Space-time overall is four-dimensional, or (3 + 1)-dimensional, where time is the fourth dimension. It's well-known that the time dimension is related to the second law of thermodynamics: time has one direction (forward) because entropy (a measure of disorder) never decreases in a closed system such as the universe.
Space in our Universe is three dimensional, and when you combine it with time, you get a four dimensional quantity. When it comes to the notion of spacetime curvature, this is what General Relativity refers to.
An event is represented by a set of coordinates x, y, z and t. Spacetime is thus four dimensional.
As far as cosmologists can tell, space is almost perfectly flat. But what does this mean? The theory of general relativity, under which space itself can curve, allows for the universe to take one of three forms: flat like a sheet of paper, closed like a sphere, or open like a saddle.
It is modeled using the Einstein Field Equations (EFE) as a 3+1 dimensional space. It is often illustrated to the layperson as a 2 dimensional flat surface because it is easier to do illustrations as isometric projection then present something like a 3D wire frame.
Our Universe as we know it has four dimensions: the three dimensions of space (up and down, left and right, back and forth), and one dimension of time that keeps us all ticking along.
We, along with space and time, considered the mass as the fifth dimension of the universe, and generated five-dimensional universe and solved the Einstein's field equations in some simple cases, and obtained solutions around a star in five-dimensional universe, which is, otherwise flat.
(While a black hole is a three-dimensional object, its surface has just two spatial dimensions.)
We know that our Universe is three dimensional: space, and all of the objects which exist inside it, have a width, a breadth, and a height.
Drawing upon the Holographic Principle, the premise behind the Fermilab project is that space is two dimensional, and that the third dimension is inextricably linked with time. If that's the case, our 3D world is merely an approximate illusion.
The fifth dimension is a micro-dimension which is accepted in physics and mathematics. It's here to have a nice and seamless tie between gravity and electromagnetism, or the main fundamental forces, which seem unrelated in the regular four-dimensional spacetime.
There's no time without space
Additionally, according to Einstein's general theory of relativity, the gravity of a large object can impact how quickly time passes.
He was a superb mathematician and physicist with uncanny intuition and excellent technical mastery, but he did not have any special organ in his brain that let him draw or see in four dimensions. Two common methods of visualizing the fourth dimension are to use color or time.
In general relativity, spacetime is not 'flat' but is curved by the presence of massive bodies. This artistic representation visualises spacetime as a simplified, two-dimensional surface, which is being distorted by the presence of three massive bodies, represented as coloured spheres.
In General Relativity, four-dimensional spacetime is curved. There are basically three possible shapes to the Universe; a flat Universe (Euclidean or zero curvature), a spherical or closed Universe (positive curvature) or a hyperbolic or open Universe (negative curvature).
Physics > Space and Time
According to Einstein , you need to describe where you are not only in three-dimensional space — length, width and height — but also in time. Time is the fourth dimension.
In physics, information has sometimes been proposed as the fifth dimension, the first three being the three axes of space, and the fourth being time. This is because information influences and shapes the physical reality of the universe similar to space and time.
We could think of the universe as a sphere expanding indefinitely and infinitely. Or it might curve and bend in ways that could make it a closed system (like a donut), where if you were to travel in a straight line for long enough, eventually you'd end up back where you started: space would be finite.
The world as we know it has three dimensions of space—length, width and depth—and one dimension of time. But there's the mind-bending possibility that many more dimensions exist out there. According to string theory, one of the leading physics model of the last half century, the universe operates with 10 dimensions.
In everyday life, we inhabit a space of three dimensions – a vast 'cupboard' with height, width and depth, well known for centuries. Less obviously, we can consider time as an additional, fourth dimension, as Einstein famously revealed.
A hypersphere is the four-dimensional analog of a sphere. Although a sphere exists in 3-space, its surface is two-dimensional. Similarly, a hypersphere has a three-dimensional surface which curves into 4-space. Our universe could be the hypersurface of a hypersphere.
So you don't necessarily have to look up but you can look out and see heaven. Heaven is a fourth dimension if you will," he tells Walters.
According to this model, there are only three dimensions of linear direction: variations of up, right, and forward. In other words, height, length, and width. But even with all the practicality of Euclid's model, the concept cannot be mathematically proven, opening the doorway to another fourth direction.
We live in a world of three dimensions.
We move through space , either left or right, forward or backward, up or down. Everything around us, from the houses we live in to the objects we use in everyday life, has three dimensions: height, length, and width.