Theory of Everything
by Petr Chylek (December 2025)
Since the beginning of String Theory [1] in the 1960s, hundreds, perhaps even thousands, of physicists have specialized in this area. The theory suggests that what are called elementary particles are actually tiny vibrating strings. The need for the self-consistency of String Theory requires a ten- or eleven-dimensional space. Among other implications, this points to the existence of many universes similar to ours, leading to the concept of a multiverse.
Although the general public is familiar with the idea of multiple universes from popular articles and lectures, physicists remain uncertain about it. Many support the concept of the multiverse, while others question whether it belongs to physics. Some view the multiverse as existing at the boundary of physics, philosophy, and religion.
Before String Theory, particle physics research mainly focused on the quark model developed from the works of Murray Gell-Mann and George Zweig [2]. What were considered to be “elementary particles” at the time were actually composite particles made of smaller units called quarks. This led to the development of the “Standard Model” [3] of elementary particles. The model was quite successful; it explained the existence of most observed particles and their interactions. The latest addition to the model was the discovery of the Higgs boson in 2012 [4], for which Peter Higgs received a Nobel Prize in physics in 2013.
In nature, there are four fundamental forces: gravity, electromagnetism, and the weak and strong nuclear forces. Shortly after the Big Bang, there was only one force. However, as the initial high temperature quickly decreased, the original force split into the four forces we observe in the universe today. Three of these forces (electromagnetic, weak, and strong nuclear forces) are explained by current quantum field theories, while the fourth force, gravity, is described by Einstein’s theory of general relativity.
Most physicists believe that all of nature should be described by a single equation or law that explains all phenomena across every dimension, from the submicroscopic level of elementary particles to cosmic phenomena like galaxies and black holes. Although physicists have spent more than a hundred years trying to develop “the theory of everything,” they have yet to succeed. They still need to develop a theory of quantum gravity that can be integrated with the other three forces at work in the universe.
The fact that physicists have not succeeded so far does not mean they haven’t tried. String Theory is an example. The hypothesis is that elementary particles are tiny strings, about 10-35 cm, which is 0.000…01 cm, with 34 zeros before the final 1. Strings of different lengths, diameters, and shapes vibrate at various frequencies, producing the observed particles and their interactions. To be mathematically consistent, the theory requires a nine-dimensional space plus time. The three spatial dimensions correspond to the space we observe, while the remaining six spatial dimensions are compactified into a tiny volume, rendering them unobservable.
In general, abstract spaces with more than four dimensions, three spatial dimensions plus time, have been used in mathematics and physics for a long time to develop methods that produce results where four-dimensional space would not suffice.
How well has String Theory been supported by evidence? The theory has achieved some successes, including the emergent graviton, a particle with zero mass responsible for gravity. The point is that the graviton does not need to be added to string theory; it naturally emerges from it.
String Theory has experienced several failures and updates. Currently, the latest version, called M-theory [1], exists within 10-dimensional space plus time. Instead of vibrating one-dimensional strings, it involves vibrating multidimensional membranes. One version of M-theory suggests that our universe is actually a three-dimensional vibrating membrane. Only time will tell if M-theory produces observable effects that can confirm or reject it.
In the 1960s, while I was an undergraduate in the Department of Theoretical Physics at Charles University in Prague, I was deeply fascinated by the beauty of quantum mechanics. A simple equation, the Schrödinger equation, could explain many of the phenomena we observe in the world. However, I was also disappointed that, even though many variables were quantized, space and time were considered continuous.
Back then, I developed a simple model where both space and time were quantized. I wrote a paper about it and submitted it to Nature in 1965 or 1966, which was then, and still is, one of the most respected science journals. The editor sent the manuscript to several experts for review. About a month later, I received two reviews. One reviewer pointed out that the model was too speculative and couldn’t be verified experimentally. The report from the second reviewer was more interesting. He stated that Aristotle (384-322 BC) had already considered quantization of time and rejected the idea. Based on these two reviews, the editor of Nature rejected the paper.
I searched for Aristotle’s writings, and in fact, he considered the possibility that space and time might be quantized. He reasoned that if they are quantized, there could only be one speed of motion. Aristotle argued that because we observe objects moving at different speeds, the model is flawed and must be dismissed. Therefore, he concluded that space and time are not quantized but continuous.
Here, I should clarify the difference between continuous and quantized variables. Consider a line and select two arbitrary points, A and B, on it. If the line is continuous, there are always an infinite number of points between A and B, no matter how close together the two points are. If the line is quantized, there are always only a finite number of points between the chosen pair of points A and B.
In the model I submitted to Nature, I also concluded that only one nonzero velocity exists. In my interpretation, however, an object can either move at that specific velocity or stay at rest. The velocities we observe are then averages over the time intervals when an object moves at a particular velocity and when it remains at rest. This way, any observed velocity of real objects can be achieved.
The quantized nature of time suggests that our universe exists only at specific moments and is absent in the intervals between them. Our universe vanishes many times each second and is then immediately recreated. Due to our senses, it appears to us to exist continuously. This is similar to old movies that projected about 25 images per second onto a screen; because of the limitations of our senses, we perceive continuous movement.
If our universe only exists at specific moments in time, then other universes could exist in the same space in time between those moments. In fact, there is room for an infinite number of universes to exist at different times within the same physical space as ours. The idea of multiple universes with quantized time becomes more significant with the discovery of dark matter. Dark matter is defined as mass detected in our universe through its gravitational force, but which has not been seen to emit or interact with electromagnetic radiation (light). In other universes, we can assume similar forces exist as in our universe. Gravity is the only known long-distance force. It might “leak” into neighboring universes, affecting masses in those universes through gravitational interactions. This could explain the origin of dark matter.
We can better understand the concept of multiple universes sharing the same space by considering a similar, though imperfect, analogy. Imagine a movie screen where two old black-and-white films are projected simultaneously. However, one film is projected with red light and the other with green light. Two people sit side by side, watching the screen. One wears red glasses, and the other wears green glasses. They both look at the same screen at the same time but see different movies.
Similarly, in our three-dimensional space, different universes can exist at various moments in the quantized time. This is just a rough idea. However, many breakthroughs in physics began as unusual concepts, which, after years, evolved into workable models. So, we just have to wait.
Notes
[1] S. Gubser, The Little Book of String Theory, Princeton University Press, Princeton, New Jersey, 2010.
[2] Quark Model, Wikipedia, https://en.wikipedia.org/wiki/Quark_model.
[3] Standard Model, Britannica, https://www.britannica.com/science/standard-model.
[4] What is “God’s Particle?”, New English Review, March 2025.
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Petr Chylek is a theoretical physicist. He was a professor of physics and atmospheric science at several US and Canadian universities. He is an author of over 150 publications in scientific journals. He thanks Lily A. Chylek for reading the earlier version of this article and for her comments and suggestions.