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What is infinity, and how does it work? | Robert Hammond | TEDxLFHS


and astronauts a physicist and

and astronauts a physicist and mathematician are all vacationing in

mathematician are all vacationing in

mathematician are all vacationing in Scotland aboard a train outside their

Scotland aboard a train outside their

Scotland aboard a train outside their train window they observe a single black

train window they observe a single black

train window they observe a single black sheep in a field the astronaut exclaims

sheep in a field the astronaut exclaims

sheep in a field the astronaut exclaims look all Scottish sheep are black the

look all Scottish sheep are black the

look all Scottish sheep are black the physician corrects him no only some

physician corrects him no only some

physician corrects him no only some Scottish sheep are black and the

Scottish sheep are black and the

Scottish sheep are black and the mathematician Ponder’s waiting for the

mathematician Ponder’s waiting for the

mathematician Ponder’s waiting for the train to pass and eventually he says

train to pass and eventually he says

train to pass and eventually he says gentlemen in Scotland there exists one

gentlemen in Scotland there exists one

gentlemen in Scotland there exists one field that has at least one sheep at

field that has at least one sheep at

field that has at least one sheep at least one side of which is black I’ve

least one side of which is black I’ve

least one side of which is black I’ve heard I first read this joke in a book

heard I first read this joke in a book

heard I first read this joke in a book entitled The Simpsons and their

entitled The Simpsons and their

entitled The Simpsons and their mathematical secrets written by this man

mathematical secrets written by this man

mathematical secrets written by this man Simon son I remember being exactly

Simon son I remember being exactly

Simon son I remember being exactly amused but I do remember how intriguing

amused but I do remember how intriguing

amused but I do remember how intriguing it was and how it emphasized the

it was and how it emphasized the

it was and how it emphasized the restrictive nature of mathematics and

restrictive nature of mathematics and

restrictive nature of mathematics and how the common sense and reasoning that

how the common sense and reasoning that

how the common sense and reasoning that comes from the scientific fields of

comes from the scientific fields of

comes from the scientific fields of astronomy and physics just don’t apply

astronomy and physics just don’t apply

astronomy and physics just don’t apply it to math today I want to talk about a

it to math today I want to talk about a

it to math today I want to talk about a certain area of mathematics as more or

certain area of mathematics as more or

certain area of mathematics as more or less become a recreational playground of

less become a recreational playground of

less become a recreational playground of unsolvable problems and unanswerable

unsolvable problems and unanswerable

unsolvable problems and unanswerable questions this is of course the

questions this is of course the

questions this is of course the conceptualization of infinity and we

conceptualization of infinity and we

conceptualization of infinity and we think of infinity at first we might

think of infinity at first we might

think of infinity at first we might picture a number unreachable on the

picture a number unreachable on the

picture a number unreachable on the number line or bigger than any other but

number line or bigger than any other but

number line or bigger than any other but really it is more of a quality than a

really it is more of a quality than a

really it is more of a quality than a quantity in itself used to describe

quantity in itself used to describe

quantity in itself used to describe unending scenarios or infinitely many

unending scenarios or infinitely many

unending scenarios or infinitely many things so what is infinity how does it

things so what is infinity how does it

things so what is infinity how does it work how can it be used or how can it be

work how can it be used or how can it be

work how can it be used or how can it be avoided what mathematicians do to answer

avoided what mathematicians do to answer

avoided what mathematicians do to answer these questions is they create special

these questions is they create special

these questions is they create special scenarios for themselves these scenarios

scenarios for themselves these scenarios

scenarios for themselves these scenarios require very special property to change

require very special property to change

require very special property to change our understanding of what infinity is

our understanding of what infinity is

our understanding of what infinity is after all if we keep thinking of it in

after all if we keep thinking of it in

after all if we keep thinking of it in the same way then our understanding will

the same way then our understanding will

the same way then our understanding will never change perhaps the most common use

never change perhaps the most common use

never change perhaps the most common use of infinity is to describe expressions

of infinity is to describe expressions

of infinity is to describe expressions like this one this is what we call an

like this one this is what we call an

like this one this is what we call an infinite sum where we start with one

infinite sum where we start with one

infinite sum where we start with one number then add another one and add

number then add another one and add

number then add another one and add another number and so on forever and we

another number and so on forever and we

another number and so on forever and we never stop increasing our total value

never stop increasing our total value

never stop increasing our total value and in this particular sum we have 1/2

and in this particular sum we have 1/2

and in this particular sum we have 1/2 plus 1/4 plus 1/8

plus 1/4 plus 1/8

plus 1/4 plus 1/8 forever and somehow we end up at one a

forever and somehow we end up at one a

forever and somehow we end up at one a finite value our total is always

finite value our total is always

finite value our total is always increasing and yet it does not reach

increasing and yet it does not reach

increasing and yet it does not reach infinity this requires this possesses

infinity this requires this possesses

infinity this requires this possesses the very specific scenario that I

the very specific scenario that I

the very specific scenario that I mentioned earlier allow me to present

mentioned earlier allow me to present

mentioned earlier allow me to present another scenario that takes advantage of

another scenario that takes advantage of

another scenario that takes advantage of the freedoms of mathematics called

the freedoms of mathematics called

the freedoms of mathematics called Thompson’s lamp here we have a lamp it

Thompson’s lamp here we have a lamp it

Thompson’s lamp here we have a lamp it can be turned on and off like a basic

can be turned on and off like a basic

can be turned on and off like a basic lamp and it can be only on or off at any

lamp and it can be only on or off at any

lamp and it can be only on or off at any moment in time

moment in time

moment in time this lamp is programmed to turn on and

this lamp is programmed to turn on and

this lamp is programmed to turn on and off at very specific times within the

off at very specific times within the

off at very specific times within the span of one minute at the start of the

span of one minute at the start of the

span of one minute at the start of the minute the lamp is on after exactly 1/2

minute the lamp is on after exactly 1/2

minute the lamp is on after exactly 1/2 minutes

minutes

minutes the switch is flipped and it turns off

the switch is flipped and it turns off

the switch is flipped and it turns off after 1/4 minute it turns back on an

after 1/4 minute it turns back on an

after 1/4 minute it turns back on an eighth of minutes it turns off so you

eighth of minutes it turns off so you

eighth of minutes it turns off so you see the pattern after exactly what half

see the pattern after exactly what half

see the pattern after exactly what half the remaining time expires the switch is

the remaining time expires the switch is

the remaining time expires the switch is flipped and the lamp changes its state

flipped and the lamp changes its state

flipped and the lamp changes its state so this goes on until one minute is

so this goes on until one minute is

so this goes on until one minute is reached and after one minute is it

reached and after one minute is it

reached and after one minute is it possible to tell whether the lamp is on

possible to tell whether the lamp is on

possible to tell whether the lamp is on or off

or off

or off well if we think about it each time the

well if we think about it each time the

well if we think about it each time the lamp is turned on it is then immediately

lamp is turned on it is then immediately

lamp is turned on it is then immediately turned off again and vice versa if when

turned off again and vice versa if when

turned off again and vice versa if when it is turned off it is that immediately

it is turned off it is that immediately

it is turned off it is that immediately turned back on again so which one is it

turned back on again so which one is it

turned back on again so which one is it what have we done is it both neither or

what have we done is it both neither or

what have we done is it both neither or is it on or off we can do nothing but to

is it on or off we can do nothing but to

is it on or off we can do nothing but to simply guess what we’ve done is done and

simply guess what we’ve done is done and

simply guess what we’ve done is done and infinitely infinitely many things in a

infinitely infinitely many things in a

infinitely infinitely many things in a finite amount of time

finite amount of time

finite amount of time this is called a xenon super task named

this is called a xenon super task named

this is called a xenon super task named after the mathematician Zeno doing and

after the mathematician Zeno doing and

after the mathematician Zeno doing and incidentally infinitely many things in a

incidentally infinitely many things in a

incidentally infinitely many things in a finite amount of time does not let us

finite amount of time does not let us

finite amount of time does not let us answer whether Thompson’s lamp is on or

answer whether Thompson’s lamp is on or

answer whether Thompson’s lamp is on or off but it does allow us to change our

off but it does allow us to change our

off but it does allow us to change our concept of infinity into more of a

concept of infinity into more of a

concept of infinity into more of a mathematical idea than a physical one if

mathematical idea than a physical one if

mathematical idea than a physical one if we were to do the Thompson plant

we were to do the Thompson plant

we were to do the Thompson plant experiment again except following the

experiment again except following the

experiment again except following the laws of nature then I would merely turn

laws of nature then I would merely turn

laws of nature then I would merely turn the lamp on or off at intervals of 1

the lamp on or off at intervals of 1

the lamp on or off at intervals of 1 minutes but I would never be able to

minutes but I would never be able to

minutes but I would never be able to answer the question of what happens

answer the question of what happens

answer the question of what happens after I’ve done that infinitely many

after I’ve done that infinitely many

after I’ve done that infinitely many times another paradox that results from

times another paradox that results from

times another paradox that results from the use of infinity and this annoyance

the use of infinity and this annoyance

the use of infinity and this annoyance super task is called the Russ littlewood

super task is called the Russ littlewood

super task is called the Russ littlewood paradox suppose we start with a sheet of

paradox suppose we start with a sheet of

paradox suppose we start with a sheet of paper and what we want to do is write

paper and what we want to do is write

paper and what we want to do is write down infinitely many numbers on that

down infinitely many numbers on that

down infinitely many numbers on that sheet of paper at step one we write the

sheet of paper at step one we write the

sheet of paper at step one we write the numbers one through ten and then erase

numbers one through ten and then erase

numbers one through ten and then erase the smallest number which is one at step

the smallest number which is one at step

the smallest number which is one at step two we do the same for 11 through 20 and

two we do the same for 11 through 20 and

two we do the same for 11 through 20 and then erase 2 as you can see at each step

then erase 2 as you can see at each step

then erase 2 as you can see at each step we have nine more numbers on the page

we have nine more numbers on the page

we have nine more numbers on the page than we have the previous step and that

than we have the previous step and that

than we have the previous step and that gain of nine yet after we do this

gain of nine yet after we do this

gain of nine yet after we do this infinitely many times the final result

infinitely many times the final result

infinitely many times the final result is a blank sheet of paper so how is this

is a blank sheet of paper so how is this

is a blank sheet of paper so how is this possible how can we write infinitely

possible how can we write infinitely

possible how can we write infinitely many numbers and write nine numbers more

many numbers and write nine numbers more

many numbers and write nine numbers more on the page each time and yet have a

on the page each time and yet have a

on the page each time and yet have a blank sheet at the end of the page this

blank sheet at the end of the page this

blank sheet at the end of the page this is because we were erasing the numbers

is because we were erasing the numbers

is because we were erasing the numbers no matter how many numbers we had

no matter how many numbers we had

no matter how many numbers we had written initially if we raise infinitely

written initially if we raise infinitely

written initially if we raise infinitely many numbers we erase all of them now

many numbers we erase all of them now

many numbers we erase all of them now another way of doing this task which is

another way of doing this task which is

another way of doing this task which is very similar is only writing the first

very similar is only writing the first

very similar is only writing the first nine numbers and then multiplying the

nine numbers and then multiplying the

nine numbers and then multiplying the smallest by ten at each step here we’ve

smallest by ten at each step here we’ve

smallest by ten at each step here we’ve written one through nine and then

written one through nine and then

written one through nine and then multiplied one by ten to make it ten we

multiplied one by ten to make it ten we

multiplied one by ten to make it ten we do the same thing for 11 to 19 and

do the same thing for 11 to 19 and

do the same thing for 11 to 19 and multiply two by tend to make it 20 on

multiply two by tend to make it 20 on

multiply two by tend to make it 20 on the left and the right both sides show

the left and the right both sides show

the left and the right both sides show the exact same numbers

the exact same numbers

the exact same numbers however after we’ve done this infinitely

however after we’ve done this infinitely

however after we’ve done this infinitely many times the results are drastically

many times the results are drastically

many times the results are drastically different on one side we have a blank

different on one side we have a blank

different on one side we have a blank sheet of paper and at the other side we

sheet of paper and at the other side we

sheet of paper and at the other side we have infinitely many numbers followed by

have infinitely many numbers followed by

have infinitely many numbers followed by infinitely many zeros this is a very

infinitely many zeros this is a very

infinitely many zeros this is a very famous paradox in mathematics that

famous paradox in mathematics that

famous paradox in mathematics that occurs from the use of affinity so well

occurs from the use of affinity so well

occurs from the use of affinity so well in physical world there will be never

in physical world there will be never

in physical world there will be never exist a measurable quantity that reaches

exist a measurable quantity that reaches

exist a measurable quantity that reaches infinity while simultaneously in

infinity while simultaneously in

infinity while simultaneously in mathematics it creates endless paradoxes

mathematics it creates endless paradoxes

mathematics it creates endless paradoxes left and right however in mathematics

left and right however in mathematics

left and right however in mathematics the escape from the physical

the escape from the physical

the escape from the physical restrictions of nature are really what

restrictions of nature are really what

restrictions of nature are really what makes it its own sandbox or

makes it its own sandbox or

makes it its own sandbox or imitations can answer all kinds of

imitations can answer all kinds of

imitations can answer all kinds of questions whether they can be answered

questions whether they can be answered

questions whether they can be answered or not this sandbox is what makes

or not this sandbox is what makes

or not this sandbox is what makes mathematics not what is usually thought

mathematics not what is usually thought

mathematics not what is usually thought of a world of black and white are

of a world of black and white are

of a world of black and white are correct or incorrect but instead a field

correct or incorrect but instead a field

correct or incorrect but instead a field of study where we can ask whatever

of study where we can ask whatever

of study where we can ask whatever questions we want to about the possible

questions we want to about the possible

questions we want to about the possible the impossible the finite and the

the impossible the finite and the

the impossible the finite and the infinite thank you

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