The colored circle represents the hologram, out of which the knotted optical vortex emerges. Credit: University of Bristol
How might a holographic connection reveal deeper insights into our universe? A quarter century ago, physicist Juan Maldacena proposed the AdS/CFT correspondence, an intriguing holographic connection between gravity in a three-dimensional universe and quantum physics on the universe’s two-dimensional boundary. This correspondence is at this stage, even a quarter century after Maldacena’s discovery, just a conjecture.
What are the implications of this connection? It’s a statement about the nature of the universe that seems to be true, but one that has not yet been proven to actually reflect the reality that we live in. And what’s more, it only has limited utility and application to the real universe.
Yet, the mere appearance of the correspondence is thought-provoking. It indicates that there is something deeply fundamental to the hologram, that the physics of the volume of the universe might just translate to the physics on the surface, and that there is more to be learned there.
These insights are far from just mathematical tricks. While it’s normal to cast problems of physics in a new language, the AdS/CFT correspondence is so much more than a mathematical curiosity.
How does it relate to gravity? Remember that the essential goal here is to describe gravity, which for centuries we believed to be just another force of nature. But gravity does stand alone and unique among all the forces, even beyond its quantum intractability.
Why is gravity so significant? Kepler, Newton, and Einstein made critical contributions here. Kepler discerned something special about the motions of the heavenly objects and Newton labeled it a force, while Einstein cast gravity not in terms of pushes and pulls, but in terms of the very fabric of spacetime itself.
So, what does the holographic principle teach us about gravity? The holographic principle, whether applied to the surface of a black hole and its mysterious contents or the relationship between string theory and quantum physics, is telling us something meaningful about gravity. But Einstein already taught us what gravity is, it’s no mere force, but the natural response we living entities experience when we encounter the bends and wrinkles of spacetime.
Ultimately, gravity is much more than just a force. Gravity is the spacetime playground that we all exist within. Another name for general relativity is geometrodynamics—the dynamics of geometry itself. Gravity is space and time and matter and energy all rolled into one breathing
