the scientific method is essentially a
guideline for how science is done and
although what I'll be presenting sounds
like a series of steps, typically it is
not as linear or as straightforward as
this presentation is going to lead you
to believe, but we have to start
somewhere
and so where we're going to begin is
with the hypothesis. now sometimes you
will hear a hypothesis described as an
educated guess. that really isn't a good
definition of a hypothesis because a
hypothesis first and foremost must be
testable, and if you're just guessing
about something, that may or may not be
testable. so for science we need a way of
testing our hypothesis. as an example I
propose that if I were to look at other
stars (here's my star) that I hypothesize
that around that star I'm going to find
planets orbiting it
now that in and of itself can count as a
hypothesis, but I need to specify how
would I test this, and that's where the
prediction comes in. this is going to be
how a hypothesis is tested. if I can't
predict anything, I am not dealing with a
hypothesis. if I can't test anything I am
not dealing with a hypothesis. so my
hypothesis I'm going to predict I'm
going to take pictures of my star and on
my pictures I'm going to expect to see
planets. so this is how I'm going to test
the hypothesis. I'm going to go out, I'm
gonna take some nice pictures, and look
to see if I find any planets. so that's
my first step. now my next step then is
to actually test the hypothesis and
that's my experiment. now in astronomy
when we think of experiments we usually
think of something in a laboratory. not a
lot of astronomy can take place in a
laboratory, so astronomers do a lot of
their experiments either in an
observatory, where we do an observation,
or we make computer models, which aren't
nearly as sexy sounding as going out to
an observatory. but actually probably
about 80% of astronomy is done at a
computer creating models using the
laws of physics and seeing how those
laws apply in different situations. now
my particular hypothesis that there are
planets around other stars that I'm
going to be able to take pictures and
see those planets, that I can do in an
observatory. so I'm testing the
hypothesis to see if my prediction comes
true
because that's very powerful making a
prediction on a brand new idea and
seeing if that actually comes true or
not. so I go out, I take pictures of stars,
and I develop my pictures. and I look at
them, and I see a nice field of stars, and
I don't see a single planet. and the
reason why I won't see a planet is
because stars are very very bright, and
very very big. planets are very very
small and very very faint, and so if you
have something very tiny and very faint
next to something very big and very
bright and you take a picture, you're not
going to see the tiny faint thing under
most circumstances. so I am sad to report
that my prediction did not come true. and
so I need to go to my next step. so
because my prediction didn't come true I
am going to modify. now I have a choice: I
could either modify the hypothesis or I
could modify the experiment or I could
completely throw out my original idea. so
in this case I'm going to modify. now I
think my hypothesis was correct, but I
think my experiment was flawed. so
because my predictions did not come true
(I did not get pictures of planets) I'm
going to try something different.
in our own solar system here's our Sun
and for simplicity sake we're going to
pick just one planet. in this case I'm
gonna pick Jupiter because Jupiter is
the biggest, and we'll emphasize that
that is not drawn to scale. now we think
of the solar system as being the Sun
sitting still and the planets orbiting
around the Sun, but the fact of the
matter is although the Sun is big, and it
certainly is going to dominate all the
gravity that takes place, the planets
exert a gravitational pull on the Sun. so
the Sun is pulling on Jupiter.
Jupiter is also pulling on the Sun. so
the Sun is going to move in reaction to
that, and it's going to follow a very
small orbital path. now I've very vastly
exaggerated that drawing. in reality it's
gonna be more like the Sun is in one
spot and kind of, if this is the center
of the Sun, the center of the Sun does a
little wiggle in its place. so the Sun is
going to be kind of wobbling back and
forth in place. now visually that would
be difficult to see, but astronomers have
a technique that allows us to measure
motion - it's called Doppler shift. you can
see another tutorial if you want to
learn about that, but the idea is we can
measure when things are moving. so I'm
going to instead of looking to actually
take a picture, I'm going to look to
measure the motion
of my star and see if that works.
and it turns out that yes that does work.
and using that technique, I think it's
close to 2,000 planets around other
stars have been discovered. so my
experiment just worked. so you would
think okay you're done, but I'm not.
there's one more step. so the last thing
we need to do before we are certain that
we are right is called peer review. and
the idea of peer review is basically
make sure others get the same results
because I could have done something
wrong. and in fact one of the first
announcements of a planet going around
another star turned out they didn't take
into account the fact that here on
planet earth we are moving in orbit
around the Sun. so when we measure
motions, we need to subtract our own
motion. they forgot to do that,
so the motion that they thought they
were measuring of the star moving back
and forth was actually earth moving back
and forth. so in a sense, yes they did
discover a planet, but the planet they
discovered was Earth! so peer review is a
way of catching things like that. you
want them to test it to make sure they
get the same results. they want to look
for any mistakes you might have made. in my case, my peers did the same thing. they
got the same results. we're looking good.
so our last stage of our goal with
any idea in science is to become an
accepted theory, and in order for
something to be an accepted theory it
needs to repeatedly confirmed by
experiment. now my planet example is
fairly straightforward: either they're
planets or not. it's now widely accepted
that yes there are planets around other
stars because we have found so many and
the results consistently are confirmed
but this word "theory" in day to day
language is very different from how we
use the word "theory" in science. you'll
hear people say "oh that's just a theory"
well, in science, "just a theory" is kind of
an oxymoron, because a theory has gone
through all of this to get to that point.
so we put a big "don't do this" red bar
through that. if you want to say
something along those lines, what you
really should say is "that's just a
hypothesis" because that is your initial
idea before it has been tested. now if
it's not even testable, then I recommend
saying "that's just nuts." so a theory is a
very powerful thing. you don't want to
dismiss something that's called a theory.
gravity is a theory. now we don't say
it's been "proven," so we can't use that
word. because often you're dealing with
ideas that are so broad we can't prove
the whole realm of what it covers.
relativity comes to mind. the theory of
relativity is very broad, and it is still
being tested. there are two theories that
are very controversial: evolution and the
Big Bang. both of them have been
repeatedly confirmed by experiment.
that's why they are called theories. they
are very broad. we can never say that
either has been proven, but what we can
say is observational evidence
consistently upholds it
so when we look at all the observational
evidence, it is consistently upholding
the idea of evolution. observational
evidence consistently upholds the idea
of the Big Bang. observational evidence
consistently upholds the theory of
relativity. observational evidence
consistently upholds the theory of
gravity. all of those theories have
repeatedly been tested and confirmed. so
that's our scientific method. now even
accepted theories can be thrown out when
we find something that contradicts it.
for close to 2,000 years we believed
earth was the center of the universe. it
wasn't until the invention of the
telescope that we found that that was in
fact incorrect. so there was an accepted
theory. there were models in place that
made predictions that were consistently
confirmed, and yet it was wrong. so
science is being brave enough to say "I
was wrong and I need to change my ideas"
and that's a key element to the
scientific method - admitting when
something no longer works and changing
to new ideas. and that's why the
scientific method is so powerful because
it provides that framework that
incorporates into it the whole idea of
modifying and throwing out ideas that
don't work. that's how science works
