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Historisches Museum Bern, Bern, Switzerland

46° 56′ 35″ N, 7° 26′ 57″ E

Albert Einstein’s Annus Mirabilis (Miracle Year)

In 1905, Albert Einstein was living in Bern, Switzerland. He was working at the patent office as a clerk examining patent applications. That same year he submitted his doctoral thesis and published four papers that changed physics forever. These Annus Mirabilis papers covered the photoelectric effect, Brownian motion, special relativity, and the relationship between matter and energy.

Einstein won the Nobel Prize in 1921 for his explanation of the photoelectric effect. It had been observed that when matter absorbs light, it emits electrons. Einstein explained that light was not absorbed continuously, but rather in discrete packets of energy (termed quanta). This insight was one of the underpinnings of the wave-particle duality of matter, and was later shown experimentally to be correct.

The paper on Brownian motion helped put an end to the idea that atoms were a mere theoretical device. The paper showed that it should be possible to observe the motion of atoms and molecules under a microscope. The French physicist Jean Perrin used this paper as the motivation to study Brownian motion and was able to determine experimentally that Einstein was correct, publishing his results in the book Les Atomes in 1913.

The paper discussing special relativity introduced the notion that the speed of light was fixed and independent of the motion of the light source; the paper also expanded on Newton’s laws of motion. While Newton was correct for speeds that he was able to observe, Einstein showed that different laws apply at speeds close to the speed of light.

Einstein’s final paper introduced the famous equation E = mc2 and showed the equivalence between mass and energy. The equation helped predict the energy possible in a nuclear explosion, and had the surprising side effect of showing that when a system gains energy, it gains mass and vice versa (for example, a compressed spring has greater mass than an uncompressed one).

Einstein’s incredible year is celebrated in Bern at the Historisches Museum Bern with a special, permanent exhibition called the Einstein Museum. It is also commemorated at the Einstein Haus.

The Historisches Museum Bern is a general history museum with exhibits of Swiss archeology, and the work of artists from the Bern area. The only scientific portion is the special Einstein exhibition within the main museum. It’s a large space dedicated to explaining Einstein’s life and work, from his childhood through his study at ETH Zurich, his work in Bern, the theories of special and general relativity, and his years at Princeton.

The entire exhibition is presented in English, and there’s an English-language audio guide. As well as displaying objects relating to Einstein’s life, the exhibition contains well-reasoned discussions of relativity, the Michelson-Morley Experiment (see sidebar), and the muon experiment (which examined muons created by cosmic radiation hitting the Earth’s atmosphere and verified that Einstein’s prediction of time dilation—the idea that time is not constant—was a reality). All in all, the exhibition is not to be missed.

Also in Bern is the Einstein Haus. During his Annus Mirabilis, Einstein was living in this apartment at Kramgasse No. 49 with his wife and son. The apartment has been restored to its 1905 state and has a small exhibition concerning Einstein’s scientific achievements.

Practical Information

The Historisches Museum Bern website is at http://www.bhm.ch/, and the Einstein Haus website is at http://www.einstein-bern.ch/. Both have English-language sections.

The Michelson-Morley Experiment

During the 19th century, physicists believed that light needed to travel through a medium; they believed that even a vacuum was actually filled with a mysterious substance they termed the luminiferous ether. They postulated that since sound waves need air to travel through, and waves travel on the surface of water, there must be an equivalent medium transporting light.

This ether was predicted to be present everywhere, but was completely undetectable. In 1887 two American scientists, Albert Michelson and Edward Morley, set out to detect the ether by exploiting the motion of the Earth through the imagined ether wind. The ether itself was assumed to be static, but as the Earth orbited the Sun, it would move through the ether at different angles, creating an apparent ether wind.

Michelson and Morley’s experiment used interference to try to detect a slight difference in speed between two beams of light that had traveled at right angles to each other for exactly the same distance. They thought that they would see a difference in speed between these two beams because the light had traveled at different angles to the ether wind. By rotating the experiment, they expected to maximize this effect, with one beam moving with the ether wind and the other “cross wind.”

For their experiment, Michelson and Morley placed a granite slab into a large bowl of mercury. The slab floated in the mercury, which damped vibrations while allowing the apparatus to be rotated in different directions across the ether wind. On the granite slab they placed a light source directed at a half-silvered mirror set at 45° (Figure 33-1).

Half the light passed straight through the mirror, hit another mirror, and was reflected straight back to the half-silvered mirror, where half of it bounced off into the eyepiece of a telescope. The other half of the light bounced off at 90° and hit another mirror, which bounced it straight back to the half-silvered mirror. From there, half the light passed through the mirror and into the telescope.

The two scientists expected to see an interference pattern, because although the two parts of the reflected light had traveled exactly the same distance, they thought that the speed of the light would be different and hence waves would be arriving slightly out of phase. Moreover, as they rotated the apparatus, they predicted that the interference pattern would change as the relative speeds changed.

Figure 33-1. The Michelson-Morley experiment

The entire apparatus was enclosed in a wooden box to prevent air currents and rapid changes in temperature from affecting the outcome. Michelson and Morley rotated the slab slowly and measured the fringes of interference seen, and they performed the experiment at different times of the day to try to understand the effect of the Earth’s rotation on the strength of the wind.

They found that the ether wind was much, much weaker than expected. It was so weak, in fact, that what they observed was likely due to inaccuracies inherent in their equipment. Since 1887, the experiment has been repeated multiple times with more and more accurate equipment pushing down the upper bound on the speed of the ether wind each time. Today, the ether wind is assumed to not exist at all.

Some call the Michelson-Morley experiment the most famous failed experiment of all time: it did fail to find what the scientists were looking for, but in true scientific fashion, they honestly reported their results and attempted to interpret them.

Little did they know that eight years later, in 1905, Einstein would predict that no matter what the circumstances, the speed of light would be fixed.