4. Newton’s Laws of Motion
• I. Every body continues in a state of rest or
uniform motion in a straight line unless it is
compelled to change that state by forces
impressed upon it.
• II. Rate of change of momentum is
proportional to the impressed force, and is in
the direction in which this force acts
• III. To every action, there is always opposed
an equal reaction.
5. “..the Supreme God is a Being eternal, infinite, absolutely
perfect…He endures forever and is everywhere present; and
by existing always and everywhere, he constitutes duration
and space..”
Newton, Principia (General Scholium).
Absolute Space, Absolute Time
6. Universal Gravitation
• “the attractive force between any two
bodies depends on the product of the
masses of the bodies and on the square
of the distance between them”
• “the attraction always is in a
duplicate proportion to the Distance
from the Center Reciprocall”
7. The Mystery of Mass
• Mass can represent the resistance of a
body to being accelerated (inertial)
• ..or the strength of gravity produced
(active)
• ..or the tendency to feel gravity
(passive)
• Are these masses the same?
8. The Principle of Equivalence
maF 2
r
GMm
F
Why should these masses be the
same?
Perhaps this Equivalence is because of
a some sort of Principle?
9.
10. The Einstein (R)evolution
• Albert Einstein was born in Ulm on 14 March 1879
• After failing the entrance exam the previous year, he
entered the Institute of Technology (Zurich) in 1896.
• “Too lazy” to continue as a scientist, he left in 1902 to
become a patent clerk in Bern.
• In 1905, he revolutionized science with the special
theory of relativity. “E=mc2” and all that.
• In 1915, he went even further, with the general
theory of relativity.
11. General Relativity
• The “Principle of Equivalence”
• Acceleration and Gravity
• The curving of space
• ..and the bending of light!
12.
13.
14.
15. Light Bending..a comedy of
errors.
• Newton 1704 “Do not Bodies act upon Light at a
distance, and by their action bend its Rays?”
• 1802 Johann Georg von Soldner, calculates bending
of light by the Sun: 0.87 seconds of arc
• 1907 Einstein thinks about light bending, but then
shelves the idea.
• 1911 Einstein tries again using “E=mc2”; gets
Soldner’s answer: 0.87 seconds of arc.
• 1915 Einstein tries again, and finds a mistake - a
factor of two. The new value is 1.74 seconds of arc.
18. Eddington and the Expeditions
• Arthur Stanley Eddington was born in 1882.
• In 1912 becomes Plumian Professor of Astronomy
and Experimental Philosophy at Cambridge.
• Earlier in 1912 Eddington had been involved in an
Eclipse expedition to Argentina. It rained.
• 1916 de Sitter tells him about Einstein’s prediction
and suggests the idea of light bending measurements
during an eclipse.
• 1917, Frank Watson Dyson, the Astronomer Royal
realises the eclipse of 29 May 1919 would be perfect.
19.
20. The Eclipse of 1919
• Date: 29 May 1919
• Path of Totality is across the South
Atlantic from Sobral to Principe
• Duration is long…7 minutes or so at
Principe.
• Near the Sun during totality was not just
one star, but a cluster of stars: The
Hyades
21.
22. War and Peace
• BUT Eddington was a Quaker, and therefore
a pacifist.
• The First World War had started in 1914, but
conscription was not introduced in the British
Army until 1916.
• Eddington refused to be drafted…
• He was saved by a deal by Dyson, which
protected him on condition he agreed to lead
an expedition in 1919 if the war was over.
23. The Equipment
• Funding: £100 for equipment, £1000 for travel
and labour costs
• Two “astrographic” object glasses, one to
Principe (Oxford), Sobral (Greenwich), both
stopped down to 8 inches.
• A 4 inch telescope taken to Sobral as a
backup
• All were equipped with coelostats
• The two astrographic object glasses were
mounted in stainless steel tubes
24.
25. The Irish Connection
• All the optical equipment was made by Grubb
in Dublin.
• The Oxford astrographic moved to Keele
University in 1962
• The RGO moved to Herstmonceux
• The 4-inch telescope and coelostat are on
display at Dunsink Observatory
36. The Results
• Eddington went to Principe, off the coast of (then)
Spanish Guinea
• Crommelin went to Sobral (Northern Brazil).
• Eddington was nearly rained out
“THROUGH CLOUD. HOPEFUL”
• Crommelin was luckier “ECLIPSE SPLENDID”
• In the end Eddington got 1.610.40 seconds,
Crommelin 1.980.16
• After some controversy, Einstein was declared the
winner!
37.
38. The Controversy
• Principe astrographic: 2 “poor” plates. ( =1.62 ±
0.45)
• Sobral astrographic: 18 “poor” plates ( = 0.86 ±
0.48)
• Sobral 4”: 8 “good” plates: ( = 1.98 ± 0.18)
• Eddington included the Principe results, despite not
really getting enough measurements for an
astrometric solution
• The Sobral astrographic suffered from serious optical
problems but plates were remeasured in 1979:
=1.55 ± 0.34
39.
40. The Aftermath
• This made Einstein more
famous than any scientist
before or since.
• Reconciliation of Britain and
Germany
• What might have been…the
two expeditions of 1912 and
1914 failed to take
measurements when the
prediction was wrong!
• Much better measurements
were made in 1922, and
later using radio
observations.
41. Curiosities
• Einstein became the most famous
scientist ever - it was not 1905, but
1919, that made Einstein a household
name.
• What would have happened if the
measurement had been made when
Einstein had the wrong answer?