Ray Cummings, considered the father of science fiction, described time as “nature’s way of preventing everything from happening at once.” John Wheeler, an American theoretical physicist, added, “And, space is its way of preventing everything from happening to me.” If there wasn’t time, everything would happen at once. And if there wasn’t space, everything would happen in the same place.

Side note: Wheeler collaborated with giants like Bohr and Einstein, worked on the (in)famous Manhattan project and taught physics at Princeton, where his graduate students included Richard Feynman and Kip Thorne. Dr. Thorne, who teaches at Caltech, is one of the producers of the movie, “Interstellar.”

There are so many different worlds. We have but one. But, we live in different ones.

What exactly is time? Well, it depends on the world from which the question is posed. We could, simplistically, divide the worlds we’re aware of, into three distinctly separate ones based on our powers of perceiving them. First is the world of classical mechanics described by Isaac Newton. Second is the world of relativistic mechanics described by Einstein as a space-time continuum. And last but not the least, is the quantum mechanical world of sub-atomic particles, which Bohr, Heisenberg, Pauli, Dirac, Schrodinger and others collectively described.

Dire Straits. “Brothers in Arms.” (video)

httpv://www.youtube.com/watch?v=2eB5tUZwEys

The world as we know it.

Newton’s laws of motion and gravitational theory concern themselves primarily with the world as we know it. They describe a familiar world of bodies filled with masses that are acted upon by forces and the ensuing consequences of such forces or lack of them. Newton explained a lot of things observed on earth and in the skies neatly. Kepler used Newton’s laws to show that planets moved in elliptical rather than circular orbits, which appeared to be true.* For example, Newton showed that Kepler’s laws of planetary motion would apply in the solar system, as consequences of his own laws of motion and gravitation. Nearly every mechanical invention over the next several hundred years became possible through these suddenly obvious insights, which we take for granted today.

*Corrected. Many thanks to @chasing_mirage for pointing out that Kepler and his laws preceded Newton.

However, the laws of classical mechanics became increasingly problematic when used to explain ‘minor’ anomalies that began to be observed when more accurate telescopes and other measurement systems came along. For example, Newton’s laws, as amazing as they are, led to a strongly held but erroneous belief that the speed of light was relative, and puzzlement when measurements showed otherwise. Another famous example is an anomaly in Mercury’s orbit, which, try as they might, scientists could not explain.

Time in Newton’s world is ‘not relative’. In other words, time provides an immutable backdrop to the grand stage of the universe on which bodies move relative to, collide with, or attract one another. Material objects possess masses and are capable of moving large distances with predictable speeds. But there is no such notion as ‘the speed of time’ in Newton’s world.

For all practical purposes, Newton’s laws explain the world to people like us, who lead unscientific lives and are unaffected by cosmic anomalies and mysterious events that go on in the universe. We understand why something that is tossed up in the air returns. And, so on.

Newton’s laws describe a world of massive objects, low speeds and large distances. They began failing, when applied to ‘other’ worlds with minuscule objects, enormous speeds or sub-atomic distances, a matter which caused great consternation by the end of the 19th century.

Time slows down when you’re having fun..

Einstein formulated the Special Theory of Relativity in 1905 to address Newtonian limitations, in which he proposed a radically different relationship between space and time. Instead of being an unchanging backdrop to the cosmic drama, time, he said, was an active participant and suggested that its nature was ‘relative,’ just as the nature of space was relative. He predicted that time would move slower when an object moved faster. To be more accurate, time would go by relatively slower on an object such as a planet or a spaceship, which was moving relatively faster than another one. This dilation of time, he said, would be noticeable only at very high speeds, typically exceeding 10% of the speed of light.

Einstein thus began describing our broader universe, a world of massive objects, large distances and enormous speeds. At the heart of his Special Theory was an assertion that the speed of light was an ‘absolute’ and a constant in our universe.

Think of our universe as a massive computer program which is designed to reflexively change space and time to keep the speed of light ‘c’ constant anywhere in it. Einstein called the combination of space described by location (x,y,z) and time ’t’ as the ‘space-time continuum,’ a four dimensional interwoven mesh, whose intrinsic nature was to dynamically adjust itself to keep ‘c’ constant.

Regardless of where you measure the speed of light in the universe or the conditions under which you measure it, the speed of light is constant. Why? No one knows. That’s the way things are, in our version of the universe.

You already live in a space-time continuum. You just don’t know it yet.

What’s space-time continuum? It’s a mesh of things that have happened, presently happening or will happen. If you didn’t realize it, we already employ the concept in our day to day lives. When you arrange to meet a friend, you exchange four pieces of information. When you say, “I’ll meet you at the Starbucks near the intersection of Los Gatos Boulevard and Highway 85, at 9am tomorrow,” you’ve provided ‘x’ and ‘y’ coordinates of the meeting point, have indicated that the ‘z’ coordinate (height) is zero and that the time coordinate is 9 in the morning on a day, which is one day after today. No one ever just goes, “Let’s meet at 9am tomorrow,” or, “Let’s meet at the Empire State Building,” because it would raise the questions of where and when. History is another great example of a space-time continuum; a compendium of events which have occurred at specific places and times in the past.

Gravity.. is working against me…

It’s now time speak of that invisible elephant in the room – gravity.

Believe it or not, this thing called gravity, which we experience every second of every day of our lives, is one of the least understood phenomena in physics. Newton described it as a property which is both exuded and experienced by anything that is made of matter. He described the gravitational forces of attraction between two objects as being dependent on their masses and the distance between them. It turned out that things were not quite as straightforward as that. For example, light, a massless entity, was observed to “bend” as it traveled through neighborhoods of even small stars like the sun.

John Mayer, “Gravity.” (video)

httpv://www.youtube.com/watch?v=MUhmXKmHHd0

Einstein spent the next ten years coming up with a General Theory of Relativity which explained the nature of gravity quite differently. Gravity, Einstein said, was not just some intrinsic property of matter. He described it as something which arises when matter interacts with the space-time continuum. Say what?

Okay, let’s try this again.

In the beginning, there was a lot of energy concentrated perfectly in a place called ‘singularity’ which was smaller than a billionth of an atom. One fine day, the singularity began to expand. In fact, it took just a few nano seconds before the singularity expanded to form the space-time continuum or the universe as we call it. Space and time were born simultaneously like a four-headed baby, in a spontaneous moment of cosmic creativity.

Somewhere, sometime in those first few inflationary moments, Mother Nature pulled yet another rabbit out of her hat. Something called matter arose in space-time continuum. Why and how matter arose is a great mystery of our universe. The current theory we have is that of the Higgs field, present throughout the universe, instrumental in transferring mass to those particles known to have mass. Some one described a universe as something that happens from time to time. I guess you could say the same about matter.

So, anyway.. coming back to gravity.

As matter mysteriously arose in the space-time continuum, it began creating distortions in it. The word used in physics for distortions is “space-time curvature.” Imagine if you placed a bowling ball on a rubber sheet. It would create a depression in it, which is another way of saying that the bowling ball creates a curvature. Gravity, Einstein said, is a result of matter interacting with space-time to create curvatures. The larger the mass, the greater the curvature and thus greater the gravitational force or field.

It turns out that when the curvatures are very very large, i.e. when there are intense gravitational fields, they can cause time to slow down. This is called gravitational time dilation. For example, both Jupiter and the Sun have masses significantly larger than that of the Earth. Clocks on both Jupiter and the Sun would tick slower than one on the Earth. The clock on Jupiter would gain only about 10 minutes every 100 years compared to the one on Earth, which wouldn’t make a trip to Jupiter worth while. A clock on the Sun would gain about 4.6 days every 100 years. A clock on Mercury, a planet smaller than the Earth, would tick slower * faster. You get the gist now, I’m sure.

*Corrected. Silly typo! Thanks again to @chasing_mirage for catching this.

Think of gravity as something that results from matter creating curvatures in space-time, and time as one of the variables which gets stretched (slowed down) more and more as the curvatures gets larger and larger.

Just so we are clear, you will feel time lapsing at ‘normal speed’, at one tick per second, regardless of whether you’re on the Earth, on Jupiter or inside a black hole. You will not experience time going by faster or slower. It’s like everything stretches or contracts at the same time so you can’t tell any difference, unless you become aware of a reference point that lies at a different curvature on the space-time continuum. The phrase used to describe this in physics is that you and other objects are traversing along different space-time paths.

Time, the great vector.

A Greek philosopher, Heraclitus, said, “You cannot step into the same river twice.”

In philosophical terms, Heraclitus described a fundamental property of time in our universe: that it moves forward and only forward. We can move forwards and backwards, and up and down in space but are prisoners in the present. We, it appears, are condemned to watching as moments tick by, rigidly positioned at the intersection of the past and the future. This notion of the arrow of time, as it came to be called, arose first in a field called thermodynamics, in which a gentleman named Ludwig Boltzmann described something called entropy using statistical methods. Simply speaking, entropy represents the ‘amount of disorder’ in systems. Boltzmann astutely observed that entropy was such a thing, which only increased in our universe. It’s a way of saying that things in the universe as a whole, happen only in a forward direction, and are not reversible. You can make an omelette from eggs, but you can’t get eggs back from an omelette.

The relationship between entropy and time is an intuitive one. If we were to somehow be able to “restore” order and decrease disorder in the universe, conceivably we could engineer it back to its original state, which is just another way of saying that we could reverse time itself. The fact that we find the universe today in a state of ‘higher entropy’ implies that it once started off in a ‘low entropy’ state. Why did that even happen? Why was it not in a steady state to begin with? Why does it accumulate disorder? What causes it to do so? Would it not make sense for it to decrease its disorder? How long will entropy increase in the universe? And when entropy reaches some sort of a maximum, will our universe and time begin reversing their directions? These are all fascinating questions, to which there are only speculative answers today. All we know for now is that our universe is becoming more and more ‘disorderly’, and time marches resolutely and uni-directionally forward.

Side note: Boltzmann was so profoundly distressed by philosophical objections to his findings that he became acutely depressed in his later years and eventually committed suicide.

The Third World of Uncertainty.

Deep down in the recesses of matter, at the sub-atomic level, there exists a world of great uncertainty, where an entirely different set of natural laws govern. As we break matter down into elements, then atoms and eventually sub-atomic particles, a dramatically different picture emerges. There are several things that are weird about this quantum mechanical world, as compared to the worlds of Einstein and Newton. Before I get there, let me try first to describe this world and how we came to stumble upon it.

One of the first clues to the quixotic nature of sub atomic particles came from experiments performed on the behavior of light. Of the many that were attempted, the most famous experiment in capturing the central puzzles of quantum mechanics is the Young’s double slit experiment, conducted in 1801.

It’s relevant to note that, at the time Young performed his experiment, light was thought of to be a ‘wave’ which is to say that light was not thought of be composed of ‘particles’ with mass. Young merely set out to prove the wave nature of light with his experiment. It’s a pretty simple experiment which consists of passing light through two narrow slits placed close to each other on a piece of cardboard or metal. As expected, light diffused and spread as it passed through the slits, forming a predictable ‘interference pattern’ on a screen, which is caused when waves of light interfere with each other. Every one was overjoyed, and Young slept soundly at night after that.

Fast forward a hundred years to the early 1900s. By this time, there was enough evidence to believe that light might be, in fact, be composed of minuscule packets containing discrete amounts of energy, also known as ‘quanta’. Max Planck and then Einstein built equations to describe the energy that could be contained in each packet of light called photon, which led to the discovery of the ‘photo electric’ effect, for which Einstein received the Nobel Prize. This set the stage for the study of what came to be known as quantum mechanics.

The tale of Young’s double slit experiment saw a dramatic twist around this time. A curious person asked, “What if I were to shoot a single photon through the double slits, which one would it pass through?” By this time, scientists had built equipment capable of generating single photons and detectors which could spot them as they moved along.

When a single photon was shot at the double slits, one of the most mysterious events ever observed in physics happened. The photon appeared to pass through both slits at the same time to form a familiar diffraction pattern earlier seen by Young. How was it possible that a single photon could enter through two slits at the same time? Did the photon pass through one slit, and then somehow traveled back in time back through it and then re-enter the other slit to interfere with itself to form wave patterns? Mind boggling stuff. There is no accepted answer to why this happens till this day.

And now comes the really weird part. Another curious person decided to place a detector after the slit. The detector was like a security guard, keeping a close eye on the photon to identify the slit through which it passed. A magical event happened. When the detector was placed, the photon decided that it was going to behave itself, and exactly like a particle. Something about the act of observation, which the photon somehow seemed to be aware of, made it abandon its wave nature. This experiment has been repeated with other particles such as electrons with similar perplexing results.

Quantum mechanics describes the world of minuscule things (sub atomic particles), which are separated by minuscule distances. As things stand, it is believed that there are twelve fundamental particles (an electron is one of them) which combine to form higher order particles such as protons, neutrons, etc. which in turn combine to form atoms and molecules, eventually culminating in things like babies, trees, rocks, water, clouds, earth, moon, stars and all such matter that exists in the universe. The Standard Model is a set of equations which describe the state of each functional particle and the conditions under which it forms and exists.

Let’s talk about time in this world.

What’s intriguing is that the arrow of time does not show up in the laws of physics which govern these fundamental particles. The world of electrons, bosons, quarks and other fundamental particles is what is called a probabilistic one. The existence of the particles at a particular position is defined by a set of probabilities. An electron could manifest itself in positions A, B and C, each with a probability of ‘p’. In other words, it exists everywhere and yet nowhere. At any given instant, the wave function describing the electron “collapses” to manifest it at a specific position. The same is true for other particles. It’s like Mother Nature is trying to make up her mind as she goes along, considering infinite possibilities and ruling in favor of one, at each and every instant.

Let’s say we were to somehow be able to build a gigantic model using every tiny bit of data starting from the Big Bang to now, and run a simulation on a massive supercomputer. Even if we did that, we would not be able to predict with certainty what would happen the very next second. That’s because even Mother Nature is yet to decide what she is going to do next.

Here’s the great paradox: Formation, existence and transformation of the fundamental particles, which make up all matter, don’t appear to subject to the arrow of time. They exist in a timeless state of no causality, memory, metabolism, death, etc., in a world of probabilistic fluctuations. The arrow of time seems to be an overlay, almost an after thought, on top of these laws of physics, and applies only to the higher order blocks of matter built from fundamental particles. Our worlds become less and less predictable as we zoom inwards. Weird.

This theory of fundamental unpredictability made many uncomfortable, including Einstein who ironically was considered the founding father of quantum mechanics. Einstein’s relativistic description of space-time continuum, just a few years before quantum mechanics came along, implied the exact opposite: that the world was determinate and that there were no such things as free will, choice and uncertainty. That the universe was a giant program juggling to adjust many parameters to keep a few from changing. The space-time continuum wasn’t evolving. It was already there. The future had already transpired, and everything in the universe was merely traversing its own space-time path towards a predictable and fulfilled destiny. Quantum mechanics came along and put forth this great notion that the future was yet to happen, and yet was not necessarily influenceable or subject to manipulations by higher order matter. The great angst brought about the new revelations prompted Einstein to respond tersely that “God does not play dice with the universe,” and an exasperated Heisenberg, who led the young turks of quantum physics, to retort, “Please don’t tell God what he must or not do.”

For the last seven or eight decades, much scientific energy has been expended in attempting to reconcile these seemingly irreconcilable worlds into one Grand Unified Theory of Everything, with no tangible success so far.

Interstellar.

The movie took my breath away. It made me happy, sad and even cry. America may be losing its edge on a few fronts, but by God, it still makes the best movies in the world.

Official trailer of “Interstellar.” (video)

httpv://www.youtube.com/watch?v=0vxOhd4qlnA

Interstellar is an awesome example of how science can form a real foundation for movie making. It’s the story of Coop, an astronaut who goes on a mission to find a new world to which humans can escape from Earth, which is in its final stage of destruction. The heart tugging relationship between Coop and his daughter, Murph, which plays out over the space-time continuum provides an emotional backdrop to the intergalactic quest. It’s a movie not just about science. At the heart of it, it’s a work of art which makes us wonder about the magnificence of everything. It gives us pause to ponder things, which might escape us otherwise in our humdrum lives.

Tomorrow never comes. Or does it?

So, is time travel possible? What happens when we enter a black hole? What happens when we die? Would we acquire the ability to move forwards and backwards on the space-time continuum, inside a four dimensional Tasseract? There are some fantastic scenarios that Interstellar portrays, much of it attributable to an artistic liberty and a creative license to imagine.

Of course, time travel is possible. We traveled from yesterday to today. 🙂 Seriously, since the arrow of time points only forward, it’s possible that travel to the past may be impossible, although it has not been mathematically or theoretically proven to be impossible.

Another way of looking at time travel into the past is to examine the nature of causality or ‘cause-effect’, a phenomenon made possible by the ‘flow’ of time. Cause always precedes effect in our universe. Effect may not be allowed to go back in time, to modify or destroy its cause, thanks to the uni-directional arrow of time.

If we were somehow able to enter a higher dimension from which we could witness the space-time continuum, it is then possible that we would be able to move along it to the past and the future. This would raise interesting paradoxes. What if you went into the past and somehow convinced your dad to never have children?

In which case, would we be allowed to revisit the past, if we solemnly promised to refrain from interfering with and changing it? If that were possible, we would merely observe the past as passive observers, just as we are when watching a movie. Wait, we can already do that by recording the past with a video camera, or simply in our memories. Memory is a special form of time travel into a specific part of the past in which we have participated, isn’t it?

Kids these days….

Why does time go by slower on Miller’s planet?

Miller’s planet, in Interstellar, is a water world, located just outside the event horizon of a massive black hole called Gargantua. A black hole is an anomaly in the universe, believed to have enormous mass concentrated in a singularity similar to the one from which the universe began. A blackhole can be looked at as a massive space-time curvature, inside or near which time slows down dramatically due to gravity.

“Wait, they aren’t mountains. They are tidal waves.” In a spectacular moment in the movie, Coop and crew realize that Miller’s planet, which because of its wobbling, really resembles a huge bowl in which water is careening from one edge to another causing tidal waves the size of mountains.

Since Miller’s planet is located within the gravitational field of Gargantua, a black hole with a mass of 100 million suns, each hour on it (we’re told) corresponds to 7 years for someone outside its field. By the time Coop and his partner return to their spaceship, their colleague and Coop’s daughter on Earth have aged by 23 years.

Later, Coop is pulled into the black hole, in which he spends a few minutes, during which another eighty years pass by on Earth. During this time, he enters the mysterious Tasseract, where he travels back in time to guide his past self and then Murph towards solving the set of equations, which allows them to eventually leave Earth, resettle near Saturn and find him. Is it really possible to exit a black hole once you’ve entered it? Unlikely. Is it possible that you can travel back to the past and alter it? Unlikely. Is it possible that our descendants, from the future, can help us escape our present? An exhilarating leap of faith and hopeful imagination.

All we are is.. dust in the wind.

The nature of tIme has been a matter of much speculation for thousands of years, even before Einstein and modern savants came along. Western philosophical and religious view of time has always been a linear, uni-directional one, with starting and ending points. Judeo-Christian-Islamic schools of thought portray time as coming into existence with the ‘creation’, and ending with ‘judgement day’, when the past, in its entirety, will be reviewed with an intent to judge faith and dispense justice. Eastern mystics took more exotic and intriguing stances on time. The Hindus and the Buddhists described time as a “kaala chakra,” cyclical in nature, without beginning or end, stretching into infinity, much as science views the universe. Creation and destruction of things are events that repeat themselves periodically on this cycle. Even Brahma, the creator himself, is subject to the laws of oblivion, and yields his way to a new Brahma when his end arrives. Vedic thinkers intuitively grasped the uncertainty which lies hidden beneath it all, and concluded that the purpose of life lay in enquiry aimed at drawing the distinction between the real and the unreal.

Regardless of our personal beliefs, aspirations and desires to shape our worlds as we wish them to be, and our chosen paths in the pursuit of what we like to call the Truth, enquiry into the nature of things leads us eventually to the comforting possibility that we are, in a true sense, nature gazing upon herself. That, while we may be insignificant lumps of carbon, hydrogen and oxygen on an inconsequential, tiny planet in some corner of a magnificent universe, we have, within our grasp, a great power: the ability to let go, and look upon the worlds with wonder and awe.

Happy journeys.

Kansas, “Dust in the Wind.” (video)

httpv://www.youtube.com/watch?v=12DeNdF0KPA

The information in this post is drawn from many sources- mostly my readings over the years and my notes from them. One of the great blessings of ignorance is the ability to over simplify. In my anxiety to tell things simply, it is entirely possible that I may have mis-stated things. It is also possible that I may have misunderstood things. In fact, it is unlikely that this is error proof. If you spot anything amiss, please do let me know. I stand ready to be corrected. Thanks for reading.