A P o li t ic a l H is t o r y o f G r av i t y

1

E i n s t e i n a nd P o li t i c s

2

“ T e m p l e o f R e l a t i v i t y ”

3

“ T h e H a pp i es t T h o u g h t... ”

R a d a r , M i ss il es , a n d G r a v i t y

4

L on g G es t a t i o n

E in s t e in la b o re d f o r n e a r ly 10 y e a r s o n h is t h e o r y o f g r a v it a t io n . A f t er s e v er a l f a ls e s t a r t s , h e a rr iv e d a t h is fie ld e q u a t io n s in N o v e m b er 1915 .

Ei n s t e i n ’s Zu ri c h n ot e b ook , c a. 191 3

5

D r o pp in g t h e B a ll

E l e v a t o r a t r e s t: ba ll f a ll s t o fl oo r E l e v a t o r i n f r ee f a ll: ba ll hang s i n

m i da i r

Space s h i p acce l e r a ti ng : fl oo r r i s e s t o ba l l

Space s h i p a t r e s t: ba ll hang s i n m i da i r

6

An “ As y m m e t r y i n t h e E x p l a n a t i o n ”

Ei n s t e i n : T h e r e a r e n ’ t r e a l l y 4 phe n o m e n a — on l y 2 ! T h e b a l l ei t h er f a l l s t o w a rd t h e f l o o r o r i t d o es n ’ t .

Th e s a me p h e n ome n on h a d b e e n g i v e n s e p a r a t e d e s c r i p t i on s :

Th e e a r t h ’ s gr a v i t a t i o n a l a t t r a c t i o n pu l l s No f o r c e s p u s h o n t h e b a l l , s o i t s t a y s a t th e b a l l d o w n w a r d . re s t , w h i l e t h e f l o o r ac c e l e r at e s up w a r d .

Bu t n o e x p e r i m e n t c o u l d di s t i n g u i s h be t w e e n t h e t w o d e s c r i p t i o n s .

G r a v it y a n d a c c e le r a t io n a r e int e r c h a nge a ble .

7

An “ As y m m e t r y i n t h e E x p l a n a t i o n ”

Ei n s t e i n : T h e r e a r e n ’ t r e a l l y 4 phe n o m e n a — on l y 2 ! T h e b a l l ei t h er f a l l s t o w a rd t h e f l o o r o r i t d o es n ’ t .

Th e s a me p h e n ome n on h a d b e e n g i v e n s e p a r a t e d e s c r i p t i on s :

Th e e a r t h ’ s gr a v i t a t i o n a l a t t r a c t i o n pu l l s No f o r c e s p u s h o n t h e b a l l , s o i t s t a y s a t th e b a l l d o w n w a r d . re s t , w h i l e t h e f l o o r ac c e l e r at e s up w a r d .

Bu t n o e x p e r i m e n t c o u l d di s t i n g u i s h be t w e e n t h e t w o d e s c r i p t i o n s .

G r a v it y a n d a c c e le r a t io n a r e int e r c h a nge a ble .

8

Fo llo w t h e L ig h t B e a m

Vi e w o u t s i d e s p ac e s h i p Vi e w i ns i d e s p ac e s h i p

In s i d e t h e ac c e l e r at i n g s p ac e s h i p , t h e l i gh t be am ap p e ar s t o be n d t o w a r d t h e f l o o r . E n t e r t h e Eq u iv a le n c e P r in c ip le : t h e sa m e p h e n o m e n o n m u st o ccu r w h e n th e sp a ce sh i p i s at r es t in a gr a v i t a t i o n a l f i e l d .

9

Fo llo w t h e L ig h t B e a m

Vi e w o u t s i d e s p ac e s h i p Vi e w i ns i d e s p ac e s h i p

In s i d e t h e ac c e l e r at i n g s p ac e s h i p , t h e l i gh t be am ap p e ar s t o be n d t o w a r d t h e f l o o r . E n t e r t h e Eq u iv a le n c e P r in c ip le : t h e sa m e p h e n o m e n o n m u st o ccu r w h e n th e sp a ce sh i p i s at r es t in a gr a v i t a t i o n a l f i e l d .

10

Sp a ce ti m e i s C u rv e d

If a l i g ht b e am ’ s pat h i s c u r v e d b y g r av i t y , t hi s i s l i k e s ay i n g t hat sp a ce t i m e i t se l f i s cu r v e d b y g r a v i t y . T h e g e o m e t r y o f sp a ce t i m e ne e d no t be Eu c l i d e a n .

par al l e l l i n e s

in t e r io r a n g le s o f in t e r s e c t a t r i an gl e > 1 8 0 ˚

su r f a ce o f a sp h e r e

11

A littl e he l p f r o m h i s f ri end s

I n 1912 , E i n s t e i n fo un d hi m s e l f b a c k i n Z ü r i c h w i t h h i s f r ie n d f r o m sc h ool d ay s , M a r c el G r o ss m a n n — w h o w a s n o w a pr ofe ss io n al m a t h e m a t i c ia n . Ei n st ei n e v e n t u ally

a rriv e d at t h e fi e l d e qu at i o n s of M a r ce l G r ossm ann an d A lb e r t E in ste in

G e n e r a l R e l a t i v i t y .

R 

-

2 g 

R =

c u r v a t u r e o f s p ace ti m e = d i s t r i bu ti on o f m a tt e r a nd e n e r g y

12

Ge o me t r y S u p r e me

T o E i n s t e i n , g r a v i t a t i o n w a s no t h i ng b u t g e o m e t r y . T h e r e wa s n o “ f o r c e ” o f g r a vi t y : o b j e c t s s i m p l y f o l l o we d t h e sh o r te st p a th s th r o u g h cu r v e d sp a ce ti m e .

13

Q u e st i on s?

14

S p a c e t i me a n d W a r

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15

Re l a ti v i ty o n th e E a ste rn F ro n t

On e o f t h e e a r l y a d e p t s w a s t h e Ru s s i a n m a t h e m a t i c i a n , Vs e v o l o d Fr e d e r i k s , w h o h a d b e e n s t u d y i n g i n G öt t i n g e n .

G öt t i n g e n I n s t i t u t e f or Th e o r e t ic a l P h y s ic s

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Fr i e d m a n n Fo c k Ga m o w La n d a u

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Eq u at i o n s i n t h e T r en c h es

An o t h e r co l l e a g u e , Ka r l Sc h wa r z s c h i l d , d i s c o v e r e d h i s no w - fa m o u s s o l u t i o n t o E i n s t e i n ’ s eq u a t i o n s a s a d i v ers i o n w h i l e se r v i n g i n t h e G e r m a n A r m y o n th e R u s s i a n f r o n t.

K. S c h w a r z s c h i l d ,

ca . 1 9 0 8

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So o n a f t e r p ubl i s h i n g h i s p a p e r , h e d i e d fr o m a r a r e s k i n d i s e a s e c o n t r a c t e d o n t h e Ru s s i a n f r o n t .

17

Ec l i p s e an d I m p r i s o n m en t

St i l l a n o t h e r o f E i n s t e i n ’ s c o l l e a g ue s , t h e G e r m a n as t r o n o m e r Er w i n F r e u n d l i c h , t r i e d t o t e s t a c r u c i a l pr e di ct i o n o f E i n s t e i n ’ s t he o r y : t hat g r av i t y co u l d b e n d th e p a th o f s ta r l i g h t.

E. F r e u n d l i c h

Mo o n

Appa r e n t po s i t i o n o f di s t a n t s t a r

Ac t u a l po s i t i o n s o f di s t a n t s t a r s

Appa r e n t po s i t i o n o f di s t a n t s t a r

Ei n s t e i n l e t t e r , 1 9 1 3

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Fr e u n d l i ch f o u n d h i m se l f o n t h e w r o n g si d e o f t h e R u ssi a n bo r d e r w h e n w a r br o k e o ut , a n d w a s s e n t t o a p r i s o n c a m p .

18

Re l a ti v i ty o n th e W e ste rn F ro n t

Ev e n a ft e r w a r h a d b r ok e n ou t , Ein s t ein m a d e s ev er a l t r ip s to v i si t co l l e a g u e s i n L e i d e n , si n ce th e N e th e r l a n d s w a s sti l l a ne u t r a l c o u nt r y .

Ei n s te i n v i s i ti n g P a u l Eh r e n f e s t’ s g r o u p i n L e i d e n , 1 9 2 0 s

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Ei n s te i n a n d d e S i tte r , c a . 1 9 3 2

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Beyo n d t h e Bl o c k ad e

Th e w a r c h o k e d o f f a l l d i r e c t c o n t a c t b e t w e e n sci e n ti sts i n G e r m a n y a n d B r i ta i n . Ar t h u r Ed d in g t on le a r n e d a b ou t g e n e r a l r e la t iv it y fr om Wi l l e m d e S i t t e r , w h o s e n t h i m e x t e n s i v e En g lis h - la n g u a g e p r im e r s .

A. S . E ddi n g t o n , c a . 1 9 2 0

Image is in the public domain.

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Ed d i n g t o n ’ s A n n o u n c em en t

Im m e di at e l y af t e r t he w ar , a B r i t i s h e x pe di t i o n l e d b y Ed d i n g t o n

wa s s u c c e s s f u l .

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Wo r l d w i d e f a m e :

Ei n s t e i n i n N e w Y o r k Ci t y, 1 9 2 1 .

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information, see https://ocw.mit.edu/help/faq-fair- use/ 21

Bac k l as h : d eu t s c h e Ph ys i k

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Jo h a n n e s S t a r k Ph i l i p p L e n ar d ocw.mit.edu/ Image is in the public domain. help/faq- fair -

use/

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St a rk a n d L e n a r d A tt a c k

T w o - p a rt s tr a t e g y : 1 . E i n s t e i n ’ s w o r k w a s r e p u g n a n t t o t h e A r y a n s e n s i b ili t y . 2 . K e y re s u l t s had b ee n p l ag i a r i z e d fr o m e a r l y A r y a n rese a r c h ers . ( “ F ir st of a ll, y ou ’ r e w r o ng, an d se con d of a ll, w e g ot th e r e fir st! ” )

	T h e li tt l e - k n o w n J o h a nn So l d ne r h a d wr i tt en a p a p e r i n 1803 ( w h i ch S t a r k a n d L en a r d r e p ub li s h e d i n 1921 ) , i n w h i ch h e h a d us e d N e w t o n i a n g r av i t y t o d e r iv e t h e b en d i n g o f li g h t ne a r th e s u n . ( So l d ne r ’ s r e su l t w a s o n e - h a lf o f E i n s te i n ’ s v al u e . )
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23

Q u e st i on s?

24

Wh a t G o e s U p . . .

An n u a l n u m b e r o f p u b l i c a t i o n s o n GR wo r l d wi d e , 1 9 1 5 - 1960

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25

M I T : F r o m R a d L ab t o R L E

194 0

194 5

26

M I T Ra d La b , WW II

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B e n W il s o n

B a lli s t i c M i ss il e D e t e c t i o n

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27

T r a j e c t o r y E s t i m a t i o n

I r wi n I . S ha p i r o

M i lls to n e ra d a r , 195 7

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https://ocw.mit.edu/help/faq-fair- use/ 28

d

“ T h i s r e c o r d i n g t e c hn i qu e app e a r s t o b e e s p e c i a ll y p r o m i s i n g f o r t h o s e e x p e r i m e n t s i n w h i c h a p r i o r i

k n ow l e dg e i s l a c k i n g i n s e v e r a l

r e s p e c t s a n d o n l y a b r i e f p e r i o d i s a v a i l a b l e f o r o b s e r v a t i o n . ”

Li n co ln La b d i r e cto r C a r l O v e r hag e to Lt . G e n e ra l R o s co e W i ls o n ( Ai r F o r ce ) , 24 M a r c h 195 9

T a r ge t P r a c t i c e

T e s t o f e qu i p m e n t a n d d e s i g n :

u s e m ag n e t ic t a pe f o r d a t a r e c o r d i n g ; u s e c e r t a i n t y pe s o f d i g i t a l c o de f o r r e a l -

t i m e d a t a p r o c e ss i n g ;

“ P l a n e t a r y E p h e m e ri s P r o g r a m ” : u s e r a d a r i n put s t o e s t i m a t e f ut u r e p o s i t i on o f o b j e c t s i n t h e s ky ; b u i l d s o n s t a t is t i c a l p r o c e d u r e f o r B M E W S .

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M i lls to n e co n t r 2 o 9 l r oo m

H a y sta c k r a d a r , 196 4

N e w Ch a ll e n ge s

T h e L a b w o u l d p u r s u e d u a - l u se p r o j e c t s w i t h H a y s t a c k : ex p a n d e d p l a n e t a r y r a d a r a s tr o n om y p l u s mo r e ad v a n c e d m i ss ile d e f e n s e .

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D u a l - u s e “ p lu g - in ” mod u le s