Laplace’s Demon is a thought experiment in determinism that describes a being with knowledge of the present, which allows it to also know the past and future.
Laplace’s Demon is not a mythical creature that haunts Laplace, Louisiana, but rather a thought experiment that was described over two centuries ago.
In a famous line condensed as “God does not play dice with the universe,” Albert Einstein expressed the idea that there is order in the universe, rejecting the concept of randomness.
This brings us to determinism, which presents the entire universe as an infinite series of predetermined events that cannot be disrupted. This idea has captured the interest of philosophers and physicists alike, with Laplace’s Demon representing determinism.
Is everything predetermined? (Photo Credit: twenty20)
Causal Determinism
Causal determinism suggests that every event is caused by previous events. The events of today are the result of past events, and the events of the present will cause future events. This implies that everything has been predetermined since the beginning of time.
This also means that free will does not exist. Every action we take is determined by cause and effect. The past determines the present, and the present determines the future. Quite mind-boggling, isn’t it?
The deterministic model of the universe is not widely accepted, especially among today’s scientists.
Now, let’s examine Pierre-Simon Laplace and the demon he created based on these ideas.
Laplace’s Demon
In 1814, Pierre-Simon Laplace described a thought experiment in his book A Philosophical Essay on Probabilities. This idea later became known as Laplace’s Demon.
Pierre-Simon Laplace (1749–1827) (Photo Credit: James Posselwhite/Wikimedia commons)
Laplace wrote:
“We should then regard the present state of the universe as the result of its previous state and the cause of the state that will follow. If we had an intelligence that could comprehend all the forces animating nature and the exact positions of every being within it – an intelligence vast enough to analyze this data – it could encompass the movements of the largest celestial bodies and the smallest atoms. For it, nothing would be uncertain, and the future, like the past, would be present before its eyes.”
Let’s break it down.
What we now refer to as Laplace’s Demon is an imaginary being. This being possesses complete knowledge of the universe at a specific moment, as well as the computational ability to understand and analyze this knowledge.
When we say everything in the universe, we mean everything. The movement patterns of subatomic particles, every detail about every force at work in the universe, the position and velocity of every single particle. From electrons to airplanes to stars.
In essence, there is much more information available than even Dr. Strange could perceive! Therefore, if there existed a being with such knowledge and the ability to comprehend and analyze it, that being would possess the power to accurately predict the future and describe the past. This would be true omniscience.
The reason behind this lies in the assumption of a deterministic reality as a fact. Laplace’s thought experiment considers “the present state of the universe as the effect of its anterior state and as the cause of the one which is to follow.” The present is a result of the past and a cause of the future.
Laplace’s demon is a being who possesses knowledge about everything in the universe for a single moment, and as a result, knows both the past and the future. Therefore, if one possessed complete and detailed knowledge about the universe at a specific moment and had enough intelligence to analyze all that data, that knowledge would enable them to describe any moment in the past or future.
To simplify, if one knew everything about a specific moment, they would know everything about every other moment in the past and future.
Challenges to Laplace’s demon have been raised over the course of two centuries since the thought experiment was proposed. While it has received some support, there have also been strong arguments against it. Let’s examine the major ones.
Quantum mechanics presents an indeterministic model of the universe, which poses a significant challenge to the deterministic thinking model. According to quantum mechanics, subatomic particles do not adhere to the rules of classical mechanics. Their behavior cannot be predicted; only probabilities can be cited. This poses a problem for our demon, as it requires accuracy rather than probability.
Heisenberg’s uncertainty principle is a particular obstacle for Laplace’s demon. This principle states that it is impossible to simultaneously determine the position and velocity of a particle. Certainty about one of them increases the uncertainty about the other. Since the demon needs to precisely know the position and velocity of every particle in the universe to make predictions, the uncertainty principle renders this impossible.
While particles can be represented by a wave function that contains their position and speed, even this level of determinism is challenged by the existence of black holes. It is simply not possible to predict the final state of objects that enter a black hole.
The second law of thermodynamics introduces the concept of entropy, which is disorder. The entropy of a system always increases, and consequently, the entropy of the universe always increases as well. As time progresses, a system becomes more disordered and increasingly difficult to predict accurately.
Laplace’s Demon is also intended to determine the past by reverse-engineering the present. However, the concept of thermodynamic irreversibility complicates this. Some things cannot be restored to their initial state by examining their current state. Determining the initial state becomes impossible.
Chaos Theory
Chaos theory consists of various components. One commonly known component is the butterfly effect, which illustrates the significant impacts of small actions. However, the main essence of chaos theory lies in its unpredictability. For instance, when a butterfly flaps its wings, it may either cause a tornado or simply create a mild breeze in a distant place. The outcome cannot be determined with certainty.
Even minute changes in a system can result in substantial variations. Even if all the variables in a system are known, the system can still exhibit unpredictable behavior over a series of iterations.
Free Will
The concept of free will contradicts determinism. So, what does this mean for Laplace’s Demon?
Laplace’s Demon must possess complete knowledge of itself. If an entity has perfect knowledge of both the past and the future, it can defy predictions and exercise free will. Consequently, Laplace’s Demon would have the power to disprove its own existence. The argument is that predicting the outcome of a system from within the system is impossible.
An illustration of free will is often used to refute the existence of the demon. For example, imagine the demon does exist and you are standing in front of two doors that lead to the same hallway. You ask the demon to predict which door you will choose. Regardless of the demon’s prediction, you have the ability to choose the other door, thus exercising free will.
The demon may know the available choices, but can it accurately predict which one will be chosen? (Photo Credit: Pixel-Shot/Shutterstock)
Now, let’s consider a scenario where the demon is a disembodied entity that does not interfere with the universe. This scenario also fails because any prediction made from outside the system can only be approximate. To make an accurate prediction, even the slightest interaction with the system is necessary.
Does God Play Dice?
In one of his lectures, Stephen Hawking addresses Laplace’s Demon and responds to Einstein’s statement about God playing dice with the universe. Hawking suggests that God does indeed play dice with the universe.
If one were to possess complete knowledge about a specific moment, would that knowledge extend to encompassing the entirety of the past and future?
Considering the principles of quantum mechanics and chaos, Laplace’s Demon cannot exist.
Nevertheless, Laplace’s Demon remains a crucial concept in understanding the deterministic model of the universe. Determinism has been of immense value in science, as it heavily relies on the principle of cause-and-effect.
The universe is an extensive and potentially unsolvable puzzle. Certainty is scarce, but every significant idea strives to diminish some of that uncertainty.