I have long felt that the deepest motive for humanity to enter space, and even to imagine interstellar migration, is not merely to display the power of civilisation. Nor is it simply fear that Earth may one day become uninhabitable, or the wish to find a backup location for the long-term survival of the species. Such reasons can certainly be valid and can support particular space programmes, but they are not the deepest reason.

The deeper reason is curiosity. Human beings keep looking towards what lies at a distance. As long as there is somewhere we have not reached, understood, or genuinely entered, it continues to draw us. Yet space exploration has a special feature: it cannot have a final completion. The moment we reach what we called the far distance, it becomes a new here, and a further distance reappears. Humanity is always moving towards the far away, but we ourselves also remain at a distance. We are part of the inexhaustible object of curiosity that we seek to explore.

In that sense, moving through space and remaining still may not be as fundamentally different as we usually imagine. Physically, of course, they are different. A spacecraft travelling from Earth to the Moon, Mars, or a more distant star system passes through real distance, consumes energy, and takes time. But once we ask whether the universe contains an absolute here and an absolute there, the matter is no longer simple.

We can say that Earth moves, that the Solar System moves, and that the Milky Way moves through the universe because we have constructed a cosmological coordinate system. We can describe Earth as orbiting the Sun, the Solar System as orbiting the Galactic centre, and the Milky Way as having a velocity relative to the cosmic microwave background. This is not arbitrary imagination. Such descriptions can be repeatedly tested through observation, calculation, navigation, and spaceflight. They are stable and effective.

But effectiveness does not mean that they are the one and only appearance of the universe independently of humanity.

Human beings can share this coordinate system because we have similar biological foundations, a common evolutionary background, and broadly corresponding ways of sensing, imagining, and reasoning. People from different cultures, languages, and places can learn, translate, and correct one another until they share a picture of the universe that seems to exist outside any individual. Yet this commonality first shows that our species shares stable conditions of cognition. It does not necessarily prove that the universe itself comes equipped with this coordinate system, waiting for us to discover it.

This is where Kant remains important. He did not impose limits on reason merely to reserve a place for God. More accurately, his long analysis led him to see that however we know the world, we cannot entirely step outside the conditions of our own knowing. Space and time are the basic forms through which human sensibility can intuit objects. Categories such as causality, substance, unity, and possibility are the basic conditions through which the understanding organises experience into an intelligible world.

This does not mean that space, time, and causality are false, nor that the external world is merely human fantasy. It means that the world we experience has already been organised through the structures of human sensibility and reason. We cannot stand outside ourselves and see being exactly as it is without any form of cognition.

The disturbance introduced by the quantum world makes this point sharp again.

Why does quantum entanglement seem so difficult to understand? Not simply because the physics is technically complex, but because it touches our deepest spatial intuition. We naturally assume that two things far apart should be two independent things. They may affect each other, but the influence should travel through space, take time, and follow some traceable process.

Yet entangled quantum systems that are spatially separated display correlations that cannot be explained by local hidden variables. They do not thereby allow controllable information to be sent faster than light; causal limits remain. But our intuition is forced to confront a question: is spatial distance really sufficient to separate the states of two objects completely?

Perhaps human thought has already pulled the two quanta apart from the outset. We first define them as two objects in space, then ask why they remain correlated across such a distance. At a deeper level, however, they may first be different manifestations of a single quantum state. Entanglement need not mean that two absolutely separate things suddenly make contact across distance. It may also arise from our having divided one whole into two parts.

If there were a form of cognition not bound by human space, time, and categories—let us call it a God’s-eye view—it might not see an astonishing interaction between two distant quanta at all. It might see only one whole, presenting different results in different locations and under different measurement conditions. Distance might still be an attribute of being, but not the basic condition that determines whether reality is divided into separate entities.

Of course, we cannot therefore simply say that distance does not exist. For human beings, distance is very real. Experimental apparatuses are separated by distance, light has a finite speed, a spacecraft needs time to reach Mars, and a human body cannot instantly travel from Canberra to the Moon. Distance is not an arbitrary fiction; it is a stable structure that we have established and repeatedly tested under the constraints of the world. What quantum theory unsettles is not distance itself, but our tendency to treat it as absolute—to assume that spatial separation must entail wholly independent entities and wholly local causality.

The uncertainty principle, quantum entanglement, and Schrödinger’s cat continue to create philosophical unease not necessarily because the universe itself is absurd, but because human reason is meeting one of its own boundaries. We are accustomed to understanding the world as composed of distinct objects, each with a definite position, a definite state, and clear causal relations. At the quantum level, these concepts may no longer hold together in the way we are used to.

Perhaps this is what deserves our closest attention in quantum theory. It has not simply told us what the universe ultimately is. It has first compelled us to recognise that the concepts we take to be most natural and least in need of explanation may themselves be conditions through which human beings know the world.

When humanity explores space, it may not ultimately be exploring only distant galaxies. It is also testing how far its own reason can go. At every step outward, we may discover that what most needs to be understood anew is not the universe alone, but our own way of understanding it.