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					     TIME
 Is time travel possible?
Can time run backwards?
Section A

   A child’s conception of time
   Natural time keepers
   Newton’s idea of time
   Relativity
   Twin paradox
   Quantum mechanics


           Adam Worsley            2
Section B


   Is time travel possible?



   Can time run backwards?




           Adam Worsley        3
A child’s conception of time

   Stage I (age6/7)-child believes that
    the speed of the measuring motion is
    affected by the motion they have
    been asked to time

   Stage II-able to divide motion of
    clock into units

   Stage III (age 8/9)-transform units
    into true units of time
            Adam Worsley                  4
Natural time keepers

   Daily passage of the sun

   Babylonian civilisation

   Aristotle’s beliefs
    ‘time does not exist, for the past no
    longer exists and the future does not
    yet exist’

            Adam Worsley                    5
Newton




         Adam Worsley   6
Newton’s idea of time

   ‘absolute true, mathematical time, [which]
    of itself, and from its own nature, flows
    equably without relation to anything
    external.’
   Equations of motion:
                       v  u  at
                            1
                       s     u  v  t
                            2
                       v 2  u 2  2as
                               1
                       s  ut  at 2
                               2

             Adam Worsley                        7
Newton’s basic law of
mechanics


                      2
          d r
      F m 2
          dt

       Adam Worsley       8
Galilean transformations

   x  x  vt
   y  y
   z  z
                      V V v
                       x      x

   t  t
                      V V
                       y      y


                      V V
                       z

       Adam Worsley               9
Velocity of light


   Michelson and Morley
    experiment-found no change in
    the speed of light

   Should we abandon the
    Newtonian ideas that have
    existed for many years?
          Adam Worsley              10
Albert Einstein




   The laws of physics are the same in
    all inertial frames
   The velocity of light is c in all inertial
    frames
              Adam Worsley                       11
Time dilation




                       t0
          t 
                              2
                          v
                       1 2
                         c
        Adam Worsley              12
Twin paradox

   Just seen that all observers that
    move relative to themselves
    appear to run more slowly

   Can now see that they also
    regard people who move
    relative to themselves as ageing
    more slowly too!
           Adam Worsley                 13
Is time travel possible?
   Many reasonable space-times that permit
    travel into the past have been found which
    are allowed by relativity

   Time dilation allows time travel of one
    observer relative to another.

   Faster than light travel (only managed
    particles to reach 99.99%speed of light)

   Warp space-time (wormholes)

   Worrying implications
             Adam Worsley                        14
Can time run backwards?

   Newton’s equations suggest it
    would be possible

   Strange concept-bull in a china
    shop

   likely then there is a far greater
    chance that the china will go
    from being unbroken to broken.
           Adam Worsley                  15
Quantum mechanics

   Conflict with classical view
   ‘for all observers in the universe, the
    past and future boundary conditions
    of any region of space-time are the
    boundary conditions in the
    mathematical sense, which together
    determine the reality inside the
    region.’
   Present determined by past and
    future?

            Adam Worsley                      16
If we do eventually find that
the present is determined by
the future then we would
expect one day time’s arrow
is likely to change and time
will go backwards!



      Adam Worsley              17

				
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posted:4/13/2011
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