II. Einsteins Theory of Relativity
Topic is Gravity
1915 - Einstein wrote publication of his General theory of Relativity which was primarily a theory of Gravity.
Michelson-Morley Experiment
A.A. Michelson & E.W. Morley used an interferometer to show that the speed of light is not affected by Earth's motion around the sun. Speed of light is also unaffected by motion of Binary Stars.
Is the speed of light absolute?
First measured by Olaus Roemer in 1675. Experimental Evidence for the absoluteness of C came in 1887. C= Speed of light
Paradox
Is a situation that seems to violate common sense or contradict itself. The paradox is resolved when the rules of nature are better understood.
New common Sense
It's all relative Jackie moves by at speed of light, passing by relative frame: Her time runs slower, Her length contracts, and her mass increases. Jackie sees reference frame as she passes She is stationary; she sees frame moving by at high speed. Law of nature is same for everyone. Frames time runs slower, Length contracts, and Mass increases.
Gravitational Lensing
Light will always travel at a constant velocity. Therefore, it will follow the straightest possible path through spacetime. If spacetime is curved near a massive object, so will the trajectory of light.
Matter Distorts Spacetime
Matter distorts spacetime like weights on a taut rubber sheet. The greater the mass, the greater the distortion of spacetime.
What is "relative" in Relativity?
Motion... All motion is relative. Measurements of motion (and space and time) make no sense unless we are told what they are being measured relative to.
Albert Einstein (1879 - 1955) Swiss/American Physicist
Nature conceals her secrets because she is sublime, not because she is a trickster.
Gravitational Redshift
Observed on white dwarfs: Spectral lines emitted or absorbed on the surfaces on stars. Appear at a lower frequency (cycles/s) than surface than on Earth.
Plane Reference
Plane VS. Ground below it Plane: Passengers see ball moving 10 km/hr. Ground: Plane is moving at 900 km/hr.
Isaac Newton
Saw gravity as a mysterious "force" He could explain it actions, but not how it was transmitted through space.
What is Relative?
Seeing something move is seen from the point of view. Seeing something that you know is moving but its going the opposite direction of something else will be seen as static while the bigger object rotates.
Einsteins Theory: Two Step
Special theory of relativity: (1905) how space and time are interwoven. General Theory of Relativity: (1915) Effects of gravity on space & time.
Is the Speed of Light Absolute?
Subatomic Particles have been accelerated to speeds of 0.9999 C. No matter how much energy we put in, they never reach C. The Pie + meson particle decays in 18 sec when at rest. At high velocities, it lasts longer... proving time dilation. The equation E = MC^2, exemplified by nuclear reactors and bombs, is a direct consequence of special relativity
Reference Frames
Two or more objects which do not move relative to each other share the same reference frame. Objects moving relative to the other are in different reference frames.
Solar Eclipse of 1919
Two stars near the sun... Were observed to have a smaller angular separation than... Is usually measured for them at night at other times of the year.
The "UP" Paradox
Children: Regard "UP" as a single direction with us as the center. Adults: "UP" is defined relative to center of the Earth.
Albert Einstein
He theorized that time and distance can not be measured absolutely. They only have meaning when they are measured relative to something.
Hermann Minkowski (1864-1909) German physicist
Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality.
Spacetime
The 4-dimensional combination of space & time that forms shapes and distorts spacetime. Space (time) itself can be curved. If traveling a straight line, it is actually curved motion due to earth being a sphere.
The Equivalence Principle
The effects of gravity are exactly equivalent to the effects of acceleration.
What is absolute in Relativity?
The laws of nature are the same for everyone. The speed of light (in a vacuum, C, is the same for everyone C = Speed of light
Accelerated Motion
The special theory of relativity states that all motion is relative. For objects moving at a constant velocity with respect to each other. Everyone (every reference frame) can claim to be stationary. Ability to distinguish between motion & non-motion.
