Before we look at Einstein it is worth remembering that all things come from above - from the Divine that is. The problem is correctly interpreting the messages that pound down in the form of Spiritual Rain, hence: "God rains down on the good and bad." Sanctification is the Truth and the interpretation of that Truth. Through Einstein's hard work in his years of study, the World has benefited greatly from him, but did you know that many scientists were envious of Einstein. Where many were working flat out in laboratories, Einstein worked everything out in his head just like the Ancients who did not need to build the Scriptural structures that were written - the Prophets had merely to work out Scriptures using their Divinely given intelligence. So to re-cap on sanctification - it is where one has worked out Divine Revelation; and that revelation being for the benefit and education so that all can benefit. Einstein did not need to con people with fantasy's of divine revelations and dumbo spiritual experiences - he was one with a sound mind, and I know for certain had he been around 2-3 thousand years ago, he would have been in heaven. In ancient times there were more Einstein's and geniuses than the world has ever seen, and had Einstein met the genius Baptist, or even the Messiah Himself, Einstein would have handcuffed himself to them - he would never have lost sight of them!
If there is any evidence of what the Divine can do with people who think that they are not bright, and may not have the capabilities to learn phenomenal things, then read Einstein briefly. The Genius Spirit is given by God to those who truly want a mind and are prepared to sacrifice for it. The Seed of Israel had to put their right hands on the sacrificial lambs head - representing the head of the Messiah. The right hand signifies that the person truly wants the head of the Messiah. Many wanted the head of the Genius Baptist, because they thought that Yochanon (John) was the Messiah. And many thought that the Messiah himself was the Baptist - it is only when one gets very close to their teaching that you realize how worlds apart they really were. The Apostles of the Messiah were taught by the genius Baptist (water being a level of teaching) before they were ready for the Wine of the Messiah, and not forgetting, the Apostles were Hebrews so they would have had the teaching of their parents and other teachers. Moreover, they would have had the added benefit of seeing and attending the Great Hearing and Foot festivals(Symposiums) in which the Seed had to attend 3 times a year. So the head is important, not only did the Baptist lose his on request - the Messiah's head covering was removed completely from the rest of his burial clothing - why?
Einstein, Albert (1879-1955)
German-Swiss-US theoretical physicist: conceived the theory of relativity.
Einstein's Theories of Relativity
Einstein's Special Theory, and later his General Theory, were such monumental contributions to physics that many biographers have tried, with little success, to explain what made him such a genius. Einstein was born in 1879 in Germany, but he later renounced his German citizenship and became a Swiss citizen. Very little in terms of his childhood could have led anyone to think that he would have made such a gigantic intellectual contribution. Indeed, he did not even speak properly until he was three years
old, and his parents were concerned that he might be having learning difficulties! He was a solitary child who later returned to isolation: 'The individual who has experienced solitude will not easily become a victim of mass suggestion', he once said. Einstein hated regimentation of any kind, including the rote learning of the type that occurs at school. This made him rebellious of school-teaching methods, but it also encouraged him to be self-taught and to think independently. Mathematics was his best subject
and he later studied the subject at the Swiss Federal Polytechnic School in Zurich. In 1902 he obtained a position as patent clerk at the Swiss Patents Office in Berne. While he worked there he did theoretical physics in his spare time and published his earth-shattering ideas on the photoelectric effect, Brownian motion, and the Special Theory of Relativity. The Special Theory of Relativity was Einstein's theoretical way of solving some of the problems associated with classical physics that seemed to be contradictory.
For example, according to classical physics, charged particles are associated with a magnetic field when they are moving. The question arises: moving with respect to what? A charged particle on the surface of the Earth that is stationary with respect to the Earth is still moving, since the Earth is moving. The mathematical equations that described magnetic fields associated with charged particles required an absolute frame of reference in order to say whether or not a particle was moving. Einstein eliminated
the need for this absolute framework and his Special Theory which was a theoretical study of objects moving at a constant speed, removed many other apparent contradictions of classical physics. In Einstein's analysis of motion and electromagnetism, there is no need for an absolute frame of reference: the laws of physics are the same for any observer, regardless of his or her motion. Newton's Laws of Motion allowed an object to travel at any speed. Provided that a sufficiently large force could be exerted on the
object for a sufficient length of time, there was nothing to stop it from reaching speeds as high as, or even greater than, the speed of light. However, one of Einstein's most important premises was that the measured speed of a uniformly moving object could never be greater than the speed of light. His equations, and those of FitzGerald and Lorentz, predicted zero length and infinite mass of an object traveling at the speed of light, and at speeds greater than that of light the mass and length of an object cease
to have any meaning - they become imaginary. Einstein already had some support for this idea: nobody had ever observed any object moving faster than light. Indeed, this statement is still true today. Einstein also said that the speed of light in a vacuum would always be measured to be the same value, regardless of the speed of the light source or the observer measuring it. To understand the significance of this proposition, consider a stone that is thrown from a moving train. Its speed (measured by an observer
on the ground in the background scenery) will be greater if it is thrown in the direction the train is moving than if it is thrown in any other direction. The speed with which the stone is thrown is added to the speed of the train if it is thrown in the direction of the train's motion, whereas the stone's speed is subtracted from the train's speed if it is thrown in the exact opposite direction. Light, on the other hand, behaves rather differently. Consider a torch being shone from a moving train. Instead of
travelling faster if it is shone in the direction of the train's movement than if it is shone in a different direction, the light travels at the same speed in any direction. Even if the train moves at half the speed of light, the measured speed of a light beam that is shone in the direction of the train's motion is the same as it would be if the train were not moving, instead of being one and a half times that speed. A consequence of these assumptions about the speed of light is that it is impossible to calculate
the absolute speed of an object. Einstein saw no use for an ether against which to measure absolute speed. Everything could be explained without ether, and this certainly would agree with the fact that nobody had ever detected it. If the measured mass of an object increases as it approaches the speed of light, what, then, becomes of the Law of Conservation of Mass (that matter cannot be created or destroyed), which, at the time the Special Theory was formulated, was widely accepted as fact? Surely an increase
in mass means creation of matter, in contradiction of this law? Einstein arrived at an answer to this problem when he derived his famous equation, E=mc2. This equation shows that the energy (E) of an object is related to its mass (m) and the speed of light (c). Einstein reformulated the Law of Conservation of Mass and transformed it into the Law of Conservation of Mass-Energy: matter and energy cannot be created or destroyed, but they can be converted one into the other. Einstein's Special Theory immediately
provided an explanation for radioactivity, which had been a puzzle to physicists. Now it could be seen how seemingly endless amounts of energy were given off by radioactive atoms: small amounts of matter in the nucleus of the atoms were being converted to energy. The Law of Conservation of Mass-Energy was being obeyed. Indeed, after Einstein's Special Theory of Relativity was announced, physicists searched for and found the decrease in mass of radioactive nuclei that was required to produce radioactive energy.
The equation, E=mc2, indicates that when an object is converted to energy, the amount of energy produced is equal to the mass of the object multiplied by the speed of light, multiplied again by the speed of light. Because the speed of light is very large, this means that a small quantity of matter can be converted into an enormous amount of energy. This is the principle of nuclear power and atom bombs: small amounts of matter from nuclear reactions are converted into large amounts of energy. In view of the fact
that Einstein was an overt idealist and pacifist, it is ironic that the destructive use of the matter-to-energy conversion provided some of the strongest evidence for his theory. Einstein's Special Theory of Relativity also provided some novel interpretations of the concept of time. Newton had ascribed a knowledge of absolute time to God, just as he had done with an absolute frame of reference for motion. A consequence of the constant, finite speed of light was that measurements of time, in addition to those
of length and mass, also vary according to the motion of an object. Einstein's mathematical equations showed that as a body approaches the speed of light, time appears to lengthen. For example, to an object moving at ninety-eight per cent of the speed of light, one second becomes five seconds long. This phenomenon is called time dilation. As with changes in measured length and mass, the effects of speed on time are insignificant at speeds encountered in ordinary daily life, but they do become significant as the
speed of light is approached. Evidence for time dilation has been forthcoming from several sources. For example, nuclear accelerators exist that allow subatomic particles to attain very high speeds, approaching that of light. Some of these particles are unstable and break down at a defined rate. As they move faster, the particles break down more slowly: the time taken for them to decay becomes longer as they approach the speed of light. Another piece of evidence that supports Einstein's contention that time slows
down as objects move faster comes from measurements of the rates of ticking of highly sophisticated atomic clocks. Such clocks have been shown to run more slowly on fast moving jet planes and on satellites than similar clocks on Earth. The Special Theory of Relativity deals with the effects of uniform motion on length and mass of an object and on time. Einstein later developed his General Theory of Relativity, which is concerned with non-uniform motion and proposes a new way of looking at gravity. To Newton,
gravity was a force of attraction between two objects: large objects exerted a greater gravitational pull than small ones. Einstein did away with this idea. He showed that gravitational attraction was equivalent to acceleration (increase of speed); this was called the Equivalence Principle. An object in an upwardly accelerating container is pulled down to the floor of the container in exactly the same way as an object is pulled towards the Earth by gravity. To Einstein, gravity was not a force between objects,
but a curvature of space-time that was caused by the presence of mass. An object does not fall to the Earth because it is being attracted by the Earth's gravitational pull: it falls because it takes the easiest route along the curvature of space-time created by the Earth's mass. An analogy is that of a ball-bearing placed on a sheet of elastic material. The ball-bearing (Earth) creates a depression in the sheet (space-time), and the sheet is curved around the ball-bearing, becoming more steeply curved nearer
the ball-bearing. The General Theory of Relativity was testable, like all good theories. It predicted, for example, that light should be bent by gravity. Light passing close to the Sun would, according to Einstein, be bent by the curvature of space-time caused by the Sun. This should be measurable under the correct circumstances. The best situation in which to observe this bending of light by the Sun is a total eclipse of the Sun. In 1919 such an eclipse occurred off the coast of West Africa, and a group of British
scientists organised an expedition to test Einstein's theory by measuring the positions of stars in the neighbourhood of the Sun and looking for the predicted bending. The results were in agreement with Einstein's theory, and this caused a sensation that made Einstein a household name around the world. When Einstein received a telegram informing him of this confirmation of General Relativity, he was remarkably calm about it. One of his students who was with him at the time commented on how exciting the event
was, but Einstein apparently responded with little emotion and said, 'But I knew that the theory was correct'. When asked what he would have thought if the results had disagreed with his theory, Einstein replied, 'Then I would have felt sorry for dear God, because the theory is correct.' However, a letter written by him at the time to his mother does indicate that he really was excited by the confirmation of his prediction. Although many physicists later doubted the accuracy of the measurements made during the
1919 solar eclipse, numerous other observations have since supported Einstein's idea about gravity. In addition, Einstein knew that his General Theory provided an answer to a puzzle, that of the peculiar orbit of the planet, Mercury, which classical physics could not explain. It had been known since the mid-nineteenth century that the orbits of the planets around the Sun are nearly, but not quite, closed ellipses. The planets precess; that is, they return to a slightly different place after each orbit, producing
an orbit consisting of loops rather than a closed ellipse. Mercury - the planet nearest to the Sun - precesses to the greatest extent. When Newton's theories were applied to Mercury's precession, they could not explain it properly. The phenomenon baffled many physicists, especially because no other planet close to the Sun was found that might be exerting a force on Mercury and causing the anomaly. Classical physics simply did not explain this orbit. However, General Relativity explained it exactly: when Einstein
applied his equations describing the effects of the Sun on the curvature of space-time, Mercury was predicted to have the precise orbit that was found. Einstein's General Theory not only provided a brand new way of looking at Nature and explaining properties of the Universe, but also gave birth to modern cosmology, the study of the origins and properties of the Universe. His equations of General Relativity predicted that the Universe was not static - it was either expanding or contracting. Although Einstein rejected
this idea, believing that the Universe was static, other physicists used his equations to propose models of an expanding Universe, and this gave rise to the Big Bang theory for the origin of the Cosmos. Einstein's 'thought experiments' had clearly revolutionised our understanding of existence, and will continue to do so.
Einstein's Theoretical Physics
Einstein's publication on the photoelectric effect in 1905, which restored the idea that light consists of particles (photons), eventually earned him the Nobel Prize for Physics. However, Einstein is much better known for his Theories of Relativity, the first of which was also published in 1905. As a physicist, there is little doubt that he would have been highly esteemed by his fellow scientists even if he had not developed his Theories of Relativity, because his other contributions to physics were very
great indeed. It is a rare event in the history of the world when a scientist as great as Einstein appears: not only did he provide answers to many puzzling questions that classical physics failed to explain, but he also dramatically changed the way we think about the world around us. Einstein's relativity theories also gave birth to modern ideas about the origin of the Universe. Every physicist alive today is taught in a way that is deeply influenced by Einstein's work and few would doubt that Einstein is the
greatest physicist the world has ever seen. During his life, Einstein became a highly respected and well liked public figure, a situation that is normally somewhat rare for a scientist to achieve. The key to his popularity was probably that he was viewed as a great genius, with a kind, unpretentious personality and idealistic political and moral values, and also the fact that his scientific ideas provided a deep insight into the workings of the Universe. He also became involved in several political situations,
including the development of the atom bomb; and he was offered the Presidency of Israel, but declined. Einstein was, like Maxwell and Planck, a theoretical physicist: his experiments were carried out in his mind. (One practical thing he did was to develop and patent, with the Hungarian physicist, Szilard (1898-1964), a noiseless household refrigerator.) When one considers just how much such 'thought experiments' have contributed to science and technology, one is left with the realisation that pure thinking and
its mathematical expression are at least as important to human progress as experimental science. Once, when asked by someone if they could see his laboratory, Einstein took a fountain pen from his pocket and said, 'There it is!' On another occasion he commented that his most important piece of scientific equipment was his wastepaper basket, where he threw much of his paperwork containing mathematical computations. There is a misconception amongst some people that Einstein effectively showed that Newton's Laws
of Motion were wrong. Some critics of science have suggested that this is evidence that scientists have got it all wrong, and that they are constantly contradicting themselves. Newton's First Law of Motion, also known as the Law of Inertia, states that an object will remain at rest or continue in the same direction in a straight line with constant speed unless it is subjected to a net applied force. His Second Law states that an object will accelerate when a net force acts on it, and the net force (F) is equal
to the object's mass (m) multiplied by its acceleration (a), that is, F=ma. Newton's Third Law of Motion states that when one object applies a force upon another, the second object exerts the same force upon the first, but in the opposite direction. This can be seen clearly in space: when an astronaut throws an object in one direction, the object exerts an equal and opposite force, causing the astronaut to be pushed in the opposite direction. What Einstein did was to show that although Newton's Laws work perfectly
well under everyday conditions, his Laws of Motion need to be modified when objects approach the speed of light (300 000 kilometres per second; 186 000 miles per second). At speeds normally encountered in daily life, which are a tiny fraction of the speed of light, moving objects behave in such a way that Einstein and Newton's descriptions of them become indistinguishable. Indeed, Einstein really refined Newton's Laws of Motion so that they worked at all speeds: this modification of existing ideas is the normal
way by which science progresses. Einstein revolutionised the whole of physics, particularly with his work on Relativity, which involves two main theories: the Special Theory of Relativity, which he published in 1905, and the General Theory of Relativity, which he published in 1916. Before these are described, some knowledge of the scientific context of Einstein's ideas is required. Einstein's frame dragging.
(November 1997)
Every science eccentric likes to target Einstein, explaining confidentially that he (it is usually a "he") has been able to show that Einstein got it wrong. Somehow, these "proofs" never seem to impress mainstream scientists, who are more interested in the evidence gained from observations. Real scientists are especially interested in observations which bear out Einstein's views, because so much of our modern science seems to be perfectly explained by Einstein's ideas. And at least the
observations serve to keep the "crackpots" at bay. Einstein predicted an effect, called "frame dragging," 80 years ago. Like many other aspects of Einstein's famous theories of relativity, it is so subtle that no conventional method could measure it. In simple terms, frame dragging results in space and time get pulled out of shape near a rotating body. In an extreme case, a rotating Tipler machine may even interfere with the causality principle through frame dragging. Using recent observations
by x-ray Astronomy satellites, including NASA's Rossi x-ray Timing Explorer, a team of astronomers reported in November that they had found evidence of frame dragging in discs of gas swirling around a black hole. Drs Wei Cui, Nan Zhang, and Wan Chen began with Einstein's prediction that the rotation of an object would alter space and time, dragging a nearby object out of position compared to predictions by the simpler math of Sir Isaac Newton. This effect had not been observed in the eighty years since Einstein
predicted it. In this, it was unlike the other, more familiar Einsteinian predictions, such as the conversion of mass into energy (as seen in atomic bombs and stars) and back, the Lorentz transformations that make objects near the speed of light grow thinner and heavier and stretch time, and the warping of space by gravity (as seen when light is bent by a massive object) And no wonder: the effect is incredibly small, about one part in a few trillion, which means that you have to look at something very massive,
or build an instrument that is incredibly sensitive and put it in orbit. Cui, Zhang, and Chen took the first option, and studied radiation coming from around black holes in binaries with other visible stars. Over time, the black hole strips material from the star, producing an accretion disc of material which gets hotter as it approaches the event horizon of the black hole, and gives off radio waves, visible light, and-just before it disappears-x-rays. They found that the discs precessed, wobbling like a child's
toy top. By studying the radiation from supraluminal jets in two black holes, called GRS 1915+105 and GRO J1655-40, they found that the rate of precession was far greater than could be explained by the sorts of effects seen in children's toys. Conclusion: Einstein's frame-dragging is real. The sensitive instrument option will follow next: NASA is developing it as Gravity Probe B, described in the entry on general relativity. This is a satellite containing precision gyroscopes inside a liquid helium bath. Gravity
Probe B will point at a selected star, and sensitive instruments will measure how much the gyros precess after conventional effects are nullified. The leftover effects should provide a precise measure of frame dragging. Because the Rossi satellite observations are somewhat uncontrolled, the final proof of frame dragging will come when Gravity Probe B points at a known star of known mass, and turns in consistent results. Back to November 1997 Science Review contents.
Einstein proved right, even when space-time is seriously curved.
(April 1998)
Since the early 1940s, physicists have accepted that a massive object would warp space, bending it so steeply that any object getting too close would fall into it, generating x-rays as it goes. Now a careful observation of the x-rays from a neutron star called 4U 1820-30 has revealed evidence of just such an effect. The observation was carried out from NASA's Rossi X-Ray Timing Explorer satellite over the course of a year. The Rossi Explorer had already measured the x-rays coming from such sources, and
shown that the brightness of neutron stars varied as much as a thousand times a second, making them the most rapidly variable objects in the universe. Neutron stars have a mass about ten times as great as the sun, but are only about 15 km (10 miles) in diameter. This density produces highly curved space-time, according to Einstein, and that is an interesting place to look at, if you are a physicist. In Newtonian physics, gases can orbit in circular orbits at any distance, but Einsteinian relativity says that
if you have curved space-time, there are no stable circular orbits. So where does the gas come from? If the neutron star is in a binary with an ordinary star, it tears matter away from the other star, so it spirals down into an orbit around the neutron star, traveling at speeds close to the speed of light. As a black hole or a neutron star spins, it sets up huge forces that force this gas into a disc, called the accretion disc. The disc may wobble around its outer edges, but in close to the massive object, the
disc must line up with the equator of the object. Somewhere on that accretion disc, there is a region where matter passes inside the last stable orbit, and then it tumbles catastrophically inwards. The point of instability (where matter pours in) rotates around the accretion disc as it spins, pulled by the gravity of the neutron star. X-rays pour out from this point, like the beam of a lighthouse, and with a frequency for the x-rays which depends on the distance of the disc's inner edge from the neutron star.
The disc is in balance, pulled inwards by gravity, and pushed outwards by the radiation coming from the star, but if a large block of material falls in, this may block the radiation hitting the disc (but not the gravity), allowing the disc edge to tumble in, producing the characteristic oscillation. If Einstein is right, say the experts, then there should be a limit to the frequency of the x-rays, and this should define the point of no return. So they watched the radiation coming from the star. They watched the
brightness, which told them how much material was falling in, and they watched the frequency, but again and again, it hit a ceiling, an upper limit. Four times, they say, is no coincidence - Einstein wins again! The oscillations stabilized at 1050 hertz, even when the x-ray power increased, there was still this simple limit applied to the radiation. The main point to this, they say, is that the x-ray brightness oscillations could be used to determine the masses and dimensions of neutron stars. Of course, everybody
knew that Einstein was right about ordinary space, where the curvature of space is minimal, but now we have good direct evidence that it also works around seriously dense objects, in strongly curved space-time. Two papers describing the theory and the results have been accepted for publication in the Astrophysical Journal. One final comment from Professor Frederick Lamb, one of those who has been at the centre of this exciting work: "Studying how matter moves in the strongly curved space-time near neutron
stars also has allowed us to extract interesting new bounds on the masses and dimensions of these stars and on the stiffness of the superdense matter inside them. The new evidence reported today suggests that the strong nuclear force is more repulsive than many nuclear physicists had expected and that the superdense matter in neutron stars is rather stiff." Other key names: Coleman Miller, Dimitrios Psaltis, William Zhang.
Back to April 1998 Science Review contents.
Einstein and the Photon
In 1905, Albert Einstein published four theoretical papers in distinguished scientific journals. Two of them were concerned with his Theory of Relativity. Another was on Brownian motion, which refers to the random jerky movements of microscopic particles suspended in air or a liquid. The fourth paper proposed an explanation for the photoelectric effect, and it was this article that revived the long-forsaken particle theory of light and brought Planck's ideas into the scientific limelight. It has been said
that any one of the four of Einstein's 1905 papers would have made him an eminent physicist. Most people remember him for Relativity, although when he later received the Nobel Prize for Physics, in 1921, it was for his theoretical work on the photoelectric effect. Einstein was well aware that the wave theory of light did not explain the photoelectric effect: 'The usual idea that the energy of light is continuously distributed over the space through which it travels meets with especially great difficulties when
one tries to explain photoelectric phenomena', he said. He was acquainted with Planck's explanation of blackbody radiation, that light was emitted and absorbed as quanta of energy, and it was to this that Einstein turned in order to solve the photoelectric effect problem. The solution, Einstein proposed, was to regard light as being made up of particles or quanta in much the same way that Planck considered light to be absorbed and emitted from blackbodies as quanta. These quanta of light later became known as
photons, from the Greek word meaning 'light'. However, whilst Planck believed that parcels of light were absorbed and emitted by blackbodies because of the properties of the bodies themselves, Einstein said that the properties of blackbodies were irrelevant and that light was made up of particles anyway, regardless of whether it was emitted and absorbed by objects. If Planck's model is thought of as being taken from a barrel only in pint portions then in Einstein's theory the beer is already present in the barrel
as pint portions, even before it is tapped! According to Einstein, each photon of light penetrating a metal surface would collide with an electron in the metal and transfer its energy to the electron. If the amount of energy transferred from a particular photon was high enough, it would enable the electron to reach the metal's surface and be ejected, so producing the photoelectric effect. If the intensity of incident light was increased it would mean, according to Einstein, that more photons of a given frequency
would reach the metal surface in a given amount of time. Therefore, increasing the intensity of incident light should cause more electrons to be emitted and their energy should be unaltered. This is exactly what happens. Einstein also showed that increasing the frequency of light should increase the energy each photon transfers to the ejected electrons but should have no effect on the number of electrons emitted. This, also, is precisely what occurs in the photoelectric effect. Exact quantitative measurements
of the effect of incident light intensity and frequency on electrons emitted during the photoelectric effect were not available when Einstein published his 1905 paper. However, his mathematical analysis of the phenomenon predicted exactly what results should be obtained. These predictions were the acid test of Einstein's theory. If scientific results hitherto unobtained are correctly anticipated by a theory, scientists can have confidence in the theory. In 1916 the US physicist, Robert A. Millikan (1868-1953),
accurately carried out the required experiments on the photoelectric effect. His data agreed perfectly with Einstein's predictions. Light did, indeed, appear to be made up of photons. Whilst the wave theory of light did not explain blackbody radiation or the photoelectric effect, the photon idea did not easily explain interference or diffraction. Indeed, interference and diffraction had been used for many years to support the wave theory. Einstein was aware of the failure of the photon idea to explain diffraction
and interference. Nowadays we have come to accept that at the level of the very, very small our everyday view of the world does not necessarily hold and that light is both a particle and a wave. This is known as wave-particle duality and applies to all forms of electromagnetic radiation. When it comes to levels of size as small as photons, both wave and particle aspects can be detected. When light undergoes interference or diffraction it can be considered to be a wave. When it is involved in the photoelectric
effect or blackbody radiation, it may be thought of as being particulate. Sir William Henry Bragg (1862-1942), the British physicist, put it more plainly, 'On Mondays, Wednesdays and Fridays light behaves like waves, on Tuesdays, Thursdays and Saturdays like particles, and like nothing on Sundays.' The wave-particle nature of light was extended to matter by Prince Louis de Broglie (1892-1987), a French physicist, who proposed that not only can electromagnetic waves behave as particles, but also particles can
behave as waves. According to de Broglie, even objects as large as a human being or a planet have some wave-like features, although these are minuscule and the particle-like properties dominate. However, electrons are very small particles and de Broglie's theory suggested that electrons should show some wave properties that could be detected. His ideas were subsequently confirmed when electrons were found to show the phenomena of diffraction and interference and their wavelength was measured. Indeed, the wave-like
properties of electrons have been particularly useful in the development of electron microscopes, which allow small objects to be seen using a beam of electrons instead of a beam of light. Electron microscopes are more powerful than microscopes that use visible light and have been particularly valuable in obtaining images of objects such as viruses and the interiors of living cells, which cannot easily be seen with optical microscopes. After Einstein had revived Planck's theory of the absorption and emission
of light by blackbodies, the Danish scientist, Niels Bohr (1885-1962), used the ideas of the quantum to propose a new model for the structure of the atom. Bohr explained why atoms of a particular element absorbed and emitted light at specific frequencies. In his model of the atom, negatively charged electrons are distributed around a positively charged nucleus. However, the electrons cannot occur just anywhere around the nucleus: they must exist in states of defined energy, called energy levels. When an atom
absorbs light, the light energy is transferred to an electron and this electron 'jumps' to a higher energy level, but this will occur only if the energy (and therefore frequency) of the light photon is enough to allow the electron to change from the lower to the higher energy level. The electron cannot jump to a place in between the two energy levels: it must be in one or the other level. As a result, the atom absorbs packets (quanta) of energy. Likewise, an atom will emit light energy when an electron jumps
from a higher energy level to a lower one, but since only defined jumps can occur the energy of light emitted must have discrete values. Photons emitted and absorbed are therefore of a particular frequency. Bohr's model of the atom showed that the energy levels of electrons are quantised. Quantum physics, which is required to understand the very small, such as atoms, subatomic particles and electromagnetic radiation, has revolutionised physics. Many physicists are seeking an explanation of the origins of the
Universe by combining quantum physics with a theory that allows scientists to understand the very large. One theory that allows the very large to be explained mathematically is Einstein's Theory of Relativity, and it is this theory that might perhaps be considered to be the second of the two most important developments in twentieth century physics; quantum physics being the first of these advances. In view of the tremendous impact that quantum theory had on physics, it is extraordinary that it began with an inspired
guess by Max Planck, who simply wanted a mathematical equation that would explain why blackbodies absorb and emit electromagnetic radiation in the way that they do, and that it was strengthened enormously when Albert Einstein sought an explanation for the photoelectric effect. Einstein's father was an electrical engineer whose business difficulties caused the family to move rather frequently; Einstein was born while they were in Ulm. Despite a delay due to his poor mathematics he entered the Swiss Federal Institute
of Technology in Zürich at the age of 17, and on graduating became a Swiss citizen and sought a post in a university, or even in a school. However, he had great difficulty in finding any job and settled for serving in the Swiss Patent Office in Bern. It worked out well; he was a good patent examiner and the job gave him enough leisure for his research. In 1903 he married a fellow physicist, Mileva Maric; their illegitimate daughter, born in 1902, was adopted; two sons followed. This marriage ended in divorce
in 1919 and he then married his cousin Elsa, who had two daughters by a previous marriage. It was while at the Patent Office that he produced the three papers published in 1905, each of which represented an enormous achievement, covering Brownian motion, the photoelectric effect and special relativity. Einstein's first university post was secured in 1909, when he obtained a junior professorship at the University of Zürich, and a full professorship at Prague (1910) and Zürich (1912) followed. In 1913 he was made
Director of the Institute of Physics at the Kaiser Wilhelm Institute in Berlin. The general theory of relativity was completed during the First World War and following its publication (1915) Einstein was awarded the 1921 Nobel Prize for physics for his work of 1905. He began to undertake many lecture-tours abroad and was in California when Hitler came to power in 1933. He never returned to Germany, resigning his position and taking up a post at the Institute of Advanced Study, Princeton. Einstein put much effort
into trying to unify gravitational, electromagnetic and nuclear forces into one set of field equations, but without success. He had some involvement in politics, in that he helped initiate the Allied efforts to make an atomic bomb (the Manhattan project) by warning Roosevelt, the American president, of the possibility that Germany would do so, in a letter in 1939. In 1952 Einstein was offered, and sensibly declined, the presidency of Israel. He was also active in promoting nuclear disarmament after the Second
World War. He led a simple life, with sailing and music as his main relaxations. The first of his papers of 1905 considered the random movement of small suspended particles (Brownian motion, discovered in 1828). The bombardment by surrounding molecules will make a tiny particle in a fluid dart around in an erratic movement, and Einstein's calculations provided the most direct evidence for the existence of molecules when confirmed experimentally by Perrin (1908). The next paper by Einstein tackled the photoelectric
effect by considering the nature of electromagnetic radiation, usually thought of as waves obeying Maxwell's equations. Einstein assumed that light energy could only be transferred in packets, the quanta used by Planck to derive the black body radiation spectrum. Einstein then was able to explain fully the observations of Lenard (1902), in which the energy of electrons ejected from a metallic surface depended on the wavelength of light falling on it but not on the intensity. The result became a foundation for
quantum theory and clothed Planck's quanta with a physical interpretation. Finally, Einstein set out the special theory of relativity (restricted to bodies moving with uniform velocity with respect to one another) in his third paper. Maxwell's electromagnetic wave theory of light indicated that the velocity of a light wave did not depend on the speed of the source or observer and so contradicted classical mechanics. Lorentz, FitzGerald and Poincaré had found a transformation of Maxwell's equations for a region
in uniform motion which left the speed of light unchanged and not altered by the relative velocity of the space and observer (the Lorentz transformation). Einstein correctly proposed that the speed of light is the same in all frames of reference moving relative to one another and, unknown to him, this had been established by the Michelson-Morley experiment (1881, 1887). He put forward the principle of relativity, that all physical laws are the same in all frames of reference in uniform motion with respect to
one another. When applied it naturally gives rise to the Lorentz-FitzGerald transformation, with classical mechanics obeying this rather than simple addition of velocity between moving frames (the Galilean transformation). A further consequence derived by him was that if the energy of a body changes by an amount E then its mass must change by E/c2 where c is the velocity of light. From 1907 Einstein sought to extend relativity theory to frames of reference which are being accelerated with respect to one another.
His guiding principle (the principle of equivalence) stated that gravitational acceleration and that due to motion viewed in an accelerating frame are completely equivalent. From this he predicted that light rays should be bent by gravitational attraction. In 1911 he reached a specific prediction: that starlight just grazing the Sun should be deflected by 1.7" of arc. During a total eclipse of the Sun in 1919 Eddington measured this in observations made at Principé in West Africa, finding 1.61" of arc.
This dramatic confirmation immediately made Einstein famous world-wide and made it clear that he had moved the foundation of physics. In 1915 he had published the general theory of relativity in complete form, using Riemannian geometry and other mathematical ideas due to H Minkowski (1864-1909) (in 1907), Riemann (1854) and C Ricci (1853-1925) (in 1887). Mass was taken to distort the 'flatness' of space-time and so to give rise to bodies in space moving along curved paths about one another. While the resulting
'gravitational' attraction is very close to that predicted by Newton's law, there are small corrections. Einstein and M Grossmann (1878-1936) estimated that the ellipse traced out by Mercury around the Sun should rotate by 43" of arc per century more than that given by Newtonian theory. The observed value is indeed 43" of arc larger and Einstein reported: 'I was beside myself with ecstasy for days'. General relativity produced many other startling predictions, such as that light passing from one part
of a gravitational field to another would be shifted in wavelength (the Einstein redshift). This was observed astronomically in 1925 and terrestially, with a 23 m tower on Earth using the Mossbauer effect, by R Pound and G Rebka in 1959. Gamma rays moving from the bottom to top of the tower were found to have a longer wavelength. Cosmological models of the universe were also completely changed by general relativity and Friedmann (1922) put forward a model that represented an expanding universe obeying Einstein's
equations. During the 1920s and 1930s Einstein engaged in debate over quantum theory, rejecting Born's introduction of probability ('God may be subtle, but He is not malicious'). He also sought to find a unified theory of electromagnetic and gravitational fields, without success. By 1921 he had been prepared to say 'Discovery in the grand manner is for young people... and hence for me a thing of the past'. Einstein is probably the most popular scientific figure that the world has ever known. People may recognize
a caricature of Newton when they see a falling apple in the picture, but Einstein's own face is immediately recognizable. Again, people who would not recognize a Newtonian equation if they fell over it, will immediately recognize 'e = mc2'. They may even be able to more or less explain what it means, if only by referring to nuclear weapons. Einstein is almost as popular as a target for the eccentrics of science, the people with weird theories and strange notions, the sellers of perpetual motion machines and other
forms of free energy. They always begin with the premise that Einstein got it wrong (and they got it right), and then proceed from there. To work out why Einstein should be singled out for this special attention, we need to look slightly more closely at what he achieved. The two versions of relativity that Einstein proposed, special relativity and general relativity, are not the most intuitive ideas in science. It is highly disturbing to be told that space and time are changing shape all around you, but that
you cannot tell this is happening, because you are changing as well. Newton's laws were a bit mysterious, but after some thought and experiment, you could see that they were indeed true, which is why Alexander Pope wrote: "Nature and Nature's laws lay hid in night: God said 'Let Newton be.' and all was light." But Einstein was another matter, and so Sir John Collings Squire was moved to add two more lines: "It did not last: the Devil shouting 'Ho. Let Einstein be.' restored the status quo. It often
happens in science, that when the time is ripe, the same discovery is made in several places, almost at once. Three people rediscovered Mendel's laws at the one time, Leibniz and Newton were neck and neck with the calculus, Robert Stephenson and Sir Humphrey Davy both claimed the safety lamp as theirs, and Charles Wheatstone and Edward Davy were very close with the development of their telegraphs. Alexander Graham Bell and Elisha Gray lodged patent claims on the telephone on the very same day, and J. J. Thomson
was barely the first in the race to discover the electron. Physicists who know the history of their subject say that if Einstein had not proposed special relativity when he did, one of several other physicists would have done so within a year. If Hendrik Lorentz missed out, they say, Jean Perrin or somebody else would have cracked it, within the year. It was in the air, you see. Special relativity's time had come, but at the time, it was just one of Einstein's interests. In 1905, he published three distinct and
separate papers on three distinct and separate topics. He gave us his first ideas on relativity that year, but he also explained the photo-electric effect, and even fewer know that he explained Brownian movement or motion. At the time, the other two papers were more exciting, for his work on the photo-electric effect led to a much better understanding of concrete practical physics, shed light on the work of Max Planck, and introduced for the first time the notion of wave-particle duality. It was actually this
work on the photo-electric effect which earned Einstein his 1921 Nobel Prize. The Brownian motion explanation proved beyond doubt for the first time that matter must be made of molecules. Of course, his work on relativity has proved to be of greater lasting importance, but at the time, even Einstein could not be confident that his ideas would prove to be right, and he commented wryly that "... if relativity is proved right, the Germans will call me German, the Swiss will call me a Swiss citizen, and the
French will call me a great scientist. If relativity is proved wrong, the French will call me Swiss, the Swiss will call me a German, and the Germans will call me a Jew." Considering that, and seeing he spent his later years in the United States of America, Einstein is probably better regarded as a world scientist.
Einstein's Special Theory, and later his General Theory, were such monumental contributions to physics that many biographers have tried, with little success, to explain what made him such a genius. Einstein was born in 1879 in Germany, but he later renounced his German citizenship and became a Swiss citizen. Very little in terms of his childhood could have led anyone to think that he would have made such a gigantic intellectual contribution. Indeed, he did not even speak properly until he was three years
old, and his parents were concerned that he might be having learning difficulties!
He was a solitary child who later returned to isolation: 'The individual who has experienced solitude will not easily become a victim of mass suggestion', he once said. Einstein hated regimentation of any kind, including the rote learning of the type that occurs at school. This made him rebellious of school-teaching methods, but it also encouraged him to be self-taught and to think independently. Mathematics was his best subject and he later studied the subject at the Swiss Federal Polytechnic School in
Zurich. In 1902 he obtained a position as patent clerk at the Swiss Patents Office in Berne. While he worked there he did theoretical physics in his spare time and published his earth-shattering ideas on the photoelectric effect, Brownian motion, and the Special Theory of Relativity. The Special Theory of Relativity was Einstein's theoretical way of solving some of the problems associated with classical physics that seemed to be contradictory. For example, according to classical physics, charged particles are
associated with a magnetic field when they are moving. The question arises: moving with respect to what? A charged particle on the surface of the Earth that is stationary with respect to the Earth is still moving, since the Earth is moving.
The mathematical equations that described magnetic fields associated with charged particles required an absolute frame of reference in order to say whether or not a particle was moving. Einstein eliminated the need for this absolute framework and his Special Theory which was a theoretical study of objects moving at a constant speed, removed many other apparent contradictions of classical physics. In Einstein's analysis of motion and electromagnetism, there is no need for an absolute frame of reference:
the laws of physics are the same for any observer, regardless of his or her motion.
Newton's Laws of Motion allowed an object to travel at any speed. Provided that a sufficiently large force could be exerted on the object for a sufficient length of time, there was nothing to stop it from reaching speeds as high as, or even greater than, the speed of light. However, one of Einstein's most important premises was that the measured speed of a uniformly moving object could never be greater than the speed of light. His equations, and those of FitzGerald and Lorentz, predicted zero length and
infinite mass of an object travelling at the speed of light, and at speeds greater than that of light the mass and length of an object cease to have any meaning - they become imaginary.
Einstein already had some support for this idea: nobody had ever observed any object moving faster than light. Indeed, this statement is still true today.
Einstein also said that the speed of light in a vacuum would always be measured to be the same value, regardless of the speed of the light source or the observer measuring it. To understand the significance of this proposition, consider a stone that is thrown from a moving train. Its speed (measured by an observer on the ground in the background scenery) will be greater if it is thrown in the direction the train is moving than if it is thrown in any other direction. The speed with which the stone is thrown
is added to the speed of the train if it is thrown in the direction of the train's motion, whereas the stone's speed is subtracted from the train's speed if it is thrown in the exact opposite direction. Light, on the other hand, behaves rather differently. Consider a torch being shone from a moving train. Instead of travelling faster if it is shone in the direction of the train's movement than if it is shone in a different direction, the light travels at the same speed in any direction. Even if the train moves
at half the speed of light, the measured speed of a light beam that is shone in the direction of the train's motion is the same as it would be if the train were not moving, instead of being one and a half times that speed.
A consequence of these assumptions about the speed of light is that it is impossible to calculate the absolute speed of an object. Einstein saw no use for an ether against which to measure absolute speed. Everything could be explained without ether, and this certainly would agree with the fact that nobody had ever detected it. If the measured mass of an object increases as it approaches the speed of light, what, then, becomes of the Law of Conservation of Mass (that matter cannot be created or destroyed),
which, at the time the Special Theory was formulated, was widely accepted as fact? Surely an increase in mass means creation of matter, in contradiction of this law?
Einstein arrived at an answer to this problem when he derived his famous equation, E=mc2. This equation shows that the energy (E) of an object is related to its mass (m) and the speed of light (c).
Einstein reformulated the Law of Conservation of Mass and transformed it into the Law of Conservation of Mass-Energy: matter and energy cannot be created or destroyed, but they can be converted one into the other. Einstein's Special Theory immediately provided an explanation for radioactivity, which had been a puzzle to physicists. Now it could be seen how seemingly endless amounts of energy were given off by radioactive atoms: small amounts of matter in the nucleus of the atoms were being converted to
energy. The Law of Conservation of Mass-Energy was being obeyed.
Indeed, after Einstein's Special Theory of Relativity was announced, physicists searched for and found the decrease in mass of radioactive nuclei that was required to produce radioactive energy.
The equation, E=mc2, indicates that when an object is converted to energy, the amount of energy produced is equal to the mass of the object multiplied by the speed of light, multiplied again by the speed of light.
Because the speed of light is very large, this means that a small quantity of matter can be converted into an enormous amount of energy. This is the principle of nuclear power and atom bombs: small amounts of matter from nuclear reactions are converted into large amounts of energy.
In view of the fact that Einstein was an overt idealist and pacifist, it is ironic that the destructive use of the matter-to-energy conversion provided some of the strongest evidence for his theory. Einstein's Special Theory of Relativity also provided some novel interpretations of the concept of time. Newton had ascribed a knowledge of absolute time to God, just as he had done with an absolute frame of reference for motion. A consequence of the constant, finite speed of light was that measurements of time,
in addition to those of length and mass, also vary according to the motion of an object. Einstein's mathematical equations showed that as a body approaches the speed of light, time appears to lengthen. For example, to an object moving at ninety-eight per cent of the speed of light, one second becomes five seconds long. This phenomenon is called time dilation.
As with changes in measured length and mass, the effects of speed on time are insignificant at speeds encountered in ordinary daily life, but they do become significant as the speed of light is approached.
Evidence for time dilation has been forthcoming from several sources. For example, nuclear accelerators exist that allow subatomic particles to attain very high speeds, approaching that of light. Some of these particles are unstable and break down at a defined rate. As they move faster, the particles break down more slowly: the time taken for them to decay becomes longer as they approach the speed of light.
Another piece of evidence that supports Einstein's contention that time slows down as objects move faster comes from measurements of the rates of ticking of highly sophisticated atomic clocks. Such clocks have been shown to run more slowly on fast moving jet planes and on satellites than similar clocks on Earth.
The Special Theory of Relativity deals with the effects of uniform motion on length and mass of an object and on time. Einstein later developed his General Theory of Relativity, which is concerned with non-uniform motion and proposes a new way of looking at gravity. To Newton, gravity was a force of attraction between two objects: large objects exerted a greater gravitational pull than small ones. Einstein did away with this idea. He showed that gravitational attraction was equivalent to acceleration (increase
of speed); this was called the Equivalence Principle. An object in an upwardly accelerating container is pulled down to the floor of the container in exactly the same way as an object is pulled towards the Earth by gravity.
To Einstein, gravity was not a force between objects, but a curvature of space-time that was caused by the presence of mass. An object does not fall to the Earth because it is being attracted by the Earth's gravitational pull: it falls because it takes the easiest route along the curvature of space-time created by the Earth's mass. An analogy is that of a ball-bearing placed on a sheet of elastic material. The ball-bearing (Earth) creates a depression in the sheet (space-time), and the sheet is curved around
the ball-bearing, becoming more steeply curved nearer the ball-bearing.
The General Theory of Relativity was testable, like all good theories. It predicted, for example, that light should be bent by gravity. Light passing close to the Sun would, according to Einstein, be bent by the curvature of space-time caused by the Sun. This should be measurable under the correct circumstances. The best situation in which to observe this bending of light by the Sun is a total eclipse of the Sun. In 1919 such an eclipse occurred off the coast of West Africa, and a group of British scientists
organised an expedition to test Einstein's theory by measuring the positions of stars in the neighbourhood of the Sun and looking for the predicted bending. The results were in agreement with Einstein's theory, and this caused a sensation that made Einstein a household name around the world.
When Einstein received a telegram informing him of this confirmation of General Relativity, he was remarkably calm about it. One of his students who was with him at the time commented on how exciting the event was, but Einstein apparently responded with little emotion and said, 'But I knew that the theory was correct'.
When asked what he would have thought if the results had disagreed with his theory, Einstein replied, 'Then I would have felt sorry for dear God, because the theory is correct.' However, a letter written by him at the time to his mother does indicate that he really was excited by the confirmation of his prediction.
Although many physicists later doubted the accuracy of the measurements made during the 1919 solar eclipse, numerous other observations have since supported Einstein's idea about gravity. In addition, Einstein knew that his General Theory provided an answer to a puzzle, that of the peculiar orbit of the planet, Mercury, which classical physics could not explain.
It had been known since the mid-nineteenth century that the orbits of the planets around the Sun are nearly, but not quite, closed ellipses. The planets precess; that is, they return to a slightly different place after each orbit, producing an orbit consisting of loops rather than a closed ellipse. Mercury - the planet nearest to the Sun - precesses to the greatest extent. When Newton's theories were applied to Mercury's precession, they could not explain it properly. The phenomenon baffled many physicists,
especially because no other planet close to the Sun was found that might be exerting a force on Mercury and causing the anomaly.
Classical physics simply did not explain this orbit. However, General Relativity explained it exactly: when Einstein applied his equations describing the effects of the Sun on the curvature of space-time, Mercury was predicted to have the precise orbit that was found. Einstein's General Theory not only provided a brand new way of looking at Nature and explaining properties of the Universe, but also gave birth to modern cosmology, the study of the origins and properties of the Universe. His equations of
General Relativity predicted that the Universe was not static - it was either expanding or contracting. Although Einstein rejected this idea, believing that the Universe was static, other physicists used his equations to propose models of an expanding Universe, and this gave rise to the Big Bang theory for the origin of the Cosmos. Einstein's 'thought experiments' had clearly revolutionised our understanding of existence, and will continue to do so.
Einstein's publication on the photoelectric effect in 1905, which restored the idea that light consists of particles (photons), eventually earned him the Nobel Prize for Physics. However, Einstein is much better known for his Theories of Relativity, the first of which was also published in 1905. As a physicist, there is little doubt that he would have been highly esteemed by his fellow scientists even if he had not developed his Theories of Relativity, because his other contributions to physics were very
great indeed. It is a rare event in the history of the world when a scientist as great as Einstein appears: not only did he provide answers to many puzzling questions that classical physics failed to explain, but he also dramatically changed the way we think about the world around us.
Einstein's relativity theories also gave birth to modern ideas about the origin of the Universe. Every physicist alive today is taught in a way that is deeply influenced by Einstein's work and few would doubt that Einstein is the greatest physicist the world has ever seen.
During his life, Einstein became a highly respected and well liked public figure, a situation that is normally somewhat rare for a scientist to achieve.
The key to his popularity was probably that he was viewed as a great genius, with a kind, unpretentious personality and idealistic political and moral values, and also the fact that his scientific ideas provided a deep insight into the workings of the Universe. He also became involved in several political situations, including the development of the atom bomb; and he was offered the Presidency of Israel, but declined. Einstein was, like Maxwell and Planck, a theoretical physicist: his experiments were carried
out in his mind. (One practical thing he did was to develop and patent, with the Hungarian physicist, Szilard (1898-1964), a noiseless household refrigerator.) When one considers just how much such 'thought experiments' have contributed to science and technology, one is left with the realisation that pure thinking and its mathematical expression are at least as important to human progress as experimental science. Once, when asked by someone if they could see his laboratory, Einstein took a fountain pen from his
pocket and said, 'There it is!' On another occasion he commented that his most important piece of scientific equipment was his wastepaper basket, where he threw much of his paperwork containing mathematical computations.
There is a misconception amongst some people that Einstein effectively showed that Newton's Laws of Motion were wrong. Some critics of science have suggested that this is evidence that scientists have got it all wrong, and that they are constantly contradicting themselves.
Newton's First Law of Motion, also known as the Law of Inertia, states that an object will remain at rest or continue in the same direction in a straight line with constant speed unless it is subjected to a net applied force.
His Second Law states that an object will accelerate when a net force acts on it, and the net force (F) is equal to the object's mass (m) multiplied by its acceleration (a), that is, F=ma.
Newton's Third Law of Motion states that when one object applies a force upon another, the second object exerts the same force upon the first, but in the opposite direction. This can be seen clearly in space: when an astronaut throws an object in one direction, the object exerts an equal and opposite force, causing the astronaut to be pushed in the opposite direction.
What Einstein did was to show that although Newton's Laws work perfectly well under everyday conditions, his Laws of Motion need to be modified when objects approach the speed of light (300 000 kilometres per second; 186 000 miles per second). At speeds normally encountered in daily life, which are a tiny fraction of the speed of light, moving objects behave in such a way that Einstein and Newton's descriptions of them become indistinguishable. Indeed, Einstein really refined Newton's Laws of Motion so
that they worked at all speeds: this modification of existing ideas is the normal way by which science progresses. Einstein revolutionised the whole of physics, particularly with his work on Relativity, which involves two main theories: the Special Theory of Relativity, which he published in 1905, and the General Theory of Relativity, which he published in 1916. Before these are described, some knowledge of the scientific context of Einstein's ideas is required.
Every science eccentric likes to target Einstein, explaining confidentially that he (it is usually a "he") has been able to show that Einstein got it wrong. Somehow, these "proofs" never seem to impress mainstream scientists, who are more interested in the evidence gained from observations. Real scientists are especially interested in observations which bear out Einstein's views, because so much of our modern science seems to be perfectly explained by Einstein's ideas. And at least the
observations serve to keep the "crackpots" at bay.
Einstein predicted an effect, called "frame dragging," 80 years ago. Like many other aspects of Einstein's famous theories of relativity, it is so subtle that no conventional method could measure it. In simple terms, frame dragging results in space and time get pulled out of shape near a rotating body. In an extreme case, a rotating Tipler machine may even interfere with the causality principle through frame dragging. Using recent observations by x-ray Astronomy satellites, including NASA's Rossi
x-ray Timing Explorer, a team of astronomers reported in November that they had found evidence of frame dragging in discs of gas swirling around a black hole. Drs Wei Cui, Nan Zhang, and Wan Chen began with Einstein's prediction that the rotation of an object would alter space and time, dragging a nearby object out of position compared to predictions by the simpler math of Sir Isaac Newton. This effect had not been observed in the eighty years since Einstein predicted it. In this, it was unlike the other, more
familiar Einsteinian predictions, such as the conversion of mass into energy (as seen in atomic bombs and stars) and back, the Lorentz transformations that make objects near the speed of light grow thinner and heavier and stretch time, and the warping of space by gravity (as seen when light is bent by a massive object) And no wonder: the effect is incredibly small, about one part in a few trillion, which means that you have to look at something very massive, or build an instrument that is incredibly sensitive
and put it in orbit. Cui, Zhang, and Chen took the first option, and studied radiation coming from around black holes in binaries with other visible stars. Over time, the black hole strips material from the star, producing an accretion disc of material which gets hotter as it approaches the event horizon of the black hole, and gives off radio waves, visible light, and-just before it disappears-x-rays.
They found that the discs precessed, wobbling like a child's toy top. By studying the radiation from supraluminal jets in two black holes, called GRS 1915+105 and GRO J1655-40, they found that the rate of precession was far greater than could be explained by the sorts of effects seen in children's toys. Conclusion: Einstein's frame-dragging is real. The sensitive instrument option will follow next: NASA is developing it as Gravity Probe B, described in the entry on general relativity. This is a satellite
containing precision gyroscopes inside a liquid helium bath. Gravity Probe B will point at a selected star, and sensitive instruments will measure how much the gyros precess after conventional effects are nullified. The leftover effects should provide a precise measure of frame dragging. Because the Rossi satellite observations are somewhat uncontrolled, the final proof of frame dragging will come when Gravity Probe B points at a known star of known mass, and turns in consistent results.
1997 Science Review contents.
Einstein proved right, even when space-time is seriously curved
Since the early 1940s, physicists have accepted that a massive object would warp space, bending it so steeply that any object getting too close would fall into it, generating x-rays as it goes. Now a careful observation of the x-rays from a neutron star called 4U 1820-30 has revealed evidence of just such an effect. The observation was carried out from NASA's Rossi X-Ray Timing Explorer satellite over the course of a year.
The Rossi Explorer had already measured the x-rays coming from such sources, and shown that the brightness of neutron stars varied as much as a thousand times a second, making them the most rapidly variable objects in the universe. Neutron stars have a mass about ten times as great as the sun, but are only about 15 km (10 miles) in diameter. This density produces highly curved space-time, according to Einstein, and that is an interesting place to look at, if you are a physicist. In Newtonian physics, gases
can orbit in circular orbits at any distance, but Einsteinian relativity says that if you have curved space-time, there are no stable circular orbits. So where does the gas come from? If the neutron star is in a binary with an ordinary star, it tears matter away from the other star, so it spirals down into an orbit around the neutron star, traveling at speeds close to the speed of light. As a black hole or a neutron star spins, it sets up huge forces that force this gas into a disc, called the accretion disc.
The disc may wobble around its outer edges, but in close to the massive object, the disc must line up with the equator of the object. Somewhere on that accretion disc, there is a region where matter passes inside the last stable orbit, and then it tumbles catastrophically inwards.
The point of instability (where matter pours in) rotates around the accretion disc as it spins, pulled by the gravity of the neutron star. X-rays pour out from this point, like the beam of a lighthouse, and with a frequency for the x-rays which depends on the distance of the disc's inner edge from the neutron star. The disc is in balance, pulled inwards by gravity, and pushed outwards by the radiation coming from the star, but if a large block of material falls in, this may block the radiation hitting the
disc (but not the gravity), allowing the disc edge to tumble in, producing the characteristic oscillation. If Einstein is right, say the experts, then there should be a limit to the frequency of the x-rays, and this should define the point of no return. So they watched the radiation coming from the star. They watched the brightness, which told them how much material was falling in, and they watched the frequency, but again and again, it hit a ceiling, an upper limit. Four times, they say, is no coincidence -
Einstein wins again! The oscillations stabilized at 1050 hertz, even when the x-ray power increased, there was still this simple limit applied to the radiation. The main point to this, they say, is that the x-ray brightness oscillations could be used to determine the masses and dimensions of neutron stars.
Of course, everybody knew that Einstein was right about ordinary space, where the curvature of space is minimal, but now we have good direct evidence that it also works around seriously dense objects, in strongly curved space-time. Two papers describing the theory and the results have been accepted for publication in the Astrophysical Journal. One final comment from Professor Frederick Lamb, one of those who has been at the centre of this exciting work: "Studying how matter moves in the strongly curved
space-time near neutron stars also has allowed us to extract interesting new bounds on the masses and dimensions of these stars and on the stiffness of the superdense matter inside them. The new evidence reported today suggests that the strong nuclear force is more repulsive than many nuclear physicists had expected and that the superdense matter in neutron stars is rather stiff."
April 1998 Science Review contents.
Einstein and the Photon
In 1905, Albert Einstein published four theoretical papers in distinguished scientific journals. Two of them were concerned with his Theory of Relativity. Another was on Brownian motion, which refers to the random jerky movements of microscopic particles suspended in air or a liquid. The fourth paper proposed an explanation for the photoelectric effect, and it was this article that revived the long-forsaken particle theory of light and brought Planck's ideas into the scientific limelight. It has been said
that any one of the four of Einstein's 1905 papers would have made him an eminent physicist. Most people remember him for Relativity, although when he later received the Nobel Prize for Physics, in 1921, it was for his theoretical work on the photoelectric effect. Einstein was well aware that the wave theory of light did not explain the photoelectric effect: 'The usual idea that the energy of light is continuously distributed over the space through which it travels meets with especially great difficulties when
one tries to explain photoelectric phenomena', he said.
He was acquainted with Planck's explanation of blackbody radiation, that light was emitted and absorbed as quanta of energy, and it was to this that Einstein turned in order to solve the photoelectric effect problem. The solution, Einstein proposed, was to regard light as being made up of particles or quanta in much the same way that Planck considered light to be absorbed and emitted from blackbodies as quanta. These quanta of light later became known as photons, from the Greek word meaning 'light'. However,
whilst Planck believed that parcels of light were absorbed and emitted by blackbodies because of the properties of the bodies themselves, Einstein said that the properties of blackbodies were irrelevant and that light was made up of particles anyway, regardless of whether it was emitted and absorbed by objects. If Planck's model is thought of as being taken from a barrel only in pint portions then in Einstein's theory the beer is already present in the barrel as pint portions, even before it is tapped! According
to Einstein, each photon of light penetrating a metal surface would collide with an electron in the metal and transfer its energy to the electron. If the amount of energy transferred from a particular photon was high enough, it would enable the electron to reach the metal's surface and be ejected, so producing the photoelectric effect.
If the intensity of incident light was increased it would mean, according to Einstein, that more photons of a given frequency would reach the metal surface in a given amount of time. Therefore, increasing the intensity of incident light should cause more electrons to be emitted and their energy should be unaltered. This is exactly what happens. Einstein also showed that increasing the frequency of light should increase the energy each photon transfers to the ejected electrons but should have no effect on
the number of electrons emitted. This, also, is precisely what occurs in the photoelectric effect. Exact quantitative measurements of the effect of incident light intensity and frequency on electrons emitted during the photoelectric effect were not available when Einstein published his 1905 paper. However, his mathematical analysis of the phenomenon predicted exactly what results should be obtained. These predictions were the acid test of Einstein's theory. If scientific results hitherto unobtained are correctly
anticipated by a theory, scientists can have confidence in the theory. In 1916 the US physicist, Robert A. Millikan (1868-1953), accurately carried out the required experiments on the photoelectric effect. His data agreed perfectly with Einstein's predictions. Light did, indeed, appear to be made up of photons.
Whilst the wave theory of light did not explain blackbody radiation or the photoelectric effect, the photon idea did not easily explain interference or diffraction. Indeed, interference and diffraction had been used for many years to support the wave theory. Einstein was aware of the failure of the photon idea to explain diffraction and interference. Nowadays we have come to accept that at the level of the very, very small our everyday view of the world does not necessarily hold and that light is both a
particle and a wave. This is known as wave-particle duality and applies to all forms of electromagnetic radiation.
When it comes to levels of size as small as photons, both wave and particle aspects can be detected. When light undergoes interference or diffraction it can be considered to be a wave. When it is involved in the photoelectric effect or blackbody radiation, it may be thought of as being particulate.
Sir William Henry Bragg (1862-1942), the British physicist, put it more plainly, 'On Mondays, Wednesdays and Fridays light behaves like waves, on Tuesdays, Thursdays and Saturdays like particles, and like nothing on Sundays.' The wave-particle nature of light was extended to matter by Prince Louis de Broglie (1892-1987), a French physicist, who proposed that not only can electromagnetic waves behave as particles, but also particles can behave as waves. According to de Broglie, even objects as large as a
human being or a planet have some wave-like features, although these are minuscule and the particle-like properties dominate. However, electrons are very small particles and de Broglie's theory suggested that electrons should show some wave properties that could be detected. His ideas were subsequently confirmed when electrons were found to show the phenomena of diffraction and interference and their wavelength was measured.
Indeed, the wave-like properties of electrons have been particularly useful in the development of electron microscopes, which allow small objects to be seen using a beam of electrons instead of a beam of light. Electron microscopes are more powerful than microscopes that use visible light and have been particularly valuable in obtaining images of objects such as viruses and the interiors of living cells, which cannot easily be seen with optical microscopes. After Einstein had revived Planck's theory of
the absorption and emission of light by blackbodies, the Danish scientist, Niels Bohr (1885-1962), used the ideas of the quantum to propose a new model for the structure of the atom.
Bohr explained why atoms of a particular element absorbed and emitted light at specific frequencies. In his model of the atom, negatively charged electrons are distributed around a positively charged nucleus. However, the electrons cannot occur just anywhere around the nucleus: they must exist in states of defined energy, called energy levels.
When an atom absorbs light, the light energy is transferred to an electron and this electron 'jumps' to a higher energy level, but this will occur only if the energy (and therefore frequency) of the light photon is enough to allow the electron to change from the lower to the higher energy level. The electron cannot jump to a place in between the two energy levels: it must be in one or the other level.
As a result, the atom absorbs packets (quanta) of energy. Likewise, an atom will emit light energy when an electron jumps from a higher energy level to a lower one, but since only defined jumps can occur the energy of light emitted must have discrete values. Photons emitted and absorbed are therefore of a particular frequency. Bohr's model of the atom showed that the energy levels of electrons are quantised. Quantum physics, which is required to understand the very small, such as atoms, subatomic particles
and electromagnetic radiation, has revolutionised physics. Many physicists are seeking an explanation of the origins of the Universe by combining quantum physics with a theory that allows scientists to understand the very large. One theory that allows the very large to be explained mathematically is Einstein's Theory of Relativity, and it is this theory that might perhaps be considered to be the second of the two most important developments in twentieth century physics; quantum physics being the first of these
advances.
In view of the tremendous impact that quantum theory had on physics, it is extraordinary that it began with an inspired guess by Max Planck, who simply wanted a mathematical equation that would explain why blackbodies absorb and emit electromagnetic radiation in the way that they do, and that it was strengthened enormously when Albert Einstein sought an explanation for the photoelectric effect.
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Royden John Elson
Roy Elson