-
Not Synced
Every day we face issues like climate change
-
Not Synced
or the safety of vaccines
-
Not Synced
where we have to answer questions whose answers
-
Not Synced
rely heavily on scientific information.
-
Not Synced
Scientists tell us that the world is warming.
-
Not Synced
Scientists tell us that vaccines are safe.
-
Not Synced
But how do we know if they are right?
-
Not Synced
Why should be believe the science?
-
Not Synced
The fact is, many of us actually don't believe the science.
-
Not Synced
Public opinion polls consistently show
-
Not Synced
that significant proportions of the American people
-
Not Synced
don't believe the climate is warming due to human activities,
-
Not Synced
don't think that there is evolution by natural selection,
-
Not Synced
and aren't persuaded by the safety of vaccines.
-
Not Synced
So why should we believe the science?
-
Not Synced
Well, scientists don't like talking about
science as a matter of belief.
-
Not Synced
In fact, they would contract science with faith
-
Not Synced
and they would say belief is the domain, faith.
-
Not Synced
And faith is a separate thing apart and distinct from science.
-
Not Synced
Indeed they would say religion is based on faith
-
Not Synced
or maybe the calculous of Pascal's wager.
-
Not Synced
Blaise Pascal was a 17th century mathematician
-
Not Synced
who tried to bring scientific reasoning to the question of
-
Not Synced
wether or not he should believe in God
-
Not Synced
and his wager went like this:
-
Not Synced
Well, if God doesn't exist but I decide to believe in him
-
Not Synced
nothing much is really lost.
-
Not Synced
Maybe a few hours on Sunday.
-
Not Synced
[Laughter]
-
Not Synced
But if he does exist and I don't believe in him,
-
Not Synced
then I'm in deep trouble.
-
Not Synced
And so Pascal said, we'd better believe in God.
-
Not Synced
Or as one of my college professors said,
-
Not Synced
"he clutched for the handmill of faith".
-
Not Synced
He made that leap of faith
-
Not Synced
leaving science and rationalism behind.
-
Not Synced
Now the fact is though, for most of us
-
Not Synced
most scientific claims are a leap of faith.
-
Not Synced
We can't really judge scientific claims for ourselves in most cases.
-
Not Synced
And indeed this is actually true for most scientists as well
-
Not Synced
outside of their own specialties.
-
Not Synced
So if you think about it, a geologist can't tell you
-
Not Synced
wether a vaccine is safe.
-
Not Synced
Most chemists are not experts in evolutionary theory.
-
Not Synced
A physicist cannot tell you, despite the claims of some of them,
-
Not Synced
wether or not tobacco causes cancer.
-
Not Synced
So, if even scientists themselves have to make a leap of faith
-
Not Synced
outside their own fields,
-
Not Synced
then why do they accept the claims of other scientists?
-
Not Synced
Why do they believe each other's claims?
-
Not Synced
And should we believe those claims?
-
Not Synced
So what I'd like to argue is yes, we should.
-
Not Synced
But not for the reason that most of us think.
-
Not Synced
Most of us were taught in school that the reason we should
-
Not Synced
believe in science is because of the scientific method.
-
Not Synced
We were taught that scientists follow a method
-
Not Synced
and that this method guarantees the truth of their claims.
-
Not Synced
The method that most of us were taught in school,
-
Not Synced
we can call it the text book method,
-
Not Synced
is the hypo-deductive method.
-
Not Synced
According to the standard model, the textbook model,
-
Not Synced
scientists develop hypotheses, they deduce the
-
Not Synced
consequences for those hypotheses,
-
Not Synced
and then they go out into the world and they say:
-
Not Synced
Are those consequences true?
-
Not Synced
Can we observe them taking place in the natural world?
-
Not Synced
And if they are true, then the scientists say:
-
Not Synced
Great, we know the hypothesis is correct.
-
Not Synced
So there are many famous examples in the history
-
Not Synced
of science of scientists doing exactly this.
-
Not Synced
One of the most famous examples
-
Not Synced
comes from the work of Albert Einstein.
-
Not Synced
When Einstein developed the theory of general relativity
-
Not Synced
one of the consequences of his theory
-
Not Synced
was that space time wasn't just an empty void
-
Not Synced
but that it actually had a fabric.
-
Not Synced
And that that fabric was bent
-
Not Synced
in the presence of massive objects like the sun.
-
Not Synced
So if this theory were true then it meant that light
-
Not Synced
as it passed the sun
-
Not Synced
should actually be bent around it.
-
Not Synced
That was a pretty startling prediction
-
Not Synced
and it took a few years before scientists
-
Not Synced
were able to test it.
-
Not Synced
But they did test it in 1919
-
Not Synced
and low and behold it turned out to be true.
-
Not Synced
Starlight actually does bend as it travels around the sun.
-
Not Synced
This was a huge confirmation of the theory.
-
Not Synced
It was considered proof of the truth of this radical new idea
-
Not Synced
and it was written up in many newspapers around the globe.
-
Not Synced
Now sometimes this theory or this model
-
Not Synced
is referred to as the deductive-nomological model.
-
Not Synced
Meaning those academics like to make things complicated.
[Laughter]
-
Not Synced
But also because in the ideal case it's about laws.
-
Not Synced
So nomological means having to do with laws.
-
Not Synced
And in the ideal case, the hypothesis isn't just an idea,
-
Not Synced
ideally it is a law of nature.
-
Not Synced
Why does it matter that it is a law of nature?
-
Not Synced
Because if it is a law, it can't be broken.
-
Not Synced
If it's a law then it will always be true
-
Not Synced
in all times and all places
-
Not Synced
no matter what the circumstances are.
-
Not Synced
And all of you know at least one example of a famous law.
-
Not Synced
Einstein's famous equation, E=MC2,
-
Not Synced
which tells us what the relationship is
-
Not Synced
between energy and mass.
-
Not Synced
And that relationship is true no matter what.
-
Not Synced
It turns out though that there are
several problems with this model.
-
Not Synced
The main problem is that it's wrong.
-
Not Synced
It's just not true. [Laughter]
-
Not Synced
And I'm going to talk about three reasons why it's wrong.
-
Not Synced
So the first reason is a logical reason,
-
Not Synced
it's the problem of the fallacy of affirming the consequent.
-
Not Synced
So that's another fancy academic way of saying
-
Not Synced
that false theories can make true predictions.
-
Not Synced
So just because the prediction comes true
-
Not Synced
doesn't actually logically prove that the theory is correct.
-
Not Synced
And I have a good example of that too,
again from the history of science.
-
Not Synced
This is a picture of the Ptolemaic universe
-
Not Synced
with the Earth at the center of the universe
-
Not Synced
and The Sun and the planets going around it.
-
Not Synced
The Ptolemaic model was believed
-
Not Synced
by many very smart people for many centuries.
-
Not Synced
Well why?
-
Not Synced
Well the answer is because it made
lots of predictions that came true.
-
Not Synced
The Ptolemaic system enabled astronomers
-
Not Synced
to make accurate predictions of the motions of the planet.
-
Not Synced
In fact more accurate predictions at first
-
Not Synced
than the Copernican theory which we now would say is true.
-
Not Synced
So that's one problem with the textbook model,
-
Not Synced
a second problem is a practical problem
-
Not Synced
and it's the problem of auxiliary hypotheses.
-
Not Synced
Auxiliary hypotheses are assumptions
-
Not Synced
that scientists are making,
-
Not Synced
that they may or may not even be aware that they're making.
-
Not Synced
So an important example of this comes from
-
Not Synced
comes from the Copernican model
-
Not Synced
which ultimately replaced the Ptolemaic system.
-
Not Synced
So when Nicolaus Copernicus said,
-
Not Synced
actually the Earth is not the center of the universe,
-
Not Synced
the sun is the center of the solar system,
-
Not Synced
the Earth moves around the sun.
-
Not Synced
Scientists said, well okay, Nicolaus, if that's true
-
Not Synced
we ought to be able to detect the motion
-
Not Synced
of the Earth around the sun.
-
Not Synced
And so this slide here illustrates a concept
-
Not Synced
known as stellar parallax.
-
Not Synced
And astronomers said, if the Earth is moving
-
Not Synced
and we look at a prominent star, let's say, Sirius.
-
Not Synced
Well I know I'm in Manhattan so you guys can't see the stars,
-
Not Synced
but imagine you're out in the country,
imagine you chose that rural life.
-
Not Synced
And we look at a star in December, we see that star
-
Not Synced
against the backdrop of distant stars.
-
Not Synced
If we now make the same observation six months later
-
Not Synced
when the Earth has moved to this position in June,
-
Not Synced
we look at that same star and we see it against a different backdrop.
-
Not Synced
That difference, that angular difference, is the stellar parallax.
-
Not Synced
So this is the prediction that the Copernican model makes,
-
Not Synced
astronomers looked for the stellar parallax
-
Not Synced
and they found nothing, nothing at all.
-
Not Synced
And many people argued that this proved
that the Copernican model was false.
-
Not Synced
So what happened?
-
Not Synced
Well in hindsight we can say that astronomers were making
-
Not Synced
two auxiliary hypotheses, both of which
-
Not Synced
we would now say were incorrect.
-
Not Synced
The first was an assumption about the size of the Earth's orbit.
-
Not Synced
Astronomers were assuming that the Earth's orbit was large
-
Not Synced
relative to the stars.
-
Not Synced
Today we would draw the picture more like this,
-
Not Synced
this comes from NASA,
-
Not Synced
and you see the Earth's orbit is actually quite small.
-
Not Synced
In fact, it's actually much smaller even than shown here.
-
Not Synced
The stellar parallax therefore,
-
Not Synced
is very small and actually very hard to detect.
-
Not Synced
And that leads to the second reason
-
Not Synced
why the prediction didn't work,
-
Not Synced
because scientists were also assuming
-
Not Synced
that the telescopes they had were sensitive enough
-
Not Synced
to detect the parallax.
-
Not Synced
And that turned out not to be true.
-
Not Synced
It wasn't until the 19th century that scientists were able to detect
-
Not Synced
the stellar parallax.
-
Not Synced
So, there's a third problem as well.
-
Not Synced
The third problem is simply a factual problem
-
Not Synced
that a lot of science doesn't fit the textbook model.
-
Not Synced
A lot of science isn't deductive at all, it's actually inductive.
-
Not Synced
And by that we mean that scientists don't necessarily
-
Not Synced
start with theories and hypotheses, often they just
-
Not Synced
start with observations of stuff going on in the world.
-
Not Synced
And the most famous example of that is one of the most
-
Not Synced
famous scientists who ever lived, Charles Darwin.
-
Not Synced
When Darwin went out as a young
man on the voyage of the Beagle,
-
Not Synced
he didn't have a hypothesis, he didn't have a theory.
-
Not Synced
He just knew that he wanted to have a career as a scientist
-
Not Synced
and he started to collect data.
-
Not Synced
Mainly he knew that he hated medicine
-
Not Synced
because the sight of blood made him sick so
-
Not Synced
he had to have an alternative career path.
-
Not Synced
So he started collecting data.
-
Not Synced
And he collected many things including his famous finches.
-
Not Synced
When he collected these finches he through them in a bag
-
Not Synced
and he had no idea what they meant.
-
Not Synced
Many years later back in London,
-
Not Synced
Darwin looked at his data again and began to develop
-
Not Synced
an explanation
-
Not Synced
and that explanation was the theory of natural selection.
-
Not Synced
Besides inductive science,
-
Not Synced
scientists also often participate in modeling.
Adrian Dobroiu
2:50 is the hypothetical deductive method. --> the hypothetico-deductive method.