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Time's Arrow Introduction


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Time's Arrow Introduction

  1. 1. • 3 questions: • What’s the oldest you’ve ever been? • How do you time travel everyday? • What’s the best way to try and live forever?
  2. 2. Time’s Arrow
  3. 3. The Arrow of Time ‘Let us draw an arrow arbitrarily. If as we follow the arrow we find more and more of the random element in the state of the world, then the arrow is pointing towards the future; if the random element decreases the arrow points towards the past. That is the only distinction known to physics. This follows at once if our fundamental contention is admitted that the introduction of entropy (randomness) is the only thing which cannot be undone. I shall use the phrase ‘time’s arrow’ to express this one-way property of time which has no equivalent in space.’ Arthur Eddington (1927)
  4. 4. ‘It is equally insisted on by our reasoning faculty, which tells us that a reversal of the arrow would render the external world nonsensical.’ Another question: • What would happen if the arrow of time was reversed?
  5. 5. Another question: • Can time flow in reverse? Déjà vu, from French, literally "already seen", is the phenomenon of having the strong sensation that an event or experience currently being experienced has been experienced in the past, whether it has actually happened or not.
  6. 6. ‘The symmetry of time (T-symmetry) can be understood by a simple analogy: if time were perfectly symmetrical a video of real events would seem realistic whether played forwards or backwards. An obvious objection to this notion is gravity: things fall down, not up. Yet a ball that is tossed up, slows to a stop and falls into the hand is a case where recordings would look equally realistic forwards and backwards. The system is T-symmetrical but while going "forward" kinetic energy is dissipated and entropy is increased. Entropy is: 1. A thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system 2. Lack of order or predictability; gradual decline into disorder.’
  7. 7.
  8. 8. what goes around comes around you have to be cruel to be kind because I’m a healer, everything I do heals you do what you do best, not what's best to do here there is no why multiply zero by zero and you still get zero she loves me, she loves me not because ducks are fat