A couple of years ago physics professor Chad Orzel (and his dog Emmy) endeavored to explain physics to humans with How to Teach Physics to Your Dog. That book went on to become a worldwide success, with translations into ten languages to date. How do you follow up? By diving deeper into an especially strange and wonderful aspect to physics — the part we get from Einstein. And thus How to Teach Relativity to Your Dog, the latest scientific adventure from Chad and Emmy, and also, the universe. Here’s Chad to talk to you about his position on it all.
In a way, a book about Einstein’s theory of relativity is uniquely suited to a series about Big Ideas. Relativity, at its heart, is a theory built on a single Big Idea:
The laws of physics do not depend on how you’re moving.
For all its fearsome reputation, everything stems from that single, simple idea. Whether you’re moving or standing still, floating in space or on the surface of a planet, you will see the laws of physics work in exactly the same way.
All that stuff about the speed of light being the same for everyone? The speed of light is a consequence of the physics of electromagnetism, expressed in Maxwell’s equations. Since the laws of physics do not depend on how you’re moving, you will always see light move at exactly the same speed.
All that stuff about moving clocks running slow, moving objects shrinking, and twins who are different ages? Because physics is the same for all observers, and the speed of light is a constant, moving observers must disagree about how much time passes between two events, and even about the order in which they occurred.
All that stuff about gravity warping space and bending light? It’s a consequence of what Einstein called “the happiest thought of my life,”the realization that there’s no difference between falling due to gravity and floating in space. Once you recognize that, the bending of light and the warping of space follow.
Einstein’s great achievement wasn’t that he invented all these weird phenomena– other scientists like Hendrik Antoon Lorentz, George FitzGerald, and Henri Poincaré; came up with most of those well before Einstein. Einstein’s great contribution was showing that all the weird stuff is inevitable once you accept the central principle that the laws of physics do not depend on how you’re moving.Einstein succeeded where others had failed because he provided clear,compelling, and logical explanations for the strange results that others had balked at.
If relativity is so inevitable, though, why does it seem so weird? And what does a dog have to do with any of this?
Relativity seems weird because its biggest effects occur in situations that are very far removed from our everyday experience: objects moving very close to the speed of light, or exotic objects like black holes whose mass is great enough to significantly warp space and time.Relativity’s predictions have been confirmed to an amazing degree of precision in experiments ranging from subatomic particles to the entire universe. But those experiments require sensitive scientific equipment– particle accelerators, telescopes, and ultra-precise atomic clocks– that isn’t the sort of thing you have lying around in the garage.
That’s because relativity produces big effects only in circumstances that are very far removed from our everyday experience. When we approach the theory, we bring with us a lot of experience witheveryday situations, where relativity makes almost no difference, and relativity confounds the expectations we have based on that experience.
Which is where the dog comes in. Dogs, unlike humans, come to physics with very few preconceptions about how the world ought to work. To adog, the world is an endless source of surprise and wonder. The slowing of a moving clock is no more perplexing to a dog than the operation of a doorknob, which puts them in a good place to begin to understand the theory.
And we’ve got a terrific dog to help with this process: our German shepherd mix, Emmy, back for more after How to Teach Physics to Your Dog (previous Big Idea). Each chapter of the book opens with a dialogue between me and Emmy, in which she latches on to some aspect of relativity as relevant to her interests, and I gently explain how it really works. That’s followed by a more detailed explanation for interested humans, interrupted occasionally by questions from Emmy, who helps clear up points that people reading the book might find confusing. And, of course, since relativity involves multiple moving observers, there are cameos from a bunch of other dogs owned by friends and family, and even from my sister’s dastardly cat, Nero.
So, while the central idea of Einstein’s theory is that physics doesn’t depend on how you’re moving, the central idea behind How to Teach Relativity to Your Dog is that the best way to understand Einstein’s theory is to think like a dog. If you can put aside human preconceptions about what ought to happen, and work through the consequences of the principle of relativity, you can better appreciate the power and beauty of the theory.