This article explores the concept of entropic gravity, a long-standing but minority view in physics that posits gravity is not a fundamental force but rather an emergent phenomenon arising from the growth of entropy, or disorder. It details a new argument by a team led by Daniel Carney, which presents two ad hoc models demonstrating how apparent gravitational attraction could result from microscopic interactions aiming to maximize entropy. These models, while currently only explaining Newtonian gravity, are significant as a proof of principle and for opening new avenues for experimental testing, particularly concerning quantum superposition and wave function collapse. The discussion highlights the theory's roots in black hole thermodynamics and contrasts it with the leading holographic principle, suggesting a re-evaluation of gravity's fundamental nature.
Exploring Entropic Gravity: Is Disorder the True Source of Attraction?
Historical Context & Emergent Gravity: The article begins by noting Isaac Newton's and Albert Einstein's dissatisfaction with gravity's nature, setting the stage for the persistent idea that gravity might be an "emergent" collective effect from deeper, microscopic physics, rather than a fundamental force.
Carney's Modern Hypothesis: Daniel Carney's team proposed a modern mechanical model where an unseen "gas" or "thermal system" randomly interacts with masses, causing the familiar gravitational effects we observe, such as planetary orbits.
Gravity as Entropy Rising: This approach, known as entropic gravity, posits that gravitational attraction stems from the same principles governing heat (thermodynamics)—specifically, the random jiggling and mixing of particles and the tendency for entropy (disorder) to increase.
Black Hole Thermodynamics Clues: Einstein's General Relativity predicts singularities in black holes and exhibits parallels to heat physics (e.g., black holes only grow, never shrink), suggesting that space-time itself might consist of microscopic components behaving thermally. Ted Jacobson's 1995 work further cemented this by deriving general relativity from the assumption of space-time's thermal properties.
Carney's Illustrative Models:
Qubit Lattice Model: In this model, space is filled with a grid of quantum particles (qubits). Masses polarize nearby qubits, creating pockets of order (low entropy). The system then pushes the masses closer together to contain this order in a smaller region, thereby maximizing overall entropy and mimicking Newtonian attraction.
Non-local Qubit Model: Without a physical grid, qubits interact such that their energy capacity depends on the distance between masses. Closer masses reduce qubit energy capacity, requiring more qubits to hold the system's total energy, leading to higher entropy and thus apparent attraction.
Strengths & Limitations: Carney acknowledges these models are "ad hoc," requiring fine-tuning, and lack independent evidence for the "qubits." Crucially, they only explain Newton's law of gravity (weak fields), not the strong-field regime of Einstein's General Relativity. Critics like Mark Van Raamsdonk express skepticism about their true connection to gravity.
Experimental Testability: A key takeaway is that these models, despite their limitations, open new experimental avenues. They predict that quantum fluctuations in very weak gravitational fields might become observable, and could be tested by experiments designed to investigate wave function collapse (e.g., those led by Angelo Bassi).
Broader Implications: While a "long-shot theory" compared to the leading holographic principle, entropic gravity is seen as a valuable alternative to explore. If proven correct, it would fundamentally change our understanding of gravity, suggesting it's not a fundamental law but a statistical tendency driven by entropy.