Galileo was quite controversial, of course,
in his time, because he was claiming that something that we all could see with our own
eyes wasn't true. We could all see that the earth doesn't move
and that the sun, and moon, and stars go around the earth. And we believed that as a race for about 2,000
years. And Galileo was saying that your eyes are
lying to you. The earth actually moves and it's not the
center of the universe. And he was put under house arrest for it. And we don't like to be told that our senses
aren't telling us the truth. And then Galileo took it another step. He said, it's not just that our senses are
lying about movement of the earth, he said that he thought that tastes, odors, colors,
and so on reside in consciousness. Hence, if the living creature were removed,
all these properties, these qualities, would be utterly annihilated. That's almost a direct quote in the translation. So he was saying that our senses are also
making up the tastes, odors, and colors that we experience. They're not properties of an objective reality. They're actually properties of our senses
that they're fabricating. And by objective reality in this case, I'm
going to use that term in a very specific way. By objective reality, I mean what most physicists
would mean. And that is that something is objectively
real if it would continue to exist even if there were no creatures to perceive it. So the standard story, for example, is that
the moon existed before there was any life on Earth and, perhaps, before there was any
life in the universe. But it still existed. Its existence does not depend on the perceptions
of any creatures. And so that's the sense in which I'll talk
about objective reality. And what Galileo was saying was that colors,
odors, tastes, and so on are not real in that sense of objective reality. They are real in a different sense. They're real experiences. And so I'll talk about real experiences. So your headache is a real experience, even
though it could not exist without you perceiving it. So it exists in a different way than the objective
reality that physicists talk about. So Galileo was quite brave and quite out of
the box in his thinking by saying not only the earth in his movement, but even colors,
tastes, and odors are our perceptual constructions. But he wouldn't go the next step. He wouldn't say that shapes, and mass, and
velocities of objects, and space, and time themselves are our constructions. He thought that those were objectively real. So the shape of the moon, the position of
the moon, is an objectively real thing, including its mass and its velocities. So, this is a distinction that was later called
the primary and secondary qualities of distinction by John Locke. Primary qualities are things like position,
mass, shape, and so forth. These are presumed to exist even if no creature
observes them. Whereas colors, and odors, and tastes are
secondary qualities that are sort of mostly the contribution of our senses. And in brief, what I'm saying is we need to
take the next step beyond what Galileo said. It's not just tastes, odors, and colors that
are the fabrications of our senses and are not objectively real. It's, rather, that space-time itself and everything
within space-time-- objects, the sun, the moon, the electrons, quarks, their shapes,
if objects have shapes, their masses, their velocities-- all of these physical properties
are also our constructions. And I've come to that conclusion. It was a bit of a shock to me. We always assume that our senses are telling
us the truth. So it was quite a stunning shock to me when
I realized that maybe we needed to take a step beyond Galileo on this. And the reason I'm saying this is because
of evolution by natural selection. Most of my colleagues in the cognitive and
neurosciences assume that our senses tell us the truths that we need to survive. That seeing reality accurately will make you
more fit. And I would say that that makes perfect sense. The argument is that those of our ancestors
who saw reality more accurately had a competitive advantage over those who saw it less accurately
in the basic activities of life, like feeding, fighting, fleeing, and mating. And because they had a competitive advantage,
they were more likely to pass on their genes which coded for the accurate perceptions. And so after thousands of generations of that,
we can be quite confident that we see reality as it is. Of course, not all of reality. No one claims that our senses exhaustively
tell us all the truths about objective reality . But from an evolutionary point of view,
the idea is we see those aspects of reality accurately that we need to survive. And so when we see space and time, we see
physical objects with their shapes and motions, and so forth, we're seeing truths, objective
truths. Truths about objects that would exist even
if no creature were there to perceive them. That's the standard view. And it seems intuitively plausible-- the argument
that I just gave is actually in the textbooks in my field. But it turns out that we don't have to just
deal with plausibility here. Evolution by natural selection is a mathematically
precise theory. There is the field of evolutionary game theory
that was established in the 1970s by John Maynard Smith and has flourished. It's now a very advanced and very interesting
mathematically precise field. It unites Darwinian evolution by natural selection
with the tools of game theory. And it's very, very powerful. So we don't have to guess or wave our hands
anymore. We can actually run simulations and prove
theorems about the effects of natural selection on our senses. We can ask a technical question. Does natural selection favor organisms with
sensory systems that tell them truths about reality, objective reality? It's a clean technical question. And it turns out there is a clean technical
answer that comes from evolution. And it is quite surprising. I first started this about 12 years ago with
a couple of graduate students of mine-- Justin Mark and Brian Marion. We ran hundreds of thousands of evolutionary
game simulations in random worlds with resources and creatures that had to forage for these
resources. And we played god. Some of the creatures got to see the truth. Others didn't. And the ones that didn't, we had them just
perceived the fitness payoffs. And we can talk a little bit about fitness
payoffs a little bit later. That's a key, key notion in evolution. And what we found was in the simulations organisms
that saw the truth never out-competed never outperformed creatures in our simulations
that saw none of the truth and were just perceiving the fitness payoffs. So that gave me some confidence that maybe
there was a theorem here. And so I proposed a theorem to a very talented
mathematician named Chetan Prakash with whom I've worked for many years. Chetan and I discussed it, worked on it. And Chetan brought it home. He proved the theorem. An organism that sees reality as it is is
never more fit than an organism of equal complexity that sees none of reality and is just tuned
to the fitness payoffs. Translated, that means if you see the truth,
you'll go extinct. And so the question is, of course, what our
fitness payoffs? And what's going on there? And it's a technical term in game theory. The payoffs are what sort of drive the game. But I think an analogy can help. Think of life as like a video game. In a video game, you have to, in many video
games, you have to try to grab as many points as quickly as you can at the level that you're
at. And if you get enough points in the minimal
time, you might get to the next level. If you don't, you die. And you have put in some more money or start
over. And the idea is that life is like that. It's like a video game, but instead of the
points in a game, we have fitness payoffs. Getting the right kind of food, high-quality
food, not eating poisonous things, breathing the right kind of air, finding the right mate
and so forth. These are all fitness payoffs that we can
get. And if we get more fitness payoffs than the
competition-- it's not like getting millions of fitness payoffs, you just have to do a
little bit better than the competition-- then you have a better chance of passing on your
genes that code for your strategies for getting fitness payoffs. So you don't go to the next level like in
a video game, but your genes and your offspring go to the next level. And so that's, informally, the idea of fitness
payoffs. They're what drive success or failure in evolution
and life. And what we discovered was two things-- First,
that fitness payoffs themselves destroy information about the structure of the world. It's truly stunning. Fitness payoffs depend on the state of the
world. And I can give you an example. So what is the fitness payoff of, say-- I
like this example of a T-bone steak. Well, for a hungry lion looking to eat, that
T-bone steak offers a lot of fitness payoff. It will help it to stay alive and be strong. For that same lion that's well fed and looking
to mate, the T-bone steak offers no fitness payoffs. And for a cow, in any state, a T-bone steak
is not a good thing. So the payoffs depend on objective reality,
whatever that might be, whatever the state of the world might be. And also on the organism, like lion versus
cow, its state, hungry versus fed, and its action, eating versus mating, for example. So fitness payoffs, as you can see, are complicated
functions. They depend on the state of the world, whatever
the world might be, but also on the organism, its state, and its action. And if we fix an organism, state, and action,
then fitness payoffs are functions from the world, whatever the world might be, into a
set of payoff values, say from 1 to M, fitness payoff values where 1 means you're dead, M
means you're getting the most you could possibly get. And what we've discovered is that function,
those fitness functions, almost surely destroy information about the structure of the world. I can give you a concrete example of what
I mean by that. So suppose-- and by the way, when I said that,
I don't need to know anything about the world. I don't need to propose I know anything what
reality is. These terms hold anyway. That's the nice thing about the mathematics. You might say, well, you know, how could you
prove such a theorem unless you know what the world is? It turns out you can. These theorems hold regardless of what the
world is. Suppose we take, for sake of argument, a world
in which there really is oxygen concentration. There is air and there's oxygen. And oxygen concentration can go from 0 percent
to 100 percent. That's what mathematicians would call a total
order 0 is less than 1 less than 2, all the way up to 100. That's a total order. And it turns out that-- so that would be a
structure in the objective world in this example. Now the percentages of oxygen that will maintain
human life is about 19.5 percent to 22.5 percent. If you get outside that range, you'll be in
distress and eventually die. And so there's this very narrow range of oxygen
concentrations that are useful for life. So suppose you had a creature that had only
two colors that they perceived. So a very simple creature. It just sees green and red. And let's assume that we're going to say green
is greater than red, just we'll just put an order on green and red. We can put an arbitrary order on them. So green is greater than red. And suppose-- look at two different creatures. One sees as much of truth as possible with
just two colors. In that case, you might use red for 0 percent
of oxygen to 50 percent. So red is for very little oxygen to medium. And green would be from medium to 100 percent. That way if you saw red, you'd know there
was less oxygen. And if you saw green, you'd know there was
more. And so you're knowing as much about the truth
of the objective reality-- namely the amount of oxygen-- as you could possibly know given
the limits of your sensations. So that will be a truth organism. Now consider a fitness organism that only,
again, has two colors, green and red. To encode fitness, you could do the following:
Let's use red for 0 through 19.5, which will kill you. And for 22.5 to 100, which will also kill
you. In other words, we use red for those amounts
of oxygen that will not sustain life. And we'll use green for that narrow band from
19.5 to 22.5 that will sustain life. So if I see green, I know I'm good. I don't need to change anything. I'm going to live. If I see red, I know I'm in trouble. I need to do something differently. But notice if I see red, I have no idea about
the truth, about how much oxygen there is. There could be 100%. There could be 0%. I have no idea. So that concrete example gives you an intuition
about why seeing the truth is a very different thing than seeing fitness and why that they're
really at odds. They're not the same thing. Our intuitions are, of course, if I see the
truth, that will make me more fit. And this example makes it very, very clear
that seeing the truth is the opposite in most cases of seeing what's fit. And we were actually able to prove that--
this is now inside baseball language, but I'll throw it out there-- the set of fitness
payoffs, if the world has N states, N as in Nancy, and the fitness payoffs have M values,
M as in Mark. There are going to be M raised to the N power,
total fitness payoffs, very simple math, combinatorics. And you can for any structure in the world
that you want to consider, a total order, a symmetric group, a cyclic group, a measurable
structure, a topology, you can ask in each case how many of those M to the N fitness
payoffs will preserve that structure. Mathematicians call them homomorphisms. So the homomorphisms of a topology are what
we call continuous functions. The homomorphisms of measurable structures
are what we call measurable maps and so forth. It's straightforward to show in each case
that the probability-- well, nah, I wouldn't say straightforward. If you a mathematician working with you, then
looking over their shoulder, it looks straightforward, but, of course, it's hard work for the mathematicians. But it's combinatorics. And some of the combinatorics is pretty straightforward
for mathematicians. In each case, we show that the ratio, the
number of homomorphisms, the fitness payoffs, that preserve the structure of the world,
that tell you something about the truth, to the total number of fitness payoffs, that
ratio-- so the truth preserving payoffs versus all payoffs, we look at that ratio. And that ratio goes to 0 as the number of
states in the world increases and the number of fitness payoffs increases, and that means
the fitness payoffs generically destroy information about the structure of the world. Our senses will be tuned to the fitness payoffs. And being tuned to the fitness payoffs means
that you will not be tuned to the structure of the world, because the fitness payoffs
have lost that structure. And so that's how devastating this is. So we're in a dilemma here. We have two things that we deeply believe. We deeply believe in evolution by natural
selection. And we deeply believe in physicalism. That space-time and physical objects as we
perceive them are a true representation of reality as it is. Those two claims are in conflict. Both cannot be true. And that's what we've done. I'm saying that space and time and physical
objects don't exist unless they're perceived. And someone might say, "Well, look, Don, if
you think that that train coming down the tracks is just some little thing that you're
creating on the fly, you're making that up, it's just an icon in your desktop, or a symbol
in your virtual reality, why don't you step in front of that train? And after you're dead, and your ideas with
you, we'll know that that train was real and it really can kill." And I wouldn't step in front of the train
for the same reason that I wouldn't, for example if I'm, say, writing an email. And the email icon is blue and rectangular
and in the middle of the screen. That doesn't mean the email itself on the
computer is blue and rectangular in the middle of the computer. So I don't take the icon literally. It's not literally true about what's in the
reality. But I do take it seriously. I would not drag that icon to the trashcan
carelessly. If I drag the icon to the trashcan, I could
lose all of my work. So I take my icons seriously, but not literally. And that's the case with the train as well. Evolution by natural selection has shaped
us with perceptions that are designed to keep us alive. So if I see a snake, don't pick it up. If I see a cliff, don't jump off. If I see a train, don't step in front of it. We have to take our perceptions seriously,
but that does entitle us to take them literally. So another objection is, I look over there
and see a train, and I ask all of my friends, they'll also say that they see a train. So given that we all see the train, surely
that means that, therefore, there is a train in objective reality. There really is a train. And that seems very compelling. Of course, we all look, we see the moon. We all agree that there is a moon. So therefore, the moon must really exist. But again that's a logical error. In the visual example that we looked at earlier
with the cubes that were floating in front of the disks, we all would agree that we saw
a cube. But we would all agree that the reason you
saw a cube was because you created the cube. The cube doesn't exist unless you create it. So the reason we agree about trains, and the
moon, and cars, and apples, and so forth is because we have a similar interface. We're constructing similar objects. And because we construct our worlds in similar
ways, we tend to agree. Although 4 percent of us have synesthesia
and can view the world in very, very different ways from the rest of us. So the bottom line is agreement only means
agreement, it doesn't mean that we're seeing objective reality. Descartes famously said, "I think, therefore
I am." And that does raise a really interesting question
about consciousness and what we call the physical world. A physicalist would say, "Look, I know about
things like umbrellas, and the moon, and rocks. I mean all of this concrete, stable stuff,
I know about that reality. But when you talk about consciousness and
conscious experiences, I'm not sure that you're really talking about anything real. It might just be an illusion. It might be a figure of speech. We could be very, very deeply wrong." So that's the view of most of my hard-nosed
physicalist colleagues. "I know about this physical world out there. That's really solid. It's something we can really look out and
test. This stuff about consciousness is airy fairy,
wiggly. I don't know what you're talking about. It's too squishy for me." But there is a completely different point
of view. It's to say, "Look, when I look over here,
I'm having an experience, say, that I would call an apple. And so I know that I'm having an experience. And when I close my eyes, my experience of
the apple stops. Now I'm just experiencing a gray field. And you want to tell me that, in fact, there's
a red apple that still exists even when I'm perceiving a gray field. Well, that's actually more than I know. All I know is that when I open my eyes, I'm
experiencing a red apple. And when I close my eyes, I'm not. It's an extra step. And it's a big jump to say that experience
of the red apple is actually true of a real red apple. And that red apple still exists even when
I'm stopping, when I don't have that experience. That's more than I know. I think it's far less problematic and less
going out there on a limb to just say I have my experiences. And I don't know what the objective reality
is that's out there." So physicalism is actually a stronger and
more problematic claim. It's saying that there is a reality that in
some way matches our experiences and continues. I'm just saying we have these experiences. So the "cogito, ergo sum" that "I think, therefore
I am," I think Descartes wasn't just talking about thinking in the normal sense of like
abstract cogitation, doing reason. I think he was talking about perceiving. And in that sense, I would say yes. I'm having experiences. I'm perceiving. My, thoughts my rationality, I'm experiencing
that as well. That's the starting point. And I would say I wouldn't go all the way
with Descartes. He says therefore I am. I don't know what the word "I" refers to there. Certainly conscious experiences seem to exist
from that. The "I" may be another construct, another
symbol that I make. So the symbol that I call Don, the I, may
not be absolutely necessary for the experience. So I don't know if I'd go all the way with
Descartes on that. But I would go part of the way and say, yes,
saying that there is a world of experience is going less out on a limb than saying that
there is a world of objective objects that resembles my world of experience, in addition
to my experiences. So in my own scientific investigations, I've
proposed a very controversial theory. And I've gotten lots of very pointed and sharp
criticism, some in print, some published, some in person. And what I found is I've learned a lot from
each of the criticisms. In many cases, they forced me to think about
an aspect of the theory that I had not thought about that way before. And in some cases, they put me into days of
doubt, where I was looking at that part of the theory, wondering about it, and then either
revising the theory or realizing, "oh, wow, the theory has resources that I didn't realize
to deal with that problem." And that's the power of a nice theory, by
the way, a mathematically precise theory. When you write down the theory, the theory
then becomes your teacher. It becomes smarter than you in a way. When Einstein wrote down the equations of
general relativity, he did not know that they entailed the existence of black holes. In that sense, the equations were smarter
than Einstein. Einstein didn't believe in black holes for
decades. The equations were very clear that they could
exist. Einstein said, no. And it turned out Einstein was wrong and the
equations were right. So it is very interesting. We do these theories because we can learn
from them. But when you have criticisms, it forces you
to-- it forced me to examine parts of my theory very, very carefully and ask, "Is this correct? Do I need to revise? Or are there the resources within the theory
to handle this objection?" And in many cases, I discovered new strengths
in the theory that I hadn't known before. And then I would use them later on as advertisements
for the theory: "You might say such and such is a problem, here's the answer." And that often, then-- a lot of my colleagues
now when I talk with them, I know the first 10 objections they're going to have because
I've been given those objections. I've thought about them. So I give them the objections. I give them the answers. And so it forces the discussion to a new level
which is good. All the easy objections, quote unquote "easy
objections" are taken out of the picture. Let's go deeper. Give me an objection I've not heard before
so I can learn something new. And that's sort of the attitude. Take the objections. Learn from them. It's always a growing experience. If you have the attitude "If someone is disagreeing
with me, no, I'm not going to listen to that," that's when you stop learning.
