Orbital Path Podcast: First Light

John Mather has seen many first lights, not the least being the first light of the universe, and soon he will see the first light of the James Webb Space Telescope.

NASA

In astronomy, the term “first light” refers to the instant when light is allowed to flow into a brand-new eye. In a very real way, the universe has never been seen exactly this way before. We’re talking about telescopes here, of course, although I like the idea of any new eye opening up being a first light. John Mather has seen his share of first lights. He was the Principle Investigator (the scientific leader) of two NASA missions that made observations about the universe so profound that they still give me chills (and earned him the Nobel Prize for Physics in 2006). He is also the P.I. of the James Webb Space Telescope which is planned for launch in late 2018.

But John is also the leader of the team that showed us a first light in a very different, and far more literal use of the term. There was, really, a first light in the history of time. I suppose that makes sense to most of us these days; we’ve accepted the idea that the universe did have some kind of a beginning, or at least it changed in a very dramatic way, about 13.7 billion years ago –what we now call the Big Bang. Before that moment, we really don’t have much to say.  It’s not that the universe had to come from nothing.  In fact, it might have existed for any amount of time, if you can call it “time,” in a hyper-compressed state where even time shouldn’t be able to flow. But the problem is that our physics breaks down and refuses to make predictions about what reality behaves like when temperatures and densities are that high. Certainly any sort of particle, including photons, cannot exist under such circumstances. So there was no light as we know it. But then something changed. The universe expanded; space and time came into being, and energy fractured into particles; at first, ones we barely even have names for, but then more familiar ones like electrons, neutrinos, quarks, and photons. There was a moment when light was created for the first time. Not that it could flow anywhere; the universe was so hot and dense, all light could do was bounce off the tightly-packed particles in tiny, truncated little hops. It took about 400,000 years for the universe to cool and expand enough until there was a moment — and I’m talking a *moment* here, a tiny fraction of a second, when the paths cleared and light could for the very first time fly freely throw space. There was a first light of the universe.

Incredibly — and here come those goosebumps — that’s what John and his team saw. They built a telescope (a satellite, in fact) that was sensitive enough to detect the remnants of those first photons. They’re all around us. Space expanded in all directions at once; there is no empty center to the expansion of the universe. The Big Bang happened right here, at the end of your nose, and every other single point of space in the universe, as it happens. 13.7 billion years ago, the space between your fingertips was so dense that no light could flow through it. That space expanded, but those first photons are still there. Time and the expansion of space has sapped away almost all their energy, and today they glow with a temperature only about 3 degrees above absolute zero. But they are still here. Using those photons, John Mather and his team mapped the temperature and density of the universe as it was 400,000 years after the Big Bang. And if that isn’t amazing enough, within this ancient “baby picture” of the universe, they found the fingerprints of dark matter, dark energy, and possible hints of what set off the Big Bang.

Now John is counting down the minutes to the first light of the Webb Telescope. With a mirror more than 7 times the size of Hubble’s, it can see much farther (and fainter) objects than we’ve ever been able to before. It has a number of different first lights ahead of it. The telescope is incredibly complex, and must be folded up like an origami flower to fit inside the rocket that will launch it 4 times farther away than the moon. It will take nearly two months for everything to unfurl and turn on, and I, like thousands of people around the world, will breathe a huge sigh of relief when we know that all has gone well and the telescope is turned on to catch its first light. In more metaphorical terms, one of the first lights Webb will be privy to (we hope) is being able to see the very first stars and galaxies to ever exist in our universe. It should be able to see so far out into space that the light reaching us is about 13 billion years old: back to the era when the first star turned on. Think of that: with the Webb telescope, we hope to see the first stars begin to glow, the first galaxies begin to arrange themselves. And then we have a ring-side seat to watch the history of the universe unfold. Another first light for John Mather.


Orbital Path is produced by PRX and supported by the Alfred P. Sloan Foundation. Don't miss PRX's other science podcasts: Transistor and Outside Magazine.

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