256
R. Barrett and P. P. Delsanto
have the right to say about what we call the past [24]. As we have seen in
Chap. 6, the Theory of Relativity has shown that the order of events in spacetime can depend on the state of motion of the observer. Simultaneity is not
something that two observers moving with respect to each other need agree
on. However, neither relativity nor classical physics allows the order of two
events to be interchanged when one is the direct cause of the other. This is
the heart of the paradox that Wheeler’s experiment reveals.
One explanation of this experiment, but not one that attracts many
adherents, is that we live in a deterministic universe, where everything is preordained. An example would be if the universe were a simulation, and we are
comprised of bits of software code. This idea was developed in the series of
Matrix movies [25] that were popular in the early years of this century. In
this case, there is nothing random about the choices an observer makes, even
if he or she is under the illusion there is. Our actions are already recorded in
the book of time, where past and future lose their meaning.
The explanation, now generally accepted is that it is only at the moment of
observation that the photon displays either a particle or wave nature. The act
of observation collapses the wave function. Before this the light is described
as a superposition of states, some where it passes through one slit, some where
it passes through the other, and some where it passes through both. Passage
through the slits is not in itself an act of observation, and does not result in
collapse of the wave function.
When the observation is finally made, either at the photographic plate or at
one of the telescopes, one cannot infer from this what state the photon was in
at an earlier time, for then it was in a superposition of all possible states. The
phenomenon of collapse of the wave function is one of the most contentious
aspects of QM. Some maintain that reality does not exist until we measure it,
and that if everybody were to shut their eyes at once, the moon would vanish
from existence. This is an extreme interpretation. It is more appropriate to
say that quanta exist as unique objects which display both particle and wave
characteristics, and that these different characteristics are brought to the fore
in different experiments.
Experimenters have performed Wheeler’s experiment over very large
distances and for increasingly massive particles. In 2017 a team of Italian
physicists at the Italian Space Agency’s Matera Laser Ranging Observatory
(MLRO) split light on the ground and sent the two beams to a satellite
3500 km away. There they carried out the “delayed choice” part of the experiment, with results that showed the quanta had maintained their wave/particle
duality over the length of the journey [26].
R. Barrett and P. P. Delsanto
have the right to say about what we call the past [24]. As we have seen in
Chap. 6, the Theory of Relativity has shown that the order of events in spacetime can depend on the state of motion of the observer. Simultaneity is not
something that two observers moving with respect to each other need agree
on. However, neither relativity nor classical physics allows the order of two
events to be interchanged when one is the direct cause of the other. This is
the heart of the paradox that Wheeler’s experiment reveals.
One explanation of this experiment, but not one that attracts many
adherents, is that we live in a deterministic universe, where everything is preordained. An example would be if the universe were a simulation, and we are
comprised of bits of software code. This idea was developed in the series of
Matrix movies [25] that were popular in the early years of this century. In
this case, there is nothing random about the choices an observer makes, even
if he or she is under the illusion there is. Our actions are already recorded in
the book of time, where past and future lose their meaning.
The explanation, now generally accepted is that it is only at the moment of
observation that the photon displays either a particle or wave nature. The act
of observation collapses the wave function. Before this the light is described
as a superposition of states, some where it passes through one slit, some where
it passes through the other, and some where it passes through both. Passage
through the slits is not in itself an act of observation, and does not result in
collapse of the wave function.
When the observation is finally made, either at the photographic plate or at
one of the telescopes, one cannot infer from this what state the photon was in
at an earlier time, for then it was in a superposition of all possible states. The
phenomenon of collapse of the wave function is one of the most contentious
aspects of QM. Some maintain that reality does not exist until we measure it,
and that if everybody were to shut their eyes at once, the moon would vanish
from existence. This is an extreme interpretation. It is more appropriate to
say that quanta exist as unique objects which display both particle and wave
characteristics, and that these different characteristics are brought to the fore
in different experiments.
Experimenters have performed Wheeler’s experiment over very large
distances and for increasingly massive particles. In 2017 a team of Italian
physicists at the Italian Space Agency’s Matera Laser Ranging Observatory
(MLRO) split light on the ground and sent the two beams to a satellite
3500 km away. There they carried out the “delayed choice” part of the experiment, with results that showed the quanta had maintained their wave/particle
duality over the length of the journey [26].