INTERNATIONAL SPACE SCIENCE INSTITUTE SPATIUM Published by the Association Pro ISSI No. 18, February 2007

SPATIUM 18  Editorial

Omnia rerum principia parva sunt. Associate Professor at the Univer- The beginnings of all things are sity of Michigan have endeavoured Impressum small. successfully to translate the fascinat- ing ideas of Albert Einstein for a This famous quote of Marcus Tul- larger audience, not just in Bern, but lius Cicero is more than true for the in many stations all over the world middle drawer of an ordinary desk and to highlight some of the traces SPATIUM at the Kramgasse 49 in Bern. This he continues to leave in our daily Published by the drawer was called the office for the- life. We are greatly indebted to the Association Pro ISSI oretical physics by its owner, clearly authors for their kind permission to a euphemism initially, but more publish herewith a revised version than appropriate by the time when of their multi-media presentation. its contents prompted nothing less than a revolution of theoretical Association Pro ISSI physics. Hansjörg Schlaepfer Hallerstrasse 6, CH-3012 Bern Brissago, January 2007 Phone +41 (0)31 631 48 96 The desk belonged to the patent see clerk of third rank Albert Einstein, www.issibern.ch/pro-issi.html who during the office hours had to for the whole Spatium series treat the more or less ingenious in- ventions filed to the Patent Office, President while in his spare time had set out Prof. Heinrich Leutwyler to invent a new physics. University of Bern Layout and Publisher One might expect that such high- Dr. Hansjörg Schlaepfer flying studies could at best occupy CH-8173 Neerach a few scientists in their laboratories. Printing It was worse off: even the brigh- Stämpfli Publikationen AG test representatives of the world- CH-3001 Bern wide science community needed at least twenty years to fully grasp the epochal power of the patent clerk’s ideas while for the great public Ein- stein’s theories continue to stand for Front Cover the inaccessibility of science. This composite image provides a glimpse to the remotest regions of Nevertheless, much has been said the universe explored by the Hubble about Albert Einstein on the occa- Space Telescope so far. The evolu- sion of the hundredth anniversary tion of the cosmos is certainly a of the annus mirabilis 1905 in Bern, topic that Albert Einstein discussed the year, when the middle drawer with his two colleagues of the Aka­ of his desk became really the office demie Olympia in Bern, Conrad for theoretical physics. Rudolf von Habicht and Maurice Solovine. The Steiger, Professor at the University overlay image shows an excerpt of of Bern and Director of the Inter- a message he wrote to the latter. national Space Science Institute to- (Credit: ESA, NASA, Hansjörg gether with Thomas H. Zurbuchen, Schlaepfer)

SPATIUM 18  Einstein in Bern: The Great Legacy1

Thomas H. Zurbuchen, University of Michigan, Ann Arbor, MI, USA Rudolf von Steiger, International Space Science Institute, Bern, Switzerland Brian Grimm, Paper Cardinal Design, Oakland, CA, USA

solved problems in science. One stars to astronomical telescopes. The Introduction problem concerned the way light assumption of a thin, nearly mass- interacts with metal surfaces and less ether had been questioned by obviously is able to eject electrons an experiment by Michelson and out of these surfaces. The second Morley some 25 years earlier that problem had to do with the appar- failed to find any evidence for such The French philosopher and math- ently random zig-zag motion of an ether. ematician Henri Poincaré2, in 1902, pollen observed under the micro- published a book entitled “La Sci- scope, called Brownian Motion. The Only a few years later a young pat- ence et l’Hypothèse”. In this book third problem was the failure of ex- ent clerk by the name of Albert Ein- he identified what were – in his perimental physics to detect how stein had solved all three of these opinion – the most important un- light propagates, for example, from problems in a convincing manner.

Figure 1: Beautiful Bern. Looking over the roofs of downtown Bern to the hills of the Bernese Mittelland to the permanently snow-covered High Alps with the Blüemlisalp in the centre. (Credit: Bern Tourism, Bern)

1 The present text follows a lecture by R. von Steiger in the Historisches Museum in Bern, 22 August 2006. Similar talks were held by T. Zurbuchen and R. von Steiger in over 20 locations world-wide 2 Jules Henri Poincaré, 1854 Nancy, France – 1912 Paris, French mathematician, physicist and philosopher.

SPATIUM 18  Setting the Stage

The story plays in Bern, the capital of Switzerland, in the very heart of Europe. The historical roots of Bern date back to the La Tène time, the 5th to 1st centuries B.C. Modern Bern was founded by Duke Berch- told V von Zähringen in 1191. A legend tells us that he decided to name the new city after the first an- imal he would catch on a hunt; this was a bear, prompting him to name the place Bern. Bern is considered one of the most beautiful cities in Europe. It is located close to the Aare, a river originating in the Swiss Alps that brings clean water from the mountains to the city. Naturally, the U-shaped river bend was an at- tractive location for the city in me- dieval times, providing protection from three directions. Today, Bern houses approximately 150,000 peo- ple. To outsiders, Bern is known for its history, spanning many centuries, its bear pit housing the animal also found in the Bern flag, and its am- biance that is certainly unrivalled. To its visitors, Bern is often de- scribed as “gemütlich” – you imme- diately feel the warmth of its peo- ple, and its beauty.

In the old part of the city, in a house whose origins date back to the first city expansion in 1218, a story unravelled that was so ground- breaking and new that it still has ­effects today. In this house at Kram- Figure 2: Bern, Kramgasse 49. It is here that the Einsteins lived between 1903 3 and 1905. From this house Albert Einstein revolutionized physics by his publications gasse 49 (Figure 2) Albert Einstein in 1905. (Credit: Einsteinhaus Bern) lived from October 1903 to May

SPATIUM 18  1905. It was one of the seven differ- steins shared the kitchen and the The Great ent locations where he resided dur- bathroom with four other families, ing his seven year stay in Bern. while their own apartment con- ­Scientific Trilogy tained two rooms and a foyer. Noth- For all practical purposes, things did ing of this simple setting revealed not go very well during that time. that here one of the most ingenious He had finished his exams, allow- human spirits ever silently was at ing him to submit a doctorate at the work. And his objective was noth- The genius could not be halted by University of Zurich. Out of the ing less than to answer the three ma- the measly setting. Rather he dis- three graduating students applying jor open issues identified by Henri cussed the ardent problems together for a doctorate, two were hired as Poincaré three years before while with his colleagues of the Akade- teaching assistants, but Einstein was dealing with such mundane items mie Olympia, Conrad Habicht and not. He was married to Mileva as shower heads or refrigerators, Maurice Solovine (Figure 3), and Maric and they had a child, so the during his office hours. He did not then went back to his desk, the mid- sheer economical necessities forced even have unlimited access to li- dle drawer of which he called his him to accept a job at the “Amt für braries as he generally worked in office for theoretical physics, and geistiges Eigentum” – the Swiss of- the patent office during the time put his thoughts to paper. fice for intellectual property, or, as when the library was open. we now call it, the Patent Office. He was hired as a clerk of third rank. We will now concentrate on what The Photoelectric Effect The office hours were from 7 a.m. Einstein wrote in three of his most to 6 p.m. every working day and important papers, but let’s not for- In March 1905 Albert Einstein pub- from 7 a.m. to 5 p.m. on Saturdays. get how, under what conditions he lished a short article in the Annalen Only Sundays were off. The Ein- lived when writing these papers. der Physik entitled Über einen die Erzeugung und Verwandlung des Lichts betreffenden heuristischen Ge­ sichtspunkt, a paper that in 1921 earned him the Nobel Prize. At that time, all physicists knew what light was. Whether from stars, the Sun, or from radio antennas, light clearly propagated as a wave. Just like sound, light can propagate around the cor- ner – you can easily see this for your- self. Just drop a coin in a mug, then back away until you lose sight of the coin. Next fill the mug with water. Voilà, the coin reappears though it still rests on the bottom of the mug. Light propagates very much like sound, bending, adding, and subtract- ing, and very much behaving like liq- Figure 3: The members of the Akademie Olympia. From left to right: Conrad uid waves on a lake or sound-waves Habicht, Maurice Solovine and Albert Einstein. (Credit: ETH-Bibliothek, Zürich) in air. Just like sound-waves in air, light-waves were assumed to propa- gate in a medium, the so-called ether, 3 Today, this is the location of the Einstein house. which spanned the universe.

SPATIUM 18  Einstein’s explanation shook the energy content is not sufficient to understanding of light at its basic free the electrons in the metal. This roots. He argued that light is made is why the red light does not cause of particles, called photons. Each a significant increase of current. In photon has an energy content contrast, the blue photons, when which is determined only by its col- hitting the surface, cause an electric our. So, with that new concept, the current to flow, as they possess explanation of this intriguing ex­ enough energy to free electrons in periment becomes quite simple: the metal plate. Note that this effect when the photons of the light works no matter how dim the light sources hit the metal surface, they may be. Blue light particles do sim- interact with the electrons in the ply have sufficient energy, and in- metal. A certain minimum energy creasing the brightness just brings Figure 4: The photoelectric effect. is required for an electron to be more of them out of the metal and The experimental setup demonstrating freed from the metal and to con- thus further increases the current. the different properties of blue and red light respectively. tribute to the electric current. The red light is made from lower-energy Einstein’s interpretation was highly photons in larger quantity whose controversial at that time. Based on There was, however, a problem with this notion as illustrated in Fig- ure 4. The experimental arrange- ment consists of two lamps, one red and one blue, shining on a metal plate. The metal plate is hooked up with a wire, so that electric current from this plate can be measured. Electric current basically is made out of a bunch of moving electrons, negatively charged particles. Now, without any lamp on, there is a very slight current, almost nothing at all. Then, the red lamp is turned on. The current increases only slightly, but does not become really strong at all. The blue lamp has exactly the same wattage and therefore emits exactly the same power as the red lamp. But when this blue lamp is turned on, the current really jumps. What hap- pened? Although we irradiated the plate with exactly the same power, Figure 5: Brownian Motion. The British botanist Robert Brown observed in 1827 the blue light causes the electrons to that the pollen of plants suspended in water was moving around in a random way. This leave the metal plate, while the red sketch shows what might have been the path of one such pollen, bumped by billions light has practically no effect. of collisions with the smaller and hence invisible water molecules in the solution.

4 Robert Andrews Millikan, 1868 Morrison, Illinois – 1953 San Marino, California, American physicist, Nobel Prize 1923.

SPATIUM 18  a series of experiments, Robert Brownian Motion interpreted as showing that the pol- Millikan4 validated all predictions len grains were really little animals made by Einstein relative to the Only two months later, in May swimming in the water. Brown was photoelectric -effect, but he came 1905, Albert Einstein solved the aware of this and therefore per- to the conclusion that despite the second of Henri Poincaré’s great formed a series of experiments that ­apparently complete success of the Ein­ challenges. The Scottish botanist involved sprinkles of glass, rock and stein equation for the photoelectric Robert Brown5, during extensive other inorganic material in the wa- effect, the physical theory on which it work with his microscope some ter. No matter what type of small was designed to be the symbolic expres­ seventy years earlier, had made a particles he used, Brown observed sion is found to be untenable. Einstein’s strange observation. The pollen of the very same motion in all exper- theories continued to be contro­ Equisetum suspended in a water iments. Therefore he had to ex- versial and only through the wise ­solution untiringly rushed around clude the earlier interpretation and foresight of the Nobel committee in a random zig-zag motion, Figure progress to a notion that the mo- did Einstein get the ultimate recog- 5. Such observations had been made tion was not of biological origin, nition for this paper in 1921. prior to Brown, but were generally but had its roots in the physical properties of water and its interac- tion with these grains.

Einstein’s view of Brownian Mo- tion is surprisingly straightforward: the suspended small particles are constantly bombarded by the water molecules which in turn are much smaller and therefore not visible un- der the microscope. If a water mol- ecule had the diameter of a tennis ball, the size of the pollen would be approximately 100 metres. These tiny water molecules restlessly strike the particle and push it continu- ously. Billions of such collisions oc- cur every second. Random fluctu- ations may cause a whole convoy of particles to hit the pollen knocking it this way and some time later it may experience a push from an- other direction and so on, as shown in Figure 5.

Einstein solved the problem by in- terpreting water to be made of small Figure 6: The Michelson-Morley experiment Before Einstein, it was assumed that light propagates in the ether at rest in the universe. Therefore, the light ray parallel to particles and not, as was assumed the Earth’s motion (a-c) should return faster to the semi-reflective mirror as compared before, a jelly-like, continuous liq- to the perpendicular light beam (a-b). But the experiment proved otherwise. uid. It was already known at the time that many issues in thermody- namics, the part of physics that de- 5 Robert Brown, 1773–1858, Scottish botanist, discoverer of Brownian Motion. scribes how heat is created, ex-

SPATIUM 18  changed and transported, could be tablished this new notion without stein based his reasoning not on a explained in the context of average any doubt. Secondly, and much particular experiment, but rather he properties of particles, bumping more importantly, his interpretation was motivated by the problems sci- into each other and moving around. of the statistical nature of fluids entists had with light and its prop- On the average, the model of these opened the door to the modern, agation. At the time, physicists interacting particles describes quite statistical description of particles. thought that light, just like sound in well how heat behaves. However, On the average, things are pretty air, propagated in a medium, gen- this picture was largely assumed to predictable, but for an individual erally called ether, as we have seen be a model only and leading scien- particle, things become random and above. That ether would presuma- tists refused to assume that there therefore unpredictable. bly sit at rest in the universe. This would be any departures from that hypothesis was tested by Albert average behaviour on the level of Michelson6 and Edward Morley7 in the individual particle. Einstein’s in- Special Relativity Cleveland in 1887, Figure 6. The ba- terpretation established two very sic idea of their experiment is quite important new aspects. Firstly, the One month later, in June 1905, straightforward: the Earth orbits fact that water consisted of small, ­Albert Einstein addressed the the- around the Sun at a speed of about individual particles was established ory of relativity, which of the three 30 kilometres per second, or firmly. While this idea was brought problems is perhaps farthest away 1/10,000 of the speed of light. The up long before Einstein, his inter- from our everyday experience. In light beam in a laboratory directed pretation of Brownian Motion es- contrast to the first two topics, Ein- along the path of the Earth’s mo-

Figure 7: The heart of downtown Bern. The Kramgasse, where the Einsteins lived between 1903 and 1905, seen from the ­Münster tower (Photo: Frank Rutschmann).

SPATIUM 18  tion should speed up or slow down system is a three-dimensional map ling each point of space with time in the ether at that rate depending allowing points in space to be brought by letting a clock run there. By do- on the actual direction while its in relation to each other. A co-ordi- ing so, our co-ordinate system has speed should not be affected by the nate system attached to the Earth can become four-dimensional: three Earth’s velocity when it is directed be used, for example, to measure dis- space dimensions and one time di- perpendicular to the Earth’s mo- tances between two cities. We may mension, but it continues to be quite tion. The outcome of this experi- centre the co-ordinate system, for simple. The question Einstein asked ment was very disappointing: the example, in Bern. Then, Zurich is himself is how events in one system speed of the light was found to be some 80 km to the north-east. As we can be transferred into another co- independent of the direction rela- are free to centre our co-ordinate ordinate system, or more specifically, tive to the Earth’s motion. While system where we like, we might cen- how physical experiments in one co- this experiment was a failure in the tre it at the Sun constantly oriented ordinate system relate to physical ex- eyes of many scientists, it was an in- relative to the stars. In this co-ordi- periments in another system which spiration for Einstein. nate system, the Earth is roughly 150 is moving relative (this is why we million kilometres away circling the speak of relativity!) to the first one To understand Einstein’s reasoning, Sun approximately in one year. So with a constant speed. Such systems we have to introduce the concept of far, so good and simple. But now we are called inertial co-ordinate sys- a co-ordinate system. A co-ordinate can add time to the picture by label- tems. Of course, the results of the ex-

6 Albert Abraham Michelson, 1852 Strelno, Poland – 1931 Pasadena, California, German-American physicist, Nobel Prize 1907. 7 Edward Williams Morley, 1838 Newark, New Jersey – 1923, American scientist.

SPATIUM 18  periments should be independent of the co-ordinate system much like the distance between Bern and Zurich must be independent of the co-or- dinate grid we use. This, however, is particularly tricky for a field of phys- ics called electrodynamics, the sci- ence that describes the propagation of light as well as the electrical and magnetic phenomena, like for exam- ple the processes on the surface of the Sun or the behaviour of the Eu- ropean electrical network.

Einstein focused his analysis on two principles and their consequences. The first principle is the Principle of Relativity: the laws of physics are the same in each co-ordinate system, or the other way round: one cannot distinguish between (iner- tial) co-ordinate systems based on physical experiments. The second principle is a direct consequence of the negative result of the Michel- son-Morley experiment. It simply states that the speed of light is ab- solute and constant in all co-ordi- nate systems. When defining these principles, Einstein was firmly guided by ob- servable phenomena: time is what you can read off a clock. Clocks can be synchronized only by ex- changing signals at finite speed such as the speed of light. The con- clusions drawn by Einstein are truly amazing: if the speed of light is absolute, time and space must be relative!

We can verify this striking conclu- sion by an experiment, see Figure 8. It starts in the depths of space when an exploding star accelerates parti- Figure 8: Demonstrating the relativity of space and time. The fast moving muons experience the dilatation of time that allows them to travel farther than their cles to very high speeds, nearly to limited lifetime would suggest. (Credit: BHM) the speed of light. Some of these so-

SPATIUM 18 10 called cosmic rays enter the upper Jungfraujoch. So, apparently about tem, we know that the distance from atmosphere of the Earth and collide half the muons counted at the alti- Jungfraujoch down to Bern is 3,020 with air particles. These collisions tude of Jungfraujoch make it to Bern metres, and the particle’s speed is create a whole shower of new and without any problems and are seen roughly the speed of light. Due to mysterious particles; most of them as small sparks in this chamber. the muon’s high speed, Einstein ar- collide with other air molecules or gues that the time as experienced by decay very quickly so they don’t What happened? We argued before the muon slows down dramatically. make it very far. Some particles in that no muon can travel further than That means, that, as seen by our the shower, however, the so-called 660 metres even at the speed of light clocks, the muon’s life is extended muons, interact only weakly with before decaying. And still they travel or, in Einstein’s terminology, time is the air molecules. They can travel through the altitude difference of relative. By translating from the therefore all the way to the ground. 3,020 metres, five times as much. muon’s co-ordinate system to our Muons are the heavy cousins of Einstein’s notion of relativity helps coordinate system attached to the electrons, but while electrons have us to explain our findings. We can Earth, time is dilated. an unlimited lifetime, the lifetime do so from two different points of of a muon is a mere 2.2 microsec- view, either in a co-ordinate system On the other hand, we can look at onds. So, we expect no muon to fixed to the Earth, or in a co-ordi- this experiment as if we were sit- make it from the upper atmosphere nate system fixed to the flying muon. ting on the muon. Again, we know down to the ground, as it will de- In the Earth-fixed co-ordinate sys- that the muon lives a mere 2.2 mi- cay before getting there, even when propagating at the speed of light. More specifically, we expect the muon to travel no more than 660 metres before decaying. But our ex- periment proves otherwise!

In order to identify the muons, we use spark chambers. These are stacks of metal plates separated by thin gaps with a high voltage across. When a muon passes through, it leaves a trace of visible sparks in the chamber, which allows us to notice its pres- ence. Now, we set up one such spark chamber at the Jungfraujoch at an altitude of 3,580 metres and the other in Bern at 560 metres. While we expect the spark chamber on the Jungfraujoch to see many muon counts thanks to its high elevation, no counts in Bern are expected as it is deeper in the atmosphere than the muon’s expected travelling distance of 660 metres before decaying. In the experiment both chambers hap- Figure 9: The world-famous Zytglogge tower. The tower itself was part of the original city walls at the beginning of the 13th century. The great bell was cast in pily count muons, the one in Bern 1405. The clock is more recent, its mechanism dates back to 1530. (Photo Hansjörg a bit fewer than the one high up on Schlaepfer)

SPATIUM 18 11 croseconds on average. Its speed is ning of a whole new field of phys- laser seen in Figure 10 is a carbon nearly the speed of light. But now, ics. We will now look at some ex- ­dioxide laser operating at a wave- what happens with the distance? amples where his contributions are length of 10.6 micrometres. This is Einstein again explains this. As seen fundamental. in the invisible infrared – the red by the muon, the distance experi- ray is merely a small conventional enced between Jungfraujoch and laser to guide the operator. In the Bern contracts. As Einstein puts it: Photo Effect ➔The Laser picture you can see Dr. Berchtold space is relative also. Thus, neither von Fischer from the Lindenhof space nor time remain absolute, but Einstein’s explanation of the pho- hospital in Bern operating on an rather they are relative to their state toelectric effect prompted scien- apple. He normally operates on of motion. What remains absolute tists over the next two decades to breast cancer and has co-developed is the speed of light. develop quantum theory, and en- a new scheme that allows sparing gineers endeavoured to manipulate as many lymph nodes as possible, these tiny components of light. thus reducing post-operation com- The laser is just one device which plications considerably. This is only Einstein and Us exploits the notion of light quanta. one of countless applications today Incidentally, Einstein himself laid that can trace their source back to Today the groundwork for the laser Einstein’s photon hypothesis. through his later discovery of stim- ulated emission in 1918. The term laser is an abbreviation of Light Am­ Brownian Motion ➔ As stated above, Albert Einstein’s in- plification by Stimulated Emission of Nanotechnology terpretations were highly contro- Radiation. This type of light – versial at his time. So it is no won- which does not exist in nature – Brownian Motion gave Einstein the der that it took many years to fully has a wealth of applications today, hint that matter is indeed composed grasp their content. Eventually such as for example, transmitting of atoms. An atom is extremely though, the strengths of his ideas billions of bits per second between small. Most of the things we use in became obvious and scientists and spacecraft, or as scalpels that make our everyday life have sizes of me- engineers began to exploit their po- extremely sharp cuts with much tres, like our bodies, or a fraction of tential in favour of our everyday less bleeding than conventional millimetre like our hair. For the world. Each one of the three papers scalpels. They can also be used to much smaller world at Brownian discussed here marked the begin- burn and evaporate tumours. The Motion, microscopes allow us to ac-

Figure 10: Einstein in the operating theatre. The coherent light of lasers finds an overwhelming variety of applications today. This sequence shows a surgeon demonstrating a carbon dioxide laser writing Einstein’s famous formula on the skin of an apple.

SPATIUM 18 12 tually see how cells evolve and how scope (STM) which won the No- is moved very close to a material. viruses attack; but the most amaz- bel Prize for Gerd Binnig8 and Then, some electrons can jump (or ing microscope ever developed is Heinrich Rohrer9 in 1986. A very “tunnel”) from the material to this the Scanning Tunnelling Micro- small tip, made only of a few atoms, tip and are detected as a current, see Figure 11. The closer the tip, the more electrons can jump the gap. Atoms are like bumps in materials and the tip, moved very accurately, allows one to measure a landscape this ­extremely small. Let’s just quickly get a sense of the dimensions we are dealing with here: Washington, D.C. is roughly 4,500 km away from Los Angeles. Stretching a platinum wedding ring from coast to coast, from Los Angeles to Washington, would lead to a distance between two neighbouring atoms of just one centimetre. On this scale the thick- ness of a hair would be roughly 3,000 metres.

These nanoworlds have the most amazing structures. Figure 12 to the left shows a nanostructure that has Figure 11: The principle of the Scanning Tunnelling Microscope. A very small been getting a lot of press recently: tip only a few atoms wide is moved closely over the surface of a sample. With decreas- a carbon nanotube. These tubes ing distance of the tip from the surface an increasing number of electrons become able to jump to the tip and be detected in the form of an electric current. This allows gen- have a thickness of only 10 atoms erating an image of the sample’s surface. or so, but are unbelievably strong, about a hundred times stronger than steel at only a sixth of the weight. We are currently learning to grow these structures and to use them. The trick is to grow such tubes en masse, leading to materials that have almost miraculous properties. There are already prototypes of a new dis- play type allowing for monitors that are a lot sharper than what we use today. Also, nanotubes will certainly have countless applications for air Figure 12: Glimpses into the nanoworld. On the left side, a carbon nanotube is depicted. Its thickness is a mere 10 atoms. The image to the right shows the structure and space travel. of a carpet made up of such nanotubes.

8 Gerd Binnig, 1947 Frankfurt am Main, German physicist, Nobel Prize 1986. 9 Heinrich Rohrer, 1933 Buchs, Switzerland, Swiss physicist, Nobel Prize 1986.

SPATIUM 18 13 Special Relativity ➔ ories in many different ways. We use make the system useless, if it weren’t Cosmology them in building rockets and in get- adjusted for Einstein’s equations. So, ting spacecraft into orbit. when you next take a taxi in the Finally, let’s look at the consequences city of Bern, remember that the taxi of the paper on special relativity, One of the most popular applica- driver, guided by a GPS receiver, written in June 1905, with its three- tions using Einstein’s theory of tacitly applies the laws found here page addendum of September 1905. ­relativity is the Global Positioning by Albert Einstein a century ago. In this short text, Einstein came to System, GPS for short. It consists his famous equation E=mc2 .This of a constellation of 24 spacecraft Relativity perhaps has the most im- notion states that energy and mass orbiting the Earth at a distance of portant consequences for our un- are equivalent and thus may be ex- 20,183 kilometres. There, the Earth’s derstanding of the universe and the changeable. Simple as it sounds it gravity is slightly weaker than here diverse objects we find in it. One changed our view of the world. To- on the surface. According to the consequence was observed first in gether with his paper on general rel- theory of general relativity, this 1919 by Sir Arthur Eddington10 on ativity, which included gravity, Ein- causes the clocks aboard the satel- his famous scientific expedition (see stein described all the processes lites to tick a bit slower than ours. also Spatium 14). The Sun seems to around us, how the Sun creates its While the difference is minute, it deflect light, like a giant lens, mov- energy, how planets orbit the way would cause the GPS to provide ing the apparent location of stars they do. When we explore these position information with an error ever so slightly. Light from a distant worlds, we take advantage of his the- of some 100 metres, which would star may be distorted just like a lens distorts it. Einstein’s theory of gen- eral relativity predicts this, and the theory of relativity triumphs. The reason light gets deflected is because gravity curves space itself. Light looks for the fastest path, which is not necessarily straight.

Einstein’s theories have their most important consequences when ap- plied to the history, the current state, and the future of the universe. Those belong to the most important ques- tions humans have struggled with over the last millennia: What hap- pened to the universe before the so- lar system was formed? This ques- tion has an amazing and unexpected Figure 13: Mysterious cosmos. Baryonic matter (including neutrinos, etc.) forms answer, which actually was derived the stars and the galaxies. It is this type of matter which we experience in our daily life. from Einstein’s equations: The uni- But this is only a small fraction of what constitutes the universe. The vast majority, namely dark matter and dark energy, is a theoretical assumption required to explain as- verse, we observe, started roughly tronomical observations. 14 billion years ago and is now ex-

10 Sir Arthur Stanley Eddington, 1882 Kendal, UK – 1944 Cambridge, British astrophysicist. 11 Abbé Georges Henri Lemaître, 1894 Charleroi, Belgium – 1966 Löwen, Belgium, Belgian priest and physicist. 12 Alexander Alexandrovich Friedman, 1888 St. Petersburg – 1925 Leningrad, Russian cosmologist and mathematician.

SPATIUM 18 14 panding at a rapid speed. In 1927, a der to solve his equations in the way Conclusions Belgiam catholic, Montsignor Le he considered reasonable, and only Maitre11, concluded that such an ex- a static, eternal universe appeared panding universe was a solution that reasonable back then, he had to put came directly out of Einstein’s equa- in an additional term called the cos- tions. A Russian physicist, Alexander mological constant. When he real- Does this sound familiar? We are in Friedman12, had come to the same ized that the universe is indeed ex- a situation again where somebody, conclusion even before, but he died panding, he dropped the term and like Henri Poincaré, could write a of typhus fever during WWI, before called it his “biggest blunder” (grösste paper summarizing the most impor- his solution was widely known. This Eselei), because it made him fail to tant problems we do not currently expansion was first observed by Ed- predict that the universe cannot be understand, and a successor to Albert win Hubble13, an astronomer work- static and eternal. And yet this very Einstein should come and solve ing at the Californian Institute for term is now used by cosmologists these open issues. Certainly, for most Technology, in 1929. Hubble found when describing the accelerating physicists, dark matter and dark en- that every galaxy seemed to move expansion of the universe. ergy are such problems: What is the away from us, at a speed that in- nature of our universe, and what is creased with increasing distance – This adds to the puzzle we have to- it made of? Or, more specifically, similar to a huge explosion. But not day, summarized in Figure 13. In fact, what is the nature of dark matter and an ordinary one at that: It’s not that we have an almost embarrassing sit- of dark energy? galaxies explode into a previously uation right now: We know that the Our story started in Bern. This city, existing empty space, but space itself universe is made of multiple con- with its beauty, and its charm, af- is created in the “explosion”, and it stituents. We observe stars and gal- fected the world in one of the most looks to everyone anywhere in the axies made of atoms. This constitu- profound ways thanks to one of its universe, not just us, that we are at ent is called baryonic matter, the most important inhabitants ever: Al- its centre. The Hubble Space Tele- ordinary matter we know from our bert Einstein. On 31 December scope has continued these observa- daily life. But there is another class 1999 Time magazine selected him as tions and has managed to even go of matter, called dark matter, as it the Person of the Century – a lonely beyond that. Looking at the largest does not directly interact with pho- patent clerk who was asking impor- distances and comparing to obser- tons, therefore we cannot see it, but tant questions and did not back off vations at the smaller distances, the we can measure its gravitational when people did not agree with Hubble telescope provided one of force on ordinary matter. Both or- him. For those of us who have been the most exciting and puzzling re- dinary matter and dark matter to- affected by Einstein throughout our sults of the last few years: In contrast gether are still only a minor part of professional and personal lives, the to what we would expect, the ex- the universe. The major part is made Bern year of 1905 will always remain pansion of the universe appears to up of the mysterious dark energy a miracle. be accelerating: the explosion is still that drives the expansion. Neither But the most important effect Ein- powered today by a mysterious force. dark matter nor dark energy, how- stein’s work has on our world is that Cosmologists found an appropriate ever, is fully understood today. it became more beautiful. Einstein name for it: dark energy. It turns out pointed out the underlying texture that Einstein had even put this effect of nature that people did not see into his equations – even though he ­before he came along. Science can personally never believed in the ac- do that, and will do that again in the tual existence of dark energy. In or- future.

13 Edwin Powell Hubble, 1889 Marshfield, Missouri – 1953 San Marino, California, U. S. American astronomer.

SPATIUM 18 15 SPATIUM

The Project and its Authors

In late 2004, when preparations for Swiss Embassies in Washington, Francisco, the Adler Planetarium in the centennial of Einstein’s annus D.C., Seoul, Beijing, and Tokyo, the Chicago, the Historical Museum in mirabilis got intense, the two first Swiss Centers in Boston and San Bern and more. authors independently received in- vitations to give a talk about that singular event in the history of sci- ence. Even though neither of us is Rudolf von Steiger was born in a theoretical physicist or a historian Bern. He completed his Diploma of science we decided to team up (1984) and Ph.D. (1988) in Physics and jointly develop such a talk, to- also at the University of Bern. Af- gether with video specialist Brian ter a postdoctoral year at the Uni- Grimm with whom we had worked versity of Maryland he returned to before. Bern, where he joined the newly founded International Space Sci- Our principal qualification for giv- ence Institute (ISSI) in 1995. Today ing such a talk is that we had both he works as a director of ISSI with studied in Bern, the city, where Ein- a guest professorship at the Univer- stein lived 100 years ago. So we de- sity of Bern. cided to begin our presentation with some impressions of this beau- Thomas H. Zurbuchen was born in tiful town. The second message is Heiligenschwendi. He completed that Einstein did not only develop his Diploma (1992) and Ph.D. relativity, but also gave theoretical (1996) in Physics at the University explanations of Brownian Motion of Bern. Then he moved to the Uni- and of the photoelectric effect, each versity of Michigan in Ann Arbor, of which can rightly be considered where he works today as an Asso- as of equally fundamental impor- ciate Professor for Space Science tance. In the third part of the talk and for Aerospace Engineering. we advance time by 100 years to see what came to be of these three sem- Brian Grimm is a video artist and inal topics by giving examples of the owner of Paper Cardinal De- the numerous applications today. sign based in Oakland, California. He specializes in technical and The talk has been given by both of ­scientific animations for facilitating us numerous times in 2005 and efficient and effective communi­ 2006 in the USA, in Asia and Eu- cation. Together with his partner rope. It is a pleasure to thank here Tanja Andrews he is also the author our supporters and hosts: the Swiss of the award-winning video blog Department of the Exterior, the on www.freshtopia.net.