The
shape of the universe is an issue very important for cosmology, since
the final destination of the own universe depends on the form that has. However, it is still impossible to find out.
The shape of the universe depends on its density, i.e. the amount of mass and energy. The problem is that we don't know which size has the universe or how much energy and matter there are in total. So we can not calculate its density.
Einstein's theories posed three possible ways: closed, open, or flat. Although the shape of the universe continues to be an enigma, the majority of scientists believes that it is almost flat.
Open universe: the density of matter and energy is too low, the universe is curve outward. It will take the form of a saddle. It will be an infinite universe, infinite expansion. Gravity will be so weak that there can be no stars, planets, or even atoms. Matter will be separated and will disintegrate until being reduced to elementary particles. The universe will cool and die. This end is called the Big Chill.
Flat universe: if the amount of matter and energy is adequate, the density will be balanced. It is what is called the critical density. Then the universe is flat. Gravity and expansion will be in balance. The universe expands, but more and more slowly.
Translation for educational purposes authorized by: Astronomía: Tierra, Sistema Solar y Universo
The shape of the universe depends on its density, i.e. the amount of mass and energy. The problem is that we don't know which size has the universe or how much energy and matter there are in total. So we can not calculate its density.
Einstein's theories posed three possible ways: closed, open, or flat. Although the shape of the universe continues to be an enigma, the majority of scientists believes that it is almost flat.
Type of universe  Density  Form  Final destination 
Closed universe

High

Spherical

Collapse and Big Crunch

Open universe

Low

Saddle

Cooling and Big Chill

Flat universe

Critical

Flat

Slowed down expansion

The shape and fate of the universe
The universe can have three possible ways:
Closed universe: if there is too much matter and energy, the density is very high. The universe curve inward and will shape of sphere. It will be a finite universe. Gravity will be stronger than the expansion, all matter will be grouped, and the universe will collapse. This end is called the Big Crunch. Open universe: the density of matter and energy is too low, the universe is curve outward. It will take the form of a saddle. It will be an infinite universe, infinite expansion. Gravity will be so weak that there can be no stars, planets, or even atoms. Matter will be separated and will disintegrate until being reduced to elementary particles. The universe will cool and die. This end is called the Big Chill.
Flat universe: if the amount of matter and energy is adequate, the density will be balanced. It is what is called the critical density. Then the universe is flat. Gravity and expansion will be in balance. The universe expands, but more and more slowly.
Today
it is believed that the universe is almost flat, but there are still
many doubts, it is shown that the universe is expanding ever faster, and
this seems like a contradiction with the theory.
Translation for educational purposes authorized by: Astronomía: Tierra, Sistema Solar y Universo