Hubble's Discovery of the Expanding Universe
📌 Edwin Hubble concluded the universe was expanding by observing that light from distant galaxies was red-shifted.
🌌 Red-shifting of light, explained by the Doppler effect, indicates that all observed galaxies and stars were moving away from Earth.
🧠 This observation implies that everything in the universe is moving away from everything else, not that Earth is the center.

The Balloon Model Analogy
🎈 The balloon represents the space within the universe, and spirals drawn on it represent galaxies.
⬆️ As the balloon is inflated (representing cosmic expansion), all spirals move away from each other simultaneously.
📏 The model demonstrates that the **space *between* galaxies stretches**, causing the observed redshift of light from distant objects.

Key Points & Insights
➡️ Hubble's conclusion stems from the consistent red-shift observed in light from virtually all visible galaxies.
➡️ The stretching of space itself is the mechanism causing galaxies to recede from one another, analogous to points moving apart on an expanding surface.
➡️ The observation supports the model where the entire universe is expanding, with no single central point of origin for the expansion.

📸 Video summarized with SummaryTube.com on Nov 11, 2025, 11:19 UTC