February 28, 2024

# There are indications that the universe may be flat, even though the Earth is not.

Among the many mysteries, there is one deceptively simple, but one that arouses our curiosity: after all, what is a form UniverseðŸ‡§ðŸ‡·

To get to the correct answer, we have to solve Gas Dark matter, dark energy, and some other very important problems, but we don’t have the tools to do that yet.

So, for now, we have our best guess: The universe is, as far as we know, three-dimensional. planðŸ‡§ðŸ‡· Now, that doesn’t mean we live in Flatlandia or some other way a land It is flat (in fact, it is not).

### Engineering question

It’s about the geometry of the universe, and a flat universe has a very simple geometry, something you probably encountered in math class at school: two parallel lines will never meet, and the sum of the interior angles of a triangle is always 180 degrees.

The geometry of the universe is estimated based on the properties of the various components: electromagnetic radiation, ordinary matter, dark matter, and dark energy.

If the sum of all the densities matches an exact number called the “critical density”, then Universe It’s flat. A smaller or larger value produces completely different geometries, as you can see below.

If the density of the universe is less than the critical density, it will be shaped like a saddle or a Pringle (If the universe is two-dimensional). In this universe, two parallel lines not only never meet, but also diverge more and more. This is known as the “open universe”.

On the other side of the critical density is the “closed universe”. The universe, in this case, has a geometry that has the 2D equivalent of the surface of a sphere.

This doesn’t mean the universe is a big sphere, it’s just ways we can understand the complexity of 4D geometry using something we know.

on me Universe Closed parallel lines meet twice. This may sound completely wrong, but it’s easy to imagine.

Observations of the components of the universe tell us that it is in fact very close to a critical density, very close to being flat, with uncertainty in the closed region of the universe. UniverseðŸ‡§ðŸ‡· Although the geometry is simple, there are many physics problems to solve.

First of all, it is still not known exactly what they are. issue dark And the dark energy, which could affect the geometry of the universe. Even if we ignore it, there are more issues for us to solve.

For the universe to have a density very close to today’s critical density, it would need to have exactly the critical density during the Big Bang. However, there is no reason for this to happen.

There are scenarios that solve this and other problems, such as cosmic inflation, but there are still no experimental confirmations. The size of the universe, whether it is infinite or not, depends on its shape (among other factors). But this, as they say, is another story.