It’s All Relative

Shakespeare famously wrote,

All the world’s a stage,
And all the men and women merely players.

Little did he know that for the next 300 years, physicists would view the universe in a similar way. “[Classical] physics was like a play,” says theoretical physicist (and my good friend) Sean Carroll.

There was a stage, and there were actors. And the stage was space and time, and the actors were the particles and forces and fields that moved in that spacetime.

That was the best working metaphor for the universe in 1905 when Einstein published his Theory of Special Relativity, which, number one, posits that the rules of physics are the same for everyone, no matter where in the universe you are. Secondly, SR says that the rubber hits the road at the speed of light (c in E=mc²)–roughly 300,000 kilometers per second. Nothing, and I mean nothing, goes faster than that.

Because of c, we observers experience the universe relative to that speed, and–get this–when we’re in motion, time moves more slowly. Whaaaaa? This paradox of spacetime happens “because rulers and clocks—the things that mark time and space—are not the same for different observers. If the speed of light is to be held constant as Einstein said, then time and space cannot be absolute; they must be subjective.” Mind equals blown.

We might not feel the effects of relativity when we’re running down the block or rambling across Italy on Eurorail, but they’re there. No, relativity isn’t responsible for the jet lag you suffer upon returning home from Europe, but let’s say you decide to seek out new life and new civilizations aboard the Starship Enterprise. If the ship is moving fast enough–any speed approaching the speed of light–you might well return to your home planet to find your twin sibling has aged… considerably.

Albie put it in more understandable (although not exactly scientifically accurate) terms:

When you are courting a nice girl, an hour seems like a second. When you sit on a red-hot cinder, a second seems like an hour. That’s relativity.

Gravity, however, didn’t fit into the math of SR, so Einstein sought to marry Newton’s view of gravity to his new view of light. What he thought would take him a few months to work out ended up taking a decade, but in November 1915, Einstein finally delivered four lectures at the Prussian Academy of Science culminating in “not just a new theory of physics but a new kind of theory,” notes Carroll.

Einstein says in General Relativity the stage is an actor. The stage moves around. The stage has lines–it has motivation.

Einstein’s Theory of General Relativity describes the universe as dynamic and changeable–a universe where space, time, mass, and gravity are all interrelated. In GR, spacetime bends under greater gravitational pull, so not only does time move more slowly when you’re going really fast, it also moves more slowly the closer you are to a gravitational field. In other words, light bends when it gets near big objects, and that was an entirely new idea. “It goes back to E=mc²,” says Carroll. “All forms of energy cause gravity. And everything has energy.”

Thanks to Einstein, we know spacetime “has a life of its own. It’s not a static thing, and this changes… what spacetime is to us… That’s what makes him Einstein. That’s what gets him on the cover of Time Magazine for the Person of the Century.”

“Okay,” you’re thinking. “I’m half way through a very long blog post, Gia. What does this ‘General-Relativity-Stage-Is-An-Actor’ thing have to do with me?”

Everything, my friend. Tomorrow, when you’re dashing off to celebrate Thanksgiving with family and friends, you can be grateful to Einstein for giving you the underlying math that makes GPS technology possible. GR also paved the way for our understanding of the stuff in the universe we can’t see–black holes, dark matter, and dark energy. Einstein’s work was central to Georges Lemaître’s Big Bang Theory–the idea that the universe had a beginning and was not, as previously thought, infinite. Lemaître worked with Arthur Eddington whose 1919 expedition to West Africa provided photographic evidence that, as Einstein predicted, the mass and energy of the sun bends the starlight around it–proof that General Relativity is right. (Wanna fun physics movie to watch after overdosing on holiday treats? Put on Einstein and Eddington for a bit of history that will have you tearing up in no time.)

Einstein is the collective light bulb above all our heads–a symbol of creativity and perseverance. His achievements are not only being celebrated today on the centenary of General Relativity, but they’re also being lauded all year long as 2015 has been designated the International Year of Light.

During this month of gratitude, I think it’s important to remember how often we in the first world take light for granted. We flip a switch and the room is aglow; we swipe right and the screen illuminates. Elsewhere in the world, over 1.5 billion people lack access to electricity grids. Thanks to the blue LED (the invention of which was awarded the 2014 Nobel Prize in Physics), we now have a bright, incredibly energy efficient light source, and through “cheap local solar power,” the LED has the potential to increase the quality of life for impoverished people around the globe. That’s the power of physics. That’s the power of creativity. That’s the power of perseverance.

I, for one, have so many things to be grateful for as a player on this great stage. It’s far too easy to dwell on the recent tragedy in Paris than to look around and see all the beauty in the universe. Part physicist, part philosopher, Einstein wrote:

He who, against his better judgment, says ‘yes sir, no sir, three bags full sir’ to the aberrations of the crazy crowd, does not deserve that the sun is shining on him.

Once again, Albie, you’re right.

Courtesy of the American Institute of Physics
Courtesy of the American Institute of Physics

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