What is this oval thing and why to physicists find it so inspiring? It came from a European satellite called Planck, and scientists have been raving about it since it was released earlier this month. Why?
We all feel the inspirational quality of those Hubble pictures showing distant galaxies swirling through the blackness of deep space. Intuition doesn’t lead us to marvel at this blotchy image, but to puzzle over it. Why is it blotchy? What do the colors mean? Why is it oval?
The stock explanation found in all the news stories and press releases is this: The image is a “baby pictures” of the universe, and it represents microwaves from the big bang (but we’re told everything came from the big bang so it’s not clear why this is different).
I wanted a better explanation and I got it from our local physicists, including Drexel’s Dave Goldberg, and Penn’s Mark Trodden, who helped me appreciate that that the microwave photons that generated this picture have an incredible story to tell.
It’s helpful as a reminder that though we can’t see microwaves with your eyes, they are a form of light. Light comes in a wide spectrum of wavelengths and our eyes are geared to see just a narrow range while our specially tuned telescopes and satellites have shown otherwise invisible features shining in ultraviolet, infrared and microwaves.
So why are these microwaves interesting enough for us to send up a satellite just to detect them? Well, these are part of what’s called the cosmic microwave background and its existence was one of the key predictions of the big bang theory more than 50 years ago. Physicists realized that if you went back far enough in time, all the matter would be squished together and the universe would be so hot that electrons and protons would not be able to stay combined in atoms. In that state of things, light would be tied up in this soup of particles. The universe would be opaque.
But once this early universe expanded and cooled enough, this incredible event would occur – recombination – in which atoms of hydrogen would condense out of the soup. And basic physics of light and matter would tell you that light would be free to propagate through space. This event is thought to have happed about 380,000 years after the big bang – or more than 99% of the way back to the beginning. Over time, as the universe expanded, that light would be stretched into the long-wavelength range – a static of microwaves.
Much of this cosmic microwave science happened right down the road from Philadelphia. The astronomers who predicted those microwaves were at Princeton University, and those who first detected them with an antenna were from New Jersey’s Bell Labs.
But the really interesting thing about these microwaves was that they could prove a couple of bold predictions. Scientists thought the early universe should have behaved just like a hot piece of earthly matter. That is, it radiated light the same way a hot piece of coal does – with a particular pattern called black body radiation. The person who first figured out the pattern of blackbody radiation was German physicist Max Planck, after whom this latest satellite is named.
Not only that, physicists realized that these microwaves would carry a sort of imprint of the universe during this recombination phase during the universe’s infancy. Scientists thought there would have to be areas of slightly more matter because these would have to act as the seeds of galaxies and clusters and sheets of galaxies that we observe with telescopes. If that primordial soup was perfectly smooth, there would be no structure to our universe.
The microwaves would have a slightly longer wavelength where there was more matter.An earlier satellite called COBE that flew in the 1990s found the blackbody pattern and the seeds of the structure of the universe. But scientists still wanted to study this microwave background in more detail, so they launched more satellites, the latest being Planck, which brought the picture above, showing the seeds of the structure of the universe.
From Mark Trodden I got better picture than I’d had before of what we’re seeing when we look at the image from Planck. We’re seeing a sphere from the inside – the interior surface of a sphere surrounding Earth. Why a sphere? It’s not because we’re the center of the universe but because in the big bang picture, everything is expanding away from everything else, so any point will look to people who live there as the center.
The universe is full of cosmic microwaves from that recombination event, but the only ones reaching the Planck satellite at any given time have been travelling a specific distance through space. They delineate the surface of a shell that surrounds us at a distance further than any star. For that reason it’s called the surface of last scattering.
And that gets to why it’s oval – which Drexel’s Goldberg explained to me. (His new book is called The Universe in the Rear View Mirror). The cosmic map uses the same oval shape you often see for maps of the Earth – something called a MollWeide projection, designed to translate the surface of a sphere onto a flat sheet without distorting the relative areas of the land masses on the edges. In the case of the Planck date we’re seeing from the inside, but if we want to translate it to a flat sheet, we need the same kind of projection.
Which brings me consider some of the accusations I sometimes get from creationists that the non-believers are “materialists”, stuck in a world of just atoms and space, aimlessly swirling around with no magic and no wonder.And yet look at all the things material does and what weirdly predictable rules it follows. People predicted how light would emerge from an event more than 13 billion years ago by noting how hot coals and other materials radiate energy. We detect the seeds of galaxies in microwaves from space. With such wonders coming from our material world, do we really need to add magic?