Carlo Rovelli on physics and philosophy

Theoretical physicist, philosopher, and international bestselling author Carlo Rovelli joins Lauren and Colin for a conversation about the quest for quantum gravity, the importance of unlearning outdated ideas, and a very unique way to get out of a speeding ticket. Rovelli is a Distinguished Visiting Research Chair at Perimeter Institute. He is also the author of seven popular science books, including The Order of Time, Reality is Not What it Seems, and the breakout bestseller Seven Brief Lessons on Physics, which has been translated into more than 40 languages. View the episode transcript here.

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Conversations at the Perimeter is co-hosted by Perimeter Teaching Faculty member Lauren Hayward and journalist-turned-science communicator Colin Hunter. In each episode, they chat with a guest scientist about their research, their motivations, the challenges they encounter, and the drive that keeps them searching for answers.

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Episode Transcript

(00:00):
(light electronic music)

(00:09):
- Hi, everyone.
Welcome to Conversations at the Perimeter.
Today, Colin and I areso excited to bring you
this conversation with Carlo Rovelli.
Carlo is a theoretical physicist,
with expertise in bothphysics and philosophy,
and his research interestsinclude loop quantum gravity,
the nature of time,
and the relationalinterpretation of quantum theory.

(00:31):
- And Carlo is also a bestselling author
of popular science books.
His "Seven Brief Lessons on Physics"
was a breakout success, soldmore than a million copies,
has been translated intomore than 40 languages.
I've been a fan for years,
so it was just a thrillfor me to talk to him,
not just about his research,
but how and why he translates
these difficult scientifictopics into concepts

(00:52):
that people like me can understand.
- He also has some other great books
called "Reality Is Not What It Seems",
there's also "The Order of Time",

and "Helgoland (01:00):
Making Sense of the Quantum Revolution".
And he has another new book coming out
called "There are Placesin the World Where Rules
Are Less Important than Kindness:
And Other Thoughts on Physics,Philosophy, and The World",
and I have to say, I just love the title
of this upcoming book, andI can't wait to read it.
- And I loved this conversationthat we had with Carlos,
so let's have a listen.

(01:21):
(light electronic music)
Thank you for joining us,it's lovely to have you here.
- Thank you, it's wonderfulfinally being back
at the PI after this long absence.
- I was struggling withways to introduce you
to our audience becausethere are so many things,
you know, theoreticalphysicist, and author,
and world traveler, and philosopher,

(01:42):
so I decided I didn'twant to introduce you.
Pretend I'm a stranger on aplane and I've just sat down
next to you, and I'vebuckled up, and I say,
"Hey, what do you do for a living?"
- I would say, "Hi, my name is Carlo.
I was born in Italy, and I goaround and talk with people.
I have ideas, I try to do them.
What about you?"
- (laughs) I talk to people like you,
trying to figure out whatthey do, so it's a good thing

(02:03):
we sat next to each other on this plane.
You didn't mention theoretical physics.
Is that because what you consider
yourself doing is morejust talking to people
about a variety of subjects?- No, if you have
to define me, what I am primarily,
I'm definitely a theoretical physicist.
The rest of the things thatI do are part motivating,
part around that.
My competency, if I have any,

(02:24):
it's in theoretical physics.
I don't like to define myself,even in front of myself.
I like to keep things open.
And when I started writingbooks for the large public,
there was a moment inwhich I was telling myself,
"Wait a moment, are youjust turning into a writer
instead of a scientist,"
and then I realized that thisis a meaningless question.
I'm just doing what I'm doing,and things are connected.

(02:47):
The only meaningful questionis how many hours I devote
for one and the other, that might be it.
- I ask partly because you're currently,
you have a position in London, Ontario,
at the Rotman School of Philosophy,
which seems, at least on the surface,
to be a strange place for atheoretical physicist to be.
Can you explain what you'redoing at a school of philosophy?
- (chuckles) I talk with philosophers.

(03:09):
I love to talk with philosophers
because I think it's useful for physics.
I have this convention since a long time.
I've been interested inphilosophy since I was a kid.
When I was a student studying physics,
I also continued to study philosophy,
and I think that a clear-cutseparation is a bit artificial
and is damaging for both disciplines.

(03:31):
- How so?
- Not all physics needsto talk with philosophy.
If you have to solvethe Maxwell's equations
for a certain antenna, you justhappily ignore philosophers,
and a lot of physics is just concrete,
specific problems.- Right.
- But, of course, there's apart of physics which is not
to apply knowledge that wehave for solving problems,
it's to find out what is theknowledge we have at the basis,

(03:55):
and that part, it's the kindof things that, you know,
Einstein, Maxwell, or Newton, or Galileo,
or Boltzmann were doing, or Heisenberg,
and that kind of activity, traditionally,
was done by people who wereschooled in philosophy.
I mean, Einstein had a deepknowledge of philosophy,
and so Heisenberg, and certainly Newton.
Galileo, he was an avidreader of Aristotle.

(04:17):
There's a mistake in the understanding
of physics, and science in general.
Science is just collecting data
and writing equationsthat predict this data.
I mean, that's just a little part of it.
The largest part of it is figuring out
a set of notions, concepts,a conceptual structure,
how to think about that.
When you go from, you know,

(04:38):
the Ptolemaic to the Copernican system,
you don't just collect data,you rearrange the order
of the world in a different way.
That's what Einstein did,
that's what Maxwell and Faraday did,
that's what Heisenberg did,and Boltzmann, and so on.
So, the core problems infundamental physics today,
like quantum gravity, theproblem in which I am,
do require the same kind of rethinking

(05:00):
the conceptual basis of a discipline,
and the philosophersare very good in that,
not because they solvethe problem of physics.
I mean, relativity was found by Einstein,
who was a physicist, but he'sa physicist who was listening
to what the philosophers were saying.
Philosophy has a capacityof critical thinking,
which is very deep, has imagination.
Philosophers come out withcompletely different ways

(05:21):
of thinking aboutreality, sometimes crazy,
and we don't care about them,but that's not the point,
sometimes very useful.- Sometimes I think
theoretical physicists comeup with ideas of reality
that strike me as crazy too.
- Sometimes they do, sometimeseven perhaps too much crazy,
and they should listento philosophers who say,
"Wait, come on, don't exaggerate, guys."
- Are there certain openquestions in physics
that you think would most benefit

(05:41):
from input from philosophers?
- Yes, and they change, of course,
because physics is aprocess, and right now,
the number of open questionswhere philosophical thinking
and philosophical clarity is useful,
some of them, for instance,have to do with time.
In trying to write aquantum theory of gravity,
of course, space and time have to change

(06:03):
because now we're lookingat the quantum property
of space and time.
We have so many prejudices about how space
should be and how time should be.
A careful philosophicalanalysis of what we know,
I find it useful, even in simple things.
One very well-known problem about time

(06:24):
is that the past isdifferent from the future,
and so, what's the root
of this differencebetween past and future?
Is that something intrinsicin time itself, or not?
And the answer is not just academic.
Well, yeah, it is academic,
but (chuckles) the question is important
because if we want to understand more,
understand how quantum gravity works,
we have to get clarity about these things.

(06:46):
The nature of observer is another one.
We now are in this funnysituation with quantum mechanics,
which is a fantastically good theory,
but it's formulated interms of an observer.
So, why?
Do we need a guy with a PhD in physics
to understand how the things work?
No, I mean, things work bythemself, without an observer,
so how to make sense of that,
and these are questions that physicists

(07:08):
have been struggling with, and they are,
and they will come up with a solution.
I think solutions are beingdebated around the table.
Philosophers can listen, contribute,
and provide perspective.
- I have your book here,
"Reality Is Not What ItSeems", about quantum gravity,
and we'll get more into quantum gravity,
but what struck me most wasthe book essentially begins

(07:28):
with the ancient Greeks.
Quantum gravity and loop quantum gravity
are relatively new fields of physics,
but to explain them, youwent back thousands of years.
What inspired you to go so far back
to bring us to the presentof quantum gravity?
- "Reality Is Not What It Seems",
it's actually the first popular book
that I wrote about science.
I wrote it quite late, afterso many people had told me,

(07:50):
"Why don't you write a popularbook about quantum gravity?"
It was at least 20 years thatpeople were telling me that,
and pushing, and some publishers also,
like, "Come on, Carlo, you have
this beautiful science, whydon't you write about that?"
Also because people were sickand tired with string theory,
I mean, just can't standstring theory anymore,
so let's do some good quantum gravity.
But I didn't know how to do it,
because how do you tell quantumgravity to people, right?

(08:13):
I mean, you have todigest general relativity,
you have to digest quantummechanics, so it's a long story.
For long, I hesitated becauseI wanted to do physics
and not waste time writing.
Then I started considering the idea,
but I couldn't find the right way,
and then there was a flash.
I had so many things to do,but I couldn't organize them.
I mentioned, in one ofthe prefaces of my books,

(08:33):
and I don't remember which edition,
I was driving from Italy to France,
where I had moved at the time,in the middle of the night.
And then I said, "Well, Ineed to explain this concept,
I need to explain this concept,
I need to explain this concept."
I need to tell the reader
what is a field, an electric field.
It's not clear.
I need to tell the reader whatexactly we mean by geometry.
It's subtle.
I need to tell the reader that particles

(08:55):
are not precisely particles,
so there's some discreteness,there's some granularity.
And then I started thinking, well,
maybe I should say whenthese ideas were born,
so the ideas needed to understand,
if I tell how they were born,
and suddenly the entirehistory, the narration,
came in front of my mind.
I said, "Of course, I justtalk about Democritus."

(09:16):
- Right.- I talk about Galileo,
I talk about Faraday,I talk about Maxwell,
what problems they were addressing,
how they came out withthat particular solution,
and why we're using this notion now,
and how this notion built up, changed,
and came all the wayto a point of reality.
No, and this is theevolution of the world.
In the Renaissance,

(09:37):
there's this idea thatthis is res extensa.
Then Newton comes and says,
"Okay, I go out the world,it's space, time passes,
and there are some little stones
that move around with forces."
And then Faraday comes, "Wait, wait, wait,
you're missing something,there's a field,"
okay, and Maxwell putthe order in the field.
And then, Einstein comes and says,
"Look, the space and thetime are actually mixed,

(09:57):
so you should not havetwo different things.
You should-- Spacetime.
- Spacetime, and then Iinstantaneously realized
that spacetime is a field.
Wow, okay, now we connect the notion
of field with spacetime,
and quantum mechanics connect the notion
of a particle with a field.
So, unless you go through theway that things developed,
you don't get them, so Idecided to write a book

(10:18):
without details, but withthe core flow of ideas.
- When that epiphanyhit you while driving,
I know what happened after that.
- You know what happenedafter that, I got a ticket.
- Yeah, because you were driving too fast
'cause you were-- I was driving too fast.
It was an empty in the night highway.
I was so excited,
so excited.- You had the pedal
to the metal.- Yes, the first chapter

(10:39):
is gonna be saying this,and then (imitates siren).
I said, "Shit,"
and then I looked at thespeedometer or whatever,
don't know how you call itin English, and I'm going,
you know, 180 kilometersper hour on the highways.
Oh, no.
So, I had to pull on theside, and the policeman said,
"What the hell are you doing,"
and I was, you know, I just told him.

(10:59):
I said, "I'm sorry, I justwas going extremely fast.
The reality was I was not even in a hurry.
I just got an idea how towrite a book (chuckles)
and was so happy with that,I just was excited, excited."
And the policeman said, "Okay,good luck with your book,"
and let me go.- He let you go.
I'm dying to use thatexcuse someday, you know.
No, I was speeding because I figured out

(11:20):
how to write a book about quantum gravity.
I don't think it will work for me,
but I'm glad it worked for you.
- Yeah, it's good to knowthat works. (chuckles)
I have a question.
A lot of what you're talking about,
it seems that it's very fundamental,
this idea of unlearning things,
both when you're writing a book,
to encourage your readersto unlearn some things,
or even in your research.

(11:41):
I think that when we'rethinking about something,
we can be stuck in certainways of conceptual thinking
or be making some assumptionsand not even realize it.
Are there certain strategiesthat you've learned,
perhaps from philosophers,
that encourage you to challenge
your conceptual ways of thinking?
- Oh, that's a very good question.
I don't know the answer.
I think the most fundamentalpoint about learning,

(12:03):
that difficulty of learningis not to learn something new,
that's easy, the difficulty of learning
is to unlearn what we think we know.
We are all deeplyconvinced that we are right
about the way (chuckles) we see the world,
everybody, including myself,
so we just don't give upeasily the ideas we have,
and we don't learn unless we give up
the ideas we have.- You wrote once that science
is born from an act of humility.

(12:25):
Is that true?- Yeah.
Do you mean, by humility,
the idea that we can acceptthat we don't know everything?
- That, but even stronger.
The idea that what we thinkwe know, we might be wrong,
and so what we don't know is so much more
and so large that we shouldn'trely so much on what we know.
Yeah, I think, humility,
there is this beautiful letter by Newton.

(12:47):
Newton was arrogant, pretentious,
perfectly aware that hewas the greatest thinker
of his time, and three centuries later,
we still think he's the greatest thinker,
maybe in science, of all the times.
He was aware of that,
and at the end of his life,he writes this letter.
He says, "I don't know howthe others are looking at me
or will be looking at me,but I myself look at myself

(13:08):
like a kid playing withlittle pebbles on the shore
in front of the ocean of our ignorance."
That's why he succeededin being Newton, I think,
because he was perfectly aware
that there was everythingto be discovered.
- So, he was both arrogant and humble
at the same time.- Humble, exactly.
Arrogant and humble, there's a mix,
the mixture of the two.- Right.

(13:28):
- You can be arrogant withrespect to the others,
humble with respect to yourwork and your ignorance,
and the fact that we might be wrong.
I've been reading this summer,
because we're doing anaudio book in English,
Galileo's greatest book.
It's the dialogue of themassive systems of the world.
It's a fantastic book.
It's a book that convincedhumankind, in fact,
that the earth is moving, spinning,

(13:49):
and is going around the sun.
It has all the argumentsfor the earth to move,
but when reading it, asurprise is that the arguments
are just a few pages.
A large part of the bookis to convince a reader
that it's possible to questionwhat he took for granted.
It's all about, look, you think that,
but that might not be right.
It's only when, threequarters into the book,

(14:11):
he said, okay, nowyou're open to the book,
I haven't argued anything.
Only at that point, he brings argument
for the movement of the earth,
which, by the way, are wrong.
- (laughs) Yeah.
- Are mistaken, we knowthat, but nevertheless,
he convinced the world that,not by giving good argument,
in fact, he is wrong, but by showing
that there's nothing wrongin accepting that something

(14:33):
completely obvious to you, it's not right.
But that was not your question.
Your question, well, what'sa strategy we can go to
for not being trapped in our own beliefs,
and I don't know.
Scientists are like everybody else.
- Right.- Is it more
than being aware of that,keep repeating it to ourself?
(chuckles) That, I don'tknow what's the right way

(14:55):
of doing so.- Yeah.
- Do you remember a momentin your earlier life
when maybe physics, or science itself,
sort of revealed to youthis new way of looking
or unlearning things you may have known
and opened your eyes to new possibilities?
Was there an epiphany there,
or was it a series of happenings?
- It was a series of happenings,
starting from when I was a student.

(15:18):
I fell in love with science late,
when I was already auniversity student in physics.
In studying modern physics,it was a series of shocks,
like, oh, my God, somehowreality is not what it seems.
That became the title of my book.
So, it was a strongexperience at that time.
- Is that a phrase thatyou've had in your mind
for a long time before the book came out,

(15:39):
that reality is not what it seems?
Is that sort of the realizationyou had those years ago?
- The concept, yes.- Yeah.
- For sure, somehow it grewwith me in various manners.
The phrase itself, I'm not sure.
I think it came from the text of the book,
and then I picked it upbecause it represented
what was going on.
- You mentioned quantum gravity before,

(15:59):
and there's a line in your book,
"Seven Brief Lessons on Physics".
It's just such a simple short line,
"There is a paradox at theheart of our understanding
of the physical world."
That paradox is essentially, I think,
the root of quantum gravity,
that paradox between general relativity
and quantum mechanics.
Can you elaborate a bit moreon why that's a paradox,

(16:20):
what paradox we're struggling with,
and why we need a solution to it?
- I believe it is an apparent paradox,
that it's strikinglyparadoxical, the way it looks.
It's what a student of physics learns
when he goes to school at the university
and he just minimally thinks,

(16:41):
because you go to classeson quantum mechanics
and you get your explanation of the world,
and the world is all about discreteness.
Light is photons, and it'sjust discrete particles.
They're minute particle bits of things.
Everything is in bits and chunks.
It's probabilistic.
There is this strange,
interactive thing fromwhich, in quantum mechanics,

(17:03):
you predict how thingsinteract with one another.
So, you say, okay, that'sthe way reality is.
I mean, okay, God didreality like that, I mean,
we don't know what she thinks or why,
but that's the way reality is.
And then you go to the other class,
with this other teacher that teaches you
about general relativity,and this is, you know,
an equally immense,fundamental, successful theory,
and the universe is perfectly continuous.

(17:25):
There's nothing probabilistic,
deterministic equations of motion.
Everything is perfectlyobjective out there.
You can write the history ofspacetime in a single equation.
And then I think, wait a minute.
I mean, either one or theother, there cannot be, I mean,
my teachers stoppedtalking to one another,
(chuckles) haven't talkedto one another for 30 years.
So, it's really twototally different images

(17:46):
of how reality works.
God can be complicated, I don't know,
but not so self-contradictory.
The world is either thisway or the other way,
or some way which is compatible with both.
- And is that the question
of quantum gravity?- That's quantum gravity.
Exactly.- Speaking of quantum gravity,
as part of this show,
we collect questions from other listeners,
and a mutual friend ofours, Carlo, Lin-Qing Chen,

(18:09):
she's a postdoctoral researcherin Brussels, Belgium,
she sent in a question for you.
- Oh, fantastic.
- Hi, Carlo, this is Lin-Qing.
So, in our quest for atheory of quantum gravity,
do you think we will neednew fundamental principles
that both quantum mechanicsor general relativity
have not yet revealed to us,

(18:32):
and what is your strategyfor finding them out?
Thank you.
- The answer I have, I'm not sure,
but that answer onwhich I'm working is no.
No to the question, do you think
there is some fundamentalprinciple that we'll be missing?
I think that the idea that, oh,
we are missing something crucial,
fundamental down there is just wrong.

(18:54):
The point is that we have totake seriously what we learn
with quantum mechanics andseriously what we learn
about general relativity,and bring them together,
and they do go together.
I'm a very conservativeguy from this perspective.
I don't believe we need something new,
a supersymmetry with otherworlds, many dimensions,
breaking the Lorentz invariance,

(19:15):
of correction to quantum mechanics.
Nature has been sayingno to all the attempts
to test this alternativehypothesis so far,
so I don't see any evidencethat we're missing something.
General relativity, it's about spacetime,
so it's a shape of spacetime,
a shape of space and a shape of time,
which means how differentclocks move with respect
to one another and howmeters measure jobs,

(19:38):
and that's quantum, andso we have to understand
the quantum properties of time
and the quantum property of space.
That's radical.
So, the assumption isconservative, but if you follow up,
this is completelyradical because it means
this continuous spacethat you thought it was,
forget about it.
The time evolution in a singlevariable, forget about it.

(19:58):
You have to replace theusual way of thinking space,
the usual way of thinking time
with something consistentwith quantum mechanics,
but not this quantummechanics in spacetime,
quantum mechanics off spacetime.
So, for instance, youhave to have mathematics
and a physical intuition that allows you
for having quantumsuperposition of spacetimes,
plural, of geometries.

(20:20):
Like, there is shooting acat that can be both awake
and asleep, or somebodysaid dead and alive.
- I like your version better.- (laughs) Yeah.
- I like cats, so.- Yeah, exactly.
So, shooting a cat in quantum mechanics
is it can be both awake and sleeping.
And so, in the same sense,
space can have a shapeand also another shape
in a superposition of the two,
and, of course, this requires imagination,

(20:41):
finding the right conceptto talk about that.
That's also wherephilosophy comes in useful,
and the right mathematics,
and I think there are, I mean,
loop quantum gravity isan example of a theory
that attempts to do that.
We don't know if it is right.
It's very conservative,
and that's why the answer toLin-Qing's question is no.
So, there's no otherprinciple to be added,

(21:01):
but it's completely radicalthen because it forces us
to rethink the basic notions.
- And you mentioned evidencewhen you were giving
this explanation, looking for evidence
to support various theoriesof quantum gravity.
What kind of evidencewould you be looking for?
- Recently, there hasbeen a lot of evidence
that helps us, and in science,

(21:21):
evidence is never definitive,it's always indications,
like in life, by the way. (laughs)
It's not that you kill a theory.
It's very rarely that youreally, really kill a theory
with an experiment, but youcreate problems to a theory,
and when a theory has too many problems,
you look somewhere else,
and there have been a lotof these things recently.
The strongest and the mostunexpected for many people

(21:44):
has been the absence oflow-energy supersymmetry.
There was a big part of the community
that was completelyconvinced, sort of 99.9%,
that supersymmetry wasgoing to be detected-
- By the Large Hadron Collider?
- At CERN, right.- Yeah.
- It was LHC,
and it wasn't.
It was a shock, there weretitles of the journals,
like, you know, thisis a crisis of physics.

(22:05):
Of course, it's not the crisis of physics.
It's only the crisis forthose who expected it,
which is not physics,
it's just a particular school of thought.
But that's nature talking,
and when nature istalking, we should listen.
Another example is breakingthe Lorentz invariance,
the symmetry at the basis ofEinstein special relativity,
which is Lorentz invariance.
Some people thought, also,that was like supersymmetry.
It was a very nice idea.

(22:25):
You can make the pointof quantum gravity easier
if you don't have Lorentz invariance.
So, people try to provide theories
which break Lorentz invariance
and might be quantum gravity theories.
So, this was tested,
15 years now ofastrophysical observations,
and all the expected signs
of breaking Lorentz invariance, zero.
Once again, nature talks.

(22:46):
As far as we know, nature issaying, "No, no, no, no, guys,
that's not the right wayto look for the solution."
So, I think nature isgiving indication, I mean,
a lot of people expect anegative cosmological constant.
Even today, there is alarge part of the community
that continues to docalculations and calculations
and calculations with anegative cosmological constant,
or AdS/CFT.
AdS means anti-de Sitter,which means there's a space

(23:07):
with an effective negativecosmological constant,
and you accept that thecosmological constant
has been measured by theastronomers, by the cosmologists.
In a very convincing way,they got the Nobel Prize,
the ones who did that, and it's positive.
So, once again, I think my interpretation,
my reading of that as a scientist,I mean, I might be wrong,
but my reading of that is thatnature is talking, listen.

(23:27):
That's not the right direction.
- How will nature speak to you to advance
loop quantum gravity, say.
- There are two or three directions
where me and many of mycolleagues are looking into.
For the moment, zero,
so we have no negativeresponse from nature,
but we don't have any positive response
(laughing) from nature.- Can you explain that a bit?
- We don't know, so there'snothing that has come

(23:49):
as a contradiction to what we expected,
but there's nothing that has come
to confirm predictionsof the theory either,
so I cannot say that quantum gravity
is confirmed in any sense.
So, where could theconfirmation come from?
I see three possible directions.
One is the early cosmology.
There's a lot of literature,papers, and papers written.
So, the universe, we know,came out in the Big Bang,

(24:10):
the very early moment, atthe beginning of its life,
deep into quantum gravity regime,
so that's where quantumgravity should appear.
A lot of colleagues haveapplied loop quantum gravity
to describe what happens there.
It seems to be working, and to see if one
can predict effects of what happened there
that can be tested in thecosmic background radiation,

(24:32):
it's possible, measurementsgetting more precise.
I hope they will convertit with something useful,
but for the moment, there's nothing.
That's one, the second one is black holes.
I'm working on black holes.
Loop quantum gravity isconsistent very much with the idea
that a black hole evaporates.
That's Hawking's realization,that black holes evaporate.
They become smaller, smaller,smaller, and then, at the end,
they don't just disappear,pop out of existence,

(24:54):
but there's a remnant,which is a white hole.
So, there's a quantumgravity transition jump
from a black hole to a whitehole, with a little throat,
but a huge inside.
And then this white hole,slowly, things come out,
where the information slowly comes out,
lives for a very long time.
So, this is a scenario,
it might have astrophysical consequences.

(25:14):
These have been explored by this group,
including London and thepeople I'm working with.
There's one of these possibilities,
which I'm particularly attracted to,
which is that these littlethings that float around
in the universe are actually dark matter,
or a component of dark matter.
If so, it might be that we havealready observed something,
we just haven't recognized it.

(25:34):
- Dark matter being another great puzzle
of modern physics.- Dark matter,
it's a big puzzle, and that's the opposite
of the quantum gravity puzzle,because it's not a puzzle
in our understanding, it'sa puzzle in what we see.
You look at the universe around us
and we see galaxies,starts, clouds of hydrogen,
all sorts of stuff, and thenthere is this stuff out there,
something that produces effect out there.

(25:55):
We see the gravitationaleffect of these things.
We have quite convincing evidence
that it's not usual matter.
It's not just atoms ormolecules or protons
or neutrinos or photons,
it's something else, and it's a lot.
There's quite as much normalmatter and dark matter,
even more dark matter, andnobody knows what it is,
so it's fantastic.
People who say that we'reclose to the end of physics

(26:17):
and close to the theory ofeverything, come on, guys,
we don't even know what we see around us.
So, dark matter is reallyan important question.
We have a lot of possible explanations,
but many are non, confirmednon, really, credible.
I like the black hole ones
because it does not relyon any new assumption.
Well, if there's black holes,
it's just nothing we know exists.

(26:38):
- It's funny, you said it's a mystery,
we don't know, and that's fantastic.
That's not always the casein a lot of professions,
where the lack ofknowledge about something
is something you're excited about.
Are you glad that physics isnowhere near being complete?
- Oh, infinitely so, of course,
otherwise it would be boring, right?
Imagine what a disaster ifsomebody wrote, "Okay, I got it,
everything, this is the finalequation of everything."

(27:00):
- But that's what you're going for.
- No.- No?
- No, zero.- Is quantum gravity
not sort of that grand, unifying theory?
- No, it's a step on the way.
It's just figuring out whatis the quantum property
of space and time.
I'm not working formaterial of everything,
I'm working just for a next step
in understanding what's around.
- Once we've figured out thequantum nature of spacetime,

(27:20):
does that open up new questionsor help us answer old ones?
- I suppose loop quantumgravity is confirmed.
With a colleague, Marios Christodoulou,
we have an experiment which we proposed,
which might even bedoable in 10 years or so,
which would actually testthe discreteness of time
predicted by loop quantum gravity.
So, suppose this can be done, and bingo,

(27:40):
the right numbers, becauseloop quantum gravity
predicts that space is discrete, right?
It's granular, likelight is made by photons,
spaces make this grainof space, but also time,
I expect it has this granularity.
We have an idea of, perhaps,
with some slight advances in technology,
not excessive, it could be tested.
Now, suppose this comes out right.

(28:01):
Loop quantum gravity is correct, perfect,
the right numbers are there, now what?
Well, now we still have a universe
described by a funny standard model,
where the weak interactionsand the strong interactions
are completely separated,described by similar theories,
but not really unified in any way.
Gravity described by still another theory.

(28:22):
19 parameters for the standard model.
Who chose them? Why?
Three generations.
Suppose with quantum gravity,we figure out the Big Bang,
and what seems likely is that it was not,
that the initial exposure was a bounce.
It's an idea studied by various people.
- That our universe is the result
of a previous one collapsingand expanding again?
- Some universe wascollapsing, in some sense,

(28:42):
under its own weight.
It gets to the sort ofmaximum compression,
where quantum gravity comes in.
It bounces, and then what we see
as the Big Bang is this bounce.
I think it's a reasonable hypothesis.
It seems to be morereasonable than the Big Bang.
Suppose we figured this out.
Have we solved everything?
No, of course, I mean,
where was the collapsinguniverse coming from?

(29:04):
(chuckles) I mean, what was there?
It seems, today, so impossiblydifficult to figure out
what was in the collapsing universe,
but at the time of my great-grandfather,
it seemed impossible to discover
what was the chemicalcomposition of Jupiter.
I mean, it was consideredan unsolvable problem.
I mean, now we know,in Jupiter, everything,
even, you know, if there were ants there,

(29:25):
we would've seen that.
So, science finds new problemsand grows at all levels
if the mystery is not a reason of sadness,
it's a reason of joy becausea new thing's discovered.
It's the beauty of understanding.
- You're still, like Isaac Newton,
playing with pebbles on thevast sea of what we don't know?
- Absolutely.- And regarding this,

(29:46):
you know, general ideaof working in a field,
where you maybe don't yet haveevidence for or against it,
it just reminds me ofsomething you write about
in your book, "Seven Brief Lessons".
When you're talkingabout Einstein's theory,
you write about how, a lot of times,
something very important iskind of considered useless
at the time when it's developed.
One example you gaveis that Rehman's work,

(30:08):
that was generalizingGauss's explanations,
was considered useless at the time,
but it was then a fundamentalpiece of Einstein's theory.
So, it seems that this is very crucial,
to work on things wherewe don't actually know
exactly what the application will be
or exactly how long itwill be, but I'm wondering
if you think that physicistsneed to find, in general,
some kind of a balancebetween working on problems

(30:30):
where we have an idea of the time horizon
for the applications versusworking on these problems
where we don't reallyknow where it will lead.
- Yes, obviously there is abalance to be searched there.
If you look at this fromthe main whole of Perimeter,
as this is the same city,hard to find balance,
but if you look at it on a large scale,

(30:51):
99.9% of the money putinto research worldwide
is to practical applications.
Of course, we need practicalapplications, right?
We need people who studychemistry of materials
because we need the certainmaterials for something,
healing people and replacing bones.
I'm just defending.
Applied science is great,
but to concentrate resourcestoward applied science so much,

(31:12):
as is done today, Ithink, it's a disaster.
We need people who dothe kind of pure science
or fundamental science or basic science,
I mean, all these wordsare imprecise, all of them,
namely who don't think about application.
Our science is built
upon a number
of key results obtainedthrough the same tests.

(31:33):
If you look at each one,
no one was looking for application,
and if he had looked forapplication at his own time,
he wouldn't have got there.
So, it's obvious that we needto just ask the question,
what's behind things?
How can I understand betterat the fundamental level?
Applications will comeout, sometimes fortunately,
sometimes unfortunately
because sometimes applicationsare to kill people

(31:55):
and to make war.
- So, you're the organizerof a research initiative
called The Quantum InformationStructure of Spacetime,
and this brings together theorists,
experimentalists, and philosophers.
Can you tell us why youthink it's so useful
to bring together that group of people
and what you're trying toanswer through this initiative?

(32:17):
- Thank you for this question.
The Quantum InformationStructure of Spacetime,
the short name is QISS,QISS, written with a Q.
It's a big consortium with big grants,
mostly used for supporting young people.
A group of PI here, in fact,
two groups of PIs are part of it,
and there are about dozensof group all over the world,

(32:38):
from Hong Kong to Mexico, to California,
and the aim is to bringtogether two communities,
or actually three communities.
The two communitiesare quantum information
and quantum gravity,
and the idea is thatquantum gravity people
have been using quantuminformation notions,
or beginning to use it in various ways,
and quantum informationpeople are starting to think

(32:59):
about how quantum informationworks in space and time.
Let me say it this way,
and so the same problemsare being addressed,
but from a completelydifferent perspective.
And the third community is philosophers
because this dialogue opensfundamental questions,
like what we were saying before,
the direction of time or thenature of what is information,
what we mean by information,and in quantum gravity,

(33:21):
it's a theory which isnot written in spacetime.
So, in some sense, spacetimehas to be rethought
to come out on the theory in some way,
and these are philosophical questions.
So, these are different communities
which are being broughttogether, and in June this year,
they will be not far fromPI in London, Ontario,
so it's just a short drive from PI,
a conference bringing together this,
and it's a conferencethat we have organized.

(33:43):
It's not a standardconference with, you know,
speeches and a few questions,and, "Why do you say that?"
Each half-day, we'llhave a few 10/15 minutes
very short flash presentations,
and then a couple ofhours of open discussion,
everybody with everybody,with a good chair,
who sort of likes balance and follows.
Discussion compares all points of view

(34:03):
because there are thesecommunities, quantum information,
quantum gravity, and philosopherswho look at these things,
which have different waysof viewing the same thing.
So, we want to compare and, of course,
learn from these differences.
- Are there frustrationsthat tend to come up
when people with such differentbackgrounds and education
are trying to discuss atopic with each other?

(34:25):
- Yeah, there are thingsyou take for granted,
then a person who's a good scientist
comes to you and says, "You're wrong."
You say, "Wait, (chuckles)what do you mean I'm wrong,
you are wrong," and that's frustrating,
but that's great because I think
that's how the process of knowledge works.
You know, we learn from experiments,
but we even more learn
from continuous exchange of perspective,
and the more we listento other perspectives,

(34:47):
and that's a great opportunity, I think,
because quantum information has boomed
for various reasons inthe last decade, probably,
and there are very good ideas there,
which I think are relevantfor quantum gravity.
On the other hand, thepeople of quantum information
are not aware that some of the things
that they are struggling withhave already been addressed
by quantum gravity, right?
So, there's really adialogue to start here,

(35:11):
and the philosopherhas an interest in both
and have things to say about both.
So, I hope that this dialogue in three,
based not just in presentation,
but in discussion, will work,
and I look forward to that.
- After two years of lockdown,
of pandemics and people staying at home,
have you felt, distinctly,
the absence of in-person gatherings
with other researchers and scientists,

(35:32):
you know, getting togetherin the same place?
- A little bit, yes.
For me, this has not been dramatic
because we are all on theinternet, we're on Zoom,
but being always on Zoom is also painful.
This morning, finally,it's the first day I'm back
in PI after so long, finally!
I was with a young colleaguein front of a blackboard,
writing things, and I said,"No, wait, this is not,"

(35:54):
as, oh, what a pleasure. (chuckles)
It was so long that this didn't happen.
- And from reading the websitefor this QISS initiative,
it seems that a major goal is to deepen
the understanding of information.
Could you just tell us whatyou think of information
as meaning and why youthink that information
is so fundamental?
- Information is a very trickyworld 'cause the spectral

(36:16):
of meanings is very wide, extremely wide.
When you talk about information,people often get confused
because in a debate, in a dialogue,
people mean different things,
and it goes from the most complex one,
I mean, do you haveinformation about your father?
Of course, I know a lot about my father,
to the most basic one,

(36:36):
my little card here
contains so many megabytes of information.
Obviously, the two are connected somehow,
but the two are very different,completely different.
About your father is somethingthat has to do with meaning.
In that case, with rathereven emotions, (chuckles)
but certainly is interpretedinformation in some sense,
so it has to do with somethingthat needs to be decoded,

(36:58):
that has to be translated.
In the case of the memorycard, just counting something,
it's a number of counting something.
It's like counting the number of atoms,
so counting the number of something.
In this spectrum, what is interesting
is exactly the spectrum,
that it has so many possible meanings,
but what's most interestingis the basic one,
and the basic one,

(37:18):
there's a very simplenotion of information
which is purely physical,which is correlation,
when two things know about one another.
If you glue two things, ifone points in one direction,
the other also points in that direction.
If you know one, you know the other one.
So, one has information about that,
meaning that there is acorrelation between the two.
That's the basic notion of information,
it's purely physical, nothing mental,
no meaning, no significance.

(37:39):
That's the basic notion of information,
and I think this notion ofinformation is fundamental,
not because the worldis made by information,
the world is made by stuff,
by variables, by things which are,
but because the worldis made by relations,
the properties of things arerelative to something else.
So, if you want to describethe structure of the world,
you're always talking about how one thing
affects another one,

(38:00):
so how they get correlatedto the other one.
So, immediately, you can quantify
how much things affect one another
by using the notion ofinformation, and this means,
not information as aningredient of the world,
but as a key ingredient ofour thinking about the world.
I think quantum mechanics itself
can be largely thought of in this way.
I've been thinking thissince back in the '90s,

(38:20):
when I started thinking about the notion
of quantum mechanics, and because of that,
I think, in quantum gravity,
it also could be afundamental role to thinking
about information systemshelping out one another,
but once we go into this wayof thinking about physics,
not as how systems are,
but how systems haveinformation about all of that,
how they're correlated, then it's easier
to understand that there's a continuity

(38:41):
to the most complicatednotion of information.
So, the mental is not so faraway from the physical now
'cause we start taking the physical
from the right perspective,
from which it's easier to reconstruct
the more complicatednotion of information,
meaning, for instance, wetalk about memory traces,
and we build it up moreand more complicated.
So, it's a very versatile,rich, confusing,

(39:04):
but key notion for understandingthe world information
because the world is madeby relations, not by things.
- In reality, it's not what it seems.
There's a passage that I love,
and I even told youabout it after I read it,
because you go through so much of the book
explaining the historicalcontext of quantum gravity
and explaining the conceptsin very easy-to-follow terms,
which I appreciate, andthen later in the book,

(39:26):
you say, "If, dear reader,you have found the journey
so far a little rough, hold on tighter
because we're now flyingbetween voids of air."
And then you get into yournew ideas, which you said,
"If the ideas seem confused,
it's because the person withthe confused mind is me."
First of all, that'ssomething I don't often see
in popular science books, isthe warning to the reader,

(39:48):
like, it's okay to be shaken by this,
it's okay to not fully get it.
So, you gave this warning,and then you expressed ideas
that you personally don'thave a full concept of.
Can you explain a littlebit about what that's like,
going into territory thatis less historically sound
and more speculative, andputting your own ideas out
on the line like that?

(40:08):
- There is a lot aboutthe world we understand,
and there's a lot we don't understand.
It doesn't make much sense
what we too often do, in my opinion,
which is to pretend that we understand
the part we don't understand.
University professors thatteach and lecture on physics,
they shouldn't pretend thatthey know everything about it.
They don't know about it,and they may be wrong.

(40:28):
I mean, they might be teachingthings which are wrong,
so they should say, look,this is what we understand,
this is what I understand,
and be aware that theremight be something wrong,
and if there's something confusing,
it might well be because it is confusing
or because a person is confused
or because the community is confused.
A good example is quantum mechanics.
Quantum mechanics is a hundred years old,

(40:49):
spectacularly successful,
used in technologicalapplications everywhere,
but it's still confusing,
and the fact it's confusing may be good
because it may be that westill haven't got something,
some right way of looking at it,
so let's say it's confusing.
I think this makes, also, things easier
for the student at universityor for the reader of a book

(41:09):
who is not presented this, you know,
both white, clean piece of stonesaying, this is it, period.
We are humans.
Science is a human activity,like everything else.
It's dirty, it'simprecise, there are holes,
so I think it's betterto present what it is.
- I connected with theidea that you yourself
are struggling with these ideas,

(41:30):
and when you read a book byan expert on any subject,
you assume the expert knows everything,
and for you to say laterin the book, you know,
here's what I'm grappling with, it helps.
I think it helps the reader understand
that this is a difficult,
complex pursuit.- Yeah, my book,
my books are a littlebit different in spirit
from most popular science booksbecause they also are aimed
at a slightly differentaudience, and in fact,

(41:53):
I've remarked, from thereactions that I get,
that the typical reader of science books
likes my books less, andthe people who like my book
are a little on the extreme sides,
are either people whoknow zero about science
or people who know a lot about science.
And I understand thereason because I think,

(42:14):
at these two extreme categories,
when I'm talking about them,the typical science book,
it's written for somebody whowants to know more and more
and more and more andmore about some domain,
so you give more details,you give more information.
You say, "Oh, and we knowthat, and we know that,
and we know that," andyou know, there are kids,
nerds that really want toknow more and more and more
about the neutrinos and all thepossible details about that.

(42:35):
I don't do that, I do the opposite.
I take away, I take away, I take away.
I strip away as much as possible,
trying to reduce to whatseems to be the core
that we have understood about something
and to present it in a waythat it stays together,
it holds on, and allows thereader to understand what it is
and what seems to me the realthing we have understood.

(42:57):
And then, of course,
those who know nothingabout science, they like it,
because they say, "Oh,great, I get to that, yeah,"
and those who know a lotabout science also like it,
because they say, "Oh,wow, that's a good way
of doing things, maybeI didn't think this way,
maybe I was thinking the other way.
That's a new perspective on things."
And a lot of my best colleagues tell me,
"Ah, I have read your book, wow!
I didn't think aboutthis way of putting it.

(43:18):
Great, great, I learned something."
Even my greatest enemy, thechief of the opposite, you know,
band theoretical physics,who is a Nobel Prize winner,
sent a message to me andsaid, "Fantastic, I loved it."
But the students of physics,
who've just studied that at school,
reads what I'm saying and knows,
because they say, "Wait a minute, I mean,
there's all missing here."

(43:38):
I got an email saying,
"You talk about quantummechanics in the seven lessons.
You don't even mentionthe Schrödinger equation."
I thought, yeah, that's right,
I don't mention the Schrödinger equation,
but that's not the core.- The right story.
- Right, so yes, and thisconnects to your question,
what you were sayingbefore, because to do that,
you need to understandsomething all the way through.

(43:58):
So, once we have totallydigested something,
then you can just, bingo,you know, in one phrase.
- You can whittle it down to the essence.
- To the essence, right?- Yeah.
- I mean, take Copernicus.
If you read the book of Copernicus,
300 pages of calculations,detail, geometry, perspective.
It's horrendouslycomplicated, then the equant,

(44:18):
the epicycles still, andthen this and this and that,
and to make this complicated,and the moon is complicated.
What is it, 400 yearshave gone from Copernicus?
Now we have digested everything,can say it in two lines,
the earth is spinning
and is orbiting around the sun.
That's what Copernicus hasqualified, so it's totally clear.
It's strange if you thinkabout we are actually moving.

(44:39):
It's revolutionary.
It changes everything.
The earth isn't violent, like the others,
but it can be said in two lines.
Once we have really understood something,
at the end, we can say it in two lines
in a way that has it, has it really,
and the people understand what it is.
So, my ambition, but we're not there,
would be to do the same Ijust did with Copernicus,
the same with, you know,the standard models,

(45:01):
special relativity, generalrelativity, quantum mechanics,
quantum field theory, quantum gravity.
- You said in one piece you wrote,
"Sometimes dreams come true.
I felt there was a storyabout the adventure
of physics that had to be told,
but I thought people were not interested,"
but you were wrong.
You were dead wrong because alot of people were interested.
You know, millions ofpeople have read your book.
It's translated into dozens of languages.

(45:22):
What do you think you got wrong
about estimating people'sinterest in this subject matter?
- (laughs) It was not just me wrong,
the "Seven Brief Lessons on Physics"
was printed in about 5,000 copies.
That was the estimate of the publisher
that was going to sell.- Yeah.
Do you think it wasbecause you whittled down
to the essence and youleft out the equations?

(45:43):
- No, I think it's because,
mostly because of the lastchapter of the seventh.
I think that's what made the book.
It's a book that isnot just about physics,
it's a book that triesto go down to the essence
and then asks the question, all right,
so what does it mean for us?
How does it reflect onthe way we see ourself
and the way we think about thematerial, the physical world,

(46:06):
and our, let me use a strongword, spiritual world.
Let me tell you my interpretation of that.
I and my friends, andmany people around me,
share a view of the worldwhich is not much known
by a large majority of the population,
and it's a view of theworld that is neither
the world is made by little atoms

(46:27):
bouncing with one another and that's it,
emotions, the sense of lives, whatever,
that's bullshit that comes later.
It's neither that, but it's neither
the material world is irrelevant,
there is a spiritual world,with God, morality and things,
that's what the reality is.
Somehow, a lot of peopleare unhappy with both

(46:48):
because they don't believethe spiritual world
too much anymore becausewe're in a secular society,
which doesn't hold anymorefor a large number of people,
but neither people find convincing,
a sort of cold and ground cynicism,
which has no hold formeaning, for emotion,
for our aim, for what we are thinking

(47:08):
and desiring and suffering.
So, the fact that somehowpeople find in my book
a perspective where the two things
can very well stay together,
and there's no contradictionbetween one another,
is when a lot of people jump in and say,
"Oh," but then thereare people who can think
that what matters for me is my emotions,
but also, there's nothing in contradiction

(47:29):
with fundamental science there.
I think that this is the bringing together
that made people react.
- And regarding this goalthat you have in your writing
of getting to the essence of a concept,
I would think this wouldbe uniquely challenging
when you're talkingabout something like time
because the average personwill probably talk about time
at least once in a typical day.

(47:49):
So, there must be a lotthat you need to strip away
because the average personhas a lot of assumptions
that they're making about this word, time.
Can you tell us aboutwhat that process was like
when you're describing time?
- I wrote a book justuniquely, entirely about time,
and that was not an easy-to-write book
because exactly for thereason you're asking.

(48:10):
When I decided how to write this book,
I exactly asked myself this question.
And so, the first half, thelongest half of the book,
one chapter after chapterdemolishing something
we take for granted, our time,
and on good grounds, on things we know.
So, we think that time hasthis property, and you know,
it seems obvious to be that,that's the way we think,
and now I tell you it's not the case,

(48:32):
and I show why we know it's not the case.
So, the first part of the book, in part,
it's just a way of tellingBoltzmann's theory,
of telling Einstein's special relativity,
putting the various piecesof the story together,
but not just for talking about physics,
for talking, look, what this implies
with respect to our notion of time.
Special relativity definitelychanges our notion of time.

(48:54):
Notion of present everywherein the universe doesn't hold,
but it's hard to think ofthe world without a notion
of present everywhere in the universe.
The question, what is goingon right now on Andromeda,
the galaxy, is meaningless.
There's no meaning, whatis going on right now.
There's no now in Andromeda.
It's like asking, what isgoing on here in Beijing?
We're not in Beijing, soit's not here in Beijing,

(49:14):
Beijing is elsewhere.
The book was designed exactly
to address what you are saying,
to take away, one by one,the suppositions of people
that the people givefor granted in science.
Some of my colleagueswhich are very reflective,
a written book, there'sabsolutely nothing they learn
because they have gone through that,

(49:35):
but there are a lot of my colleagues
that teach special relativityand never have stopped
in thinking what,actually, they're teaching,
and I think that's wrong.
I mean, physics is interestingbecause it tells us something
about the world, not justbecause you write equations,
and then you make a prediction
and it matches with what you measured.
- Are you yet at astage where you can give
just this one or two sentence definitions

(49:56):
that's the core of what time is?
- No, with time, it'svery complicated, (laughs)
and the reason is becausewe haven't got to the end
of understanding it.
There are things about time
which I think were generally confused.
A lot of things we havefigured out with total clarity,
like the nonexistence of a present
everywhere in the universe,
but there are issues abouthow to think about time

(50:18):
in a wholly consistent waywith everything we know,
which I don't think we'll figure out.
Even the direction of time is implicated
because we have connected it to entropy,
to the microscopic description,
but there are definitely holes
in our understanding, in my opinion.
- I found that book, "The Order of Time",
to really make my brain meldand squish in other directions.
I was listening to the audiobook, and at one point,

(50:39):
I was rushing somewhere, andsomething you wrote about time
made me think, why am I rushing anywhere,
a rush is an illusion.(Carlo laughing)
So, I appreciated yourwriting of that book.
I also really liked BenedictCumberbatch reading it to me.
That was a nice experience.
Boy, it helps when these concepts are-
- He's astonishingly good.- Are so mind-bending.

(51:00):
- Yeah, he's really good.- Yes, yes,
I've been listening tohis voice and saying,
"Wow, who wrote these wonderful things,"
because it's too good for,it's certainly not me.
He has a way of making it a principle,
but also, it's like it's talking to you
and telling you like a friend-
- Yeah, but we actually haveanother student question
about your books.- Yeah.
This question was sent in by a PhD student

(51:23):
here at Perimeter.
- This is Mac Du Shen, astudent at IQC in Perimeter,
writing, how did you first get started
into writing science books,
and how has that writinghelped your own research?
Do you find writing a technical paper
or a more accessiblebook more challenging?
- Probably a book for a general audience.
You write a paper, a scientific paper,
after you've figured something out.

(51:44):
So, you just get confused in a problem,
and either alone or with somesomebody else in physics,
we worked mostly in little groups,
two or three in theoreticalphysics, you sort of come out,
and at some point, it's clear,
and then you write it down,
and you write down what you've understood.
So, the writing is relatively easy.
I'm picky, I'm complicated inwriting scientific articles.

(52:05):
I try to write them clear,
so I spend time writing andrewriting and rewriting,
perhaps more than what I should or could.
But the writing is, you knowwhat you're saying exactly,
while when you're writing a book,
you still don't know what you're saying.
You're picking up what you'resaying in the writing itself,
and writing, for me, isa complicated process.

(52:25):
My books are the result ofa large number of revisions
and a large number of cancellations,
because I say, no, this isnot useful for what comes,
and that's just superfluous.
So, the same phrase, Irewrite it 10 times and say,
"No, that's not clear, I mean,
is there a way to say it better?"
That's the heart of writing for me.
- I was just gonna say, for you,
it seems that this must beparticularly challenging

(52:47):
because you're not just writing
a book for the general public.
As you said, you're hoping that your book
will be influentialfor the general public,
and also for experts in the field,
even though the material is not technical
or maybe doesn't rely on math.
So, I would assume writingsomething that can be a good fit
for both of those audiencesmust be very challenging.

(53:08):
- Yes, it is, and I havethese two readers in mind,
the super expert one who knows everything,
and the one who knows nothing,
which is good because thinkinglike the super expert one
is what, you know, warns mefrom not saying something,
which is, oh, if I say that,he's gonna complain, (chuckles)
and thinking about the typical grandmother
who doesn't know anythingstops me from saying things,

(53:29):
oh, but that's too complicated, I mean,
how can anybody get this point?
So, I always have these struggles,
so this simplifies becauseit gives me guidance,
but yes, it's also a complication to try
because I'm putting myown ideas in the books,
mostly because it's myown perspective of things,
writing a book of quantum mechanics,
which is entirely from the perspectives
of Heisenberg, Born, Dirac,

(53:51):
rather than from theperspective of Schrödinger.
So, it's taken quantummechanics because I think
it's the most interesting thing.
I'm not the only one, but there are people
who think different, whothink, no, no, no, no,
quantum mechanics is allabout the Schrödinger equation
and the wave functionevolving, that's all there is.
I think that's wrong.
My books are a way ofdefending a perspective,
but the two things help one another

(54:12):
because in the moment in which you try
to explain something simple,you get clarity yourself.
I mean, for me, it'san exercise of science.
I feel I'm doing sciencewhen I'm doing that
and clarifying my mind,
and reading of the great masters,
who were infinitely better thanme, I mean, reading Galileo,
when he wrote these books,
it seems to me he's doingexactly the same thing.

(54:33):
I mean, he's talking to people.
That's a book writtenfor the cultivated person
of the European Renaissancein the 17th Century,
not for his colleagues, astronomers,
because it explain things one by one,
but obviously it's debatingwith his colleagues,
astronomers, in the book.
It's making the subtlepoints of the argumentation,

(54:55):
proving him right and them wrong,
and that's what makes that book so great.
Now, of course, I'm not Galileo,
and I'm not writing the dialogueof the two great systems,
but it's this kind of popular science,
which other people are doing,
which is presenting ideas ina way which are comprehensible
to defend these ideas,which I'm trying to do.
- Are you working on any books now?

(55:16):
- Yeah, I am, but I'm notsure I should talk about that.
- (laughs) Are you alwaysworking on one book or another?
- No, no, I have not been writing
for one year, or more.
I just stopped completely.
I am under strong pressure, of course,
from publishers andthings for writing more.
Let me just give you this,
I'm not covering a largeportion of physics,
I want to do the narration,

(55:37):
tell the story of how atheoretical physicist like me
gets into a specific problem,
gets fascinated by the problem,
works through and comesout with some ideas,
and is struggling on.
So, whether this particular thing
is right or wrong is irrelevant.
I want to tell how istheoretical science in the doing.
- Sort of humanizing the process

(55:58):
or putting a-- Yes, yes.
- Making it relatable to non-science.
- Yes, so what is actually going on,
including changing minds andrealizing things didn't work,
and so on and so forth.
- I don't actually haveany further questions.
We've kept you for morethan an hour, I believe.
- Wonderful.- So, thank you so much
for chatting with us.- Thank you.

(56:19):
- I'll just ask a question
I always ask people when I interview them,
what keeps you up at night these days?
- Last night, I was awake
with (laughing) my going away.
- It was a relevant question.- Yeah.
There is a beautifulexperiment in quantum gravity,
in fact, that's been proposed.
There are some people whoare questioning the way
to think about that, andI think they're wrong.

(56:40):
So, I'm trying to find out aright theoretical description
of this experiment, and in doing that,
it's fun because it's basic physics,
but it's the writing andthinking I do in new ways,
and there are technicalissues, technical problems,
so I keep going around these things here.
So, it's not a big, huge question,
it's a very small, specific question.

(57:00):
- Well, we'll have tohave you back another time
so you can tell us, tellus the results of that.
So, thank you again, thishas just been a pleasure.
- Thank you very much.- Thank you.
- That was very nice.
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Rate, review and subscribe toConversations at the Perimeter

(57:23):
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