I can’t be the only one here displeased by our current timeline. It’s pretty hard to experience endless COVID, debates about whether it’s genocide or just a little ethnic cleansing, and climate change conferences headed by oil executives, without feeling we would all do better in a different reality.
And like all of you, I’ve been brainwashed with sci-fi concept of multiple universes — in execrable series like "Loki" and umpteen Marvel creations of varying degrees of coherence, or cool versions like the totally bonkers and tender movie “Everything Everywhere All at Once” or the atmospheric TV series version of Philip K. Dick’s “The Man in the High Tower,” or literary fiction like Jorge Luis Borges’ 1941 short story, "The Garden of Forking Paths."
The idea of multiple universes actually dates back to the Ancient Greeks like Democritus, or even earlier to pre-Socratic philosopher Anaximander and his idea of infinite worlds, but today, science fiction creations are mostly inspired by cosmology and quantum mechanics.
In cosmology, the study of the universe and how it came to be this way, the idea is that after the Big Bang, the early universe grew very quickly — increasing in volume by a factor of around 1078 in the first very tiny fraction of a second. And it could have done so unevenly, birthing patches of universe that behave differently than our own
“A little piece of spacetime could have grown really far away out here really, really quickly, while another piece of spacetime grew way out here, really really quickly. So they would become causally disconnected,” Dr. Nicole Yunger Halpern, a Harvard-trained physicist who now works at the Joint Institute for Quantum Information and Computer Science in Maryland, told Salon.
“It’s possible that even across the entire history of the universe so far, light would have not had enough time to reach us from the other patch [of spacetime]. So the other patch could essentially be its own little universe.”
The separate patch, or bubble of spacetime (each constituting its own universe) could, in theory, feature its own physical laws. Science fiction writers tend to borrow the term “multiverse” from cosmology but apply it to concepts of multiple universes that are more directly inspired by quantum mechanics, with the universes being different branches of what’s called the wave function, which will come in handy later.
Yunger Halpern is actually a specialist in quantum information, not cosmology. In her 2022 book, “Quantum Steampunk: The Physics of Yesterday’s Tomorrow,” she looks back at the engines and motors that powered the Industrial Revolution — then understood in terms of classical thermodynamics — through the framework of quantum mechanics and quantum information, getting down to the level of the smallest particle and the nature of reality itself.
“In quantum physics, we can have quantum objects that can be in superposition of different states, for instance, an atom can in some respects act as though it were simultaneously in multiple locations.”
It’s not just that we don’t know where the atom is when it’s in this state, but that its position is technically not well defined — it’s neither here nor there. Or it’s both here and there. The wave function, mentioned above, is a mathematical description of the quantum state of this confusing bit of universe.
This leads to the idea that our world kind of splits, or branches: there’s one world, or branch, in which the atom is over here, and another where it’s over there. This is called the Many Worlds Theory, (or Proposal, or Interpretation) of quantum mechanics, which American physicist (and avid science fiction reader) Hugh Everett came up with mid-last century, leading an adherent of Niels Bohr, the famed father of quantum physics, to call Everett “undescribably [sic] stupid.”
In 1979, in a fascinating paper, physicist and feminist Evelyn Fox Keller somewhat snidely lauded the “ingenuity” of physicists in developing the Many Worlds Hypothesis: “this hypothesis demonstrates remarkable ingenuity in that it manages to retain both the confidence in the object reality of the system, and its literal correspondence with theory. Of course, a price has been paid – namely the price of seriousness.”
Maybe in the better branch of the wave function I’m heading to there won’t be so many haters.
Everett was, incidentally, encouraged by his supervisor, legendary Princeton theoretical physicist John Wheeler – inventor of the word “wormhole,” among other out-there concepts – who in the 1950s spurred his students to develop all sorts of creative, or bonkers, responses to questions about why the universe is the way it is (and who did his level best to bring Bohr, with whom he’d worked on nuclear fission, around to Everett’s idea).
But, I knew it was coming… Yunger Halpern went on to say the dreaded words: “There is a really common misconception in science fiction…”
Damnit.
“It’s that any time a choice is made, and there are multiple options,” she continued, “in one world, one option is chosen and in the other world, another option is chosen. For instance, I think I’ve seen one or more writers say something like ‘oh, when there’s a war, in one world, one side wins, in another world, another side wins’.”
So, that’s not how the multiverse works? No. This superposition business occurs in quantum systems — not everyday systems like the one in which civilians get bombed and history gets written. Quantum systems are unfathomably teeny-tiny, and the largest one to be experimentally put in a quantum superposition so far, Yunger Halpern said, involved a molecule of about 2000 atoms. Basically the size of a protein.
Dr. Yunger Halpern then further dashed my hopes of gathering up all my proteins and high-tailing it to a different branch of the wave function: “If it’s really our whole world that is put into this superposition such that a whole copy of the world is on one branch, one possibility, a whole copy is another possibility and so on, then the worlds can’t communicate.”
No way from here to there
But once you start with quantum mechanics, you don’t just develop useful stuff like machines to get the hell out of Dodge and into a better universe. Physicist Carlo Rovelli, for example, notes in his delightful and skinny 2014 book, “Seven Brief Lessons on Physics”, that without quantum mechanics there would be no transistors.
You also question the nature of reality. For the most part, even when physicists, rather than philosophers, are doing the thinking, it is through various thought experiments that we explore the idea that there might be more than one universe out there, and thus more than one reality or more than one timeline.
Albert Einstein famously upset Isaac Newton’s applecart by figuring out space and time aren’t separate and light energy isn’t like a continuous ray, but is “packaged” as photons that are both particles and waves. But he couldn’t or wouldn’t take the next step in accepting the possible reality of very strange ideas. First, Danish physicist Niels Bohr realized electrons jump between energy levels in atoms – absorbing or emitting photons to do so – and then the German physicist Werner Heisenberg realized that electrons only exist when they are observed or disturbed, according to their probability of being in a particular place. Einstein could not get over the idea that there might not be an objective reality out there, unaffected by those who observe or interact with it. As he famously put it, “God does not play dice with the world”.
While aspects of quantum mechanics (including the idea that observing an electron or other particle by measuring or interacting with it causes it to lose its wave-like behavior, collapsing into a definite state) remain the subject of debate, the number of creative theories that attempt to account for insights about the randomness that exists at the subatomic level have grown.
As every sci-fi fan knows, multiple parallel universes provide a window to go back in time, kill your grandfather, and get stuck in a hopeless loop of impossibility. Or you can glue a butterfly’s wings together so it can’t flap, thus averting the appalling set of events that were going to cause the ultimate collapse of civilization. So, do quantum mechanics let us go back to a different time, if not out to a cooler place? Well, in a recently-published thought experiment on the simulation of time travel, Yunger Halpern and her co-authors, David R. M. Arvidsson-Shukur and Aidan G. McConnell, create a closed timeline curve.
“We showed how you can effectively send information to the past,” she said.
Ok, that is cool. This thought experiment in metrology (the science of measurement) makes use of the phenomenon of quantum entanglement, in which quantum particles are more strongly interactive than regular (“classical”) particles. Yunger Halpern explained that this is really about measurement, which quantum entanglement can make easier or more precise (as it’s already doing for computation, and communication, and cryptography, for example).
So let’s say you want to measure a particular number. The physicists imagined that you could prepare a photon (a quantum particle of light, though it could really be any quantum particle) in such a way that it will interact with the number you want to measure, which then gets ‘imprinted’ on the photon state. Then you measure the photon, not the actual number, which you then infer from the photon measurements. OK brainiac, but how do you know the right way to prepare this photon to get it to carry as much information as possible about the thing you want to measure? You can’t really know that until after you’ve done the experiment and learned more about that number you’re after.
“So we have a kind of chicken and egg scenario,” Yunger Halpern said. “We perform our experiments, we perform our measurements, and then later, we learn about how we should have prepared our photon. Wouldn’t it be nice if we could send this information back in time back to when we were preparing our photon?”
Indeed it would. “If we could create a closed timelike curve, we can do that,” she said.
While a closed timelike curve may or may not even exist in practice, it can live in a thought experiment like this one.
But what does this gedankenexperiment offer to those who desperately would like to be in some time other than now, and some reality other than here?
“Our proposal,” Yunger Halpern restated with finality, “is how you can enhance metrology with quantum advantage not realizable through classical means.”
That’s all very well, if tricky to parse. Basically it means that working at the quantum level can improve our ability to measure things by providing information we otherwise couldn’t have. But we’re not photons, and nobody’s sending us back in time.
Ok, what about forward, then? Could we speed up to the glorious future — I’m Gen X and my hoverboard still hasn’t arrived — and skip all the stuff in the middle? Well…
“Forward time travel is possible if you can approach the speed of light,” says Paul Halpern (no relation to Yunger Halpern), a physics professor and prolific science writer whose book about the concept of the multiverse, The Allure of the Multiverse: Extra Dimensions, Other Worlds, and Parallel Universes, was just published.
Yesssss! That’s more like it.
But as usual, science is out to burst this writer’s bubble. As it turns out, you can’t approach the speed of light. (Well, not with that attitude).
Let me also warn you about physicists George Ellis and Joe Silk, who cautioned us all in Nature back in 2014 against overly exempting the attractive and brain-bending idea of multiple universes from expectation of experimental verification. Their concern is that by letting physics consist excessively of unverifiable, unfalsifiable thought experiments (completely unmoored, I might add, from perfectly reasonable expectations like development of time travel tourism or mass immigration to a war-free, global heating-free universe), it risks amounting to pseudoscience.
“Surprisingly,” said Halpern, “I found in my interviews that some very hard-headed astrophysicists who are very knowledgeable see the idea of a multiverse as enticing.” One such interview was with Dr. Virginia Trimble, a professor of physics and astronomy at the University of California, Irvine.
“She told me that all the other ideas for extending space have turned out to be true, from other solar systems, other galaxies, so why not other universes? And then there are people who are convinced that ideas of multiverse models are so strange that they shouldn’t even be talked about, they’re not even science.”
My informants are not too concerned.
Thought experiments of the kind that Yunger Halpern conducted – or like the thought experiments that led Einstein to conclude space is curved and time is relative – derive from known physical principles and build on previous work.
What’s the use of them, though? It’s true that creative or totally unhinged science does often result in highly practical technologies, such as for exploring space, healing the sick, or blowing us all up faster. But while we are stuck in this particular timeline, simply exercising our sense of wonder is one of the best options available.
“The idea of alternate worlds, alternate realities has always fascinated me,” said Halpern, who, plucking multiverse ideas from his book, told Salon about Australian physicist Brandon Carter’s “weak anthropic principle”, in which multiple universes – together, the multiverse or, in Carter’s term, the world ensemble – become a solution to the fact that you need intelligent life to observe and develop explanations for the universe in the first place.
“[We’d be] the sort of best case scenario of a lot of possibilities in which all the factors came together and led to intelligent life. And there’s all these other, countless other universes out there that don’t fit that criteria. So we’re not there to speak about it [and] that’s led Marvel and other sources of comics and science fiction and movies to come up with more multiverse ideas”.
Most of those ideas blithely ignore the fact that even if there are other universes, they’re billions and billions of light years away and probably disconnected from our own, and besides, both universes are expanding so we’re getting further and further away from each other all the time.
But deepening our understanding of the limits of our knowledge and the mindbending ideas that are pushing right up against them is a way to exercise that wonder muscle, not just for professional quantum physicists and cosmologists, but curious laypeople as well – especially, perhaps, those of us who already find ourselves questioning reality every time we read the news.
So, noted Halpern with considerable understatement, it’d be kind of frustrating if we could prove they were out there.
“It might be disappointing to people that what they imagined as the multiverse is a little different in science, but hopefully,” he added, “it will inspire them to read the sciences and appreciate what science has to offer as well.”
