# TIME by nyut545e2

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• pg 1
```									     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
   Quantum mechanics

Section B

   Is time travel possible?

   Can time run backwards?

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

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

   Stage III (age 8/9)-transform units
into true units of time
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’

Newton

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

Newton’s basic law of
mechanics

2
d r
F m 2
dt

Galilean transformations

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

t  t
V V
y      y

V V
z

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?
Albert Einstein

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

t0
t 
2
v
1 2
c

   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!
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
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.
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?