What is Cosmic microwave background (CMB)?

The cosmic microwave background is like a leftover glow from when the universe was a baby.

Imagine you're baking a cake in a super hot oven. When you take it out and let it cool, it still gives off some warmth, that’s kind of what happened to the universe. Long ago, everything was very hot and dense, like a super-charged cake mix. Then it started cooling down and expanding, just like your cake as it cools.

The cosmic microwave background is this leftover heat from when the universe was still young, about 380,000 years old. It's like the universe’s first "glow" that we can see today, but not with our eyes, we need special tools to feel it, like a really sensitive thermometer.

Even though it's super far away, this glow reaches us now. It's so faint that it feels like a gentle whisper from the beginning of time. Scientists use big machines called radiometers to detect this whisper, kind of like how you might use a microphone to catch a soft voice in a quiet room.

This "whisper" helps scientists understand how the universe began and what it’s made of, just like how we might figure out what's inside a cake by tasting its warmth.