The Gravitational Deflection of Starlight

Randy WaynePlant Biology Retreat, August 25, 2012

Plants Move in Response to Light

…and Gravity

But What is Light and Gravity?

Newton

Light is a corpuscle.Gravity is a force.

Einstein

Light is a geometrical point that has energy and momentum.Gravity is not a force but a result of matter warping a four-dimensional spacetime continuum.

How Do Light and Gravity Interact?

Newton

“Do not Bodies act upon Light at a distance, and by their action bend its Rays…?”

Einstein

Gravity influences the motion of light, not by acting on light itself, but by directly acting on a four-dimensional space-time continuum through which the point-like photon passively propagates.

Johann von Soldner

Johann von Soldner (1801) calculated that the deflection of starlight by the sun would amount to 0.84 arcseconds by treating “a light ray as a heavy body” and using Newton’s Law of Universal Gravitation.

Albert Einstein

When Albert Einstein started the General Theory of Relativity in 1911, he considered matter to influence time. He predicted that the deflection of starlight by the sun would be 0.84 arcseconds (the same as that predicted using Newtonian mechanics—although he was unaware of Soldner’s work).

The Test between General Relativity and Newtonian Mechanics

Einstein asked Erwin Freundlich to test the General Theory of Relativity by measuring the deflection of starlight during an eclipse on 21 August 1914.

Germany Invaded Belgium, which was Neutral, on 4 August 1914

World War I Prevented the Test between General Relativity and Newtonian Mechanics• While Freundlich was in

Crimea to observe the eclipse, WW I broke out.

• He was arrested as a German spy and was unable to observe the eclipse.

• (Good thing for Einstein—because the actual deflection would have been twice that that Einstein had calculated).

On 25 August 1914 Germany Destroyed the Magnificent Library in Louvain

Times of London 29 August 1914

“Appeal to the Cultured World”4 October 1914

• As representatives of German Science and Art, we hereby protest to the civilized world against the lies and calumnies with which our enemies are endeavoring to stain the honor of Germany…in a struggle that has been forced on her. As heralds of truth…we raise our voices against these….

• It is not true that we trespassed in neutral Belgium. It has been proved that France and England had resolved on such a trespass, and it has likewise been proved that Belgium had agreed to their doing so. It would have been suicide on our part not to have preempted this.

• Have faith in us! Believe, that we shall carry on this war to the end as a civilized nation, to whom the legacy of a Goethe, a Beethoven, and a Kant, is just as sacred as its own hearths and homes.

The Manifesto was signed by 93 German intellectuals, including, Max Planck, Walther Nernst, Fritz Haber, Philipp Lenard, Emil Fischer, Adolf von Baeyer, Paul Ehrlich, Ernst Haeckel, Richard Willstatter, Wilhelm Ostwald, Wilhelm Roentgen and Wilhelm Waldeyer.

“An Appeal to Europeans,” by Einstein and NicolaiMid-October 1914

“…technology and traffic clearly drive us toward …a common world civilization....Those, however, of whom one should expect such convictions — that is, principally scientists and artists — have thus far almost exclusively uttered statements which would suggest that their desire for the maintenance of these relations has evaporated….”

Armistice Day11 November 1918

,

Albert Einstein

When Albert Einstein completed the General Theory of Relativity in 1915, he considered matter to warp not only time, but space and time. Einstein predicted that the deflection of starlight by the sun would be 1.75 arcseconds, twice the deflection predicted using Newtonian mechanics (or using his incomplete theory).

Arthur Eddington

• As a result of his internationalist and pacifist views, Arthur Eddington was one of the few allied scientists willing to consider the General Theory of Relativity, which was developed by Einstein, a German physicist.

• Eddington helped organize expeditions to observe the solar eclipse on 29 May 1919 in order to test the validity of Einstein’s theory.

“...all of England has been taken by your theory. It has made a tremendous sensation. It is the best possible thing that could have happened for scientific relations between England and Germany. ”

– Eddington (1919) in a letter to Einstein

Albert Einstein Wins the 1921 Nobel Prize in Physics "for his services to Theoretical Physics….”

J. B. S. Haldane (1924)

“I do not doubt that he [Einstein] will be believed. A prophet who can give signs in the heavens is always believed….Einstein has told us that space, time, and matter are shadows of the fifth dimension, and the heavens have declared their glory.”

“Einstein has given us signs in the heavens to corroborate his theory and mankind will never go back on signs in the heavens.”

--From “A Debate on the Theory of Relativity Open Court Publishing Co., Chicago, 1927)

Last Supper of Scientists

Ernest Rutherford told S. Chandrasekhar that Einstein’s fame was due to the timing of the eclipse expedition on 29 May 1919

“The war had just ended, and the complacency of the Victorian and Edwardian times had been shattered. The people felt that all their values and all their ideals had lost their bearings. Now, suddenly, they learnt that an astronomical prediction by a German scientist had been confirmed…by British astronomers. Astronomy had always appealed to public imagination; and an astronomical discovery, transcending worldly strife, struck a responsive chord. The meeting of the Royal Society, at which the results of the British expeditions were reported, was headlined in all the British papers: and the typhoon of publicity crossed the Atlantic. From that point on, the American press played Einstein to the maximum. ”

What Did Einstein (and the rest of us) Ignore?

• Light has angular momentum, which is just a number if a photon is just a geometrical point.

• But, if a photon has radial extension, which must be true if photons near each other interfere, then angular momentum leads to rotational motion (rotational kinetic energy).

• If the total kinetic energy of a photon is equipartitioned between the translational kinetic energy and the rotational kinetic energy, the photon would have one-half of the expected translational kinetic energy.

If a photon had one-half the translational kinetic energy as expected, it would bend twice as much in a gravitational field.

Is there evidence for rotational motion?

John Nicholson: Astrophysicist

John Nicholson (1912) introduced the importance of angular momentum in understanding the spectrum of atoms, and interpreted Planck’s constant, as a “natural unit of angular momentum,” indicating that angular momentum might be quantized and “the angular momentum of an atom can only rise or fall by discrete amounts when electrons leave or return.”

Arnold Sommerfeld: Moment of Momentum

“…in the process of emission…, we demanded…the conservation of energy….With the same right, we now demand the conservation of momentum and of moment of momentum: if in a change of configuration of the atom, its momentum or moment of momentum alters, then these quantities are to be reproduced entirely and unweakened in the momentum and moment of momentum of the radiation.”

Why is Einstein so Sacred?

• In the wake of the horrors of World War I, Einstein, according to Abraham Pais, “carried a message of a new world order in the universe.”

• According to Pais, Einstein knew how to use language. Everyone knows what “space” and “warp” mean, yet hardly anyone understands what “warped space” is. Einstein himself said to a Dutch newspaper in 1921, “It is the mystery of the non-understanding that appeals to them….”

• According to Pais, Einstein was genuinely photogenic.

Emil du Bois-Reymond (1872)Ignoramus et ignorabimus

“We do not know and will not know",

David Hilbert (1930)

“We must not believe those, who today, with philosophical bearing and deliberative tone, prophesy the fall of culture and accept the ignorabimus. For us there is no ignorabimus, and in my opinion none whatever in natural science. In opposition to the foolish ignorabimus our slogan shall be: Wir müssen wissen — wir werden wissen! ('We must know — we will know!')”