Albert and the Atom Bomb

"Weren't you trying to explain how stars shine?"

Oh yes, back to nuclear energy. The nuclear energy industry, nuclear weapons and stars have one thing in common: mess around with atomic nuclei and big things happen. There are two types of nuclear reactions; nuclear fusion and nuclear fission. Nuclear fission is the splitting of the nucleus of big atoms like uranium or plutonium into smaller atoms. This is what happens in a typical nuclear reactor and a typical nuclear bomb. Nuclear fusion is knocking two small atoms together to make a bigger atom and happens in stars and hydrogen bombs. This also produces a totally new element.

"So big atoms split and little ones stick."

Precisely. In stars four hydrogen atoms start sticking together to make one atom of helium. When four hydrogen atoms fuse to make one atom of helium, something is lost in the process. Helium is a little less heavy (or has less mass as a scientist would say) than four hydrogen atoms. That lost bit of matter is converted in the collision into energy like us.

"So why are nuclear explosions different from normal explosions?"

A normal bomb or explosion is just a chemical reaction. At the end there are the same number and same type of atoms as there were at the start, they're just rearranged. In the process lots of heat and gas are released that makes things blow apart. All the atoms stay the same but just end up joined up in different ways to make a new set of molecules. In an atomic bomb or the Sun it's the atoms themselves that are changed or destroyed by nuclear reactions. So you end up with different types of atoms.

"So where does the energy come from in nuclear bombs?"

Ever heard of 'E = Mc²’?

"That was Einstein. Wait a minute Albert that’s you!”

Everyone seems to remember that equation. Anyway this is the key to understanding what happens when matter is converted into energy in a star.

"I'm not that good with equations I’m afraid."

Don't worry, this is the only one I'll throw at you during our journey and it's easy enough to explain how it works as an equation. Remember, equations are only a type of short code that captures an idea, so every equation has an English description. In 'E = Mc²' M is mass (the amount of material or matter), c is the speed of light (300,000,000 metres per second) and c² is a sort of short hand to mean the speed of light multiplied by itself (a really big number).

"So that's the same as 'E = M multiplied by c multiplied by c' "

Exactly, so you see, it's not as complicated as it looks.

"Hold on, what about 'E', what's that?"

Sorry, 'E' stands for energy. If you want to know how much energy, 'E', is made when you loose that little bit of mass in a fusion reaction to make helium you multiply that amount of mass that is lost, 'M', by the speed of light, 'c', and multiply the answer by the speed of light again. The final answer is the amount of energy. Because 'c' or the speed of light is such a large number, even a tiny amount of mass lost creates a huge amount of energy. This wonderfully simple equation says that a little matter turned into pure energy releases a lot of energy. If all the mass in a normal 60 Watt light bulb could be converted into electrical energy, there'd be enough energy to power an identical light bulb for 80 million years. The reason you still have to pay for electricity to keep your electric lights working is that all this energy is trapped. Even in fusion reactions only a tiny percentage of the mass of the starting materials ends up as energy. Luckily stars are so huge that they can get energy from nuclear fusion for billions of years. Sadly that little equation can also measure the misery humans can inflict on each other.

“I don’t understand?”

Wars and bombs. Remember I told you that stars are like continuous nuclear explosions? Well that same equation explains why atomic bombs are so destructive. In sensible hands atomic energy will be a great benefit for humanity, but powerful hands are rarely sensible in my experience. Remember my friend Leo Szilard that I invented those new types of refrigerator with? Well he turned into a brilliant physicist who worked out how an atom bomb might work. Leo helped me write a letter I sent to the US president Franklin D Roosevelt at the start of World War II in 1939 telling him that an atomic bomb could be made and would be immensely powerful. It also seemed Germany was starting to take an interest in an atomic bomb, so we felt forced to do it only to prevent a greater evil if Germany had developed the bomb first. Two hundred thousand innocent people paid with their lives in proof of that harmless little equation in Hiroshima and Nagasaki. I just hope the world has learnt that lesson, though I’m sure the point could have been made without so many innocent people having to die. One demonstration on an uninhabited island near Japan would have worked as well. What I really don’t understand is why Truman needed to drop the second bomb on Nagasaki after he knew the first had been so destructive. It can only have been on account of two of the worst human sentiments; revenge and a desire to humiliate the enemy.

“Do you wish you’d never discovered that equation then?”

The equation? No. I regretted writing the letter to Roosevelt but who knows what would have happened if I hadn’t. I think Roosevelt understood the significance of the atomic bomb. When Roosevelt died, President Truman took over and seemed to see the atom bomb as just another bomb, bigger and better than normal bombs. He was told America had the bomb so that was that, he wanted to bomb Japan in revenge for Pearl harbour. As to the equation, mathematics never hurt anyone, people do that. I only wrote it down. It has existed since the universe began and without it there would be no stars or starlight and no humans to make mistakes. Because it exists stars can shine for billions of years and that finally explains how humans had enough time to evolve on the planet called Earth. I just hope that humans evolve enough sense to look after our planet for the next billion years.

"So are all those scientists that worried about the age of the Earth happy now?"

Well they have enough time for all the theories of geology and evolution to make sense, but they're just worrying about different things now. Global warming, something no-one worried about in my first lifetime, seems to be worrying a lot of people now. As soon as scientists solve one problem there is always another one to solve and we’ve barely scratched the surface of science yet. We'll get to global warming much later in our trip but there's a lot of science to talk about before we get there.

"So we're only starting the journey now?"

This is still just the beginning. It will take us three thousand years to reach Earth but it would have taken us just as long to get from the centre of Deneb to here. There is so much going on in the centre of a star that light particles can't travel more than about a centimetre without colliding with some atom or other. A tiny fraction of a second later the collision produces another light particle or photon which makes a dash for it until colliding with something else. Finally photons get released from the surface and can make it into open space. But with all the random bouncing backwards and forwards it takes thousands of years for the energy of a single photon to reach the surface and escape. Even in our super giant star Deneb, light could travel from the centre to the surface in only a few minutes if there was nothing in the way. Like in a long car journey, getting out of the city is often the slowest part.

"So there’s no point in asking are we there yet?"

Not for a few quadrillion miles.

"Where are we actually going?"

Our destination? A rather pretty, bluey-green circle surrounding a pool of blackness that is situated in the back garden of a house on a planet called Earth. But there is a lot of space and time between here and there.

Stars and Atoms

Our journey will almost be over before the human race arrives at a reasonably accurate answer to the question of how old the sun is and where it gets its energy from. As stars are pretty much the most important things out here in space, it makes sense to explain how stars really work now rather than wait for humanity to work it out over the next few thousand years. The source of energy that makes the sun shine and the stars shine is a continuous nuclear bomb, an H-bomb or Hydrogen bomb. The surface of a star like the sun is around 6,000 ^oC but the core is nearer 15 million ^oC which for those of you more familiar with gas ovens is about gas mark 79,000.

"So long can this H-bomb burn for?"

Stars, in fact the whole universe, are made up of mostly of this material called hydrogen, and stars are huge so they can shine for billions of years. The sun has been shining for 4.5 billion years and can keep going for another 4 billion years. This energy comes from the process of nuclear fusion, where atoms are combined to create completely different atoms and in the process release colossal amounts of energy.

"I’m not sure I really understand what an atom is"

An atom? Atoms are what everything is made from. They are the building blocks of the universe, sort of like LEGO. Atoms, like LEGO, come in different shapes but atoms are really minute, so small you can't see them even with a microscope. This atom idea dates back almost to the start of our journey. Democritus of Abdera was an ancient Greek philosopher from around 400 BC and developed the first well thought out concept of the universe being made up of atoms. As a young man he travelled to Athens to meet Anaxagoras, the hot rock man, but was very upset when Anaxagoras refused to meet him. Democritus has the consolation that his own ideas have lasted far longer than the famous older philosopher who snubbed him. At one time everyone thought that atoms were unchangeable. You could break things down into the individual atoms but they thought that you couldn't turn one atom into another or break up an atom. There aren’t even that many types of atoms, only 92 different types exist naturally.

"You're trying to tell me that everything is made up from just 92 types of atoms?"

I am indeed and each of these different types of atom is called an element. They vary from the very smallest which is hydrogen to the biggest which is uranium. Even more surprising is that despite all these different types of atoms or elements, nearly three quarters of the whole universe is made up of hydrogen atoms. So most of the universe is made out of a single type of atomic LEGO brick.

There's a diagram called the Periodic Table, first developed by the Russian Dmitri Ivanovich Mendeleev in 1869 that lists out all the atoms/elements in terms of size. Hydrogen is the smallest, followed by helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon…

“OK, I believe you. I don’t think I’ll be able to remember all 92 anyway.”

Well like I always say, imagination is more important than knowledge. As long as you can imagine a universe made from 92 different elements that is more important than remembering all their names. That’s what reference books are for, to hold all the boring facts you can’t remember or don’t really need to remember.

You don’t even need lots of different types of atoms to make complicated things. Human bodies are amongst the most complicated things in the universe, but incredibly humans and most living things are basically made up of just six elements; carbon, nitrogen, oxygen, hydrogen, calcium and phosphorus. These six types make up 99% of your atoms with the last 1% a range of other rarer atoms.

"That's not many types of building blocks; LEGO would be dull with only six types of blocks"Well when you start combining atoms or LEGO blocks there’s an almost infinite range of things that can be built. Take just six LEGO blocks of the same size with 2 by 4 little studs, all the same shape and colour, and you could make 102,981,500 different shapes. How fast could you click together 6 LEGO blocks?“Oh, two or three seconds I suppose.”

Well at that speed it would take you almost ten years to try all possible ways of clicking together just six LEGO blocks. So it’s no wonder that you can build an entire universe out of 92 different types of atoms.

“It must take a while to make a universe then?”

Oh, it does. This one is almost fourteen billion years old after all. .

"So is light made of atoms?"

No, although all physical things in the universe from stars to humans are made from atoms we’re not. We photons are different; we're a form of energy and exist just as we are. Like heat, we can affect atoms but aren't made of atoms. Take a fire. The smoke coming out of a fire contains atoms but the light and heat you feel from a fire is energy and, in fact, is a type of photon like us. But let’s finish off atoms first. Atoms were initially thought to be the smallest division of matter but, in fact, atoms themselves are made of particles. An atom is made up of a nucleus which defines what sort of atom it is and a cloud of particles called electrons that spin around the nucleus. The electrons have a negative electrical charge and are the particles that help to carry an electrical current through a wire. The electrons are also the parts of atoms that can link atoms together to make different combinations of atoms that are called molecules. Your body is held together by these interactions of electrons which are called, reasonably enough, chemical bonds.

"Hold on Albert, let me get this staight. Atoms join together to make molecules."

That's right.

"Are humans just big molecules then?"

Well humans are made up of thousands of different types of molecules and each of those molecules is made up of atoms. By combining different atoms in different shapes the same six atoms (with a few extras thrown in here or there) can make up all the important molecules in a human like DNA and proteins. Have you heard of DNA?

"Like in Jurassic park?"

Fascinating thought recreating dinosaurs. I just read about it while I was waiting for you to join me. I'll explain all that a bit later but let's sort out the basics first. Now, where was I? Oh, yes, the glue between atoms is made up of electrons which make up chemical bonds. These bonds are where two atoms both think an electron belongs to them and hold onto them tightly.

"So if both atoms are holding onto the same electrons then the two atoms stick together, like a pair of kids 'sharing' the same toy."

Well sort of, but it does get a little more complicated from here. There are a few more names to remember about how atoms are put together, but it's worth the effort because you need these facts to know how stars shine. The nucleus is made up of two types of particles called protons and neutrons. The number of protons in a nucleus defines what element it is and neutrons somehow help to hold everything together. Remember the periodic table I just told you about?

"Hydrogen, helium, lithium and all that?"

Precisely. Well one proton means that atom is hydrogen, two protons means helium, three makes lithium and so on.

"And it doesn't matter how many electrons or neutrons, two protons in an atom is always helium?"

That's right. The protons determine the essence of what an atom is. The neutrons and electrons are important but not as critical. Take a dog. If it looses a leg and some of its fur it's still a dog inside and will still look like a dog even if it is three legged and a bit mangy looking. Legs and fur are like neutrons and electrons, important pieces of whole picture but the essential doginess is set by the protons.

As well as defining the type of atom, protons also carry a positive charge that helps to hold the fast moving electrons in their orbits. Remember the electrons have a negative charge and like the opposite ends of two magnets, positive and negative attract each other. So protons help the atom to hold onto its electrons. The simplest element hydrogen has a nucleus of one proton and one electron whizzing around it. Oxygen has eight protons, usually eight neutrons and usually eight electrons. A really heavy atom like Uranium-238 has 92 protons and 146 neutrons. Still with me?

"I think so."

There are a few more names worth hearing about, mainly because the names are so weird. You'll also impress people if you know this last piece of the atomic jigsaw puzzle. Even protons, neutrons and electrons are not the end of the story. They are made up of smaller particles called quarks. Scientists have made up some curious names for these quarks like ‘up’, ‘down, ‘strange’, ‘charmed’, ‘truth’ and ‘beauty’. In an attempt to be taken more seriously some scientists have renamed truth and beauty to top and bottom, but I rather like the original names. A proton contains two up quarks and a down quark whereas a neutron has one up and two down quarks. Naturally they are all held together with particles called gluons.

"You're making this up as you go along."

No Honestly that's what they are called. But don't worry about quarks, unless you just like the names, we can still explain most of the universe without thinking about quarks. All the same it's nice to know that everyone of you has inner beauty, truth and charm no matter how well it's hidden at times.