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Paradoxes

Schrödinger’s Cat

Coastline of Ireland

Koch Snowflake

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ParadoxesParadoxes• Mathematics cannot be applied to everything, and

cannot explain everything. • A paradox is a set of statements which contain

contradictions. • The existence of paradoxes causes problems for

mathematical logicians which they cannot solve.

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• 20 people live on an island. • Some people cut their own hair, the rest use

the barber who only cuts the hair of people who do not cut their own hair.

• 10 people never cut their own hair. • Draw a Venn diagram of the people on the

island:

Russell’s ParadoxRussell’s Paradox

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Let A = people who cut their own hairLet B = people who do not cut their own hair

Russell’s ParadoxRussell’s Paradox

A B

In which circle is the barber?

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• A cat is placed inside a box, a device which operates randomly is placed inside the box which will release a deadly gas killing the cat.

• There is no way of knowing without opening the box if the cat is alive or dead.

• Logically the cat is either alive or dead, so we simply open the box to find out which!

Schrödinger’s CatSchrödinger’s Cat

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Schrödinger’s CatSchrödinger’s Cat

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Coastline of IrelandCoastline of Ireland

• How long is the coastline of Ireland?• If we use a 10 km stick to measure it, we might get

2,500 km. • As we measure it in more and more detail going in

and around every cove it will grow to 25,000 km.• If we look close enough we can make it 100,000 km

or any length we wish!

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Coastline of IrelandCoastline of Ireland

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Koch SnowflakeKoch Snowflake

• Helge von Koch (1870 – 1924)• Draw a simple equilateral triangle• On each of the three sides place another

equilateral triangle exactly one third and in the middle of the side

• Continue with each of the new sides

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Koch SnowflakeKoch Snowflake

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Koch SnowflakeKoch Snowflake

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Koch SnowflakeKoch Snowflake

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