28 集

Part 24: The reactions and conditions under which life has evolved and may evolve on other worlds.

These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

24. Chemistry and Context for Life University of Arizona

    • 科學

Part 24: The reactions and conditions under which life has evolved and may evolve on other worlds.

These short videos were created in August 2007 by Dr. Christopher D. Impey, Professor of Astronomy at the University of Arizona, for his students. They cover a broad range of terms, concepts, and princples in astronomy and astrobiology. Dr. Impey is a University Distinguished Professor and Deputy Head of the Astonomy Department. All videos are intended solely for educational purposes and are licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. The full list of collections follows below:

01. Fundamentals of Science and Astronomy
02. Ancient Astronomy and Celestial Phenomena
03. Concepts and History of Astronomy and Physics
04. Chemistry and Physics
05. Quantum Theory and Radiation
06. Optics and Quantum Theory
07. Geology and Physics
08. Solar Neighborhood and Space Exploration
09. Outer Planets and Planetary Atmospheres
10. The Solar System
11. Interplanetary Bodies
12. Formation and Nature of Planetary Systems
13. Particle Physics and the Sun
14. Stars 1
15. Stars 2
16. Stars 3
17. Galactic Mass Distribtuion and Galaxy Structure
18. Galaxies
19. Galaxies 2
20. Galaxy Interaction and Motion
21. Deep Space and High-Energy Phenomena
22. The Big Bang, Inflation, and General Cosmology
23. The Big Bang, Inflation, and General Cosmology 2
24. Chemistry and Context for Life
25. Early Earth and Life Processes
26. Life on Earth
27. Life in the Universe
28. Interstellar Travel, SETI, and the Rarity of Life
29. Prospects of Nonhuman Intelligences

    • video
    Unification

    Unification

    Transcript: Unification is the idea that the four fundamental forces of nature are all manifestations of some simple unified super force. On the face of it, this seems unlikely. The four fundamental forces span a range in strength of a factor of ten to the power forty. Two are infinite range forces, and two are short-range within the atom. But physicists made progress in the 1970s when they showed that the electromagnetic and weak nuclear forces could indeed be unified at the energies reached by accelerators, and since then physicists have made theoretical progress on grand unified theories which unite the electroweak, or electromagnetic and weak nuclear forces, with the strong nuclear force. Observational verification of this might come in the next generation of accelerators, but it could also come from astronomical observations of the early universe. The ultimate goal in this game is to bring in the fourth force, the weak force of gravity, and unite the worlds of the quantum and cosmology. Quantum cosmology is an exceptionally difficult theoretical undertaking that is subject to the efforts of the world’s best physicists.

    • 1 分鐘
    • video
    Broken Symmetry

    Broken Symmetry

    Transcript: It's a premise of unified theories of nature that the world is governed by an underlying single superforce, but we live in a world where the symmetry is not obvious. Matter vastly dominates antimatter, and the four forces of nature have vastly different strengths and effects on our world. Symmetry in physical theories is only reached at the very highest energies, and as the energy falls the symmetry is broken. There are more mundane examples of the same effect. Think of water where the molecules are all randomly oriented, a symmetric situation, but in ice the particles must align in a particular situation. Or a magnet, where as the temperature is raised, the particular alignment of the magnetic domains becomes randomized. Or consider a set of pencils standing on their end which is a high energy configuration. As they fall, lowering their energy, they take up a particular set of orientations with no more symmetry. The example in the universe we live in is the asymmetry that results from the separation of the strong nuclear force from the weak nuclear force in the electromagnetic force as the universe cooled in the very early fazes of the expansion. The slight asymmetry gave the result of a slight excess of matter over antimatter. Without the broken symmetry, if matter and antimatter had been utterly equal at that epoch, they would have annihilated completely leaving a universe filled only with radiation. We should be thankful for the broken symmetry, because without it we would not exist.

    • 1 分鐘
    • video
    Planck Era

    Planck Era

    Transcript: Given our knowledge of the fundamental forces of nature, cosmologists speculate about an early phase of the universe on an unimaginable iota of time after the big bang, ten to the minus forty three seconds after the big bang, when the forces of nature were all equal. This is called the Planck era or the Planck epoch after one of the founding figures of quantum mechanics. In this tiny instant of time after the big bang the temperature was ten to the power thirty-two Kelvin. The size of the universe was ten to the minus thirty-five meters, much smaller than a proton. The universe was a seething space time foam where there was no distinction between particles and energy or even between particles and the space they occupy. This represents the limit to our knowledge. With no current theory for the quantum nature of gravity, astronomers can only speculate what the universe was like at the instant of its creation.

    • 1 分鐘
    • video
    Super Strings

    Super Strings

    Transcript: As theorists in physics attempt to unify gravity with our ideas of matter, they’ve come up with a series of theories called superstring theories or brane theories, brane in this case being spelt b-r-a-n-e. In these theories, we replace the idea of particles with the idea of one dimensional strings. All the properties of particles result from the many modes of interaction, oscillation, vibration, and creation and annihilation of tiny little strings. These are microscopic entities far smaller than the nucleus of an atom. All of the properties of normal particles including their mass are derived quantities from the behavior of these superstrings. In many of these theories, theorists have to consider multi-dimensional space, beyond the three dimensions we are familiar with. Some of the theories have six dimensions, others have ten, even eleven. The theories are utterly speculative. The mathematics is fiendishly difficult, but there are many clever people working in this subject and time will tell whether they are headed towards the ultimate theory of matter.

    • 1 分鐘
    • video
    Chaotic Inflation

    Chaotic Inflation

    Transcript: Cosmologists can trace the big bang back to a quantum seed. In the inflationary model, the physical universe, the totality of space-time, must be very much larger than the observable universe that we can see. Alan Guth, one of the founders of inflation, has said that the universe may be the ultimate free lunch because in fact the entire cosmic expansion can be created from a quantum fluctuation, from energy borrowed from the vacuum of space. Another idea is chaotic inflation which hypothesizes many regions of space-time, all quantum fluctuations, creating different physical properties. In the sea of space-time foam, many universes might emerge. Some would be stillborn. Others might be short-lived, and a few might take flight as ours has done. All the universes could have different laws of physics with the laws of physics in our universe just one representation. Chaotic inflation is pure speculation, but its an evocative idea to make it clear that our universe might not be the only one.

    • 1 分鐘
    • video
    Limits to Knowledge

    Limits to Knowledge

    Transcript: Astronomers have learned much about the universe as a whole and now know its expansion rate, its size, its age, the density of matter and radiation, and the way in which structure formed. There are still deep mysteries regarding dark matter and dark energy. But the big bang model makes successful predictions going back to the first minute after the big bang, and it’s possible to meaningfully speculate about the first tiny fractions of a second. In their search for ultimate theories, modern cosmologists are the heirs to Democritus and Pythagoras, trying to find and understand the harmonies in nature.

    • 42 秒

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