TTC - Particle Physics for Non-Physicists

greetings and welcome to particle

physics my name is Steven Pollak I'm a

professor of theoretical nuclear and

particle physics at the University of

Colorado in Boulder those words may or

may not mean a whole lot to you right

now theoretical nuclear and particle

physics it's a branch of physics and by

the end of this course you're going to

have a very good sense of what those

words mean and what it is that I study

and that we're going to be learning

about in this course particle physics

it's a branch of physics physics as a

whole is just the study of what the

world is made of how things work how

they behave why they behave that way

it's trying to understand things and

phenomena both natural and technological

in the ordinary world you talk the ball

up in the air and it follows an arc and

we can understand that path it makes

sense it follows certain laws of physics

particle physics is a branch of this

study where we really try to get down to

the bare bones what is the world made of

at the smallest level what are the

simplest building block and the most

fundamental rules and ideas which govern

how things work why they behave the way

they do particle physics is about the

particles that make up the world that we

live in I could describe particle

physics in five words those five words

are somewhat technical they're defined

by physicists to have very definite

meaning but they also connect with our

everyday intuitions and uses of those

words force and energy matter

faith and time those are the five

building blocks of the field of particle

physics and in fact of much of physics

itself force and energy refer to how and

why things interact matter what are the

things what is the world made of space

and time what is the framework in which

all of that stuff is going on these are

the concepts of particle physics and as

we go on in the course we will be deal

especially with the middle the matter

and also with all of the other elements

the forces that that matter feel the

energy that is involved in these

interaction the space and time in which

they live look around you for a moment

think about the world that you are in

right now the physical world in the

object and the phenomenon there are hard

things wherever you might be me that are

so hard you could try to break or bend

them and you couldn't

there are also soft things like your

hands or your skin

there's ethereal stuff like the air that

you live in that you can just barely

detect or sense and then there's the

things going on in that world the sound

that's hitting your ears and the light

that's striking your eyes the color the

texture all of that stuff is the realm

of physic and you could imagine that

this enormous diversity of phenomena is

overwhelmingly complicated and you can

have it the sense of the world as being

filled with a whole bunch of different

things and we could study any one of

them that might be a branch of science

and it's hard to imagine that you can

tie it all together but we can this is

one of the wonderful things that we have

learned about the world is that

everything physical from object in this

room objects in outer space objects in

the deepest deepest galaxies and

everything in between all arises from a

very simple set of rules and a very

simple set of ideas and fundamental

building blocks so that's what we're

going in this course what are those

ideas what are those building blocks how

can we make sense of them let's go back

2500 years this is an old question

people have been puzzling about what the

world is made of from time immemorial

and I guess they didn't write it down in

the days of cave people but we do have

records of Greek philosophers thinking

about this what is the world made of

we're going to be learning in future

lectures about some of these folks and

their ideas but let me summarize sort of

two viewpoints that arose 2,500 years

ago there was Democritus

a Greek philosopher from about 400 BC

who had this idea he wasn't the

originator of the idea he was following

in a long tradition of other

philosophers who were thinking about how

the world work and his idea was that

everything is made of little chunks he

called them a Tomo which means

unbreakable or uncuttable let me give

you a kind of a concrete metaphor to

think about Democritus IV and realtor

knees let me hand you a stick of butter

okay this butter is an object if the

physical object and it has certain

characteristic it is yellow and it's

soft and it melts if you heat it up and

it has a certain heft to it you can

describe it you can study it and

understand it it's the material object

now what if I chop it in half and throw

away half and you're left behind with a

half stick of butter I think we would

all agree there's still butter there

it's left massive but it's still

definitely butter we haven't changed the

essence or character of the material so

if you want to understand butter it

doesn't matter how much I give you so

what if I chop it in half again and

again and again but now you've got a

path of butter still butter there is no

difference between the pad of butter and

the original stick except for how much I

gave you

and now Democritus is imagining what if

I keep cutting it in half and in half

and half again and again ultimately

believes Democritus 2,500 years ago we

will come down to a chunk an individual

indivisible uncuttable chunk of butter

it's physical it's real it's a little

thing that you could imagine seeing or

looking at although it turns out that

it's much smaller than anything you

could actually see with your eyes and

this is democritus's idea of atoms they

live in the void they move around they

interact with one another they're real

solid physical object okay that's an

idea it's a philosopher's idea and there

were other philosophers at that time who

disagreed completely in fact Aristotle

probably one of the most famous

philosophers of that era disagreed a lot

and in fact most of what we know about

democritus's ideas come from Aristotle's

critiques

Aristotle had an idea which by modern

standards is a little more nebulous he

believed the world is made of earth air

water and fire but they're not physical

chunk there are more like characters or

quality and so matter is infinitely

divisible you can keep cutting that

butter into smaller and smaller and

smaller bits forever it's butter all the

way Aristotle's ideas survived for

thousands of years he was a very

brilliant man in many respects had a lot

of influence in fields of religion and

religious philosophy and philosophy in

general many of its scientific ideas

this one in particular are really quite

discredited now there is no evidence of

what Aristotle had to say and there is a

lot of evidence for what Democritus

believed but neither of those fellows

was a scientist in any modern sense of

that word they believe that you can

understand the world just by thinking

about it just be a philosopher ask

yourself how should the world be for it

to make sense that turns out to be a

very unproductive way of understanding

how things work it's much better to go

into the laboratory and ask nature how

are things not what do we believe is the

way it should be but just take data

collect information and ask yourself now

this butter behave and you can discover

it took over 2,000 years it was in the

1800s that people began to come up with

concrete evidence that indeed butter is

composed of what we would now call

molecules and then at a later time we

discovered that those molecules

themselves are understood to be built up