The Shadow of Absolute Spacetime in Relativity

Author: Zhang Suhang, Luoyang, Henan

Abstract

Newton constructed a system of separate absolute space and absolute time: space is a fixed, unchanging void container, while time flows independently, uniformly, and in one direction, with the two not interfering with each other. Special relativity broke through this cognition of a split spacetime, unifying space and time into a four-dimensional spacetime whole, and successfully explained high-speed effects such as length contraction and time dilation—a tremendous leap in physical thought. However, this paper proposes a speculative conjecture: Einstein's spacetime revolution did not complete a thorough conceptual renewal. Special relativity still retains the underlying presupposition that "there exists a constant, unchanging four-dimensional spacetime substrate." In essence, it replaces Newton's two independent absolutes with a single four-dimensional holistic absolute. Some frontier difficulties encountered in modern physics research may have their roots precisely in this residual absolute spacetime mode of thinking. Only by abandoning the presupposition of a fixed, unchanging spacetime ontology and understanding spacetime as an inherent physical property of the universe, whose manifested form changes with the relative velocity level of the observing system, may it be possible to open up an entirely new way of understanding spacetime.

Main Text

The spacetime picture of Newtonian classical physics is very intuitive. In Newton's conception, space is like an infinitely large, never-deforming rigid box; all things move inside the box, and the box itself is not affected by matter or motion. Time is a river that flows uniformly, independent of all matter; no matter what changes occur in the world, the rate at which time passes remains forever constant. Space and time are mutually independent, each possessing absolute, unchanging properties. This model perfectly suited the low-speed, small-scale production and observational activities of ancient and early modern humans, and supported the development of mechanics and astronomy for several hundred years.

With the development of electromagnetism, irreparable contradictions appeared in Newton's absolute spacetime framework. Maxwell's equations derived a constant speed of light, but this could not be explained self-consistently within Newton's absolute space framework. Einstein founded special relativity and achieved a key intellectual breakthrough. He no longer regarded space and time as two mutually independent entities, but integrated the two into a unified four-dimensional spacetime continuum. The Lorentz transformation reveals that between different inertial reference frames, spatial coordinates and temporal coordinates become coupled with each other. Moving objects undergo length contraction, and moving clocks undergo time dilation. Neither spatial length alone nor temporal interval alone possesses absolute meaning any longer; measurement results depend on the reference frame. From this point of view, Newton's separate absolute space and absolute time were overthrown. This was a milestone advance in humanity's view of spacetime.

But if one continues to inquire at a deeper level, special relativity still retains a hidden premise: the four-dimensional spacetime interval is a Lorentz invariant. No matter what inertial motion state an observer is in, and no matter how the reference frame is transformed, the four-dimensional spacetime interval between two events always remains constant. In other words, although different observers obtain different measurement results for the spatial component and the temporal component, they all share the same fixed, unchanging four-dimensional spacetime ontology.

Here the remnant of the old conception becomes apparent: Newton's core belief was that "there exists an absolute substrate independent of matter and observers," except that this substrate was split into two parts, space and time. Special relativity merely merges the two substrates into a single four-dimensional holistic substrate. The substrate itself is still an objective, fixed background that does not change with the relative velocity of observation. The core mode of thinking of the old absolute spacetime—presupposing an eternal, unchanging spacetime stage—has not been thoroughly abandoned. This is the shadow of absolute spacetime remaining in the relativistic system.

It is precisely this residual conception that may limit subsequent physical exploration and become an intellectual obstacle to frontier problems related to spacetime. For a long time, theories studying gravity and spacetime geometry have mostly unconsciously assumed by default that spacetime is a pre-existing continuous background, and that matter moves and interacts upon this background. Even though general relativity proposes that matter can curve spacetime, at its foundation it still retains the presupposition of spacetime as a continuous substrate. Much exploratory work on the nature of spacetime merely continuously modifies the geometric rules of this substrate, without questioning the inherent premise rooted in the absolute spacetime view that "spacetime itself is a fixed background."

Stepping outside this inherent framework, a new conjecture can be proposed: there is no pre-existing, fixed, unchanging four-dimensional spacetime ontology. Spacetime is not the stage of the universe, but an inherent physical property of the universe itself. This property has no single fixed external form; the geometric appearance it presents to an observing system is determined by the relative velocity level between the observing system and the universe.

When the relative velocity is in the macroscopic low-speed range, spacetime manifests as a Euclidean flat form, and Newtonian mechanics is sufficiently useful. When the speed approaches the speed of light and enters the sub-light-speed range, synchronization effects such as length contraction and time dilation appear. But this is only a low-dimensional mapping distortion of the higher-dimensional spacetime structure within this velocity range, belonging to a contrast effect brought about by observation across reference frames; the spacetime ontology itself does not undergo topological change. If motion speed can break through the light-speed threshold, then a true topological reconstruction of the spacetime ontology will be triggered, and spacetime folding will occur. At the same time, based on the common origin of spacetime, time depends on spatial changes; once the spatial configuration changes, the measurement of time must change synchronously.

According to this line of thought, spacetime is no longer a fixed background waiting for matter to fill it. Low speed, sub-light speed, and superluminal speed are merely different appearances manifested by the spacetime properties of the universe under different conditions. Once the residual presupposition inherited from absolute spacetime—that "there exists an unchanging spacetime substrate"—is abandoned, many difficult problems related to spacetime may obtain entirely new perspectives for understanding.

Conclusion

Einstein's theory of relativity destroyed Newton's separate absolute space and absolute time, and is a tremendous leap in humanity's understanding of spacetime. However, this revolution stopped there and failed to thoroughly abandon the underlying presupposition that "there exists a constant spacetime ontology." The thought of the old absolute spacetime still lurks in the foundations of the theory. Some of the difficulties encountered in contemporary physics in researching the nature of spacetime are more or less constrained by this residual conception.

If we wish to go further in understanding the nature of spacetime, it is necessary to thoroughly discard the presupposition of a fixed spacetime background. Regard spacetime as a dynamic physical property of the universe, whose manifested form changes with the level of relative velocity. From this perspective, length contraction and time dilation are only shallow mappings under high-speed conditions, while spacetime folding is the intrinsic form of spacetime at a higher velocity level. This may be a new way of thinking that penetrates appearances to explore the underlying truth of spacetime.