Answer:
Cosmic Microwave Background Radiations (CMBR)
Step-by-step explanation:
The big bang was that point from which the universe started to exist, releasing a huge amount of Cosmic Microwave Background Radiations (CMBR) into the space.
CMBR is an electromagnetic radiation that are the the oldest remains of the big bang explosion. With the continuous expansion of the universe after the explosion, this radiations ere constantly spreading in all the direction for the last 13.5 billion years approximately.