Question

Homework questions 1) Why did astronomers expect to find that the universe was decelerating? What is it actually doing? 2) What is meant by the "critical density of the universe? How is it related to the different models of the universe? 3) How was the interactions of particles different when the universe was a hundredth of a second old, 3 minutes old, and 500,000 years old? 4) Why don't we know what the universe was like at its actual birth (time = 0 seconds)? 5) What is the cosmic microwave background? Why is it important to astronomers? 6) What does the textbook mean when it says that it has been "ignoring 95% of what is out there"? 7) What is dark matter? Why is it difficult to detect? 8) What does the inflationary hypothesis predict about the density of the universe? Why does it predict this? 9) What is a Grand Unified theory? How is gravity related to this? 10) What is meant by cosmic evolution? 11) Give two examples of how the basic building blocks of life are found beyond earth. 12) What are stromatolites? How did they affect our ancient atmosphere? 13) How has the definition of "habitable environments" been expanded from meaning simply "any environment that humans can live in"? 14) In your opinion, where beyond earth should NASA spend the most resources looking for life and why? 15) In your opinion, should SETI focus more on broadcasting radio messages, putting messages on spacecraft, or listening for radio signals? Why?

Answer 1

1) early studies were based on theories and not on actual data, also assumed that the gravity of matter ( like dust) within universe was slowing down universe expansion. But recent studies tells that the universe is accelerating.

Earlier of universe expansion, the density of matter was high and results in slow rate of expansion.

But later, the expansion was more, the matter also expanded and hence density of matter decreased, this results in speeding up expansion.