It’s hard to believe, but it’s true: this is the actual shape of the Universe (photo).

Measuring the shape of the Universe is challenging. The answer to the question of what shape the Universe has is highly controversial because when we think about the shape of something, we tend to envision an object visible from the outside. However, the Universe does not have an external perimeter, and nothing exists outside of it, as there is no outside, writes Space.

What shape does the Universe have?

To begin with, astronomers find it difficult to understand the shape of the Milky Way since we live inside our galaxy. However, observations of other similar galaxies provide insights into the shape of the Milky Way. The situation is much more complex with the Universe, as scientists do not have a similar analogy for comparison.

The geometry of the Universe is determined by the density of matter within it. Einstein's general theory of relativity describes how matter can warp space, meaning that the density of matter can influence the curvature and geometry of space on the largest scales. Additionally, quantum effects during the Big Bang may also have impacted the shape of the Universe.

Scientists measure the geometry of the Universe by comparing the average density of matter in space to the critical density of matter, which determines the curvature of space.

The Universe has critical density if it contains an average of six hydrogen atoms per cubic meter. However, matter is not evenly distributed throughout the Universe. When it comes to the density of matter in the Universe, scientists envision a uniform distribution of every atom within it. The definition of the shape of the Universe is also influenced by invisible dark matter, which makes up 85% of all matter in the Universe.

There are three possible geometric shapes for the Universe: open, closed, or flat.

• If the density of matter in the Universe is greater than the critical density, then the Universe can be considered closed and has positive curvature. In such a Universe, one could embark on a journey through space, moving in a straight line, ultimately returning to the starting point. Positive curvature is convex rather than concave, indicating that the Universe has the shape of a spherical surface.
• If the density of matter in the Universe is less than the critical density, then the Universe is open and has negative curvature. Therefore, it should take the shape of a saddle and have infinite extent.
• If the Universe has the same density of matter as the critical density, then the Universe is flat. Measurements show that the density of matter nearly coincides with the critical density, suggesting that our Universe is flat. A flat Universe has Euclidean geometry, meaning that the Universe possesses flat geometry.

What other shapes could the Universe have?

Although many measurements indicate that the Universe is flat, some scientists have discovered that a flat Universe does not necessarily exclude complex shapes. For example, it could have a shape known as a 3-torus.

A one-dimensional circle is known as a 1-torus. A 2-torus, which exists in two dimensions, has the shape of a doughnut. Now, imagine a 3-torus, which exists in three dimensions. Picture a cube turned inside out, with opposite sides bending and deforming until they twist together and touch. This is a 3-torus.

Scientists believe that different shapes of a 3-torus could maintain the illusion of a flat Euclidean geometry of the Universe. Theoretically, such a shape could have emerged as a result of quantum effects during the Big Bang.

At the same time, other scientists have proposed 18 mathematically possible shapes that correspond to a flat Universe, and perhaps one of them is the true shape of our Universe.

The future fate of our Universe

• In a closed Universe, gravity will eventually halt the expansion of space. In this case, the Universe will begin to contract until all matter gathers at a single point, resulting in what is known as the Big Crunch. This is essentially the reverse of the Big Bang.
• In an open Universe, there is not enough gravity to slow down the expansion of space. The accelerated expansion driven by dark energy will continue until the Big Rip occurs, meaning the Universe will tear apart.
• However, in a flat Universe, space will expand forever, but this expansion will gradually slow down. Ultimately, this process will lead to what is known as the Big Freeze. In the end, a cold dark cosmos awaits. If our Universe is flat, this is the fate that lies ahead.

It is important to note that scientists do not yet know how dark energy will behave in the future, which means that the ultimate fate of our Universe remains undetermined.