What is the deepest level of reality? In this Quanta explainer, Vijay Balasubramanian, a physicist at the University of Pennsylvania, takes us on a journey through space-time to investigate what it’s made of, why it’s failing us, and where physics can go next.

Explore black holes, holograms, “alien algebra,” and more space-time geometry: https://www.quantamagazine.org/the-un...

00:00 - The Planck length, an intro to space-time
1:23 - Descartes and Newton investigate space and time
2:04 - Einstein's special relativity
2:32 - The geometry of space-time and the manifold
3:16 - Einstein's general relativity: space-time in four dimensions
3:35 - The mathematical curvature of space-time
4:57 - Einstein's field equation
6:04 - Singularities: where general relativity fails
6:50 - Quantum mechanics (amplitudes, entanglement, Schrödinger equation)
8:32 - The problem of quantum gravity
9:38 - Applying quantum mechanics to our manifold
10:36 - Why particle accelerators can't test quantum gravity
11:28 - Is there something deeper than space-time?
11:45 - Hawking and Bekenstein discover black holes have entropy
13:54 - The holographic principle
14:49 - AdS/CFT duality
16:06 - Space-time may emerge from entanglement
17:44 - The path to quantum gravity

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Quanta Magazine is an editorially independent publication supported by the Simons Foundation: https://www.simonsfoundation.org