Il tempo di quel che c’è | Francesca Vidotto | TEDxUdine

[Music]

good morning

my name francesca vidotto and I am one

theoretical physics to be precise mine

work consists in trying to write

the equations describing space e

the weather these equations are

important for example if we want to

try to understand what’s inside a

black hole or like our universe

started to expand

they are situations a little different from the

Our daily life, however, is

situations so extreme in which

it becomes important to try to understand the

time and understanding time also means

understand what reality is understanding what

it is real then the reality what

unreal seem meanwhile seem

questions that is not the gold trade

Physical ask themselves instead no but they seem

even easy questions what is there

easy reality I am here I exist you

you exist I’m seeing you floor exists

the screen exists your chairs on which

you are seated exist easy trivial

let’s try with the question a little more

complicated

there are dinosaurs who are voting yes

raise your hand who is voting no, not me

I see no dinosaurs here I never have

seen dinosaur in my life listino a

museum but were not fake us dinosaurs

we exist however we can say that

they existed in the past and in the future

for example we can say that they exist

of human colonies on mars but not

it could be that in the future they exist

so maybe it’s just a matter of

try to formulate a little better

question maybe we should ask ourselves that

what now exists then what exists

now it requires defining what the

here I’m

present as a thin line one

line without thickness that divides the

passed from the future then for example

I can order many lines one behind

the other of the lines of simultaneity

of the lines on which I put all things

that exist at the same time and I can

order the dinosaurs in the past

us now and in the future the colonies

smarter but it is not so unfortunately

fortunately in the equations of physics

that I can not study

this we have learned thanks

ad einstein in his theory of

relativity his two theories of the

relativity after einstein we know that

this stratification of time this

description of the present is not like the

world works the world is not like that but

let’s try to understand a little better

now let’s imagine for example I do

help imagining that there is mine

sister here my sister and I have

of very precise watches or better than

this we synchronize our watches and

then

I stay in the Netherlands and live

she, for example, goes to live in the countries

high in the mountains on the blimaly himalayas

when we meet again we look at the

our watches and we see that its a

well ahead of my what it means

it means that his acts that given a little

more than mine then time passes

differently depending on where there

we find

who we are close to a mass more

time flows slowly more than the

our clock ticks more

slowly

So this is true for watches but

it’s also true for us it’s true for

anything is true of yours

true cells for particles

elementary that interact and true for

everything

this ticking slower when it is

close to a large mass also implies

the fact that since my sister is

been in the mountains has aged a bit

more than me, poor sister, we do it

contrary

let’s do that instead of my sister

that goes close to a large mass like

what can be done

we send her on a space mission on

a more massive planet of the

we send it to you, for example, on Jupiter

but let’s go on more massive jupiter

so time for her now flows

slower

yet still it is not enough there is one

the more extreme we send one

Space mission even more extreme the

we send a hole near a black hole

black is a supermassive object where

the whole mass is concentrated in one

very small space and where the weather

it flows very slowly

so time depends on where we are

we find

but even if my sister and I are there

we found the same place in the

same place, however, is my sister

he began to turn around one

crazy speed

even in that case our flow

time would be different for her

it would pass once more

I slowly and when we will meet

I would find out that she has aged less than

but then it’s okay the time flows in

different way the rhythm of time is

different for each observer though

you still do not understand why this

it should change our nation of

present because the stratification of the

time should disappear

we are there for a moment at the bottom of a

observer

time passes with a certain speed

for the other it flows with another

speed

but I can always order events

in the past present one will be one

slightly older and the other will be one

a little younger

but I can always put events

one after the other in one order I can and no

it’s right here the point I can not in

theoretical physics of the equations of

einstein I find out that I can not can not

because it does not exist, this does not exist

stratification and why every clock

at his pace trying to understand better

what does it mean

what implies the fact that every year

loggia its rhythm

time is not a line without thickness

at a small thickness, look for what it wants

to say the fact that something exists

question I asked you at the beginning if

my sister was here a meter away from me

how can you say that she exists like

I’ll say that the things that are here

they exist because I am

interacting with the floor I’m

interacting with this remote control

I’m watching you and there are some

particles of light that bounce on

you and get my eyes and I know that

you exist and they do it with one

speed that is over the speed

of light is a limited speed

so when I say my sister

exists here beside me

in reality what happens is that there

they are photons that come to me and there

they put a few billionths of a second

to arrive then in reality mine

sister exists there next to me though

in fact, the present is as if

become a little bit more often

often becomes has a temporal thickness

a few milliseconds

let’s see if my sister always a

do very extreme missions and now the

instead we send to the moon on the moon

this extended present begins to have

a thickness of 2 seconds begins to

become something relevant too

for our telecommunications for

example , try to look at mine

sister with a telescope you’ll see her

image two seconds after what’s up

happening and it would take two seconds there

they would put the photons two seconds to

get there if you have a telescope again

better and send my sister

[Music]

we do not even do a thing too much

extreme we choose the star system

closer to our proxima centauri

there is a planet habitable from those

set off

we send my sister there in that case

but the light takes four years to

get there from there so if I with a

telescope I try to look at what’s going on

making my sister see an image that

it took us four years for a of for

get there again but why

this implies that the present is extended

and often, in short, I could always say it goes

well I’m watching an image of

four years ago

my sister right now is

doing four years in the future some

what for her right now I am

passed also for her have passed

four years was doing something else

four years later it will be four years

Older is not really like that

because four years for me could

to be

the four years for her could be

no in my present in mine now but

they could be in the future, for example

if if she had taken a rocket

as before he had moved a great one

speed once again his pace

of time would be different for which those

four years for me I am not now

for her I am a moment in my future

then you see the arrangement of things

of events becomes difficult becomes

that is impossible, this extended present

it’s a space, a space where i

events and the set of events that I

I can not order I can not decide

which comes first and which comes after there

he was all grouped together in one

present extended therefore the present has

an extension is an extension for me but

it also has an extension for my sister

it has an extension for everyone of you

an extension for each observer

the universe

and how big this is this

thickness of the extended present well depends on

from every pair of observers every

pair of observers every interaction

that I consider in one of his present is extended

associated for everyone different for each

different pair and then sorting

temporal thing comes first thing comes

after I can do it only for these

couples can not do it globally

the ordering is only partial therefore the

present does not exist does not exist either

past does not exist also teaches the

I can not do this in the future

stratification of time I can not

sort things out then let’s get back to the

question first

what exists can also formulate

the doc try to formulate the question

at first he said ok this is one

more precise question

when to better formulate what

it exists now in the present but then

presents there is not even think about it

a little longer and my partner is away

more my present becomes extended

even this present can

extend to the whole universe can

happen that in my present is stretched

there is another observer whose

extended presents includes things in mine

passed into my future

so this network of observers each

with its present it is defined a

unique large present that includes

all the universe in which they exist together

the dinosaurs and the men on mars

exist yes exists together the big

bang

together with the end of the universe

the universe is a single great universe

block in which all the things that exist

they exist together at the same time

think about it for a moment, think about the child

of a movie now we live in the era

digital

but if you have a film reel

you see the reel there is everything

but together when you watch the movie

watch frame by frame and

this gives me the impression of

time flow of changes

of the image even if the coil of the

film exists all together in the universe

block a little bit so things exist

all together change

our perception of change

then only an illusion

the block universe is something in which

everything exists all together is not there

change only invasion change

and I do not think so

I believe no, I believe that in fact the

change interactions between the

observers these these interactions

that are interactions between the particles

this is what I want to describe

in my work but they are also the

interactions between observers between a

astronaut is someone who has remained

on earth they are the only thing that exists

basically we said at the beginning ie

to say what something exists

we have to interact otherwise it does not have

sense to say that something exists then

I believe that interactions are everything

what exists, however, we must

give up something we must

give up the idea that time can

scroll everything together the same for everyone

change exists but exists only

locally it exists only with respect to one

particular savior when I speak of

an interaction when I talk about a

change

I have to do this by specifying for which

observer this change exists

same change may not be true

it may not have happened yet for one

another observer then you see how much

it is important to respond to this

demand

this philosophical question, however, that is

at the heart also of physics what

there are only changes that exist

there are only interactions changes

they are local are relative

time does not exist the present does not exist

the past exists and the future does not

there

and all that exists is these

relative changes we can not

think of time as a single flow

like a single big clock that

ticks the same for everyone everyone to his

watch but pay attention to the thing

important is that every single one

interaction every change every

everyone’s watch is no less true

the fact that it is partial that it is

relative does not make it less true

these relative partial interactions

I am everything that exists there is not

nothing else is no less true only

all that exists then reality

it is not a single block but it is the plot of

all these changes that yes

cross that interacting between

they are a tangle of the stories of

each thanks