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Group Lec 002 May 15, 2:45-4:45pm Van Vleck B102Group Lec 001 May 16, 12:25-2:25pm Camberlin 2103
EXAMS:
The Origin of Helium
• Immediately after the Big Bang, only protons and electrons existed
• Shortly after the BB, temperature and density was high enough for deuterium to form by fusion
• After 100 seconds or so, temperature cooled enough so that deuterium could fuse into helium nuclei
• The temperature continued to cool, and fusion stopped after a few minutes.
• Big Bang theory predicts that around 24% of the matter in the early universe was helium, which matches what we see.
The Epoch of Inflation
• Modern technology allows us to test theories back to a time 10-33 seconds after the Universe Birth (UB).
• Physics as we know it ceases to function at 10-43 seconds after the UB, called the Plank Time
• Using particle colliders, scientists have uncovered a number of clues about what happened in the early universe, after the Plank time
• The early universe underwent a period of very rapid expansion
• By 10-33 seconds, the universe expanded from the size of a proton to the size of a basketball
• This expansion is called inflation
Expansion Forever? Or Collapse?
• The fate of the universe is ultimately controlled by its total amount of energy– Energy of expansion (positive)
– Gravitational energy that can slow the expansion (negative)
– Binding energy
• If the total energy is positive or zero, the expansion continues forever
• If the total energy is negative, the expansion will halt, and the universe will contract and eventually collapse.
Dark Energy
• Dark energy may provide the solution to the mystery
• Dark energy remains constant everywhere, regardless of the universe’s expansion
• Provides an outward push to accelerate expansion
• Dark energy must make up around 70% of all of the energy in the universe
• Much work remains to be done on this frontier…
Life on Earth
• Life formed on Earth relatively soon after the planet’s formation– For ¾ of the Earth’s history,
only algae and single-celled life forms existed
– Slowly, more complex lifeforms developed
• By 250 million years before the present, dinosaurs and early mammals had evolved.
• Hominids, our distant ancestors, developed 5.5 million years ago
• Homo Sapiens evolved only 500,000 years ago!
Figure 83.04
• Life tends to draw on the substances that are most plentiful: Carbon, Nitrogen, Oxygen and Hydrogen
• Amino acids are organic molecules containing these substances
• Amino acids form proteins, which provide structure and energy to cells
• All life contains DNA – this instruction packet contains all the information needed to build an organism
The Origin of Life
• So how did amino acids form out of the substances available on the early Earth?
• Probably started thanks to complex chemical reactions in the atmosphere and surfaces of Earth
• The Miller-Urey experiment attempted to duplicate the environment of the early Earth
• A variety of complex organic molecules formed in their “atmosphere”
The Search for Life on Mars
• It appears that Mars at some point in its history was very much wetter and warmer than it is today
• Scientists have been looking for life there
• The Viking landers (1970’s) tested for the presence of microbes, but returned inconclusive results
• We are still looking!
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