Computer Science 129

1. Computer Science 129 Science, Computing and Society Week 4 Chapter 3 chapter 3

2. INTERESTING STORY IN THE NEWS • EACH WEEK WE WILL READ ABOUT A SCIENTIFIC TOPIC IN THE NEWS chapter 3

3. GRE/GMAT WORDS • Homogeneous – common origin • Loquacious – talkative • Pragmatic – practical values and results • Volatile – explosive, unstable chapter 3

4. Chapter 3 INFORMATION IS PHYSICAL Edward Fredkin: “the universe is a computer” Consider flight simulators Fredkin believes computer running the program of our universe is not located in our universe chapter 3

5. Chapter 3 Strange theory….but…. Processing information is a common feature of the universe Brains do it! All communication is just information processing chapter 3

6. Chapter 3 The main idea of this is: • Information is something real and important in the description of nature • Information is not abstract • Information is physical chapter 3

7. Chapter 3 Consider Complex systems: the universe is full of them Chemicals in our bodies - Black holes –Summer thunderstorms All are information-processing mechanisms They acquire information about the environment and use it to decide what to do next. chapter 3

8. Chapter 3 Information processing systems are essentially “observers” But, in classical physics, observers are irrelevant Laws of nature should be unaffected by observation – they are there whether anyone sees them or not chapter 3

9. Chapter 3 19th century Physicist James Maxwell proposed a hypothetical observer known as his demon This demon related to the story of Thermodynamics chapter 3

10. Chapter 3 The 1st and 2nd Laws of Thermodynamics Thermodynamics – study of energy (heat) change (Empirical Laws) 1st - Total energy of a system plus the surroundings is constant – or The Law of Conservation of Energy 2nd – Entropy (disorder) of the universe increases – energy can’t even break even chapter 3

11. Chapter 3 The Second Law requires any use of energy to produce some “waste heat” that is too degraded to do further work Order gives way to disorder - or entropy chapter 3

12. Chapter 3 James Maxwell – known for explaining Electricity and Magnetism using mathematics (Maxwell’s Equations) Maxwell believed the 2nd Law was a statistical law – based on probabilities Consider speed of molecules (temperature) chapter 3

13. Chapter 3 In measuring temperature you can precisely measure the average speed of the molecules not the exact speed of any one molecule chapter 3

14. Chapter 3 Maxwell’s demon – 2 rooms with same temperatures – door between is controlled by demon – demon lets fast moving molecules into one room and slow into the other One room hot, other very cold – demon could heat or air-condition a house Demon gets useful energy from waste heat – breaking 2nd Law Or did it? chapter 3

15. Chapter 3 No – it is still called the second LAW of thermodynamics The Demon be made, then it must find out how fast a molecule is going – measuring it, all of which requires energy – more energy that it could get out http://maxwells-demon.freeonlinegames.com/ chapter 3

16. Chapter 3 Shannon’s Entropy Shannon’s math measured information in bits (information theory : 2^1=1 bit and two possibilities, 2^2=2 bits and 4 possibilities) chapter 3

17. Chapter 3 • Remember our base 2 system? • 1 bit = 2 possibilities ; zero=0, one=1 • 2 bits = 4 possibilities ; zero=00, one=01, two=10, three=11 • 3 bits = 8 possibilities ; Zero=000, one=001, two=010, three=011, four=100, five=101, six=110, seven=111 chapter 3

18. Chapter 3 Entropy in computer science measures uncertainty Using bits to quantify weather uncertainty: chapter 3

19. Chapter 3 In the morning there are the following possibilities: Sunny all day Cloudy then Sunny Cloudy all day Sunny then Storm Storm all day Cloudy then Storm Sunny then Cloudy Storm then Cloudy 8 possibilities require 3 bits (2^3=8) or 3 bits of uncertainty chapter 3

20. Chapter 3 Jill is the weather person on channel Z Her weather forecast is essentially: Good Bad This can be represented with 1 bit (2^1=2) If we have 3 bits of uncertainty and 1 bit of information – missing 2 bits – even if she is always right, we still have more uncertainty than we do information chapter 3

21. Chapter 3 Shannon’s equations look very similar to the 2nd Law of Thermodynamics This raises the question: Is there a real connection between the entropy of physics and the entropy of information? chapter 3

22. Chapter 3 Information is always embodied in some physical representation – ink on paper – holes in punch cards, magnetic patterns on a floppy disk – arrangement of atoms in DNA Information is Physical chapter 3

23. What You Should Know • WHAT IS THE FIRST LAW OF THERMODYNAMICS? • WHAT IS THE SECOND LAW OF THERMODYNAMICS? chapter 3

24. What You Should Know SHORT ESSAY: EXPLAIN MAXWELL’S DEMON AND HOW DOES MAXWELL’S DEMON RELATE TO THE SECOND LAW OF THERMODYNAMICS? chapter 3

25. What You Should Know HOW DOES INFORMATION THEORY WORK? chapter 3

26. What You Should Know SHORT ESSAY: EXPLAIN HOW SHANNON’S ENTROPY WORKS. GIVE EXAMPLES. chapter 3