An interesting history of Time and Space
In this chapter we will explore the how the different concept of time and space got evolved into today's science theories. Right from the Aristotle to Einstein to Stephen Hawking
Since the time of Aristotle to Newton to Einstein, the
history of time and space changed drastically, the possibilities of time being a
progression of motion entity to a physical entity as spacetime.
There
are many philosophies and theories on time and space, so here we are going to
discuss the summarized aspect of those theories to get the basic understanding
of time and space throughout history of philosophy and science. This
development in the philosophy of time and space is very crucial for us to
proceed further in this book.
Plato – 4th century BCE
The philosophers
from ancient Greece were among the first to the raise question on nature
of time. They discussed in detail, what exactly is time, whether it is linear or cyclical,
whether time is infinite or has a start and endpoint.
According to
Plato, present is a sort of ‘mean’
in the sense of being at once at starting point of the future and end point of
past. By this theory he means that there must always be ‘past’ and ‘future’ to
get ‘present’ (accordingly time is infinite). Plato identified time as the
measure of motion of the celestial bodies such as sun, moon and earth etc. So
if time is the measure of motion then the motion should also be infinite and
that motion must always have a past motion and future motion.
Aristotle
– 4th century BCE
Aristotle
was student of Plato and he was able to put the Plato’s time (the motion of
heavenly bodies) into more logical way. He explained time itself is nothing but
an attribute of movement and motion
of all other bodies. The motion can be galactic motion to the progression of
thoughts running in mind.
It
is a measure of continuous motion or it is change of number with respect to
before and after. Therefore time cannot exist without any motion itself but
certainly a kind of intelligence is required to measure it. Aristotle argued
that motion itself cannot be termed as time because it can be fast or slow
depending upon the body. According to him time
is infinite and this universe has
always existed and will always exist.
St.
Thomas Aquinas - 13th century AD
Now
the above explanation of time by Aristotle led to an argument that if time is the
measure of motion and it is also running in thoughts then there should be two
different times. Let’s suppose if someone measure the duration of a day in his
thoughts then he would still be able to roughly measure the duration of a day when
there will be no motion. This led to a further discussion of real time and
imaginary time.
Aquinas
tried to separate real time
dependent on motion and imaginary time
(independent of motion) depends on thought flow. But he was never able to establish
any relation between both of them.
René Descartes - early 17th
century AD
Regarded
as the first modern philosopher; according to him all the materials have a spatial extension property but not temporal sustenance. This means
that all the materials have some spatial dimensions such as length, breadth and
height. However regarding temporal sustenance, it says that past things are
just in our memories, they does not exist now, so all the material in past also
does not exist, as we can observe only present things. This was considered as a
problem as where the present things come from? Therefore he gave a solution to
this problem as that God creates present with all the material every moment. So
time is a kind of constant re-creation of God. This view was further developed
by Presentism theory later in 20th century.
Sir
Isaac Newton - 1687
Isaac
Barrow (Teacher of Isaac Newton) was first to reject the Aristotelian
definition of time that it is an attribute of motion. He completely changed the idea of time given by Aristotle that it depends
on the motion. He
argued that time is eternal and it was there before the universe and it will be
there after the universe.
Isaac Newton
wrote a book in the year 1687 “Philosophiæ
Naturalis Principia Mathematica”. He
further developed the theory of
Isaac Barrow and defined that Absolute time (ab. Time) runs constantly throughout the universe
independent of any motion, it is infinite in nature and it should be considered
as a dimension in which all the events occur. Similar theory for Absolute space (ab. Space) was given
that it is independent of anything and infinite in nature. It means that
absolute Time and Space exist before the universe and they will exist after the
universe without being affected by anything.
Gottfried
Leibniz - 1715-16
During
the years 1715-16, Leibniz had some correspondence with Newton
regarding the possibility of absolute time, he believed that time makes no
sense if there would be no object to interact with. In fact the event taking
place among the various objects are time themselves. If someone tries to think
of any moment in time, he would only be able to think of that event took place
in time. This philosophy is often called relational
time.
Immanuel
Kant
- 1781
In
his famous philosophical book “Critique of Pure Reason”, he described time and space as our
different notions to think. These notions makes us to experience things in a
sensible way, in this way time and space are not physical entities themselves.
Our mind is built to see Space as a three
dimensional geometry (length, breadth, height) and Time as linear mathematical line to understand the sequence,
duration and intervals of events.
Albert
Einstein – 1905 & 1916
Special
Theory of Relativity 1905 & General
Theory of Relativity 1916
Since
the publication of these theories, our understanding of time has been changed drastically,
the new notion of time as one dimension of Spacetime in
special relativity, and dynamically curved spacetime in
general relativity is much more prevalent now. The spacetime is a real entity
woven together and is considered as fabric of universe. At the time of bigbang
explosion, all the dimensions unwarped (including spacetime) and that was the
start of time and expansion of space.
Special
Theory of Relativity suggests that spacetime can
be explained as four dimensions in Euclidean geometry and universe is a four
dimensional spacetime block. Time can be referred as fourth dimension in
which universe is existing in past but we have already passed through that time
and universe is existing in future but we have not encountered it yet.
For example if we
moving on a road and passing few places behind hence they exist, but we have
passed through that location so we cannot see them now. Similarly few places
are yet to come on our way but we have not reached there to see them.
General
Theory of Relativity suggests that
spacetime fabric of universe is dynamically curved due to the presence of
matter. This curve causes time dilation depending
upon the gravity. There
are many practical significance of this theory; one of them is time dilation
effect on the clocks of International space station and GPS satellites compared
to the clocks on earth. Gravity is less compared to earth’s surface because International
space station (ISS) is approx. 408 kms and GPS satellites are generally more
than 20,000 kms above the earth surface.
First theory restricts to travel in spacetime
because nothing can travel more than speed of light. However second theory
suggests spacetime is bend due to gravity, hence allowing a person to travel in
spacetime through the bend (shortcut) spacetime and reaching to another
point in spacetime (past/future). These theories opened up the possibility
of time travel and it was one of the revolutionary ideas in the history of
time and space.
We will discuss these theories in details in the chapter
of spacetime and time travel.
Recent developments in 20th
century
The philosophy of
time in which the present is only real is called presentism, according
to presentism only present
objects and present observation can be said as exist. Past does not really exist
now and future is yet to become present to exist. This theory is inspired by
the philosophy given by Rene Descartes in 17th century.
The philosophy in
which past and future are equally real as present is called as Eternalism.
It refers all the past
and future events exist but we cannot observe them at present. The flow of time
is just an illusion of consciousness because in reality, time is always
everywhere. Eternalism is based on Einstein’s special theory of relativity up
to an extent.
A little
different approach can also be seen by few philosophers/scientists that past
exists but future does not exist because universe is a growing block. Future is
not yet born because it depends on the “present”.
Adolf Grünbaum - 1963
According
to Adolf Grünbaum, time is just a measure by the clock. We use time to measure
the sequence of the events and to measure the duration of those events.
In
his book “Philosophical Problems of Space
and Time”, he defined time as “time
applies the contemporary mathematical theory of continuity to physical
processes, it is a linear continuum of instants and is a distinguished
one-dimensional sub-space of four-dimensional spacetime”.
Stephen Hawking
- 1988
In addition to
Einstein theory of relativity (Spacetime), Stephen Hawking in his famous book “A Brief History of Time”, proposed imaginary time and said that point of singularity might not be the beginning of universe. This imaginary
time can help us to determine the state of singularity. According to him there
is an imaginary time also which can be explained as perpendicular line to the
real time line. It is very similar to the imaginary numbers in mathematics. As
we can see in real time, universe does have a start point in time known as bigbang
but that imaginary time has no boundary conditions very similar to North Pole
of earth with no boundaries.
Quantum theory of multiverse: Although
we are discussing the history of time and space but some parts of this theory
needs a special mention here to understand above Stephen Hawking’s imaginary time. According to this theory, in the
disconnected time lines there are potentially infinite number of parallel
universes, this creates the possibility of multidimensional time (including
imaginary timeline) in which other dimensions of time can sometimes interact or
merge into one but we may not have been able to observe it yet.
Source:
https://absolute-time-space.com
https://books.google.com/books?id=uQfhDwAAQBAJ
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