Scientific American The book, Trespassing on Einstein’s Lawn, is the story of my 17-year journey with my father to figure out the nature of ultimate reality and what we discovered, quite frankly, is not what any marketing team wants to hear. Quantum mechanics, relativity, black hole physics, cosmology and string theory all point to the same radical, paradigm-shifting conclusion: every observer’s reference frame defines its own universe, singular and complete, and even though any reference frame is as good as any other, we can only speak about one at a time. [...]
My belief in this cosmic solipsism is a sad lesson in irony, really, because this whole thing – my career, my universe, my book—began with a conversation. I was fifteen years old, having dinner in a Chinese restaurant, when my father leaned over and asked, “How would you define nothing?” He told me that he was trying to understand how you can get something from nothing, how a universe could be born. [...]
Our first major breakthrough came when we realized that physics can pin down what’s real and what isn’t. It’s one of those things that’s somehow stupidly obvious and yet deeply profound: something is real if it’s invariant. That is, something is real if it remains unchanged from one reference frame to the next. Just look at a rainbow. You’ll see one in the sky if you’re in just the right reference frame with the Sun shining in from behind you, and droplets of water in the atmosphere refracting the light. It’s pretty, but good luck trying to grab it. A rainbow is not a physical object stapled to the sky. It’s a product of your reference frame. Which is to say, it’s not real.
Ok, so what is real? Space? Time? Particles? Forces? Well Einstein showed that space and time aren’t real– they change from one reference frame to another. However, something remains invariant in the process: a unified, four-dimensional spacetime. “Space by itself and time by itself are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality,” the mathematician Hermann Minkowski declared.
And the thing my father and I learned is that ever since Einstein, theoretical physics has been one long death march for invariants. With his infamous discovery that black holes radiate, Stephen Hawking declared particles observer-dependent (along with fields and the quantum vacuum to boot). String theory did away with the invariance of dimensions and M-theory did away with the invariance of strings. By studying what happens when stuff falls into a black hole, Leonard Susskind discovered that the unified spacetime Einstein had left unscathed is itself observer-dependent. As for nature’s four fundamental forces, Einstein did away with gravity (“We are able to ‘produce’ a gravitational field merely by changing the system of coordinates,” he wrote) while the development of gauge theory took care of the other three. Every last one of the so-called fundamental ingredients of nature has turned out to be a shadow. Unreal.[...]
The death of the last remaining invariants is a new development in physics, but the specter of solipsism has been looming for decades, ever since the first generation of quantum physicists struggled to understand what the theory meant. “It is conceivable we must give up on any ‘one-world’ view of physics,” the legendary physicist John Archibald Wheeler scrawled in his journal as he wrestled with the mystery of the quantum. Quantum theory seems to go haywire when you assume that multiple observers occupy the same universe. I might open Schrodinger’s box to find a dead cat, but what if the cat, the box, and I are sitting inside an even bigger box, one that some other observer—my father, perhaps— hasn’t opened yet? To me, that cat is dead, but to my father it’s simultaneously dead and alive, and so am I. If there’s only one reality, which one is it? Quantum mechanics is just boxes within boxes – unless you stipulate that there’s only one box, in which case the whole issue of writing books becomes a little thorny.[...]
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