Gravity 0: Discovering Gravity

by Shane L. Larson

You and I live in the future. We are connected to each other in ways that would have stunned people who lived only a century ago. I had the good fortune growing up to know my great-grandmother, who lived to be 98 years old. My Grandma Dora was born in 1895, at a time before electricity and telephones and automobiles were commonplace. The mode of transportation when she was born was the horse and buggy, though steam had been harnessed and train lines were beginning to gird the world. The Wright Flyer would not make its first epic flight at Kitty Hawk until 1903, when Grandma Dora was 8 years old. But she lived to see humans sail the void of space, space shuttles ply the skies, and humans walk on the Moon. In just about 100 years, the span of a single human life, she saw the world change.

(L) My great-grandmother Dora [center] with her sisters Mary [left] and Arta [right] in the early 1900s. (R) Around this same time, the Wright Brothers made their historic flight at Kitty Hawk, in 1903.

When she was just a girl, there was a young man living halfway around the world, in Bern, Switzerland. The Industrial Revolution was in full swing, and creative minds the world over were trying to imagine how to use technology and machines to change our lives, and how to patent those ideas and make money. Some of those attempts to capitalize on the rapidly evolving world wound their way through the Bern Patent Office (the Swiss Federal Institute of Intellectual Property) to the desk of Albert Einstein. For the young Einstein, a trained technical professional, the job at the patent office was just that — a job. He very much wanted to be a professor and work on science, so in the evenings he committed himself to physics the way some of us work day jobs but in the evenings work on writing novels (or blog posts about science). In 1905, those evening endeavours paid off when Einstein published four seminal papers that transformed his life, physics, and the world forever.

(L) Einstein when he was working at the Patent Office in Bern. (R) Einstein’s living room, still preserved, in the first floor apartment where he worked on special relativity during his years at the Patent Office.

Among those papers was the original paper to describe special relativity — the laws that govern physics at high speeds, approaching the speed of light. Nestled in that paper is one of the most important discoveries in physics and the one most germane to our story here:

Nothing can travel faster than the speed of light.

This was a stunning realization, because up to that point no one had ever really imagined that we couldn’t go faster than light. The speed of light had been measured famously by Danish astronomer Ole Romer in 1676 and by French physicist Hippolyte Louis Fizeau in 1849. But there had never been a reason to believe that the speed of light was the ultimate speed limit in the Cosmos.

Folklore is that Newton witnessed the falling of an apple when visiting his mother’s farm, inspiring him to think about gravity. It almost certain is apocryphal that it hit him on the head, but this was the beginning of the Universal Law of Gravitation, one of the most successful descriptions of Nature ever invented.

With Einstein’s realization, we began to examine the laws of physics that had been discovered up to that point, and we found a curious fact. Some of those laws, unbeknownst to us, had the secret about light hiding in them, like a pearl in an oyster.  Most notable among these were Maxwell’s Equations for Electrodynamics. Curiously, Newtonian Gravity did not have the ultimate speed limit. The classical Universal Law of Gravitation, which Newton had penned more than 200 years earlier, was built on the idea of instantaneous communication over any distance, an impossibility if there was a maximum speed of travel. Einstein recognized this and set about to resolve the issue. He would dedicate the next 10 years of his life to the endeavour. During those years, he would finally leave his job at the patent office for the life of an academic, holding professor positions at several universities around Europe. All the while, he worked steadfastly on merging gravity and special relativity.

This was not a simple matter of “imagining something new.” Newtonian gravity worked perfectly well in the solar system, where things moved slowly and gravity was weak. Einstein knew that whatever Nature was doing with gravity, it had to look like Newtonian Universal Gravity at slow speeds and in weak gravity, but not be confined by instantaneous propagation of signals. He went through a meticulous procession of thought experiments, explored new applications of mathematics (the language of science) and developed new intuitive ways of thinking about gravity. His long hours and years of brain-bending culminated in 1915 with his presentation of the Field Equations of General Relativity, now known as the Einstein Field Equations.

In 1902, Georges Méliès (L) created the film “Le Voyage Dans La Lune” where an enormous cannon (C) was used to launch a space capsule carrying explorers to the Moon (R).

I think about this age of the world often, my thoughts fueled by memories of talking with my great-grandmother. What was the world like when the young Einstein was thinking about lightspeed and gravity?  It was an age of horse and buggy travel. What was the fastest people could imagine travelling in that era? In 1903 the great French director Georges Méliès told at tale of travelling to the Moon — “Le Voyage dans la Lune” — using a new technology called “moving pictures.” In that remarkable tale, he imagined a band of intrepid explorers attaining great speeds by being launched from an enormous cannon, still far slower than the speed of light.

The horse and buggy set the speed of life in those days. This is an ambulance for the Bellevue Hospital in New York in 1895, the year my grandmother was born.

The speed of life was slow in those days, far slower than the speed that Einstein was contemplating.  But still Einstein was able to apply his intellect to a question that perhaps seemed outrageous or unwarranted. At the time, the derivation of general relativity was mostly a curiosity, but today, a century later, it plays a central role in astrophysics, cosmology, and as it turns out, in your everyday lives!

Applications of general relativity, and the frontiers of general relativity in modern physics and astronomy. (TL) GPS system. (TR) Planetary orbits (LL) Black holes (LC) Wormholes (LR) Singularities.

In 2015 we are celebrating the Centennial of General Relativity. That means all your gravitational physicist friends will be all a-pitter-patter with excitement for the next 12 months, and impossible to quiet down about gravity at dinner parties.

On the off chance that you don’t have any gravitational physics friends (gasp!), for the next 13 weeks I’ll be exploring the landscape of general relativity right here at this blog. We’ll talk about how we think about gravity, the history of testing and understanding general relativity, modern observatories that are looking at the Universe with gravity instead of light, and some of the extreme predictions of general relativity — wormholes, black holes, and singularities.

My great-grandmother, Dora Larson.

My great grandmother passed away shortly after I went to graduate school, where I made gravity and general relativity my profession. In a time shorter than the span of her life, this little corner of physics had grown from the mind of a patent clerk into one of the most important aspects of modern astrophysics, at the frontiers of scientific research. Grandma Dora and I never got the chance to sit around and talk about black holes or the equivalence principle, but I often wonder what she would have thought of all the hoopla that gravity commands in modern life and modern science? What would she have seen, through eyes that saw the world grow up from horse drawn carts to space shuttles and GPS satellites?

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This post is part of an ongoing series written for the General Relativity Centennial, celebrating 100 years of gravity (1915-2015).  This is the introductory post of the series. For the first time, I’m trying short 3.5 min videos with each post to capture the essential bits of each one. Here is the YouTube Playlist with all the videos (let me know how you like them — it’s an experiment!).

Links to the successive blog posts in this series are below for reference:

Gravity 0: Discovering Gravity (28 Dec 2014)

Gravity 1: Seeing the Invisible (7 Jan 2014)

Gravity 2: The Road to General Relativity (15 Jan 2015)

Gravity 3: Curvature & the Landscape of the Cosmos (24 Jan 2015)

Gravity 4: Testing the New Gravity (7 Feb 2015)

Gravity 5: Putting Einstein in the Navigator’s Seat (12 Feb 2015)

Gravity 6: Black Holes (28 Feb 2015)

Gravity 7: Recipe for Destruction (Making Black Holes) (7 Mar 2015)

Gravity 8: Black Holes in the Cosmos (15 Mar 2015)

Gravity 9: The Evolving Universe (27 March 2015)

Gravity 10: Signatures of the Big Bang (8 April 2015)

Gravity 11: Ripples in Spacetime (24 April 2015)

Gravity 12: Listening for the Whispers of Gravity (14 May 2015)

Gravity 13: Frontiers (27 May 2015)