Who invented time?

Humans have long been aware of the cyclic nature of time in the
regular way that night follows day and the passing of the seasons.
We are also aware of the linear nature of time flowing from past to
future. Events that are now in our past will remain there never to
return but will recede further and further back.
Early in the history of mankind, it became necessary to divide
up a day into smaller units of time. Since the motion of the Sun
across the sky—long before it was known that this was due to the
Earth’s rotation—took (roughly) a fixed amount of time it is not
surprising that one of the earliest timekeepers was the sundial,
invented over five thousand years ago in ancient Egypt.
The big change to mechanical clocks came in the sixteenth
century when Galileo discovered that a pendulum of a given
length will always take the same time to complete one full swing.
But it was not until the mid-seventeenth century that the first
pendulum clock was built. This accuracy allowed for much more precise timekeeping than before, and hours were divided into
minutes and minutes into seconds. Nowadays, pendulum and
clockwork timekeepers are slowly being replaced by ever more
reliable ones. Adigital watch contains a tiny quartz crystal which
vibrates thousands of times a second when electricity is passed
through it. These vibrations are so regular you could set your
watch by them. (Sorry!) Can you imagine how difficult life would
be for us today with its appointments, schedules and deadlines if
the smallest unit of time we had was the hour?
Today the most accurate timekeepers in the world are atomic
clocks which can measure intervals of time with extraordinary
precision. They rely on the fact that certain atoms, when pumped
with energy, emit light at a precise frequency that is unique to that
type of atom. The most famous of these are caesium clocks which
now set the world standard for time.
While the ‘second’ is the standard unit of time, it is clearly
a human invention. If there is intelligent life elsewhere in the
Universe they would measure time using their own ‘currency’
which could well derive from the time it takes for their home
planet to complete one revolution or one orbit round their sun.
Until recently, our ‘second’ was defined as one sixtieth of a sixtieth
of a twenty-fourth of the time it takes the Earth to complete one
revolution around its axis (i.e. a day).
This was how one second was defined, but not any more.
These days, we are so obsessed with time that this definition is
no longer adequate. You see there is a problem. It turns out that
the Earth is slowing down. Not enough so as you’d notice, just
a second every few years, but this is enough to mean that, in our
high tech world, weneed anotherwayof measuring time. So, since
all atoms of caesium always radiate light that has a frequency of
9,192,631,770 cycles per second, scientists decided that they would
turn the statement around and say that one second is defined to
be the interval of time required for light from caesium atoms to
oscillate 9,192,631,770 times. This is called co-ordinated universal
time. The length of one day according to co-ordinated universal
time is therefore 24×60×60×9,192,631,770 vibrations of a caesium
atom. This has meant that every few years we must add in a leap second to take into account the slowing down of Earth’s spin so
that the new definition of time does not drift away from the old
one.
What about time as a concept in itself, rather than how we
humans measure it? Until Isaac Newton completed his work
on the laws of motion, time was considered to be the domain
of philosophy rather than science. However, Newton described
mathematically how objects move under the influence of forces,
and since all movement and change requires the notion of time for
it to make sense, he used what is known as a realist view of time.
This ‘common sense’ view is still with us today, despite the fact
that we know it is wrong as we shall see in the next chapter.
Newtonian time is absolute and relentless. He described it
as a medium which exists entirely on its own outside space and
independent of all processes that occur within space. In this view,
time is said to flow at a constant rate as though there were an
imaginary cosmic clock that marks off the seconds, hours and
years regardless of our, often, subjective feelings about its passage.
According to Newton, time is absolute, true and mathematical. We
have no influence over its rate of flow and cannot make it speed
up or slow down. We also know how unreliable we sometimes
are at judging intervals of time. Imagine you were to drop off
to sleep on a train journey that normally takes one hour and you
wake up feeling that only about ten minutes have elapsed. When
you check your watch you see that it is a whole hour later and this
is confirmed when you look out the window to see that you are
close to your destination. Of course it could be that your watch
malfunctioned and that the train speeded up considerably while
you slept for what really was only ten minutes, but this is highly
unlikely since we know how unreliable human subjective time
keeping can be. We all have this gut feeling that Newtonian time
is really ‘out there’ and flows at the same rate everywhere in the
Universe.
The world’s major religions all have something to say about
the nature of time. The monotheistic religions believe in an
omnipotent God who created the Universe and who exists outside
our space and time. He is omniscient in the sense that He knows not only the past but the future, and He is omnipresent in being in
all places at all times. An eternal God who therefore exists outside
our Universe does not conflict with the notion in modern physics
of the Universe (which includes space and time) coming into being
at the Big Bang.
What has been a major topic of debate among scientists,
philosophers and theologians, however, is the part God plays
in Newton’s deterministic clockwork universe. According to the
mechanistic view that Newton’s laws of motion give us of the
Universe, it is possible, in principle at least, to know the position
and velocity of every particle in the Universe. Given that each
particle will follow a well-defined trajectory and be under the
influence of forces that, again in principle, can be well defined,
it is possible to work out their positions at any future time and
hence to know the state of the Universe in the future. The future
is therefore mapped out and preordained.
Such a reductionist view of the world might seem to leave
no room for human free will. Since we too are made up of atoms
we are subject to the same laws of physics as any other object;
then presumably what we consider to be free will is no more
than mechanical processes in the brain obeying Newton’s laws
like everything else.
In practice of courseweare not even able to calculate the future
positions of a few balls on a pool table after they are scattered by
the cue ball, let alone the future positions of all the particles in the
Universe. But, according to this ‘deterministic’ view it should at
least be possible in principle to do so, provided we had a powerful
enough computer. Such a computer would have to run a program
of such stupendous complexity that it would contain many more
unknown variables than there are particles in the Universe. This is
because each particle needs (at least) six numbers to define its state
at any given time: the three that tell us where it is in 3D space and
three more to tell us how fast it is moving and in which direction.
To a good approximation, we would not need all this
information since an atom in a distant galaxy is not going to affect
things on Earth, but even if we restrict ourselves to the atoms on
Earth we are still dealing with a pretty impressive number. After all, there are more atoms in a single glass of water than there are
glasses of water in all the oceans of the world.
Nevertheless, I emphasize that, as long as the number of
particles we are dealing with is not infinite, then we can consider
an imaginary computer that could calculate the future position of
all the particles in the Universe if it knew what they were doing
now. And knowing the future implies knowing what all bodies
are going to do next. Such knowledge should extend to humans
too since we are all only made up of atoms.
Today physicists no longer adhere to this idea of a
deterministic universe. That way of thinking was overthrown
when the theory of quantum mechanics was developed in the
mid-1920s showing that, at its most fundamental level, nature is
random and unpredictable1. Despite this, many physicists believe
that the future is already out there, not because of the Newtonian
picture of a clockwork universe, but because it follows on from the
way the theory of relativity unifies time with space. This idea that
the future already exists goes beyond the Newtonian view, which
only claims that the future can be predicted.
As for the nature of time, not everyone was happy with
Newton’s realist view of an external absolute time, even before the
twentieth century’s two scientific revolutions in modern physics of
relativity theory and quantum mechanics. Scientists, philosophers
and theologians have long debated several issues which I will
discuss briefly here. They concern the three concepts of the origin
of time, the flow of time and the direction of time.