1 computer science 129 science, computing and society week 4 chapter 3
TRANSCRIPT
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GRE/GMAT WORDS
• Homogeneous – common origin
• Loquacious – talkative
• Pragmatic – practical values and results
• Volatile – explosive, unstable
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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
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Chapter 3
Strange theory….but….
Processing information is a common feature of the universe
Brains do it!
All communication is just information processing
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The main idea of this is:
• Information is something real and important in the description of nature
• Information is not abstract
• Information is physical
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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.
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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
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19th century Physicist James Maxwell proposed a hypothetical observer known as his demon
This demon related to the story of Thermodynamics
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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
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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
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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)
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Chapter 3
In measuring temperature
you can precisely measure the average speed of the molecules
not the exact speed of any one molecule
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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?
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No – it didn’t
The Demon , must 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 of the system
http://maxwells-demon.freeonlinegames.com/
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Chapter 3
Shannon’s Entropy
Shannon’s math measured information in bits
(information theory : 21=1 bit and two possibilities, 22=2 bits and 4 possibilities, 23=3 bits and 8 possibilities and so on)
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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
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Chapter 3
Entropy in computer science measures uncertainty
Using bits to quantify weather uncertainty:
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Chapter 3
In the morning there are the following possibilities (pretend these are like math givens. There are only these possibilities, no more, no less):
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 (23=8) or 3 bits of uncertainty
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Chapter 3
Jill is the weather person on channel ZHer weather forecast is essentially:GoodBadThis can be represented with 1 bit (21=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
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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?
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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
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What You Should Know
• WHAT IS THE FIRST LAW OF THERMODYNAMICS?
• WHAT IS THE SECOND LAW OF THERMODYNAMICS?
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What You Should Know
SHORT ESSAY:
EXPLAIN MAXWELL’S DEMON AND HOW DOES MAXWELL’S DEMON RELATE TO THE SECOND LAW OF THERMODYNAMICS?