8
R. Barrett and P. P. Delsanto
to exist, and to do so in a scientific way, i.e. using only our own rationality.
From its very beginning, our task is formidable since, as we shall now see,
even the notion itself of existence is not totally clear.
At first a debate about the meaning of existence might appear futile, but
Segismundo’s story warns us that it is not. Our dreams are sometimes so vivid
that only when we wake do we realize that they were but dreams. Actors in
a movie or theatrical play must immerse themselves totally in their characters, else they lose authenticity. For the duration of the performance, they
give up their own personalities, and cry or laugh, suffer or rejoice as the characters they represent would presumably do, in order to interpret their roles
convincingly. A suspension of disbelief by the audience is avidly sought by
the director, and can be quickly shattered by one out-of-character line or
anachronistic prop.
Also, reality may at times be so confusing, that we can hardly believe our
eyes and recognize what is indeed real. The ancient Greeks remarked, already
2500 years ago, that if we look at a stick standing slanted and half immersed
in water, we see it as if it were broken at the water surface. In this case, the
illusion, illustrated in Fig. 1.1, is caused by a well-known physical effect, i.e.
the refraction 3 of light rays at the water’s surface. In other cases, such as those
in Figs. 1.2, 1.3 and 1.4, it is our brain that constructs the illusion.
In Fig. 1.2, the tone of the red colour appears to be darker in the righthand half of the diagram. This is known as the Bezold Effect, and is produced
by the different coloured backgrounds in the two halves.
Figure 1.3 displays an image of a blivet, or “devil’s fork”. The image
represents a physical impossibility, as such a shape cannot possibly exist.
This type of fantastical optical illusion has been developed into an art form
by M.C. Escher in a series of beautifully detailed drawings, e.g. Ascending and
Descending (1960) [2].
Other optical illusions can be produced simply by the image being taken
from an unusual viewpoint. Figure 1.4 is a photograph of the so-called “super
moon” taken at Bondi, Sydney, on November 15th, 2016. 4 The apparent
large size of the moon is a consequence of the photograph being shot with
a 600 mm lens. The moon-watchers in the foreground are actually located
hundreds of metres from the camera. When we look at the image, our brains
assume the foreground is much closer than this, and overestimate the size of
the moon accordingly.
3 Refraction is the bending of a ray (or wave) of light, heat or sound as it passes obliquely through
the interface between one medium and another or through a medium of varying density.
4 The moon was actually at its closest to the earth in 68 years on November 14th, but overcast
conditions in Sydney prevented it being photographed on that day.
R. Barrett and P. P. Delsanto
to exist, and to do so in a scientific way, i.e. using only our own rationality.
From its very beginning, our task is formidable since, as we shall now see,
even the notion itself of existence is not totally clear.
At first a debate about the meaning of existence might appear futile, but
Segismundo’s story warns us that it is not. Our dreams are sometimes so vivid
that only when we wake do we realize that they were but dreams. Actors in
a movie or theatrical play must immerse themselves totally in their characters, else they lose authenticity. For the duration of the performance, they
give up their own personalities, and cry or laugh, suffer or rejoice as the characters they represent would presumably do, in order to interpret their roles
convincingly. A suspension of disbelief by the audience is avidly sought by
the director, and can be quickly shattered by one out-of-character line or
anachronistic prop.
Also, reality may at times be so confusing, that we can hardly believe our
eyes and recognize what is indeed real. The ancient Greeks remarked, already
2500 years ago, that if we look at a stick standing slanted and half immersed
in water, we see it as if it were broken at the water surface. In this case, the
illusion, illustrated in Fig. 1.1, is caused by a well-known physical effect, i.e.
the refraction 3 of light rays at the water’s surface. In other cases, such as those
in Figs. 1.2, 1.3 and 1.4, it is our brain that constructs the illusion.
In Fig. 1.2, the tone of the red colour appears to be darker in the righthand half of the diagram. This is known as the Bezold Effect, and is produced
by the different coloured backgrounds in the two halves.
Figure 1.3 displays an image of a blivet, or “devil’s fork”. The image
represents a physical impossibility, as such a shape cannot possibly exist.
This type of fantastical optical illusion has been developed into an art form
by M.C. Escher in a series of beautifully detailed drawings, e.g. Ascending and
Descending (1960) [2].
Other optical illusions can be produced simply by the image being taken
from an unusual viewpoint. Figure 1.4 is a photograph of the so-called “super
moon” taken at Bondi, Sydney, on November 15th, 2016. 4 The apparent
large size of the moon is a consequence of the photograph being shot with
a 600 mm lens. The moon-watchers in the foreground are actually located
hundreds of metres from the camera. When we look at the image, our brains
assume the foreground is much closer than this, and overestimate the size of
the moon accordingly.
3 Refraction is the bending of a ray (or wave) of light, heat or sound as it passes obliquely through
the interface between one medium and another or through a medium of varying density.
4 The moon was actually at its closest to the earth in 68 years on November 14th, but overcast
conditions in Sydney prevented it being photographed on that day.