Study GuideAstronomy–The Universe1. Beyond the Big Bang TheoryTheBig Bang theorydoes an excellent job of explaining how the universe evolved after about30secondsfrom its beginning. It helps us understand the expansion of the universe, the formation ofatoms, and the cosmic background radiation we observe today.However, when scientists lookeven earlierin time, several important questions remain unanswered.These questions push us to gobeyondthe standard Big Bang model.1.1The CommunicaƟon (Horizon) ProblemWhen we observe the universe on very large scales, it looks almost thesame everywhere. Thetemperature, density, and overall structure are remarkably uniform.But here’s the problem:•Light travels at afinite speed.•In a standard Big Bang expansion,far-apart regionsof the universe should never have hadtime to exchange information.So how did these distant regions “agree” to have the same properties?This mystery suggests that something unusual must have happenedvery earlyin the universe’shistory to allow all regions to become uniform.1.2 The Origin of GalaxiesGalaxies formed from tinydensity fluctuationsin the early universe. These fluctuations show uptoday as very small temperature differences in the cosmic background radiation—about1 part in100,000 (10⁻⁵).The question is:•Why did these fluctuations exist at all?Pure randomness predicts a universe that ismuch smootherthan what we observe. This meanssomephysical process from an even earlier timemust have created the initial unevenness thatlater grew into galaxies.Preview Mode
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