Space and time are apparently **fundamental** in the universe. The origins and the nature of space and time has fascinated humans for millenniums with no comprehensive understanding of why and how they are so. That space and time are so **ubiquitous** but they are so **elusive** to elucidate, is an ongoing **challenge** to philosophers and scientists, even in the 21st century.

Why is it so difficult to do so?

Let’s explore this intractable problem by first defining what is space and time.

**1. What is space?**

From http://en.wikipedia.org/wiki/Space

Space is the boundless three-dimensional extent in which objects and events have relative position and direction.

**2. What is time?**

From http://en.wikipedia.org/wiki/Time

Time is a dimension in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them.

The above definition of time is **problematic** as the words “events”, “past”, “present”, “future”, “duration” and “intervals” are all temporal descriptions (which are related to time itself) and hence the definition of time as such, is circular.

So, how can time be defined without circularity?

We can try to define time wrt **change** (the process of becoming different). However, if we do that, it implies if there is no change, there is no time which is very odd indeed, although it is consistent with the taoist philosophical concept that change is universal in the universe which entails time is also universal in the universe, if time is related to change.

OTOH, the other apparently seemingly strange consequence of associating time with change is that there is variable time for variable change, i.e. there is no fixed duration of time as measured by clocks. However, we can contend that clocks do not measure time per se as all clocks depend on the constant motion or oscillation of some entity (from pendulums to Cesium atoms) which gives us the illusion/delusion of the regular passing of time.

http://www.sciencedaily.com/releases/2005/04/050415115227.htm

Time is represented through change, such as the circular motion of the moon around Earth. The passing of time is indeed closely connected to the concept of space.

Thus, for convenience, we can measure time with clocks (despite knowing it is not necessarily so), for the purposes of commerce, legality, travel and science etc.

What is spacetime?

http://en.wikipedia.org/wiki/Spacetime

In physics, spacetime (also space–time, space time or space–time continuum) is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as existing in three dimensions and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions.

Since spacetime is a mathematical model and not necessarily as such in reality, it is prudent to consider spacetime as just that.

What is the philosophy of space and time?

http://en.wikipedia.org/wiki/Philosophy_of_space_and_time

Philosophy of space and time is the branch of philosophy concerned with the issues surrounding the ontology, epistemology, and character of space and time.

And what are the origins and nature of space and time?

From this interesting article in Nature:

http://www.nature.com/news/theoretical-physics-the-origins-of-space-and-time-1.13613

No account of what is space and time in general relativity or quantum mechanics:

If nothing else, they say, neither of the two great pillars of modern physics — general relativity, which describes gravity as a curvature of space and time, and quantum mechanics, which governs the atomic realm — gives any account for the existence of space and time. Neither does string theory, which describes elementary threads of energy.

Gravity as thermodynamics without bending space-time?

From that, he found, the mathematics yielded Einstein’s equations of general relativity — but using only thermodynamic concepts, not the idea of bending space-time.

“This seemed to say something deep about the origins of gravity,” says Jacobson. In particular, the laws of thermodynamics are statistical in nature — a macroscopic average over the motions of myriad atoms and molecules — so his result suggested that gravity is also statistical, a macroscopic approximation to the unseen constituents of space and time.

Causality, causal dynamical triangulations and discrete space:

But, like Sorkin, Loll and her colleagues found that adding causality changed everything. After all, says Loll, the dimension of time is not quite like the three dimensions of space. “We cannot travel back and forth in time,” she says. So the team changed its simulations to ensure that effects could not come before their cause — and found that the space-time chunks started consistently assembling themselves into smooth four-dimensional universes with properties similar to our own

Quantum entanglement and space-time are the same thing?

So, in effect, Van Raamsdonk concluded, the three-dimensional universe is being held together by quantum entanglement on the boundary — which means that in some sense, quantum entanglement and space-time are the same thing.

Or, as Maldacena puts it: “This suggests that quantum is the most fundamental, and space-time emerges from it.”

This is the state of investigations into the origins and nature of space and time at present.

Are we close to elucidating the origins and nature of space and time?

Which is more fundamental, space or time, in the universe?

And, what is time?

Only time will tell.