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Universe 2315

Feb 04, 2018

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    The Origin of the Universe

    and the Arrow of Time

    Sean Carroll, Caltech

    How can we make sense of our unnatural-looking universe?

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    The single most surprising thing aout the universe!

    things change"

    #ggs reak, ice cues melt, stars emit radiation,we record memories of the past" And it all happens in

    a consistent $direction% &from the past to the future'

    throughout the universe! the arrow of time"

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    (h) does time have a direction?

    *t+s not a feature of the microscopic laws of ph)sics"Those work euall) well forwards or ackwards in time

    the) are $invariant under time reversal% &t-t, pi-p

    i'"

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    Toda)+s take-home messages!

    ." The origin of time+s arrow is cosmological"

    /" (e don+t understand wh)"

    0" (e might need to consider what happened

    beforethe 1ig 1ang"

    2" This is not 3ust recreationaltheolog)"

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    #ver)one knows wh) there is an arrow of time! entrop)"

    The /nd 4aw of Thermod)namics sa)s that entrop)tends to increase &in closed s)stems' as a function

    of time" 5ot invariant under time reversal6

    Alan 7uth+s office

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    phase

    space

    sets of macroscopicall)

    indistinguishale microstates

    #ntrop) measures volumes in phase space"

    1olt8mann! entrop)

    increases ecause

    there are more high-

    entrop) states than

    low-entrop) ones"

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    #ntrop) increases ecause

    there are more wa)s to e high-entrop)

    than low-entrop)"

    *f )ou start in a low-entrop) state,

    evolving to higher entrop) is

    the most natural thing in the world"

    1ut wh) did the entrop) start out so low?

    A uestion aout initial conditions! the earl) universe6

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    The low entrop) near the 1ig 1ang is responsile

    for ever)thing aout the arrow of time"

    4ife and death

    1iological evolution

    9emor)

    The $flow% of time

    (ithout the arrow of time, we would e in thermaleuilirium -- ever)thing static, nothing ever changing"

    The uestion is! wh) aren+t we in thermal euilirium?

    :;enrose

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