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This personal reflection is part of a series called The Big Ideas, in which writers respond to a single question: What do we believe?

I believe in justice. I believe that the Earth is round. I believe that my name is Carlo and that my fathers name was Franco. I believe that life is worth living. My beliefs are rooted in me. They define me. I hold them dear and I strenuously defend them against any challenge.

But I am not certain about them.

We never have total certainty, nor do we need it or want it. Between full ignorance and total certainty there is a vast intermediate space where we conduct our lives.

We grow, and we gather more reliable knowledge, by being genuinely open to the questioning of our beliefs. This is the core teaching of scientific thinking. The most reliable beliefs are those that survive questioning.

If we believe that the Earth is round and that penicillin cures pneumonia, for example, it is because scientists doubted the proclamations of our ancestors that you could sail a ship off the edge of the Earth, or that incantations were a legitimate form of medicine.

Albert Einstein questioned Newtonian science, and quantum theory questions the picture of the world of classical mechanics. There was a time when we thought that reality was simple: particles in space, moving in time. Now space bends and weaves, and time depends on where we are and how we move. Quantum physics subverted most of what we used to believe about matter.

This doesnt mean, however, that we are in the dark, or that we should feel paralyzed by a lack of perfect knowledge. If I ask for street directions from a person or from my smartphone theres no guarantee that the answer will be correct. The person might have misinterpreted my question, or I may have misspelled the address I entered into my smartphone. But that wont stop me from deciding on a direction and walking.

Our forefathers believed that only white, property-owning men could be trusted to vote; that Black people were better off enslaved; and that witches floated when tossed into a pond. Thank heavens some people in the past had the strength to challenge the standards of their time. If they hadnt, wed still be stoning women in the streets.

Such drifts in what we believe do not make our convictions any less valuable, either. No person, book or institution holds definitive truth. Openness to change means that our beliefs are strong, and that we can make them stronger. It means that we, the finite critters who inhabit this planet, are capable of doing better.

The same is true for our political beliefs. Iron determination grounded in the firm political convictions of individuals and groups created the modern world. But we do not live in a perfect world far from it. If we have the will to challenge established conventions, we can make the world better for everyone.

But beware: Eagerly embracing shiny new ideologies can be even more dangerous than hanging on to hold ones. The neophyte is passionate. Fresh converts may not see the evil in their new credo. Germany fell in love with the glittering order of Nazism. A little over a decade later, with Europe in ruin and millions dead, the country experienced a brutal awakening. The ugliness and horror of the Nazi years suddenly became visible.

If left unchallenged, old beliefs can be suffocating; but the passion that novel beliefs inspire can be a recipe for disaster. The balance is never easy; we have no other tool to guide us than our limited and always insufficient intelligence. No other reliable adviser than uncertainty.

Experience causes our beliefs to change, and they change because we all hold different beliefs and are constantly comparing them. The vast diversity and interconnectedness of humankind is the fertile humus that creates an endless network of exchanges, which nurtures our beliefs but also allows them to evolve. Like the constantly drifting and intermixing genetic pool of a species, our beliefs are the result of our continuous exchanges with the rest of the world and the people who live in it.

Far from being truly ours a mark of our individuality beliefs are a precious shared wealth that humankind continuously trades. We receive them, elaborate on them, mix them with beliefs weve previously received and pass them on. They glide across us. We are nodes in their evolution.

This network of exchanges is our shared culture: the never-ending dialogue that constantly grows and enriches itself. Our best political, moral and scientific beliefs are the evolving configurations of this long dialogue.

I believe in justice. I believe that the Earth is round. I believe that my name is Carlo and that my fathers name was Franco. I believe that life is worth living.

But I also know how slippery the notion of justice is, how it has been misused to enable all sorts of crimes.

The Earth is round, but I know that it is not really round, as a true sphere is. Its shape is more subtle.

My name is Carlo, and my father grew up being called Franco until the day he discovered that Franco was just a name his mother liked, and that his birth certificate, registered by his father, said that his name was actually Giulio.

And although I believe that life is worth living, I also know that there are crises and true hardships that compel too many people to think otherwise.

I hold dear to my beliefs. But I will never stop questioning them.

Carlo Rovelli is a theoretical physicist. His latest book is Helgoland: Making Sense of the Quantum Revolution.

Read more:

Carlo Rovelli: What We Believe About Certainty - The New York Times