Can you trust your senses?
WHAT DO YOU KNOW?
AN INTRODUCTION TO
SCEPTICISM
• Today you are going to learn something
that will shock and surprise you. You will
find it very difficult to believe. Most of you,
in fact, will not believe it.
• Nevertheless it is true.
• Please spend a few minutes writing your
answers to the following questions
• Where are you right now?
• How do you know?
• What is the year?
• How do you know?
• Who are you?
• How do you know?
• In fact, everything you think you know is a
lie
THE TRUTH IS…..
• Your senses have been lying to you
• In fact, you are a brain floating in a vat of
fluid in a laboratory. The year is 3577
• Your brain is wired to a computer that is
controlled by scientists
• The computer sends electrical signals to
your brain to make it believe it is receiving
information from its senses
• All of the world around you, all of the
people and all of your memories are in fact
part of a computer programme.
DON’T BELIEVE ME?
• What will you do to try and prove me
wrong?
• I can understand that, it would be much
too difficult for you to accept the truth.
• I am one of the scientists in the laboratory
and I think what is being done to you is
cruel. I am trying to help you see your real
situation.
• That is why I’ve hacked into the
programme to show you this slide show.
• I am going to show you a few things to try
and prove to you that what you think is
real, is in fact an illusion.
• Choose one of the cards below. Keep
your choice secret. Do not tell anyone
else.
• Now I want you to visualise your card in
your mind as hard as you can for a
moment or two. Try and really see it as if
it were still in front of you
• To help me, I want you to SILENTLY say
the name of your card in your mind three
times
• Give me a minute…..
• I am accessing the programme that
controls your thoughts
• There, I have removed the card you were
thinking of from the deck
STILL DON’T BELIEVE ME?
• Can you remember any dream that you
had recently?
• When you were having the dream, did you
know that you were dreaming? Or did the
dream seem real to you at the time?
• Most of the time, when we are dreaming
we usually totally believe that we are
awake
• Once we wake up, our dreams seem
crazy, but at the time they feel real
• So how can you be sure that what seems
like reality now is not in fact a dream?
YOUR SENSES LIE TO YOU ALL
THE TIME
• All of what you believe that you know
about the world comes from the evidence
of your senses – what you see, smell,
touch, taste and hear.
• But your senses lie to you all the time.
• Let me show you. Look at the next picture
and tell me which circles are moving…
• In fact, none of the circles are moving, it is
a still image.
• Can you see the spiral in this next picture?
• In reality, there is no spiral, just a series of
circles
• This next one probably feels as if its
coming out of the screen at you
• Which letters are moving on this picture?
• Which way are the rollers moving?
• So you see, you can’t always trust what
your eyes tell you
• The same is true of your other senses.
They sometimes lie to you as well.
• So how do you know that your senses
aren’t lying to your right now? Can you
really trust your eyes when they tell you
that you are in a classroom in a school in
Burnham?
• How do you know that your senses
haven’t been lying to you your whole life?
THE WORLD IS NOT AS IT
SEEMS
• As you know, light travels very quickly.
But it still takes time.
• Because of this, when you look at the
stars at night, you are not seeing the stars
as they are, you are seeing the stars as
they were. You are seeing a copy of the
stars, almost like a film. Some of the stars
that you can see in the night sky are
probably no longer there
You are effectively seeing the
ghosts of stars
• The sun that you see is actually the sun as
it was around eight minutes ago. For all
you know, the sun might no longer exist
• In the same way, the screen that you
believe that you are looking at now is the
screen as it was a fraction of a second
ago. Not only does the light take time to
reach your eye, but it also takes time for
your brain to process that information.
So, would you take the red
pill or the blue pill?
Would you want to know the
reality of the matrix?
Scepticism
• This lesson will be successful if you can
– explain philosophical scepticism
– Explain Descartes Cogito
– Evaluate the strengths and weaknesses of the
Cogito
Big Question!
• The point of view we’ve been talking about
today is sometimes called ‘Global
Scepticism’. This means that you doubt
that ANYTHING you think you know is
really true.
• What effect could global scepticism have
on your life? Think Pair Share
Rene Descartes
• Was a 16th Century
Philosopher, who used
scepticism to establish
the foundation of his
beliefs.
• He used 3 stages of
doubt to establish what
he could be certain of.
Sometimes we can be deceived
• Is this pencil bent?
Dreaming
• http://www.youtube.com/watch?v=66TuSJ
o4dZM
• How can we know we are not always
dreaming?
There is a demon who is always
deceiving us
• So Descartes came up with the idea that
the only thing we can be sure of is that
– I think, therefore I am.
– What does this mean?
Scepticism
• This lesson will be successful if you can
– explain philosophical scepticism
– Explain Descartes Cogito
– Evaluate the strengths and weaknesses of the
Cogito