By Lucy Ives from Electric Lit:
Some people employ a theory of parallel universes to explain time travel. Maybe I am one of them.
If you ask me, a science simpleton, what I mean by “parallel universe,” my answer may vary depending on the day, but usually I mean something like, a hypothetical plane of reality, coexisting with, yet distinct from, our own. The main difficulty here is that I do not know what I mean when I call something “hypothetical.” Maybe I mean that that hypothetical plane of existence (a.k.a. parallel universe) is elsewhere and unseen, yet actual. Maybe I mean that that plane is something I want to think about right now and sort of cherish, not a combo of time and space where I plan to attempt to exist but rather a pattern I have not yet perceived. It’s not, actually, actual. It’s a thought I’m mentally cuddling.
I’m not sure that I believe in time travel, strictly speaking: certainly, not into the past. I don’t think “I” can go back to the Middle Ages and wander the reeking, pissed-upon hallways of a poorly illuminated castle. I wouldn’t want to do this, anyhow. People seem to forget how common murder used to be.
What I do believe in are coincidence and symmetry, even as I believe in movement (travel!) into the future. Events have a tendency to repeat, and often we can’t tell that they are repetitions, even when they are.
Take for example: me. It is morning and I have gone for a run. I haven’t gone back in time. I mean, I am running in a circle, so I will return to the original point in space from which I departed eventually, but meanwhile time will flow forward, onward, on, rippling along with the space I’ll cover, and soon I’ll be back at my hotel, and then I’ll be showered, staring confusedly at my naked self in a steamed-up mirror, and, then, eventually dressed and ready to depart. And there will be nothing unusual about my day. I won’t get “back” to anywhere.
I’ll only keep on going. I’ll move ahead, out of the present, even as the mirror displays to me an image of myself as I was a fraction of a second before the instant when I looked.
This is my general experience. I am this organism that is knit in space and time.
The one thing I have not told you yet, and that I have to suppose you therefore do not know, is that the place where I am in this instance is a small city in America where, many years ago, I used to live. Thus, I’m currently engaged in more than one type of spiral.
Let’s call this city “Iowatown” (not its real name).
Now imagine me running.
I am not a thin person, but I am strong and have biggish calves that carry me quickly. I’m bounding through all the new construction, listening to a song about female aggression. The singer is going to date your boyfriend. The singer can’t help it. Your boyfriend is extremely persistent and the singer is casual about her entanglements. You, addressee of this song, don’t stand a chance. I listen, running and panting, directing myself along my one-point-five-mile loop, and I identify with the singer, not with the person to whom the song is allegedly addressed. I believe myself to have the correct disposition toward these lyrics.
I’m far enough into town now, into the residential part of “Iowatown,” and I do regret my inability to drop the quotes, that I seem not merely to be moving in a standard fashion into space. This is the tricky part of my experience that I was attempting to intimate. I feel, in that cliché, like I am going back in time.
But I’m not, I think to myself, I’m not, I’m not, although here I am, planted in front of the old house, a warren of slapdash rentals, where we used to spend all our time together, and where your downstairs neighbor was a grinning monomaniac who claimed he’d been a professional boxer in his youth.
. . . .
The house is still white, bluish. It still has that porch in front with the pattern of circles punched in the wood below the railing. There is still the elaborate fire escape, the one that touched your bathroom window. Someone else must live up there now. Someone may, even at this moment, be standing on that same police-blue wall-to-wall carpeting, gazing out the window at a pausing jogger.
Meanwhile, the prehistoric sun beats down upon the little sidewalk where I stand in my running attire. The sun warms me, although I feel extremely far from my skin. I may have begun running inside a narrative, but now that I am here, here before the residence where you used to live and where we lived together, I see that this is not merely my destination. It is a net or a kind of a mirage, and it has caught me.
And when we met, if you will recall, we were both walking on the street not far from here. I felt, that day, that I was being watched, as if from some point in the sky, a pinprick. You, meanwhile, didn’t look, not at first. You were engrossed in a copy of Kurt Cobain’s diary, which you had borrowed from the university’s library, and which I thought was an ingenious thing for a graduate student to be reading, although I did not tell you so at the time and, then, never told you later. Something started in that moment that was different from all other things that had begun in my life thus far. That tiny piercing in the heavens stayed there, unblinking. You lifted your hand from the page you were reading; eyes previously cast down went up. You seemed to hear a voice: you were being notified. You recognized me from somewhere, from some hallway or classroom. You beckoned. There was no pause in this, no flinch. You were not shy. You seemed to have practiced for this encounter for months. And when, in the subsequent one point five decades, I thought of it and you, I sometimes wondered if everything had indeed been rehearsed, if not predetermined.
Link to the rest at Electric Lit
In the interest of balance I think I should offer an alternative viewpoint, even though PV is not really where we should be discussing the more esoteric parts of speculative physical theory (and by and large I prefer not to disagree with Felix).
So, to start with a dogmatic statement: when it comes to speculative physics (the multiverse, string “theory”, etc.) the popular scientific press like Scientific American or – even worse – New Scientist, are pretty well useless and should be avoided like the plague. If you want someone reliable, I’d recommend Natalie Wolchover of Quanta Magazine (https://www.quantamagazine.org) though she sometimes gets things wrong, and Jim Baggott is also pretty good (even when writing in New Scientist).
Turning to the multiverse, I’m going to be even more dogmatic and say that there is no reason – either theoretical or empirical – to suppose anything other than our universe exists. There is plenty or speculation – mostly based on the eternal inflation hypothesis – but nothing of real substance. If you are going to push your theories into areas that you cannot observe you need a mathematically well-defined theory (model) that has passed all the empirical tests of its observable predictions: this gives you confidence in its currently unobservable results – which explains why no-one was surprised when gravitational waves were observed. Such solid theories do not exist for multiverse predictions – despite what you may have read even non-eternal inflation is not well established (and has been subject to very substantial criticism, particularly from the likes Paul Steinhardt, who is one of the founders of the theory but has changed his mind or late).
Of course, if there was any observational evidence to support the existence of a multiverse things would be very different. Claims for such evidence come and go, but they always go when the data is examined more closely. What’s more, most such discussions are not about actual evidence but how – if someone’s model worked in exactly the right way – it might have an observable result, though always with the caveat that if the effect is too small to observe or does not occur at all, this is no reason to assume the model is wrong.
Everett’s many-worlds interpretation is, of course, a quite different kind of beast and it has always seemed odd to me that anyone groups it with cosmological multiverses. Quantum Mechanics interpretations are a rabbit hole I prefer to avoid, but as they change neither the equations nor the predictions of QM, selecting an interpretation seems to be mostly a matter of aesthetics, and I see no reason why such a choice requires me to accept the “reality” of many-worlds.
And when it comes to picking my poison, I select QM and GR without the multiverses (and living with their incompatibilities, which really don’t affect me much as long as I keep well away from black holes). String Theory I still don’t believe exists: I’m a traditionalist and want to see something like GR’s field equations, not some kind of perturbative expansion association with the M-theory hypothesis that a string theory exists even if we don’t know what it is. I’m afraid that xkcd still pretty much sums up my feelings on this: https://xkcd.com/171
As for SF though, I have no more problems with parallel universes than FTL drives (or the way people in space opera flit around without any concern for the normal laws governing Newtonian rocketry, inertia and mass ratios). If it’s a good story, like Stephen Baxter’s “Raft”, it’s fine with me (though I’ll admit that I don’t like the philosophy implicit in Niven’s “All the Myriad Ways” and this dislike carries over into my reaction to the story).
FWIW, I cited SciAm because it offered the shortest, clearest description of the models, not because it’s the only one I’m familiar with. And for story fodder you don’t need the math.
Beyond that, I’ve repeatedly said nothing ages a story faster than tying it solely to the physics of the day. SF endures best when limiting itself to the science needed by the story. That hill I’ll die on.
“nothing ages a story faster than tying it solely to the physics of the day”
In theory, I strongly agree with this. However, when it comes to planetary science almost every space probe turns up something totally unexpected and overthrows the predictions that were being made so confidently a short time earlier, and all the stories based on those theories are apparently outdated; but I’m still happy to read these stories, be it Leigh Brackett or ERB’s Mars, the jungles of Venus or the twilight zone of Mercury and be damned to the observations that have made the fictional solar system so much less fun! (even though the science is fascinating and I never actually believed in the canals of Mars).
Feel free to have living worlds, Moon, Mars, Venus, etc…, don’t let the boring reality of our copy Solar System hold you back.
The whole basis of the myth of the multiverse is the bizarre assumption that this Earth that we live on is the one, the only, the original Earth.
We live on a copy Earth. It is a copy of a copy of a copy…. It is one of millions of copy Earths in a copy Milky Way.
There is no need for a “parallel universe” to have these copy worlds. They are not “alternate” realities. We can be, and probably are, surrounded by all of the copy Earths, each with a different history unique to them. We would never see them.
I love the novel Contact by Carl Sagan, but the nonsense of “I love Lucy” episodes being detected by other worlds is just that, “nonsense”. The copy Earths are scattered through the copy Milky Way. None of them are close enough to detect.
Wiki – Omphalos hypothesis
The concept so offended people that they are still outraged by it. Because the very basis of the hypothesis makes it impossible to prove or disprove until someone from a copy Earth travels to our copy Earth and says, “Hi.”
Once I stumbled across the Omphalos hypothesis, all stories were suddenly possible, without ever violating “Reality”.
When people say, “That never happened. That’s not possible.” I point out that they are confusing the events that happened on our copy Earth with the events that happened on the copy Earth told in the story.
Let that sink in a bit.
That means that King’s IT described what really happened, and that Pennywise does exist, did exist, on some other copy Earth. That all the stories, that you safely thought were just “stories”, are not “just” stories.
Talking Parallel universes?
Well, now…
First you need to choose a *type* of Multiverse. Because there are many.
https://www.thoughtco.com/types-of-parallel-universes-2698854#:~:text=1%20Quilted%20Multiverse.%20%28Level%201%29%3A%20Space%20is%20infinite%2C,8%20Simulated%20Multiverse.%20…%209%20Ultimate%20Multiverse.%20
If we’re talking Physics, there are three main classes:
Type 1 – Regional universes within an infinite continuum/Multiverse, each one beyond the Cosmic Horizon of the rest. Because the observable volume contains a finite number of particles, every possible combination of particles exists somewhere.
Type 2 – Quantum Many Worlds branching universes. Every possible outcome of every event produces a new “branch” universe. A common root leading to infinite divergence.
Type 3 – Parallel Branes (independent continuums) that are truly separate, each developing its own way. Again, with infinity to work with, macroscopic parallels exist somewhere with identical and near identical versions all over.
(The Fourth category is effectively the world of Fantasy since there is no constraint to follow Physics.)
There are good theoretical and observed clues that suggest some kind of multiverse exists. Which type? TBD.
Philosophy has a whole range of multiverse theories addressing the question of possibility vs reality. The most interesting to me is Modal Realism which states that *everything* possible exists. Somewhere. Other theories posit the reality of Impossible Worlds, too. So Zelazny’s AMBER and COURTS OF CHAOS are allowed.
In SF multiverses have been around since pretty much forever under a variety of names and justifications. And anybody familiar with DC COMICS should be familiar with the concept since they’ve been playing with it since 1961. TV, too. STAR TREK, SLIDERS, STARGATE SG1, etc.
Too good a source of fun story ideas to ignore, much like the various forms of Interstellar travel. Especially the ones that aren’t quite parallel.
Even more fun is that physics is catching up with both concepts.
I would have continued in physics if you were teaching the subject, Felix.
I was just quoting a SCIENTIFIC AMERICAN special from a few years past.
What I found interesting is the three types of multiverses align with General Relativity, Quantum Mechanics, and String Theory. You get to pick your poison. 😀