What Exactly Is Spacetime?

Have you ever heard the term “spacetime” thrown around in various science articles around the web?  Just what exactly is “spacetime” and how does it relate to standard theories about space? I think Wiki manages a rather good description of this odd substance, so let’s start there.  Wiki defines spacetime as:

spacetime is any mathematical model that combines space and time into a single interwoven continuum. The spacetime of our universe is usually interpreted from a Euclidean space perspective, which regards space as consisting of three dimensions, and time as consisting of one dimension, the ‘fourth dimension’. By combining space and time into a single manifold called Minkowski space, physicists have significantly simplified a large number of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels…In cosmology, the concept of spacetime combines space and time to a single abstract universe.

From this summary we get the clear picture that spacetime is a purely mathematical construct used to build mathematical models.  In physical reality, there is no such thing as a substance called spacetime.  This important fact is often overlooked when scientific theories are presented to the public.

If we compare the definition of spacetime to the definition space, we see a stark contrast.  Wiki defines space as, “the boundless three-dimensional extent in which objects and events have relative position and direction.” There is no mention of “abstract” or “model” in that definition of space.

The spacetime concept merely defines a spatial coordinate and event system. The obtuse hieroglyphics often found in mathematical models which invoke this abstract mathematical universe are all related to defining where things are in relation to one another, as well as defining how objects move, their velocity, and the timing of events.

What often gets lost in the process of all this modeling is the fact that space itself has no physical properties that act upon matter. Often theories of bending space are presented as scientific fact, when in reality there is no such thing as bending space.  What scientists are really presenting are models of bending spacetime, which is a mathematical abstraction.

Some scientists confuse the properties of the model with the properties of real space.  The objectification of a model as being something real is called reification.  Again, I’ll go with Wiki’s description of this phenomena. Wiki states, “Reification generally refers to making something real, bringing something into being, or making something concrete.”  More specifically, the scientists are engaged in what’s called a reification fallacy, which Wiki defines as:

Reification (also known as concretism, or the fallacy of misplaced concreteness) is a fallacy of ambiguity, when an abstraction (abstract belief or hypothetical construct) is treated as if it were a concrete, real event, or physical entity. In other words, it is the error of treating as a concrete thing, something which is not concrete, but merely an idea.

Another common manifestation is the confusion of a model with reality. Mathematical or simulation models may help understand a system or situation but real life will differ from the model (e.g. ‘the map is not the territory’).

One of the most common reified models the general public may be familiar with looks something like this:


Reified model of spacetime

In reality, there is no such thing as bending space.  Space, which is nothing, has no physical properties that can act upon matter.

If you were to ask a mathematician if spacetime has real physical properties that can act upon matter, they would probably stare at you with a blank face.  This is because the question forces them to directly face a form of cognitive dissonance they’ve been carrying around with them since grad school.

They instinctively know the answer to that question is no.  They are well aware that spacetime is nothing more than a mathematical concept.  However, many of their theories depend on this mathematical abstraction actually being a real entity that is capable of acting upon matter.

The foremost example of reification in action comes from gravitational waves.  Again, Wiki is just spot on with the definitions today.  Wiki defines gravitational waves as:

In physics, gravitational waves are ripples in the curvature of spacetime that propagate as a wave, travelling outward from the source. Predicted in 1916 by Albert Einstein to exist on the basis of his theory of general relativity, gravitational waves theoretically transport energy as gravitational radiation.

Given that wiki defines spacetime as a pure mathematical abstraction, the bending of a mathematical abstraction cannot impart real force on a real object.  It is instructive to note that the search for gravitational waves turned up nothing for decades.

The LIGO gravitational wave observatory never detected a gravitational wave up to 2016. LIGO’s fourth science run [S4] and GEO600, which were in operation together, did not detect any gravitational waves. LIGO’s fifth science run [S5], which had all three interferometers running continuously in triple-coincidence for an entire year, did not yield any gravitational wave candidates.

Now suddenly, the LIGO team claims to have discovered gravitational waves.  As the NYT article points out, different scientists made the same claim back in 1969, and again in 1974, and again in 2014.  Each time the claims were later overturned.  Supposedly the event they detected this time was “50 times greater than the output of all the stars in the universe combined.”  – Does that sound plausible to you?  Recently scientists concluded that there are over a trillion galaxies in the observable universe, each containing an average of 100 billion stars.

All that power condensed into a tiny point in space, but we couldn’t see it because “black holes.”  Yeah, and I have a bridge in Alaska I’d like to sell you.  While I have no doubt that the LIGO team detected some signal in their interferometers, just what exactly caused that signal is entirely up for debate. Dr. Hilton Ratcliffe provides an excellent skeptical overview of the results here.   Thornhill also provides some excellent skepticism here:

Only real tangible matter can act upon real tangible matter.  This fact of science is respected in all other fields of science apart from cosmology.  Cosmology is the only field of science where abstract mathematical concepts are taken to be actual physical entities capable of imparting force to matter.

Defining gravity as bending spacetime creates other intractable problems. For example, quantum mechanics, which deals with objects on the atomic scale, has absolutely no working theory of gravity. In other words, scientists have no idea what actually causes gravity.

Supposedly a mysterious “massless” particle called a graviton is theorized to be the gravitational force carrier at the atomic level.  The Fermi National Accelerator Laboratory defines the graviton as being, “entirely theoretical constructs that delicately walk the knife-edge precipice between the domains of scientific respectability and the shady world of hand waving.”

A great deal of time and effort has gone into coming up with a theory of gravity that can define it at the atomic level, as well as at the macro level.  Creating such a theory would “unify” quantum mechanics and General Relativity.  It should be obvious this is impossible because General Relativity treats gravity as if it is a function of bending spacetime (a mathematical abstraction), while atomic level forces must be related to real physical particles or force carriers.  This leaves scientists trying to tie two completely different mathematical models together, both of which fundamentally have no basis in the real material world.  The attempt to unify the two has been going on for well over 100 years.

I could go on describing more problems that arise from reification until the cows come home, but I think you get the picture.  So let’s summarize.  Space does not bend.  No scientist has ever put forth a theory of bending space.  The only theories that have been put forth involve bending spacetime, which is merely a mathematical abstraction.  No black hole event horizon has ever been directly observed.

The mathematical abstractions were initially created to describe the observed movement of real objects, without defining what actually imparts force upon them.  This situation is similar to Newton’s laws of gravitation, which describe the action of gravity, without offering a hypothesis as to what causes gravity.  Over time, scientists have taken to assuming that bending spacetime is the actual cause of gravity, while forgetting that spacetime is merely a descriptor, not an actual causal agent that can do real work.