A not-so-scientific introduction to theories about our reality.
Simulation Theory
First popularized by British philosopher Nick Bostrom, Simulation Theory argues that our reality may be nothing more than an advanced computer simulation.
As our society advances, with virtual reality and augmented worlds becoming indistinguishable from our own, there will come a point in time where we could create a simulation so advanced that it functions as a complex virtual world independent from our own reality. Humans would be able to enter the simulation and live in this digital world, potentially going on to create another simulation that also functions as an independent world. Therefore, multiple realities could exist inside of one reality, and an infinite number of these simulations could exist.
Simulation Theory has been entertained by many powerful scientists and philosophers. They argue that if it were possible for humans to create such a simulation, then perhaps we are already inside of one. It has been suggested that the limitations our world has (such as the speed of light) give reason to believe that we are inside of simulation.
The simulation may only be able to support information of certain types within various perimeters. Matter can only be so small, and light can only travel so fast. Matter can only be as small as atoms, light travels only up to a certain speed (299,792,458 m/s), and the plank length is the smallest possible unit of length. These might all be limitations of our simulation, and these limitations may differ between simulations.
Brain In A Vat
Brain In A Vat is a famous thought experiment that requires one to assume that there is an entire reality outside of yourself that you are not a part of. Consider for a moment that you are not actually a organic, biological, organism. Instead, you are a brain floating inside a vat of fluid that is connected to a machine meant to simulate your senses, experiences, and daily life. Everything you know to be true is actually just an idea created by your brain, which is being observed by viewers outside of your reality.
How would you, just a brain floating around in a vat, come to understand the nature of your reality? How would you figure out that you are really just a brain in a vat? If everything you experience through the world is through your five senses, and there is a sophisticated computer manipulating your brain to experience these sensations, would you know it?
First, consider something you know to be true. For example “I know that I am not a brain in a vat.” Now, consider that if you know that you are not a brain in a vat, then you KNOW that you are not a brain in a vat. However, you DO NOT know that you are NOT a brain vat. Thus, you do not know that you are not a brain in a vat.
Similarly, you could actually be an alien, or a human from the future, who possesses advanced technology that allows you to hook yourself into a machine which simulates different lives. You hook yourself into this machine, and you experience the life that you are currently leading from birth until death. When it’s over, you are back in the future. While it feels like you have just lived an entire lifetime, only minutes have passed in your world.
See also: Boltzmann Brain.
Hologram Theory
An idea proposed by Leonard Susskind suggests that our world is actually just an intricate hologram. Considering that most of our mathematical laws and physics knowledge are described in 2-D rather than 3-D, it is a possibility that all of our 3-D reality is actually just a projection on a 2-D surface. This is similar to how 3-D televisions work, with two-dimensional objects being projected with added depth and curvature in order to make them appear three-dimensional. It is now suggested that there could be infinite dimensions, each one more complex than the last. The dimensions are nothing but a hologram, projecting all of the realities from all of the dimensions below them onto a “screen”.
According to Brent Swancer for Mysterious Universe, “the [hologram] idea is attractive in that it could explain some discrepancies seen between quantum physics and general relativity, as well as the unusual behavior of the universe in its early days after the big bang.”
The Hologram Theory makes some calculations and theories of the universe easier, and some researchers have even claimed to have captured possible evidence that it is real. One study published in 2017 for Physical Review Letters [Source?] claimed that observational evidence of the universe being a hologram was found in the cosmic microwave background, which is a sort of white noise and glow left over from the big bang.
See Also: The Intriguing Holographic Universe Theory and Its Roots in Ancient Philosophy.
Hollow Earth Theory
Although this theory is mostly the stuff of conspiracy, folklore, and mythology, it is one that has been found across multiple religions and cultures, including Greek and Norse myths, Christianity, and Tibetan Buddhism. Although it is an ancient concept, often intertwined with explanations of the afterlife, credit for the idea is often given to an American physician named Cyrus Reed Teed. In 1869, after a bad electric shock during an experiment, Cyrus came to an epiphany that all life on earth existed within an inverted sphere and that the universe was spread out into the interior.
According to Teed, who outlined his ideas in the 1898 book, The Cellular Cosmogony [click to view PDF without ads], the universe lies within the hollow of a massive rock measuring 8,000 miles in diameter. Within this vast hollow we live our lives on the inner surface of the cavern, so when we look “up” we are actually looking deeper within the cavity rather than out. Around us are apparently three layers of atmosphere, comprised of air, hydrogen, and boron. At the center of this massive sphere is our sun, which we don’t see directly but rather perceive through its refraction at the top of our atmosphere.
To account for the obvious movement of the sun across the sky, Teed claimed that in this universe light could dramatically bend in curved trajectories to reach us. To explain night and day, he explained that half of the sun was dark and the other half light, and that its rotation between these two sides create night, day, and the seasons.
Multiverse Theory
Perhaps you’re familiar with the idea of parallel realities. There has been speculation that multiple different universes may exist in which anything could be possible. Dinosaurs roaming around with humans, space travel being common-place, or Germany winning WW2. You name it, it is all possible in the multiverse (Rick and Morty, anyone?). The Multiverse Theory suggests that there is more than just one universe, and perhaps there could billions.
Suppose you are faced with two decisions: Decision A and Decision B. What if instead of one reality, where you either make Decision A OR Decision B, there are actually billions of different realities, one in which you make Decision A, and one in which you make Decision B.
For every decision that you make or for every event that occurs, a new reality is formed that follows that timeline. There could also be a reality that contains all of the decisions and events that you didn’t make, and where certain events never even happened.
This idea gets really weird when you consider the implications: a universe could exist in which the Big Bang never happened, or one where humanity never evolved and/or came to be.
It also gets complicated. Imagine that this theory is real, and when you make a decision two different realities are formed: one in which you make Decision A, and one in which you make Decision B. Now imagine that making Decision A leads to you having to make another decision: Decision 1A or Decision 2A. Same with Decision B, but after making it, you are presented with Decision 1B or 2B.
Now there is a reality where you make Decision A, followed by Decision 1A, and all of the consequences of those decisions transpire. There is also a reality where you make Decision A, followed by 2A. THEN there are the realities where you make Decision B, as well as the realities where you make decision B followed by Decision 1B or Decision 2B. This goes on for infinity, growing more and more complex as decisions are made and events transpire.