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)
‘It is equally insisted on by our reasoning
faculty, which tells us that a reversal of the
arrow would render the external world
• What would happen if the arrow of time was
• 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.
‘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
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.
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.’
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
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