PHYS 190 Lecture Notes - Big Bang, Sultanate Of Ifat, Antineutron
30 Apr 2018
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Professor
Its$13.8$billion$years$since$the$Big$Bang,$but…
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What$is$the$meaning$of$distance$in$an$expanding$universe?
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The$light$rays$spreads$apart$more
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…objects$are$seen$as$they$were in$the$past,$but$also$as$if at$their$"current"$
distance,$which$can$be$more than$13.8$billion$light‐years
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Simlpy$the$amount$of$time$since$light$left
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Usually$quote$unambiguous$"look$back"$time
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Look$back$time$=$approx.$13$billion$years
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Wavelenghs$Doppler$shifted$by$factor$of$~8$(speed$~$97%$of$speed$of$light
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"apparent"$distance$~$30$billion$Lys
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COSMOLOGICAL$DISTANCES$AND$TIME
Suppose$that$the$universe$is$14$billion$years$old,$Which$of$the$following$would$
be$true$if$an$object$had$a$look‐back$time$of$15$billion$years?
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We$would$see$the$object$as$it$was$one$billion$years$after$the$Big$Bang
A.
We$wont$be$able$to$see$an$object$at$that$distance$for$another$billion$years
B.
The$universe$at$that$distance$doesn’t$exist$yet$for$us,$so$there$really$isnt$
anything$to$be$seen$that$far$away
C.
Both$B$&$C
D.
BREAKOUT$QUESTION
This$is$suppose$to$be$1$billion$years$before$BB
Partial$history$and$more$to$come$later
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Big$bang:$time$zero
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Though$some$parts$still$not$fully$understood
The$physics$we$already$know$works$at$lest$this$close$to$BB
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1/10$=$0.1$approx$10^‐10$secs
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A$BRIEF$HISTORY$OF$THE$COSMOS
Temperatures$high$enough$for$radiation$to$create$matter$/$anti‐matter
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But$matter$/$anti‐matter$almost$immedialy$annihilate
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UNIVERSE$AT$ABOUT$10^‐10$SECS
WEEK$13$LECTURE$2
Thursday,$ March$ 29,$2018
2:23$PM
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