Some Words About Quantum Physics
Quantum Theory as a means to describe Nature on an atomic level is a powerful tool. But it is incomplete as a description of the world, because it can be used to predict only events that have a quantum outcome.
The most elementary particles, the building blocks of all matter we observe in our universe, are governed by quantum theory. What we observe at higher levels of complexity are also quantum effects – atoms and molecules are made up of electrons and nuclei, which themselves are made up of quarks and gluons.
Our reality seems to be dominated by quantum processes and is often referred to as the “quantum world” or “quantum reality”. However, there is no such thing as quantum reality. Nature is described by physical laws that need not be quantized in order to exist. Quantum theory is therefore a tool, which provides a description of the microscopic world, but not of the whole reality.
A recent paper published in Nature Communications by CERN scientists proposes that quantum theory can be applied to describe the dynamics of gravity, and thus offer a new perspective on Einstein’s theory of general relativity. However, this does not mean that quantum physics describes our universe in its entirety. It is merely a new way to look at how gravity behaves at small scales.
Time to rethink Einstein?
This proposal is based on a conceptual framework called emergent gravity, which was introduced over 20 years ago by Erik Verlinde from the University of Amsterdam. Emergent gravity rests on two pillars: firstly, general relativity as we know it is an incomplete theory because it describes only the big picture, and secondly, gravity is emergent.
In this case, “emergent” means that it is a property of the whole system and cannot be described in terms of the properties of its parts. For example, the temperature is an emergent property of a pot of water or steam that cannot be described in terms of its individual molecules (in fact it cannot even be defined at the molecular level).
In Verlinde’s theory, gravity emerges from the entanglement between all particles in the universe. It originates from entropy – a quantity that can never decrease – which he first identified as a fundamental property of space-time geometry. Entropy increases with time because it corresponds to information being lost forever by not being accessible anymore. It can also be understood as the number of possible microscopic configurations of a system.
Entropy increases with time because it corresponds to information being lost forever by not being accessible anymore. It can also be understood as the number of possible microscopic configurations of a system.
Entanglement is one of the most intriguing properties of quantum physics. For two particles to be entangled, they must have interacted in the past, and when measured today, their quantum states will depend on each other, even if they are far apart in space and time. Entanglement is therefore not limited by either distance or time: its effects are instantaneous and don’t weaken with distance. For example, if two people separated by thousands of kilometers are entangled, then whatever happens to one immediately affects the other – no matter how far apart they are.
Verlinde’s theory is based on the idea that gravity is not a fundamental force of Nature, but rather an emergent phenomenon.
The paper published in Nature Communications proposes that quantum theory can be used to describe the dynamics of gravity, and therefore offers a new perspective on Einstein’s theory of general relativity. However, this does not mean that quantum physics describes our universe in its entirety. It is merely a new way to look at how gravity behaves at small scales.
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