by Dhrubo Neel
People yearn to understand the universe’s greatest mysteries. Here’s the conundrum, though: mysteries don’t exist in the cosmos itself. It doesn’t want to come out as mysterious or dramatic. That’s just the way things are: what exists, exists; what doesn’t, doesn’t. There is another (perhaps several) dimension between existence and non-existence that is closed off and uncharted. The gray door between light and darkness is now being peered at by modern science. The U.S. Department of Energy’s Dark Energy Spectroscopic Instrument (DESI) may have recently found a key to that door. It made a novel observation in April: the first compelling observational evidence for string theory, which holds that the entire cosmos is composed of microscopic vibrating strings.
However, at the same time that this revolutionary assertion was being made, researchers using the Large Hadron Collider (LHC), the most potent particle detector in the world, made hints about the potential finding of a hypothetical particle called the pentaquark. Its presence could undermine the fundamental tenets of string theory if it is demonstrated.
Prior to Pulling the Strings
We must face some weird facts about the subatomic realm before delving into string theory—facts so strange that our vocabulary frequently falls short of adequately describing them.
One example is “spin.” An electron’s spin is completely different from what we imagine when we think of a spinning football. According to quantum theory, observation is not the same as seeing. It indicates something more akin to a photon colliding with another, producing quantifiable consequences.
Many people attempt to explain gravity by comparing it to a heavy ball on a stretched sheet. This is a simple metaphor, but it is ultimately simplistic. Despite our common perception, space-time is not a sheet. It is more akin to an ultra-fine, massless, chargeless, invisible cosmic soup that reacts to mass.
We see little colored balls when we think of atoms, electrons, and protons, or the quarks inside protons. We were instructed in this manner. Naturally, we imagine tiny, trembling threads when we learn that these particles might truly be vibrating, one-dimensional strings.
We are also confused by time. In space-time, “time” conjures up the image of a ticking clock. However, the time in space-time is not consistent. The ticking rates of a mechanical clock near a black hole and on Earth would be drastically different. The curvature of the surrounding space determines how time flows.
Let’s talk about string theory.
Take an apple, please. Complex molecules are what we get when we break it down. Reduce those to atoms. Divide atoms into protons, neutrons, and electrons. Three quarks are found inside protons. But what’s on the other side? This is when the idea of vibrating strings enters the picture.
To create distinct particles, these microscopic strings vibrate in various ways. All stuff, from you and me to Neptune and the Andromeda galaxy, is a representation of various string vibrations, just as loosely connected carbon atoms produce graphite and securely bonded carbon atoms form diamonds.
However, these strings need additional dimensions—beyond the three we now know plus time—in order to be mathematically feasible.
The Maze in Eleven Dimensions
Math demonstrates that three spatial dimensions and one time dimension are insufficient to adequately characterize string creation. Eleven is required.
Think of it as a cosmic bedsheet. It appears two-dimensional to the unaided eye, but upon closer inspection, minute folds—hidden additional dimensions—are visible. Only with the help of those folds can strings vibrate correctly and create the particles we see.
No other theory has been able to bring together general relativity, which describes the grandest cosmic phenomena, with quantum mechanics, which rules the smallest particles, if string theory is right. It might potentially provide a quantum explanation for gravity. Our understanding of the ocean may be improved by studying a single water molecule.
The hitch is that string theory is limited to equations. These strings have not been “seen” by us. Strings cannot be detected in the same way as photons or electrons. Even our most potent detectors cannot detect them because they are too little and unusual. Scientists are searching for indirect proof because of this.
What Was Seen by DESI?
DESI studies the expansion rate of the universe and produces a 3D map of it. It discovered something strange one day in April: the pace of expansion of the cosmos is decreasing with time.
This slowdown is consistent with the predictions of string theory. Space-time would expand more slowly if it were actually composed of vibrating threads. DESI found just that, making it the most compelling observational support for string theory to yet.
We need to travel to quantum space-time to understand this. According to quantum field theory, excitations in unseen fields give rise to particles. For example, particles are given mass via the Higgs field.
String theory states that these fields contain microscopic vibrating threads. A “vacuum” is actually full with almost immobile strings rather than being empty. We refer to these variations as quantum fluctuations.
Therefore, imagine space as a huge, motionless ocean. Tiny waves can be seen in certain areas, but in others the water is so motionless that it appears to be nonexistent, although it is.
The graviton, a hypothetical particle that carries gravity, is one kind of ripple from these strings. However, this graviton throws the calculations into disarray in standard quantum field theory, leading to infinities and equations breaking.
String theory excels in this situation. Particles in string theory are small loops that resemble vibrating rubber bands rather than points. The mathematical traps of infinite density or energy are avoided by these strings.
Furthermore, out of all the vibration patterns predicted by string theory, one sticks out because it is similar to the graviton’s characteristics: massless, light-speed, and spin-2.
Consider a tensioned guitar string. Despite appearing motionless, it has potential energy. It vibrates when lightly touched, creating sound. The graviton is the “sound” in string theory, and the string is the source of gravity.
Stars and other massive objects continuously release gravity waves, therefore they don’t require a pluck. Scientists are more confident that something resembling the graviton might exist after detecting these gravitational waves.
However, the Argument Isn’t Over
String theory is still theoretical—just ink on paper—despite everything adding up. A novel concept has surfaced in the meantime: the pentaquark, a fictitious five-quark particle. It could completely refute string theory if it exists.
By colliding protons, scientists at the LHC are actively looking for this particle.
Supersymmetry, the idea that every particle has a partner (bosons have fermions and vice versa), is also essential to string theory. However, there has never been a supersymmetric partner found.
The beauty of science, however, is that although confirming a theory is a significant event, refuting it can also be revolutionary.
The search for the truth goes on regardless of whether the thread breaks or endures.
Dhrubo Neel is a writer, lives in Dhaka, Bangladesh.
dhrubonil@yahoo.com, +8801976324725