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>>NEIL DEGRASSE TYSON: Welcome back. This is the 17th Annual Isaac Asimov Panel Debate.
And we’ve been going strong ever since the year 2000,
when an idea surfaced in the hearts and minds of the family of Isaac Asimov, exploring a
way for his
memory to be preserved in the programs of this institution. And Isaac Asimov was a friend
of the American Museum of Natural History.
Much of the research for so many of the books that he wrote took place in and around the
halls and in our libraries. And so perhaps there’s no more fitting
tribute to him and to his memory, than to keep this celebration going. So, thank you
We are also streaming live on the Internet. And I’m your host for this evening, Neil
deGrasse Tyson. I’m the Frederick P. Rose director of the Hayden Planetarium.
Just a couple of newsy notes.
This year we sold out in three minutes. And it’s not a particularly sustainable model.
So, we’re going to have top people looking at how to improve that next year.
We don’t know how yet, but the least we can do is offer it live streamed on the Internet
on amnh.org. So, I welcome everyone
from the Internet universe, as well as the universe gathered here.
Tonight’s topic is: Is the Universe a Computer Simulation? Yeah.
Do you want it to be a computer simulation?
I mean, this topic is—we’re going to—you’ll see.
We’ve got some highly thoughtful, talented,
respected people to weigh in on this. I will introduce them individually, and then we will
start the panel.
By the way, unlike most debates you might have heard about or read about, where there’s
point/counterpoint and an argument is presented and attacked,
that’s not what’s going to happen here. We’re using the word debate loosely. Think
of yourself as eavesdropping
on scientists at a break-out room in a conference on this topic. So, we’ll all be sort of
arguing with one another, and you’re listening in. That’s really what’s going on here.
And you get to see how scientists think. You get to see how arguments are contested.
You get to see how resolution arrives, if it arrives at all.
So, afterwards we will have a brief time for question and answer before we adjourn before
9:00 Eastern time zone—Eastern daylight time.
So, join me in welcoming my first panelist this evening. He is a professor of philosophy
at New York University, where he’s also director of the Center for Mind, Brain and
Consciousness, David Chalmers. David, come on out.
>>DAVID CHALMERS: Hey. Looking forward to this.
>>NEIL DEGRASSE TYSON: Thank you. Next we have a nuclear physicist, who’s a post-doctoral
research associate at MIT
up in Cambridge, Massachusetts. And let’s give a warm welcome to Zohreh Davoudi. Zohreh.
Next, we have someone who is actually no stranger to this panel. This may be his third visit
to it. In part, the topic of this year
was selected because he brought it up a couple of years ago. And I said, man, we could do
a whole subject on that alone.
Let’s give a warm welcome back to James Sylvester Gates.
Another non-first timer is professor of physics up at Harvard,
a specialist in nuclear particle physics. Give a warm New York welcome to one of our
a graduate of Stuyvesant High School, Lisa Randall.
Did I do this out of order? No, we didn’t. Good.
And last among the five—yeah, I did do it out of order. My bad. Yeah, sorry. You guys
know where you need to sit. Talk among yourselves while I do this.
There’s a friend and colleague, an astrophysicist, also from MIT,
who’s done some deep thinking about this very subject and has even written a book on
Let’s give a warm New York welcome to Max Tegmark.
How about now? There we go.
Oh, by the way, we are lit for live streaming. And the intensity of the lights on the stage
is such that
two of our panelists—I think they just want to look cool, but they said they need to wear
sunglasses for this event. And that’s cool. Later on I might join you. I brought my pair
with me as well.
If I’m feeling cool I might do just that.
So, Zohreh, I’d like to start with—no. who should I start with here? Yes, let me
start with you, Zohreh.
Could you tell me why this topic interests you? Just give a couple of minutes just as
an introduction here.
>>ZOHREH DAVOUDI: Sure. So, as Neil said, I’m a theoretical physicist.
My interest is in nuclear physics. In fact, I got my PhD in 2014 from Institute of Nuclear
Theory in University of Washington.
And the research I was focused on there, and at the moment, is trying to use the knowledge
of the laws of nature and,
in particular, strong interactions to start from a bottom-up approach and try to see what
comes out in a physical system.
And that’s actually relevant to why I got interested in the simulation idea. And, in
by just watching the progress that researchers in this field of simulating a strong interactions
have made in several past few years,
we started to wonder how could we not think about the universe itself based on the laws
that we’ve discovered not simulated.
So, that the way that we actually simulate the universe, it might actually give us hints
that the universe itself could be a numerical simulation. And then
you would start thinking, well, let’s make assumption that if that scenario is the case,
and if that simulation is actually—has similarities with what we do in our research
and just drawing parallels between our algorithms and techniques that we use to simulate laws
of nature, and making assumption that they are similar,
then what can we actually conclude about the universe as a simulation.
Can we actually make predictions for the signatures that we should go after and test?
So, that’s that approach we took. And it was a fun idea and fun paper became of it
with my collaborators Martin Savage and Silas Beane at the University of Washington.
And that’s basically why I’m here. I’m trying to—
>>NEIL DEGRASSE TYSON: So, the prospect of this being true didn’t freak you out at
>>ZOHREH DAVOUDI: No, I think it’s a fun idea.
>>NEIL DEGRASSE TYSON: Okay. Just it’s fun for you?
>>ZOHREH DAVOUDI: Yes.
>>NEIL DEGRASSE TYSON: Okay. Fine. So, Max, you’ve got a book on this, too, right? So,
what’s going on with you?
>>MAX TEGMARK: Yeah. Well, already as a kid I was always very fascinated by these very
about what’s really going on with this reality. I remember actually
lying in this hammock I had put up between two apple trees back in Stockholm, Sweden
when I was 13, reading Isaac Asimov actually.
I’m very honored to get to be here.
It really makes you think about these big, big questions. And the more I learned about
later on as a physicist, the more struck I was
that when you get deep down under the hood about how nature works, down to looking at
all of you as just a bunch of quarks and electrons, the rules—
>>NEIL DEGRASSE TYSON: And you, too. It’s not just us. Yeah.
Looking at you as a quark, no, you would come under this category as well.
>>MAX TEGMARK: Yes. I am a quark blob, too, I confess.
But if you look at how these quarks move around, the rules are entirely mathematical as far
as we can tell. And that makes me wonder, if I were a character in a computer game,
who starting asking the same kind of big questions about my game world,
I would also discover eventually that the rules seemed completely rigid and mathematical.
I would just be discovering the computer program in which it was written.
So, that kind of begs the question: How can I be sure that this mathematical reality isn’t
actually some kind of game or simulation?
>>NEIL DEGRASSE TYSON: So, you’ve analogized yourself to Super Mario in a—that’s who
>>MAX TEGMARK: I don’t know if that’s a good thing or a bad thing.
>>NEIL DEGRASSE TYSON: So, Jim, I just remembered you started all of this a few years ago, in
my mind at least,
just triggering the idea that in your research you found things that forced you to consider
the likelihood that somebody programmed us. Could you—
>>JAMES GATES: Well, first of all, I would disagree with you. I’m not sure somebody
but that’s—you and I had a conversation where I pointed out that in my research I
had found this very strange thing. Physicists, I like to say
we all belong to a company called Equations-R-Us
because that’s how we make our living, is by solving equations. And so I was just going
through solving equations, and I was then driven to things that Max knows about,
these things called error-correcting codes. Error-correcting codes are what make browsers
work. So, why were they in the equations that I was studying about quarks and leptons and
And that’s what brought me to this very stark realization that
I could no longer say that people like Max were crazy.
>>MAX TEGMARK: Okay.
>>JAMES GATES: Or stated another way, if you study physics long enough, you, too, can become
>>NEIL DEGRASSE TYSON: That’s a corollary to that idea. Yeah.
>>JAMES GATES: And I’m also a science fiction fan like Max, who talked about his encounter
I was reading at age eight, as opposed to 13, sir.
>>MAX TEGMARK: I hang my head in shame.
>>NEIL DEGRASSE TYSON: Snap.
>>MAX TEGMARK: Got off to a slow start.
>>JAMES GATES: I was reading at age eight a science fiction book by an author named
Paul French. And some people in the audience might know
that’s a pseudonym for Isaac Asimov.
>>NEIL DEGRASSE TYSON: Oh.
>>JAMES GATES: So, science fiction drove me into science in some sense. And then now in
my 65th year of life, I find out I have to make friends with Max and people like that.
>>NEIL DEGRASSE TYSON: So, Lisa, I kind of brought you on the panel because I knew
you—I mean, you’re a rationalist in all this. And so I was expecting—I don’t know
what to expect.
I just needed to anchor this in somebody who I knew was not going there. So, where—
>>LISA RANDALL: Yeah. So, actually—well, I can’t say I decided to be on the panel
because I think I said what date is it, and they were like, “Thank you for agreeing
to be on the panel.”
But I have to say I’m curious not so much about the question of whether we’re a simulation
because I think it’s only interesting
insofar as there are ways to test it.
And we can come back to that, I think, very much in terms of how the laws of physics operate
and whether we can actually distinguish that. But I actually am very interested in why is
so many people think it’s an interesting question. Like why is the audience here? Why
is this panel here?
Because really to first approximation we can’t really distinguish it.
So, I think the interesting question is: Why do we feel compelled
to want this to be true, or even think this could be true? And how do the laws of physics
operate? And are there really ways that we could eventually
test whether there is something that distinguishes just a true universe?
But I have to just say if the inference is simulation, I don’t understand why it gave
me a cold today.
>>NEIL DEGRASSE TYSON: Okay.
>>LISA RANDALL: So, my voice might go. But I also think sometimes some of the ridiculous
things in the universe and think,
really, why would that be part of the simulation? And I realized that if I was doing a simulation,
I would definitely put those things in. So, there you go.
>>NEIL DEGRASSE TYSON: Okay. Well, thank you for that. Now, we couldn’t have a panel
without a philosopher. David, we needed some philosophical—
>>DAVID CHALMERS: I know how you love philosophers, Neil.
>>NEIL DEGRASSE TYSON: I’m on record for some comments about philosophers that got
him a little ticked off.
Buy, anyhow. So, David, what do you—philosophers have been at this for a while, yourself included.
So, how do you see all of this
happening or fitting in to the worldview?
>>DAVID CHALMERS: Well, philosophers like to ask the big questions
about the world; the foundational questions. And this is one of them. Actually, I blame
Isaac Asimov for all this, at least in my case.
I got into thinking about these big questions when I was a kid. I read just about everything
that Asimov was writing. Not just the science fiction, but the science fact, the history,
the detective novels. I read multiple volumes
of his autobiography. But throughout Asimov’s work, this was a guy that was just interested
in the big questions about the nature of reality at all levels. And that, ultimately,
drove me to think about questions about consciousness and the mind, which I could approach as a
because philosophy allows you to step back and say what is the science here telling us.
But this question about the simulation corresponds to another of the great questions of philosophy,
which is basically how do we know anything
about the external world at all [unintelligible 15:46] said how do you know you’re not being
fooled by an evil genius
into having an impression of this world around us? Even though none of it really exists.
Well, the contemporary version of that question is: How do you know you’re not in a simulation
like The Matrix? In which case, allegedly,
none of this really exist. And, to me, that question is just extremely interesting because
nothing we could know could rule out the hypothesis that we’re in a simulation.
But you also want to think about what follows.
Some people think if we’re in a simulation, then none of this is real. I think if you
adopt the kind of perspective which,
say, Max was suggesting a second ago, where the universe is all mathematical or informational,
this allows us to reorient
our attitude to this question and say, okay, maybe we’re in a simulation. But if we are,
all this is perfectly real
because all the information is there in the simulation.
All the math is there. All the structure is there in the simulation.
So, I’d say, well, maybe we’re in a simulation. Maybe we’re not. But if we are, hey, it’s
not so bad.
>>NEIL DEGRASSE TYSON: If I do this, you feel that.
>>DAVID CHALMERS: Yeah.
>>NEIL DEGRASSE TYSON: Okay. So, that’s real. That was a real punch. Yeah.
So, Zohreh, let me ask you, I see you coming to this almost from the most pragmatic side.
You’ve done experiments with your colleagues. Or you’ve had
hypotheses with your colleagues. Could you just detail for me where you landed in one
of those papers that you guys published?
>>ZOHREH DAVOUDI: Sure. So, what we did is not actually doing the experiment. We proposed
that experiments could go and
look for the signs of possible underlying simulation for the universe.
And the reason we thought about this, as I said, is because we’ve been simulating strong
interactions, which means that
instead of just looking at the larger structures, we’d start from the underlying degrees of
freedom of our theory, the quark, gluons,
and that we understand. And there are very simple laws governing the interactions among
However, when you think about all these complex systems
of atomic nuclei and larger systems in the universe, the ordinary matter in our universe,
it all emerges from those
simple, fundamental building blocks and these interactions.
So, we’ve been trying to just input those simple mathematical structure with a few degrees
of freedom, these quarks and gluons,
and then see how these, for example, atomic nuclei emerge from these simulations.
>>NEIL DEGRASSE TYSON: So, you’re building the universe from the ground up?
>>ZOHREH DAVOUDI: Exactly. But what are the limitations? We don’t have infinite computational
resources. We have
very large super computers in the national labs, for example, that we can compute these
and build up these systems.
However, we are still limited. And the reason is that if you’re interested in simulating
the universe, and you don’t know what the size is—
it could be finite or infinite. However, we are limited to a finite size.
On the other hand, if you think about even a finite side, there are infinite numbers
of points on these
in this finite size that you have to simulate to get the physics right. However, we are
not capable of inputting infinite number of information in our computers.
Also, we want the simulations to be quantum, which means that there is not just one single
path of evolution from one point to the other. There are infinite number of paths.
Some are more important than others. And, therefore, there’s another type of infinities
that we have to implement in our simulations to get the answer right.
>>NEIL DEGRASSE TYSON: Yeah, but just because you can’t—we can’t do it because we’re
why should that mean the whole universe is limited?
>>ZOHREH DAVOUDI: So, wait. So, this is the point.
>>NEIL DEGRASSE TYSON: I’ll wait. I got time.
>>ZOHREH DAVOUDI: All right. So, we can do it,
and then you—based on assumption that if there is an underlying simulation for the
that has this problem, that has the problem of finite computational resources—just as
we do—then what happens?
Then the laws of nature, the quantum mechanics and whatever interactions have been going
on, has to be
put on a finite set of space-time points in a finite volume, and then just a finite number
of quantum mechanical paths to a process can be evaluated.
So, these are the assumptions. So, if the simulator of the universe, in whatever form
it is, is just finite computational resource and not infinite,
then it’s limited to simulate the universe in this kind of limited scenario, just as
we do. And then by making that assumption, and then going back and look at our simulation
and see what kind of signatures we see in the observables we calculate,
that could tell us that we started from a non-continuum space-time.
Then apply it to an underlying simulation of the universe and make the same assumption,
then what would you see? And that’s basically what we look for,
and list a few observables in our universe that might lead to actually constrain this
scenario under this assumption.
And one of which is looking at the spectrum of cosmic rays. Because what happens if these
very high energy cosmic rays that approach the earth,
they are actually traveling in a discrete space-time, as opposed to a continuum. Then
that basically special relativity that would describe the relation between the energy and
momentum of this particle is modified.
And then you would ask what would that modification mean
in terms of the observation we make in our observatories, for example, spectrum and distribution
of these cosmic rays.
And if we see something that would be hint, that would be consistent with the scenario
of a limited computational resources of the universe. And then you might think about
other signatures and maybe taking this scenario more seriously and think about [unintelligible
>>NEIL DEGRASSE TYSON: So, cosmic rays, it would be your pathway to the limits of what
has ever been measured.
>>ZOHREH DAVOUDI: Exactly.
>>NEIL DEGRASSE TYSON: And then seeing at that limit you’re probing the limits of
the programmer of the universe.
>>ZOHREH DAVOUDI: Right. Because these cosmic rays are the most energetic particles that
we’ve ever been able to observe.
We can’t even produce them in laboratories. These are very high energy cosmic rays.
>>NEIL DEGRASSE TYSON: They’re higher than anything we produced in our particle accelerators.
>>ZOHREH DAVOUDI: Exactly.
>>NEIL DEGRASSE TYSON: Yeah.
>>ZOHREH DAVOUDI: Yes. By orders of magnitude. And, therefore, because these are very energetic,
they can actually probe
the fabric of space-time. This is our way of probing if the universe—if the underlying
space-time is discretized or just a continuum.
>>NEIL DEGRASSE TYSON: So, Max, like I said, you’ve written a book on this. Yet, you
told me offline that you have an argument that would argue that—
>>MAX TEGMARK: That maybe we’re not simulated after all?
>>NEIL DEGRASSE TYSON: Yeah. Maybe we’re not a simulation after all. So, where does
>>MAX TEGMARK: Yeah. So, before giving a counter argument, let me give the pro argument. Of
>>NEIL DEGRASSE TYSON: So, you can give arguments in both directions here?
>>MAX TEGMARK: It’s fun to argue with yourself.
>>NEIL DEGRASSE TYSON: Okay.
>>MAX TEGMARK: Of course, we all—as David mentioned—have seen the argument,
the idea, of us being simulated in The Matrix and in science fiction going even far beyond
that. But the guy who really started
foreseeing scientists to take this a bit more seriously, and gave this idea a bit more scientific
street cred, I think,
is Nick Bostrom, my fellow Swede—Nick Bostrum—who published this very dry academic article that’s
pointing out that—
>>NEIL DEGRASSE TYSON: He’s a philosopher?
>>MAX TEGMARK: Indeed, indeed.
And he pointed out that it seems like the laws of physics allow us to build amazingly
way beyond what we have now; solar system-sized things, which could simulate minds that would
feel just like us. And then he went on to say
it seems overwhelmingly likely, if you don’t wipe out here on earth, that in the future
the vast majority of all computations and all minds
will be inside of such a computer. And, therefore, he said if almost all minds are simulated,
we’re probably simulated. So, that’s the pro argument.
Now, it sounds good, but—
>>NEIL DEGRASSE TYSON: So, just to clarify, so what you’re saying is
if simulating universes becomes a pastime among those who have access to high powerful—
to highly powerful computers, and we are in a universe, we’re probably in a simulated
universe, even if one of those universes is actually real.
>>MAX TEGMARK: Right. That’s basically—
>>NEIL DEGRASSE TYSON: Is that a fair—
>>MAX TEGMARK: That’s a fair summary, yeah. And if you’re not sure at the end of the
night whether you’re actually simulated or not, my advice to you is
go out there and live really interesting lives and do unexpected things so the simulators
don’t get bored and shut you down.
>>NEIL DEGRASSE TYSON: Is that the cause of death? Okay.
>>MAX TEGMARK: But now in terms of the counterargument, if you just take Nick seriously—
>>NEIL DEGRASSE TYSON: That’s the cause of death.
>>MAX TEGMARK: There’s something fishy here. Because suppose you buy into this and you’re
I’m sold on Nick’s argument. We are simulated.
Let’s talk then about our simulated universe. We’re measuring the laws of physics here
in the simulated world. And we find that in the simulated world we can build all these
supercomputers in the future,
and there’ll be all these simulated minds and so on. And we can make the same argument
all over again and convince ourselves that actually
we’re doubly simulated. And then we’re a simulation in the simulation, and then you
can repeat the argument again and say, well, okay, we’re in a simulation in a simulation.
But in the future, there’re going to be all these simulated, simulated computers and
they’re going to have all these minds. So, we’re actually triply simulated. No, we’re
and it goes on and on all night.
>>NEIL DEGRASSE TYSON: So, the turtles all the way down.
>>MAX TEGMARK: Turtles all the way down. And at this point, I get this sinking feeling
that there’s something
rotten at the core of this argument.
>>NEIL DEGRASSE TYSON: Okay.
>>DAVID CHALMERS: The answer is we’re at level 42.
>>NEIL DEGRASSE TYSON: Good answer.
>>JAMES GATES: No, no, 137.
>>NEIL DEGRASSE TYSON: One-thirty-seven. That’s the fine structure constant.
>>JAMES GATES: Of course.
>>MAX TEGMARK: And I think where the problem lies
is that when you make this argument about what kind of minds are really the most common,
the most simulated and non-simulated,
it assumes to answer that you have to know what the actual laws of physics are.
But if you start making these other arguments, we have no clue as to what the laws of physics
are. It doesn’t matter what the laws here in our simulation—
if it is one—are. We need to know what the real laws of physics are in the basement universe
that’s the foundation. And, if so, we don’t really have access to that.
So, that’s the philosophical nitpick, which seems to be swept under the rug here.
>>NEIL DEGRASSE TYSON: Jim, where—
>>JAMES GATES: Where am I?
>>NEIL DEGRASSE TYSON: Yeah.
>>JAMES GATES: Well, first of all, I have a finger. And I look at it, and it seems to
And so my point of view is very conservative. It was Carl Sagan who once said that, “Extraordinary
statements,” and I’m paraphrasing—
>>NEIL DEGRASSE TYSON: Claims, yeah.
>>JAMES GATES: Right. “Extraordinary claims require extraordinary evidence.”
Now, Zohreh has told us about a kind of evidence. And that’s the kind of evidence that would
convince me as a physicist. But what I do
is sort of a mathematical model of physics. And in our previous encounter here on this
stage, I had a chance to tell you about these error-correcting codes,
which are very specific kind of digital data. It’s not just general digital data. It’s
a very specific kind that seem extraordinarily unlikely.
And I have to tell you that one of the reasons I enjoy talking to audiences like this is
they get us experts out of our comfort zone. And so one of the first non-physicists that
I talked to,
or that I read reflected on my comment, said effectively—
this is not exact words, but effectively he said if the simulation hypothesis is valid,
then we open the door
to eternal life and resurrection and things that formerly have been discussed in the realm
of religion. And the reason is really quite simply. Because if you think about a computer—
if we are a simulation, then we’re like programs in a computer, as long as I’m a
computer that’s not damaged, I can always rerun the program. So, if you really believe
that we are in a simulation, and there’s some structure that runs that simulation,
unless something damages that structure, then we can be repurposed. And so it starts to
break down a very funny barrier
between what people often think as the conflict between science and the conflict between faith.
>>NEIL DEGRASSE TYSON: So, what you’re saying is that if we are simulated, that means there’s
a code that’s doing it,
and that code was started at some point. And in principle, it could just be rebooted, and
then all of this would happen exactly the way it happened before
because it’s running the same computer program. In principle.
>>JAMES GATES: If one accepts the simulation hypothesis as an accurate description of nature—
>>ZOHREH DAVOUDI: I would say that’s a useless exercise.
What would be more interesting is to actually—
>>NEIL DEGRASSE TYSON: The word was useless, Jim, in case you missed that.
Okay, you heard that. Okay.
Emphasis on useless exercise. Go, Zohreh. Go.
>>ZOHREH DAVOUDI: Trying to repeat what you’ve already done with huge computation resources
is useless. What is more interesting
is to go and change the parameters of the simulation—the input parameters. Just put
the same laws of nature, and then just change a little bit
the value of the parameters—the very fundamental parameters of our universe. And then let it
run and see what happens. It’s actually very interesting idea—
>>NEIL DEGRASSE TYSON: It’s a fun thing to do, as a scientist.
>>JAMES GATES: But in changing those parameters
you might cancel out my existence, in which case I don’t think that’s very useful.
>>NEIL DEGRASSE TYSON: The universe without Jim. So, Lisa, isn’t this some of the foundation—
couldn’t we account for a multi-verse in this very way? That multiple-verse is multiple
universes as I understand them
will have slightly different laws of physics. Maybe they are themselves the experimenter’s
>>LISA RANDALL: Okay. So, let’s slow down a bit here.
So, first of all, I actually want to address some of the things that have come up already.
One of the questions is probability;
Bostrum’s argument or whatever,
that we’re likely to be in a simulation. I mean, part of the problem is that probabilities
have to have a well-defined meaning, or are only useful when they have a well-defined
So, among all possible scenarios we can actually say which one is more or less likely. When
we run into infinities, when we run into—
it stops making sense. I mean, I could say really by probability I’m very likely to
because there’s a lot more Chinese than Americans. But I’m clearly not Chinese.
So, probabilities are tricky, and you have to be careful what you mean when you’re
Another thing is I actually find the egotism of thinking that if there was simulators around
that they’d come up with us
kind of audacious and ridiculous. I mean, I think it’s a very self-centeredness to
this whole thing that kind of I find hilarious.
But in terms of feedback—in terms of error-correcting code,
I think it’s very likely that there were going to be feedback mechanisms in whatever
universe survives because if there aren’t, I mean, there’s always going to be mistakes.
And if mistakes can propagate and just cut things off,
those universes don’t survive. So, there have to be—I mean, for any universe, simulated
or non-simulated, there has to be error correction. So, that has to be part of it.
>>NEIL DEGRASSE TYSON: Right. That assumes that the programmer makes the same kind of
programming—is susceptible to programming errors and programming bugs that we are.
>>LISA RANDALL: It’s not even intentional. It could be just that the computer itself
is subject to error. I mean, it’s only firing things somewhat random—I mean, ultimately,
there’s uncertainty in everything. Nothing is created perfectly.
>>NEIL DEGRASSE TYSON: Quantum uncertainty.
>>LISA RANDALL: So, [unintelligible 32:51].
>>JAMES GATES: Can I jump in here?
>>NEIL DEGRASSE TYSON: What?
>>JAMES GATES: Because she’s raised—in fact, I think an incredible point about this.
>>LISA RANDALL: As long as you come back to me afterwards.
>>JAMES GATES: Maybe I take a few times? I’ll [unintelligible 32:59] minutes back later.
>>NEIL DEGRASSE TYSON: Yes, okay.
>>JAMES GATES: This point about error correction is something that
when people have—general public has looked at my work, they say, “Oh, you must believe
in simulations.” And I’ve said, no, actually I don’t.
And the reason is because precisely the point the Lisa points out.
If you look in all of nature and ask are there any other places in nature—not in engineering,
not in computers, not in the things that we build,
but in nature herself, is there a discussion in science about error-correcting codes?
It turns out there’s one place and one place only that I have been able to identify. That’s
in evolution and genetics. And there’s been a discussion—
>>LISA RANDALL: Or any biological system.
>>JAMES GATES: Right. Or any biological—right.
And it’s not that we think life is some kind of programmed simulation. It’s because
the universe itself,
as Lisa had said, has to have feedback mechanisms that basically sustain a structure that propagates
faithfully forward in time. And I think that’s in fact the most critical point. And you have
your time now.
>>LISA RANDALL: Thank you. And anyone who wants to take my time to agree with me—
[laughter and talkover]
>>LISA RANDALL: But as far as the multi-verse theory goes,
so we have to be careful by what we mean by that. I mean, at some underlying level we
still think it’s
physics in action. Now, what might change in different universes, we might actually
have different forces. We might actually have different strengths of interactions;
the kind of thing that gets simulated. I mean, we simulate strong interactions the way that
>>NEIL DEGRASSE TYSON: Just to be clear, strong interactions are the forces that bind atomic
>>LISA RANDALL: So, protons.
>>NEIL DEGRASSE TYSON: Yeah, protons that are the same charge
that are sitting right next to one another in a nucleus. And how’s that even possible
when we were taught that like charges repel?
So, there’s got to be a really strong force down there holding it together. And there
is a really strong force. It’s called the strong force. Okay, so go on.
>>LISA RANDALL: Which is strong.
>>NEIL DEGRASSE TYSON: Yeah. Okay.
Just to be clear.
>>LISA RANDALL: So, and there can be different possibilities for what these parameters can
be. It’s still underlying you still believe that there’s the laws of physics that are
So, the question—I mean, so it’s not a simulation. It’s just—
I mean, it’s in principle possible that there are universes we don’t communicate
that are so far away we’ll never send a signal, they’ll never send a signal. So,
for all intents and purposes, there just are
different universes. That doesn’t mean they’re simulated. It just means they’re different
from ours and they can have different properties.
To really distinguish a simulation, you really do have to see
just our whole notion of the laws of physics breaking down, or some of the fundamental
underlying properties. So, it would be extremely interesting to look for the kind of
violations of [unintelligible 35:43] that were discussed earlier, or things like quantum
entanglement no longer hold it. Not because of interaction of the environment, but just
the computer just couldn’t keep track of stuff. I mean, that’s stuff that gets so—
I mean, a lot of the simulation idea—I mean, to simulate the universe, you need the computational
power of the universe. So, all of the simulations are based on the idea that there are some
approximations that we don’t see,
but you have to be able to hide them. So, what we’re really looking for is the breakdown
of the assumption that those approximation s are valid.
>>NEIL DEGRASSE TYSON: But, David, what do your philosophical circles say about proposing
an experiment that might falsify these ideas?
>>DAVID CHALMERS: Look, I don’t think you’re going to get conclusive experimental proof
that we’re—we’re certainly not going to get conclusive experimental proof that
you’re not in a simulation. I suppose we could get some kind of various—
>>NEIL DEGRASSE TYSON: Well, why not? You just declared something. Why can’t a clever
person come along and—
>>DAVID CHALMERS: Because any evidence that we could ever get could be simulated. That’s
basically the reason. Sorry. Maybe—
>>NEIL DEGRASSE TYSON: So, if I find evidence that we’re not simulated, the great simulator—
>>DAVID CHALMERS: They could have just planted that for you.
>>NEIL DEGRASSE TYSON: —put that in.
>>DAVID CHALMERS: Yeah. They’re one step ahead. However—
>>NEIL DEGRASSE TYSON: We’re done. We’re done here.
>>DAVID CHALMERS: Maybe we—we probably could get pretty strong evidence
that we are simulated. If someone wrote up in the sky, “Sorry, guys”—the stars
suddenly rearrange themselves into, “Sorry, guys, it’s all a giant simulation.”
And then they took over the Internet and—
>>NEIL DEGRASSE TYSON: Except it would be in Chinese to get the most number of people
to read it.
>>DAVID CHALMERS: Then we’d probably have a pretty good reason to think
we’re in a simulation. Either that or the weirdest non-simulated universe that anyone
ever imagined. So, for a philosopher anyway,
it’s not fundamentally a matter of experimental proof. It’s cool. I really like Zohreh’s
experimental evidence that we’re in a simulation. But I think around here it’s really important
to make a distinction
that there’s a hypothesis that we’re in a simulation. There’s a hypothesis that
the universe is computational.
Those are closely related. If we’re in a simulation, the universe is fundamentally
computational. But it’s not true that this universe is fundamentally computational we’re
necessarily in a simulation.
Because the simulation hypothesis is a combination of two things.
>>NEIL DEGRASSE TYSON: That’s an official thing, the simulation hypothesis.
>>DAVID CHALMERS: Yeah. The simulation hypothesis says we’re in a computer simulation. A computer
simulation’s a computation
that was created by someone for a purpose. So, basically the simulation hypothesis is
that computation hypothesis,
plus something else about someone who created it. And around here is where you might be
able to get a little
theological and say, okay, well, it’s a naturalistic version of the god hypothesis.
But, anyway, my worry about Zohreh’s stuff,
which is really cool, it’s really evidence for the much weaker hypothesis that the universe
is some form of discrete computation and is completely neutral
on the question of whether this is actually a simulation in the sense of something that
>>NEIL DEGRASSE TYSON: With intent.
>>DAVID CHALMERS: —by a simulator.
>>NEIL DEGRASSE TYSON: So, Max, do you mind if I call you Mario from now on? Because if
you’re Mario in the computer game—
>>MAX TEGMARK: Starts with M-A, so [unintelligible 38:46] for the two letters, yeah.
>>NEIL DEGRASSE TYSON: I imagine Mario—someone coming into a Mario game
and calculating how high he jumps and how fast he runs and coming up with the laws of
physics of the game, and possibly then questioning
why is it that and not something else perhaps. And so, fine, but is there—why would that
allow someone in the game to have any understanding of what’s outside the game?
>>MAX TEGMARK: Yeah, that’s a really deep and good question. Mario might—if Mario
can ever—even if he figures out exactly the rules of his world—
>>NEIL DEGRASSE TYSON: Then he just figures out the rules.
>>MAX TEGMARK: —he won’t even know if he’s running on a Mac or a Windows box or
a Linux box
because all he has access to is this higher level of this sort of emergent reality. And
we might, at some level, be stuck
in that situation in physics also. It’s quite fascinating to think that so much of
what we’ve figured out, for example, about how a glass of water works
with waves and vortexes and things, we figured out already without having a clue about the
substrate. We didn’t even know there were atoms. But the same kind of questions that
which I think are awesome, the kind of questions where you ask suppose this is actually somehow
suppose the simulators cutting corners, how would that show up?
Actually, it has been incredibly useful in the past. If you imagine going back 200 years
and trying to simulate this water as an infinitely—
a continuous liquid where there’s a pressure and a density that has to be defined with
infinitely [many 40:25] decimal places and infinite points,
that sounds horrible to simulate. So, maybe whoever did this cut corners. Maybe there’s
a smallest kind of chunk of object—let’s call it atom or something—
you can figure out then what are the departures from this simplified continuous physics that
I’m guilty of teaching my undergrads at MIT about this morning?
And you would figure out a way there’s this one little thing, which is different.
>>NEIL DEGRASSE TYSON: He trained down a few hours ago from Cambridge.
>>MAX TEGMARK: Yeah.
>>NEIL DEGRASSE TYSON: Thank you for coming and for—
>>MAX TEGMARK: Brownian motion that things should jiggle around in a weird way. And Einstein
got the Nobel Prize for it importantly. And I think that the sort of thing you’re doing
Look for corner-cutting evidence. I suspect that whether we’re simulated or not there
are a lot of things that are wrong about what we assume today.
I am very skeptical that we really have a continuous space that can be stretched infinitely
many times. It seems like some sort of simplification that we came up
because it was easier to do the math.
>>ZOHREH DAVOUDI: But do you ever ask why should that be the case? Why do we need a
discretized universe? I mean,
if you put away the simulation hypothesis or a computational hypothesis,
why should we even think about a discretized universe? Why not continuum?
It’s [unintelligible 41:42].
>>NEIL DEGRASSE TYSON: So, this is an important—
>>MAX TEGMARK: Yeah.
>>NEIL DEGRASSE TYSON: I don’t want to call it a problem in physics, but a reality of
that our macroscopic world looks continuous to us. And that has a certain simplicity of
modeling. And then as you get smaller and smaller and smaller, it’s no longer continuous
and it’s discrete, which may be easier to calculate than being able to be divisible
all the way down to an infinitesimally small bit.
Because now you need that much bigger computer to do it. By the way, we have—
>>LISA RANDALL: So, you know something that none of us actually know.
This is actually a real question, whether space is discrete at really small scale.
>>NEIL DEGRASSE TYSON: Well, we run into this problem when we do flyovers in the Hayden
Planetarium. We have a data set for a planetary surface—
let’s say Mars—and you had a given distance. And from that distance you can see Olympus
Mons, the biggest mountain around, and Valles Marineris,
and you say, fine, now I want to get closer.
Well, to get closer, and have more information come to you, you have to swap in a higher
resolution map. And we try to do that continuously, so you don’t realize that.
So, you keep doing this, and then you reach a point where we don’t have more resolution
to give you. So, we actually hold you back,
so you don’t go closer. But if you did, all of a sudden you see these discretized
pixels of the Martian surface.
And that’s basically because we don’t have the data. We’re not there. It doesn’t
exist for us.
>>DAVID CHALMERS: So, anyone’s who’s used one of these virtual reality devices, like
the Oculus Rift, knows there’s something called the screen door effect.
It’s like you can—if you look closely enough you can see the pixels, so it’s not
a perfect simulation. So, I guess really what Zohreh is doing is saying, well, we can get
empirical evidence for a screen door effect in real physics.
>>ZOHREH DAVOUDI: Yeah, I think it’s actually a deeper question than that. It’s not about
not having enough data to resolve those distances, but to some extent that’s true.
But the problems is something that even bothered Feynman a lot
that why do you need infinite numbers of degrees of freedom, or infinite amount of information,
to describe a very tiny chunk of the space-time? That just doesn’t make sense.
You can pretty well describe the physics without actually needing that infinite amount of information.
>>NEIL DEGRASSE TYSON: What I meant to add is that when we’re zoomed down to Mars,
it’s not only that we don’t have the data,
even if we did have the data, you would need that much bigger
disk space to have it ready and loaded to be able to go from the bird’s eye view down
to any kind of small—
I mean, we rapidly run out of capacity to calculate.
>>MAX TEGMARK: And that’s a great controversy that even mathematicians have been really
arguing passionately about for over 100 years.
Gauss, one of the greatest mathematicians ever, said—or Kronecker actually said God
had created the integers
and everything else was just the work of man. All this continuous real numbers with decimal
places and stuff.
I mean, frankly, as a physicist it feels kind of hubristic
to say that you need an infinite amount of information to figure out the height of my
wine glass or anything. Nature seems perfectly about to figure out what’s—
>>NEIL DEGRASSE TYSON: There’s water in that glass, by the way.
>>MAX TEGMARK: Yeah, what to do. And we have this toy model that you need an infinite amount
of information to do things.
I think you’re on to something very deep [unintelligible 44:56] and that nature actually—infinity
is just something we made up for convenience.
And as we dig deeper, we’re going to find that maybe even space and time itself is at
some level digital.
>>LISA RANDALL: So, can I just say something by way of clarification? Which is just in
we don’t actually prove any theory. We can rule out theories.
So, we can rule out a lot of alternative theories, but in any case you can always have the possibility
that you can dig deeper and find
that whatever theory you thought was the most fundamental has some underlying structure.
And so that’s why all the physics we’ve done works. That’s why we really don’t
need to have an infinite amount of information at any time
because we don’t have access to an infinite amount of information. And we can’t even
ask the question or tell whether or not there’s this underlying infinite amount of information.
So, it’s not just we can’t just ask the question whether the universe is a simulation.
We can’t ask if any physical theory is absolutely correct. We’ll never know the answer to
All we can know is that we’ve tested it up to a certain level, at a certain level
of precision, over a certain range.
And so these questions all [unintelligible 46:05], and that’s why I can describe this
glass of water without knowing about atoms,
because I didn’t have—wasn’t doing an experiment where the effects of the atoms
became manifest. And the same might be true of the universe as a whole.
So, we can have in the back of our mind there may or may not be an infinite number of degrees
of freedom. But that’s not what we’re actually testing.
>>MAX TEGMARK: Let’s disagree on one thing, though.
I think there’s one fantastic example where we can tell it makes a huge difference. I
think the biggest embarrassment we have
arguably in fundamental physics and cosmology right now is this fact that inflation,
if it goes on forever, makes this multi-verse, and then we can’t calculate probabilities,
like you so eloquently said in the beginning.
That comes exactly from the infinity assumption; the idea that you can take a piece of space
and just keep stretching it into twice the size forever. So, I think you should question
>>LISA RANDALL: Well, it doesn’t have to be infinite. It could just be a large number.
It could be 10 to the 500. I mean, it doesn’t really matter if we say it’s infinite. Why
don’t we just say it’s a lot?
>>MAX TEGMARK: But you can calculate probabilities as long as it never gets infinite. It’s
exactly infinity that [unintelligible]—
>>NEIL DEGRASSE TYSON: So, he’s cool with 10 to the 500, is what he’s saying, which
seems like a really big number.
>>LISA RANDALL: I know.
>>NEIL DEGRASSE TYSON: That like equals infinity to me, I think.
>>LISA RANDALL: But that’s exactly the point. That’s exactly the point.
>>NEIL DEGRASSE TYSON: Jim, is there any functional difference at all
between admitting that we live in a computer simulation and saying that’s basically a
What’s the difference?
>>JAMES GATES: Well, first of all, I’ve decided my name should be Morpheus, not Jim.
>>NEIL DEGRASSE TYSON: Okay. Well, let me—
>>MAX TEGMARK: I’m Mario. Nice to meet you, Morpheus.
>>NEIL DEGRASSE TYSON: Morpheus.
>>JAMES GATES: Exactly.
>>NEIL DEGRASSE TYSON: Yes. You have to see the movie The Matrix and play video games
to follow this conversation at this moment. Morpheus.
>>JAMES GATES: But as I said, for non-scientists—
because I’m going to make this partition. I think for non-scientists, an acceptance
of the simulation hypothesis as an accurate view of our universe
is equivalent, I believe, to the notion of a deity. I don’t understand how, for a non-scientist,
you can make that distinction. For a scientist, however, we are [rather] secular.
The definition of science is actually a secular definition. And, in fact, it’s the definition
that comes to us from Galileo.
Einstein quotes Galileo as being the father
of all science because Galileo—and these are Einstein’s words—drums into us that
contemplation alone, without observation of nature,
is totally useless in trying to come up with an accurate view of nature. So, it’s that
ability of us—our human ability to observe the universe
that actually defines science. So, if you can’t give me something that I can observe,
I don’t know how to do science.
>>NEIL DEGRASSE TYSON: Okay. So, what you’re saying is
that if in fact there is a programmer who would be philosophically equivalent to a Creator,
and you can’t observe them,
they’re just outside the realm of science.
>>JAMES GATES: I think that’s the definition.
>>NEIL DEGRASSE TYSON: David, do you have to be defined by that?
>>DAVID CHALMERS: Well, I think there’s a theological reading, if you like, to the
simulation hypothesis. It says all this was created,
but what’s interesting is at the same time it can be seen as a kind of a naturalistic
theology. A naturalistic hypothesis—from the point of view—
>>NEIL DEGRASSE TYSON: Is that the first time the phrase has ever been uttered? A naturalistic
>>DAVID CHALMERS: I think it’s out there already.
>>NEIL DEGRASSE TYSON: Oh, it’s out there. Okay. All right.
>>DAVID CHALMERS: Simulation theology [unintelligible 49:36].
Simulation theology is the coolest kind of naturalistic theology, from the point of view
>>NEIL DEGRASSE TYSON: Actually, there’s a book in 1750—or who was it?
>>DAVID CHALMERS: Yeah, David Hume was into naturalism.
>>NEIL DEGRASSE TYSON: No, there was—who was the fellow who wrote the book Natural
There was a book with that very title.
>>DAVID CHALMERS: Yeah.
>>NEIL DEGRASSE TYSON: But not natural simulation or simulated theology.
>>DAVID CHALMERS: If you think about is from the point of view of the simulated—
I mean, we in this universe can create simulated worlds, and there’s nothing remotely spooky
about that. People are already doing it with virtual reality and the Sims and Second Life.
And whatever this is is just a far more sophisticated version of that.
So, we just need to move that picture to the next universe up and say,
hey, maybe that’s what’s happening to us. So, we got a creator, but our creator
isn’t especially spooky.
It’s just some teenage hacker in the next universe up
whose mom’s calling him in to dinner.
>>NEIL DEGRASSE TYSON: Working in the basement, yeah.
>>DAVID CHALMERS: So, I think you could be led to at least entertain this idea
by perfectly naturalistic ideas as, say, Nick Bostrum was and say, okay,
maybe this is the kind of theology which even someone who’s got no sympathy for spooks
and gods and ghosts, needs to object to.
>>NEIL DEGRASSE TYSON: So, that’s an interesting point
because we don’t think of ourselves as deities when we program Mario, even though we have
all power over how high Mario jumps.
Because that’s a line in the code. So, you’re right. You just take it up
a few notches. There’s no reason to presume they’re all powerful other than just they
fully control everything we do, say and think.
>>DAVID CHALMERS: Could be they’re all powerful. I got into this from watching my five-year-old
playing with one version of the Sims or Sim Life or something. He’d make a whole town.
He’d build up the buildings,
and you got the trees and the jungles and the creatures. And then he’d say now comes
the good part,
and he’s send down fires and floods and such. I was like, finally, I understand the
God of the Old Testament.
>>NEIL DEGRASSE TYSON: Because it is true in our world we have fires and floods.
I played one of those Sims—Sim City because I’m a city kid. And—the early, early low-res
simulation. And there’s a feature,
you build up the—you need money. You’re mayor of a city, and you construct buildings
and you need the schools and the fire departments.
And then every now and then Godzilla stomps through your city
and you say that’s not real. I’m trying to be real. But then it’s kind of real in
the sense that some major disaster can—
you will confront like Hurricane Sandy or 9/11. Now, you’ve got to redistribute resources.
So, I look at our real world, and these things actually do happen. So, are they just trying
to mess with us? Is that—
>>DAVID CHALMERS: The way I think about—I mean, who knows if there’s actually a simulator
who’s actually doing any of this. But if you do take the simulation hypothesis seriously,
it’s got a couple of elements of a traditional god. This person could be all knowing about
our universe, could be all powerful. The one thing which is probably missing is
wisdom and benevolence. If there’s a simulator, I refuse to worship you. You may be out there,
but you have established yourself as being worthy of worship. I refuse to [unintelligible
>>NEIL DEGRASSE TYSON: Right. Because they’re all powerful and all knowing, but not all
>>DAVID CHALMERS: There’s no reason to think they’re all good.
>>MAX TEGMARK: Cut him some slack. He’s only five years old.
[laughter and talkover]
>>DAVID CHALMERS: You’re going to be maturing one of these days.
>>NEIL DEGRASSE TYSON: Zohreh?
>>ZOHREH DAVOUDI: Yeah. So, I think there is a big danger in trying to compare
our idea of simulation with what comes with computer games, whether you’re talking—at
least in my point of view and I think a physicist’s point of view.
What’s called the simulation is you just input the laws of physics,
and nature and universe emerges. You don’t actually try to make it look like it’s something
going on. You don’t try to—
the same as with computer games. You don’t interfere with what you’ve created. You
just input something that is very fundamental
and just let it go, just as our universe.
>>MAX TEGMARK: Like [deitism]?
>>ZOHREH DAVOUDI: Yeah.
>>NEIL DEGRASSE TYSON: In other words, you set the laws into motion
and let the universe unfold.
>>ZOHREH DAVOUDI: Exactly.
>>NEIL DEGRASSE TYSON: However those laws prescribe.
>>ZOHREH DAVOUDI: Because a priority—you don’t know what happens because the universe
is complex. The laws of physics are simple,
but you don’t know what kind of complexities you should expect. And then you just get it
and things emerge, and we just watch.
>>NEIL DEGRASSE TYSON: But, Lisa, in the search for the Theory of Everything,
isn’t that got a little bit of this in it? Once you find the Theory of Everything—and
you’ve been on two of our Theory of Everything panels here—
you’re going to find out the one equation that the five-year-old working in the garage
wrote down that made our entire universe.
>>LISA RANDALL: Well, you might recall, since I’ve done this a couple times, that the
Theory of Everything,
I think, is very badly named for a lot of these reasons. Because even with the equations,
as was pointed out earlier,
you could start your system in very different ways. You can have different conditions. And
there’s a lot that we don’t understand.
I mean, even if I understood quantum gravity at a fundamental level and could derive all
that’s still not going to help me predict waves at a practical level. I mean, the computer
simulation will never be that detailed,
in my opinion. It’s much better to go to different levels and figure out what’s going
on at what I would call an effective theory approach. So, even with the fundamental equations—
now, I mean, clearly if you had infinite computing power, then you would just be literally mimicking
the universe. And possibly you could do that. But short of that,
you’re going to have to find these approximations, these descriptions that are sort of somewhat
in between. They’re still science.
They’re not something I’m just making. There’s still equations that work, and they
ultimately are attributable
to whatever is that fundamental equation. But that doesn’t mean it’s fundamentally
how we’re computing it. It doesn’t mean it’s fundamentally how it’s working.
>>NEIL DEGRASSE TYSON: But, Zohreh, you started this whole discussion by
describing—trying to obtain an understanding of the basic forces of nature and the particles