You may have read (somewhere on this blog) that my summer research concerns this thing called the “CMB” – the Cosmic Microwave Background (sometimes called the Cosmic Background Radiation, or CBR). Being able to study the CMB is, in some ways, a fulfillment of dreams I had when I was 10. I’m sure you’ve heard of the Big Bang; the supposed beginning of the universe, or as some would claim, “the beginning of time” (whatever that might mean). Well, back when Garrett was a little 10 year old, the Big Bang was still called the “Big Bang Theory.” And back then, I had to wonder why humans thought that everything started with a really, really, really big explosion. How could we make any educated guess that the ENTIRETY of the universe just blew up out of nothingness? Nearly 10 years later, I now know why scientists supported the big bang theory: because it predicts the existence of the CMB.
So, what is the CMB?
(…Was that not helpful? Sorry, I’ll explain.)
In 1964, the physicists Arno Penzias and Robert Wilson were testing a sensitive communications antenna at Bell Labs. In an attempt to test the antenna in a radiation-free environment, they calibrated the device to a relatively quiet wavelength in the microwave range. They found that their antenna detected a constant low level background noise in any direction they could point it. After accounting for all foreseeable errors, they concluded that the universe was filled with a constant radiation background.
Penzias and Wilson couldn’t explain their finding, but in fact, it had already been predicted. In 1948 Georg Gamow, Ralph Alpher, and Robert Herman did some theoretical work regarding the Big Bang Theory, a theory then considered to be incredibly speculative. Their work (essentially) calculated the temperature of the universe, and they found that the universe should be permeated by a residual radiation corresponding to a temperature of 2.45 Kelvin. Funny enough, the radiation measured by Penzias and Wilson corresponded to a temperature of 3.5 K.
And that’s all the CMB is – a bunch of photons (packets of energy). Granted, they’re incredibly special photons. It’s the oldest bunch of radiation we can detect! And the great age of the CMB is what makes it so useful; it’s a snapshot of our Universe at an early age. I can’t stress enough how important the CMB is. When Penzias and Wilson detected it, they created a fundamental benchmark for the fields of Cosmology, Particle Physics, Astronomy, etc.. If any theoretical model of the universe has the potential to be correct, it must explain the CMB. Thus, the CMB has become a type of “laboratory” for physicists. By analyzing its properties, we are able to test and eliminate theoretical models. This is exactly why the “wildly speculative” Big Bang theory gained a wealth of support after the CMB’s discovery. The Big Bang Theory predicted our observations and their origin, and rightly received public approval.
The picture above is a modern map of the CMB (taken by the Wilkinson Microwave Anisotropy Probe; a.k.a. the WMAP satellite). The many colored spots on the image correspond to regions of varying temperature, with the traditional (blue/green/yellow/red) hot-to-cold scale (note, our galaxy’s radiation has been subtracted from the image). I’ll explain the details of this image in a future post.
(PBS Voice:) If you’d like to learn more about the Cosmic Microwave Background, a brief (but comprehensive) review can be found on Wayne Hu’s webpage ( background.uchicago.edu/~whu/). Or, you can check out one of the many accessible undergraduate texts on Astronomy or Cosmology.
References: Historical facts credited to Matts Roos, from his text “Introduction to Cosmology.”