In a parallel universe, another you

This essay is part of a series called The Big Ideas, in which the writers answer a single question: What is reality? You can read more by visiting The Big Ideas series page.

When I was 8 years old, a revelation changed my life forever.

The year was 1955, and newspaper headlines announced the death of a renowned scientist. A photo accompanied an article, showing his desk littered with papers and books. As I recall, the photo caption said that among the piles of material was an unfinished manuscript.

I was fascinated by this discovery. What could be so challenging that this man, often hailed as one of the greatest scientists of all time, could not complete this work? I had to find out and over the years I visited libraries to learn more about him.

His name was Albert Einstein. His unfinished work explored what would become known as the theory of everything, an equation, perhaps no more than an inch long, that would allow us to unify all the laws of physics. This would give us, as Einstein hoped, a glimpse into the mind of God. “I want to know what he thinks,” he famously said. He was trapped.

Today, many of the world’s leading physicists are embarking on this cosmic quest, whose far-reaching reverberations encompass our understanding of reality and the meaning of existence. It would be the culmination of thousands of years of scientific investigation, as ancient civilizations also wondered how the universe was created and what it is made of. The ultimate goal of the theory of everything is to combine Einstein’s theory of relativity with the bizarre world of quantum theory.

In essence, relativity theory investigates the most massive phenomena in the cosmos: things like black holes and the birth of the universe. The realm of relativity is nothing less than the entire cosmos. Quantum theory, on the other hand, explores the behavior of matter at the tiniest level. His domain encompasses the smallest particles in nature, those hidden deep within the atom.

Unifying these two spheres of thought into a single, coherent theory is an ambitious undertaking that builds on and builds on the work that Einstein started. But to do that, scientists must first determine a crucial truth: where the universe came from.

This is where our two spheres of thought clearly diverge.

If we agree with Einstein’s theory of relativity, the universe is a kind of bubble that is expanding. We live in the skin of this bubble, and it exploded 13.8 billion years ago, giving us the Big Bang. This gave rise to the singular cosmos as we know it.

Quantum theory is based on a radically different picture – one of multiplicity. Subatomic particles, you see, can exist simultaneously in several states. Take the electron, a subatomic particle that carries a negative charge. Wonderful devices in our lives, like transistors, computers, and lasers, are all possible because the electron, in a sense, can be in many places at once. Their behavior challenges our conventional understanding of reality.

Here’s the key: in the same way that quantum theory forces us to introduce multiple electrons simultaneously, applying this theory to the entire universe forces us to introduce multiple universes – a multiverse of universes. By this logic, the lone bubble introduced by Einstein now becomes a bubble bath of parallel universes, constantly splitting in two or bumping into other bubbles. In this scenario, a Big Bang could happen perpetually in distant regions, representing the collision or merging of these bubble universes.

In physics, the concept of the multiverse is a key element of a leading area of ​​study based on the theory of everything. It’s called string theory, which is the focus of my research. In this photo, the subatomic particles are just different notes on a tiny, vibrating string, which explains why we have so many of them. Each string vibration, or resonance, corresponds to a distinct particle. String harmonies correspond to the laws of physics. The string melodies explain the chemistry.

By this thought, the universe is a symphony of strings. String theory, in turn, postulates an infinite number of parallel universes, of which our universe is just one.

A conversation I once had with theoretical physicist and Nobel laureate Steven Weinberg illustrates this. Imagine yourself sitting in his living room, he told me, listening to the radio. In the room are the waves of hundreds of different radio stations, but your radio is tuned to only one frequency. You can only listen to the station that is consistent with your radio; in other words, it vibrates in unison with its transistors.

Now imagine that your living room is filled with waves of all the electrons and atoms vibrating in that space. These waves can hint at alternate realities – with, say, dinosaurs or aliens – right there in your living room. But it’s difficult to interact with them, because you don’t vibrate coherently with them. We let go of these alternate realities.

There is an exercise that my colleagues and I sometimes present to our Ph.D. theoretical physics students. We asked them to solve a problem calculating the probability of someone waking up on Mars tomorrow. Quantum theory is based on what is known as the Heisenberg uncertainty principle, allowing for a small probability that we could exist even in distant places like Mars. So there is a small but calculable probability that our quantum wave will tunnel through spacetime and end up there.

But when you do the math, you find that for that to happen you would have to wait longer than the lifetime of the universe. That is, most likely you will wake up in your bed tomorrow, not on Mars. To paraphrase the great British geneticist JBS Haldane, reality is not only stranger than we suppose, but stranger than we imagine. I can suppose.

It’s been more than six decades since Einstein’s death, but I keep going back to that picture of his desk I saw at age 8, the work he left unfinished, and its profound implications. In the quest to merge two opposing perspectives on the universe, we are left with a number of deeply disturbing questions. Can we also exist in multiple states? What would we be doing if we had chosen a different career? Married someone else? What if we could somehow change important episodes from our past? As Einstein once wrote, “The distinction between past, present and future is just a stubbornly persistent illusion.”

Maybe there are copies of us living completely different lives. If this theory of everything is correct, then perhaps there is a parallel universe where we are billionaires planning our next adventure, or where we subsist like bums desperately looking for our next meal. Who knows? A simple quantum fork in the road could have made all the difference.

Michio Kaku is a professor of physics at the City University of New York and author of “The God Equation”.

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