RNTIMRTTER AND ANTI-UNIVERSES 191
orientation. Hence, C-reversed and P-reversed universes are in principle possible.
Nobel laureate Richard Feynman posed an interesting question
about these universes. Suppose one day we make radio contact with
aliens on a distant planet but cannot see them. Can we explain to them
the difference between "left" and "right" by radio? he asked. If the laws
of physics allow for a P-reversed universe, then it should be impossible to convey these concepts.
Certain things, he reasoned, are easy to communicate, such as the
shape of our bodies and the number of our fingers, arms, and legs. We
can even explain to the aliens the laws of chemistry and biology. But if we
try to explain to them the concept of "left" and "right" (or "clockwise"
and "counterclockwise"), we would fail each time. We would never be
able to explain to them that our heart is on the left side of our body, in
which direction the Earth rotates, or the way a DNA molecule spirals.
So it came as a shock when C. N. Yang and T. D. Lee, both at Columbia University at the time, disproved this cherished theorem. By
examining the nature of subatomic particles they showed that the
Looking Glass, P-reversed universe cannot exist. One physicist, learning of this revolutionary result, said, "God must have made a mistake."
For this earthshaking result, called the "overthrow of parity," Yang and
Lee won the Nobel Prize in Physics in 1957.
To Feynman, this conclusion meant that if you are talking to aliens
on a radio, it is possible to set up an experiment that could enable you
to tell the difference between left- and right-handed universes by radio
alone. (For example, electrons emitted from radioactive cobalt-60 do
not spin in equal numbers in a clockwise or counterclockwise fashion,
but actually spin in a preferred direction, thereby breaking parity.)
Feynman then envisioned that a historic meeting finally takes
place between the aliens and humanity. We tell the aliens to stick out
their right hand when we first meet, and we will shake hands. If the
aliens actually stick out their right hand, then we know that we have
successfully communicated to them the concept of "left-right" and
"clockwise-counterclockwise."
orientation. Hence, C-reversed and P-reversed universes are in principle possible.
Nobel laureate Richard Feynman posed an interesting question
about these universes. Suppose one day we make radio contact with
aliens on a distant planet but cannot see them. Can we explain to them
the difference between "left" and "right" by radio? he asked. If the laws
of physics allow for a P-reversed universe, then it should be impossible to convey these concepts.
Certain things, he reasoned, are easy to communicate, such as the
shape of our bodies and the number of our fingers, arms, and legs. We
can even explain to the aliens the laws of chemistry and biology. But if we
try to explain to them the concept of "left" and "right" (or "clockwise"
and "counterclockwise"), we would fail each time. We would never be
able to explain to them that our heart is on the left side of our body, in
which direction the Earth rotates, or the way a DNA molecule spirals.
So it came as a shock when C. N. Yang and T. D. Lee, both at Columbia University at the time, disproved this cherished theorem. By
examining the nature of subatomic particles they showed that the
Looking Glass, P-reversed universe cannot exist. One physicist, learning of this revolutionary result, said, "God must have made a mistake."
For this earthshaking result, called the "overthrow of parity," Yang and
Lee won the Nobel Prize in Physics in 1957.
To Feynman, this conclusion meant that if you are talking to aliens
on a radio, it is possible to set up an experiment that could enable you
to tell the difference between left- and right-handed universes by radio
alone. (For example, electrons emitted from radioactive cobalt-60 do
not spin in equal numbers in a clockwise or counterclockwise fashion,
but actually spin in a preferred direction, thereby breaking parity.)
Feynman then envisioned that a historic meeting finally takes
place between the aliens and humanity. We tell the aliens to stick out
their right hand when we first meet, and we will shake hands. If the
aliens actually stick out their right hand, then we know that we have
successfully communicated to them the concept of "left-right" and
"clockwise-counterclockwise."