The concept of 27 dimensions originates from string theory in physics. String theory aims to provide a unified description of all particles and forces in nature by modeling subatomic particles as tiny vibrating strings. The number of dimensions in string theory started at 26 in early formulations but has increased over time as theorists have expanded the theory. The most widely studied version today has 10 dimensions for the strings themselves and 22 dimensions describing other physical properties. While not all dimensions are spatial, together they are frequently described by physicists as constituting a 27-dimensional universe.
Background on String Theory
String theory arose in the 1960s and 1970s as physicists explored the shortcomings of quantum physics in describing the natural world. They found that modeling particles as one-dimensional strings rather than zero-dimensional points could avoid some mathematical dilemmas. By the mid 1980s, five consistent versions of string theory had been described with slightly different properties and particle contents. This theory requires strings to vibrate and interact in a 10-dimensional space, with 6 dimensions compactified or curled up at tiny scales. Superstring theory forms the basis for most string theory research today.
In the 1990s, theorists realized that the five string theories were actually different manifestations of a single underlying 11-dimensional theory. Each version represented a different way the 11 dimensions could be compactified down to 4 observable spatial dimensions. This unified theory was named M-theory. Research continues today to understand the mathematical structure and experimental predictions of M-theory as a potential “theory of everything.” The extra dimensions allow for novel solutions to longstanding problems in physics.
Development of 26 and 27 Dimensions
In early string theory formulations with 10 string dimensions, physicists focused on compactifying the strings down to 4 observable spatial dimensions plus time. The other 6 dimensions were wrapped up tightly at each point in space-time. This resulted in a grand total of 26 dimensions when combined with the 15 dimensions of supersymmetry and the 5 dimensions of the theoretical supergravity theory on which string theory builds.
As string theorists further developed the mathematics of compactification, they found even more dimensions were needed to support the compactified physics. Each possible shape and size of the 6 compactified dimensions requires its own dimensions to curve the strings through those spaces. In the late 1990s, physicists found they could derive all five string theories from a single 11-dimensional theory called M-theory compactified in different ways. M-theory combined with the hidden dimensions of the compactified strings brought the total count to 27 dimensions.
Spatial Dimensions vs. Mathematical Dimensions
It is important to understand that the 27 dimensions in modern string theory are not all directly physical or spatial dimensions. Eleven of the dimensions relate directly to the vibrating strings. Six of those eleven are the familiar spatial dimensions of length, width, and depth that we observe in our 3D world. The other 5 string dimensions are compactified at each point in space-time.
Sixteen of the 27 dimensions describe supersymmetry partners to the 11 string dimensions. Supersymmetry assigns a partner particle to every standard model particle to solve some mathematical problems. The remaining 4 dimensions are related to the structure of spacetime and interactions between strings. While complex mathematically, many of these extra dimensions are not directly physical in the traditional sense.
Description of the 27 Dimensions
Here is a brief overview of the make-up of all 27 dimensions in modern string theory:
11 Dimensions of M-Theory
- 3 spatial dimensions – length, width, height
- 1 time dimension
- 7 compactified dimensions
The 11 dimensions provide room for the vibrating strings to correctly reproduce properties of elementary particles and forces. 6 dimensions are the familiar spatial ones. 1 dimension is time moving forward. The other 4 are compactified dimensions curled up at tiny scales.
16 Dimensions of Supersymmetry
Each of the 11 dimensions above has a supersymmetric partner to create balance in the mathematical equations. This adds 11 more dimensions for a total of 27 in current theories.
4 Dimensions of Supergravity
Supergravity theory describes the interaction between gravitational force and supersymmetric particles. Adding the dimensions of supergravity to the strings and supersymmetry produces the 27 total dimensions.
Significance of the 27 Dimensions
The 27 dimensions fill out a picture of reality that could resolve longstanding problems in physics. Here are some of the key indications from 27 dimensions:
Unifies Quantum Mechanics and General Relativity
Two of the most fundamental theories of physics are quantum mechanics describing small particles and general relativity describing gravity and large objects like planets. But the math behind these theories does not work together. Having 27 dimensions could provide a framework to unify quantum mechanics and general relativity.
Predicts Elementary Particles
By modeling particles as vibrating strings, the extra dimensions give string theory a way to predict all of the different elementary particle masses and types. Other theories only put particles in by hand. String theory offers a mechanism to derive them mathematically.
Explains Properties of Particles
In addition to predicting the types of elementary particles, string theory relates particle properties like spin and charge to different vibrational patterns. Extra dimensions give room for strings to vibrate in ways that replicate the exotic properties of particles.
Incorporates Gravity
General relativity only applies gravity to particles modeled as single points. String theory adds gravity by relating strings to points. The interactions between strings naturally include a description of gravitational forces in the equations. Gravity emerges from strings extending through extra dimensions.
Solves Hierarchy Problems
One major issue in physics is explaining why gravity is so much weaker than other forces. Compactified extra dimensions provide a solution by diluting gravity’s effects. Gravity can propagate through the compactified dimensions while other forces are confined to 3D branes in the higher dimensional space.
Proposed Experiments to Detect Extra Dimensions
While the 27 dimensions are currently theoretical, physicists are working to design experiments that could detect signatures of extra dimensions. Here are some possible ways scientists hope to reveal physical evidence for higher dimensions in the coming years:
High Energy Particle Colliders
By colliding particles at high energies, some debris could be ejected into the compactified dimensions. This would appear to us as missing energy and momentum that escapes into the higher dimensional space. Upgrades to the Large Hadron Collider may allow it to reach high enough energies to probe extra dimensions.
Gravitational Wave Detection
Precise measurements of gravitational waves could reveal small deviations from 3D general relativity caused by higher dimensional effects. As detectors like LIGO improve, they may find signatures of gravitational echoes caused by gravity propagating through compactified extra dimensions.
Dark Matter Searches
Experimental searches for dark matter could potentially detect supersymmetric partner particles that are hidden from us in the folded extra dimensions. Any discovery of supersymmetric dark matter would provide indirect evidence of the extra spatial dimensions required by string theory.
Challenges and Criticisms of Extra Dimensions
While promising, string theory with extra dimensions faces criticism and unresolved issues among physicists as well. Here are some of the major challenges still to be addressed:
Highly Mathematical and Abstract
The theory relies on very advanced, abstract mathematics that is difficult for even most physicists to understand. The dimensions are more mathematical than directly physical, making the theory seem detached from reality in the view of some critics.
No Testable Predictions
Because the extra dimensions are compactified at tiny scales or mathematically abstract, string theory has not yet made any conclusive predictions that could be experimentally tested. This lack of testability has led some to question whether it qualifies as a scientific theory.
No Proof of a Single Unified Theory
While the five string theories can be unified mathematically in certain ways, there is no proof yet that there is a single fundamental theory accurately modeling all physical phenomena. The extra dimensions remain mathematically speculative.
Does Not Include All Forces
String theory has successfully incorporated gravity and modeled Standard Model particles and forces. However, it has not yet found a way to include the force of weak nuclear decay definitively within its framework.
Conclusion
The idea of 27 dimensions originates from string theory’s attempts to model particles and physical forces in aunified mathematical framework. The theory builds on 10 dimensions for vibrating strings plus up to 16 additional dimensions when including supersymmetry and aspects of supergravity theory. While not all 27 dimensions are directly observable spatial dimensions, together they could resolve major problems in physics if experimentally confirmed. Researchers continue working to find ways to test the higher dimensional signatures and predictions of string theory and M-theory. If proven to model reality accurately, 27 dimensions could indeed represent the ultimate unification of physics.