Ruminations on multiverses; Quantum types (Introduction)

by David Turell , Friday, January 27, 2017, 01:10 (2639 days ago) @ David Turell

There are two types of multiverses: branched tiny local ones as in quantum theory or multiple diverse ones like soap bubbles in every direction:

http://nautil.us/issue/44/luck/the-multiple-multiverses-may-be-one-and-the-same?utm_sou...

"Physicists and philosophers have long argued over what quantum theory means, but, in some way or other, they agree that it reveals a vast realm lying beyond the range of our senses. Perhaps the purest incarnation of this principle—the most straightforward reading of the equations of quantum theory—is the many-worlds interpretation, put forward by Hugh Everett in the 1950s. In this view, everything that can happen does in fact happen, somewhere in a vast array of universes, and the probabilities of quantum theory represent the relative numbers of universes experiencing one outcome or another. Indeed, it turns out our classical ‘world’ is only a small part of a much larger reality.

"This array of universes seems, at first glance, to be very different from the one that cosmologists talk about. The cosmological multiverse grew out of models that seek to explain the uniformity of the universe on scales larger than galaxies. The putative parallel universes are distant, distinct regions of spacetime, the result of their own local big bangs, evolving from their own bubbles of quantum foam (or whatever it is that universes sprout from). They are out there in roughly the same way that galaxies are—you could imagine getting in a starship and traveling to them.

"Everett’s many worlds, in contrast, are down here. The concept emerged from efforts to understand the process of laboratory measurement. Particles leaving trails in cloud chambers, atoms deflected by magnets, hot objects emitting light: it was these sorts of hands-on experiments that motivated quantum theory and the search for a coherent interpretation. The quantum “branching” that occurs during a measurement gives rise to new worlds that overlap with the space where we live.

"And yet these two kinds of multiverses have much in common. We can visit either sort only in our mind’s eye. Try as you might to reach another bubble universe in your starship, the intervening space would expand faster than you could possibly cross it; bubbles are thus cut off from one another. Likewise, we are by our very nature blind to other universes in the quantum multiverse. These other worlds, though real, remain forever out of view.

"Moreover, although the quantum multiverse was not developed for cosmology, it is peculiarly well suited to it. In conventional quantum mechanics—the Copenhagen view, embraced by Niels Bohr and his collaborators—one has to distinguish between the observer and the thing being observed. That’s fine for standard laboratory physics. The observer is you, and the experiment is the thing you’re observing. But what if the object under investigation is the entire universe? You can’t get “outside” the universe in order to measure it. The many-worlds interpretation makes no such artificial distinctions. In a new paper, Caltech physicist Sean Carroll, together with graduate students Jason Pollack and Kimberly Boddy, directly applies the many-worlds interpretation to creation of universes in the cosmological multiverse. “Everything that’s very wishy-washy in conventional quantum mechanics becomes, in principle calculable [in the Everett view],” Carroll says.

"Finally, the two kinds of multiverse make identical predictions for our observations. The only difference is that they situate the possible outcomes in different places. Carroll sees an equivalence between “the cosmological multiverse, where different states are located in widely separated regions of spacetime, with a localized multiverse, where the different states are all right here, just in different branches of the wave function.”

***

"Not everyone accepts the multiverse, let alone that varieties of multiverse are similar. But, keeping in mind that these ideas are still tentative, let’s see where they take us. They suggest a radical idea: that the two multiverses may not, in fact, be distinct—that the many-worlds view is the same as the cosmological multiverse. If they seem different, that is because we have been thinking about reality in the wrong way.

***

"Hugh Everett didn’t live long enough to witness the renewal of interest in his version of quantum mechanics. He died of a heart attack in 1982, at the age of 51. A staunch atheist, he was certain that this was the end; his wife, following his instructions, threw his ashes out with the trash. His message, however, may finally be taking root. It can be summed up in four words: Take quantum mechanics seriously. When we do so, we find that the world is—surprise!—larger and richer than we had imagined. Just as Voltaire’s silkworm saw only his web, we see only a small sliver of the multiverse, but, thanks to Everett and those who followed in his footsteps, we may yet slip through the crack in the crystalline shell, “where the earth and the heavens meet,” and glimpse what lies beyond."

Comment: I've skipped a lot of theoretical possibilities the author presents, but the point is obvious. We sit in a small corner of reality watching quanta cross back and forth across a wall we cannot cross to understand the other side.