For more than a century, one of cosmology’s biggest paradoxes has remained unresolved: if the second law of thermodynamics says the Universe is becoming increasingly disordered, how did it produce galaxies, stars, planets—and ultimately life?
A new theoretical study by Professor Ginestra Bianconi of Queen Mary University of London proposes a possible answer. Published in Physical Review D, the research suggests that the apparent contradiction disappears when scientists distinguish between the Universe’s total entropy and its local entropy density.
Under the proposed framework, the Universe can become more complex in localized regions even as its total entropy continues to increase, potentially offering a new perspective on one of physics’ most enduring mysteries.
What Is the Entropy Puzzle in Cosmology?
The second law of thermodynamics is widely regarded as one of the most fundamental principles in physics. It states that the total entropy—or the measure of disorder or the number of possible microscopic arrangements—in an isolated system tends to increase over time.
Albert Einstein famously underscored its importance, writing:
“The second law of thermodynamics occupies a unique position among the laws of Nature.”
Yet the observable Universe appears to tell a different story.
Following the Big Bang, matter gradually assembled into increasingly sophisticated structures. Simple clouds of gas evolved into galaxies, stars, planetary systems, and eventually living organisms capable of consciousness and technological civilization.
This raises a longstanding question: How can complexity increase if entropy is always supposed to rise?
Physicists have long argued that these developments are not necessarily incompatible because entropy can increase overall while local pockets of order emerge. However, explaining exactly how that happens remains an active area of theoretical research.
A New Theory Reimagines Gravity
Professor Bianconi approaches the problem through a framework known as Gravity from Entropy (GfE).
Rather than treating gravity as a fundamental force in the traditional sense, GfE proposes that gravity emerges from the statistical behavior of microscopic degrees of freedom embedded within spacetime itself.
The theory draws on concepts from:
- Statistical mechanics
- Information theory
- Quantum gravity
- General relativity
- Thermodynamics
In essence, gravity is interpreted as an emergent phenomenon arising from the way information is organized within spacetime.
How Does Gravity from Entropy Work?
Central to the theory is the idea that spacetime can be described using two interacting geometric metrics.
One metric represents the physical geometry of spacetime, while another is associated with matter fields and spacetime curvature.
The relationship between these two metrics is quantified through a mathematical quantity called Quantum Geometric Relative Entropy (QGRE).
Rather than simply measuring disorder, QGRE measures the informational difference between the two spacetime descriptions.
Within the theory:
- Gravity emerges from the interaction between these metrics.
- At low energies, the equations reduce to Einstein’s General Relativity.
- Under extreme conditions, new gravitational behavior appears.
This makes the framework compatible with well-tested physics while allowing room for new predictions.
The Key Finding: Total Entropy and Local Entropy Behave Differently
The study’s most significant result comes from analyzing the thermodynamic behavior of an expanding Universe.
Using the standard Friedmann–Robertson–Walker (FRW) cosmological model, Professor Bianconi found that two seemingly contradictory things can occur simultaneously:
- The Universe’s total entropy increases over time.
- Entropy per unit volume decreases as space expands.
This distinction may help resolve the apparent paradox.
As the Universe expands, its overall volume grows dramatically.
Although the total amount of entropy continues increasing—as required by the second law—the entropy contained within each individual unit of space becomes progressively smaller.
That reduction in local entropy density may create conditions favourable for increasingly organised structures to emerge.
In other words, global disorder and local organisation are not mutually exclusive.
What Role Does Dark Energy Play?
The Gravity from Entropy framework also naturally produces a dynamic dark energy component.
Unlike the cosmological constant in Einstein’s equations, which remains fixed, this dark energy evolves over time.
Within the theory, the dark-energy contribution functions as a form of internal thermodynamic energy.
The model also generates:
- Effective temperature
- Effective pressure
- Local entropy
- Thermodynamic evolution equations
Together, these quantities suggest that spacetime itself may possess an intrinsic thermodynamic character.
If future observations detect signatures consistent with a changing dark energy component, they could provide a way to experimentally evaluate aspects of the theory.
Building on Decades of Research
The proposed framework builds upon ideas first developed in the 1970s.
Physicists Jacob Bekenstein and Stephen Hawking demonstrated that black holes possess entropy and emit thermal radiation.
Those discoveries fundamentally changed scientists’ understanding of gravity by revealing deep connections between:
- Information
- Thermodynamics
- Quantum mechanics
- Spacetime geometry
Gravity from Entropy extends those concepts by proposing that gravity itself emerges from informational properties of spacetime.
Can This Explain the Emergence of Life?
The study does not claim to explain how life originated.
Instead, it proposes a theoretical mechanism through which increasingly complex structures could arise naturally within an expanding Universe that still obeys the second law of thermodynamics.
If local entropy density decreases while total entropy rises, the formation of ordered systems—from galaxies to biological organisms—may become easier to understand within a unified physical framework.
The theory therefore addresses one of cosmology’s central conceptual challenges: reconciling irreversible thermodynamic evolution with the emergence of complexity.
Can Scientists Test the Theory?
At present, Gravity from Entropy remains a theoretical proposal rather than an experimentally confirmed model.
However, unlike many speculative quantum gravity ideas, it may eventually generate observational predictions.
Potential areas for future testing include:
- The evolution of dark energy
- Cosmological expansion history
- Deviations from General Relativity under extreme conditions
- Large-scale structure formation
Whether these predictions can distinguish GfE from existing cosmological models remains an open question.
Why This Research Matters
Modern physics is built upon several remarkably successful theories, but they remain difficult to reconcile.
General relativity describes gravity exceptionally well on cosmic scales.
Quantum mechanics governs microscopic particles with extraordinary precision.
Thermodynamics explains the irreversible flow of time through entropy.
Yet no single framework fully unites all three.
Professor Bianconi’s work attempts to bridge these disciplines by suggesting that gravity itself may emerge from the statistical and informational properties of spacetime.
If the framework proves mathematically robust and experimentally testable, it could offer new insights into why the Universe became increasingly structured while remaining consistent with one of physics’ most fundamental laws.
For now, the proposal remains an intriguing addition to ongoing efforts to understand how complexity, gravity, and the arrow of time are connected.
