Tag: Many Worlds

So Many Lunches

On By rolcottIn CosmologyLeave a comment

<shudder> “I don’t like Everett’s Many Worlds multiverse, Sy. When I think of all those A‑B entanglements throughout space I just see history as this enormous cable with an exponentially growing number of strands and it keeps getting thicker and more massive. Besides, that’s all about observations at the micro level and I don’t see how it can build up to make two me’s enjoying our different lunches.”

“Most physicists agree with you, Susan, although there have been entire conferences devoted to arguments for, against and about it. His proposal does solve several known problems associated with other interpretations of quantum mechanics but it raises some of its own. To my mind, it just tastes bad. How about another multiverse idea?”

“Is it as cumbersome as that one?”

“Well, it still involves infinity, but probably a smaller one. I think the best way to describe it is to start with black holes. Each one has a region at its geometric center where spacetime is under such stress that we don’t have the physics to understand what’s going on in there. You with me?”

“So far. I’ve read some of your posts about them.”

“Cool. Anyway, one conjecture that’s been floating around is that maybe, especially for the supermassive black holes, the energy stress is so high that Nature relieves it by generating a new blister of spacetime. The blister would be inside the Event Horizon so it’s completely isolated from our Universe. Visualize one of those balloon artists who twists a patch on the surface of a blown-up balloon and suddenly it grows a new bubble there.”

“Like yeast budding new yeastlets?”

“That’s the idea, except these spacetime buds would be rooted inside our Universe like a yeast cell’s internal vesicles rather than budding from the cell’s surface. Because it’s isolated, each bud acts as an independent Universe.”

“But Hubble has shown us a trillion galaxies. If there’s a supermassive black hole at the center of nearly every galaxy…”

“Yup, lots of Universes. But it gets better—”

“I see where you’re going. Each baby Universe can have its own collection of black holes so you can have a cascade of Universes inside Universes like a matryoshka doll. Except the people in each one think theirs is the size of a whole Universe. If there are people there.”

“All of that’s possibly true, assuming there are baby Universes and they have the same physical laws and constants that we do. The speed of light could be different or something. Anyway, I was going to a less exotic scheme. The Observable Universe is the space that contains all the light that’s been directed towards us since the Big Bang 13.7 billion years ago. Thanks to the expansion of the Universe, it’s now a sphere 93 billion lightyears in diameter. Think of it as a big bubble, okay?”

“Mm-hm. You’re thinking about what’s outside that bubble?”

“Mm-hm. Of course light and information from outside haven’t had time to get to us so we have no chance of observing what’s out there and vice‑versa. Do you agree it’s reasonable to assume it’s all just more of the same?”

“Sure.”

“Well then, it must also be reasonable to assume that our observability bubble is surrounded by other observability bubbles and they’re surrounded by more bubbles and so on. The question is, does that go on infinitely far or is there an outermost shell?”

“By definition there’s no way to know for sure.”

“True, but it makes a difference when we’re thinking about the multiverse. If there’s only a finite number of bubbles, even if it’s a big number, then there’s a vanishingly small chance that any of them duplicates ours. No copies of you trying to decide between noodles for lunch or a sandwich. If the number is infinite, though, some cosmologists insist that our bubble in general and you in particular must be duplicated not just once but an infinite number of times. Some of you go for noodles, some for sandwiches, some maybe opt for pizza. All in the same consistent Universe but disconnected from each other by distance and by light’s universal speed limit. Does that count as a multiverse?”

~~ Rich Olcott

Noodles or A Sandwich?

On By rolcottIn Cosmology, Physics: Quantum Mechanics, UncategorizedLeave a comment

“Wait, Sy, your anti-Universe idea says there are exactly two um, sub‑Universes. Even the word ‘multiverse‘ suggests more than that.”

“You’re right, Susan, most of the multiverse proposals go to the other extreme. Maybe the most extreme version grew in reaction to one popular interpretation of quantum theory. Do you know about the ‘Many Worlds‘ notion?”

“Many Worlds? Is that the one about when I decide between noodles for lunch or a sandwich, the Universe splits and there’s one of me enjoying each one?”

“That’s the popular idea. The physics idea is way smaller, far bigger and even harder to swallow. Physicists have been arguing about it for a half‑century.”

“Come again? Smaller AND bigger?”

“Smaller because it’s a quantum‑based idea about microscopic phenomena. Doesn’t say anything about things big enough to touch. Remember how quantum calculations predict statistics, not exact values? They can’t give you anything but averages and spreads. Einstein and Bohr had a couple of marquee debates about that back in the 1930s. Bohr maintained that our only path to understanding observations at the micro‑scale was to accept that events there are random and there’s no point discussing anything deeper than statistics. Einstein’s position was that the very fact that we’re successfully using an average‑based strategy says that there must be finer‑grained phenomena to average over. He called it ‘the underlying reality.’ The string theory folks have chased that possibility all the way down to the Planck‑length scale. They’ve found lots of lovely math but not much else. Hugh Everett had a different concept.”

“With that build‑up, it’d better have something to do with Many Worlds.”

“Oh, it does. Pieces of the idea have been lying around for centuries, but Everett pulled them all together and dressed them up in a quantum suit. Put simply, in his PhD thesis he showed how QM’s statistics can result from averaging over Universes. Well, one Universe per observation, but you experience a sequence of Universes and that’s what you average over.”

“How can you show something like that?”

“By going down the rabbit hole step by step and staying strictly within the formal QM framework. First step was to abstractify the operation of observing. He said it’s a matter of two separate systems, an observer A and a subject B. The A could be a person or electronics or whatever. What’s important is that A has the ability to assess and record B‘s states and how they change. Given all that, the next step is to say that both A and B are quantized, in the sense that each has a quantum state.”

“Wait, EACH has a quantum state? Even if A is a human or a massive NMR machine?”

“That’s one of the hard‑to‑swallows, but formally speaking he’s okay. If a micro‑system can have a quantum state then so can a macro‑system made up of micro‑systems. You just multiply the micro‑states together to get the macro‑state. Which gets us to the next step — when A interrogates B, the two become entangled. We then can only talk about the combined quantum state of the A+B system. Everett referred to an Einstein quote when he wrote that a mouse doesn’t change the Moon by looking at it, but the Moon changes the mouse. The next step’s a doozy so take a deep breath.”

“Ready, I suppose.”

“B could have been in any of its quantum states, suppose it’s #10. After the observation, A+B must be an entangled mixture of whatever A was, combined with each of B‘s possible final states. Suppose B might switch to #42. Now we can have A+B(#42), separate from a persisting A+B(#10), plus many other possibles. As time goes by, A+B(#42) moves along its worldline independent of whatever happens to A+B(#10).”

“If they’re independent than each is in its own Universe. That’s the Many Worlds thing.”

“Now consider just how many worlds. We’re talking every potential observing macro‑system of any size, entangled with all possible quantum states of every existing micro‑system anywhere in our Observable Universe. We’re a long way from your noodles or sandwich decision.”

“An infinity of infinities.”

“Each in its own massive world.”

“Hard to swallow.”

~~ Rich Olcott