“To exist in this vast universe for a speck of time is the great gift of life. Our tiny sliver of time is our gift of life. It is our only life. The universe will go on, indifferent to our brief existence, but while we are here we touch not just part of that vastness, but also the lives around us.” –Terry Goodkind
Our view of the Universe changed forever in the 1960s with the discovery of the cosmic microwave background, known today to be the leftover glow from the Big Bang. This microwave-wavelength radiation, coming uniformly from all directions in the sky, was discovered with this telescope.
But it was only in relatively modern times that we were able to discover tiny, fundamental imperfections in the uniformity of this radiation. There have been two major missions — both satellites — that have taught us about what these imperfections look like across the whole sky.
The first one was the Cosmic Background Explorer, or COBE, satellite.
COBE was able to look at this leftover microwave radiation at three different frequencies with an angular resolution of just seven degrees. Visually (okay, in infrared), here’s what COBE saw when it looked up at the sky.
We then tried to subtract out the stuff coming from our own galaxy and known sources. Why? Because we want to measure the picture that’s leftover from the Big Bang, without any of the intervening stuff getting in the way. So if you look at the image below, the middle panel represents the “known stuff” from our galaxy that we subtract out, giving us the panel on the bottom as our best estimate of the extragalactic background in the Universe.
All of this stuff, the part from our galaxy and the part from extra-galactic sources, needs to be taken into account. Why? Because we’re trying to measure the imperfections from the Big Bang, and that means only looking at the stuff from 13.7 billion years ago, not the stuff in between us and the microwave background.
So we apply this knowledge to remove the extragalactic sources, and make a temperature anisotropy map, where we can see, relatively, which spots are hotter and colder than average. This was done, and here are the final results from COBE, with the best background subtraction we were able to do.
This was in the 1990s. But in the 2000s, the next generation satellite, the Wilkinson Microwave Anisotropy Probe, or WMAP, came along.
Instead of looking at three frequencies, WMAP looked at five. Instead of seven-degree resolution in microwave wavelengths, WMAP achieved half-a-degree resolution.
And it had much better luck subtracting its backgrounds — both galactic and extragalactic — than COBE did. Here’s a WMAP poster that shows the galactic and extragalactic backgrounds and how they were subtracted off, if you care to click and enlarge it.
The results? WMAP was able to show us what the primordial imperfections in the radiation of the Universe were to unprecedented accuracy. (Although, to be 100% honest, I don’t completely trust the galactic plane, and don’t think you should, either.)
And we learned a whole lot from analyzing this data, including the best measurements of the age and composition of the Universe!
But there are plenty of other questions that WMAP and COBE haven’t answered. For example:
- Is the light from the microwave background polarized, and if so, what can that teach us about gravitational waves?
- What’s going on with smaller angular scales? (This is known as the Sunyaev-Zel’dovich Effect.) What can we learn about the effects of intergalactic gas on the microwave background from it?
- How does structure form from gravitational collapse? How quickly do gravitational potentials change in the Universe? Measuring the red- and blue-shifts of the cosmic background light due to collapsing galaxies and clusters should help answer this.
So what do we do? We come to the present day, where we’ve just recently launched the cosmic microwave background satellite for the 2010s. What is it? PLANCK, named after the famous German physicist Max Planck.
Well, instead of 3 or 5 wavelengths, Planck will measure nine. As sensitive as WMAP was, Planck will be a full 10 times more sensitive in its capabilities. It will be able to measure polarization. And instead of 0.5 degrees, Planck will be able to get down to sizes of under 0.2 degrees on the sky.
Well, what’s with all of the hype? The European Space Agency has just released the results from Planck’s all-sky survey, which will be used for galactic and extragalactic background subtraction. Want to see?
Of course, you should click on that picture to get the full, high-resolution version, because these features are spectacular.
For example, here’s what some large-scale structure looks like towards the galactic center.
The European Space Agency has been good enough to put together a video (available at this link) of Planck and its first results, and also of showing the same image as above annotated with some of the more interesting things that Planck has seen.
There’s little doubt that Planck will have lots to teach us about the Universe to much better accuracies than WMAP was ever capable of. Will there be any surprises or contradictions? We’ll know for sure in 2012… until then, everything looks like it’s right on schedule in perfect working order!