Albert Einstein

One of Albert Einstein’s most notable contributions to physics was his theory of relativity. The theory of relativity is composed of two sub-theories, one named general relativity and the other special relativity.

Einstein’s theory of relativity changed the way that time, motion and gravity were understood. It is based on two important ideas: the principle of relativity, which states that a body moving at a constant velocity acts according to the same laws as a body at rest, and the principle of the speed of light, which states that the speed of light is the same for all observers regardless of their relative motion to the light.³

But what do those two principles actually mean? They mean that we can only measure motion relative to a given frame of reference, instead of motion being an absolute, like Isaac Newton had believed.

The equation for speed is: speed = distance/time

This means that if speed changes according to one frame of reference, then distance and/or time must also change.

Einstein used a thought-experiment to flesh out his theory of relativity. He described a scenario where one person is moving at a constant speed on a train, and another is standing on the station platform watching the train. Two bolts of lighting strike either end of the train as the midpoint of the train is directly in front of the person on the platform. Since the laws of physics are the same for someone at a constant speed and someone at rest, both observers must agree on the speed of light.⁴

The lightning strikes at the front and back of the train are the same distance away from the person on the platform, meaning that each reaches his/her eye at the same time. That person would therefore say that the lightning strikes happened at the same time.⁴

However, because the train is moving, for the person on the train, the light from the strike at the end of the train reaches their eye a bit later. Since the distances that the light strikes travel are different, the time must be as well. For the person on the train, the lightning strikes happened one after the other. So, who is right?

According to Einstein, both are right. Einstein called this phenomenon special relativity, which showed that time is relative to each observer at a different reference point.

Since special relativity only described the ways that things in constant motion behaved, Einstein wanted to expand relativity to encompass acceleration and gravity. Einstein concluded that acceleration and gravity were different forms of the same thing, allowing him to come up with what is commonly thought of as the world’s most famous equation:

e= mc2  (energy= mass x speed of light2)

Einstein came to this conclusion with another thought-experiment. Imagine an object is sitting at rest and emits two pulses of light in opposite directions. Since each pulse carries energy, the object itself must lose some energy.⁴ Einstein then questioned how this scenario would look to a moving observer. The speed of the two beams of light has to look the same, since the speed of light is constant, meaning that the amount of energy each beam carried has to be different. Since e= mc2 , then if energy is different, mass must be a little different too.⁴

From this equation, Einstein concluded gravity had to be determined by more than mass and distance (as Isaac Newton had suggested); it also had to be affected by time. Einstein concluded that space and time were not separate, leading to the concept of spacetime.

Einstein believed his scientific revelations had significance for the way that people think about time in general:

“Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That’s relativity.”[5]

Albert Einstein was born in Ulm, Germany, on March 14th 1879.⁶ Despite being an icon in the scientific world today, Einstein’s genius was not apparent in all areas of his early education. He thrived in science, mathematics and music, but struggled in the languages and was actually a bit of a rebellious student.⁷ He even dropped out of high school before returning to education later at the Swiss Polytechnic Institute in Zurich (that doesn’t mean you should drop out! – see the survivorship bias to find out why).⁸

1905 was an important year for Einstein. He published four papers that came to be known as the annus mirabilis papers, meaning “miracle year” in Latin.⁸ These papers explained special relativity, the existence of atoms, and the photoelectric effect, and led to Einstein receiving his PhD from the University of Zurich.⁸

Einstein’s theory on the photoelectric effect was another of his great contributions to science. It was built on an idea put forward by German physicist Max Planck, who believed that light waves were not continuous and instead consisted of bundles of energy called photons.⁹ From Planck’s initial ideas, Einstein concluded that the frequency of a wave of light hitting a metal was what determined how many electrons were emitted from the metal, where previously, scientists had thought the amplitude of the light was what affected its ability to disrupt electrons in the metal.¹⁰ This theory earned Einstein the Nobel Prize in Physics in 1921.¹¹

Understanding the photoelectric effect was the beginning of what is known today as the quantum revolution, allowing us to better understand the behavior of matter and energy on an atomic and subatomic level.¹² The entire computer and smartphone industry is built based on the knowledge gained from quantum physics, as are GPS systems and MRI scanners. Einstein’s willingness to step outside the box has led to, and continues to lead to, scientific breakthroughs that have benefited us all.¹³

Einstein was willing to abandon popular existing theories when they were no longer helpful in solving new issues. Instead of trying to tweak the theories, he came up with new ones. He said, “We cannot solve our problems with the same thinking we used when we created them”.¹⁴

That is why Einstein relied on creative thought experiments to come up with scientific theories. He claimed that “invention is not the product of logical thought, even though the final product is tied to logical structure”.¹⁵ Even though he respected his peers, he knew that “unthinking respect for authority is the greatest enemy of truth”.¹⁵

Einstein was also a big proponent of peace. He renounced his German citizenship to avoid becoming part of the military,¹⁶ and believed in the equality of all people regardless of place:

“I am by heritage a Jew, by citizenship a Swiss, and by makeup a human being, without any special attachment to any state or national entity whatsoever.”[15]

For Albert Einstein, it did not matter who you were or where you came from:

“I speak to everyone in the same way, whether he is the garbage man or the president of the university.”[15]

“I would teach peace rather than war. I would inoculate love rather than hate.”[15]

Most of Einstein’s work has now been published online, making it easy to access. Most of his work is dense with scientific knowledge, however, he purposefully wrote Relativity: The special and the general theory for non-experts that still had an interest in science. If you prefer, you can also listen to the book as a podcast here.

If you were intrigued by the mention of Einstein’s miraculous year, then you should check out John Ridgen’s 2005 book, Einstein 1905: The Standard of Greatness. It is difficult to grasp the photoelectric effect in just a few sentences, and since it has had implications in many aspects of our daily lives, Ridgen’s user-friendly account of his accomplishments is a great place to take a deeper dive.¹⁷

If you’re more interested in who Albert Einstein was past his scientific mind, then The Born-Einstein Letters, 1916-1955 allows you to read the correspondence between Einstein and his fellow quantum physics friend, Max Born. The two spoke about science, but also about politics, the war and their musical preferences, revealing a more human side to Einstein’s genius.¹⁸

Another great resource is the first season of National Geographic’s Genius TV Series. The series begins in Einstein’s early years and follows him through his scientific journey, providing its audience with a robust historical context under which Einstein’s scientific creativity emerged.

1. Robson, C. (2013, March 1). Newtonian physics vs. special relativity. Futurism. https://futurism.com/newtonian-physics-vs-special-realtivity
2. Albert Einstein Quotes. (n.d.). Goodreads. Retrieved August 19, 2020, from https://www.goodreads.com/quotes/213547-out-yonder-there-is-this-huge-world-which-exists-independently
3. Jones, A., & Robbins, D. (2016, March 26). Einstein’s special relativity. dummies. Retrieved August 19, 2020, from https://www.dummies.com/education/science/physics/einsteins-special-relativity/
4. Waldrop, M. (2017, May 16). Einstein’s relativity explained in 4 simple steps. National Geographic. Retrieved August 19, 2020, from https://www.nationalgeographic.com/news/2017/05/einstein-relativity-thought-experiment-train-lightning-genius/#close
5. Albert Einstein Quotes. (n.d.). Goodreads. Retrieved August 19, 2020, from https://www.goodreads.com/quotes/370132-put-your-hand-on-a-hot-stove-for-a-minute
6. History.com Editors. (2009, October 27). Albert Einstein. HISTORY. https://www.history.com/topics/inventions/albert-einstein
7. Sack, H. (2018, June 30). The annus mirabilis in physics – Albert Einstein and the year 1905. SciHi Blog. https://scihi.org/annus-mirabilis-albert-einstein/
8. Fraser, J. (2017, December 28). How much did Albert Einstein study? Forbes. https://www.forbes.com/sites/quora/2017/12/28/how-much-did-albert-einstein-study/#4b71333728bc
9. Cassidy, D. (2004). Einstein on the photoelectric effect. Niels Bohr Library & Archives. https://history.aip.org/history/exhibits/einstein/essay-photoelectric.htm
10. Photoelectric effect. (n.d.). Khan Academy. Retrieved August 19, 2020, from https://www.khanacademy.org/science/physics/quantum-physics/photons/a/photoelectric-effect
11. The Nobel Prize. (n.d.). The Nobel prize in physics 1921. Retrieved August 19, 2020, from https://www.nobelprize.org/prizes/physics/1921/summary/
12. Tech Target. (2019, December). quantum theory. Retrieved August 19, 2020, from https://whatis.techtarget.com/definition/quantum-theory
13. Orzel, C. (2015, August 13). What has quantum mechanics ever done for us? Forbes. https://www.forbes.com/sites/chadorzel/2015/08/13/what-has-quantum-mechanics-ever-done-for-us/#41bc80114046
14. Stierwalt, S. (2015, August 17). Einstein’s legacy: The photoelectric effect. Quick and Dirty Tips. https://www.quickanddirtytips.com/education/science/einsteins-legacy-the-photoelectric-effect?page=1
15. Goalcast. (2019, November 27). Top 30 most inspiring Albert Einstein quotes. Retrieved August 19, 2020, from https://www.goalcast.com/2017/03/29/top-30-most-inspiring-albert-einstein-quotes/
16. Andrews, E. (2015, October 26). 9 things you may not know about Albert Einstein. HISTORY. https://www.history.com/news/9-things-you-may-not-know-about-albert-einstein
17. Martinez, A. (2006, March 1). Einstein 1905: The standard of greatness. Physics Today. https://physicstoday.scitation.org/doi/full/10.1063/1.2195321
18. Robinson, A. (2019, April 25). The best books on Albert Einstein. Five Books. https://fivebooks.com/best-books/albert-einstein-andrew-robinson/