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Today I want to talk about an issue that must have occurred to everyone who spent some time
thinking about physics. Which is that the idea of free will is both incompatible with
the laws of nature and entirely meaningless. I know that a lot of people just do not want
to believe this. But I think you are here to hear what the science says. So, I will
tell you what the science says. In this video I first explain why free will does not exist,
indeed makes no sense, and then tell you why there are better things to worry about.
I want to say ahead that there is much discussion about free will in neurology, where the question
is whether we subconsciously make decisions before we become consciously aware of having
made one. I am not a neurologist, so this is not what I am concerned with here. I will
be talking about free will as the idea that in this present moment, several futures are
possible, and your “free will” plays a role for selecting which one of those possible
futures becomes reality. This, I think, is how most of us intuitively think of free will
because it agrees with our experience of how the world seems to works. It is not how some
philosophers have defined free will, and I will get to this later. But first, let me
tell you what’s wrong with this intuitive idea that we can somehow select among possible
Last week, I explained what differential equations are, and that all laws of nature which we
currently know work with those differential equations. These laws have the common property
that if you have an initial condition at one moment in time, for example the exact details
of the particles in your brain and all your brain’s inputs, then you can calculate what
happens at any other moment in time from those initial conditions. This means in a nutshell
that the whole story of the universe in every single detail was determined already at the
big bang. We are just watching it play out.
These deterministic laws of nature apply to you and your brain because you are made of
particles, and what happens with you is a consequence of what happens with those particles.
A lot of people seem to think this is a philosophical position. They call it “materialism” or
“reductionism” and think that giving it a name that ends on –ism is an excuse to
not believe it. Well, of course you can insist to just not believe reductionism is correct.
But this is denying scientific evidence. We do not guess, we know that brains are made
of particles. And we do not guess, we know, that we can derive from the laws for the constituents
what the whole object does. If you make a claim to the contrary, you are contradicting
well-established science. I can’t prevent you from denying scientific evidence, but
I can tell you that this way you will never understand how the universe really works.
So, the trouble with free will is that according to the laws of nature that we know describe
humans on the fundamental level, the future is determined by the present. That the system
– in this case, your brain – might be partly chaotic does not make a difference
for this conclusion, because chaos is still deterministic. Chaos makes predictions difficult,
but the future still follows from the initial condition.
What about quantum mechanics? In quantum mechanics some events are truly random and cannot be
predicted. Does this mean that quantum mechanics is where you can find free will? Sorry, but
no, this makes no sense. These random events in quantum mechanics are not influenced by
you, regardless of exactly what you mean by “you”, because they are not influenced
by anything. That’s the whole point of saying they are fundamentally random. Nothing determines
their outcome. There is no “will” in this. Not yours and not anybody else’s.
Taken together we therefore have determinism with the occasional, random quantum jump,
and no combination of these two types of laws allows for anything resembling this intuitive
idea that we can somehow choose which possible future becomes real. The reason this idea
of free will turns out to be incompatible with the laws of nature is that it never made
sense in the first place. You see, that thing you call “free will” should in some sense
allow you to choose what you want. But then it’s either determined by what you want,
in which case it’s not free, or it’s not determined, in which case it’s not a will.
Now, some have tried to define free will by the “ability to have done otherwise”.
But that’s just empty words. If you did one thing, there is no evidence you could
have done something else because, well, you didn’t. Really there is always only your
fantasy of having done otherwise.
In summary, the idea that we have a free will which gives us the possibility to select among
different futures is both incompatible with the laws of nature and logically incoherent.
I should add here that it’s not like I am saying something new. Look at the writing
of any philosopher who understand physics, and they will acknowledge this.
But some philosophers insist they want to have something they can call free will, and
have therefore tried to redefine it. For example, you may speak of free will if no one was in
practice able to predict what you would do. This is certainly presently the case, that
most human behavior is unpredictable, though I can predict that some people who didn’t
actually watch this video will leave a comment saying they had no other choice than leaving
their comment and think they are terribly original.
So, yeah, if you want you can redefine “free will” to mean “no one was able to predict
your decision.” But of course your decision was still determined or random regardless
of whether someone predicted it. Others have tried to argue that free will means some of
your decisions are dominated by processes internal to your brain and not by external
influences. But of course your decision was still determined or random, regardless of
whether it was dominated by internal or external influences. I find it silly to speak of “free
will” in these cases.
I also find it unenlightening to have an argument about the use of words. If you want to define
free will in such a way that it is still consistent with the laws of nature, that is fine by me,
though I will continue to complain that’s just verbal acrobatics. In any case, regardless
of how you want to define the word, we still cannot select among several possible futures.
This idea makes absolutely no sense if you know anything about physics.
What is really going on if you are making a decision is that your brain is running a
calculation, and while it is doing that, you do not know what the outcome of the calculation
will be. Because if you did, you wouldn’t have to do the calculation. So, the impression
of free will comes from our self-awareness, that we think about what to do, combined with
our inability to predict the result of that thinking before we’re done.
I feel like I must add here a word about the claim that human behavior is unpredictable
because if someone told you that they predicted you’d do one thing, you could decide to
do something else. This is a rubbish argument because it has nothing to do with human behavior,
it comes from interfering with the system you are making predictions for. It is easy
to see that this argument is nonsense because you can make the same claim about very simple
computer codes. Suppose you have a computer that evaluates
whether an equation has a real-valued root. The answer is yes or no. You can predict the
answer. But now you can change the algorithm so that if you input the correct answer, the
code will output the exact opposite answer, ie “yes” if you predicted “no” and
“no” if you predicted “yes”. As a consequence, your prediction will never be
correct. Clearly, this has nothing to do with free will but with the fact that the system
you make a prediction for gets input which the prediction didn’t account for. There’s
nothing interesting going on in this argument.
Another objection that I’ve heard is that I should not say free will does not exist
because that would erode people’s moral behavior. The concern is, you see, that if
people knew free will does not exist, then they would think it doesn’t matter what
they do. This is of course nonsense. If you act in ways that harm other people, then these
other people will take steps to prevent that from happening again. This has nothing to
do with free will. We are all just running software that is trying to optimize our well-being.
If you caused harm, you are responsible, not because you had “free will” but because
you embody the problem and locking you up will solve it.
There have been a few research studies that supposedly showed a relation between priming
participants to not believe in free will and them behaving immorally. The problem with
these studies, if you look at how they were set up, is that people were not primed to
not believe in free will. They were primed to think fatalistically. In some cases, for
example, they were being suggested that their genes determine their future, which, needless
to say, is only partly correct, regardless of whether you believe in free will. And some
more nuanced recent studies have actually shown the opposite. A 2017 study on free will
and moral behavior concluded “we observed that disbelief in free will had a positive
impact on the morality of decisions toward others”. Please check the information below
the video for a reference.
So I hope I have convinced you that free will is nonsense, and that the idea deserves going
into the rubbish bin. The reason this has not happened yet, I think, is that people
find it difficult to think of themselves in any other way than making decisions drawing
on this non-existent “free will.” So what can you do? You don’t need to do anything.
Just because free will is an illusion does not mean you are not allowed to use it as
a thinking aid. If you lived a happy life so far using your imagined free will, by all
means, please keep on doing so.
If it causes you cognitive dissonance to acknowledge you believe in something that doesn’t exist,
I suggest that you think of your life as a story which has not yet been told. You are
equipped with a thinking apparatus that you use to collect information and act on what
you have learned from this. The result of that thinking is determined, but you still
have to do the thinking. That’s your task. That’s why you are here. I am curious to
see what will come out of your thinking, and you should be curious about it too.
Why am I telling you this? Because I think that people who do not understand that free
will is an illusion underestimate how much their decisions are influenced by the information
they are exposed to. After watching this video, I hope, some of you will realize that to make
the best of your thinking apparatus, you need to understand how it works, and pay more attention
to cognitive biases and logical fallacies.
Thanks for watching, see you next week.