Exploring Hidden Dimensions with Brian Greene

The multiverse is an overarching concept for any reality where our world is not the entirety of existence. The many-worlds hypothesis, derived from quantum mechanics, is a specific type of multiverse where every possible outcome of a quantum measurement is realized in its own distinct universe. This interpretation suggests that the universe doesn't 'split,' but rather the mathematical description allows for the language of multiple worlds when a single definite reality is observed by individual 'versions' of an observer.

Brian Greene clarifies this distinction, explaining that the many-worlds hypothesis emerged from Hugh Everett's 1957 interpretation of Schrödinger's mathematics, which forbids a transition from many possibilities to a single outcome.

String theory, which posits that fundamental particles are tiny vibrating strings, inherently requires 10 or 11 dimensions for its mathematical consistency. These extra dimensions are not arbitrarily added but are 'forced upon' the theory by its equations. The reason we don't perceive them is theorized to be their incredibly small, curled-up nature, similar to how a thin straw appears one-dimensional from a distance but has a curled-up circular dimension.

Greene states, 'There's an equation in string theory that basically looks like d the number of dimensions minus 10 times this complicated factor must be equal to zero for this theory to be self-consistent... Therefore, d must equal 10.'

A groundbreaking idea in theoretical physics suggests that quantum entanglement—where two particles are subtly linked regardless of distance—is equivalent to wormholes. This means that the quantum link between distant particles literally represents a shortcut through the fabric of space. Furthermore, these wormholes may constitute the very substrate of space itself, implying that if quantum entanglement were severed, the fabric of space would 'pulverize' and fall apart.

Greene attributes this idea to Lenny Susskind and Juan Maldacena, explaining that 'that quantum link may be nothing but a wormhole yielding a shortcut through the fabric of space that in some sense makes them very close to each other.' He adds that physicist Mark Van Raamsdonk showed that 'if you cut the quantum entanglement, the fabric of space pulverizes.'

Initially, Stephen Hawking's calculations suggested that black holes destroy information, contradicting a fundamental principle of quantum mechanics. However, later work, largely driven by string theory, indicates that information is preserved. It is believed that information about objects falling into a black hole leaves a subtle quantum 'residue' or 'imprint' on the event horizon, which can then be recovered through the Hawking radiation.

Greene states, 'just about everybody including Hawking before he passed away agrees that we believe the information does come out.' He explains the holographic principle: 'Things fall into a black hole and we believe that they leave on the surface in some sense a copy, a residue of their information and that's how it can come back out.'