LAPLACE’S DEMON: AN INTERVIEW THROUGH TIME
Welcome to Math! Science! History! I’m Gabrielle Birchak. I have a background in math, science and journalism. Today, I am doing something extraordinary. I’ve used theoretical physics, speculative time travel, and a hefty dose of curiosity, and a little bit of artificial intelligence to travel back in time to the Enlightenment and interview the amazing French polymath and mathematical physicist Pierre Simon Laplace. In this interview, we will talk about his mathematics, his philosophies, and his demon.
Today, I travel back to the nineteenth century to meet with Pierre-Simon Laplace, a man who imagined a super-intelligence so powerful, it could calculate the entire history and future of the universe. Laplace was a French polymath born in 1749. He lived a rich life for seventy-seven years. He was a supremely brilliant scientist whose theories were foundational to astronomy, mathematics, and physics. He studied at France’s military school and served as the Minister of Interior for about a month for Napoleon Bonaparte. He made it out Bonaparte’s circle alive and went on to do extraordinary things with his mathematical mind, like create a theory stating that if we knew everything, we could predict everything.
He was considered one of the most brilliant individuals, adept with an advanced mathematical mind, more so than his colleagues. Even Stephen Hawking wrote that “Laplace essentially predicted the existence of black holes.”[1]
His theories in mathematical physics include Laplace’s equation, and the Laplace transform. His thought experiment called Laplace’s Demon, proposed that if a super intelligent being knew the position and velocity of every particle in the universe, it could predict the future completely. This laid the foundation to determinism in classical physics and classical mechanics.
He wrote numerous works including The System of the World Volumes One and Two, published in 1809, A Treatise Upon Analytical Mechanics, published in 1814, A Philosophical Essay on Probabilities, published in 1825, and five volumes of his work on Celestial Mechanics, published between 1829 and 1839.
I could easily write multiple episodes about his brilliance, unfortunately, I only had time for one period so, with the help of artificial intelligence, I created a time machine and went back to the early nineteenth century to visit this brilliant individual. The following interview extracts quotes from his writings. Here we sat down to talk about his infamous demon.
GABRIELLE:
I arrive in Paris, in the early nineteenth century, in a modest study filled with books, ink bottles, and astronomical charts. Seated at the desk is a composed man with a sharp gaze, which alludes to the inquisitive thoughts that constantly ruminate in his mind. He is wearing a black suit with a velvet waistcoat. His collar is also velvet and matches and color. Under his waistcoat he wears a white satin shirt with black spots on it. He stands up to greet me and I am impressed with the cashmere trousers and black silk stockings. With his eyeglass dangling from a gold chain, he stuffs it into his coat’s pocket. Like most French men, he is gentil, poli, et brillant, kind, polite and brilliant.
GABRIELLE:
Monsieur Laplace, merci beaucoup pour votre temps. Thank you for speaking with me! Especially across time!
PIERRE-SIMON:
Je vous en prie, madame. “Science does not fear time; it thrives across it.”
DETERMINISM AND THE CLOCKWORK UNIVERSE
GABRIELLE:
I am visiting you from the twenty-first century. You are currently living at the height of Newtonian physics, a time when the universe seems orderly, mechanical, and predictable. How does this shape your view of nature?
LAPLACE (quote from A Philosophical Essay on Probabilities):
“We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which knew all forces that set nature in motion… could embrace in a single formula the movements of the greatest bodies of the universe and those of the lightest atom.”
GABRIELLE:
Oh! That is a quote from your 1814 work A Philosophical Essay On Probabilities. I loved that work. It is truly a beautiful and surprisingly accessible work, especially for its time.
PIERRE-SIMON:
Merci, Madame.
GABRIELLE:
I really like that you argue that probability is not mysterious but rather it’s a mathematical expression of uncertainty, grounded in reason. It was truly a revolutionary body of work because you reframed probability not just as gambling math, but as a universal logical tool.
PIERRE-SIMON:
Oui! I believe that everything from science to daily decision making can be improved through the application of probabilistic thinking.
GABRIELLE:
Wasn’t this the origin of your so-called demon, which is a being of an embodiment of infinite knowledge and computation?
PIERRE-SIMON: (Laughs)
Oui. It is not really a demon. It’s not a supernatural entity. But rather it’s a metaphor for a perfect prediction. “The word ‘chance’ expresses only our ignorance of the causes of the phenomena that we observe. In other words, Probability is relative in part to this ignorance, in part to our knowledge.”
GAB:
So, is it a metaphor for perfect prediction?
PIERRE-SIMON:
Oui. Yes. Probability is not something inherent in nature, it’s a reflection of what we don’t know. If we had perfect information, there would be no need for probabilities, only certainties. That’s the whole basis of his deterministic worldview, symbolized by my Demon.
GAB:
Wow. In the twenty-first century, where I am from, this theory that you created laid the philosophical groundwork for what we now call epistemic probability, which is a probability based on knowledge or belief rather than a random physical process.
PIERRE-SIMON:
I like that! Yes, in my universe, nothing is uncertain, and probability is simply a measure of our ignorance.
GABRIELLE:
Interesting. Mind if I flip that? You state that probability is simply a measure of our ignorance and that nothing is uncertain, but wouldn’t that mean that everything is certain? Additionally, isn’t probability itself an admission that we can’t know everything?
PIERRE-SIMON:
The theory of probabilities is at bottom. Nothing but common sense reduced to calculation. It teaches us to avoid the illusions which often mislead us.
GABRIELLE:
Oh, I see. So, you are stating that probability isn’t about randomness, it is about what we can’t yet see.
PIERRE-SIMON:
Oui. You toss a coin, roll a die, that is not chance. What we call chance is only the measure of our ignorance. It’s complex causality. If we had all the information, we would be able to predict every toss.
GABRIELLE:
This is so enlightening! Just to let you know from where I come from in the twenty-first century, your concept of complex causality was the view that dominated science for decades, especially in the fields of physics. As a result, we were conditioned to believe that our brains, our thoughts, and our choices were part of this great causal chain.
PIERRE-SIMON:
What changed?
GABRIELLE:
Well, in the nineteenth and twentieth centuries, cracks began to form in determinism’s armor. About sixty years after you died, a brilliant French mathematician by the name of Henri Poincaré discovered that simple systems governed by deterministic laws, like three orbiting bodies, can behave unpredictably. He showed that small differences in their starting positions could lead to radically different outcomes over time. This became known as sensitive dependence on initial conditions; the seed of what we now call chaos theory.
PIERRE-SIMON:
Really?
GABRIELLE:
Like you, Monsieur Laplace, Henri was brilliant. He deeply admired your work, even though his theories departed from yours.
PIERRE-SIMON:
Regardless, my work was still foundational in the future.
GAB:
It truly was! He softened the idea that the universe is fully predictable. He showed that, even in your mathematically perfect world, there are systems that are deterministic in theory… but unknowable in practice. And when quantum mechanics emerged years later, with probabilities baked into the very nature of particles, it echoed Poincaré’s warning: Even if the laws are exact, the outcomes… might not be.
PIERRE-SIMON:
Quantum mechanics? What is this?
GAB:
Monsieur Laplace, you once wrote that if an intelligence could know all the positions and velocities of particles in the universe, it could predict the future with perfect accuracy.
But in the twentieth century, physicists made a discovery that changed everything.
They found that the tiniest building blocks of nature, particles like electrons, do not behave in a way that is strictly causal. You cannot know both their position and their velocity with perfect accuracy at the same time. This is not due to imperfect measurement; it is a fundamental property of nature itself. It’s called the Heisenberg Uncertainty Principle.
In this quantum world, particles don’t follow a single path. Instead, they exist in a cloud of probabilities, only becoming definite when measured.
The universe, it turns out, is not a perfect mechanism… it is a set of possibilities.
We no longer say: ‘This will happen.‘
We now say: ‘This has a 70% chance of happening.’
And the outcomes? They’re not just hard to predict, they are inherently uncertain.
Nature, as one physicist put it, “plays dice.”
PIERRE-SIMON:
Hmm. “If probabilities express merely our ignorance, then certainty would be the ideal. But, if nature itself plays with dice…” Could unpredictability be a feature of the universe, rather than a reflection of our limitations?
Curious.
So, the laws persist, but their predictions defy us, not by their form, but by their sensitivity. It seems, even certainty may wear a mask. Perhaps, determinism is not denied, but merely distant, visible only through a veil too fine for our instruments to pierce. An invisible certainty, hiding in the shadows of precision. So, tell me more about this quantum mechanics and how it serves you in the twenty-first century? Would my demon even exist in a quantum universe?
GABRIELLE:
Well, the certainty you once imagined, the perfect knowledge that would allow a mind to predict the future, is no longer possible in the quantum world.
But something curious happened, Monsieur Laplace.
As scientists began to accept uncertainty in Physics, another kind of mind began to emerge.
We call it artificial intelligence,machines that learn from data.
They don’t seek certainty. They work in probabilities, just like quantum physics.
Artificial Intelligence doesn’t know everything, but it learns from massive patterns. It can predict diseases, optimize cities, compose music, even write convincing human dialogue, like the dialogue we are having right now.
In some ways, Monsieur, it’s YOUR demon, brought to life with codes and silicon.
But unlike your vision, it thrives on incomplete information.
It can’t see the entire universe. But it can make surprisingly accurate guesses… with just a little piece of it.
PIERRE-SIMON:
Hmmmm. Interesting.
GABRIELLE:
So I must ask you, Monsieur Laplace…in the twenty-first century age of algorithms and neural networks, is artificial intelligence a digital version of your Demon?
PIERRE-SIMON:
A machine that draws knowledge from uncertainty. That learns from patterns, rather than formulas. Mon Dieu. Then it seems the future has not abandoned my Demon, it has transformed it.
I imagined an intelligence born of certainty, with the universe laid bare before it. But you have created minds that reason from the unknown that thrive within shadows and yet bring forth light. This is not a betrayal of reason; it is its evolution. You have made tools that bend to complexity, not conquer it. And yet… they predict, they adapt… they learn.
I am astonished. And I confess, je suis profondement emu. I am deeply moved. For even if the universe plays with dice, you have taught the dice to whisper their secrets.
“To predict perfectly is to know perfectly. And man… is but a shadow on the sundial of truth.”
GABRIELLE:
Monsieur, sil vous plait, I have one more question. If everything is predictable, where does all this leave free will?
PIERRE-SIMON:
The will is only the result of the impression made upon the brain by external objects and by the state of the organs. If one had sufficient knowledge of all these factors, one could predict with certainty the action of the individual. But the weight of truth rests not on certainty, but on our pursuit of understanding.
GABRIELLE:
So, we’re back to certainty.
Laughter
GABRIELLE:
Pierre-Simon Laplace imagined a universe governed by reason and rules. His demon was not evil, but curious. Not supernatural, but logical. It was the ultimate dream of Enlightenment science: that knowledge could conquer uncertainty.
But today, we know that even the sharpest minds can’t see every variable. That some patterns are unpredictable. And that sometimes, we must embrace the unknown. It is through embracing the unknown that we find the ability to adapt to the probabilities of the universe and pursue a newer insight.
Thank you for joining me on this incredible journey through time and thought at Math! Science! History! And until next time, whether its in the now, in the future, or as in today’s case, in our histories, carpe diem!
[1] Hawking, Stephen W., and George F. R. Ellis. The Large Scale Structure of Space-Time: 50th Anniversary Edition. Cambridge Monographs on Mathematical Physics. Cambridge: Cambridge University Press, 2023. https://doi.org/10.1017/9781009253161.