Physics and the Universe

Today we’ll discuss worldbuilding the rules of the universe for your fictional world and why saying gravity is ‘just a theory’ doesn’t mean you can ignore it.

Hey everyone, my name is Matthew, at least in this iteration of reality, and this post is part of a series where I will be going through a science-adjacent worldbuilding process step-by-step, starting from nothing, and building a fully functional fictional world. Try saying that three times fast…

For today’s discussion, we’re going to be worldbuilding THE UNIVERSE. Okay, it’s a little less dramatic than that, and not as unimaginably expansive as you might think. What we’re going to look at is specifically the physics of the universe, outlining the rules of how it works in our fictional world and establishing some assumptions that we will need to move forward. Does the universe follow the same rules of physics as our own real-life universe? Does anything break or bend these rules? Are there other parallel universes with different rules, all bending together to form one giant-mega-MULTIVERSE?

To start, we have to determine whether our universe is alone in its existence, or whether it will have other parallel universes alongside it, forming a multiverse. This is the study of cosmology, which refers to the branch of astronomy that concerns the origin and evolution of the universe, starting all the way back with the Big Bang, to the present, and onwards into the future. There are some amazing literary examples of fictional cosmologies that are worth examining before we make our own. To start, let’s look at the cosmology of Dungeons and Dragons, which is referred to in-universe as ‘The Great Wheel’. In this cosmology there are literal dozens of different universes or ‘planes of existence’, all tied together across a multitude of universes, each with different scientific laws, magic, and unique worldbuilding of their own. This kind of kitchen sink approach can be effective if you’re looking at creating a world for a tabletop game, to allow players variety in which extra-planar lore they’d like to connect with. In this setting, players are free to jump from one universe to another, completely changing scenes and interacting with entirely different universal rules. Be warned though that as a worldbuilder, this can be an exhaustive task, and every universe beyond the primary one is additional work, especially if the story will take the character there. Another common cosmology is that of ‘heaven’ and ‘hell’, which is a pervasive theme across many real-world religions. Some religions refer to the two planes literally as I have, as ‘heaven’ and ‘hell’, but many have other names. In Ancient Greek theology, the concept of ‘heaven’ was called Elysium, while ‘hell’ was called Tartarus, a place of torment for the damned.

Without diverging into a full-blown discussion into all the different types of real-world examples of cosmology, the takeaway point is that secondary universes usually have a ‘function’ – a purpose for existence.

For the universe we’ll be worldbuilding together, let’s create a second universe that is parallel to the first, and functions as a mirrored and conjoined universe. Rather than thinking of the two universes as entirely separate, there are points where the two universes meet. I imagine this as an ebb-and-flow of joining and separating, that occurs across spacetime. At certain points in spacetime, the two universes are very close, while at other points, they are more separate. The fundamental laws of the two universes are likely to have some overlap, especially at the points where they are closer together, and there are going to be forces that can affect both universes at the same time.

Which brings us neatly into our next point of discussion, which is establishing the fundamental rules of the universe. In our real-life universe, these are scientific laws like thermodynamics, gravitation, and relativity. But you don’t need to be a physicist to have a level of understanding appropriate for worldbuilding. The reality is, all of these laws occur behind the scenes, and it’s unlikely they’re ever going to be directly explained in a story or a game, unless it’s relevant to the plot or mechanics. Because of this, most fictional universes simply imply real-life universal laws as a foundation, and only describe the ways that they are deviated from. An excellent example of this is the world of Full Metal Alchemist; where because Alchemy is central to both the story and the mechanics of the universe, its metaphysical processes are explained in terms of how they deviate from reality. Alchemy is not just ‘magic’ in the FMA universe, it is an interaction with a real-life universal law – the Law of Conservation of Mass – as well as a fundamentally different and fictional universal law, the Law of Natural Providence. If you are wanting to make a unique universal law, this is the stage to implement it, because it will affect all world-building down the line. For example, if you establish a universal law that a creature cannot utilise more magical particles than they weigh in kilograms, this applies significant constraints to world-building wizard academies, and all of a sudden you have a world where wizards are gorging themselves to gain mass so that they can cast more potent magic. Perhaps there are space-dwelling monsters the size of planets that are capable of utilising so much magic that it can affect the very fabric of the universe. Maybe this is how your universe was created in the first place? If you’re wanting a universe where time-travel is possible, and you want it to make sense, then you’re probably going to want to establish rules here around how it works.

For the universe that I will be making as we go through this series, I’m going to use real-life universal laws, but with a single adjustment to the first law of thermodynamics. For those non-physicists out there, the first law of thermodynamics includes the principle of conservation of energy, which states that energy can be transformed (changed from one form to another) but cannot be created or destroyed. This is still going to be true in our fictional universe, but we’re also going to stipulate that energy can leave the universe, to be transferred into the adjacent universe we created earlier. It still isn’t created or destroyed, simply transferred. Think of the total energy of both universes as a single pool, that can be moved from one side to the other.

We’re now dealing firmly with science-fiction, because to my knowledge as a non-physicist, there isn’t any definitive, proven, real-life evidence of another universe, let alone knowledge of how energy might be transferred between our universe and another, if such a thing is even possible at all.

Perhaps more importantly to our worldbuilding process, this transfer isn’t going to ‘look’ like energy transfer at all, at least to someone who can only view one of the two universes involved in this process. Instead, it is going to definitely look like energy creation and energy destruction, even if behind the scenes it’s not. Of course, by our reckoning in our real-life world, energy creation would be… magic! It would defy our universal laws, and that’s exactly the point. To someone viewing the universe we’ll be worldbuilding, there will be processes that are possible in-universe that are going to seem like magic to us in real-life, but by the rules of the world we’re building, it works. To any creatures in this fictional universe, they may not consider it ‘magic’ at all, but rather another form of science.

But we’re getting way ahead of ourselves, and before we look at the uses and implications of this energy transfer, we need to determine how it occurs naturally, if at all. Let’s start by saying that the transfer occurs naturally as a by-product of entropy. The higher the entropy, the more energy transfer occurs. Entropy for those playing at home, is the measure of randomness, or disorder, of the universe. Any time something is broken down into a more random and disordered state, entropy increases. The second law of thermodynamics states that the total entropy of a system must either increase or remain constant; it can never decrease. Fire for example takes matter like wood and burns it to create ash, smoke, and gases, all of which are more random and disordered than the solid fuel. This process makes the universe as a whole MORE random and disordered, which means entropy has increased, and therefore within our fictional universe, energy transfer has occurred. Without outside intervention, the ash, smoke, and gases cannot turn back into wood, and any process that can turn it back into wood MUST create zero or greater entropy in the universe as a whole as a by-product. Obviously, the fire example is absolutely minute and borderline immeasurable compared to the vastness of the universe, but it provides a good starting point for our scale. A star for example would transfer a huge amount of energy comparatively speaking, and a stellar object like a black hole even more so.

A physicist of this fictional universe could establish an equation to determine the rate of transfer, but for simplicity as worldbuilders, let’s say that any energy transferred from one universe to the other in this way is effectively equal. What this means in real terms is that entropy is actually always zero when looking at the system of the two universes; there is no increase of disorder across the two universes, because as one becomes more disordered, the other becomes more ordered. The two universes would be in a constant dance of energy transfer, with one transferring more than the other, before the energy load becomes imbalanced and the rate of transfer switches. As we said before however, to an observer of just the one universe, this would look as though entropy is increasing AND decreasing, as when energy enters one universe from the other, it adds to the total workable energy available within that universe. Let’s call the process of energy entering the universe ‘Synthesis’, and the process of energy leaving the universe ‘Severance’. This is a nice, closed loop, and we’re left with only one more question to answer; how does energy get INTO a universe from the other? We’ve established how it leaves, through entropy, but how does it get in from the other side?

Well, to make things clean, let’s say that it doesn’t just immediately jump from one universe into the next, but rather hangs in-between in a kind of ‘energetic limbo’. This energy can then be pulled into one of the two universes by a number of methods, the most basic stellar example of which is a white hole. White holes in our real-life universe are a theoretical opposite of a black hole; just as nothing can escape a black hole, nothing can enter a white hole. Instead, white holes give off energy while not allowing energy to enter. Unfortunately, in our real-life universe, the existence of white holes is at most debated, but likely not real. In our fictional universe however, a white hole is a perfect answer for how energy is able to enter a universe from another. To my understanding as a non-physicist, the concept of a white hole is theoretically possible according to our scientific laws, which as a worldbuilder means it likely doesn’t grossly violate any of the scientific laws we’re using and is a perfect inclusion for what we’re going for.

Let’s say that white holes come in three main forms: thermal, photonic, and electric, spewing out thermal energy, light energy, and electric energy respectively. These stellar bodies are extremely likely to form the hearts of galaxies, not because they are slowly sucking everything in like a supermassive black hole, but because they are slowly spewing matter out. This is also yet another wonderful moment of science fiction where we have a plausible science-adjacent rationale for what we would consider ‘magic’. Just as a fire replicates the outbound energy transfer that stars cause on a very micro scale, so too can we establish micro scale inbound energy transfer, such as with compounds and rituals, giving us the creative freedom to create occurrences that to us as viewers and readers are truly magic.

So, to recap, our universe is going to follow the same fundamental physics laws as our own real-life universe, albeit with a small adjustment to one of the principals of conservation of energy to allow for energetic transfer between it and a secondary universe.

Join me next time where we’ll move away from physics and discuss the rules of chemistry for the universe we’re building. And until next time… stay awesome!