What comes to mind when you think of space?
Metaphysical “space” is a distinct concept from the well-known “outer space”. It’s what’s left after you take away everything you can sense, everything you can see, everything you’ve ever interacted with; the earth itself, molecules, atoms, particles — all gone. So what’s left? Well it’s not nothing, it’s something: it has properties, it’s dynamic, it dictates how things move, and it’s just as real as anything else. It’s called space and it’s probably the most abundant thing in the universe.
Now spacetime is the 4-dimensional external reality that underlies our collective experiences of the space between things and the time between events. Spacetime is flexible: it can bend, twist and ripple because of its inherent springiness. It has hidden characteristics that allow for “something’s” to come seemingly “from nothing”.
Gravity is the shape of spacetime itself. Objects in spacetime cause it to curve (creating a gravity well – picture the moon flowing along the curve in spacetime caused by Earth). Space also consists of dark matter and dark energy — we call it that because we don’t really know what it is. However, it makes up 70% of the known universe and was recently discovered this century — we now know that dark energy is intrinsic to empty space.
The implications of these findings include that everything we experience is only a really tiny fraction of reality! Contrary to our senses (which cannot perceive more than 3 dimensions), we are evolving through a spacetime which we perceive only in temporal 3D crosscuts, or each individual moment which we refer to as “now”.
Now, Einstein contributed to physics the Theory of Special Relativity in which he puts forth his famous E=MC2. In this theory, he states that both space and time are personal and relative to observer, where it was previously thought that they were absolute and independent of observer. Two particles that are in motion relative to each other can disagree on 1) how much time passes between events, as well as 2) how much space lies between things, and neither are wrong.
In 1991, to test Einstein’s theory, we flew atomic clocks around world in two separate jet airplanes and compared the in-flight clock to one on ground: they no longer had same time (by few 100 billionths of a second — but still real proof!)
Does this mean that our experience is entirely subjective? Nah.
Causality stands as our only objective reality to which all observers will agree. Two observers may disagree on spatial and temporal distinctions but they will always agree on influences and causes of events. Causality is real and is what causes the temporal concepts that we need in order to perceive reality.
Reality is not 3-dimensions that evolve in time, it’s a 4D non-euclidean geometric space that we call spacetime. If we were to plot points on a spacetime graph, the points would correspond to objectively-real events, and only things that correspond to geometric relations in that space are objectively real (because they hold causal relations).
Spacetime is absolute and the concepts of the “separate entities” of space and time are made personal by way we observe and move through spacetime. Events that occur at the same time for one observer could occur at different times for another. Time, therefore, changes for anything that is moving. This time dilation proves curved spacetime, which we mentioned above.
So are we objectively real? Yes — if you are the sequence of all events that you are present, you are a geometric object in spacetime. Let’s bring back the spacetime graph: label one axis 3D and one axis Time. Suppose we connect all the points (events) on the graph with a line segment. This line segment is called a “world line”, and it represents your existence in spacetime. The line begins at the moment you were born and ends the moment you die, and tracks your experiences throughout spacetime.