CDT403Research Methods in Natural Sciences and EngineeringResearch Methods in Natural Sciences and Engineering

Theory of ScienceGOLEM ANALYSIS OF SCIENTIFIC CONFIRMATION:

THEORY OF RELATIVITY

Gordana Dodig-Crnkovic

School of Innovation, Design and Engineering

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Mälardalen University

GOLEM ANALYSIS OF SCIENTIFICGOLEM ANALYSIS OF SCIENTIFIC CONFIRMATION PROCESS

- THEORY OF RELATIVITY CONFIRMED

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Two Experiments that ”Proved” the Theory of Relativity

The Golem(Collins, Pinch)

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Michelson-Morley Experiment

After the development of Maxwell's theory of electromagnetism, several experiments were performed to prove the existence of ether and its motion relative to the pEarth. The most famous and successful was the one now known as the Michelson-Morley experiment performed by Albertthe Michelson Morley experiment, performed by Albert Michelson and Edward Morley. These two scientists conducted one of the most important null

lt i t in histor in 1887result experiments in history in 1887.

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Michelson-Morley Experiment

Using an interferometer floating on a pool of mercury, they tried to determine the existence of an ether wind by observing interference patterns between two light beams.

One beam traveling with the "ether wind" as the earth orbited the sun, and the other at 90º to the ether wind.

If light was a wave, then the speed of light should vary with the earth's motion through the ether - for example, g p ,like a boat traveling up and down stream; sometimes the current increases the boat's relative speed, other time it hinders, or slows, the boat's speed relative to the shore.

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Michelson-Morley Experiment

Th i t f f i d d b th t fl t d bThe interference fringes produced by the two reflected beams were observed in the telescope. It was found that these fringes did not shift when the table was rotated.

That is, the time required to travel one leg of the i t f t i d ith th ti i d t t l itinterferometer never varied with the time required to travel its normal counterpart. They NEVER got a changing interference pattern.

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Michelson-Morley Experiment

The experiment helped to refute the hypothesis that the earth is in motion relative to an ether through which light propagates.

The null results of the experiment indicated that the speed of light is a constant, independent of its direction of g ppropagation.

Another consequence of Michelson-Morley experiment q y pwas the building skepticism in the existence of the ether.

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Michelson-Morley Experiment

In 1907 Michelson was awarded the Nobel Prize in Physics forIn 1907 Michelson was awarded the Nobel Prize in Physics for his work in spectroscopy and precision optical instruments.

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Eddington’s 1919 Eclipse Experiment

Newton's Theory of Gravitation (1687) is one of the most important theories in the history of science. It is not able to describe both the falling of an apple and the formation of adescribe both the falling of an apple, and the formation of a galaxy. The equation of gravitational force is:

[1]

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When Newton published “Opticks” in 1704, he believed in the corpuscular nature of light, and he ensured that it must exist a relation between light and matter with the form of arelation between light and matter, with the form of a gravitational force ruled by equation [1].

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In 1804 (two centuries ago), Soldner was the first who ( g )calculated that, for small angles, the Newtonian deflection of light by a massive object should be:

[2]

where M is the mass of the deflecting object and R is thewhere M is the mass of the deflecting object and R is the deflection impact parameter.

For a light ray grazing the Sun this gives a deflection angleFor a light ray grazing the Sun this gives a deflection angle∼0.85´´ (a scheme is shown in the following figure).

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Newtonian angle of deflectionNewtonian angle of deflectionof light by the Sun

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Anomalies unexplained by Newtonian theory

Although Newton’s Theory of Gravitation was acepted by scientists along centuries, it was not able to explain severalanomalies the most famous of these being the perihelionanomalies, the most famous of these being the perihelionshift of Mercury.

Classical mechanics could explain the majority of the observed shift, but a residual shift of about 40 seconds of arc per century could not be explained by the gravitationalarc per century could not be explained by the gravitationaleffects of other planets. (A second of arc is 1/3600 of a degree).

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The Precession of Mercury's Orbit

Most of the effect is due to the pull from the other planets but there is a measurable effect due to the corrections to

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Newton's theory predicted by the General Theory of Relativity.

G it ti l f th t f tiGravitational force as the curvature of a space-time

During the earlier part of this century, Einstein extended his Special Theory of Relativity to generalized, or acceleratingreference framesreference frames.

From this study emerged a new description of gravity whichFrom this study emerged a new description of gravity whichsaw gravitational force as the curvature of a space-time, the curvature being due to the presence of mass.

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Einstein’s General Relativity not only explained the residualshift in Mercury's perihelion, but also predicted other effects, i l di th b di f li ht i it ti l fi ld G lincluding the bending of light in a gravitational field. General Relativity predicts that the bending angle for a light ray in the vicinity of a point mass to be:

[3]

precisely double the value expected from Newtonian gravity(see equation [2])!

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Einstein’s angle of deflection of light by the Sun. g g yEddington’s experiment

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In 1919, Eddington (on Principe Island) and Crommlin (inIn 1919, Eddington (on Principe Island) and Crommlin (in Brazil), monitored the position of the stelar background duringthe solar eclipse of the May, and they obtained a value for the deflecting angle of light by the sun of 1 98 and 1 60 secondsdeflecting angle of light by the sun of 1.98 and 1.60 secondsof arc respectively, with quoted errors of 0.30 seconds.

These results confirmed the Einstein’s prediction

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Eddington’s 1919 Eclipse Experiment

Eddington found that the star had indeed shifted position, and by the amount predicted by the equations of General Relativity. This apparent shift of a star's light as it passed close to the sun on its way toward us was

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shift of a star's light as it passed close to the sun on its way toward us was the first physical evidence in support of Einstein's General Relativity.

Einstein and Eddington

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Since Eddington, an enormous number of experiments to test Einstein's theory of General Relativity has confirmed it. Not aEinstein s theory of General Relativity has confirmed it. Not a single experiment to this day has cast the doubt on Einstein’s theory. *And in science that's saying a lot because the very nature ofAnd in science, that s saying a lot, because the very nature of scientific endeavor is to challenge the models we have. We are always trying to disprove Relativity, to look for a flaw, an inconsistency but none has yet been foundan inconsistency, but none has yet been found.

* (However something interesting is currently going on with neutrino experiments !): http://arstechnica com/science/news/2011/09/neutrino-experiment-sees-them-http://arstechnica.com/science/news/2011/09/neutrino experiment sees themapparently-moving-faster-than-light.ars http://public.web.cern.ch/press/pressreleases/Releases2011/PR19.11E.html

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Gravitational Lensing

http://hubblesite org/newscenter/newsdesk/archive/releases/2004/21/

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http://hubblesite.org/newscenter/newsdesk/archive/releases/2004/21/http://wikis.lib.ncsu.edu/images/0/02/Gravitational_lens-full.jpg

Light deflection or Gravitational Lensing (GL)

Concept of “Einstein Ring”

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Gravitational Lensing

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Gravitational LensingGravitational Lensing

In this cosmic ‘gravitational lens,’ a huge cluster of galaxies distorts

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the light from more distant galaxies into a pattern of giant arcs.

Gravitational Lensing

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Warping of SpaceWarping of Space

The curvature — or warping — of space was originally proposed by Einstein as early as 1915 in his theory of General Relativity.

It takes rather massive objects, like clusters of galaxies, to make space g , pcurve so much that the effect is observable in deep images of the distant Universe.

So far gravitational lenses have mainly been observed around clusters of galaxies, the collections of hundreds or thousands of galaxies thought to be

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g g gthe largest gravitationally bound structures in the Universe.

Newton's Law of Universal Gravitation hasNewton s Law of Universal Gravitation has Several Problems

1. It gave the wrong prediction for the precession of the perihelion of Mercury's orbit.

2 It did not explain why gravitational acceleration is2. It did not explain why gravitational acceleration is independent of the mass or composition of an object.

3. Instantaneous force of gravitational attraction between two objects means information about the location of one objectobjects means information about the location of one object would be transmitted to another object instantaneously by changes in the gravitational force.

4. Incorrect predictions for gravitational lensingp g g

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Einstein's General Theory of Relativity GR solved all three of the above problems, and at the same p ,time it radically changed physicists' view of the Universe. The main features of General Relativity are:

1 Space and space-time are not rigid frameworks in which events1. Space and space time are not rigid frameworks in which events take place. They have form and structure which are influenced by the matter and energy content of the universe.

2 Matter and energ defines space (and space time) c r at re2. Matter and energy defines space (and space-time) curvature. 3. Space defines how matter moves. In particular small objects

travel along the straightest possible lines in curved space (space-time).

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Einstein's General Theory of RelativityIn curved space the rules of Euclidean geometry are changed. Parallel lines can meet and the sum of the angles in a triangle

Einstein s General Theory of Relativity

Parallel lines can meet, and the sum of the angles in a triangle can be more, or less than 180 degrees, depending on how space is curved.

Einstein's theory gave a correct prediction for the perihelion shift of Mercury.

It also explained why objects fall independent of their mass: they all follow the same straightest possible line in curvedthey all follow the same straightest possible line in curved space-time.

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Einstein's General Theory of RelativityEinstein s General Theory of Relativity

Finally, in Einstein's theory the instantaneous gravitational force is replaced by the curvature of space-time. M i i l i hi d hMoving a mass causes ripples in this curvature, and these ripples travel with the speed of light. Thus, a distant mass would not feel any instantaneous change in the gravitational y g gforce.

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Golem’s Critique of Experimental Methods

To understand the true story of how scientific advances occur, Trevor Pinch, Professor of Science and Technology Studies and Professor of Sociology at Cornell UniversityStudies and Professor of Sociology at Cornell University and sociologist of science Harry Collins, Professor of Sociology, Cardiff University and School of Social Sciences, have studied contemporary descriptions of some historic experiments. The results they say do not agree with modern views ofThe results, they say, do not agree with modern views of the experiments.

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Golem’s Critique of Experimental Methods

Take, for example, the test by Eddington, of Einstein's prediction that gravity bends light. Eddington wanted to track starlight passing near the sun, and he used the sun'strack starlight passing near the sun, and he used the sun s approximate mass to calculate the deflection predicted by Einstein. The measurements had to be precise since the calculatedThe measurements had to be precise, since the calculated deflection was a hair-thin ∼1/3600-degree.

Since the sun's gravity would be bending the light, Eddington had to measure a star almost directly behind the sun.

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The Experimental SituationThe Experimental Situation in Eddington’s experiments

Because the sun's ligt would normally obscure the star, he had to work during a solar eclipse, meaning he had to set up a small, field telescope in a part of the world under a

l litotal eclipse.

Because the comparison pictures (those not affected by the p p ( ysun's gravity) had to be taken at night, Eddington had to take into account the temperature-induced size changes in the telescope. That tiny increment was about equal to the gravity induced deflection being soughtgravity-induced deflection being sought.

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SCIENTIFIC METHODSCIENTIFIC METHOD

Carl Popper: experiment (always specific) cannotprove, only support/confirm/corroborate theorythat is always generalthat is always general.

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SCIENCE IN CONSTANT PROGRESS

Science is constantly improving its theoretical and practical basis.Ei i ’ h d b d f k iEinstein’s theory represents a new and broader framework in which - geometry (for Newton it was Euclidean geometry) wasgeometry (for Newton it was Euclidean geometry) was generalized to curved space-time- velocities are allowed to reach speed of light which causes time dilatation and space contractionIn the classical limit Einstein’s theory gives Newtonian equations

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equations.