A new theory suggests that gravity could possibly be the result of entropy. If true, this would mean that everything in the universe would fall apart if it all remained unchanged.
This theory tries to reconcile Einstein’s theory of general relativity (which sees gravity as a warping of spacetime) with quantum theory (which views the universe as being made of extremely small objects that can exist in particle or wave form).
It is possible that the theory could also allow for gravitational fields to be made of dark matter, which continues to elude us.
Entropy. The word itself should cause insomnia. It means that matter and energy will degrade—ultimately leading to chaos in the universe—if things are left alone. So why is a new theory suggesting that gravity could possibly emerge from entropy?
Yup, you read that right: quantum relative entropy may determine the action of gravity. This is what physicist and mathematician Ginestra Bianconi from Queen Mary University of London proposes in a new theory. There’s just one issue—for this to work, two theories that have forever been at odds with each other need to harmonize.
The idea of quantum relative entropy mashes up the clashing concepts of general relativity and quantum theory. Einstein’s theory of general relativity sees gravity as the curvature or warping of spacetime by an object, with more massive objects having a greater effect on the spacetime surrounding them. For example, the Sun is 330,000 times the mass of the Earth. As a result, our planet is orbiting within the huge distortion in spacetime that the Sun’s enormous presence has caused, like a quarter rolling around one of those oversized funnels.
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Quantum theory, on the other hand, views the universe as being made of extremely small objects (think subatomic particles) that act as both particles and waves. Particles are minuscule pieces of matter, while waves are disturbances that transfer energy. According to quantum mechanics, the universe is described on micro and nano scales. Relativity is the opposite, in the sense that it describes matter on cosmic scales.
Finding a way to connect general relativity and quantum mechanics has proved to be an enduring headache for scientists. To that end, enter Bianconi’s theory. She posits that spacetime is actually a quantum operator, meaning that it acts on quantum states to turn them into different types of quantum states. Quantum entropy quantifies (no pun intended) how much disorder or unpredictability is in the state of something, which helps distinguish between two quantum states. Bianconi, in her work, found that she could use it to describe how spacetime and matter interact.
“Gravity is derived from an entropic action coupling matter fields with geometry [of spacetime],” she said in a study recently published in Physical Review D.
By allowing quantum entropy to describe differences between matter and spacetime, Bianconi’s theory modifies general relativity by first giving the fabric of spacetime low energy and a small curvature, and then by predicting a small cosmological constant (which explains how much and how fast the universe is expanding).
The new theory also incorporates a G-field, or gravitational field. G-fields are vector fields—which means they have both magnitude and direction—that explain how space is influenced by an object. Bianconi uses the G-field as what is known as a Lagrangian multiplier, which finds the maximum and minimum of a function. Waves, which are one of the two quantum states, are described by a wave function. Finding the maximum and minimum of a wave function with a G-field could reconcile quantum theory with general relativity.
If the clash between the theories is finally resolved, you end up with quantum gravity, which would exist in particle and wave form.
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That said, gravity existing in particle form raises another question. Dark matter is made of particles, but the nature of those particles remains an enigma, since they have never been directly observed. Bianconi thinks that, if gravity can exist as particles, the G-field might offer an explanation for dark matter.
“This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter,” she said in a press release.
There’s still a lot of work that needs to be done before this idea is anywhere near confirmed. But, there’s a chance that chaos brings about gravity, which in turn might, in one form, possibly be dark matter. Mind blown.
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Elizabeth Rayne is a creature who writes. Her work has appeared in Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.