Announcements Exam 3 is scheduled for Wednesday April 8. Will be pushed back to Monday April 13 Tentatively will cover the rest of Chapter 4, all of Chapters 5, 6, 7 & 8. New Sample Questions that include Chapter 8 are posted.

The Cosmological Principle

Our universe is obviously not homogeneous or isotropic close by

On a scale of a billion lightyears it starts to look isotropic and homogeneous

On the largest scales it is homogeneous and isotropic, mostly

Colored Card Question ClassAction website Cosmology module Cosmological Principle

Another colored- card Question If you could be instantaneously transported to the edge of the visible universe 14 billion lightyears away from Earth, you would see A.the region around you filled with glowing hot gas from the Big Bang B.nothing, if you looked in the direction opposite the Earth C.pretty much the same thing you see here, just different star patterns. D.planets, stars and galaxies unlike anything we see near Earth

One final requirement to understanding the universe The laws of physics are the same everywhere and everywhen

Coordinates

The coordinate system determines how you find the shortest distance between two points s = s

Inertial Reference Frames

Accelerated Reference Frame

A consequence of our reference frame being non-inertial is the Coriolis effect

An inertial reference frame near a gravitational object is free fall Since the inertial mass of an object is equal to the gravitational mass, an object in freefall is in an inertial reference frame

Relativity According to Galileo

According to Galileo light should add, too Speed observed by S` is c ( m / s ) Speed observed by S is c + v If the train is moving at 100 m / s then c = m / s

Moving Reference Frames

An example of moving reference frames using normal addition

Maxwell’s Equations aren’t invariant under Galilean transformation The equations governing the electromagnetic force change when a Galilean transformation is done on them

What is the reference frame of light?

The Michelson-Morley Experiment They were trying to detect the luminiferous aether. They didn’t find it. Watch the King’s Special Relativity apps Michaelson-Morley Experiment

Watch Mechanical Universe and Beyond: The Michelson-Morley Experiment

In 1889 George FitzGerald proposed another type of transformation Hendrik Lorentz added in a transformation of time as well as space so we now call it a Lorentz transformation

In 1905 Einstein explained why the Lorentz transformations are the correct transformations

Einstein had two basic postulates for Special Relativity The laws of physics are the same in all inertial reference frames. The speed of light in a vacuum is the same in all inertial reference frames The “special” of special relativity is that it only applies if the relatives velocities are constants. There must be no acceleration.

The problem of simultaneity Different observers do not see the two events as simultaneous Watch YouTube Simultaneous events video

Time Dilation: Time is not absolute The light travel time is shorter for the observer that is stationary with the light than the outside observer that sees the light moving Watch Time Dilation video

The amount of time dilation depends on the relative speed Note that it is always the other clock that runs slow. Your clock, the one stationary with respect to you, always runs at the right speed. It doesn’t matter who is moving. In fact, you can’t tell who is moving, only relative motions.