Quantum Mechanics 165
We believe that this effect is continually happening everywhere. We call this the
uctuation of the vacuum, since even in what we may think is a perfect vacuum,
particles appear and then, in a very short time interval, disappear again. How much
time are we talking about? Well, for the case of an electron and antielectron positron
“popping” into existence (we need both to conserve charge), the time interval until
they disappear is about 10
−21
s. At this point you have the right to be very skeptical—
how can anything be measured in such a short time interval? If we cannot measure
it, isn’t this science ction and not science?
Hopefully you have seen several times by now that many of our “measurements”
are not direct, but ...