7/11 Some VSL models suggest c varies with local gravitational potential—light moves slower in stronger gravity. This could explain galactic rotation curves AND gravitational lensing without dark matter! But changing c has profound implications for every physical law and constant.

8/11 ⚙️ MOG (Modified Gravity - Moffat's Theory)

John Moffat's MOG adds a new vector field to gravity (like electromagnetism for mass) plus a massive scalar field. At large scales, this effectively increases gravitational strength—mimicking dark matter's effects without actual dark matter.

9/11 MOG has had impressive successes: it fits galaxy rotation curves, cluster dynamics, gravitational lensing, AND cosmological structure formation—all without dark matter! The theory makes specific predictions about graviton behavior that future experiments might test.

10/11 🏋️ MASSIVE GRAVITY

What if the graviton—the hypothetical particle carrying gravity—has a tiny mass? Standard GR assumes massless gravitons, but a small mass (< 10⁻³² eV) would modify gravity at cosmic scales while leaving solar system tests intact.

Massive gravity could explain cosmic acceleration (dark energy!) without a cosmological constant. At distances larger than the graviton's Compton wavelength, gravity weakens, causing the universe's expansion to accelerate. No mysterious vacuum energy needed!

11/11 🌀 DSR (Deformed Special Relativity)

What if spacetime symmetries are ALMOST, but not quite, what Einstein thought? DSR introduces a fundamental length scale (the Planck length) alongside the speed of light, deforming Lorentz transformations at extreme energies.

In DSR, the speed of light might be constant, but energy-momentum relationships get modified at Planck scales. This could resolve some quantum gravity puzzles and predicts observable effects: high-energy photons from distant gamma-ray bursts might arrive at slightly different times.

BONUS: What connects these theories?

• Willingness to modify sacred cows (Newton, Einstein, even c!)
• Motivated by real observational puzzles
• Make testable predictions
• Remind us: when observations don't match theory, BOTH sides deserve scrutiny

The dark matter vs modified gravity debate isn't settled. We might need both. Or neither might be quite right. That's what makes this science exciting! 🔭

#Physics #Gravity #DarkMatter #Cosmology #TheoreticalPhysics