Posts Tagged ‘existence’

By Corey S. Powell

Ever wonder what would have happened if you’d taken up the “Hey, let’s get coffee” offer from that cool classmate you once had? If you believe some of today’s top physicists, such questions are more than idle what-ifs. Maybe a version of you in another world did go on that date, and is now celebrating your 10th wedding anniversary.

The idea that there are multiple versions of you, existing across worlds too numerous to count, is a long way from our intuitive experience. It sure looks and feels like each of us is just one person living just one life, waking up every day in the same, one-and-only world.

But according to an increasingly popular analysis of quantum mechanics known as the “many worlds interpretation,” every fundamental event that has multiple possible outcomes — whether it’s a particle of light hitting Mars or a molecule in the flame bouncing off your teapot — splits the world into alternate realities.

Multiple splits, multiple worlds

Even to seasoned scientists, it’s odd to think that the universe splits apart depending on whether a molecule bounces this way or that way. It’s odder still to realize that a similar splitting could occur for every interaction taking place in the quantum world.

Things get downright bizarre when you realize that all those subatomic splits would also apply to bigger things, including ourselves. Maybe there’s a world in which a version of you split off and bought a winning lottery ticket. Or maybe in another, you tripped at the top of a cliff and fell to your death — oops.

“It’s absolutely possible that there are multiple worlds where you made different decisions. We’re just obeying the laws of physics,” says Sean Carroll, a theoretical physicist at the California Institute of Technology and the author of a new book on many worlds titled “Something Deeply Hidden.” Just how many versions of you might there be? “We don’t know whether the number of worlds is finite or infinite, but it’s certainly a very large number,” Carroll says. “There’s no way it’s, like, five.”

Carroll is aware that the many worlds interpretation sounds like something plucked from a science fiction movie. (It doesn’t help that he was an adviser on “Avengers: Endgame.”) And like a Hollywood blockbuster, the many worlds interpretation attracts both passionate fans and scathing critics.

Renowned theorist Roger Penrose of Oxford University dismisses the idea as “reductio ad absurdum”: physics reduced to absurdity. On the other hand, Penrose’s former collaborator, the late Stephen Hawking, described the many worlds interpretation as “self-evidently true.”

Carroll himself is comfortable with the idea that he’s but one of many Sean Carrolls running around in alternate versions of reality. “The concept of a single person extending from birth to death was always just a useful approximation,” he writes in his new book, and to him the many worlds interpretation merely extends that idea: “The world duplicates, and everything within the world goes along with it.”

How did we get here?

The mind-bending saga of the many worlds interpretation began in 1926, when Austrian physicist Erwin Schrödinger mathematically demonstrated that the subatomic world is fundamentally blurry.

In the familiar, human-scale reality, an object exists in one well-defined place: Place your phone on your bedside table, and that’s the only spot it can be, whether or not you’re looking for it. But in the quantum realm, objects exist in a smudge of probability, snapping into focus only when observed.

“Before you look at an object, whether it’s an electron, or an atom or whatever, it’s not in any definite location,” Carroll says. “It might be more likely that you observe it in one place or another, but it’s not actually located at any particular place.”

Nearly a century of experimentation has confirmed that, strange as it seems, this phenomenon is a core aspect of the physical world. Even Einstein struggled with the notion: What happened to all of the other possible locations where the object could have been, and all the other different outcomes that could have ensued? Why should an object’s behavior depend on whether or not somebody was looking at it?

In 1957, a Princeton student named Hugh Everett III came up with a radical explanation. He proposed that all possible outcomes really do occur — but that only a single version plays out in the world we inhabit. All the other possibilities split off from us, each giving rise to its own separate world. Nothing ever goes to waste, in this view, since everything that can happen does happen in some world.

For decades, Everett’s colleagues mostly brushed aside his explanation, treating it more like a ghost story than serious science. But nobody has found any flaws in Schrödinger’s equation; nor can they explain away its implications. As a result, many contemporary physicists — including David Deutsch at Oxford University and Max Tegmark at the Massachusetts Institute of Technology — have come to agree with Carroll that the many worlds interpretation is the only coherent way to understand quantum mechanics.

A field guide to many worlds

The many worlds interpretation raises all kinds of puzzling questions about the multiple versions of reality, and about the multiple versions of you that exist in them. Carroll has some answers.

If new universes are constantly popping into existence, isn’t something being created from nothing, violating one of the most basic principles of physics? Not so, according to Carroll: “It only looks like you are creating extra copies of the universe. It’s better to think of it as taking a big thick universe and slicing it.”

Why do we experience one particular reality but none of the others? “What other one would you find yourself in?” Carroll says, amused. “It’s like asking why you live now instead of some other time. Everyone in every world thinks that they’re in that world.”

Carroll also has a disappointing response for one of the most compelling questions of all: Could you cross over and visit one of the other realities and compare notes with an alternate-world version of yourself? “Once the other worlds come into existence, they go their own way,” Carroll says. “They don’t interact, they don’t influence each other in any form. Crossing over is like traveling faster than the speed of light. It’s not something that you can do.”

War of the many worlds

One criticism of the many worlds interpretation is that while it offers a colorful way to think about the world, it doesn’t deliver any new insights into how nature works. “It is completely content-less,” says physicist Christopher Fuchs of the University of Massachusetts, Boston.

Fuchs favors an alternative called Quantum Bayesianism, which offers a path back to an old-fashioned single reality. He argues that the universe changes when you look at it not because you are creating new worlds but simply because observation requires interacting with your surroundings. No coffee dates, no other lives for you. “In this way, measurement is demoted from being something mystical to being about things as mundane as walking across a busy street: It’s an action I can take that clearly has consequences for me,” he says.

Coming at the critique from a different angle, Oxford’s Roger Penrose argues that the whole idea of many worlds is flawed, because it’s based on an overly simplistic version of quantum mechanics that doesn’t account for gravity. “The rules must change when gravity is involved,” he says.

In a more complete quantum theory, Penrose argues, gravity helps anchor reality and blurry events will have only one allowable outcome. He points to a potentially decisive experiment now being carried out at the University of California, Santa Barbara, and Leiden University in the Netherlands that’s designed to directly observe how an object transforms from many possible locations to a single, fixed reality.

Carroll is unmoved by these alternative explanations, which he considers overly complicated and unsupported by data. The notion of multiple yous can be unnerving, he concedes. But to him the underlying concept of many worlds is “crisp, clear, beautiful, simple and pure.”

If he’s right, he’s not the only Sean Carroll who feels that way.

https://www.nbcnews.com/mach/science/weirdest-idea-quantum-physics-catching-there-may-be-endless-worlds-ncna1068706

schrodinger-cat-two-boxes

By Tia Ghose

Bizarrely behaving light particles show that the famous Schrödinger’s cat thought experiment, meant to reveal the strange nature of subatomic particles, can get even weirder than physicists thought.

Not only can the quantum cat be alive and dead at the same time — but it can also be in two places at once, new research shows.

“We are showing an analogy to Schrödinger’s cat that is made out of an electromagnetic field that is confined in two cavities,” said study lead author Chen Wang, a physicist at Yale University. “The interesting thing here is the cat is in two boxes at once.”

The findings could have implications for cracking unsolvable mathematicalproblems using quantum computing, which relies on the ability of subatomic particles to be in multiple states at once, Wang said.

Cat experiment

The famous paradox was laid out by physicist Erwin Schrödinger in 1935 to elucidate the notion of quantum superposition, the phenomenon in which tiny subatomic particles can be in multiple states at once.

In the paradox, a cat is trapped in a box with a deadly radioactive atom. If the radioactive atom decayed, the cat was a goner, but if it had not yet decayed, the cat was still alive. Because, according to the dominant interpretation of quantum mechanics, particles can exist in multiple states until they are measured, logic dictated that the cat would be both alive and dead at the same time until the radioactive atom was measured.

Cat in two boxes

The setup for the new study was deceptively simple: The team created two aluminum cavities about 1 inch (2.5 centimeters) across, and then used a sapphire chip to produce a standing wave of light in those cavities. They used a special electronic element, called a Josephson Junction, to superimpose a standing wave of two separate wavelengths of light in each cavity. The end result was that the cat, or the group of about 80 photons in the cavities, was oscillating at two different wavelengths at once — in two different places. Figuring out whether the cat is dead or alive, so to speak, requires opening both boxes.

Though conceptually simple, the physical setup required ultrapure aluminum and highly precise chips and electromagnetic devices to ensure that the photons were as isolated from the environment as possible, Wang said.

That’s because at large scales, quantum superposition tends to disappear almost instantaneously, as soon as these superimposed subatomic particles whose fates are linked interact with the environment. Most of the time, this so-called decoherence would happen so quickly that researchers would have no time to observe the superposition, Wang said. So devices that keep coherence (or keep the particles in superposition) for long periods of time, known as the quality factor, is extremely important, Wang added.

“The quality of these things determines once you put a single excitation into the system, how long does it live, or does it die away,” Wang told Live Science.

If the excitation of the system — the production of the electromagnetic standing wave — is similar to the swing of a pendulum, then “our pendulum swings essentially tens of billions of times before it stops.”

The new findings could make for easier error correction in quantum computing, Wang said. In quantum computing, bits of information are encoded in the fragile superposition states of particles, and once that superposition is lost or corrupted, the data is also corrupted. So most quantum computing concepts involve a lot of redundancy.

“It’s well understood that 99 percent of computation or more will be done to correct for errors, rather than computation itself,” Wang said.

Their system could conceivably get around this problem by encoding the redundancy in the size of the cavity itself rather than in separate, calculated bits, Wang said.

“Demonstrating this cat in a ‘two boxes state’ is basically the first step in our architecture,” Wang said.

See more at: http://www.livescience.com/54890-schrodinger-cat-can-be-in-two-places.html#sthash.X4gB2Mc1.dpuf