When Physics Defies Experience

By Maq Masi

Where did the universe begin? Where is its centre? And if nothing can travel faster than light, how can the universe expand faster than light itself?

These questions troubled me when I first tried to understand the origin of the universe. Like most people, I had heard of the Big Bang, an event believed to have occurred approximately 13.8 billion years ago. The name itself suggested an enormous explosion somewhere in space, followed by matter travelling in every direction. Naturally, I wondered whether we could identify that original location by reversing the movement of galaxies, tracing their paths backwards until everything converged at a single point.

But the more I investigated, the less familiar the explanation became. I learnt that the Big Bang did not happen at a particular location in space. Rather, space itself was expanding. I then discovered that sufficiently distant galaxies could recede from us faster than the speed of light, even though Einstein’s theory of relativity establishes a universal limit on the local propagation of matter and information. How could both statements be true? Did the expanding universe somehow possess negative mass? Was there another kind of motion beyond the laws governing physical objects?

The answers introduced me to spacetime, cosmic expansion and eventually dark energy. Yet each new term seemed to create another difficulty. Spacetime was not an ordinary physical container. Expansion did not necessarily mean movement through space. Dark energy was neither visibly dark nor an identified substance that scientists could collect and examine. What the hell was all this?

Eventually, I began to suspect that the difficulty was not simply with cosmology. Perhaps it was with the way I was trying to understand it. I was asking questions constructed from ordinary human experience, while physics was describing relationships that have no direct equivalent in that experience. I wanted to know where something happened, how far it travelled and how fast it moved. Yet the answers suggested that the familiar meanings of where, distance and speed were no longer sufficient.

This led me towards a question that I found even more interesting than the Big Bang itself: how does the human mind understand something it has never experienced?

Our understanding of the physical world begins with sensation. We see, hear, touch and encounter things. These encounters become memories, repeated memories establish patterns, and patterns gradually develop into knowledge. A child who touches a hot cup learns something about heat. Repeated encounters allow the child to distinguish hot from cold, safe from dangerous, and eventually to anticipate consequences without touching the object again. What begins as sensation develops into a concept capable of guiding future behaviour.

Much of our ordinary vocabulary emerges through this relationship between perception, memory and experience. We understand weight because we have lifted objects. We understand distance because we have travelled between places. We understand movement because we have watched objects change position. Even when we imagine something beyond direct experience, we generally construct it by extending, combining or negating concepts already available to us. Infinity, for instance, can be approached by imagining a sequence that never ends, although every sequence we have personally encountered has been finite.

This does not mean that all knowledge originates exclusively from sensation, or that human reasoning cannot move beyond it. Mathematics and abstract reasoning demonstrate otherwise. Nevertheless, our everyday intuitions are strongly shaped by the physical environment in which we live. We have evolved to navigate objects, distances, movements and events on a human scale. We have not evolved to perceive the geometry of spacetime or the behaviour of the universe across billions of years.

Consider the word origin. In ordinary experience, everything that begins appears to begin somewhere. A river has a source, a building has a foundation, and an explosion has a location. Consequently, when we hear that the universe began with the Big Bang, we instinctively imagine an initial point from which everything emerged into surrounding emptiness. But modern cosmology does not describe the Big Bang as an explosion at one identifiable location within pre-existing space. It describes an early hot, dense state of the universe, followed by cosmic expansion. In the standard cosmological model, this expansion has no privileged spatial centre. Every sufficiently large region participates in it.

If we mathematically extrapolate the classical model backwards, we encounter a boundary at which the familiar equations cease to provide a reliable physical description. This is often associated with an initial singularity. Yet it would be premature to conclude that physics has established the absolute beginning of existence, or that the universe literally emerged from a dimensionless point. The model describes the evolution of the observable cosmic system with remarkable success, but its earliest physical conditions remain incompletely understood.

The difficulty becomes clearer when we consider expansion. In everyday language, expansion means that something grows larger. A balloon expands when inflated, metal expands when heated, and a population expands when its numbers increase. In each case, we imagine an object occupying more space than before. We therefore ask the apparently reasonable question: if the universe is expanding, what is it expanding into?

The question assumes that space must exist outside the expanding universe, just as a room exists around an inflating balloon. But that assumption is not required by general relativity. Cosmic expansion is described through changes in the spatial geometry of the universe, commonly represented by a mathematical quantity called the scale factor. As this factor increases, the distances between sufficiently separated, approximately comoving galaxies increase. There need not be an external container into which the universe grows.

This distinction matters because the word expansion invites us to imagine something that the mathematics does not demand. We borrow a familiar word because language offers no equally intuitive alternative. Yet the borrowed word carries assumptions from its original meaning, and those assumptions can become obstacles to understanding.

The same problem arises with speed. We are taught that nothing can travel faster than light in a vacuum. More precisely, the constant (c), approximately 300,000 kilometres per second, represents the invariant speed associated with the causal structure of spacetime. Massless particles such as photons travel locally at this speed in a vacuum, while objects possessing mass cannot be accelerated to it.

How, then, can astronomers speak of galaxies receding faster than light?

The answer lies in recognising that two different physical quantities are being described using the same familiar language. The speed of an object passing a nearby observer is not equivalent to the rate at which the cosmological distance between two widely separated galaxies changes. In an expanding universe, that recession rate can exceed (c) over sufficiently large distances without either galaxy locally travelling through space faster than light.

The distinction is expressed through the familiar cosmological relationship (v=Hd), where (v) represents recession rate, (H) the Hubble parameter and (d) the relevant proper distance at a given cosmic time. As the distance increases, the recession rate increases. Beyond a sufficiently large separation, the calculated rate exceeds (c). This does not violate special relativity because its local speed limit is not a universal restriction on every possible rate of change of distance in curved spacetime.

What appears contradictory in ordinary language becomes consistent once we recognise that the word speed has been applied to quantities defined differently.

Dark energy presents another challenge. Observations of distant supernovae, together with other cosmological measurements, indicate that the expansion of the universe has entered an accelerating phase. The prevailing cosmological model accounts for this through a component commonly called dark energy, often represented by a cosmological constant.

But what exactly is dark energy? The expression almost invites us to imagine an invisible substance spread throughout the universe, somehow pushing galaxies apart. Yet the name should not be mistaken for an established explanation of its underlying physical nature. A cosmological constant can be included in Einstein’s equations and is consistent with many observations. More general models describe a component with sufficiently negative pressure to produce accelerated expansion. Whether this corresponds to vacuum energy, a dynamical field, some modification of gravity or another physical explanation remains a subject of investigation.

There is nothing necessarily dark about it in the ordinary sense. The darkness lies principally in our incomplete knowledge.

I find this particularly revealing. Science sometimes gives a name to a phenomenon before it fully understands its cause. The name enables researchers to discuss, measure and model the phenomenon, but it can also create the impression that identifying something linguistically is equivalent to explaining it physically. We should distinguish between naming an unknown, describing its measurable effects and discovering what it actually is.

This is not a criticism of scientific terminology. Without provisional concepts, scientific investigation would become almost impossible. My concern is with the ease with which terminology can conceal the boundary between what has been observed, what has been inferred and what remains unexplained.

Human understanding has developed several ways of crossing this boundary. Analogy is perhaps the most accessible. Cosmologists frequently describe expanding space using the surface of an inflating balloon or raisins separating inside rising dough. These illustrations are useful because they allow us to visualise increasing distances without requiring every object to move away from a common centre. However, neither analogy should be treated literally. A balloon has an external environment, and raisin dough occupies a surrounding space. The universe need not possess either feature. An analogy becomes intellectually useful only when we understand both what it illustrates and where it fails.

Mathematics provides a more powerful method. Unlike ordinary visual imagination, mathematical relationships do not require every concept to correspond to something we have physically encountered. We can calculate the curvature of spacetime without picturing it as a bent sheet. We can describe four-dimensional geometry without directly perceiving four dimensions. We can predict the behaviour of cosmic expansion through equations even when our everyday understanding of movement offers no satisfactory mental picture.

Instruments extend our capacity further. Telescopes reveal light emitted billions of years ago. Spectroscopic measurements allow astronomers to identify cosmological redshift. Observations of the cosmic microwave background provide evidence about the early universe. Yet these instruments do not give us direct sensory experience of the universe expanding. They provide measurable information from which physical relationships are reconstructed through theoretical interpretation.

This raises an important philosophical distinction. To observe a phenomenon, to construct a mathematical model of it and to understand its ultimate nature are not necessarily the same achievements. A model may predict observations accurately while leaving fundamental questions about reality unresolved. General relativity describes spacetime through a mathematical geometry, but whether spacetime should ultimately be understood as a physical entity, a structure of relationships or something more fundamental remains open to philosophical and scientific examination.

Similarly, the question of what happened before the Big Bang cannot be dismissed merely because the familiar cosmological model does not provide an answer. It may be that our ordinary concept of before becomes inapplicable under certain physical descriptions. It may also be that a more complete theory reveals an earlier physical history. The responsible position is not to declare every unanswered question meaningless, but to recognise the difference between a question that is poorly formulated, one that remains theoretically unresolved and one for which we presently lack observational evidence.

This distinction matters beyond cosmology. Throughout human intellectual history, we have repeatedly mistaken the limitations of our existing concepts for limitations of reality itself. What cannot be imagined is sometimes declared impossible. What cannot be observed is sometimes declared nonexistent. Conversely, what can be described in convincing language is sometimes accepted as though it has been demonstrated. Each mistake arises when we fail to distinguish between the world and the means through which we attempt to understand it.

Perhaps understanding should not always be measured by our ability to produce a mental picture. I cannot visualise spacetime in its full mathematical form, but I can begin to understand the relationships that its equations describe. I cannot directly experience cosmic expansion, but I can examine the observations supporting it and the assumptions involved in interpreting them. I cannot identify the physical nature of dark energy, but I can understand why the concept was introduced and where present knowledge ends.

For me, this represents a more mature conception of knowledge. Understanding is not merely the possession of an explanation that feels familiar. It is the ability to distinguish evidence from inference, concepts from objects, and established relationships from unresolved possibilities. Sometimes genuine understanding begins precisely when an explanation stops feeling intuitive.

I began by asking where the Big Bang happened, what the universe was expanding into and how galaxies could recede faster than light. I expected answers expressed in the familiar language of location, movement and speed. Instead, I discovered that those words were carrying assumptions that did not necessarily belong to the phenomena I was trying to understand.

The universe has no obligation to conform to the scale of human experience, and human language has no guarantee of describing reality without distortion. Yet this does not condemn us to ignorance. It invites us to examine our concepts as carefully as we examine the world.

Perhaps the greatest intellectual difficulty is not that the universe lies beyond our experience, but that we continue to expect experience to define the limits of what the universe can be.