Therefore, we have to have a warning
against believing these descriptions too
strongly. We only use the statement that
an atom is round as a way of explaining
something about its symmetry. I want to
issue my warning by doing a measurement
I would like to be able to measure my
average diameter. We'll use
this.
I'd like to measure my average diameter
like this - there it is, there's my tape
this around me - take it off and what do we
divide by to get the diameter?
Audience:Half
EM Rogers: Oh no, rough work, this is a rough game,
divided by how much? Three! Three's near
enough
there's my diameter, like that. But is it
always so? It depends on how I make the
measurement. I'm going to show you. You
never know what you'll find in a
cupboard in the Royal Institution. We can
do the same thing here, we can do that and
get the same diameter, but instead if I
use a cheese wire,
then the diameter is extremely small and
the diameter is extremely small, it's
that much for a cheese wire, just
something like that. It depends on how
you make a measurement, so now we want to
give you another warning, please. We want
to show you how you view something and
attach it too easily to what you already
know. We have a house that's coming in,
it's a large room. As soon as they're
ready the camera will look into the room,
you look across at the far end from
where the camera is, there are two
windows and you will see them - oh look!
There's something there in one window.
Look, there's a doll in the window there.
Can you see the doll? Now move the doll
please, move the doll to the other window.
Is it the same doll? Move it back, move it
back again. We'll ask the young lady to
have a look herself,
look through the window yourself - and the
other window. Well how can she grow and
shrink like that? It's amazing that that
can happen, and yet to you and me it's a
perfectly respectable room. Camera, can
you see the floor at all? You see there
you are, a beautiful floor as well. Now
let us open the room, open the front of
the room and see the truth. There isn't
any truth for atoms, I don't know what
that means, but in this big model you can
see what really is there, and you might
be quite surprised. This is because when
you see something new,
any adult any growing child attaches the
new thing to old information - just look
at that, can you see it? The camera is
going to look.
Oh we need to climb in, try and walk
about in it, never mind if you slip up, look
at the ceiling, point to the ceiling, low
ceiling, high ceiling, look at the floor,
look at the windows as they really are,
and all that was because you looked through a peephole
which deceived you. There's the truth, but
I don't know how to do the truth for
atoms, I just warn you. If we say an atom
is a round ball, we will never know if it
is a round ball or not, it's just our
method of describing it. Thank you.
 
[Applause]
you
