Albert Einstein and the Theory of Relativity

Chapter 7

Great Idea:All observers, no matter what their frame of reference, see the same laws of nature

Chapter Outline

• Frames of Reference• Special Relativity• General Relativity

Frames of Reference

Descriptions in Different Reference Frames

• Coin’s path appears different depending on your frame of reference

The Principle of Relativity

• Baseball versus light• Einstein’s solution:

– The laws of nature are not the same in all frames of reference

– Maxwell’s equation could be wrong– Our intuitions about the addition of velocities could be wrong

The Principle of Relativity - cont.

• Principle of relativity– Every observer must experience the same natural laws•Special relativity•General relativity

• The speed of light, c, is the same in all reference frames

Albert Einstein

Science in the Making

• Einstein and the streetcar

Special Relativity

Time Dilation

• Time Dilation– Moving clock appears to tick more slowly

Stationary versus Moving Light Clock

Symbols for Deriving Time Dilation

The Size of Time Dilation

• Calculation of time dilation– tGG=tMM

– Stationary ground-based observer•tGG=d/c

• Distance traveled by light in 1 tick

Stationary versusMoving Light Clock

Distance and Relativity

• Length contraction– Moving object appears shorter

Spaceship at Rest and at High Speed

Objects Moving toward You at Different Speeds

So What About the Train and the Flashlight?

• Addition of velocities– Valid at small velocities– Not valid near speed of light

Mass and Relativity

• Third consequence– Mass is lowest for stationary objects

Mass and Relativity –Cont.

• Conclusions:– Nothing moving less than speed of light can be accelerated to or past c

– Object above c cannot be decelerated

– Objects at c have zero rest mass

Mass and Energy

• Einstein– All objects contain a rest energy

– Mass can be converted to energy and vice versa

2mcE

General Relativity

The Nature of Forces

• Gravitational forces and acceleration– Frame of reference

The Nature of Forces – Cont.

• Newton versus Einstein

Computer-Generated Image of a Gravity Field

Predictions of General Relativity

• The gravitational bending of light

• Planetary orbits

• The gravitational redshift

A Gravitational Lens

Technology

• Global positioning system and relativity

Who Can Understand Relativity?

Everyone!!