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Frequently Asked QuestionsCOBE1. What does COBE stand for?COBE is an acronym for the COsmic Background Explorer. 2. When was COBE launched?The COBE satellite was launched aboard a Delta rocket from the Vandenberg Air Force Base at Pt. Arguello, California on November 18, 1989. See the launch movie at:
3. What instruments are on board COBE?There are three instruments on COBE: a Diffuse Infrared Background Experiment (DIRBE) to search for the cosmic infrared background radiation, a Differential Microwave Radiometer (DMR) to map the cosmic radiation sensitively, and a Far Infrared Absolute Spectrophotometer (FIRAS) to compare the spectrum of the cosmic microwave background radiation with a precise blackbody. 4. Why are the COBE results important?The 2006 Nobel Prize for physics was awarded to John Mather and George Smoot "for their discovery of the blackbody form and anisotropy of the cosmic microwave background radiation". These results provide increased support for the Big Bang scenario of the origin of the universe, as this is the only scenario that predicts the kind of cosmic microwave background radiation measured by COBE. After the Big Bang, the universe expanded and cooled, leaving behind a trace of "left-over" heat from the Big Bang. This is the 2.7 Kelvin temperature measured by COBE. In addition, the small temperature variations (anisotropies) in the background offer important clues to how galaxies came into being. Without these variations in temperature the galaxies, stars, and planets would never have formed! Cosmology1. What is the evidence for the Big Bang?The Big Bang Model is supported by a number of important observations:
These three measurable signatures strongly support the notion that the our universe evolved from a dense, nearly featureless hot gas, just as the Big Bang model predicts. 2. What happened during the Big Bang?The Big Bang Theory postulates that 12 to 14 billion years ago, the portion of the universe we can see today was only a few millimeters across. It has since expanded from this hot dense state into the vast and much cooler cosmos we currently inhabit. We can see remnants of this hot dense matter as the now very cold cosmic microwave background radiation which still pervades the universe and is visible to microwave detectors as a uniform glow across the entire sky. 3. Are galaxies really moving away from us or is space just expanding?The Big Bang did not occur at a single point in space as an "explosion." It is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite. If it is closed and finite, then it was born with zero volume and grew from that. In neither case is there a "center of expansion" - a point from which the universe is expanding away from. In the ball analogy, the radius of the ball grows as the universe expands, but all points on the surface of the ball (the universe) recede from each other in an identical fashion. The interior of the ball should not be regarded as part of the universe in this analogy. 4. What is the Universe expanding into?By definition, the universe encompasses all of space and time as we know it, so it is beyond the realm of the Big Bang model to postulate what the universe is expanding into. In either the open or closed universe, the only "edge" to space-time occurs at the Big Bang (and perhaps its counterpart the Big Crunch), so it is not logically necessary (or sensible) to consider this question. 5. How old is the Universe?The latest calculations show our universe to be about 13.7 billion years old. 6. Why do we think that the expansion of the Universe is accelerating?Generically, the gravitational pull exerted by the matter in the universe slows the expansion imparted by the Big Bang. Very recently it has become practical for astronomers to observe very bright rare exploded stars called supernova in an effort to measure how much the universal expansion has slowed over the last few billion years. Surprisingly, the results of these observations indicate that the universal expansion is speeding up, or accelerating! While these results should be considered preliminary, they raise the possibility that the universe contains a bizarre form of matter or energy that is, in effect, gravitationally repulsive. 7. What is dark matter?"Dark Matter" generally refers to "exotic" non-baryonic matter that interacts only weakly with ordinary matter. While no such matter has ever been directly observed in the laboratory, its existence has long been suspected. Radio and optical observations of gas and stars in distant galaxies enable astronomers to determine the distribution of mass in these systems. The mass that astronomers infer for galaxies including our own is roughly ten times larger than the mass that can be associated with stars, gas and dust in a Galaxy. This mass discrepancy has been confirmed by observations of gravitational lensing, the bending of light predicted by Einstein's theory of general relativity. 8. What is dark energy?This is a truly bizarre form of matter, or perhaps a property of the vacuum itself, that is characterized by a large, negative pressure. This is the only form of matter that can cause the expansion of the universe to accelerate, or speed up. |
