Astronomy Chapter 23 Process of Science

Today, most scientists accept the Big Bang theory because its predictions agree so well with observations. But a scientific theory can always be revised or discarded if future observations do not agree with its predictions. Consider the following hypothetical future observations. Which one(s) would be inconsistent with the Big Bang theory? 1. Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K 2. Astronomers discover a nearby galaxy that has a helium abundance of 27%. 3.Astronomers discover distant protogalactic clouds with a helium abundance below 20%. 4. Astronomers find an error in previous measurements that means the temperature of the cosmic microwave background is actually 2.71 K rather than 2.73 K. 5. Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today.

1. Over the next 10 years, the temperature of the cosmic microwave background falls to 1 K 3.Astronomers discover distant protogalactic clouds with a helium abundance below 20%. 5. Careful studies of quasar spectra show that, 12 billion years ago, the temperature of the cosmic microwave background was slightly lower than it is today.

The Big Bang theory is closely linked to Hubble's discovery that the universe is expanding, which seems to imply that there was a time in the past when the expansion first began. Nevertheless, the Big Bang theory did not gain widespread acceptance among scientists until the 1960s. Why wasn't expansion alone enough to convince scientists that the Big Bang really happened?

Although expansion seems to imply a Big Bang, no other specific predictions of the Big Bang theory were tested and confirmed until the 1960s.

Classify each statement below as an observation or as an inference based on the current Big Bang model. (note that the helium abundance is defined as the mass of helium relative to the mass of hydrogen.) 1. Photons of the cosmic microwave background have traveled through space for almost 14 billion years. 2. The cosmic microwave background is radiation left over from the big bang. 3. Large-scale structures look about the same in all directions. 4. The temperature of the cosmic microwave background varies slightly with direction. 5. The cosmic microwave background temperature is 2.73 K. 6. The helium abundance is at least 25% in every galaxy studied so far. 7. Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium. 8. Large-scale structure grew around density variations present in the early universe.

Observation: 3. Large-scale structures look about the same in all directions. 4. The temperature of the cosmic microwave background varies slightly with direction. 5. The cosmic microwave background temperature is 2.73 K. 6. The helium abundance is at least 25% in every galaxy studied so far. Inference: 1. Photons of the cosmic microwave background have traveled through space for almost 14 billion years. 2. The cosmic microwave background is radiation left over from the big bang. 7. Fusion during the universe's first five minutes produced 75% hydrogen and 25% helium. 8. Large-scale structure grew around density variations present in the early universe.

Consider this statement from Part A: "Photons of the cosmic microwave background have traveled through space for almost 14 billion years." This statement follows from our model of the Big Bang, because the Big Bang model is based on the idea that __________.

the universe began very hot and dense and has been cooling as it expands

One of the inferred statements from Part A is that "Large-scale structure grew around density variations present in the early universe." Observational evidence that such density variations really existed comes from the fact that the cosmic microwave background exhibits __________.

tiny temperature variations in different directions