Sunday, January 30, 2011

Our Universe Part 1: Water

NOTE: I HAVE EXPANDED, UPDATED AND IMPROVED THE ENTIRE "OUR UNIVERSE" SERIES OF ARTICLES AS OF NOVEMBER 2012

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

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:

(Headbomb;Wikipedia) 

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.

(MissMJ;Wikipedia)

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.

2 comments:

  1. Great work, Science Girl! That glass of water is like the rabbit hole in Alice In Wonderland - the deeper we go, the curiouser things get.

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  2. Very good read Science Girl!, can't wait for the next article.

    ReplyDelete