When news broke out that Christopher Nolan was making a sci-fi movie based on space travel called Interstellar, I was eager to see how Nolan handles the grand canvas of the universe with his creative prowess. After watching the movie I am happy that it had all the essential Nolan ingredients - an audacious and improbable core, cerebral screenplay, witty dialogues, mesmerizing visuals and all connected using an emotional chord. But as a science enthusiast, the most heartening thing for me was to watch a lot of real world science littered all through the movie and the clever manner in which Nolan had exploited them for his screenplay. Right from Newtonian mechanics to Einstein's relativity to the Theory of Everything, the movie was a rollicking journey through science. Though there were some outrageuous speculative science towards the end, well thats the creative liberty provided by movie making. Now lets take a look at some of the real world science that was dealt in the movie.
Rocket Propulsion
Just before entering the black hole the AI robot TARS soberly utters, "Newton's Third Law : Can't get anywhere without leaving something behind." It is not only a witty comment that captures the emotional mood of the scene, but also suggests the physics underlying rocket propulsion. A rocket engine is similar to the internal combustion engine in cars, wherein fuel is ignited at high temperatures in a combustion chamber (Rockets carry their own oxidizer in the combustion chamber as the outer space is almost vacuum). In a car engine the combustion energy is used to drive a piston which in turn powers the vehicle. But in rockets the high pressure exhaust produced due to the combustion is accelerated to supersonic speeds using a convergent-divergent nozzle (remember Bernoulli's principle) before being ejected out. According to Newton's Second Law, this acceleration implies a net force acting on the exhaust and the reaction force to this is what provides the thrust that propels the rocket upwards.
Weightlessness
When the Endurance crew is launched into space, they start floating the moment they enter into orbit. Those who have seen videos or pictures of astronauts aboard ISS (International Space Station) would have noted that they too float. This is wrongly attributed to the absence of gravity and hence referred to as 'zero gravity'. But ISS orbits the earth at a height of 400km where the gravity is only marginally lesser than that on earth's surface. So why do astronauts aboard an orbiting spacecraft float or experience weightlessness ? To understand this lets consider a scenario back on earth where you are inside a lift in the tenth floor of a building. Now if you wanted to reach the first floor, the lift will start from rest and accelerate at some rate 'a' until it reaches the first floor. Lets assume that you were floating during this entire downward journey. This means you would have been accelerating at a rate 'g' which is the acceleration due to earth's gravity. Now if g > a then you would have hit the bottom of the lift and if g < a you would have hit the top of the lift and there is no way you could be floating. So if you had to be floating then both yourselves and the lift should be accelerating at the same rate. This can happen under some extraordinary circumstances when the lift cable snaps and both you and the lift are hurtling down at the same rate 'g'. Similarly when a satellite or spacecraft is in orbit around a celestial body (like the earth), the only force acting on it is the gravitational pull of the celestial body. And that explains the floating astronauts on orbiting vessels.
Artificial gravity
Immediately after they enter orbit, Cooper initiates a spin sequence for the spacecraft which induces some sort of artificial gravity that grounds the floating astronauts. What causes this artifical gravity? When the spacecraft starts spinning there is a centrifugal force that provides a downward force keeping the astronauts grounded. This is similar to the outward force that we experience when making a sharp bend while driving in hill stations or while riding the merry-go-round.
Black hole
One of the central characters (literally!) in the movie is a black hole called Gargantuan. Black holes are formed when white dwarf stars with mass exceeding the 'Chandrashekar Limit' have exhausted the nuclear fuel at their core. During the normal life of a star, there is a tug of war between its own gravity pulling it in and the energy produced by the nuclear reaction at the core which is pushing it out. But with time as the nuclear fuel gets exhausted, the star collapses under its own gravitational pull forming black holes . Black holes have so much of mass compressed into a very small volume that they exert an incredible gravitational pull in its vicinity. There is a region surrounding the black hole called 'event horizon' in which the gravitational pull is so enormous that even light cannot escape. And that is one of the reason that black holes are yet to be physically observed, though it is predicted that there is a super massive black hole at the centre of our own Milky Way galaxy.
Theory of Relativity
After dealing with time in a non-linear fashion in Memento, Nolan explores the concept of time dilation in this movie. When Romilly says that spending one hour on Miller's planet is equal to seven years back on earth, it sounds bewildering but is actually based on the works on one brilliant German physicist who goes by the name of Albert Einstein. Between 1905 and 1916 Einstein proposed two theories that shook our notion of space and time. The first among this was the Special Theory of Relativity which dealt a blow to the notion that time is absolute. According to this theory the flow of time is different for people who are travelling at constant velocities but in relative motion. More specifically, time runs slower for those moving at a relatively higher speed. Thats why Cooper says to his young daughter that he might be the same age as her when he returns as he might be travelling at the speed of light. The second theory is called General Theory of Relativity which deals with effect of gravity on space and time. When Newton proposed the laws of universal gravitation, it was a monumental scientific achievement because it was the first time the physical world was described in the language of mathematics. Though the law had been verified to a very high degree of accuracy, Einstein was uncomfortable with certain aspects of it and hence proposed the General Theory of Relativity. One of the key predictions of this theory which is relevant to the movie is that time runs slower in a stronger gravitational field and vice-versa. And that explains why time runs so slow on Miller's planet which is near to the black hole that exerts a strong gravitational field. (The Special theory of relativity and General Theory of Relativity aren't just theoretical predictions but have real world applications. The clocks in GPS satellites run slower than that on earth as these satellites orbit the earth at very high speeds of 14,000 km/hr. Also since they orbit the earth at heights of 20,000km, they run further slower as the earth's gravitational field is lower compared to that on surface of earth. These effects have been taken into consideration when designing the GPS satellites.)
Tidal force
When the Endurance crew land on Miller's planet, they encounter tides which are the size of mountains. These monster tides weren't randomly placed there to give a kick to the screenplay, but were caused due to the large tidal force exerted by the enormous gravitational pull of Gargantuan. It is similar to the tides caused in the earth's water surface by the moon's gravity.
Grand Unified Theory
The holy grail of theoretical physics currently is the formulation of a theory which unifies all the four fundamental forces of nature - strong force (present inside the nucleus of an atom holding together the protons), weak force (responsible for radioactive decay), electromagnetic force and gravitational force. The biggest hurdle towards this grand unification is the incompatibility between General Theory of Relativity and Quantum mechanics. General theory of relativity works well at the large scale like stars, galaxies et.al. whereas Quantum mechanics works well at the atomic scale. In our day to day life we never encounter massive objects at the microscopic level and so this discontinuity in the laws of nature is not a problem. But at the centre of the black hole there is a huge mass that has been compressed to the atomic scale and hence it is essential that the two theories reconcile with each other. So I presume that is the quantum data that Cooper transmits to his daughter which she uses to solve the gravity conundrum.
Showing posts with label science. Show all posts
Showing posts with label science. Show all posts
Saturday, November 22, 2014
Saturday, March 29, 2014
What I learnt when MH370 crashed
Whenever a commercial aircraft drops off the sky, I am engulfed with a sense of grief and fear. The grief is due to the untimely death of innocent people and the emotional toll it takes on their kith and kin. The fear is borne out of the thought that when I am airborne someday, what might happen if the aircraft develops a technical snag. Recently I had flown to Andamans with my wife which was my first major air travel. Every time there was a slight turbulence due to passing through clouds, it sent a shiver down my spine. And whenever the crew switched on the addressing system to make an announcement, I feared for the worst. But all the time I put a brave face to my wife sitting near me else she would never board a flight again. So I could imagine the terror that would have gripped the passengers on board MH370 in the last minutes of their flight. With all the technological advancements we have made, it is so frustrating and puzzling that we still have no clue about what happened to such a massive object when we have the capability to read the number plate of a car from the skies. I have been keenly following this tragic episode from day one and in this process have learnt and realized a lot of information spanning fields as diverse as maths, physics, geography and history, which I am sharing in this article.
That box ain't black !
We all know that when an aircraft crashes, the most important debris that investigators search for is the black box. This box contains data regarding vital flight parameters and also the cockpit voice recorder. And many of us might also be aware that the black box isn't actually black but rather bright orange in color so it can be easily identified. But given that over 70% of earth surface is water, how will they retrieve the black box if an aircraft crashes in the ocean ? It seems these boxes have an underwater locator beacon which gets activated once it touches water. The beacon sends ultrasonic signals every second for a period of 30 days after which the batteries die out. So it is important that the location of the box is identified quickly else it might even take years before it can be retrieved as in the case of the Air France crash. Also it can withstand impacts of 3400 times the force of gravity and temperatures as high as 2000 degrees !
Time of Useful Consciousness (TUC)
Though it sounds like a phrase with deep spiritual roots, it is purely scientific. What it denotes is how long you remain conscious at a given altitude in an environment of inadequate oxygen supply. Generally aircrafts fly at an altitude of 35000 ft where the air pressure is much less compared to sea level. So aircraft cabins are pressurized to maintain an ambient pressure that prevents hypoxia. But if the aircraft climbs above 40000 ft, depressurization sets in and you lose consciousness within TUC unless oxygen masks are used. The TUC at such altitudes is only around 10 secs which means you have only so much time to use the oxygen masks from the moment they are deployed. The reason this term has been doing the rounds is because it is being suspected that somehow the cabin of MH370 got depressurized and everyone on board had died of hypoxia including the pilots. Eventually the autopilot had taken over and the plane flew endlessly till it lost all fuel and crashed into the Indian Ocean. Similar sequence of events have happened before and are referred to as 'ghost planes'. But in the case of MH370, it doesn't explain why the flight deviated from its trajectory in the first instance.
Roaring forties
The MH370 is suspected to have crashed in a region of the Indian ocean which is one of the remote parts of the world. The nearest land is the city of Perth which itself is at a distance of 2500km. The ocean depths in these region can be as high as 4000m and the ocean bed is littered with underground volcanoes. To make the search and rescue effort more complicated, this region is notorious for winds blowing at a speed of 30-40mph and is famously called the 'Roaring forties'. And the lack of any military or commercial significance for the region, has made this part of the seabed less explored than the surface of Mars!
Earth's tilt
Since the nearest airfield is as far as 2500km, it takes the search aircrafts around 8 hours for the to and fro journey to the suspected crash region. This leaves them with only 2 hours for the search operation. Thats when I realized that it is just unlucky that this disaster had to happen around the Vernal Equinox (March 20) when the length of day and night is equal. If the crash had happened around the Southern Solstice (December 21), it would have given the search team more time because the days are longer than the nights. This is due to the earth's tilt to its plane of rotation around the sun and also the search region being roughly 40deg south of the equator. But if you look at it the other way round, it would have been worser if the crash had happened around the Northern Solstice (June 21) when the days are much shorter than the nights in the Sourthern Hemishpere. Amidst all these thoughts it stuck me that India will never host a Tennis Grand Slam even if it produced Tennis superstars like Rafa (some might say Federer) or even if India became a superpower accidently. This is because of India's proximity to the equator where the length of days is almost equal to nights all year round and hence difficult to squeeze so many matches within two weeks.
Predictability through probability
We all had our share of nightmares in our school days regarding probability theorems. We masqueraded our difficulty in understanding the subject by pointing out the lack of any real life applications apart from predicting the outcome of some irrelevant experiments like tossing of a coin. Even that it could predict accurately only if you repeated the experiment an insane number of times. But as we grew up we realized random process was at the heart of everything around us - noise in our electronic gadgets, behavior of stock markets and even the growth of bacteria inside our body ! And recently I discovered that probability distribution has been used to locate crash sites. When the Air France flight crashed in the Atlantic ocean in 2009, finding the black box and cockpit recorder was becoming difficult as the crash site was itself identified only after 5 days. By the that time the ocean currents had drifted the debris far and long. After a futile search for 2 years the French authorities turned to statisticians for help. Based on the various probable causes for the crash and using historical precedent, they constructed a probability distribution function using Bayesian statistics. And Viola! the black box was found in that region of the seabed which had the maximum probability value. Even in the case of MH370 this technique might be used to recover the black box if nothing else proves successful.
Aircraft shootdowns
And finally if you thought that air disasters occur only due to mechanical failure, electrical failure or terrorist activities, then think twice. Because there have been instances were commercial aircrafts have been shot down from the ground either accidentally or intentionally. In September 1983 during the height of Cold War, USSR shot down Korean Air Lines Flight 007 which was flying from Anchorage to Seoul carrying 269 passengers and crew. The flight had deviated from its trajectory due to some pilot error and entered restricted Soviet airspace. The Soviets suspecting a missile attack by the Americans shot down the flight killing all on board. In October 2001 the Siberian Airlines Flight 812 was struck by a S-200 surface-to-air missile fired from Crimea peninsula and crashed over the Black Sea. It is alleged that the missile was fired as part of a test fire by the Ukranian Defense forces and all 66 on board were killed. There have been many other such instances of aircraft shootdown but the credit for the most outrageous incident should go to the 'Moral Police' of our world. In July 1988 Iran Air Flight 655 was shot down by the US navy over the Indian ocean killing all 290 on board. The flight was in Iranian airspace, flying over Iran's territorial waters and was on its usual flight path. But a US missile cruiser which had entered Iranian waters mistook it for an enemy F-14 Tomcat fighter and shot it down. And to date they have never admitted responsibility or expressed apology.
P.S - I got inspired to write this article after reading this piece in The Hindu.
That box ain't black !
We all know that when an aircraft crashes, the most important debris that investigators search for is the black box. This box contains data regarding vital flight parameters and also the cockpit voice recorder. And many of us might also be aware that the black box isn't actually black but rather bright orange in color so it can be easily identified. But given that over 70% of earth surface is water, how will they retrieve the black box if an aircraft crashes in the ocean ? It seems these boxes have an underwater locator beacon which gets activated once it touches water. The beacon sends ultrasonic signals every second for a period of 30 days after which the batteries die out. So it is important that the location of the box is identified quickly else it might even take years before it can be retrieved as in the case of the Air France crash. Also it can withstand impacts of 3400 times the force of gravity and temperatures as high as 2000 degrees !
Time of Useful Consciousness (TUC)
Though it sounds like a phrase with deep spiritual roots, it is purely scientific. What it denotes is how long you remain conscious at a given altitude in an environment of inadequate oxygen supply. Generally aircrafts fly at an altitude of 35000 ft where the air pressure is much less compared to sea level. So aircraft cabins are pressurized to maintain an ambient pressure that prevents hypoxia. But if the aircraft climbs above 40000 ft, depressurization sets in and you lose consciousness within TUC unless oxygen masks are used. The TUC at such altitudes is only around 10 secs which means you have only so much time to use the oxygen masks from the moment they are deployed. The reason this term has been doing the rounds is because it is being suspected that somehow the cabin of MH370 got depressurized and everyone on board had died of hypoxia including the pilots. Eventually the autopilot had taken over and the plane flew endlessly till it lost all fuel and crashed into the Indian Ocean. Similar sequence of events have happened before and are referred to as 'ghost planes'. But in the case of MH370, it doesn't explain why the flight deviated from its trajectory in the first instance.
Roaring forties
The MH370 is suspected to have crashed in a region of the Indian ocean which is one of the remote parts of the world. The nearest land is the city of Perth which itself is at a distance of 2500km. The ocean depths in these region can be as high as 4000m and the ocean bed is littered with underground volcanoes. To make the search and rescue effort more complicated, this region is notorious for winds blowing at a speed of 30-40mph and is famously called the 'Roaring forties'. And the lack of any military or commercial significance for the region, has made this part of the seabed less explored than the surface of Mars!
Earth's tilt
Since the nearest airfield is as far as 2500km, it takes the search aircrafts around 8 hours for the to and fro journey to the suspected crash region. This leaves them with only 2 hours for the search operation. Thats when I realized that it is just unlucky that this disaster had to happen around the Vernal Equinox (March 20) when the length of day and night is equal. If the crash had happened around the Southern Solstice (December 21), it would have given the search team more time because the days are longer than the nights. This is due to the earth's tilt to its plane of rotation around the sun and also the search region being roughly 40deg south of the equator. But if you look at it the other way round, it would have been worser if the crash had happened around the Northern Solstice (June 21) when the days are much shorter than the nights in the Sourthern Hemishpere. Amidst all these thoughts it stuck me that India will never host a Tennis Grand Slam even if it produced Tennis superstars like Rafa (some might say Federer) or even if India became a superpower accidently. This is because of India's proximity to the equator where the length of days is almost equal to nights all year round and hence difficult to squeeze so many matches within two weeks.
Predictability through probability
We all had our share of nightmares in our school days regarding probability theorems. We masqueraded our difficulty in understanding the subject by pointing out the lack of any real life applications apart from predicting the outcome of some irrelevant experiments like tossing of a coin. Even that it could predict accurately only if you repeated the experiment an insane number of times. But as we grew up we realized random process was at the heart of everything around us - noise in our electronic gadgets, behavior of stock markets and even the growth of bacteria inside our body ! And recently I discovered that probability distribution has been used to locate crash sites. When the Air France flight crashed in the Atlantic ocean in 2009, finding the black box and cockpit recorder was becoming difficult as the crash site was itself identified only after 5 days. By the that time the ocean currents had drifted the debris far and long. After a futile search for 2 years the French authorities turned to statisticians for help. Based on the various probable causes for the crash and using historical precedent, they constructed a probability distribution function using Bayesian statistics. And Viola! the black box was found in that region of the seabed which had the maximum probability value. Even in the case of MH370 this technique might be used to recover the black box if nothing else proves successful.
Aircraft shootdowns
And finally if you thought that air disasters occur only due to mechanical failure, electrical failure or terrorist activities, then think twice. Because there have been instances were commercial aircrafts have been shot down from the ground either accidentally or intentionally. In September 1983 during the height of Cold War, USSR shot down Korean Air Lines Flight 007 which was flying from Anchorage to Seoul carrying 269 passengers and crew. The flight had deviated from its trajectory due to some pilot error and entered restricted Soviet airspace. The Soviets suspecting a missile attack by the Americans shot down the flight killing all on board. In October 2001 the Siberian Airlines Flight 812 was struck by a S-200 surface-to-air missile fired from Crimea peninsula and crashed over the Black Sea. It is alleged that the missile was fired as part of a test fire by the Ukranian Defense forces and all 66 on board were killed. There have been many other such instances of aircraft shootdown but the credit for the most outrageous incident should go to the 'Moral Police' of our world. In July 1988 Iran Air Flight 655 was shot down by the US navy over the Indian ocean killing all 290 on board. The flight was in Iranian airspace, flying over Iran's territorial waters and was on its usual flight path. But a US missile cruiser which had entered Iranian waters mistook it for an enemy F-14 Tomcat fighter and shot it down. And to date they have never admitted responsibility or expressed apology.
P.S - I got inspired to write this article after reading this piece in The Hindu.
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