Movie Interstellar: Plot points explained

Movie Interstellar: Plot points explained

Let me start by saying I loved the move and rate it 5 out of 5.  If you enjoy reading my technical blog entries, then you’ll enjoy watching this movie.  However, some of the movie can be hard to follow.  Some people I watched the movie with had trouble understanding exactly what was going on and why people did what they did.

This is my attempt to identify and describe the plot points.

SPOILER ALERT: There be movie spoilers ahead!

Act I – Pre launch

The Blight

The plot requires something to drive humans off the Earth.  The movie doesn’t expend much screen time explaining the problem but the premise is “the Blight” is an organism that consumes nitrogen, depletes, oxygen, and can hop from one crop species to another.

It is implied the blight has been around for a while and that it has become impossible to grow almost all crop species.  At the time the movie starts, humanity is down to just a few (possibly one) food crop and by near the end of the movie, the survivors on Earth are certainly down to just one crop corn.

The blight is also the reason food is in such short supply.

The Messages

By the end of the movie, Murph receives four messages from the future.  The movie reveals by the end that all four messages were transmitted by Cooper.  The messages (in chronological order in Murph’s frame of reference) are:

1. Noise (random books and the LEM thrown from shelf as Cooper laments and learns about how to send messages)
2. Latitude/longitude coordinates of secret NASA facility (transmitted as binary and appearing in the dust pattern on the floor)
3. “S” “T” “A” “Y” (starting letters of the book titles)
4. Black hole observation data (transmitted as Morse code into Murph’s watch’s second hand movement).

Why Cooper

NASA originally had no intentions of using Cooper as a pilot.  If he was as qualified as Dr. Brand states, then he should have been contacted as a possible pilot.

Given that NASA didn't attempt to contact him, then the only reason they accepted him as a pilot was due to the information that he received from (who everyone at the time thought was) "They".  The fact that he had other qualifications sweetened the deal.

Note that pilots require constant training to stay in top form.  A pilot who spent the last several decades farming (with no training) would not be the "best pilot they had".

The Plans

As described by Dr. Brand (Sr.), send Endurance through the wormhole to perform follow-up observations on viable planet candidates, select one, and transmit the information back to Earth.  In Plan A, this tells humanity where to set up its colony.  In Plan B, this tells humanity where to send any other spacecraft it can send to land and will be the location of the colony established by Endurance.

Plan A – NASA is constructing giant space station(s) to lift large numbers of living humans from the Earth.  (In my opinion, it is unlikely that plan A could lift more than a tiny fraction of a percent of the entire Earth’s population because they would still have to create enough spacecraft to support the remaining world population).  But the concept is if Dr. Brand Sr. can solve the Theory of Everything equation, it could be used to create anti-gravity engines, lift a large segment off the planet, and then if a viable planet is found it could be colonized.

Plan B – Endurance’s cargo includes 5000 fertilized ovum.  Endurance is equipped with basic equipment gear the ability to incubate and raise these eggs to adulthood. This is the fall back plan if Plan A can’t be executed.

Act II – the flight out

Sleepers

The crew jumps into tanks filled with water and appear to go to sleep.  Presumably, the tank sleep is a sort of hibernation that reduces their consumption of on-board stores (power, air, water, and food).  Even without cryogenic type hibernation and using something more like bear hibernation, the saved quantities of these consumables can be substantial.

Wormhole

Nothing in what we know of physics prevents the theoretical formation of wormholes as depicted in the movie.  However, there are many practical problems in actually using one.  The function this wormhole served in the movie was it permitted humanity to travel vast distances in small amounts of time.

The wormhole is a necessary plot point because humans at the technology level depicted had no chance of getting anyone alive to any habitable planet without significant help.

The relative time experienced by the people traveling through the worm hole may have been affected but based upon receiving signals back from the initial 13 explorers; this wasn’t a substantial amount of time.  The actual physics of this is peculiar.  If current theories are correct, a worm hole could (theoretically at least) connect any two locations in space.  However, the theory also permits the connecting any two locations in time.

Time dilation

It was clear to the crew when they departed that the Earth would remain viable for humanity for a minimum of years and possibly decades.  By using time dilation they increase the sense of urgency for the crew of the Endurance.  Furthermore, it allowed the movie to explore the stresses imposed upon the relationships between the two fathers (Brand and Cooper) and their daughters (Amelia and Murph).

How we experience time is always relative and dependent upon the details of our relative locations.  Time dilates in regions close to gravitational fields and for objects traveling close to the speed of light.  The effect is not normally large unless very large gravitation fields – like that of Gargantua are encountered at close range or very high fractions of the speed of light are experienced.  Effects as large as that portrayed for Miller's planet require the black hole to have very special properties (e.g. rotating at 99.8% of c).

Miller’s world’s proximity to and orbited around Gargantua generated a huge time dilation (7 years pass in the rest of the universe for every hour spent on Miller’s world).  Mann’s world also orbited Gargantua but its time dilation was much smaller and not mentioned during the course of the movie.

The effects at Mann's planet were probably noticeable but not substantial My total guess here but for every 1 minute on Mann's planet, perhaps 1 minute and 15 seconds passed for the outside Universe.

Furthermore, regions “far” from Gargantua (e.g. Edmund’s world), likely experienced time similar to that encountered by the rest of humanity on Earth (i.e. almost none).  There would be noticeable differences but they would not be substantial.  Another total guess but for every 1 minute on Edmunds' world, perhaps 1 minute and 0.5 seconds passed for the outside Universe.

During the slingshot maneuver towards the end of the movie, Cooper steers the Endurance within the "critical orbit" of the black hole.  My recollection of relativity and black hole mechanics from college (warning this is a 30 year old memory) suggests that the "critical orbit" is the closest stable orbit to the black hole.  Going inside the critical orbit means falling into the black hole if thrust is not applied.  However, this distance is considerably closer than Miller's planet and the time dilation experience would be considerably worse than that encountered at Miller's planet.  Since I haven't worked out the orbits of the different planets, I can't tell you how much, however, many decades per hour could be passing.

However, time dilation as depicted was accurately portrayed, even if how it was used was not done very elegantly or believably.

Dr. Miller’ Planet

Upon landing Dr. Miller sent the message indicating her planet was viable for an Earth colony.  However, because of the time dilation, the period of time between her sending the message and the landing of the Endurance crew was only about 90 minutes by her clock but over 10 years by ours.  The first wave she encountered likely destroyed her base/lander, killed her, and destroyed her robot.

Miller's planet was investigated by the Endurance crew because it was “energetically the easiest to get to” (as explained in the dialog – but not reality).  Dr. Miller sent the “viable = true” message back to Earth.  The movie dialog implied the wave traveling away from the site upon their touchdown was probably the wave that killed Dr. Miller.

Both Dr. (Amelia) Brand and Dr. Doyle act irresponsibly and did not return to the Ranger when directed to do so by Cooper (a Mission Commander should have been appointed prior to launch).  Amelia ignored the order because she intended to retrieve probe data.  Doyle ignored the order because he was stunned and simply stood frozen in place.  Doyle’s inaction may have been due to his emotional attachment to Dr. Miller (based upon his reactions when planet fall decisions were being made).

The giant waves were generated by the massive tides from the planet’s rotation while orbiting the supermassive black hole “Gargantua”.  I’m told the waves were unrealistic large given the other parameters of the planet (it would likely be tidally locked, shallow seas wouldn’t provide the water necessary, the planet itself would warp under such conditions, and generate massive amounts of internal energy would make the planet uninhabitable).

Dr. Romilly’s aging demonstrated first-hand how much time the trip to Miller’s planet cost as far as time passing back on Earth.

Dr. Mann’s Planet

Dr. Mann (Amelia Brand called him “the best of us all”) initially did not send the signal indicating his planet was viable.  Later when faced with isolation and desolation he finally disabled his robot KIPP and sent a signal indicating his planet was viable for humanity.  Despite, it not possessing the requirements to sustain a human colony.

He did this because he became lonely and afraid of dying alone.  He could not resist the temptation of the thought that if he sent a message indicating his planet was viable, then the crew of Endurance would come and rescue him (which is exactly how this played out).  Dr. Mann uses many rationalizations to justify his behavior even though each of them fell apart upon examination.  Either his insanity or ego overcame his wisdom so that he acted according to his own self-interests and to the detriment of all humanity.

Presumably the explosion that killed Dr. Romilly was supposed to kill the entire crew of Endurance so Dr. Mann's betrayal and failure wouldn't be discovered.  However, Amelia was already en route to save Cooper.  Dr. Mann's betrayal (and killing of the robot KIPP) eerily mirrors HAL-9000's betrayal (and killing of Discovery's human crew) in the movie 2001: A Space Odyssey.

The irrationality of Dr. Mann and the actions he takes damages the Endurance and force the rescuers to thrust away from Mann’s planet.  This ultimately sends them on a trajectory towards Gargantua.  Cooper calculates a trajectory which enables the Endurance to reach Edmund’s planet after a close approach to Gargantua.  However, in order to reach Edmund’s they must use Lander 1 and Ranger 2 as “booster rockets” to provide the necessary trajectory changes.

The maneuver used by Cooper to adjust their trajectory is plausible.  Applying thrust (and discarding boosters) at the bottom of a gravity well provides much more delta V (change in velocity) then performing the same operations at the top of the gravity well could provide.  It also allows the plot to drive Cooper to fall into the black hole (which no rational and competent pilot would allow to happen) but is necessary for the next act of the movie.

Plotwise, falling into the black hole provides a plot loophole that enables Cooper to send messages back in time to Murph. 

Dr. Edmunds’ Planet

Dr. Edmunds initially transmitted that his planet was viable for colonization.  Years later, he stopped transmitting.  The data he did transmit looked like it was the most promising of all three planets investigated (Dr. Miller’s, Dr. Mann’s, and his); however, the loss of signal worried the Endurance’s explorers and it took the most fuel to reach.

Dr. (Amelia) Brand is in love with Dr. Edmunds and suspicion that her relationship might cloud her reason causes Cooper to investigate Dr. Miller’s planet first.

The movie reveals little about Dr. Edmunds' planet until the final scenes.  Those depict the atmosphere as breathable and, therefore, that ecosphere as likely at a minimum supporting its own primitive native life.  This makes Edmund’s world by far the most viable of the planets of those depicted.

Dr. Edmunds presumably died in an accident while on the planet and not due to anything that reduced the viability of it as a colony world for humanity.  The final scenes of the movie show CASE digging up Wolf Edmunds' body, Amelia Brand burying Dr. Wolf Edmunds, and standing over his grave.  The movie does not explain what happened to Dr. Edmunds’ robot.

The Lie

Dr. Brand (Michael Caine) reveals on his death bed that he lied about Plan A.  In his deathbed confession, he states that he had solved his equations decades before.  He felt they provided no solution to humanity’s problems without observational data from the inside of a black hole’s event horizon.  Since by definition an event horizon prevents any information from getting out, this was an impossible task and Dr. Brand (Sr.) “knew” Plan A would never work.  Instead of revealing this to the rest of humanity, he kept his thoughts of the futility of Plan A to himself to ensure humanity continued working together until the very end.

Dr. Brand expected the Endurance’s crew to find a viable planet and immediately start the Plan B colony.

Act III

Added on 12/7/15:

Did Cooper need to fall into the Black Hole?

For several reason the answer is "Yes".  Just after regaining control of the Endurance, TARS mentions that there is "good news" and "bad news".  Cooper asks TARS to "give it to him straight" but the scene ends before the audience hears the news.  Cooper discusses the plan with Amelia Brand and mentions that he's found a trajectory around the black hole that allows them to "scratch their way to Edmunds' planet".  He refers directly and indirectly to both fuel and life support.

The plan requires the additional thrust of two of the ancillary craft ("Lander 1" and "Ranger 2").  The plan states that Lander 1 will detach (like a booster rocket) from the craft after expending its fuel.  Since the control linkages between Endurance and these craft was damaged by Dr. Mann, each craft must be crewed.

The chosen pilots for the ancillary craft are TARS and Cooper.  To Dr. Brand's surprise, Cooper ends up detaching for the same reason that TARS did.

In summary, the reasons are:

1. Endurance, Lander 1, & Ranger 1 each requires a pilot
2. Only enough life support on Endurance for 1 human to survive to Edmunds' planet
3. Only enough fuel for this single trajectory
4. Last but not least, the plot requires Cooper to fall into the black hole

The black hole

Little about the black hole scenes is explicitly explained.  But observation and piecing together other bits of plot we can derive the following conclusions

• “They” are not bound to our four dimensions (they are often referred to as five dimensional, but that is the minimum, they could exist in more)
• “They” are not trapped by the gravity of a black hole or its event horizon
• “They” are able to manipulate gravity (although depending upon interpretation they might not be able to manipulate time)
• “They” are able to manipulate dimensions
• “They” rescue Cooper as he falls into the black hole
• “They” either refuse to or can’t communicate in a meaningful way with humans
• “They” make a 4-dimensional construct (tesseract) to represent time as a fourth spatial dimension.  This enables Cooper to view and interact with Murph’s bedroom at any point in time
• “They” rely upon Cooper to figure out what message to send, how to send it, and to what time it should go
• At no time does matter move back in time, even though information does

Cooper uses this ability to send the four messages back to Murph.  In Cooper’s frame of reference, he sends the messages in this order:

1. Noise (random books and items knocked off the shelf)
2. “S” “T” “A” “Y” (first letter in the title of the books he knocks off the shelf)
3. Latitude and longitude coordinates for secret NASA facility sent in binary (in dust settling to the ground)
4. Black hole observational data sent in Morse code (in the movement of the watch he gave to Murph).

Black hole –

See my other posts (Initial thoughts on blackholes, black holes, the fallers perspective, Interstellar's science failings) for more information about most of this.  However, I wanted to discuss the “gravitational sling shot” portrayed.  As usual, Hollywood takes a complicated topic, applies poetic license, and portrays it simplistically – IMO too simplistically.

When the average person discusses a gravitational slingshot, they discuss it in a generic way and do not differentiate between several distinct effects that change a spacecraft’s momentum when passing close to another object.

Oberth Effect

The first of these effects is the Oberth Effect.  Simply stated, you get a greater change in momentum of you apply your thrust at the bottom of a gravity well than at the top.  Read the article for the details about why this is true.  The Oberth Effect applies for any object orbiting any other object (a two body problem).  The movie accurately portrays Cooper using the Oberth Effect to place Endurance on the correct trajectory towards Edmund’s planet.

Gravity Assist

The second of these is the Gravity Assist.  Simply stated, in a three body system – Body A can exchange momentum with Body B to increase or decrease its momentum relative Body C.  An example would be the Voyager 1 & 2 flybys of Jupiter.  In each case, the spacecraft vastly increased their momentum (velocity) in relationship to the Sun by slowing Jupiter an unmeasurable amount in its orbit around the Sun.  In the case of the movie Interstellar and Endurance’s fall towards Gargantua, Endurance does not receive any gravity assist benefit from the maneuver.  In the case of Endurance’s flyby of Mars (retrograde trajectory), this would remove velocity from Endurance’s Sun centric (body C) momentum and make the trip longer which is a “bad idea”.

Turn

The third of these is a simple turn.  Simply stated, in a two body system, when a spacecraft wants any change in vector, than it must transfer momentum with something to accomplish the maneuver.  If no nearby masses are available than the spacecraft must use its own engines to provide the momentum change and this would be very costly in propellant.

In the case of Endurance trying to reach Edmunds’ planet, they were headed in the wrong direction and needed to make a turn.  If Cooper chooses the correct trajectory towards Gargantua and makes the right course correct when near Gargantua, he can effectively choose whatever outgoing trajectory he desires – namely the course towards Edmund’s planet.  The movie accurately portrays Cooper using Gargantua to change Endurance’s trajectory towards Edmund’s planet. 

The difference between a turn and a gravity assist: in both cases Body A exchanges momentum with Body B.  In the gravity assist, the exchange is done in a special way to increase Body A's velocity / momentum / energy in regards to a third body (Body C).

Tidal Effects

Sufficiently massive black holes (such as "Gargantua") have smaller tidal effects above the event horizon.  This would enable sufficiently small objects (such as a person) to pass through the event horizon without being "speghettified/speghettification" or tidally disrupted (a more tidy way of describing recursively being ripped apart).

Tidal forces vary linearly with mass but as the inverse *cube* of distance.  The size of the event horizon varies linearly with mass only.  Meaning their is a black hole mass which allows human sized objects to pass through the event horizon without disruption.

So smaller black holes would disrupt human sized objects prior to their reaching the event horizon.  Large enough ones allow smaller objects to pass through the event horizon prior to recursively being ripped apart.

Meaning Cooper could have survived passing through the event horizon.

Act IV –

Cooper’s survival

Humanity rescued Cooper with “only minutes of oxygen left”.  How did Cooper survive for so long in space?  He didn’t.  Cooper’s time dilation meant he had only been on the Earth side of that wormhole for a few minutes.  Cooper essentially spent 90 years on the other side of the wormhole and just happened to pop out right as humanity got to Saturn.

Was Cooper just lucky or was it careful planning by “They”?  The answer is open for interpretation but I think the movie was going for ‘careful planning by “They”’.

Cooper’s recovery

The doctor tells cooper he’s 123 years old.  Assume he started his mission at the age of 33 and they spent 23 years on Dr. Miller’s planet, what happened to the other 67 years?  Time dilation, that’s what.  It also means that Cooper did not pass through the event horizon as his time dilation would have then been measured in billions/trillions of years rather than decades.

Cooper’s departure

Murph urges Cooper to depart and find Brand.  Partly for Cooper’s sake (he doesn’t relate to post-Earth humanity anymore) and partly for Amelia’s sake she believes that she is the only surviving human in the entire universe.  She’s alone and isolated on Edmund’s world.  She has also been left with the burden of resurrecting the human species by herself.  Murph correctly (IMO) believes that the company of just one other human would help Brand immensely. 

During these scenes the movie jumps back and forth between Cooper and Brand indicating their actions occur simultaneously (with black holes, worm holes, and time dilation; what does this even mean??).

The problem I see is this: cooper loses 67 years while performing the trajectory change in Endurance, falling into the event horizon, and while in the “They” tesseract.  Amelia shares the time dilation experienced by cooper during the trajectory burn but from there Amelia experiences time at an accelerated rate while Cooper’s slows down.  Amelia will have experienced a large chunk of those 67 years that Cooper missed (40 years or more?).

If/when Cooper finds Amelia she’ll be in her 70s if she survives.

Unanswered questions

Where is humanity going?

A question not posed in the movie but it is implied.  Murph tells Cooper to go to Brand.  If humanity intended to colonize Edmund’s world (Amelia's location), why would he need to do that?  Clearly the difference between when Cooper could get there and when the rest of humanity appeared would be minimal (weeks perhaps?).  This tells us that post-Earth humanity has no intention of colonizing Edmunds’ world and, without Cooper returning to her, Amelia would truly be alone.


I wonder, where does post-Earth humanity intend to go?


Added 12/7/15

Did Cooper succeed in getting to Amelia Brand?

Based upon the size of the craft, I assume it had neither the delta V nor the life support that the Endurance had.  However, I also assume Cooper and/or TARS new the approximate requirements and would not have made the attempt if it was unlikely to succeed.


Added 12/7/15

Will humanity now have two colonies?

Assuming both Amelia Brand's colony and the rest of humanity succeed in forming viable colonies, then humanity will have seeded two separate galaxies.  It's unlikely that the two populations would ever meet unless / until they develop the ability to form wormholes like "They".

Do you have any questions about the movie Interstellar?   Ask them in the Comments section.