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Midterm

AST201H1 Study Guide - Midterm Guide: Length Contraction, Special Relativity, Dark Matter


Department
Astronomy & Astrophysics
Course Code
AST201H1
Professor
Stefan Mochnacki
Study Guide
Midterm

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Astronomy)midterm)review)
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" sketch!of!“look!back!time”!:!the!further!you!look,!the!further!in!time!you!are!
looking.!!
" Dark!energy!and!dark!matter:!It!was!first!observed!through!rotation!curves!
" Special!relativity:!how!do!you!know!if!you!are!moving!?!you!don’t!because!
there!is!not!such!thing!as!moving!except!in!relative!to!something!
" Speed!of!light!:!constant!and!invariant!!
" The!fact!that!everyone!agrees!of!law!of!physics!then!weird!stuff!happens:!
length!contraction,!clock!dilation!etc…!
" Issue!of!the!twin!paradox:!but!there!is!a!solution!to!it.!Seems!like!a!paradox!
but!it’s!not.!Two!twins!traveling!shows!that!what!one!sees!is!not!necessarily!
what’s!happening.!Based!on!the!fact!that!light!takes!time!to!travel!while!the!
twins!travel.!The)twin)that)is)moving)is)young)because)clock)runs)slower)
when)moving.!!
" Gravity:!as!a!way!to!introduce!general!relativity.!!
" 4!forces!of!nature.!!
" Newton’s!law!of!motion!and!law!of!gravity!(classical!physics)!
" In!general!relativity:!anything!with!mass!bends!space!time!!
" Gravity!is!a!force!(Newton)!or!spacetime!curvature!(Einstein)!
" Eintein’s!theory!agrees!better!with!data,!but!we!still!don’t!understand!it!
completely!
" Gravity!is!weak!compared!to!all!other!forces!
" Black!hole:!extreme!gravity!or!spacetime!curvature!
" Orbits:!escape!speed!=!if!you!want!to!leave!an!object,!you!need!to!go!to!a!
certain!speed,!but!to!completely!break!free!from!this!gravity!=!escape!speed.!
When!escape!speed!exceeds!speed!of!light!=!blackhole!!
" Evidence!of!black!hole:!seeing!stars!to!be!orbiting!!
" If!you!use!nweton;s!laws,!it!turns!out!to!be!4!time!more!massive!than!the!sun!
=!only!explanation!is!that!it’s!a!black!hole!
" Another!evidence:!gravitational!lensing!=!not!actually!seen!yet,!not!enough!
precision!
" Stars:!figure!out!it’s!temperature!by!looking!at!it’s!black!body!curve!
" Things!with!lower!density!may!absorb!light!different!way:!such!cases,!worry!
about!which!wavelengths!(colors)!of!light!can!any!given!element!can!absorb!
" Figure!out!distance:!parallax!and!luminosity!=!how!many!lightbuln!does!it!
equal!
" Neutrinos:!they!are!matter!because!they!have!a!mass,!they!travel!less!than!
the!speed!of!light,!weird!property:!they!hardly!interact!with!other!matter!
because!ignorant!of!electromagnetic!forces,!their!significance:!stars!create!
them!in!abudance,!if!you!observe!them!you!can!deduce!what!is!going!on!in!
the!core!of!the!Sun!!
" Weak!and!strong!nuclear!forces:!
o Weak:!inviolved!in!radioactive!decays,!only!one!sortof!relevant!with!
course!!
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