How does cosmic background radiation differ from other types of radiation?

Answer 1

The cosmic background radiation is just electromagnetic radiation only much older.

The Cosmic Microwave Radiation (CMB) is electromagnetic radiation which was created soon after the Big Bang.

Soon after the Big Bang the Universe would have been very hot. It would have been filled with high energy photons. It would have been very bright from every direction.

As the Universe cooled the photons get absorbed and re-emitted by matter. This reduces the energy of the photons and the wavelength increases.

The Universe has always been filled with photons from the Big Bang. The CMB energy is measured as a temperature. Soon after the big bang the temperature was millions of degrees.

As time progressed the energy and hence temperature of the CMB dropped. It is now about 2.725K which is close to absolute zero. This means that the CMB photons are in the microwave frequency range.

The CMB is everywhere and if you can see in the microwave frequency range, which some instruments can do, the whole Universe appears very bright in all directions.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.