Hello, and welcome to the first Physics World
weekly podcast of 2026.
I'm Hamish Johnston.
In this episode, I'm in conversation with Alex
May,
who is the Murray Gautman
Chair in Theoretical Physics
at the Perimeter Institute
in Waterloo, Canada.
Much of Alex's research
explores how quantum information theory can help us
solve
one of the most enduring
mysteries in physics.
How to reconcile
quantum mechanics
with Einstein's
general theory of relativity
to create a viable theory of quantum gravity.
Our conversation is coming up after this message
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I'm at the Perimeter Institute in Waterloo, Ontario,
and I'm very pleased to be joined by
Alex May.
Hi, Alex. Welcome to the podcast.
Hey, Hamish. How are you doing? I'm fine.
Thanks. And I'm very excited to chat with
you about the intersection between quantum information theory
and quantum gravity.
So can we start off maybe with a
few definitions?
What is quantum information
theory? Can you give us a a simple
take on it if possible?
Yeah. So,
there's lots of context we're familiar with where
we're interested in
doing what we might call information processing.
So when you,
run a program on your computer, you're processing
information in some way. When I send you
a message over the Internet or over the
phone,
we are,
yeah, again, processing information in a different way.
In that case, we're communicating instead of computing.
There's other aspects about, you know, how you
keep information secure,
so that's called cryptography.
And
what quantum information theory is, is you're taking
the properties of quantum mechanics,
all the things that are weird and and
cool about it, and seeing how it changes
what you can do when it comes to
information processing. So how how does the strangeness
of quantum mechanics
help us compute better, help us open up
new possibilities in how we communicate, in how
we keep information secure, and and so on.
I see. And and it can be very
useful, can't it?
Quantum well, the the quantum mechanics,
itself,
there are some benefits to to using it
in a in an information
paradigm, isn't there? Yeah. That's right. So the
most famous example is with quantum computing.
So there's lots of excitement about that.
There are certain problems that,
our understanding is that using,
computers based on the principles of quantum mechanics,
we can solve them quickly,
even while
a traditional computer, what's called a classical computer,
would really struggle. It would take a long,
long time. There's lots of other ways that
we can get advantages out of using quantum
mechanics, though, beyond computing, which is maybe what
you hear about the most.
So,
another subject is what's called quantum key distribution.
So that's where using properties of quantum mechanics
to let you,
communicate securely in a way that's that's not
possible otherwise.
I see. Right.
And, Alex, you know, sort of,
when you look at it, you know, maybe
naively, that seems like a million miles away
from quantum gravity,
which,
you know, it I mean, seems to be
a very
sort of esoteric
field.
And I I just wanted to to get
started with quantum gravity by asking you,
why why don't we have a a good
understanding
or theory of quantum gravity? What what is
the what are the challenges
that you and other physicists are encountering when
you're trying to develop theories?
Yeah. So I think I think there's lots
of ways of understanding what goes wrong with
our usual approach to to understanding, you know,
a quantum theory with that
or what goes wrong when you deal with
gravity in particular.
So one
one way to understand this is in the
language of field theory. So
in quantum field theories,
field theories are sort of come in two
types. So there's renormalizable ones and nonrenormalizable
ones.
And,
maybe without specifying exactly what that means,
the the high the high level picture is
that a renormalizable
theory
kind of makes sense at all energies. K.
So it makes sense. We can make low
energy predictions, but it continues to make sense
at high energy.
The theory might not be experimentally correct at
high energy, but the theory itself is not
telling you that there's something wrong at high
energy.
A non renormalizable
theory,
it's the other way. So it's
it knows that something is wrong with it
at high energies. You try and make a
prediction of high energy, it gives you infinity,
something something goes wrong.
So
gravity,
you know, we have a theory of gravity.
We have Einstein's general relativity.
You can cast that as a as a
field theory,
as a quantum field theory, and it makes
sense at lower energies.
Right? So you can do,
you know, the kind of physics relevant
to maybe planets orbiting around stars or something
like that using general relativity or or in
this field theory framework, and and everything's okay.
But
the
the fact that this theory is nonrenormalizable
is telling you that if you try and
use this at very high energy scales, if
you try and use our understanding of gravity
at high at high energies,
things go wrong. Okay.
That by itself is not so bad. Right?
So there's lots of other field theories that
had been written written down that were nonrenormalizable
that we later figured out,
you know, were just some other more detailed
field theory at at high energies. So you
can write down a field theory that describes
neutrons,
and it's not were normalizable.
It's telling you that above some energy scale,
there's some new physics that this theory doesn't
know about.
The new physics isn't that wild. It's just
saying that, oh, actually, neutrons are made out
of some
constituent particles, and if you go to high
energies, you're gonna see that. So your original
theory didn't see that didn't didn't know about
those particles. Right?
We actually know that with gravity,
the solution is not
as simple as that. So there's a theorem
called the Weinberg Witten theorem
tells you that the graviton, like the basic
excitation in your theory of gravity
is not,
it's not just some composite particle. It's not
gonna break apart when you go up to
go to high energies.
That's not where the new physics is coming
from.
So instead, there has to be some
more exotic,
new physics that happens at high energies,
and the challenge is in identifying what that
is.
I see. And and in your research,
a a lot of your research focuses on
non local
quantum computation,
I suppose, as applied to quantum gravity.
What is NLQC,
and why is it important
to, study? Why are you interested in it?
Yeah. Okay. So
maybe we can we can sort of continue
with with the story of that I was
trying to describe in the last question where,
you know, we know that there's some,
maybe sort of exotic new physics coming in
at
that's relevant to high energies.
One possibility that's been identified for a long
time
is,
goes goes by the name of the holographic
principle.
Okay. And so this is this is the
claim,
that
the reason this theory of gravity isn't working
at high energies is that,
or at least the way to get around
this is to
give some alternative description of gravity
in one less dimension than we would usually
think it would live in. So we live
in a three plus one dimensional
space,
and the holographic principle suggests that there's some
just two plus one dimensional description
of this world. Okay? Or, you know, four
dimensional gravity is described in terms of some
three-dimensional
non gravitating, just quantum mechanical theory.
So this this sounds a little bit crazy.
It's saying that we kind of live in
some lower dimensional hologram,
but it's well motivated. You know, one way
to motivate it is from this kind of
Weinberg Witten description or picture that I was
that I was describing, but another comes from
the physics of black holes. So
with a black hole,
we've identified that the entropy of the black
hole seems to be given by the area
of the hole.
And so this is somehow saying that the
amount of information in the black hole, the
number of degrees of freedom,
is
not like the volume, like you would expect
for an ordinary,
an ordinary system, but somehow,
there's fewer degrees of freedom and there's only
an area's worth. Okay.
And we think that not just black holes,
but actually,
everything sort of works like that. So, you
know, we think we have sort
of three dimensions worth of degrees of freedom,
but,
apparently, there's there's this lower dimensional description in
terms of just
two dimensions worth of degrees of freedom.
Okay. So that that's part of the exotic
physics that seems to take over at at
high energies when you're trying to do quantum
gravity.
So
okay. So
now,
what is the subject of nonlocal quantum computation,
and and how is it related here?
Well, to get to that,
let's
go to a very different setting for a
second. So this is a setting in quantum
information theory.
In particular, it's a setting in,
in cryptography.
K?
So cryptography is all about,
establishing trust, keeping secrets,
processing information securely, so on.
And,
one thing that you could be interested in
doing in that context
is,
is in checking
where physically in space somebody is. So you're
talking to somebody, you're talking to them over
the phone, say,
but you wanna know that the person you're
talking to is located in a certain spot.
Right?
You might wanna do that as a way
of establishing trust. Right? We often trust people
based on where they are. You know, you
go to the bank,
you go to the person behind the till,
you take out your wallet, you give them
your money, your information. You've never met this
person. You didn't check their ID. You trust
them because they're behind the till. Right? So
you might use location as a sort of
proxy for for trust.
So
okay.
So starting with that idea, there's this subject
in quantum cryptography
around
trying to check where somebody is.
And what was realized by the cryptographers
is that you could use this technique, which
is this non local quantum computation,
to always allow somebody to cheat in this,
in this kind of scenario where you're trying
to check where they are. And in particular,
what they realized is
if
you think you're interacting with somebody sort of
inside of some volume,
the responses that that person gives you, right,
I give you some inputs, they give you
some outputs,
Those responses can always be simulated by somebody
who's hanging out near the boundary
of,
of that volume where you're supposed to be.
So that's unfortunate for the for the for
the cryptographic goal. Right? It's saying that there's,
at least in a in a very general
context, no way
to to be sure about where the person
you're talking to is,
but it has this very
interesting connection to this
this holography idea from point of gravity, and
that it's saying,
you know, anything happening in this volume
can be replaced by something happening
at the boundary of that volume.
And that sounds a lot like calligraphy where
it's saying, oh, there's a three-dimensional script description,
but there's some alternative, you know, two dimensional
description or lower dimensional description.
So, yeah, that's kind of the starting point.
There's some
similarity between these subjects.
And then,
you can start trying to make this connection
precise.
And, to do that, you need some precise,
theory of quantum gravity.
And,
the way that that's the context in which
this has all been made most precise is
something called the AdS CFT correspondence.
And there, we find that, you know, these
results that cryptographers had proven
years ago
about nonlocal computation lead to very precise
and new statements about gravity and ADS space
times, and that's quite a, a surprising connection.
I see. And and so
how how do you so you've got this
correspondence. You can show I'm guessing you can
show mathematically
that it's that there's a strong correspondence between
these two,
well, that sound very, very different Yeah.
Concepts.
How how does that help you
come up with a theory
of quantum gravity? Does that is that are
these like building blocks
that you can use?
Yeah. So AdSCFT
is, I mean, we can't prove it mathematically.
It's a conjecture. There's lots of evidence for
it. We can we can check many aspects
of it, and it seems to work out.
But well, maybe I should say first of
all what it is. It's it's a claim
that
two very apparently very different looking theories are
actually
equivalent.
So the two theories would be, a higher
dimensional gravitating theory and then a lower dimensional
just quantum mechanical theory, like like the holographic
principle says we should have.
It's
within a certain context. So this doesn't apply
to all theories of gravity. Right? It applies
to theories of gravity that live in a
special kind of a space time called the
asymptotically
ADF space. K.
That's
it's a little unfortunate that it only applies
to that kind of space time,
in that we don't think that we actually
live in an asymptotically ADS space. We live
in a,
somewhat different looking space time.
But, you know, nonetheless, this is some kind
of working, at least toy model of quantum
gravity. It's saying, here's this gravitational physics. It's
recorded into just some quantum mechanical physics,
and it's up to us to study how
these things fit into each other,
try and extract the key ideas there,
and then from that,
hopefully go and use those ideas to describe,
you know, quantum gravity in the actual universe.
I see. And the the this quantum cryptography
system, does that,
I mean, does that give you,
an analog
that you can,
I don't know, manipulate and probe or, I
mean, even do experiments
in the lab that could inform
your your understanding of quantum gravity?
Yeah.
I I would say, like, in
in a certain sense, it's it's
a totally quantum mechanical analog of of at
least one aspect of what happens in ADS
CFT.
It's not like a full model or something
like that, but I think it,
it explains and captures, like, one aspect of
the physics in ADS CFT.
That, like, so far has just been used
at the level of, like, here's some mathematical
result around nonlocal computation, and then
here's how we apply it to ADSCFT.
And it leads to, you know, maybe some
theorem about gravity,
some precise consequence there.
I think you could start thinking about
things like, you know, how do I make
a quantum system
that is doing one of these nonlocal quantum
computations
and is doing it in a way that,
like, looks more like a gravitating system?
And then can I go and build that
in my lab?
And,
yeah, that's a question that you could ask.
I I guess I,
I don't have
a sharp question
about ADS CFT that I want to try
and answer that way,
but I think it could be worth exploring.
Yeah. I see. And before we started recording,
we we were chatting a bit about the
intersection of quantum gravity and quantum information. Yeah.
I mean, I'm guessing that what we've just
been talking about is probably
just a small That's right. Aspect. Can can
you talk a bit, you know, about the
field in general? Is this sort of a
growing field that,
theorists are becoming more and more interested in?
Yeah. So definitely yeah. I should emphasize the
the the thing I was describing is one
one aspect of this broader,
deeper connection between,
quantum information theory and and quantum gravity and
and especially the ADFCFT correspondence, but but even
more broadly in quantum gravity than that.
And,
yeah, I think one one question I get
a lot about,
you know, these two fields is, like,
why is there any connection at all?
I think there's different ways to understand that.
One way to understand it is just that,
in a sense, quantum information theory, you know,
was built up to answer the kind of
somewhat practical questions that I was describing. How
do we compute better? How do we communicate
better?
You know, this is about stuff we want
to do, stuff we want to build.
But when you try and answer those questions,
one thing that you end up doing is
just end up developing a whole new way
to understand quantum mechanics.
And,
you know, powerful tools for for,
you know, just understanding interesting properties of quantum
mechanics. Right?
And so much of the physics that we
do,
right, is in that quantum mechanic is in
the framework of quantum mechanics. Most of physics
is in the, you know, except for gravity
at this point, in the framework of quantum
mechanics.
And and that opens up the possibility that
these same tools that we use to understand
these kind of practical questions,
can be reused in other contexts, right? And
quantum gravity is one context in which we're
seeing that, but there's others too, right? Like
in condensed matter physics, in quantum matter,
we're also seeing,
a lot of these tools from quantum information
being applied,
to to to understand those kind of systems.
And and do you think I mean, has
it, you know, the
boom, well, for lack of a better word,
in in
quantum information research and, you know, the real
depth of understanding that physicists are
have developed. Is that,
I mean, is that something that's, I suppose,
moving outside? I mean, it sounds like it's
moving outside of the quantum information community and
benefiting,
well, you know, people like yourself who are
interested in gravity and people who are interested
in lots of other different kinds of physics.
I'm has it been a I mean, it
sounds like it's been a really positive,
or it's had a very positive impact on
the physics community over the last, I don't
know, twenty, twenty five years. Yeah. I I
certainly think so, and it's certainly up something
I'm excited about.
You know, I think that
to to me, it's a whole different
starting point for understanding quantum mechanics. Like,
when we teach quantum mechanics in undergrad,
we teach it in the context,
at least traditionally, we teach it in the
context that it was developed, which is in
the context of, like, atomic physics.
But quantum mechanics is something much, much more
general than atomic physics,
And
quantum information gives you,
you know, a different lens, a different set
of examples and starting points for thinking about
quantum mechanics.
And,
it also gives you a lot simpler context
for understanding
quantum mechanics. Like I think that,
you know, when you solve the hydrogen atom,
that's an excellent thing that everybody should do.
But if you just want to understand
what are the core features of quantum mechanics
that I need to conceptually get my head
around
something like the quantum teleportation protocol. Some of
the basic aspects of quantum information theory can
be a quicker route to to to getting
that understanding, I think. So,
yeah, it's just a really clean way to
understand quantum mechanics, and that
has this knock on effect of of,
coming into all these other areas. I see.
And, you know, just sort of thinking back
to my education in physics, I mean, I'm
guessing, you know, the last time I
took a course in quantum
mechanics would have been sometime in the nineties.
And, you know, it was very much, you
know, the simple harmonic oscillator.
Yep. The hydrogen atom and all that sort
of stuff.
I mean, is
is it
is quantum information taught now? I mean, I
know that I don't think you you teach,
do you? Or maybe maybe you do teach.
I I do. You do Waterloo.
I actually, I teach in the the master's
program that we have here at Perimeter. So
we have the Psi one year master's program.
Right. And do do you teach Yeah. I
teach quantum information there, actually. Right. I see.
Yeah. Okay. And is it,
I mean, do or, you know, sort of
early career well, master's students, so they do
they find it really fascinating?
I mean, more fascinating than this than the
simple harmonic oscillator.
Yeah. I mean, I think it's it's a
it's a quick route to getting people excited
about
physics and about quantum mechanics. And,
I definitely see a lot of excitement from
my students and a lot of a lot
of interest, like, from multiple different fields. You
know? I don't know. They're interested in gravity.
They're interested in condensed matter, but they wanna
learn a little bit of quantum information as
well. They've heard that it's that it's useful.
Yeah. So you're starting to see a lot
of that. And then there's kind of a
whole other set of people that are interest
interested in or excited about quantum information because
of its applications. Right? Because they're excited about
quantum computing or quantum communication or these sort
of practical things that could happen down the
road.
Yeah. I mean, I I've I've I've just
amazed that
quantum well, I suppose quantum computation, technology,
information, you know, the, it it seems like
it's it's a
I don't think it's wrong to call it
a revolution really in in sort of our
understanding
of of the quantum world. It's, you know,
I think it's a really good time to
be a physicist.
I I think so. I think it's a
very exciting field right now. Well, that's great,
Alex. Thanks so much for coming on the
podcast, and hopefully we've encouraged
some listeners to perhaps look into the intersection
between quantum gravity and, quantum information.
Great. Well, thanks for having me.
That was Alex May in a conversation I
recorded at the Perimeter Institute for Theoretical Physics.
Thanks to Alex for a fascinating chat about
all things quantum,
and thanks to you for listening.
We'll be back again next week. I'm Hamish
Johnston,
and our producer is Fred Isles.