Krish Ramkumar
Arrow of time
Is the arrow of time a consequence
of the 2nd law of thermodynamics or the law is due to the defined
arrow of time? This question is a little hazy to me as the entity “time” is
undefined in the law. If the law does in fact define a particular arrow of time
in the universe, we need to define “time”.
According to the 2nd law
of thermodynamics, entropy (randomness) increases with time and the arrow of
time points in the direction of higher entropy. If the arrow of time in the
present universe is in the direction of higher entropy (unordered state), then
the formation of stars, star clusters and galaxies seem to be a paradox, if we
consider stars as closed systems (since the law is valid only in closed systems).
The law does not lay any restrictions on how one must choose a “system”. In
that case I could choose a star as a closed system and that would be an anomaly
from the 2nd law. Maybe these anomalies are small fluctuations in
the ever expanding universe which are compensated by very high entropy at
various other parts of the universe. But the important question is even if the
net entropy of the universe is increasing, why are stars formed in the first
place? If randomness were to increase with time in the universe, even the
formation of molecules and atoms at the quantum level seem like a contradiction
to the 2nd law. Energy dissipated by a closed system is probably the
answer to this paradox. Perhaps energy dissipated into the universe by a star
(The star could be considered as the closed system) during its formation is so
high that this increases the entropy in the universe and overshadows the
increase in order (lower entropy) within a star. In my understanding, the same
reason could be applied to star clusters as well. To me this question is still hazy. If the
universe did have some kind of innate property of moving towards randomness
(higher entropy), this brings me back to my previous question- why are stars
formed in the first place?
The arrow of time could be defined
as the direction in which the entity called “time” progresses. The arrow of
time of our universe points in the direction of increasing randomness as stated
earlier. This also means that “future” points towards expansion. This is a way
of understanding what happened before, what we call the past. The arrow of time
has most certainly enabled man to trace back to his celestial ancestors. After
all we are all star dust, remains of the Big Bang.
What if the universe were to
contract, or go in the direction of the big crunch? The arrow of time then is
reversed for the inhabitants in that universe. This simply means that what we
call as “future” would be their past. This illustrates that the contracting
universe is moving in the direction of lower entropy or high order. Perhaps the
human brain is developed only to realize and perceive the arrow of time we are
experiencing, which points towards higher entropy. We are probably trained to analyze
only those phenomena that are directed toward an unordered state. Will man be
able to perceive the universe if the arrow of time were different than what it
is in our present universe? Will man be able to understand the universe if the
universe were moving toward a state of lower order? Imaginably, our senses that
have enabled us to understand the universe so far become an obstacle in
understanding the universe after a certain point.
What happens to the arrow of time
in the vicinity of a highly ordered structure? Is this how gravity is related
to time at the most fundamental level? Possibly! Highly ordered structures have
lower entropy. These objects also curve the space-time around them depending
upon how massive they are. The curvature in space-time is considered gravity
and this entity called gravity drags time (Einstein’s General -Relativity). In
other words, if I were to go close to a black hole, just close enough that I’m
in the orbit but not too close that I might get pulled into the singularity and
then go around the orbit for a while and return back to earth, I would have
actually travelled to the future. Time in my perspective slowed down when I was
orbiting around the black hole (assumption is that a black is a highly ordered
system as the density is concentrated at a single point). Does this mean highly
ordered systems typically drag time? What I seem to infer from all this is that
the arrow of time in the vicinity of a highly ordered system is not the same as
what it is elsewhere in the universe.
References-
Brief History of time - Stephen Hawking.
Einstein’s Universe- Nigel Calder
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