Somewhere over the Rainbow

Frank Drake devised the Drake equation to estimate the number of advanced civilizations in the galaxy with the aim of gathering support for SETI (the Search for Extraterrestrial Intelligence). The earliest attempts to detect radio signals from extraterrestrials date back to the 1960s. Paul Allen has funded the Allen Telescope, Array which is dedicated to searching for such signals. When complete it will include 350 radio dishes. The citizen science project SETI@Home allows anyone with a home PC to participate in analysing the data amassed by the SETI project.

Most of the Universe is Missing!

Most of the matter in the universe exists in an unknown form called dark matter. All estimates of the mass of galaxies and galaxy clusters suggest they contain far more matter than is visible to us in the form of stars. Conventional explanations, such as the existence of large quantities of burnt-out stars known as MACHOs or dark gas clouds, have been ruled out. The most popular explanation is that dark matter consists of vast quantities of hypothetical stable particles known as WIMPs that were produced in vast quantities in the very early universe. Many laboratories around the world are searching for signs of these particles. These include the Italian Gran Sasso laboratory running the XENON100 experiment. Some theorists have suggested the evidence for dark matter would disappear if we had a better theory of gravity. Analysis of the Bullet Cluster indicates such proposals will not work.

Forces of the World Unite!

The structure of matter and the forces that are important in particle physics are now understood in terms of the Standard Model, which is currently being tested at the Large Hadron Collider (LHC). Since the 1930s, physicists have used particle accelerators to investigate the structure of matter. Three forces are important in particle interactions, the strong force, the weak force and the electromagnetic force. The weak and electromagnetic forces are now recognized as two components of a unified electroweak force. The strong force and the electroweak force act on a small collection of fundamental particles that include quarks, the subcomponents of protons, neutrons and many other particles. The final missing piece of the Standard Model, the Higgs boson, was discovered by the LHC in 2012.

Twinkle, Twinkle Little Star

The emission and absorption of light by atoms produces discrete sets of spectral lines that were a vital clue to unravelling the structure of atoms and their elucidation was an important step towards the development of quantum mechanics. In the middle years of the nineteenth century Bunsen and Kirchhoff discovered that spectral lines can be used to determine the chemical composition of stars. Following Rutherford’s discovery of the nucleus, Bohr devised a model of the hydrogen atom that explained the spectral lines that it produces. His work was developed further by Pauli, who postulated the exclusion principle in order to explain the structure of other types of atom. This enabled him to explain the layout of the Periodic Table and the chemical properties of the elements.

The Crab and the Jellyfish

Supernova explosions have been recorded as guest stars for thousands of years, but their true nature was only revealed in the twentieth century, largely through the work of Baade and Zwicky. Following Hubble’s determination of the distance to the Andromeda Galaxy, Baade and Zwicky established a new class of extremely bright stellar outburst that they named supernovae. They realized that such explosions in distant galaxies were comparable to the occasional guest star reported in the historical records including stars recorded by Tycho and Kepler. We now know that very large stars that have consumed their nuclear fuel may explode and produce a supernova. The star may be completed destroyed in the eruption or its core may collapse to form a neutron star or black hole.

From the Leviathan to the Behemoth

The world’s biggest telescopes are reflectors and every increase in size has given us a new perspective on the universe. The Rosse telescope, built in the middle of the nineteenth century by Lord Rosse in County Offaly, Ireland, was nicknamed the Leviathan of Parsonstown. It was the world’s biggest telescope for over half a century. Rosse’s drawings of the celestial objects that he viewed through the telescope were widely circulated. His drawing of the Whirlpool Galaxy is thought to have inspired Van Gogh’s painting Starry Night. The European Southern Observatory (ESO) is now constructing the Extremely Large Telescope (ELT) in Chile. It will be the largest telescope in the world when completed.

Diamonds in the Sky!

After consuming their nuclear fuel, most stars lose their outer envelopes and all that remains is the collapsed core of the star, an object known as a white dwarf. Ever since Galileo pointed a telescope at the night sky, each advance in telescope making has resulted in sensational discoveries. Alvan Clark & Sons ground some of the biggest telescope lenses ever made. Alvan Graham Clark discovered Sirius B while testing one of these lenses. Eddington deduced that Sirius B has a size similar to that of the Earth, but with the mass of the Sun, and was an example of a new class of stars—white dwarfs. The easiest white dwarf to see with a telescope orbits the star Keid. In Star Trek, the planet Vulcan orbits the star Keid A.

The Battle for the Cosmos!

We now know the universe began with the Big Bang 13.8 billion years ago, but for several years debate raged between the supporters of the Big Bang theory led by George Gamow and supporters of the Steady State theory led by Fred Hoyle. Hoyle showed that the elements were synthesized in the stars, not in the Big Bang as Gamow believed. But Gamow’s colleagues Alpher and Herman predicted the existence of the cosmic microwave background (CMB) created immediately after the Big Bang. The CMB was discovered by Penzias and Wilson and this provided the crucial evidence that the Big Bang theory is correct. The CMB has since been studied in detail by a series of space probes.

The Rosetta Stone and Quantum Waves

It was discovered in the early decades of the twentieth century that light and matter exhibit both wave-like and particle-like behaviour and this led to the development of quantum theory. Thomas Young demonstrated the wave-like behaviour of light 200 years ago. Thomas Young had wide-ranging interests and played an important role in deciphering hieroglyphic inscriptions. In 1905 Einstein showed that light also behaves like a stream of particles. Louis De Broglie suggested that particles such as electrons might also show wave-like behaviour and his prediction was soon verified in the laboratory. This led to the development of quantum mechanics, as well as important technological applications, such as the electron microscope.

The Path to Immortality

Newton’s theories of mechanics and gravity laid the foundations for the development of modern science. Newton is introduced through his activities at the Royal Mint. Newton’s ideas reigned supreme for over 200 years. Newtonian gravity was only superseded by Einstein’s theory of general relativity just over 100 years ago.