Salvador
Dali’s painting, “The Persistence of Memory,” is a splendid illustration of a
deep mystery — the concept we call time. This surreal painting shows ants
devouring a clock and time melting into oblivion. Is time an illusion that
melts away as depicted in the painting or a fundamental reality that weaves the
fabric of the cosmos with space?
Perhaps the mystery of time holds the key to the
ultimate truth that humanity is seeking. It remains to be seen whether time
will persist forever or fade way as in Dali’s paintings. In the fundamental
realm, time may be the result of some missing knowledge about reality rather
than a feature of reality.
Throughout history, humans have been intrigued
by the nature of time. Philosophers like Plato, who contemplated time as
immortal, and Newton, who elevated time as eternal, might not accept the death
of time. However, the last century witnessed the descent of time from immortal
to mortal through Albert Einstein’s equations. Now, the descendants of Einstein
are trying to annihilate time, which had been wounded in the revolution
unleashed by the theory of relativity.
Theoretical physicist and cosmologist Carlo
Rovelli points out: “We never really see time. We say we measure time with
clocks, but we see only the hands of the clocks, not time itself. And the hands
of a clock are a physical variable like any other. So in a sense we cheat,
because what we really observe are physical variables as a function of other
physical variables, but we represent that as if everything is evolving in
time.”
Some theoretical physicists argue that
information about the measurement of time could be replaced with correlated observations
in space. “To give an analogy,” Rovelli says, “I can tell you that I drove from
Boston to Los Angeles, but I passed first through Chicago and later through
Denver. Here I am specifying things in time. But I could also tell you that I
drove from Boston to LA along the road marked in this map.”
In other words, the dynamics of the universe are
not progressing as evolution in time — the currently held notion in science —
but as a network of correlated variables. Time emerges as an effect of the
actions of correlated variables. This is similar to saying that temperature
results from the interaction of a large number of molecules. Similarly, time is
the manifestation of the interaction of some variables, rather than a
fundamental quality of the universe.
In classical physics, time is a river flowing
simply in the forward direction. The observer or external forces like gravity
have no impact on the flow of time. Everything we know surfaced, survived and
departed during the course of this river, such as men and women, science and
music, thoughts and feelings. Nothing could endure but time. Like an arrow shot
by the Big Bang, time traveled (existed) for about 13.7 billion years along
with its anomalous twin “space.”
Einstein’s laws rebuked such
an absolute status for time and declared that time is relative as much as space
is and they together make the fabric of the cosmos.
The
general theory of relativity demonstrated that clocks in a stronger
gravitational field tick at a slower rate while the special theory of
relativity argued that clocks moving at high speeds will appear to tick slower
than non-moving ones. As a modern day example, atomic clocks on board GPS
satellites move faster by about 45,900 nanoseconds (which is one-billionth of a
second) a day because they are in a weaker gravitational field as they are at a
higher altitude than atomic clocks on the earth’s surface. Similarly, GPS
clocks run slower by about 7,200 nanoseconds a day, as predicted by special
theory of relativity, owing to the fact that the satellites have orbital speeds
of about 3.9 km/second in a frame centered on the Earth. To offset these time
variations the satellite clocks are reset before launch to compensate for these
predicted effects. This is the consequence of Einstein’s theory, something that
was unimaginable for the scientific community when Einstein predicted it
decades ago.
Even the time-span of our present day will
change in a strong gravitational field. “If you feel there aren’t enough hours
in a day, just wait,” says Max Tegmark, a cosmologist at the Massachusetts
Institute of Technology. “In a few hundred million years, tidal friction will
have slowed Earth’s rotation to make the day 25 hours long.”
If time is a dimension like space as suggested
by the theory of relativity, it must be plausible to go back and forth in time
as we do in other dimensions, such as up and down, left and right and forward
and backward. Yet, in our universe the cosmological arrow of time is not known
to reverse direction since the beginning of the universe.
Contrary to our expectations, however, the laws
of physics do not discriminate between past, present and future. We are
obsessed with time and time keeping and it follows us like a shadow all the
time. Physics tells us that all moments exist equally, at once. It’s only our
perception that distinguishes the present from the past or future. Or, as
cosmologist Tegmark puts it, “If life were a movie, physical reality would be
the entire DVD: Future and past frames exist just as much as the present one.”
Though back (past) and
forth (future) time travel is permitted by the laws of physics, it is riddled
with paradoxes. Among the most well known is the “twin paradox’ in which one
twin travels at relativistic speeds (comparable to that of light) through the
universe for many years leaving his twin brother behind on earth. When he
returns he would have aged much less than his sibling. The theory of relativity
dictates that in a fast moving frame of reference all clocks, and thus aging,
would move slowly.
Another paradox offers an even grimmer outcome.
What if you travel back in time and murder your grandfather? Some physicists
suggested the laws of physics must always conspire to prevent travel into the
past and thus the impossibility of such a paradox. However a few others believe
that such actions simply cause space-time to branch off into a new parallel
universe that doesn’t interfere with the current one.
Modern science is not the first to attempt to
comprehend the illusive nature of time. Mythology likewise sought such answers
too. For instance, in Devi Bhagwata Purana, Narada asks Vishnu about the
meaning of Maya, to which Vishnu replies that it is the illusion generated as a
consequence of our interaction with the physical world.
The view is echoed in Buddhism. “From the
Buddhist perspective, time is the experience of being present right now, in
this very moment. We in the West, however, like to measure things. In this way,
clock time gives us a sense of coherence and stability. But in terms of our inner
lives, no time exists except for what is happening in the present moment,” says
Joan Halifax, a Zen Buddhist and a distinguished scholar at the Library of
Congress.
The subjective nature of time is implicit in
human life, not just in cosmology or physics. Some events speed up time for us,
while others make it crawl. “Put your hand on a hot stove for a minute, and it
seems like an hour. Sit with a pretty girl for an hour, and it seems like a
minute. That’s relativity,” Einstein once explained.
Neuroscientists examining how the brain
perceives time say that the sensation of the passage of time depends on how
richly the memories are laid down. Tragic events are likely to be perceived as
more recent than they really are or events that are not registered as strongly.
Many researchers believe that information and
the mode of processing provide the sense of past and future. It is the “flow of
information” rather than the “flow of time” that creates this impression — much
like a system stores past information (memory) to be recollected and focuses
attention on the most recent information.
Often, biologists refer to a biological clock
based on which our cellular actions are carried out. So if we are completely
insulated from our surroundings, the biological clock might function to
generate the perception of time passing by.
But not everyone agrees.
“Time has little impact on biology,” says Michael West, a gerontologist who
teaches at the University of California, Berkeley. “From a gerontologist’s
standpoint, biological time is not wear-and-tear, it’s a genetic program,” says
West. “It’s sort of like a time bomb. The cells are programmed to last just
long enough for us to bear children, and no longer.” The absence of clocks in
our system do not guarantee an eternal life; we will fall apart anyway.
At another level we relate this illusive time to
death. In Sanskrit, Kala means time and the Hindu mythology refers to Kala
(Yama) as the personified god of death. It’s no surprise that time and death
are synonyms in Puranas. The conversation between Nachiketas and Yama is the
theme of Kathopanishad, one of the 108 Hindu scriptures of the Vedanta
philosophy.
Nachiketas to Yama : “Some say that when man
dies he continues to exist, others that he does not. Explain, and that shall be
my third gift.”
Initially reluctant to
explore such a subject matter, Yama engages in a deep and extensive
conversation with Nachiketas and concludes: “The Self knows all, is not born,
does not die, is not the effect of any cause; is eternal, self-existent,
imperishable, ancient. How can the killing of the body kill Him?”
Did time begin with space at the big bang? Our
current models of the universe emphasize this supposition and it should end
with space. The second law of thermodynamics, often called the “death warrant
of universe,” asserts that the entropy (disorder) of the universe must increase
and thus the cosmological arrow of time must always go forward. Thus cause
precedes effect.
All physicists agree on the absence of universal
time, because time is a matter of perspective. We can divide time periods in
any unit from years to nanoseconds or even beyond. What is the smallest
interval of time that can exist? Quantum theory says that it is Planck time,
which is equal to 10-43 seconds. Below that the meaning of time
loses any physical meaning. So we have to say the universe came into existence
when it was 10-43 seconds old. What if reality unfolded even at a
lower time interval? There are no answers at least for now.
On grander scales, time should not be larger
than 13.7 billion years, the current age of the universe. Yet, we do not know
if time had the same rate of flow in every phase or part of the universe. This
is why some physicists argue that the veil of illusion attributable to time
must be removed to learn the truth. Theoretical computations show that the
expansion of the universe at an accelerated rate may also be the result of our
false notion of time. They anticipate a subsequent revolution in physics would
be a cosmos depicted without the constraint of time. But, what if the universe
is itself an illusion followed by life?
Time is the most familiar experience we deal
with yet we don’t know much about it. Black holes provide us a clue to what one
can call the “end of time.” The intense gravitational force slows and
ultimately freezes time. For an observer outside the black hole, a falling
object would appear frozen in time.
“The black hole teaches us that space can be
crumpled like a piece of paper into an infinitesimal dot, that time can be
extinguished like a blown-out flame, and that the laws of physics that we
regard as ‘sacred,’ as immutable, are anything but,” wrote John Wheeler, the
visionary physicist who coined the term “black hole.”
As one can imagine, the pursuit of the real nature
of time or its illusion is profoundly complex. But that doesn’t impede modern
scientists from trying to crack the code. The latest attempt is by Sean
Carroll, a Caltech Physicist. His book, From Eternity to Here: The Quest for
the Ultimate Theory of Time, released in January 2010, offers a lucid and
fascinating discussion about the nature of time. He hypothesizes that our
universe may be a relatively young member of a big family and that in several
of our sibling universes time runs in the reverse direction. Some others, he
argues, don’t experience time at all; once a universe cools off and reaches
maximum entropy, there is no past or present.
In the section “Aranya Parva” in the
Mahabharata, Yama disguised as Yaksha posed many questions to challenge Yudhistra.
Yaksha asked: “What is the greatest wonder in
the world?”
Yudhishthira replied:
“Every day, men see creatures depart to Yama’s abode and yet, those who remain
seek to live forever. This verily is the greatest wonder.”
As Lee Smolin, a
theoretical physicist, once commented: “So, what is time? Is it the greatest
mystery? No, the greatest mystery must be that each of us is here, for some
brief time, and that part of the participation that the universe allows us in
its larger existence is to ask such questions. And to pass on, from schoolchild
to schoolchild, the joy of wondering, of asking, and of telling each other what
we know and what we don’t know.”
