What is the CMB?

The CMB is the closest we can see to the Big Bang.

In a previous article, we mentioned the Cosmic Microwave Background (CMB) but didn't go into what it actually was. Well, now we're going to. In a nutshell, it is - as many tv scientists like to say - the "echo of the Big Bang", but let's face it that means nothing to anyone. We should probably break down the title. So Cosmic obviously refers to it being of space, the universe, and everything. Microwave is due to an effect called "red-shifting" which happens to light as the source it was emitted from retreats away from us (we'll go into this more later). And the Background is because it is the canvas upon which the observable universe is based upon, the CMB is the furthest back in time we can see. So now the name is cleared up, on with the science.

Below you can see the latest "image" of the CMB in all its glory, courtesy of the PLANK satellite.

This oval is a map of the entire universe, at the very edge of what we can possibly see.

What you're actually looking at is a thermal image of the entirety of the universe, from Earth. So, in reality, it should be the inside of a sphere, but that doesn't make a good image, so it's been spread out and made 2-dimensional, like a map. On this map instead of seeing the difference between hills and valleys, we see a change in temperature expressed by colour changes. These temperature fluctuations are tiny, micro-Kelvin differences in temperature which probably seem like nothing but are kinda important in the long run. It's a rather pretty image to look at, in my opinion, maybe I'm weird.

What it shows us though is what the universe looked like the moment that light could begin to

The nature of the CMB made Nebulae like this possible,
and eventually galaxys and stars.

actually move long distances. Prior to this it kinda kept getting absorbed and deflected, it was a mess. We call this point in time "recombination" when particles first formed. As said it gives us the earliest information we can possibly get about the universe - some 13 billion years ago (yeah suck it creationists). And the tiny fluctuations we see are the initial building blocks for the creation of galaxies, stars and eventually planets and life.

The reason that it's a "microwave background" is - as mentioned - because of the red-shift principle, which is an extension of the Doppler Effect where waves are altered by the speed between emitter and receiver. Waves are pushed together if the emitted is coming towards you, stretched out if it is going away from you.

Light in the universe appears redder than usual because the universe is expanding in all directions away from us, so the surface which the CMB light was emitted from is also traveling away from us. This means that the wavelength of this light gets longer. Red light has a longer wavelength than blue light, hence "red-shift". You can experience this effect in day-to-day life when a train goes past you, the noise you hear sounds different as it travels away from you. And if that shift is big enough the light will go beyond red, into infrared, if the shift is even bigger (like that of 13 billion years of universe expansion) then it will go into the microwave section of the spectrum of light.

Ever noticed an Ambulance sounds different when it's
coming towards you, than when it's going away?
 That's the Doppler Effect.

The existence of the CMB proves a lot of scientific theories and remains a constant area of study for cosmologists trying to figure out what the early universe was like. It is a very tricky thing to study, with restrictions on what we can actually see, but scientists love a challenge. So to sum up the CMB is the earliest time of the universe we can see; it's made of microwaves because the universe is expanding and getting bigger, and it focuses on temperature fluctuations.

So now you know more about the start of the universe, you can go impress everyone you know but showing them pretty pictures and telling them what it actually means. If you enjoyed the article share it with your friends, if you want more information on the CMB do feel free to comment below, and if there are any other areas of science (physics, chemistry, biology, whatever) you can message us on Facebook, contact us on Twitter, or send us an ask on Tumblr.