CYA: I am NOT a physicist, this is just the stuff of dust motes from an overreaching mind. Time Travel and Alternate Universe Touristing are dangerous and should not be attempted at home!
The Pauli Exclusion Principle
So if you’re an accidental nerd like me, you’ve probably heard the Pauli Exclusion Principle being thrown around in sci fi forums, in works of science fiction themselves, or used as a pseudo cultural law concerning Time Travel. It is most noted as a reason you cannot make contact with your future/past self in time travel epics.
Relatively recently, it was also used in the TV show FRINGE as the hinge science, yes, I just did that, which (apparently) explained the melding & or collision of universes, which of course was the main conflict, and what drove the entire series forward. The blatant name dropping was accompanied by a neat little visual of two snow globes colliding, the ultimate result, we were told, was that only one universe could survive, because of you know, that incredibly complicated thing we talk so easily about: the Pauli Exclusion Principle.
However, as we’re about to learn, it is most often misused, and no, if you found your future self and shook her hand, you would not implode, or the universe would not end. At least, not because of the Pauli Exclusion Principle. It might happen for other reasons…
First, what the hell is the Pauli Exclusion Principle? According to the Gods of Wiki:
The Pauli exclusion principle is the quantum mechanical principle that two identical fermions (particles with half-integer spin) cannot occupy the same quantum state simultaneously. In the case of electrons, it can be stated as follows, It is impossible for two electrons of a poly-electron atom to have the same values of the four quantum numbers (n, ℓ, mℓ and ms). For two electrons residing in the same orbital, n, ℓ, and mℓ are the same, so ms must be different and the electrons have opposite spins. This principle was formulated by Austrian physicist Wolfgang Pauli in 1925.
Yeah, don’t worry, I got lost at Fermions too…
WHAT YOU NEED TO KNOW
Unless you are a Quantum Mechanics groupie, all you need to know about the Pauli Exclusion Principle is that no two electrons can ever be in the same quantum state.
This of course has been translated to: you can’t have two of you or else KABLOOM! Bad shit rains down from the heavens and hits the proverbial fan.
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However, there are major holes with this theory, so here we go:
1. This is assuming that if you are a time traveler (or a tourist from another dimension) then the “other” version of you is exactly the same matter as you are. So far, besides some kind of esoteric metaphysical philosophical bridge (which I’m okay with, by the way) there is no science to back this up. As far as I can tell, you two, while being genetically identical (maybe), the molecules of your bodies are independent and unique.
Think of it like this: two atoms can be hanging out right next to each other, in fact, these atoms are twins, or even the same atom from alternate universes, OR one atom is a time traveling version of the other atom, (oh goddess, my brain hurts) however you want to think about it, the two atoms are virtually indistinguishable from one another, and in fact, each atom follows the Pauli Exclusion Principle, and each has electrons in the exact same states as each other.
The Pauli Exclusion Principle deals with the electrons in a single atom, not the ones hanging out in the theoretical time traveling alternate twin atom sitting in the next seat over. So while the electrons in one atom can’t be in the same state, the electrons in the atom next to us CAN be in the same state.
Are you still with me?
2. The cells in your body decay at a such a rapid rate, even if the two of you were the exact same matter somehow metaphysically, you wouldn’t actually be the same matter physically, because the cells in our bodies literally replace themselves completely over 7 years, so as long as you travel back (or forward) with a 7 year difference matter has since (or hasn’t yet) been replaced. Follow me?
3. Furthermore, in order to actually accomplish this theoretical KABLOOEY KAPOW BADABOOM! You would still need some kind of spooky mystical quantum meld with the other version of you, because simply shaking Future Girl’s hand isn’t going to physically make any of your atoms share the exact quantum state as hers. Even touching, atoms, not to mention itty bitty little bastard particles like fermions, don’t necessarily share the “space” let alone their so-called quantum states. If you were able to somehow pull off this mystical quantum meld, the likeliest result is that one of you ABSORBS the other, or else you simply become one. Now here, you might be able to argue that the world from which the version of you that is absorbed hails from collapses, but then we’re into the many worlds theorem and it really doesn’t correlate with the Pauli Exclusion Principle, yet anyway.
In here somewhere is a pun about parasitic twins, cannibalism & dimorphic biology, but whatever.
A DEEPER LOOK FOR THE GROUPIES
The Pauli Exclusion Principle, is, essentially, used to explain the “capacity of the various electron shells and sub-shells” in atomic structure. It is highly likely that you learned about atomic structure in high school, also highly likely that you never actually took a moment to understand why atoms look the way they do. Don’t worry, I didn’t either. Here’s Pauli!
So Fermions are like little bastard particles that have odd, half integer spins. I know, I know, just bear with me. Fermions are different from Bosons, who have whole integer spins. So a fermion is 1/2, 2/3 etc. and a boson is 1, 0 etc. Now, here is where the little tricky dicks get trickier, because Fermions are only fermions because they follow the PAULI EXCLUSION PRINCIPLE! But Bosons DO NOT.
WHAT? My brain just exploded and it WAS from the Pauli Exclusion Principle. Call the presses.
Because all fermions somehow magically follow the Pauli Exclusion Principle, they cannot exist, or co-habitate the same quantum state at the same time. Huh? All I got from that is the poor little loners can’t share a desk while coworking….
Okay, lets break it down now: what this is really saying is that you can only have a maximum of 2 electrons in the same place at the same time and those guys have to have an opposite spin.
Right, now we’re getting somewhere usable.
So actually, you CAN have 2 electrons in the same freaking place at the same freaking time, these electrons just have to be spinning OPPOSITE each other. But no other electrons can then occupy that state. Which, incidentally, is why atoms look the way they do, with little particles orbiting around the nucleus in “shells” that when viewed on a classroom chalkboard look eerily similar to the solar system, with planets and celestial bodies orbiting around the sun.
Yeah, when we think about it like that, it makes sense. Two planets can not be sharing the exact same orbit or else they’d be ONE PLANET not two. But what about this opposite spin shit? That still doesn’t make sense. There isn’t two Earths existing on the same plane and spinning opposite each other, right?
Or is there?
Dun Dun Dun….
And here, my friends, we come to the quantum mechanics mind &$%#.
A QUANTUM WORLD
Essentially, based on my peanut brain understanding, quantum mechanics is the underlying set of principles that are used to explain all quantum theory, whether they fall into physical “mechanics” or not.
Don’t effing worry about it, lets continue…
According to quantum mechanics, all electrons are both particles, AND waves. In fact, a father and son both won Nobel Prizes for their work in the subject, with one winning the prize for proving electrons are particles, and the other winning the prize some time later for proving that electrons are waves. Huh. So together, whether they wanted to or not (family rivalry much?) these nerds proved that electrons are BOTH particles and waves.
In more woo woo terms, every electron in the known universe appears to have some kind of a mystical mysterious witchy woo energetic soul twin, not exactly, but, oh well. They exist in the same freaking place (relatively) but they don’t actually inhabit the same exact space, because one is a particle and one is a wave. In one way, you can kind of (but not really) think of it as one being matter and the other energy.
Hmmm, okay, now we’re progressing. (Or are we!)
CONCLUSION (KIND OF)
It’s all theoretical physics anyway, and if it sounds made up, that is because basically, it is. But it wasn’t made up out of nowhere. There was a lot of time and thought put into it before/as it was being “made up”. And most of it has been tested to some level or another.
However, know that we don’t know everything. Our scope of understanding is limited to our perspective, and by looking at things in only one way, we will never see the solutions that already exist.
Theoretical science is all about breaking the rules and then figuring out how to unbreak them. And Science Fiction has a huge part in that process. But we can’t break the rules unless we (somewhat) understand them first. Instead of just throwing out an established principle to explain away your story, try approaching it from at least a relatively logical stand point from the beginning.
The further you take your understanding of the science you will use in your story, the more developed your story will become. Besides, I postulate that by delving into the philosophical physics of quantum mechanics, you will probably discover a whole new world of possibilities than the one you originally started with!
PS >> while I’m new to the Fringe Phenomena, and I’m happy to take a stab at its hinge science, I also watched five seasons worth of episodes in approximately 3 weeks, which I think speaks for itself.
PARTING PARTY WORDS
Know more than me about the Pauli Exclusion Principle (highly likely) then sound off below! Know some uses in literature pop culture where it was done successfully? Not so successfully? A visitor from another universe with deep insight and experience? Please share in the comments…