Most people know about string theory and loop quantum gravity. But there's a whole constellation of alternative approaches—brilliant ideas pursued by smaller research groups, each with its own radical take on spacetime.

1. Causal Dynamical Triangulations
Imagine building spacetime from tiny tetrahedra (3D triangles). CDT glues these together with one crucial rule: causality must be preserved. No going backward in time as you move between building blocks.

The stunning result? At large scales, a 4D de Sitter universe emerges spontaneously. But zoom in to the Planck scale and spacetime becomes effectively 2-dimensional—a "dimensional reduction" that might solve gravity's UV divergences.

2. Asymptotic Safety (Quantum Einstein Gravity)
What if gravity IS renormalizable, but we've been looking at it wrong? Weinberg proposed in 1979 that gravity might have a "non-Gaussian fixed point"—a special regime where quantum corrections don't blow up, but stabilize.

Recent work suggests Newton's constant and spacetime dimension both "run" with energy scale. At high energies, spacetime might be fractal with dimension ~2. No strings, no loops—just Einstein's equations taken seriously as quantum field theory.

3. Quantum Graphity
The most radical: spacetime doesn't exist fundamentally. Instead, points in a complete graph (where everything is connected to everything) undergo a phase transition as the universe cools.

High energy = total chaos, no spacetime. Low energy = graph "freezes" into local structure, and boom—geometry emerges. It's like water crystallizing, but for spacetime itself. Fotini Markopoulou calls it "geometrogenesis."

4. Tensor Models / Group Field Theory
Higher-dimensional generalizations of matrix models. Tensors encode quantum geometry, and their Feynman diagrams are dual to simplicial complexes—discrete spacetimes.

The breakthrough: a new "large N" expansion that's actually tractable. This connects to loop quantum gravity, allows rigorous renormalization, and suggests spacetime might be fundamentally random at the Planck scale.

What unites these approaches? They all predict:

• Planck-scale discreteness
• Dimensional reduction at high energies
• Background independence
• Spacetime as emergent, not fundamental

Sometimes the roads less traveled are where the real discoveries hide. ✨

#Physics #QuantumGravity #TheoreticalPhysics

In 2002, Lee Smolin wrote "Three Roads to Quantum Gravity" arguing YES—that strings and loops were different perspectives on the same underlying reality. Both predict Planck-scale discreteness. Both involve extended 1D objects. Both emerged from the same 1950s insight about field-string duality.

Then in 2006, he published "The Trouble with Physics"—essentially retracting that optimism. What changed?

Smolin realized the differences weren't just technical but philosophical. String theory requires a background spacetime (violating relativity's deepest lesson). LQG quantizes geometry itself. These aren't different languages—they're different claims about what reality IS.

The trajectory matters: from "these will converge" to "we need diversity of approaches." Sometimes the most honest thing a scientist can do is change their mind when the evidence shifts.

Maybe both theories are approximations of something deeper. Maybe they describe different regimes. Or maybe the universe doesn't care about our frameworks—"string" and "loop" are like "wave" and "particle," partial views of a reality that transcends both.

The question remains gloriously open. 🧵✨

#Physics #QuantumGravity #StringTheory #LoopQuantumGravity #Philosophy

Unlike string theory, LQG is background-independent (no pre-set spacetime) and works in 4D. Area and volume are quantized. Space has a granular structure. 🌌

#QuantumGravity #Physics

The Bilson-Thompson model proposes that particles in the Standard Model are literally braided structures in the quantum fabric of space itself. In Loop Quantum Gravity, spacetime at the Planck scale forms a network of quantum threads. Bilson-Thompson asked: what if different braid patterns ARE different particles?

• Electric charge = number of twists in the ribbons
• Color charge = different braiding patterns
• Particle identity = specific knot topology

It's a beautiful "road not taken" in physics—an attempt to unify matter and spacetime through pure geometry. While incomplete (only works for 1st generation fermions), it represents one of the most elegant attempts to bridge quantum gravity and particle physics.

Imagine: your body, the stars, everything—just different ways spacetime ties itself in knots. 🧵✨

#Physics #QuantumGravity #TheoreticalPhysics

It's unproven after 55+ years, but it's our hope that the universe remains predictable and deterministic. 🌌

#Physics #BlackHoles

Instead of inflation smoothing the universe, slow contraction before the bounce did it. No multiverse, no singularity, maybe no beginning at all. 🌌

#Cosmology

Instead of inflation smoothing the universe, slow contraction before the bounce did it. No multiverse, no singularity, maybe no beginning at all. 🌌

#Cosmology

Elegant but largely ignored—the road not taken in string theory.

#StringTheory

It doesn't exist in nature (our universe has positive curvature), but AdS/CFT made it the cornerstone of quantum gravity research. Sometimes the best lab is one nature didn't build. 🔬

#TheoreticalPhysics

It's not just mathematical—our universe is evolving toward de Sitter space as dark energy dominates. In the far future, we'll live in empty, exponentially expanding space. 🌌

#Cosmology #Physics

Wondering how many people use email not provided by google/microsoft such as proton.

#fedi #fediverse #email #gmail #protonmail

A 0-dimensional brane is a point-like object, a "pinpoint" in spacetime where strings can end.

They're like fundamental particles that help us model everything from M-theory to the quantum secrets of black holes.

#StringTheory #Physics #QuantumGravity #Science

❤️ General Relativity (rules the big cosmos 🌌)
❤️ Quantum Mechanics (rules the tiny particles ⚛️)

Their baby would be called Quantum Gravity, the ultimate Theory of Everything that could finally explain black holes!

#Science #Physics #Space #QuantumGravity

MOND successfully predicts galaxy rotation curves, the Baryonic Tully-Fisher relation, and other galactic phenomena without fine-tuning.

However, it faces challenges with galaxy clusters, cosmology (like the CMB), and Solar System tests, where it still requires some form of missing mass or refinement. Relativistic versions are in development to address these issues. #MOND #DarkMatter #Astrophysics #cosmology

https://t.co/QPeYdqGhaT