What does 3K cosmic background radiation mean? 1.Immediately after the Big Bang,

Question

What does 3K cosmic background radiation mean?

1.Immediately after the Big Bang, there were more microwave radiation than other types of electromagnetic waves
The universe’s average temperature is measured to be about 3 degree Kelvin
As stars die, their temperature will eventually get to 3 degree Kelvin
The universe went through a rapid expansion earlier causing the photons’ temperature to drop so that the corresponding thermal radiation spectrum picks at microwave region.
All of above What does 3K cosmic background radiation mean?

1.Immediately after the Big Bang, there were more microwave radiation than other types of electromagnetic waves
The universe’s average temperature is measured to be about 3 degree Kelvin
As stars die, their temperature will eventually get to 3 degree Kelvin
The universe went through a rapid expansion earlier causing the photons’ temperature to drop so that the corresponding thermal radiation spectrum picks at microwave region.
All of above What does 3K cosmic background radiation mean?

1.Immediately after the Big Bang, there were more microwave radiation than other types of electromagnetic waves
The universe’s average temperature is measured to be about 3 degree Kelvin
As stars die, their temperature will eventually get to 3 degree Kelvin
The universe went through a rapid expansion earlier causing the photons’ temperature to drop so that the corresponding thermal radiation spectrum picks at microwave region.
All of above

Explanation / Answer

The cosmic microwave background radiation (CMBR, same as cosmic microwave radiation and similar) is a uniform field of microwaves across the sky.

We first found it by accident in 1964, although it was predicted before then.

It is the afterglow of the big bang. When you have an old TV tuned to static, about one percent of that static is the CMBR. When you turn on a geiger counter, a small amount of the clicks you hear are due to the CMBR.

Because the universe is expanding, new space is being created everywhere. Any two points will get further apart as time goes on.

The CMBR is being stretched out as the universe ages. Presently it is microwaves, and soon it will become radio waves. In the past, it was infrared, visible light, ultraviolet, x-rays and initially gamma rays.

Since we know the temperature the universe was at the time of the big bang (we figure it out by looking at the amount of energy in the universe now), and the speed at which the CMBR is being stretched and diminished, we can find out how long in the past the energy of the CMBR and the universe at the big bang intersected. This intersection is the age of the universe.

It's currently thought to be about 13.7 billion years ago.

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