##### Asked by: Autumn Bruuns

asked in category: General Last Updated: 30th April, 2020# Is the universe at critical density?

**Critical density**is the value at which the

**Universe**is at balance, and expansion is stopped. This value is estimated as (1-3)×10^-26 kg/m³ and it's calculated when you take the matter-energy

**density**of the

**universe**and divide it by the matter-energy

**density**of the

**universe**that is required to achieve that balance.

Correspondingly, what is the critical density of the universe?

The '**critical density**' is the average **density** of matter required for the **Universe** to just halt its expansion, but only after an infinite time. A **Universe** with the **critical density** is said to be flat.

One may also ask, is the density of the universe decreasing? The **density** of matter **decreases** as the **universe** expands because the volume of space increases. (Only a small fraction of matter is in the form of luminous stars; the bulk is believed to be dark matter, which does not interact in a noticeable way with ordinary matter or light but has attractive gravity.)

Subsequently, one may also ask, what are the possible fates of the universe if the density is lower than or equal to the critical density of the universe?

**If** the pressure of the matter is low, as is the case with most forms of matter we know of, **then** the **fate of the universe** is governed by the **density**. **If the density of the universe** is **less than** the **critical density**, **then** the **universe** will expand forever, like the green or blue curves in the graph above.

What shape of universe has a density of matter that is greater than the critical density?

This is known as an open **universe**. The **shape** of the **universe** depends on its **density**. If the **density** is more **than the critical density**, the **universe** is closed and curves like a sphere; if less, it will curve like a saddle.