Principles of Relativity

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Published on 20 Apr 2013
School
UTSG
Department
Astronomy & Astrophysics
Course
AST201H1
Professor
AST201H()Stars)and)Galaxies))) )
Professor)Michael)Reid))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))Lecture)Notes))
March)12,)2013)
Lecture'16:'Principles'of'Relativity'
Relativity'
We)can)only)measure)motion)relative'to'a'given'frame'of'reference)
The)speed)of)light)is)not)only)a)constant)in)time,)but)it)is)also)invariant)
o The)speed)of)light)never)change)
Invariance)of)Speed)of)Light)has)some)bizarre)consequences)
o Time)Dilation:))
! The)speed)measured)by)the)two)observers)disagree,)but)the)
times)agree)
! If)the)speed)of)light)is)absolute,)different)observers)must)
disagree)about)with)the)time)intervals.)
! The)consequence)goes)both)ways.)There)is)symmetry.)Both)
think)the)other)moves)slower)than)themselves)
! Happens)more)when)things)move)quickly)
o Twin)Paradox))
! The)faster)the)ship)goes,)the)less)time)the)person)on)the)ship)
will)feel)
! The)person)on)Earth)will)age)a)lot)more)than)the)person)on)the)
ship)
! The)person)on)Earth)does)not)accelerate,)but)the)twin)on)the)
ship)is)accelerating)))
o This)is)called)special)relativity)
General'Relativity')()what)we)need)to)explain)Black)hole)
o General)relativity)deals)with)similar)effects)associated)with)gravity)
and)it)includes)special)relativity))
! Gravity)"#)acceleration)are)basically)the)same)thing)
Gravity)"#)curvature)of)spacetime)
o Space)and)time)will)change,)but)speed)of)light)
will)not)change)
People)meet)because)of)curvature)if)they)along)the)
curve)of)the)Earth)
! All)of)the)space)is)curved)inwards)into)the)Sun))
)
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Document Summary

Lecture 16: principles of relativity. Invariance of speed of light has some bizarre consequences: time dilation: The speed measured by the two observers disagree, but the times agree. If the speed of light is absolute, different observers must disagree about with the time intervals. The consequence goes both ways. Both think the other moves slower than themselves. Happens more when things move quickly: twin paradox. The faster the ship goes, the less time the person on the ship will feel. The person on earth will age a lot more than the person on the ship.

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