Is our universe a hologram? It may sound like a science fiction question, but it is actually a serious scientific hypothesis that has been explored by some of the most renowned physicists in the world. Let’s see what this idea means, why some physicists think it is possible, and what evidence they have found to support it.
The holographic principle is a conjecture that states that our universe can be described by a lower-dimensional theory that does not include gravity. It means that all the information about our three-dimensional space and time can be encoded on a two-dimensional surface, such as the boundary of our universe. Quite similar to a hologram with a three-dimensional image projected from a two-dimensional film.
But why would our universe be a hologram? One reason is that it could solve some of the puzzles of quantum gravity, which is the attempt to unify quantum mechanics and general relativity. Quantum mechanics describes the behaviour of subatomic particles and forces, while general relativity describes gravity and the curvature of spacetime. However, these two theories are incompatible with each other at very small scales or very high energies, such as near black holes or at the Big Bang.
The holographic principle could offer a way to reconcile these two theories by removing gravity from the picture and replacing it with quantum fields on a lower-dimensional boundary. In this way, we could understand quantum gravity as a kind of quantum field theory, which is well-established and mathematically consistent.
One of the most famous examples of the holographic principle is the AdS/CFT duality, proposed by Juan Maldacena in 1997. This duality states that a five-dimensional theory of anti-de Sitter space (AdS), which is a negatively curved spacetime with gravity, can be equivalent to a four-dimensional conformal field theory (CFT), which is a quantum theory without gravity on the boundary of AdS. This means that anything that happens in AdS can be translated into something that happens in CFT, and vice versa.
The AdS/CFT duality has been used to study various phenomena in physics, such as black holes, inflation, and entanglement. It has also inspired other versions of the holographic principle for different kinds of spacetimes, such as de Sitter space (dS), which is positively curved and resembles our expanding universe.
However, there are also challenges and limitations to applying the holographic principle to our universe. For one thing, we do not know if our universe has a boundary or what shape it has. For another thing, we do not know if there exists an exact lower-dimensional theory that can describe our universe without losing any information or introducing any inconsistencies. Moreover, we do not know how to test this idea experimentally or observationally.
Nevertheless, some physicists have claimed to find indirect evidence for the holographic principle by studying the cosmic microwave background (CMB), which is the oldest light in our universe left over from the Big Bang. They have argued that some features of the CMB can be explained by assuming that our universe is a projection from a lower-dimensional theory with fewer degrees of freedom.
Another line of evidence comes from Stephen Hawking’s final theory before his death in 2018. Hawking and his collaborator Thomas Hertog proposed that our universe is a hologram emerging from an entangled network of qubits on an imaginary time axis. They claimed that this idea could explain why our universe has low entropy and fine-tuned initial conditions for life.
In conclusion, whether our universe is a hologram or not remains an open question that fascinates many physicists and philosophers alike. It challenges our common sense notions of reality and invites us to explore new possibilities for understanding nature at its most fundamental level.
