## Introduction

Back in time there was space and there was time, and people have visualized both entities as individual aspects. Both space and time were described through coordinates, general mathematical formalism and both appeared in related ways. But there was no notion that explained space and time are the same things. Later Albert Einstein brought the idea of general relativity and then everyone started to discuss space-time as a single concept. Space time is an interesting topic to be studied for a better understanding of our space and surroundings.

## Time and Space

Let us first understand what time and space individually for a better understanding. What is the time? According to Albert Einstein, it is just an illusion, time is relative and it changes according to the observer. Albert Einstein considered time as the fourth dimension in space. We know that space is described by three coordinates, three spatial coordinates later Einstein elaborated space with four coordinates and time being the fourth coordinate. For detailed time and space theory, we must understand what is relativity and relative motion.

In the general theory of relativity, time had been termed as a relative quantity. Einstein’s relativity theory says time slows down or speeds up according to the observer. For example, on approaching the speed of light, the person in a spaceship would age much slower than his/her twin at home, also relativity suggests that gravity can bend time.

This picture of four dimensions is known as space time and we can say the space time meaning is the combination of space dimensions and time dimension. From time and space meaning, it is clear that time is assumed to be a new dimension. Whenever any object with mass hits the space-time fabric will cause bending of space-time. This bending of space time causes the objects to propagate in curved paths and this curvature is generally known as gravity.

### What is Space Time?

The conclusion about what is space time is a single fabric or the dimension wasn't one that Einstein reached by himself. The idea of space-time was having the contribution of German mathematician Hermann Minkowski, who said in a 1908 colloquium -Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.

The space-time described by Hermann Minkowski is still known as Minkowski space-time and it is serving as the backdrop of calculations in both relativity and quantum field theory.

This new reality was that space and time, as physical constructs, need to be combined into a replacement for a mathematical or physical entity called space-time, because the equations and mathematical formulations of relativity show that both space and time coordinates of any event must get combined by mathematics for describing accurately what we see. Because we know that space consists of three dimensions, and time is the one-dimensional quantity, space-time must be a four-dimensional object.

### Space Time Continuum

Space-time is believed to be a continuum because so far as we know that, there are no missing points in the space or the instants in time, and both can be subdivided without any apparent limit in size or duration. So, physicists recently started to consider our world to be embedded in this four-dimensional SpaceTime continuum, and all the events, places, moments in history, actions, etc.. are described in the space time continuum meaning. The space time theory suggests many peculiar things which will lead to the keen observation of the concept of black holes.

Now, we assume that the world-line exists as a whole object which may be dissected here and there so that you can see where the particle is located in space at a particular instant of time. Once we determine the complete world line of any particle due to the forces acting upon it, we have solved for its complete history. The world-line will not change with time, but it will simply exist as a timeless object or entity. In the general theory of relativity, when you solve mathematical equations for the shape of space-time, this shape will not change in time but will exist as a complete timeless object. We can slice it into some parts for examining what the geometry of space looks like at a particular instant.

Despite its difficulty, relativity remains the best way to account for the physical phenomena we know about. Yet physicists and many mathematicians know that their models are incomplete because relativity is still not fully reconciled with quantum mechanics, which explains the properties of subatomic particles with extreme accuracy and precision but does not incorporate the force of gravity.

Quantum mechanics or quantum physics rests on the fact that the tiny bits making up the universe are discrete, or quantized. So photons, the particles that make up light, are like little chunks of light that come in distinct packets.

### Did You Know?

Some scientists have speculated that perhaps space-time itself also comes in these quantized quantities, assisting to relate the relativity and quantum physics. Few scientists at the European Space Agency have proposed the Gamma-ray Astronomy International Laboratory for Quantum Exploration of Space-Time (GrailQuest) mission, which might fly around our planet and make ultra-accurate measurements of distant, powerful explosions called gamma-ray bursts that would reveal the up-close nature of space-time. Such a mission wouldn't launch for a minimum of a decade and a half but, if it did, it might perhaps help solve a number of the most important mysteries remaining in physics.

1. What is Time and Space? Why is it Called Space-Time?

Ans: Initially while studying non-relativistic mechanics we were only aware of the three dimensions and henceforth studied the coordinates accordingly. Later when Einstein proposed his theory of relativity he brought the idea of time being an illusion and different dimension and called that fourth dimension along with space dimensions as space-time.

2. What is Space-Time Made of and How are Space and Time-Related?

Ans: Space-time made of four coordinates, three space dimensions and a one-time dimension. Space and time relation is given by the coordinates. They’re interrelated to one another by coordinate systems in relativistic mechanics.