The Philosophy of Other Worlds


The physics and metaphysics of alternative universes

Other worlds are common in fantasy and science-fiction, but they actually have quite a solid basis in physics as well. Here, I’ll talk about “other worlds” as other universes, not just other planets within our own universe, but places that are not directly connected to us in space and time. Think The Golden Compass, Alice in Wonderland, Narnia, and hundreds of sci-fi books that I don’t know about.

People have thought about other worlds for centuries. The idea of spirit realms, Heaven and Hell, and purgatory were commonly held beliefs even in times B.C. Even a multiverse was posited by Leucippus, the ancient Greek philosopher who also posited atoms.

There are many different options for other worlds, so I’ll go through them all:

1) Other Dimensions

curled dimensions
Having another spatial dimension (or two, or three…) could cause worlds of different dimensions to be separated. We live in a world with three visible spatial dimensions: things are 3-D in our universe, not flat (2-D) or linear (1-D). I say “visible spatial dimensions” because it is possible that there are tiny dimensions that we can’t see. They could be curled up, as shown in this diagram.

Now, I admit this picture is not self-explanatory, so let me explain. Say you live in a 2-D universe. It so happens to be that flat sheet in the picture (the plane below the loops). At every point in this plane, however, there is another dimension curled up (those circles). Here it is shown as going up into the third dimension, but in our world, the “sheet” would be our 3-dimensional universe. These little curls are a higher fourth spatial dimension, which, assuming they are very VERY small, are not visible or traceable to us. Perhaps with better technology, we will someday trace them (I read about this in Lisa Randall’s Warped Passages, which is a really good book that is worth the read).

2-D intersections with a 3-D sphereAnother possibility for other dimensions are dimensions larger than our three dimensions. Our 3-D world is embedded in a higher dimensional “bulk”. You can’t imagine the higher dimensions, since we are 3-dimensional beings, but we can see what this would be like with an analogy. A 2-D world within a 3-D world would perceive a 3-D sphere passing through it as a series of different-sized discs as seen in this diagram. Likewise, if a hypersphere (4-D sphere) passed through our universe, we would see it as a series of different-sized spheres. We would see projections of the higher dimension, but not the higher dimensional object itself.

Now, the curled up dimensions don’t really relate to other worlds, unless there are super tiny worlds that exist in the curled up dimensions, but if we live in a higher dimensional space, then there are many possibilities for other worlds.Russian dolls It is like those Russian dolls: we are the little doll, and are inside a larger doll (which represents a 4th spatial dimension), and that is inside an even larger doll (5-D), and so on. So there are worlds in worlds in worlds, and you would only be able to perceive the worlds that are of the same dimension as you or lower (we are 3-D so can perceive things that are 2-D, like flat things, or 1-D, like lines), unless you are somehow a higher dimensional creature trapped in a lower dimensional world (*story idea*). The way we’d know about the higher worlds could be through the projections mentioned above, or perhaps, if our soul/spirit/mind is not bound by the 3 spatial dimensions around us, it could be aware of the higher dimensional reality around it, though when it is ensouled in a body, it cannot perceive them. But this ties into our next possibility for other worlds…

2) Higher Spiritual Planes

Kabbalah Tree of Life

This follows the same general idea as the higher physical dimensions. Instead of having higher physical dimensions, there are higher spiritual dimensions. I’m not just making this up out of nothing, for we have good reasons to believe that there are higher levels of existence (and lower). This appears in almost every religion and esoteric tradition, such as in the Kabbalah, Buddhism, Western occultism, and more. People have even had experiences travelling there (e.g. astral projection), and it is thought by many that after you die, your soul “gravitates” to the plane that corresponds to its spiritual enlightenment.

Let’s look at the Kabbalah as an example (see this amazing book for the metaphysics of the Kabbalah). The Kabbalistic tree of life is this strange-looking diagram that would only look like a tree to a poet, but let’s pretend it really does look like a tree for the moment. 
Each sphere is a sephirot, and they are each labelled by different Hebrew words. Keter is the crown, from which all the others emanate. Binah and Hokmah are the male and female principles, and Da’at is knowledge. There are many interpretations about what each sphere stands for, and they are not mutually exclusive: it’s supposed to have many meanings. Each sphere, from Malkut (the lowest) to Keter (the highest) corresponds to a different level of enlightenment/state of consciousness. During a spiritual seeker’s development, they will progress up the sephirots to go from the more impulsive animal nature to a spiritual being. This can certainly be seen as different worlds, where everyone in a lower level of enlightenment is in a lower world, unable to perceive the higher reality of existence, and those above encompass more worlds, as they are beings of a higher spiritual dimension.

3) Plato’s Cave

If you’re not familiar with Plato’s Allegory of the Cave, here is a little summary of what it is:

There are prisoners in a cave sitting chained to the spot so that they cannot turn their heads and can only look at one wall. Behind them is a fire and a roadway in front of it where unchained people walk by. They carry various objects that project shadows onto the wall that the prisoners see. These shadows comprise the whole world of the prisoners: they know nothing more than the shadows, and make a game out of predicting what the shadows will be and what they will do.

Suppose that one prisoner were released from his bonds and is shown the fire so he can see that his reality is really just projections of physical 3-dimensional objects onto a wall. The prisoner is amazed and enlightened at this knowledge. The fire burns his eyes, but slowly, he gets used to its brightness.

The prisoner is then brought out of the cave (in stages to accustom him to it) into the full light of the Sun. When he can look at the Sun and the world around him without being blinded, he sees the world for what it really is. This is even more profound than the blaze of the fire, and he has at last arrived at the more “real” world that the world in the cave was merely a shadow of.

Ignoring various physical and ethical factors that make this improbable (e.g., how do the prisoners eat? Wouldn’t they be muscle-less and weak-boned flubber from sitting so long?), this allegory is about the enlightenment that people can gain by means of philosophy. The world of shadows upon the wall is the least “real”, and is the lowest level of spiritual existence. The world of the fire is a bit higher, and from it, the prisoner can see the shadows for what they really are: only shadows, not real things in themselves. And finally, the light of the Sun is the enlightenment one obtains upon becoming a true philosopher and seeing things as they really are.

We live in a cave, unable to perceive what the world really is at a fundamental level. Even if some people are out of the cave that normal people live in, there are really caves in caves, and when one is in a higher level of existence, a higher world, they are in the cave of an even greater world. How far does this go? Perhaps it’s impossible to know unless you’re in the highest world. Get to the biggest Russian doll and look outside to see if there’s any more. If you see wood, then you’re not in the highest spiritual plane. If not, then you may be–or you’re just inside an enormous doll.

4) Parallel Worlds from Time Travel

Time travel works differently depending on your theory of time. By theory of time, I mean how time “works”. Regardless of how you do it (via relativity, a wormhole, a TARDIS, etc.), what is more fundamental is the nature of time itself. Some features of time could be that there is or is not an instant in time that you can call the present, that time had a beginning/end or does not, that you can only change things in the past that will not cause too much of a paradox, that all time travel is determined, that time itself is or is not determined… and so on.

What concerns us here is whether parallel worlds will be created because of time travel. Imagine if you could create a world just by travelling through time! (Ok, perhaps it isn’t fair to say “just” travelling through time, unless you’re the Doctor.) In the scenario that the past is determined but the future is not, then if someone travels to the past, we have a problem. Everything is set in our determined past except for the time traveler going there, because from the point of view of the time in the past, they are in the future, which is not yet set. One possibility is that this creates a parallel world, one that has the same past as the “regular” world until the point in time that the time traveler goes back to, and at this point, time expels him into a parallel world to keep the regular timeline intact, like so:

Parallel time lines created by travelling into the past

The parallel universe will start out very similar to the regular one, but it will diverge to become more and more different due to the effects of the time traveler. So after some time, they could be completely different worlds, with different people and histories, different societies and technologies.
If people time travel enough, there would be many parallel worlds, some similar, some vastly different, and the parallel worlds could spurt parallel worlds which could spurt more parallel worlds.

The regular timeline then fractures to many different worlds because of those clever time travelers. So time becomes even more relative than one would suppose just with the special theory of relativity: you can’t even say that these worlds have the same time at the start since the parallel world is created in the past of one timeline (the original one) and the present of another (the offshoot). That’s worth thinking about for a moment.

5) Quantum Mechanics (QM)

In QM, what can happen, does. At the subatomic scale, things don’t happen in the relatively predictable manner that they do in the world we are used to. Things can be in more than one place at the same time, particles at opposite ends of the universe can be tied together faster than the speed of light, and it is impossible to accurately know both the position and momentum of a particle.

One interpretation of how QM works is the Many Worlds theory. In this scenario, each quantum mechanical possibility occurs in a different world. This is in contrast with the more common Copenhagen Interpretation. In the Copenhagen Interpretation, particles exist in many states at once, but when they are observed (by a person or equipment that takes a measurement) the many states collapse into one, known as the “collapse” of the wavefunction. However, another interpretation is the Many Worlds theory introduced by Hugh Everett, in which every quantum mechanical possibility happens, but each occurs in a different world. So everything happens, and there are nearly infinite possibilities! Think about every possible universe, those that are only a little different to ours (e.g., one in which your favourite colour is red instead of purple) and ones that have entirely different planets, solar systems, and galaxies.

Oberon, Titania and Puck with Fairies Dancing by William BlakeTo tell you the truth, when people say that there are an infinite number of “you”s in parallel universes, the very first thing I think of is: “So there is a world where I am an elf queen in Middle Earth with magic powers?” Um…yes. I guess. If that magic follows the physical laws (see Part 6 below for universes with other physical laws). But whether it is really “me” is another matter entirely. If you believe that you have a soul, or anything beyond the physical matter that makes up your body, then you’d have to say that unless your soul is also duplicated (something QM doesn’t tell us about), then it is not you, but just a being that has a similar body to you.

Another aspect of Many Worlds in quantum mechanics is the creation of universes. This can be seen analogously to virtual particles. Virtual particles pop in and out of existence in the vacuum of space, being created and, most often, destroyed by annihilating with their antiparticle (for example, an anti-election is a positron, which is identical to an electron except for the fact that it has a positive charge).

Likewise, embryonic universes pop into existence in the vacuum, and although most just get “swallowed up” again, some, like ours, grow to become an actual universe. It seems to me that it’s arrogant to assume that the embryonic start of our universe was the only special one to develop into a universe: why shouldn’t others do the same? Here are our other worlds, and although they may be entirely separate “bubbles”, it may be possible with advanced technology or magic to access them.

6) String Theory

String theory is an elegant attempt of theoretical physicists to find a theory of everything, the goal being to unite quantum mechanics (which describes microscopic objects) and general relativity (which describes macroscopic objects). The basic idea of string theory is that at the most fundamental level, matter is made of strings that vibrate. These are one-dimensional strings, and their properties are determined by their vibrations. There are many different versions of string theory, but they all involve extra dimensions—10, in fact (though M-theory, a kind of string theory that unites many of the different ones with 10 dimensions, has 11). They often say that the other 7 dimensions are “curled up” so that we don’t perceive them and seem to be living in a 3-D world (not including time dimensions).

However, it is also possible that these higher dimensions are larger, and that we are living in a higher dimensional universe (like those mentioned above). If that’s the case, then we can be living in a higher dimensional multiverse that may have higher worlds that encompass more dimensions, though it is also possible that there are other worlds like ours of the same dimension that are “branes” in the “bulk” of the multiverse (I didn’t make those terms up–check if you don’t believe me!).

D3 Brand and D2 Brane

So we may be a 3-D brane hovering within the 11-D bulk, and there may be other branes of other dimensions, say, a 5-D brane or a 7-D one, that are also hovering in the bulk.

These branes can collide, merge, and other universes can be created by the collision or fission of branes. 
These worlds can have different physical laws, and because of some having higher dimensions, things would be very different from our 3-dimensional world. If we traveled to them, we would perceive them all as 3-D worlds because we can’t sense higher dimensions directly, but there are other ways in which we could detect them scientifically (e.g. by the “imprints” of higher dimensional objects talked about above).

So there we have our other worlds. Although we may not find one in a magical wardrobe, we may one day find ways of accessing these worlds and becoming multiverse travelers, or perhaps even Soul Wanderers. This may be possible through science or more spiritual means, but I think that in order to access something like this, we will have to use both in harmony with each other.

Be sure to look out for Mary-Jean’s upcoming story, “Cast Not a Shadow”, soon to be published on Sci Phi Journal.

This article was originally published on Mary-Jean’s website, The Soul Wanderers.

Mary-Jean Harris
Mary-Jean Harris writes fantasy and historical fiction, both novels and short stories. Her short stories have featured in many anthologies and websites, including Tesseracts 18 and 20, Black Lantern Journal, and various anthologies from Polar Expressions Publishing.

Mary-Jean is currently studying theoretical physics at the University of Victoria in Canada, and she has a Master's degree from the Perimeter Institute in Waterloo. She also studied philosophy as an undergraduate.

Mary-Jean's novel Aizai the Forgotten is the first in a series entitled The Soul Wanderers. To learn more, visit

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