In the realm of physics, Einstein’s General Relativity stands as a cornerstone, substantiated by extensive evidence. However, the initial development of this theory significantly influenced our understanding of time. Einstein proposed that time is akin to a spatial dimension, suggesting that our universe is a four-dimensional construct perceived by us as passive observers, much like tourists leisurely observing a riverbank. This notion was previously explored in an article discussing quantum mechanics, which challenges this perspective.

Despite the challenges, Einstein’s conceptualization of time as a dimension endures. Popular media, including films and series like Back To The Future, Star Trek, and Doctor Who, often reference his theories in their portrayals of time travel, suggesting that different moments in time coexist. But do multiple "whens" actually exist concurrently, or is the present the only reality?

Imagine you could journey back to the Cretaceous period to observe dinosaurs. Are they merely "back there," like a point along a river? Or do you need to rewind the universe to return to that moment in time?

Einstein’s theory appears to support the idea that all moments exist "simultaneously" within spacetime. While quantum mechanics introduces uncertainty into determinism, it is commonly accepted that we will ultimately experience a future, transitioning from present to past. With a century of supporting evidence, Einstein’s theory seems well-established.

Yet, a closer examination reveals that Einstein’s philosophy of space and time was inherently embedded in his theory, influencing its interpretation for a century.

To provide some historical context, while working at a Swiss patent office in 1905, Einstein formulated what is now recognized as special relativity. He illustrated how our perception of time and space varies with motion. Many are familiar with the concept that as an object approaches the speed of light, its time appears to slow down, and its length contracts.

During that time, Einstein did not link special relativity to spacetime geometry. Among the five groundbreaking papers he published that year, it took the longest to be empirically validated. Today, we routinely observe its effects in particle accelerators.

Years later, mathematician Hermann Minkowski integrated Einstein’s concepts into a framework of space and time, demonstrating that these unique "dilations" and contractions stem from our movements within a four-dimensional "spacetime." Einstein embraced this idea, incorporating gravity into his theory, which posits that spacetime is curved, with this curvature manifesting as gravity. He unveiled his theory to the world in 1915, and by 1919, it was validated through observations of starlight during a solar eclipse.

Einstein’s theory depicted the universe as a four-dimensional "manifold," a term used to describe a shape with specific properties. Within this manifold, entities had to adhere to a rigid rule: no exceeding the speed of light. In Minkowski’s universe, traveling faster than light seems the only way to revisit the past. However, Einstein identified a loophole: spacetime could be structured in ways where certain paths between points were shorter than others, allowing for potential shortcuts through time.

Another critical feature of Einstein’s manifold is the absence of universal time; each entity experiences its own "proper" time as it navigates through the manifold. Objects in close proximity and similar motion tend to experience time similarly, which is why individuals on Earth perceive time almost uniformly. The variances due to typical speeds and minor gravitational differences are minimal, measurable only by highly precise atomic clocks.

This discourse on temporal connections and the absence of a universal clock suggests that time resembles a highway. Each of us travels in our vehicles, experiencing our unique flow, with exit ramps enabling backward movement through time. Thus, those ancient dinosaurs could be merely "behind us," accessible through a time travel shortcut.

However, the situation is more complex than it seems.

General Relativity is inherently tied to Einstein’s philosophy, positing that space and time possess geometry. Consequently, it is typically presented in this manner. If something has geometry, it implies that every point exists in a particular location or time. Yet, this aspect of the theory lacks empirical evidence, as tests have only been conducted over small regions of the universe, primarily around Earth. Even deep space observations rely on "old light" that has traveled vast distances over millions or billions of years.

The dilemma arises as Einstein leaps from the idea of spacetime having geometry to the assertion that objects in "free fall," or those not subjected to external forces, follow a "geodesic" within that spacetime. A geodesic represents the shortest path in a curved space, derived from the Greek term geodaisia, meaning “to divide the Earth.”

In reality, if one were to maintain a constant heading while traversing the ocean, they would not follow a geodesic unless under specific conditions. Instead, they would trace a "rhumb line," which does not represent the shortest path. Following a great circle path requires periodic adjustments, and in Einstein’s curved spacetime, gravity provides the mechanism for these corrections. This leads to two distinct components of the theory: a curved spacetime and a force, gravity, compelling us to adhere to that curvature.

Ockham’s razor suggests avoiding unnecessary complications, prompting the idea that if we aim to explain gravity, we might eliminate the curved spacetime while retaining gravity itself. However, this leaves us with events occurring simultaneously in a singular location, necessitating a coordinate system for distinction, thereby reducing reliance on Einstein’s geometric concepts.

In 1950, Utiyama introduced a version of General Relativity aligning with this viewpoint, termed gauge theoretic gravity. This gauge theory expanded to encompass other fundamental forces—weak, strong, and electromagnetic—culminating in the Standard Model of quantum physics. While all gauge theories can be geometrically interpreted, they are not foundational for other forces. Nevertheless, gravity is often still framed in geometric terms. Gauge theory, by contrast, frames gravity as a force, which aligns more accurately with its nature rather than as a geometry requiring gravity for organization.

Returning to the highway analogy, in the Einsteinian framework, we traverse a highway where the past lies "behind" and the future "ahead." Conversely, in a gauge theoretic context, we might be likened to being on a treadmill surrounded by screens depicting various landscapes, simulating a racing experience. The forces acting upon us in both scenarios are mathematically equivalent. A spacetime coordinate merely serves as an artificial construct for labeling distinct events. The gauge theory delineates what occurs as one traverses "distances" and clarifies how different observers experience varied realities based on their interactions with the gravitational gauge force.

Imagine if the universe is not a manifold at all. What if you aren’t genuinely moving through space or time as per Einstein’s notions but are instead engaging with a gauge force that creates the illusion of movement? This perspective implies that not only is the past not a mere point "back there," but other locations are not simply "over there." Transitioning between places or times involves interacting with the gravitational gauge force, which translates, rotates, twists, and accelerates you, akin to the treadmill. Much like The Matrix, individuals experience unique versions of reality, reconciling these through shared communication and observations.

The universe need not be a computer simulation to resemble The Matrix. Gauge theory functions in this manner without invoking a separate "real" universe like the manifold we dismissed. As the phrase goes from The Matrix, "There is no spoon," similarly, there is no turtle.

While gauge theory may not currently yield significant implications for physical measurements—given its mathematical equivalence to the geometric interpretation of General Relativity—it does carry philosophical weight. If the past and future are not fixed entities "out there," they could potentially emerge from our interactions with the universe, especially when quantum uncertainty is factored in. Our choices might hold considerable influence over our experiences since the future remains unwritten, and the past is erased. However, it’s essential to note the uncertainty of this assertion.

Drawing philosophical conclusions from physics is fraught with risks, particularly when one interpretation of a theory is presented as the definitive explanation. Historically, philosophical debates often see individuals align with perspectives that resonate with their beliefs. Personally, I find the notion that my choices significantly impact my future appealing. Conversely, those like Einstein may prefer a universe where they are absolved of accountability for their actions. History suggests that just when we believe we have unraveled the universe's mysteries, it unveils further complexities beyond our comprehension.