String+Theory+talk

String+Theory+talk - String Theory Arvind Rajaraman P99...

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String Theory Arvind Rajaraman P99 presentation
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In his Principia, Newton unified the motion of falling objects and simultaneously explained Kepler s laws with his principle of Universal Gravitation. Newton
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Planetary motion (almost!) completely predicted on the basis of Newton s laws. Unification of terrestrial and planetary phenomena. Confirmed Copernican theory. Newton s Law of Universal Gravitation
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The discovery of relativity showed that Newton s theory was incomplete. In particular, action at a distance was incompatible with relativity. Einstein s theory of General Relativity unified gravity with special relativity. Einstein
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In general relativity, gravity is a manifestation of the curvature of spacetime. An object deforms spacetime, much as a ball on a rubber sheet. Other objects move in this curved space and hence do not move in a straight line. Appears like a force. General Relativity
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General relativity predicts that rotating objects will emit gravitational waves. Measurements of binary pulsars show a spin down rate precisely consistent with general relativity. General Relativity
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General relativity is a completely successful theory. There are no experimental anomalies. Predictions from General Relativity are verified to extremely high accuracy. Status of General Relativity So why are we still working on gravity?
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Current Issues 1. Quantum Mechanics and Gravity 2. Black Holes and the Information Paradox 3. Cosmological Constant problem
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One of the fundamental results of quantum mechanics is that processes are probabilistic. QM was developed as a theory to calculate such probabilities. For instance, if a electron hits a proton, it has a certain probability to do nothing, a certain probability to form a neutron, and a certain probability to form a hydrogen atom. The total probability must be 100%. This rather basic requirement is called unitarity. Quantum Mechanics and Unitarity
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A theory which violates unitarity is presumably inconsistent. For example, if your theory predicts that the electron will form a hydrogen atom with probability 200%, something is wrong, and most likely, it s the theory. But could anything as crazy as this ever happen? Sure! Quantum Mechanics and Unitarity
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The probability of an electron hitting a proton and forming a neutron can be calculated in Fermi s theory of the weak interactions. Quantum Mechanics and Unitarity
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Result: The probability is P = G F E 2 where G is the Fermi constant, E is the energy. Quantum Mechanics and Unitarity
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Probability grows with energy, eventually becoming greater than 1. Theory loses unitarity at high energies! Quantum Mechanics and Unitarity
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The Fermi theory must break down at high energies. One possibility: there may be new massive particles at high
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String+Theory+talk - String Theory Arvind Rajaraman P99...

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