# What is meant by density in units of critical density?

• indie452
In summary, density in units of critical density is the measurement of the amount of mass or energy per unit volume of space in the universe, compared to the minimum amount needed for the universe to stop expanding and collapse. It is calculated by dividing the mass or energy of the universe by its volume and is important in cosmology for understanding the structure and evolution of the universe. The units of measurement are typically kilograms per cubic meter or grams per cubic centimeter. The density in units of critical density determines the fate of the universe, with a lower density resulting in indefinite expansion and a higher density leading to eventual collapse, known as the Big Crunch scenario.

#### indie452

what is meant by density, such as the baryonic matter density in cosmology, in "units of the critical density"?

its mentioned in a question i need to do but i don't really know what it means.

that means number of baryons per unit volume of space. The critical density is the density of matter in the universe such that the universe would be flat and it's 9.9 x 10-30 g/cm3

## 1. What is density in units of critical density?

Density in units of critical density refers to the amount of mass or energy per unit volume of space in the universe, measured in terms of the critical density. The critical density is the minimum amount of mass or energy needed for the universe to eventually stop expanding and collapse.

## 2. How is density in units of critical density calculated?

Density in units of critical density is calculated by dividing the mass or energy of the universe by the volume of the universe. This value is then compared to the critical density to determine if the universe is expanding or collapsing.

## 3. Why is density in units of critical density important in cosmology?

Density in units of critical density is important in cosmology because it helps us understand the overall structure and evolution of the universe. By comparing the density of the universe to the critical density, we can determine if the universe will continue to expand or eventually collapse.

## 4. What are the units of measurement for density in units of critical density?

The units of measurement for density in units of critical density are typically kilograms per cubic meter (kg/m3) or grams per cubic centimeter (g/cm3). These units represent the amount of mass or energy per unit volume of space in the universe.

## 5. How does the density in units of critical density affect the fate of the universe?

The density in units of critical density plays a crucial role in determining the fate of the universe. If the density is less than the critical density, the universe will continue to expand indefinitely. However, if the density is greater than the critical density, the universe will eventually stop expanding and collapse. This is known as the Big Crunch scenario.