Let's Talk Physics

A stochasticly updated blog about interesting topics in Physics & Astronomy

The Cosmic Microwave Background – evidence for the Big Bang?

The origin of our Universe has been a topic of great debate in the past few decades. It’s natural for people to wonder how we got here, and if there was a “beginning” for the Universe. Georges Lemaître was the first person to propose the idea of the Big Bang back in 1927, but it wasn’t until 1965 that we found physical evidence of the Big Bang. Up until then, physicists were (as happens quite often) split into 2 camps. One group believed in the Big Bang, the others believed in a Steady State Universe. Before I tell you who won (and how), let’s explore both of these ideas.

Georges Lemaitre, the father of the Big Bang

Georges Lemaitre, the father of the Big Bang

The Big Bang is pretty much exactly what it says on the tin – the Universe started off as a single point of infinite density and contained unimaginable energy (i.e. it was very,VERY hot). Then – BOOM! The point began expanding outwards (if expanding really is the right term. I feel like mathematicians and theoretical physicists would have something else to say on the matter). The one thing we can agree on is that the Universe began getting bigger and cooler. Which is a good thing, because it allowed stars to form and for life to evolve.

The other popular theory at the time was the Steady State Theory. It very simply says that the Universe has no age – it’s always been there, and always will be. As for the expansion of the Universe, the steady state model proposed that as the Universe expanded, it generated enough matter to maintain equilibrium. That’s right, physicists decided that energy/matter could just be made whenever it needed to be to fit this model (which is pretty poor physics).

Below is a hint as to which theory has survived (so far)

So how did the big bang theory win the war? Well, something like a big bang is going to give off a lot of energy. I mean, we’re talking about the biggest explosion in the history of everthing, ever. And it happened everywhere in the Universe, at once (because at the time of the big bang, the Universe was a single point). So you’d expect that energy from this bang should still be hanging around in the Universe somewhere, and you’d be right to think that. The interesting thing is, it’s everywhere. The left over radiation from the Big Bang was first proposed in 1948. And since this radiation had been hanging around the Universe since the beginning of everything, it had cooled. To roughly 3K (for non-scientist, that’s about -270 degrees celsius). And then the break-through finally happened. In 1965, the two gentlemen below, Robert Wilson and Arno Penzias, detected this radiation. Thus, the Cosmic Microwave Background (CMB) had finally been discovered, and the Big Bang theory gained the upperhand in the fight against the Steady State theory.

Robert Wilson and Arno Penzias standing in front of the antenna used to observe the CMB

Robert Wilson and Arno Penzias standing in front of the antenna used to observe the CMB

So, since this CMB had been detected at last, people set out to see if it was everywhere – this would help further the big bang theory, as it would prove that something must have happened everywhere at once to give such a uniform spread of radiation. So the fine people of NASA launched the Wilkinson Microwave Anisotropy Probe (WMAP). And it created a map of the temperature of the Universe as we see it, as can be seen below. The red regions correspond to a hotter area than the blue areas. But, the difference in temperature between the reddest and bluest parts of the image is roughly 0.0002 K. And the average temperature of the Universe? You guessed it – the 3 Kelvin that it was predicted to be. So there we have it, the CMB  permeates everything, everywhere.

The WMAP temperature map of the Universe

The WMAP temperature map of the Universe

Fun fact – your television aerial picks up some of the CMB photons. Which means every time you see static on your television, a few of those blips of colour are caused by the CMB. So you’re seeing the energy of photons which were created in the big bang!


Ideas for Monday’s post would be much appreciated. Also, sorry this is a short post, I have a proposal due tomorrow, so I’m up to my neck in work right now. Yay for physics!


About irishphysicist

I'm a PhD student with the Departments of Physics in University College Cork, Ireland and University of Notre Dame, Indiana. I want to try and bring astrophysics to the public, and also would like world domination. But that's a story for another day.

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This entry was posted on March 14, 2013 by in Astrophysics and tagged , , , , , , , , , , .
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