Particle Physics is a relatively new and exciting area of science. It deals with the small, the very small and the even smaller. It is often defined as the study of the smallest particles known to man. It has many ramifications in exciting new areas of technology, science, and philosophy, as well as in areas where you wouldn’t expect Particle Physics, and antimatter to have any practical value, for example medicine and health care. In this essay I will be presenting the history of our scientific view of the world around us, as well as current uses and applications of particle physics and possible future developments.

The Greek’s View of the World

“Sweet or sour, hot or cold by convention, existing are only atoms and void”

- Democritus (c. 400 BC)

The first people to try and classify the world that we live in and describe it in scientific terms where Ionian philosophers in the 6^th Century B.C. They attempted to describe the world around them purely by rational thought, reasoning and logical arguments, basing their thoughts on a few axioms or first principles. (Many, if not most scientists up until even the 19th Century had disdain for experimental science, not thinking it as pure as thought, and considered manual work as demeaning, and often, if the experimental results disagreed with theory, it was the experiment that was presumed to be wrong). The Ionian Philosophers came to the conclusion that the Planet earth was composed in its entirety of but four different substances, or “elements”, EARTH, AIR, FIRE, and WATER. All other substances, where combinations of these four, in different proportions, reflecting the different properties of objects and materials that would be observed.

Other ancient Greek scholars, for example Aristotle, refined this theory slightly, believing that every element consisted of a formation of concentric spheres composed of earth, water, air and fire in order (A system that had first been proposed by Iraclitos.) The specific order was used to describe certain phenomena such as rain or thunder. Another “Fifth Element” was also proposed to exist in an outermost sphere. This fifth element was named “Aether.”

The term “Atom” (“atomos” is the Greek for indivisible) itself was first proposed by the Philosopher Democritus, who proposed the idea that there exist tiny particles that cannot be further divided. Democritus believed that the properties observed in objects at normal distance were a direct result of the arrangement on the atomic scale.

Emerging Nineteenth Century Theories

“The great tragedy of science -- the slaying of a beautiful hypothesis by an ugly fact.”

- Thomas Huxley

Because there was very little experimental evidence, there where not many developments on the fundamental principles set down by the Greeks millennia before. However in 1808 an English chemist called John Dalton put forward his Atomic Theory in a book to explain the results of a number of experiments he had performed with gases. Dalton’s Atomic theory states:

1. All matter is made up of very small particles called atoms

2. All atoms are indivisible. They cannot be broken down into simpler particles.

3. Atoms cannot be created or destroyed.

Dalton’s theory was readily accepted by 19^th Century Chemists, mainly because unlike the Greek philosophers of the past, his theories where backed up experimentally.

Text Box: John Dalton’s Elements A while after, it was realised that the atom itself consisted of even smaller, more fundamental parts of matter. There was a lot of experimentation in the 1860’s involving vacuum tubes (glass tubes at a low enough pressure that electric current can flow through them.) A chemist called William Crookes discovered in 1875 that there was radiation coming from the negative metal plate in the tube (the cathode). He proved there existence by placing a Maltese cross inside the tube, and a shadow was formed on the other end. The rays where called Cathode Rays, as they came from the cathode.

In 1897 the English scientist J.J. Thompson showed that the rays consisted of negatively charged particles, by placing a positively charged plate inside the cathode ray tubes, so that the rays where deflected from their paths and striking a fluorescent screen at a different point than it would if the positively charged plate had no effect on it, thus proving that cathode rays where negatively charged particles. He named these negatively charged particles “electrons”, a name that had been proposed in 1891 by George Stoney.

These revelations led to a new model of the atom being formulated by J.J. Thompson. This model was known as the plum pudding model of the atom. The premise behind it was that since an atom was neutral, there must be positive charges inside it also to neutralise the effect of the negative electrons. The plum pudding model of the atom had a sphere with positive charges, with negative electrons embedded in it at random, somewhat like raisins in a plum pudding, hence the name.

However, the plum pudding was proved false in 1909 by a famous experiment by Ernest Rutherford. Rutherford and his students where researching the scattering of alpha particles (Helium Nuclei) by gold foil. The experiment had a radioactive source emitting alpha particles into thin gold foil, where they would be scattered and detected by fluorescent screens. Rutherford and his students expected to find that some of the alpha particles would be deflected by some amount as they passed through the “plum pudding” atoms of the gold foil, however their results proved J.J. Thompson’s theory of the atom to be wrong, as some of the alpha particles where scattered at very large angles and a few where even going backwards. This wouldn’t happen under the Plum Pudding Model of the Atom, and could only be explained if there was a small dense core of the atom. Later experiment revealed the nucleus to consist of two different types of particles, proton and neutrons, protons having a small positive charge, while neutrons where neutral and carried no charge. The mass of both the protons and neutrons dwarfed the tiny electron, having only approximately 1/1838 the mass of the proton, however both the proton and electron have equal charges, positive and negative respectively. So the model of the atom had changed in just 100 years from Dalton’s Atomic Theory to this. However were neutrons, protons and electrons the smallest possible particles, the fundamental building blocks of matter that the Greek Philosophers such as Democritus envisaged? The answer to that, as we will see is no.

Ernest Rutherford
Quarks

“Three Quarks For Muster Mark!”

-James Joyce (From Finnegan’s Wake)

Soon after the discovery of the neutron and proton, other smaller particles where discovered. Soon there was a whole plethora of subatomic particles, and scientists needed to find a way to unify them. In the early 1960’s, physicist Murray Gell-Man noticed that there was an underlying structure behind many of these particle types. In fact there is more to it than that, as physicists have created a theory known as the standard model, with much help from the physicists Sheldon Glashow, Abdus Salam and Steven Weinberg who won the Nobel prize in 1979 for helping to unify certain sectors of the theory. The Standard Model states that there are only a few fundamental particles, namely 6 quarks, 6 leptons, and force carrier particles. All known particles are combinations of the quarks and leptons, and they interact by exchanging force carrier particles. Also, for each quark and lepton, there is an antimatter equivalent (I will explain antimatter later)

The 6 kinds of quarks are divided into three different pairs: up/down, charm/strange and top/bottom. Quarks each have a fractional electric charge.

Quarks cannot exist independently, and are always found in groups called Hadrons. Hadrons always have an integer electric charge, rather than a fractional one. Hadrons are again divided into two kinds, Baryons, which consist of three quarks. Both protons and neutrons are baryons, consisting of two up quarks and a down quark, and two down quarks and an up quark respectively. The other kind of hadron is a Meson, which consists of one quark and an antiquark. Because they contain both particles and antiparticles, most mesons are very unstable. The way that hadrons are combined from quarks is complex and is based on another property of quarks called “colour,” which I won’t go into here.

The other kind of fundamental particle is the lepton. There are six kinds of leptons, three of which are neutral, while the other three carry electric charges. The electron is a lepton; while the other charged leptons are the muon and the tau. The other leptons are the neutrinos (neutrino is Italian for “little neutral one”). The tau and the muon, are thousands of times heavier than the electron, and decay very quickly. The interesting thing about neutrinos is that they are practically impossible to detect. They can pass right through the earth, or even the sun without being stopped. However there are a few neutrino detectors around the world, for example the Super Kamiokande neutrino detector in Tokyo. (Seen left) *

What is Antimatter?

“….they are ill discoverers that think there is no land when they can see nothing but sea.”

Francis Bacon (1561-1626)

Antimatter was predicted by English physicist Paul Dirac in 1928 while trying to combine quantum theory with the ideas of relativity and Maxwell’s equations. Dirac derived an equation for the propagation of charged particles which led to unexpected results; as well as correctly describing the physical properties of an electron, it also described the properties of a new, undiscovered particle, one which would have the same mass of an electron, but positively charged. Shortly after this result was obtained by Dirac, this new particle, called the positron was observed in cosmic ray experiments. Dirac drew the conclusion that all particles that are described by his equation must have an antiparticle, and today we know this holds true for all subatomic particles. The antiproton, which holds a charge of –1 was discovered in the 1955 by Emilio Segre, Owen Chamberlain, Clyde Wiegand and Thomas Ypsilanti at the Berkeley Bevatron.

In the early 1930’s physicists only knew about four “fundamental” particles, the proton, the neutron, the electron, and the force messenger photons. However, know we know of over 100 elementary particles, and more are being discovered all the time. *

Above: Penning trap used to store antimatter at CERN

Particle – Anti Particle Collisions

The Standard Model is recognised as a very good theory by nearly all physicists. However there are some parts of it that don’t add up. One of the main problems with it is that it doesn’t try and explain gravity, which is completely ignored. Some physicists have hypothesised that gravity has a force messenger particle called the gravitron, however this particle is still hypothetical, and there is no evidence for it, other than the fact that it is known that gravity doesn’t act at infinite speeds, but rather at the speed of light.

Text Box: Peter Higgs The other problem with the standard model is that the masses of the particles don’t quite add up either. For example, two up quarks and a down quark combine to form a proton, yet a proton has much more mass than the original quarks on their own. Physicists are still trying to explain the existence of all this extra mass. Scientists at CERN as well as at Fermilab in Illinois are hoping to find something that they call the “Higgs boson.” They believe that the Higgs Boson is a particle, or a set of particles that give other particles mass. The idea that one particle can create mass in another might at first seem counter-intuitive, and going against the laws of thermodynamics and physics, however physicists often use a simple analogy to help describe it: Imagine you are at a Hollywood party. The crowd of guests is thick and evenly distributed around the room. When a big star arrives at the door, she attracts the people closest to her, and as she moves, those further from her return to their conversations. By gathering all the people crowding around her she has gained momentum, an indicator of mass. It will be hard for her to stop, and once she stops, it would be hard for her to start moving again.

This clustering effect is the Higgs mechanism, thought up by British physicist Peter Higgs in the 1960’s. Higgs theorises that a lattice known as the Higgs field, fills the universe, somewhat like the electromagnetic field, in that it affects the particles that move through it, but is also related to the physics of solid materials. While the simplest theories postulate that only one boson exists, others say that there may well be several. Before these theories can be verified, the existence of the Higgs boson has to be proven. Fermilab and CERN physicists have been searching for the Higgs boson for over ten years now. Scientists at the ALEPH experiment situated at the LEP (large electron-positron collider) at CERN believe that they may have found the Higgs boson, however the evidence gained so far is still inconclusive. *

This image at the ALEPH labs at CERN is being touted as possible evidence for the Higgs Boson

The Work of CERN

The History of CERN

“Science knows no country, because knowledge belongs to humanity, and is the torch which illuminates the world.”

- Louis Pasteur (1822-1892)

CERN is the European Organisation for Nuclear Research and the world’s largest particle physics centre. It is located at Geneva, Switzerland. During World War II many scientists had to leave Europe, and many found work in the United States. Because of this, high-energy particle physics research in Europe lagged far behind America during the 1950’s. As a result of this, a UNESCO meeting in Florence in 1950 recommended that a joint European Laboratory would be formed to conduct high-energy particle physics experiments.

Bubble Chambers

Much of the early works at CERN in the field of experimental particle physics was done with bubble chambers. Bubble Chambers where invented by Donald Glaser in 1952 (who won a Nobel Prize for Physics in 1960 for his invention). Bubble chambers consist of small chambers, from 30cm in length to over 5 metres, which are filled with liquid hydrogen (liquid hydrogen was used as the nucleus of a hydrogen model is a single proton, making it a good target material) and a beam of particles is fired into it. Because liquid hydrogen boils at only a few degrees above zero, a stream of ionising particles fired into it will cause the liquid hydrogen to boil along the path, which can then be photographed and analysed. *

One of the very first bubble chamber images produced.

The LHC

“There are grounds for cautious optimism that we may now be near the end of the search for the ultimate laws of nature.”

- Stephen Hawking

One of the ongoing projects at CERN is the construction of the LHC, or Large Hadron Collider. The LHC will follow the same course as the 27 kilometre long LEP tunnel (the LEP was decommissioned in 2000) and when it is expected to be completed in 2005 it will be probably the most advanced particle accelerator in the world, using the most advanced super conducting magnet and accelerator technologies. The LHC experiments are designed to look for theoretically expected phenomena, for example the LHCb (the “b” stands for beauty) and will be able to collide particles together with over 30 times more energy than the RHIC (Relativistic Heavy Ion Collider), which is located in Illinois, the United States. Scientists eagerly await the completion of the LHC, as it may hold the key to finding a whole new level of particles, as well as possibly finding evidence for the new Super string Theory.*

The LHC under construction

Why is the work of CERN important?

“I have heard statements that the role of academic research in innovation is slight. It is about the most blatant piece of nonsense it has been my fortune to stumble upon.”

- Hendrik Casimir

Generally science is lumped together into two main groups, basic science and applied science (and obviously again branched out into the three different disciplines, physics, chemistry and biology.) Applied Science is science designed to answer specific questions, for example how can we make cars faster, cleaner, more fuel efficient and so forth, while basic science is simply motivated by curiosity, and the quest for answers. Many people would question the importance of basic science, and why something with seemingly so little practical value should be funded by governments, when no-one knows what use, if any the answers to the questions will be, when the money could be better spend on funding specific research projects to find a solution to a problem with practical implications. However, this point of view is wrong, and often, a seemingly useless theory or discovery, will later be found to be extremely useful, for example, the nature and properties of electromagnetic waves that where found by Hertz, paved the way for the telecommunications industry many decades later, rather than the telecommunications industry discovering electromagnetic waves as a means of transferring information. Other examples of developments of particle physics that at the time where considered useless and were later found to be useful include the semiconductor industry, sterilisation of medical equipment etc, radiation processing, cancer therapy, incineration of nuclear waste and power generation.

CERN has also made some important achievements in different fields. Probably CERN’s greatest and most well known non particle physics related invention was the World Wide Web, or WWW, which was invented at CERN in the late 90’s by scientist Tim Berners-Lee. The World Wide Web was originally designed for information sharing between scientists working in different institutes and universities all over the world.

Possible dangers of High energy Particle accelerators such as CERN and RHIC

“If knowledge can create problems, it is not through ignorance that we can solve them.”

- Isaac Asimov

With the amount of energy that particle accelerators put into accelerating particles at high speed, and the way that particle collide with such energy to create some of the most exotic particles, it is inevitable that some controversy will arise over the construction of these accelerators.

Controversy over such things isn’t a new thing, for example, in 1942, Dr. Edward Teller, was invited to a secret meeting, about the possible design of a practical atomic bomb. Teller suggested the terrifying possibility, that the ignition of a nuclear explosion might create temperatures high enough that the entire atmosphere might ignite, destroying almost all life on earth. Although the idea was dismissed as nonsense by most of those present, the Director of the Manhattan Project (the project to create the Atomic Bomb) considered it serious enough to demand a study on the possibility. Fortunately, the report showed that the nuclear fireball cooled far too slowly to trigger the ignition of the entire atmosphere.

Although the projects and experiments that are carried out at CERN and RHIC and other high-energy particle accelerators are designed to advance humanity’s understanding of the world around them, unlike the atomic bomb, whose only purpose was to remove life, there are some terrifying possibilities of the results of particle collisions.

One of the concerns is the fact that when the LHC is completed at CERN in 2005, it will possibly be able to create miniature black holes, a few every second. (The possibility of the LHC creating a miniature black hole would require that the Universe as we know it consists of more than just the 4 dimensions that we all are used to, a concept that the new Super String theory is based on.) The possibility of this excites physicists, as this could give them a great insight into even more exotic particles than the leptons and hadrons they already work with. Unfortunately, as most people know, black holes have a nasty habit of eating everything in sight; having such powerful gravitational force that not even light can escape. Creating man made mini-black holes underground in Geneva would at first appear to be a fairly foolish and somewhat risky idea, what with the unfortunate side effect of the complete destruction of the planet, to be replaced with a small dense cluster of matter approximately 100 metres across. Fortunately for the denizens of earth, British astrophysicist Stephen Hawking theorised that as a result of Heisenberg’s Uncertainty principle, all black holes decay and evaporate by releasing “Hawking Radiation.” For “natural” black holes that are created by the collapse of stars, this decay would take longer than the lifespan of the universe. However for the mini-black holes that may be created at the LHC, the black holes will decay in a much shorter timescale, something to the order of 10^‑15 seconds, and will be far to small to “eat” even a proton, providing they had the time. Unfortunately, Hawking’s theory remains just that, a theory, and hasn’t been verified.

Another possibility is that the LHC will create “strange matter,” matter that consists of strange quarks, as well as the more common types. There are fears that when such a particle collides with another normal particle, it will convert it into another “strange particle,” eventually converting the entire planet. Far out this hypotheses may be, something that isn’t ruled out by the Standard Model.

The final “doomsday scenario” is probably the most terrifying, something that makes the transition of the earth into a small black hole seem like a small banger going off in comparison. Scientists have known for a while that what we consider as vacuum is actually highly structured, thanks to pioneering works by theoretical physicists such as Casimir. A few physicists believe that if a jolt of energy was triggered in a small enough space it might trigger the collapse of the quantum vacuum, radiating outwards from the acceleration chamber at the speed of light triggering the destruction of the entire universe as we know it. Again, despite how science fictionish such a thing might sound, it isn’t strictly ruled out by quantum mechanics or super string theory. Fortunately physicists have a rebuttal for most of these concerns: the LHC and other particle accelerators are simply emulating the work of the sun, which fires its own cosmic rays at speeds near the speed of light. They argue, if anything like this could happen, it would already have happened long ago, as the cosmic rays from the sun strike earth’s atmosphere. None of these doomsday scenarios are possible with the LHC, for if they where scientifically feasible, they would already have occurred. This doesn’t stop the controversy surrounding high-energy particle accelerators, with controversy likely to continue up to the completion of the LHC in 2005, not helped by the often sensationalist and ill-informed stories of American News Stories, for example, a newspaper article entitled “Big Bang machine could destroy Earth.”*

The LHC laboratories at CERN.

Uses of antimatter and other particle physics based applications:

“Anyone who expects a source of power from the transformation of atoms is talking moonshine.”

- Ernest Rutherford

Although antimatter is a relatively new concept, yet already we have seen a large number of practical applications, with other highly speculative possibilities being considered by physicists that would utilize the key concepts that where discovered by the scientists at labs like Fermilab, RHIC or CERN. The applications range from replacements and enhancements to the everyday and mundane things, to far reaching projects that may change the way we live and see the world. Many of the most exciting developments happening today in the world of science are related to quantum mechanics and particle physics. Already, over 50,000 anti-hydrogen atoms at CERN have been created, while other strange forms of matter and antimatter are being utilised in ways that could not have been imagined even 50 years ago. For example, anti-protons are being used to detect faults deep inside building structures.

Incineration Of Nuclear Waste

“The misinformation and scare tactics that the media has used in reporting events connected with nuclear energy, coupled with a lack of adequate science education, has made it impossible for most people to make intelligent decisions about what constitutes a danger, a risk, or an unimportant change in a natural phenomenon....”

Dr. Edward Teller

Text Box: Three Mile Island Nuclear Power Plant A large proportion of earth’s electricity toady is provided by nuclear power plants around the world. Nuclear power-plants themselves are considered safe, with only two major accidents involving nuclear power having occurred, one being the Chernobyl incident in the Ukraine in 1986, where engineers disregarded numerous safety procedures during their testing of reactor number 4 which caused an uncontrolled chain reaction that instantly killed over 30 people and forced 13,500 people in the surrounding 20-mile radius to be evacuated as a result of the high-radiation levels. The other “major” accident was at Three Mile Island nuclear power plant, where a pressure relief valve became stuck open at the Unit-2 reactor, exposing approximately two million people to on average 0.0014 rems, with the highest individual exposure being 0.075 rems (the unit of absorbed radiation dose in humans), while the average member of the U.S. population receives about 0.36 rems annually from naturally occurring radiation and other uses e.g. medicine and consumer products.

Nuclear reactors also release small amounts of radiation into the atmosphere, however proponents of nuclear energy will tell you that the emissions of radiation from a nuclear reactor is actually less than the amount of radiation that is released from the equivalent amount of coal power plants, without all the other pollution problems that are associated with the burning of fossil fuels.

The main problem that people have with nuclear power plants is the fact that they create large amounts of solid and liquid nuclear waste that is hard to store. Large amounts are stored underground by the United States, and both the United States and Great Britain dump concrete containers of fission products at sea. Because the half life of these by products are often very long (half–life = amount of time it takes for an isotope to decay into half its amount, e.g. Strontium 90 has a half-life of 28 years and will therefore be ½ of its original amount in 28 years, ¼ in 56 years, and so forth), it will be many thousands of years before these products are safe again.

However one proposed method to get rid of nuclear waste is incineration using an Accelerator Driven System (ADS). The ADS is a sub-critical reactor (meaning that which utilize external neutrons to drive fission chains in sub-critical neutron groups, i.e. nuclear waste). The advantage of the ADS is that it is extremely safe, with any kind of dangerous accident virtually impossible.*

Cask used to transport nuclear waste

Medicine

“Any sufficiently advanced technology is indistinguishable from magic.”

- Arthur C. Clarke

One of the most recent and exciting uses for anti-matter is in cancer treatment.

A scanning technique known as Positron Emission Tomography is a scanning technique that is used for detecting cancer. The Positrons (the anti-matter equivalent of electrons) that are used in Positron Emission Tomography are produced by the decay of radioactive chemicals that are injected into a patient, and then accumulate in cancer cells. Therefore, when a PET scan is done, tumours will appear brighter than positrons. However using a different form of antimatter, the antiproton, has a potential for not only detecting cancer, but treating it also. When antiprotons collide with the atoms in the cell it will ionise them, releasing electrons that will rip apart the molecules they are in, often killing the cell. This will kill ordinary cells, not just cancerous ones, however most of the ionisation will occur just before the antiproton comes to a full stop, so that if the energy of the antiproton beam is chosen carefully, it can burn a hole below the skin, allowing it to be very precisely aimed at a tumour.

PET scanner

This is no different to what a beam of ordinary protons will do, however what antiprotons do that ordinary protons won’t do, is colliding with ordinary matter after it has nearly come to a halt causing a matter – antimatter explosion that is far more effective at killing cells than just the ionisation operation on its own. According to CERN scientists, routine clinical application of matter-antimatter annihilation to cancer treatment should be a reality in 10 –15 years.*

Space Exploration

“Nothing tends so much to the advancement of knowledge as the application of a new instrument. The native intellectual powers of men in different times are not so much the causes of the different success of their labours, as the peculiar nature of the means and artificial resources in their possession.”

- Sir Humphrey Davy

Space exploration is back in the news again. The Spirit and Opportunity probes that landed on Mars and sent back picture enthralled the world, while overshadowing the loss of the British probe Beagle 2. Meanwhile American president George W. Bush has announced plans to land men on Mars, and create a permanent Moon Base. However the fact of the matter is that current space exploration technology and propulsion systems are extremely costly and inefficient. Rockets today run off a combination of liquid hydrogen and oxygen, and we are extremely limited as to where we can go in the solar system with such technology. Scientists are trying to find alternative methods of propulsion that will be cheaper and more efficient than what we use at the moment. Here are some of the possibilities that are currently being explored by physicists.

Antimatter For Energy and Propulsion

“A great frustration in life is discovering that sometimes those who say something can't be done turn out to be right. “

- Donald Simanek

Because of the energy produced from matter-antimatter collisions, a gram of antimatter could carry as much energy as 1,000 Space Shuttle external tanks. The problem with using antimatter as an energy source is that electrons and positrons, which would have been a viable energy source are extremely hard to store. Instead, physicists would have to use heavier combinations, such as protons and antiprotons, whose larger mass makes them easier to store and control. The problem with antiprotons and protons is that when they annihilate each other, they create gamma radiation. Also, there still aren’t nearly enough antiprotons being created at accelerators to fuel a spacecraft. However, once there is enough antimatter available, it would be a relatively simple matter in adapting it to fuel a spacecraft and the simplest method would be for antimatter reactions to heat a tungsten core, which in turn heats hydrogen which flows out through an ordinary nozzle. Another possibility being explored is to have an engine design, which would use magnetic coils to direct the particles produced by proton-antiproton annihilation. One of the most exciting possibilities is the Ion Compressed Antimatter Nuclear (ICAN-II) engine, which could be utilized for manned trips to other planet, or unmanned trips to deep space. The ICAN-II engine uses antiprotons to implode pellets with nuclear fusion targets. Huge shock absorbers would protect the ship as it is propelled through space with a series of small blasts. The ICAN-II engine would only need about 140ng (nano-grams) of antimatter for a manned trip to Mars.*

Zero-Point Energy and the Casimir Effect

"The only way of discovering the limits of the possible is to venture a little way past them into the impossible."

- Arthur C. Clarke

One of the recent discoveries in physics that is hard to grasp, is the fact that the classical concept of a vacuum, of totally “empty” space is wrong. You can take all the energy, all the heat, all the light, all the matter, and still there will be some energy left. This is often explained with Heisenberg’s uncertainty principle, which implies any non zero energy condition in the universe is impossible. The implications of this realisation are profound to say the least. Normally the idea of the vacuum implies that there is no energy in it. However, with the concept of “zero-point energy” one is quick to realise that there is enormous amounts of energy in even the smallest section of a vacuum, e.g. take light waves: for each possible colour (frequency) of light, there is a non-zero value for that amount, as postulated under the zero-point energy hypothesis. Add up all that energy and you are left with bizarre numbers, one common analogy being that there is enough energy in a cup to boil away all of earth’s oceans. The concept of vacuum energy is much more widely accepted today, than when it was first put forward, helped strongly by experimental evidence in the form of the Casimir Effect. The Casimir Effect occurs when two metal plates are pushed close enough together. When they are close enough, the vacuum energy will push them together, because light waves are too big to fit between the plates to negate the effect of the vacuum energy acting from outside the plates, and this difference in pressure will cause the plates to push together. It is unknown whether we will be able to tap into this energy or not.

Other more exotic ideas

Robert Forward’s interstellar laser sails:

This idea is based around the idea that when light strikes an object it pushes on it slightly. Robert Forward’s idea is to have a 10-million gigawatt laser to shine through a thousand kilometre wide lens onto a thousand kilometre sail. This could send a thousand-ton vehicle to our nearest star in less than 10 years. However the technology of making a ten-million gigawatt laser is still far beyond our means. A more reasonable idea is to have 10-gigawatt laser, and the vehicle will be a fine wire mesh spread over a kilometre and weighing just 16 grams, with sensors and communication equipment built into it.

Bussard Interstellar Ramjet

This idea relies on collecting protons that drift freely in interstellar space, and combining them to fuse to make a nuclear rocket. This concept has many limitations, for example, collecting enough protons in interstellar space to use, and how to fuse the protons to make fuel.*

Bibliography

Books Used:

Quarks – The Stuff of Matter- Harold Fritzcsh

Asimov’s New Guide to Matter - Isaac Asimov

The Science Book – Edited by Peter Tallack

Physics Today – Randal Henry

Chemistry Live – Declan Kennedy

A Brief History Of Time – Stephen Hawking

Websites Visited:

http://particleadventure.org/particleadventure/frameless/quarks.html

http://www.jupiterscientific.org/sciinfo/higgs.html#sm

http://www.chem.auth.gr/english/Atom.htm