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General Relativity

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General Relativity

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    1. General Relativity Theory of gravity developed by Einstein Consider accelerating reference frames “No observer can determine by experiment whether he or she is accelerating or is rather in a gravitational field.”

    2. Examples

    3. Intertial Mass & Gravitional Mass Inertial Mass is what appears in F=ma Gravitional Mass appears in Newton’s Gravitational Law and determines the gravitational force between two objects No reason for them to be the same Principle of equivalence is really just saying the two masses are the same.

    4. Bending Light

    5. Experimental Test

    6. Space Curvature We determined earlier that light follows the fastest path between two points Since the light bends, space must be curved by the presence of an object We’ll look at the rubber sheet analogy

    7. Space Curvature

    8. Black Holes Let the object be so massive that it bends space so much that light cannot escape the curvature Most galaxies appear to have one or more black holes at the center

    9. Expanding Universe Recall the Doppler shift Objects retreating have light waves that are shifted toward the red Objects approaching have light waves that are shifted toward the blue Have to use special relativity to calculate

    10. Receding objects Expanding Universe

    11. Lines from galaxies are red-shifted Amount of shift depends on distance to galaxy V=HD Doesn’t work for nearby galaxies in our local group H = 80 km/s/Mpc Hubble’s Law

    12. Implies expansion of the university Must have been an explosion in the past We are NOT in the middle Expansion looks the same from anywhere Hubble’s Law

    13. Expansion of the Universe

    14. Quasars (quasi-stellar objects) do not conform to Hubble’s Law Bright as nearby stars by have enormous redshifts Two choices Near and unusual redshift Far and unusual brightness Most likely bright galaxies with large black holes Quasars

    15. The universe looks the same to observers in different places at the same time Universe is isotropic (same in all directions) Universe is homogeneous (would look the same if we relocate to another galaxy) Only true on a very large scale Galaxies (visible matter) tends to clump in clusters Cosmological Principle

    16. Age of the Universe Use Hubble Constant Midpoint of estimated range of values is 22km/s per million light years.

    17. Cosmic Microwave Background If the universe is finite, then it was all in one spot in a tiny volume approaching a point 15 billion years ago. This is not just all the mass in one spot with empty space around it The spot was the entire universe The size of the universe has increased like blowing up a balloon and observing spots on the surface to get farther apart

    18. Penzias and Wilson built radio telescope to do communications research Had a background noise that they couldn’t get rid of Measuring they found noise unchanged in direction, time of day or time of year Later measurements showed blackbody spectrum at a temperature of 2.7 degrees Kelvin (microwaves) Cosmic Microwave Background

    19. Gamow predicted such radiation should exist as a result of the big bang in the late 1940’s and P&W discovered it in the 1960’s Strong confirmation of the theory Cosmic Microwave Background

    20. Early universe very hot and very dense No atoms, just photons, leptons, quarks Photons could not escape capture by electrons (collisions) Expansion cooled things down Once temperature down to 3000 Kelvin, atoms can form and be stable Radiation decouplde from matter Early History

    21. Universe expanded and radiation redshifted to longer wavelengths that correspond to cooler temperatures Early universe was radiation-dominated Later, after some expansion became matter-dominated Early History

    22. Standard Cosmological Model

    23. What is the curvature of space-time? The Future

    24. How much matter compared to critical density that leads to big crunch? Visible matter is only about 1% Appears to be dark matter based on motion of galaxies that cannot be explained on the basis of gravity and the visible matter Don’t know what it is The Future

    25. Any evidence expansion is slowing? Actually evidence from some supernovae that the expansion is increasing in speed!! Don’t know what this all means Lots of work for physicists to do in the future Hooray!!!!! The Future

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