy clumped into gas clouds, neutron stars, galaxies and so on, separated by the vacuum of space. What happened to the symmetry?

Think of a glass of water freezing into ice. At 0oC you notice something interesting - crystals of ice are forming in random patterns. The symmetry of the "smooth" water breaks as it undergoes a phase transition into ice. This process is true of larger systems and of the universe itself. The primordial unified force in this very young universe will very soon break into the fundamental forces as it begins to cool. The image below attempts to show how the universe underwent a series of phase changes that coincide with symmetry-breaking, and the separation of the four fundamental forces from one unified force:

Because we are considering that the fundamental forces are consequences of the interaction of strings and the multidimensional branes through which they move, we can assume that the symmetry-breaking of the unified force must coincide with the expansion of four dimensions into spacetime and the settling of six additional dimensions into very small Calabi-Yau shapes.

Keeping in mind that string theory is strictly theoretical and gravity might not be a particle-mediated force, we now have at least a theoretical framework in which the universe can "become." But wait. Things are about to get even weirder! Next: The Grand Unification Epoch.

Thursday, January 27, 2011

Our Universe Part 4: Grand Unification Epoch

Gravity, dark matter and dark energy may be establishing themselves during this epoch. We explore them as we continue to follow the evolution of the very early universe.

Following the Planck epoch, the temperature of the universe is just cool enough to allow a phase transition in which the force of gravity separates from the other three fundamental forces. The other three forces at this point are still unified into one force called the electronuclear force. This is the first of what are called symmetry breaks. This idea was introduced in "Universe Part 3: Planck Epoch."

The universe during this epoch is between 10-43 and 10-35 seconds old as it expands from one Planck length to a size that is still magnitudes smaller than that of a quark (and a quark is a very tiny building block of a proton or neutron inside a nucleus).

Dark Matter 

The popularity of string theory has taken off in the last decade thanks to its promise in helping physicists explain what gravity is. In the previous Planck epoch article I mentioned that the force of gravity, according to string theory, is mediated by gravitons, theoretical massless spin-2 particles. These particles arise as the mathematical result of a series of theoretical equations that make up string theory. According to this theory, the graviton is not really a particle but a one-dimensional string whose vibration executes the graviton function. This theory might explain why gravity is so weak on our scale compared to the other three fundamental forces. Gravity might function in more than three spatial dimensions. The graviton string might be able to move through and across dimensions.

Some theorists have extended this rationale to dark matter. Dark matter is a relatively newly discovered but significant component of our universe. When mathematical simulations of galaxy formation are carried out, theorists find that the galaxy flies apart rather that coalescing, unless its mass is bumped up to values far beyond the values calculated for a typical galaxy based on its total atomic mass. Extra mass must be there somewhere, and dark matter, calculated to make up about 80% of the matter of the universe, was proposed to fill this void. Since then, observations such as galaxal rotational velocities and gravitational lensing have lent experimental support to the existence of dark matter.

Ordinary matter, made of atoms, interacts with electromagnetic radiation such as light, but dark matter does not. That is why dark matter is called "dark." It is totally transparent to any observational tool physicists have come up with, and that makes it very difficult to prove its existence, except indirectly.

Remember that gravity's effects are not observable on the very small subatomic quantum scale and that therefore gravity can be completely left out of quantum mechanical equations. But what if dark matter is not really matter at all but a field even more tangled up within higher dimensions (and less accessible to our three dimensions so my argument goes) than the graviton is, and so its effects are felt only on a galactic scale? In other words, in terms of dark matter, our bodies could be thought of as being analogous to subatomic particles in therms to dark matter's gravitational effects. Could there be a graviton-like particle that operates across even higher dimensions than the graviton, so it is even less tethered to our three spatial dimensions than the graviton proposed for "regular" gravity? We could think of the "dark matter" graviton string as being even more smeared across dimensions than the regular graviton. This could be a new kind of gravity that is so weak on our scale its force cannot be measured but it is critical on the scale of galaxies and larger. This is just a thought exercise on my part. 

If you are intrigued by the string theory approach, I recommend reading this interview with theoretical physicist Joe Lykken on the Nova website. It serves as an interesting and accessible introduction to the odd world of strings, branes and other dimensions and it explains how these theories might help us to understand gravity. His ideas about dark matter are based on a new concept called supersymmetry. He also offers a new way to think of those strange extra dimensions. Another theory of dark matter that intrigues me is spelled out in Rusty Rockets' article that suggests that dark matter might arise from superstrings that stretch out and decay as the universe expands, releasing, as they do so, gravitational waves.

Physicists have posed a number of dark matter theories based on gravity itself, several which suggest that even general relativity is not complete in terms of describing very large objects like galaxies. Most physicists, however, believe there is a kind of matter in the universe responsible for boosting the gravitational effects of galaxies, and we just haven't found it yet.

An article recently published in Scientific American magazine (Dark Worlds by Jonathan Feng and Mark Trodden, November 2010 issue) argues that dark matter consists of weakly interacting massive particles called WIMPs and that these theoretical particles might be part of a hidden universe interlaced with our own. Sterile neutrinos have also been recently suggested as dark matter mediator particles in Scientific American (A Whole Lot Of Nothing by Michael Mayer, January 2011). These neutrinos, unlike ordinary neutrinos, do not even interact with the weak force and are therefore virtually undetectable. Researchers have already had some luck in finding them indirectly through their proposed decay particles (they should occasionally decay from dark matter into ordinary matter), a light neutrino and an X-ray photon.

The question of when dark matter arises in the universe depends on which theory you go with, whether you consider it a part of the nature of gravity itself or composed of a type of non-atomic matter. As part of gravity itself, dark matter may be present already at 10-35 seconds, when gravity is believed to separate from the original unified force.

Many physicists think dark matter may be organized into a filamentous large-scale structure in our universe, a backbone along which galaxies form. The following seven minute video explains how they are attempting to locate and map these far-reaching dark matter filaments:

Dark Energy

Whereas dark matter makes up about 80% of the mass of our universe, dark energy truly dominates our present-day universe. It makes up about three quarters of the universe's total mass-energy (recall Einstein's E = mc2). It was first proposed when physicists noticed that the expansion of the universe is accelerating, suggesting that there must be some kind of force that opposes gravity. This energy is suspected to be present throughout the universe and does not interact with any fundamental force. It is currently believed that dark energy does not directly interact with the gravitational force but rather it works against it to influence the overall expansion of the universe. In other words, it operates despite gravitational attraction. Because energy and mass are related according to Einstein's general relativity, even in a perfect vacuum, some energy will be present and exert a very small gravitational effect. This is called vacuum energy and it is believed to arise from quantized fundamental fields such as gravity (a field being a network of strings and these strings have within them vibrational potential energy). Dark energy currently acts as negative pressure in the universe because, according to classical thermodynamics, energy must be lost in order to do work (the vibration of the strings) on a system. Energy equals pressure x volume, so within the constant and finite energy of the universe (imagine: this tiny quark epoch universe has all the energy it will ever have!), pressure must become negative as the volume of the universe expands. Some researchers think this switch-over happened about 10 billion years ago

It not only becomes negative but its value increases so it correctly predicts that the rate of expansion of the universe increases with time. A (big) problem with this theory, however, is that most quantum field theories predict a vacuum energy much larger than what dark energy-driven expansion should require. Though this theory, called quintessence, has yet to be fleshed out, it seems, at least to me, to mirror the gravitational weakness conundrum - maybe dark energy is much weaker than it is predicted to be because it too is mediated through strings moving through or smeared across several dimensions. This is also just a thought experiment on my part. A physicist  explores what we know about dark energy in the following 32-minute video:

The Universe at 10-35 Seconds

The baby universe is just beginning to expand and as a result, dark energy, gravity, and dark matter may be, for the first time, unleashing their effects. All three of these forces, if they are forces, are matters of some speculation for physicists, so our understanding of the universe at this stage is far from complete. If we accept the general idea of string theory, gravitons are believed to have made their first appearance through the first phase transition, as a result of symmetry-breaking.

The other three fundamental forces do not yet exist as we know them. They are still unified into what is called the electronuclear force. The theoretical model of this force is called the grand unified theory. Within the very high-energy environment of this grand unification epoch universe, three gauge interactions (carried out by three gauge bosons) that define the electromagnetic, weak and strong forces exist only as a single interaction. A theoretical particle (some kind of undifferentiated boson) that mediates this interaction cannot be detected in a particle accelerator because its predicted mass/energy approaches the Planck limit. Theoretically such a particle would have no defining characteristics such as spin, charge or mass as these characteristics will only result later from further symmetry-breaking of this primordial force.

The three particles, called gauge bosons, that mediate, or act as carriers of, the three fundamental forces, will begin to make their appearance when another phase transition occurs. This transition will mark the beginning of a new epoch called the inflationary epoch, to be discussed next.

Wednesday, January 26, 2011

Our Universe Part 5: Inflationary Epoch

The separation of the strong force releases an enormous amount of energy, enough to drive the exponential expansion of the very early universe.

At 10-36 seconds, the inflationary epoch begins as the strong fundamental force breaks from the weak and electromagnetic forces, which are still combined at this point into one force called the electroweak force.

The strong force, one of the four fundamental forces, is melded together with the electroweak force at temperatures above 1027 K, and this is the temperature at which the strong force begins to break from the electroweak force. It's occurring right now at 10-36 seconds. This temperature is many magnitudes higher than any temperature experimentally created in a lab (see Our Universe Part 3: Planck epoch), so the strong-electroweak phase transition is currently impossible to experimentally verify. The strong force is mediated by force-carrying bosons called gluons. This inflationary epoch universe has two different kinds of bosons, along with the possible graviton. A possible but undifferentiated grand-unification force has just broken into two forces: the strong force, carried out by a gluon and an electroweak force, carried out by some kind of electroweak boson. So far, the universe contains only forces and the bosonic particles that carry them out.

If you are feeling confused about these strangely named particles, you may be somewhat relieved to know that they all tied together in a single model called the Standard Model. This CERN website provides a good introduction to it and then nicely puts all the elementary particles in their place:
The inflationary epoch universe contains only the gluon (a red square), the graviton if it exists (not shown because it is not fit into quantum field theory), and an electroweak boson that will later break into the photon, W and Z bosons of the electromagnetic and weak forces. Quarks and leptons (purple and green squares) make up atomic matter. They don't yet exist.

During this period the universe exponentially expands from quark size to about the size of a grapefruit (this may not seem like much but it's an enormous factor of about 1026), all within a very tiny fraction of a second. Dark energy may be responsible for the accelerating expansion of the universe we observe today but it does not explain the very early universe's exponentially rapid inflation. This inflation is much faster than the speed of light, which would seem to contradict Einstein's theory of relativity. And yet physicists now have direct evidence for this being so. Matter and energy cannot travel faster than the speed of light. Faster-than-light-speed expansion, or distortion, of spacetime, however, is allowed, carrying whatever energy and matter there is along for the ride.

NASA's Wilkinson Microwave Anisotropy Probe has mapped the microwave cosmic background radiation of the universe. The inflationary universe has not yet begun to emit any radiation energy but this map gives scientists an idea of what drove the inflationary epoch universe. Current cosmic inflation theory can explain the small perturbations detectable in the cosmic background radiation, as hugely magnified quantum fluctuations that once existed in the microscopic-size universe. This theory solved several problems with the Big Bang theory but it came with a few puzzling problems as well, some of which have since been worked out.

One puzzle is what is called the horizon problem. The temperature and polarization of radiation is essentially the same in any part of the universe today. This means that very distant points in the universe have the same temperature. This might not seem weird at first. These distant points were once side-by-side neighbours before inflation began so they should be the same temperature, right? The fly in the ointment is this: the inflation happened too fast (faster than the speed of light) for any information (heat energy, for example) to be communicated between points in space. Running the inflation backward might help explain this. Imagine watching an inflation film of two adjacent points in the universe as they fly away from each other to a distance of 300,000 km. If you run this film backwards at the same speed it will take less than a second for them to come back together. They seem to have surpassed the speed of light. The solution to this problem lies in the "exponential" part. Expansion got faster as it proceeded, meaning that when you run the inflation film backward the expansion rate slows down. This gives all the adjacent particles more than enough time to share heat energy. This inflation modification of the standard cosmological model solves the horizon problem and is now widely accepted.

All the above explains, in a mechanical sense, how cosmic inflation occurs but it does not explain why it occurs. The very fabric of space-time itself at this particular point in time begins to exponentially expand - what is the trigger? No one is sure, but between 10-36 seconds and 10-32 seconds a phase transition resulting in the separation of the strong fundamental force from the other two forces (together called the electroweak force) occurs, resulting in a very rapid influx of energy and leaving the universe in a very unstable state. To give you some idea of why this symmetry breaking might be so energetic, think of how strong the strong force is - it is 100 times stronger than electromagnetism, which is several orders stronger than the weak force and very many orders of magnitude stronger than gravity. 

Some physicists have suggested that the instability of the strong force symmetry breaking may have resoled in a temporary field mediated by a particle (or more precisely a string) called an inflaton. Physicists wonder how, and if, the hypothetical inflaton fits into current inflationary theory, and how recent observations of cosmic background radiation support this theory. According to cosmic inflation theory, the inflaton field settles into its lowest energy state and, as it does so, it generates a massive repulsive force that leads to a short-lived exponential expansion of the space-time matrix from quark size to grapefruit size.

The universe is still unbelievably hot and energetic. Force-mediating bosons are breaking from an unstable pre-force "goo," making the foundation for the strong, weak and electromagnetic forces we observe today.

Next: The Electroweak Epoch.

Tuesday, January 25, 2011

Our Universe Part 6: Electroweak Epoch

A lot is going in the very young universe right now. By the end of this epoch all four fundamental forces will be operating and the first particles of matter will make their appearance. The Higgs field will be ushered in, imparting mass on matter particles as well as some force particles.

The electroweak epoch begins at the same time as cosmic inflation is triggered, around 10-36 seconds. This is also the time when the strong force breaks from the grand unified force. The potential energy released from this symmetry breaking is believed by most researchers to be the trigger for inflation. This epoch will continue until 10-12 seconds, when another phase transition will occur in which the weak interaction and electromagnetism break from the electroweak force. We begin with the universe operating under three kinds of force: gravity, strong and electroweak. 

By the end of this epoch a single electroweak force will break into two fundamental forces operating in the universe today. This means that the electroweak boson itself will break into the photon of electromagnetism and three bosons of the weak force - two charged W bosons and a neutral Z boson. A single force particle will break into a massless particle with infinite range (photon) and massive particles with a range less than 10-17 m (W and Z bosons). It implies a still present but hidden symmetry between electromagnetism and the weak force in our current universe. A single force with a particular potential energy breaks into two forces, each existing at new but different lower energy potentials that can recombine into one force if enough energy (100 GeV) is put back into the system.

The electroweak force is carried by a boson, much like the gluon boson, the force carrier for the strong force. In the universe today, bosons mediate both the weak force and the electromagnetic force. These bosons come in two general kinds. The first kind are the high-mass bosons, called W and Z bosons, which interact with something called the Higgs field. They get their mass by interacting with the Higgs boson, yet another kind of boson, and they mediate the weak force. The W and Z bosons were predicted many years before they were discovered in 1979 by experiments done at CERN, earning the scientists involved a Nobel prize. Because of their mass, these bosons can operate only within short distances confined to the atom's nucleus. The second kind is a massless boson called a photon and it carries out the electromagnetic force. Photons can essentially travel forever as different kinds of radiation.

Experimental evidence suggests that the single electroweak interaction breaks into two different force fields. This field has potential energy with four degrees of freedom. Each degree of freedom represents a boson, one of four massless precursor gauge bosons called Goldstone bosons. Each of these four Goldstone bosons becomes one of two W bosons, the Z boson and one another massive boson, the Higgs boson. The other field has a different potential energy with one degree of freedom and it becomes a massless boson, the photon. When the electroweak phase transition occurs at the end of this epoch, the symmetry of the Goldstone bosons, and the fields they mediate, will break into bosons that interact with the Higgs mechanism (W+, W- and Z bosons of the weak interaction) and the Higgs boson. Another field is also created which does not interact with the Higgs boson. The particle that carries it out remains massless as the photon of the electromagnetic interaction. I explore the recent Higgs boson discovery in detail in the article, The Higgs Boson.

This is an epoch bound by two separate phase transitions, during which the fundamental forces are breaking away from an earlier grand unified force. The first mass to appear in the universe is in the form of massive energy-mediating bosons - the W and Z bosons and the Higgs boson itself. The Higgs field conveys mass to particles and it has just broken from the electroweak force, along with the weak force and electromagnetic force The Higgs field, the electroweak force and the strong force are all mediated through different kinds of bosons in the universe today. This epoch as a time when bosons are figuring themselves out. The two symmetry breaking processes that bind this epoch show us that the strong force, weak and electromagnetic boson particles are all related to each other - they are all pieces of a grand unified force.

As these new fundamental forces usher in, the universe explodes with super-dense gas-like quark-gluon plasma. This is the result of another phase transition called the QCD transition, which occurs at an energy of about 100 MeV. Quarks uncouple from the energy of the universe and behave like free particles. This is the first form of matter in the universe. It is thousands of times hotter than the inside of the Sun and denser than a neutron star. When the weak and electromagnetic forces break from the electroweak force, this epoch ends, about 10-12 seconds after the Big Bang. We will explore this quark explosion in the next article, Quark Epoch.

Monday, January 24, 2011

Our Universe Part 7: Quark Epoch

Matter makes its first appearance in the form of extremely dense hot quark-gluon plasma.

At 10-12 seconds, the weak force and the electromagnetic force have just broken from the electroweak force in yet another phase transition. This marks the first time the universe is operating under all four fundamental forces as we know them today. The universe is about 1012 metres in diameter and it is filled with hot dense quark-gluon plasma. What is this plasma and where did it come from?

Quark-gluon plasma

Quark-gluon plasma has recently been created in the lab by slamming nuclei together at extremely high speeds at Brookhaven RHIC, as shown in this brief video:

The properties of this plasma are being studied by physicists at CERN's Large Hadron Collider, and at other particle accelerators as well. This is a great breakthrough in particle physics as well as cosmology, but what exactly is this quark-gluon plasma? It is a plasma, a state of matter, similar to but different from solids, liquids and gases. Ordinary plasmas are made of atoms stripped of their electrons so they consist of positive ions (atomic nuclei) and free electrons. This plasma is different. Physicists call it an exotic plasma. It has no electrons. There are no electrons in the universe yet. There are no atomic nuclei yet either, just a sea of free quarks and gluons. These quarks are so energetic, they interact only weakly with the gluons. Inside an atom, which exists only at a far lower energy, gluons bind quarks together so strongly, you need a powerful collider to pry quarks apart. Quark-gluon plasma is the densest matter known, even denser than the inside of a neutron star. It is perfectly frictionless and exists as a gas at very energy and as a liquid at slightly lower energy. 

Quarks are subatomic particles that make up the protons and neutrons inside a nucleus. Gluons are subatomic particles that mediate, or carry out, the strong force. Gluons act on a relatively larger scale by holding protons and neutrons together in the nucleus and on a smaller scale by holding the quarks inside each proton and neutron together, as shown in the  diagram of up and down quarks inside a proton below.
(Arpad Horvath; Wikipedia)

As the universe starts off this epoch, there are no protons or neutrons because the quarks are much too energetic to be confined inside them, even though gluons now exist and the strong force is operating through them. There are no atoms and no electrons. But, in this special plasma, we have the beginnings of matter. This nearly frictionless gas/liquid has some eerie similarities to matter at near absolute zero, called a Bose-Einstein condensate, which is also frictionless.

Mysterious Higgs

Quarks have mass. Gluons do as well, and theoretically they both acquire their mass through a force carrier particle called the Higgs boson, which is expected by now to have made its first appearance in the universe. This boson mediates a field called the Higgs field, which pervades the universe and gives mass to every particle that couples with it, including itself. Some theorists use the analogy of a pool of sticky honey through which otherwise massless particles travel, converting them into particles with mass some of which ultimately form atoms, for example. The Higgs boson, the most sought after particle in science, was recently discovered. As physicists begin to work on the properties of this newly discovered boson, we may begin to understand why matter has mass. The Higgs boson is the last particle of the Standard Model of particle physics to be discovered. What exactly is the Higgs boson? Try this Scientific American article to find out why it is so special.

What is matter?

Quark particles of matter decouple from the energy of the universe at about 100 MeV. This is a phase transition, or symmetry breaking, called the QCD phase transition. QCD stands for quantum chromodynamics. QCD matter is any number of theoretical phases of matter where degrees of freedom in the theory allow for various quarks, antiquarks and gluons. These phases of matter would only happen at far higher energy than what can be produced in any collider, but they should be present in the quark epoch universe. In ordinary matter, the strong force acts only at very short distances inside nuclei to hold quarks together but in these phases of matter, the strong force becomes the dominant operating force, operating all throughout the matter. This matter is believed to be unlike a gas or an ionized plasma - it should act more like a liquid instead.

Is matter simply the frozen energy of the universe, owing to Einstein's energy-mass equivalence (E = mc2)? Most physicists think this notion is wrong for three reasons. First, quantum particles that make up matter are not stationary but instead are in a constant state of flux. All particles of matter also have energy. Second, both energy and matter are composed of particles, which in the case of energy, can have mass or not, differing only in how strongly they interact with the Higgs field. This new information complicates our concept of what makes matter particles special. Third, every energy and matter particle, according to string theory, is a one-dimensional string, each with its own distinct vibration frequency. This makes the idea of matter as a special state seem irrelavent. If you take into account the latest theoretical physics, it might be better to think of matter more as an artifact of a complex web of interacting energy fields than as a set of one or more stationary or frozen particles. 

The quark-epoch universe is unimaginably hot and dense. It continues to expand rapidly, though not at the incredible rate it did during inflation. The four fundamental forces have separated and matter is just beginning to appear - a stew buzzing with quarks and gluons. This epoch ends at about 10-6 seconds, when the energy of the universe falls below the binding energy of protons and neutrons. But that's not all. Matter has a twin, antimatter, which is simultaneously making its debut on the universal stage, and this presents physicists with yet another puzzle to work on, as we will see next, with The Hadron Epoch.