These days astronomers aren't just picking up signals from a time shortly after the universe began – they're creating maps of those signals to answer some of our deepest questions about thecosmos.
TV worth watching.
An old-fashioned TV with rabbit ears is designed to pick up veryhigh frequency radio waves. When the TV is tuned to a channel forwhich there is no nearby broadcaster, the screen shows a lot ofstatic. The static – also known as noise – is caused byrandom radio waves coming towards the TV from various manmade andnatural sources, including deep space.
In the 1960's, Arno Penzias and Robert Wilson, two researchers at BellLaboratories in New Jersey, began searching for sources of static forthe purpose of improving satellite communication. They were searchingin the "microwave" part of the radio spectrum, which lies at asomewhat higher frequency than a typical TV receives. What theydiscovered was that no matter where in the sky they pointed theirspecial antenna it always picked up some microwave noise that couldnot be accounted for. Astrophysicists eventually realized that thisnoise was a predicted side effect of the birth of the universebillions of years ago.
Distantgalaxies from the Hubble Ultra Deep Field. Credit: NASA, ESA,S. Beckwith (STScI) and the HUDF Team.
How can such an ancient signal be picked up today? The answer is thatthe universe is a big place. Light or radio waves from distancegalaxies must travel for millions or even billions of years to reachus. The more distant the source, the earlier a time it represents inthe universe's history. In theory, it should be possible to look allthe way back to the earliest times of the universe.
According to the Big Bang Theory, the universe was once a muchsmaller and hotter place, with all of its matter and energyconcentrated in a white, hot soup of particles and radiation. As theuniverse expanded and cooled, it was no longer white hot, but filledwith hydrogen gas, which later collected together to form the firststars and galaxies. Some of the static picked up by the old TVincludes a bit of the white – hot light of the early universe,traveling through space for over 13 billion years. It no longer lookswhite hot because it's lost so much energy. In fact, it no longerlooks like anything because it's now just microwave and radio noise(microwaves and radio waves are simply much lower – energy formsof light waves).
An all-sky mapof the cosmic microwave background. Credit: NASA/WMAP ScienceTeam.
Since Penzias and Wilson made their big discovery (for which they wonthe Nobel Prize), astronomers have been trying to get a better andbetter look at this relic microwave noise. It's now known as the"cosmic microwave background" – CMB for short – becauseit's farther away than anything else that can be detected. The bestviews of the entire CMB come from orbiting spacecraft. Astronomersalso use ground-based microwave detectors to study selected sectionsof the microwave background in detail.
The CosmicBackground Imager in Chile's Atacama region. Credit:CBI/Caltech/NSF.
Subtle features of the CMB can tell astronomers how much matter is inthe universe and also how much "dark matter" – a mysterious,invisible substance that played a key role in the formation ofgalaxies. Observations of the CMB have also helped confirm theexistence of "dark energy", a little understood form of energy thatpermeates space and is causing our universe to expand at anever-accelerating rate. In the future, astronomers are hoping to learnmore about the very beginning of our universe based on detailedproperties of the CMB.
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