A conceptual essay on the nature of spacetime
Authors: Ferreira Ricardo B. , Ferreira João B. 
Published: December 2020

Our mind seems to be formatted to imagine a “motionless” material particle (or more accurately a region of spacetime at rest relative to that material particle) fixed in space as an absolute reference and to consider the existence of space and time as independent universal
entities, as we perceive when we measure them with a ruler and a clock, respectively. Instead, let us first hypothesize that singularities are the absolute reference for the universe, that the speed of light in vacuum (c = 299 792 458 m/s) is universal and absolute,
and that deceleration/acceleration is the “driving force” that defines spacetime. Frames of reference anchored on material particles/objects may be grouped as having zero acceleration (inertial frames), nonzero, constant acceleration (pseudoinertial frames) or nonzero, variable
acceleration (noninertial proper frames), so that a noninertial proper frame may be considered as composed of an infinite number of pseudoinertial frames. The universality of c is ensured by its absolute constancy, when both observer and moving beam of photons are in frames of reference
differing neither in speed nor in acceleration, as is the case within inertial or pseudoinertial frames, respectively. However, its value (as that of any other speed) is measured as different when the observer is at an inertial or pseudoinertial frame and the beam of photons is moving in another,
thus differing in Lorentz factor (γ) or acceleration, respectively. Speed, velocity, and acceleration (including the effect of gravity on a material particle/object) are all defined in terms of space and time. However, space and time do not exist as independent universal entities,
as they are integral components of one and the same inextricable physical entity, spacetime. Assuming spacetime forms a continuum, it is expected that anything affecting one will affect the other. This has been widely recognized for gravity, but not for speed—something which becomes
clearer if we assume that it should in fact be acceleration/deceleration that moves a material particle from one frame of reference into another. Several conditions that are grouped under gravity-dependent and non-gravity-dependent act individually or in combination to submit a matter particle
to acceleration. Therefore, when perceived from the Earth (or any other place at v < 299 792 458 m/s), any departure from c caused by deceleration should expand space and contract time. Any further deceleration or subsequent acceleration (for as long as
v < c) will alter spacetime. Hence, in astrophysics, deceleration rather than acceleration should be the main driving or direct physical quantity. It is proposed that any deceleration/acceleration distorts spacetime. A method to combine the effects of several
conditions that define the acceleration status of a material particle in spacetime is proposed. The higher v/c and/or gravity-dependent acceleration, the greater time dilation and space contraction will be. At the singularity, time dilation and space contraction will be maxima.
The actual “position” of a material particle in spacetime may therefore be defined by the sum of all changes it suffered in deceleration/acceleration (due to changes in gravity-dependent and non-gravity-dependent accelerations) since the singularity. The impossibility of exceeding
the speed of light in vacuum is discussed and tentatively demonstrated. In line with the present hypothesis, both time and space are relative, but only partially due to the limits imposed by c, opening the possibility for the concept of spacetime partial relativity. According to our
proposal, spacetime is defined by a special form of deceleration, which we have termed relativistic or Lorentz deceleration: it is a deceleration-dependent elastic property of any matter particle moving at v < c. It expands/contracts precisely because of the
effect of deceleration/acceleration on matter particles moving at v < c. According to these views, defining a singularity should depend on the perspective. When perceived from the Earth or any other place at v < c, a singularity
is a spaceless point of infinite density, associated with the speed of light and where a second lasts forever. However, when “perceived” from within a singularity, space is there and time flows. Based on this work, a singularity may be defined in higher detail as the embryonic
state of the universe (or a part of it), associated with two universal absolute constants: the speed of photons (c = 299 792 458 m/s) and the quantity of spacetime. It also corresponds to a standard spacetime condition, in which time is dilated and space contracted
to maximum values. The Big Bang is interpreted not as an explosion or bang, but rather as an infinitesimal deceleration from the singularity, thus triggering the initial exponential space expansion and time contraction and leading to matter formation. Neither space nor time are created or
destroyed—They are always there since the singularity but vary widely in contraction/expansion magnitude with each precise spacetime condition, as deceleration-dependent fluctuations take place in spacetime. Gravity, an inherent property of matter, and entropy are key players in the
subsequent evolution of the universe. Uncountable successive and cumulative changes in deceleration suffered by material particles determine the precise conditions they occupy at each moment in spacetime, thus allowing the build-up of a gigantic and highly dynamic noninertial frame of reference,
i.e., our universe. Individual observers at single points of the universe should all see light photons moving in vacuum at 299 792 458 m/s (or any material particle/object moving at v < 299 792 458 m/s) and perceive space and time identically, each within
their own spacetime condition. Differences arise only when one observer “looks” at other observers in distinct spacetime conditions. An attempt is made to interpret spacetime and light when we “look” at frames of reference distinct from our own, since this is precisely
what we “see” when we observe the universe from the Earth. Cosmological models are typically based on several assumptions. The hypothesis formulated in the present article is no different, with a singularity as its major reference. We conceptualize on a cosmological model that
challenges some currently accepted views of the universe.