Why the Sky Is Not Real-Time | Leonard Susskind

Описание: When we look up at the sky, it feels immediate. Stars shine, planets glow, and the universe appears to unfold in front of us as if we were seeing it live. But physics tells a very different story.

In this video, we explore why the sky is not real-time.

Light takes time to travel. Even the closest celestial objects are seen with delay, and distant stars appear as they were years, centuries, or even millions of years ago. What we experience as a single, coherent sky is actually a patchwork of information arriving from different moments in the past.

Drawing on ideas associated with Leonard Susskind, this video explains how observation in the universe is never instantaneous. The sky is not a live feed of reality — it is an archive. A layered record of events spread across time, stitched together by our perception into something that feels immediate and continuous.

Relativity deepens this picture. Different observers do not agree on what “now” means, and there is no universal present shared across the cosmos. The idea of a real-time universe is not just impractical — it is physically meaningless.

This documentary-style exploration avoids equations and focuses on intuition, revealing why the night sky feels real-time even though it never is. The universe does not present itself to us directly. It delivers information slowly, unevenly, and out of sync.

Understanding this changes how we think about reality, observation, and what it truly means to see something in the universe.