## When in the early evolution of the universe did it switch from being a radiation dominated universe to a matter-dominated universe?

In the early stages of the Big Bang, most of the energy was in the form of radiation, and that radiation was the dominant influence on the expansion of the universe. Later, with cooling from the expansion the roles of matter and radiation changed and the universe entered a matter-dominated era.

**How long was the universe dominated by radiation?**

about 50,000 years

After about 50,000 years, the density of matter exceeded the density of radiation for the first time, eventually dominating the universe.

### During which epoch did the universe rapidly expand?

About 13.75 billion years ago, all of the contents and energy in the universe was contained in a singularity with infinite density and temperature. It began to expand rapidly and this expansion is known as the Big Bang.

**When did the universe become matter dominated?**

Matter is thought to have become predominant at a temperature of around 104K, roughly 30 000 years after the Big Bang. This marked the start of the matter era. See also Radiation era.

#### What is the estimated age of the universe?

13.77 billion years

In turn, knowing the composition with this precision, we can estimate the age of the universe to about 0.4%: 13.77 ± 0.059 billion years! How does WMAP data enable us to determine the age of the universe is 13.77 billion years, with an uncertainty of only 0.4%?

**What came first space or time?**

According to Albert Einstein, space and time are simply different aspects of the same entity now called ‘spacetime’. It therefore seems plausible that they came into existence simultaneously.

## How long did it take for the universe to form?

It took quite a bit more than seven days to create the universe as we know it today. SPACE.com looks at the mysteries of the heavens in our eight-part series: The history & future of the cosmos.

**What is lookback time?**

The time elapsed between when we detect the light here on Earth and when it was originally emitted by the source, is known as the ‘lookback time’. The more distant an object is from us, the further back in time we are looking.

### What happened in the recombination era?

As the Universe expanded, however, its density and temperature dropped until (after about 380,000 years) the conditions were such that ions and electrons could ‘recombine’ to form atoms (mostly hydrogen and helium). This is known as the ‘epoch of recombination’.

**What is the scale factor of the dilation?**

What is the scale factor of the dilation? So they don’t even tell us the center of the dilation, but in order to figure out the scale factor you just have to realize when you do a dilation, the distance between corresponding points will change according to the scale factor.

#### When the center of dilation is the origin of the figure?

When the center of dilation is the origin, the figure can be dilated by using the rule ( kx, ky) where k is the scale factor and ( x, y) is the original coordinate. Triangle ABC undergoes an enlargement by a scale factor of 2 about the origin.

**What is a dilation in math?**

A dilation in math is an enlargement or reduction of a figure about a center of dilation by a specified scale factor, k. It is a type of transformation that creates similar figures. The original figure will either grow in size or shrink, depending on the scale factor.

## What is the scale factor of the length of the numbers?

Well they give us the scale factor, and so what it tells us, the scale factor is 5/2. That means that the corresponding lengths will change by a factor of 5/2.