Scitech | Fourteen billion years ago…

Cosmic Microwave Background radiation sheds light on big questions

In the beginning, God said “Let there be light,” and there was light. This may not mirror the current story that science gives us today, but in both accounts the formation of the “first light” features prominently.

What is remarkable about science’s Big Bang version, however, is that this first light still exists and is out there in the universe, now as “Cosmic Microwave Background” (CMB) radiation. We can, with the right equipment, still see it.

For the past 15 years, Gary Hinshaw of NASA’s Goddard Flight Centre has been the man in charge of this equipment. As the principal investigator leading the Cosmic Background Explorer and Wilkinson Microwave Anisotropy Probe satellite missions, he is often the first person to “re-witness” the earliest visible moments of the universe. When Hinshaw visited McGill to give a public talk on Friday, September 3, entitled “Observing the Cosmic Microwave Background: A Unique Window on the Early Universe”, it was to no surprise that he was welcomed deferentially by McGill’s community of physicists, many of whom, like other scientists around the world, rely heavily on the data from Hinshaw and his team.

Hinshaw started off the talk by explaining how it is possible to still be able to see the “first light” of creation. “Modern cosmology,” he explained, “dates back to Albert Einstein and his 1917 theory of General Relativity.” In 1929, Edwin Hubble observed that the universe is expanding – this is the so-called “red-shift observation.” The universe was once, as Hinshaw explained, an “infinitely massive and infinitely dense singularity.” This is the pretext for the Big Bang, and, because everything originated from one single point, is why one can see this light anywhere in the universe.

It is important to realize though that this light was not created conjointly with the “bang.” After the universe expanded at a speed far faster than that of light, it slowly cooled into a soup of sub-atomic particles. This trapped all the photons and rendered the universe opaque.

Hinshaw explained that it was only after 379,000 years that the universe expanded and cooled enough for the “light to be liberated and clearly propagated across the universe, unimpeded.”

Today, roughly 14 or so billion years later, the universe has expanded and cooled to such an extent that this once high-energy burst of light has shifted into the microwave spectrum, thus giving rise to the CMB.

So why do physicists get excited about it? There must be more than just a pretty picture out of this, right? Hinshaw admited that if you want practical results from your science – a cure for this or a solution for that – the CMB may be disappointing. It is instead just the best tool we have for pursuing answers to not-so-small questions: where everything in the universe come from? How did the moment of creation happen?
The same way that ripples in a pond provide information of the rock that caused the disturbance, CMB preserves information about the structure of the early universe. Through careful analysis it can tell us, for example, the proportions of dark matter and anti-matter in the universe, the geometry of the universe (disappointingly a boring flat space, by the way) and a whole host of other important quantities that theorists use to test their ideas.

Hinshaw has stepped down now as chief purveyor of the CMB, but there are many new experiments beginning operation that plan to further refine the picture he and his team obtained over 15 years. There are still many competing hypothesis about events immediately after the moment of creation, and CMB will be needed to illuminate new physics for decades to come.


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