Oldest picture in the Universe: the Cosmic Microwave Background

By Adam Grodeck

Sometimes a bit of nostalgia is a welcome distraction from the dreary drag of life. I often find myself flicking through old photo albums, especially the film prints of me and my brother as young’uns. There’s a unique pleasure in doing this; baby photos are damn cute!

But the photo that you’re about to see is the mother of all ‘baby photos’. This my friends, is the earliest possible snapshot of the entire universe; this is the Cosmic Microwave Background (CMB).

With new technology that’s allowed scientists to measure it more accurately than ever before, the CMB gives us clues as to why the universe turned out as it did, and even how it all started in the first place!



The Cosmic Microwave Background (image credit: NASA/WMAP Science Team, 2012)


What the heck is the Cosmic Microwave Background?

To understand what the CMB is, we have to jump back in time. WAY back. We’re going back 13 billion years, to when the universe was just a toddler.

For over 300,000 years after the Big Bang, things were unimaginably hot and dense in our fledgling universe. So much so, that all matter existed as plasma – a boiling soup of subatomic particles. Light was just bounced around off of these particles like bouncy balls, making the universe opaque (not see-through). It’s just like trying to look into the centre of our Sun…we can’t!

As the universe expanded, things started to spread out and cool down, allowing both hydrogen and helium to form. We call this event ‘recombination’, and it heralded a first in the universe’s history; space became transparent! Light, or ‘photons’, were shot out in every direction during recombination, the very first ‘see-able’ light to exist. This light continues to travel across the universe; it’s this stuff that makes up the CMB!


Why have I never seen the CMB with my own eyes??

Light from the CMB is everywhere, even today. If you tune an old TV between two stations, about 1% of the static comes from light from the earliest visible point in the universe!

But this light is not ‘visible light’, per se. In fact, visible light makes up only a tiny part of the full ‘electromagnetic spectrum’. As the name suggests, the CMB is made up of another type of light: microwaves. This is why we can’t see the CMB with the naked eye, but we can measure it using a vast array of cunning technologies.


About 1% of analogue TV static comes from the CMB! (image credit: Richmond 9 via Flickr)


If we can’t see it, how did we find out about the CMB?

We all love a good ‘accidental discovery’ story. There’s Alexander Fleming, who noticed that a fungus that was killing his bacteria cultures (invented Penicillin), and there’s Percy Spencer, whose chocolate bar melted while working at M.I.T.’s Radiation Lab (invented the microwave oven). John Pemberton’s failed health tonic drink became Coca Cola, and even our old friend ‘Velcro’ was accidentally stumbled upon by Swiss engineer Georges de Mestral.

And right up there with this folklore is the discovery of the CMB.

In 1964, while testing very sensitive radio detectors, astronomers Arno Penzias and Robert Woodrow Wilson noticed some frustrating interference in their results.

They tried pointing the antennas in different directions, and they ran their tests at different times of the day. They even cleaned out the bird poop in their equipment! But no matter what they did, this interference persisted.

As it turns out, this was not random interference. This was residual light from the Big Bang; this was the famous CMB!

14 years later, the pair won a Nobel Prize for their discovery. Go figure!


The CMB in the 21st Century

Since the time of Penzias and Wilson, scientists have used ridiculously precise instruments to map the CMB. And boy, was it worth it!

In 2012, NASA’s WMAP spacecraft released the most accurate picture that we have of the early universe after 9 years of collecting data.


The Wilkinson Microwave Anisotropy Probe (WMAP) (image credit: NASA/The WMAP Science Team)

It may not look like much, but the different colours show tiny temperature differences between parts of space in the early universe (we’re talking about changes of a 100,000th of a degree!).

These fluctuations actually show us that bits of the universe were slightly denser than others. Over time, these spots became bigger, causing more and more gas to clump together…fast forward to now, and these spots are the stars, planets and galaxies we see.

In other words, the CMB shows us everything there is. It shows us the ENTIRE universe, and gives us the more insight than humanity has every received as to how the stuff that makes it up formed.

And if that wasn’t enough, the existence of the CMB further supports that our universe started with the Big Bang.


As far as baby photos go, the CMB really does take the cake.