What do we mean by the critical density of the universe?
What will be an ideal response?
In the absence of any mysterious repulsive force (or dark energy), a universe with the average mass density exactly equal to the critical density is the densest universe that will expand forever. A denser universe will eventually reverse its expansion and contract; a less dense universe will expand forever.
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Carbon-14 Dating: The radioactivity due to carbon-14 measured in a piece of a wooden casket from an ancient burial site is found to produce 20 counts per minute from a given sample, whereas the same amount of carbon from a piece of living wood produces 160 counts per minute. The half-life of carbon-14, a beta-minus emitter, is 5730 years. What would we calculate for the age of the artifact, assuming that the activity for living wood has remained constant over time?
A. 5700 years B. 11,500 years C. 14,800 years D. 17,200 years E. 23,000 years
The data points on this graph represent the measured spectrum of the cosmic microwave background, while the solid curve represents a theoretically calculated thermal radiation spectrum for a temperature of 2.73 K. What is the significance of the near-perfect match between the data and the theoretical spectrum?
A) It shows that the cosmic microwave background has a thermal radiation spectrum, just as the Big Bang theory predicts it should. B) It shows that all objects in the universe emit thermal radiation. C) It tells us the average temperature of gas in the Milky Way Galaxy. D) It demonstrates that the universe must contain more dark matter than ordinary matter.
Which is least expensive-for the same energy delivered?
A. coal B. gasoline C. natural gas D. AAA batteries
Max von Laue is known for his work with
A. double-slit interference. B. single-slit diffraction. C. x-ray crystallography. D. holography. E. magnetic resonance imaging.