Interstellar Explained: It’s Relative

Have you recently seen Interstellar and didn’t quite understand the physics behind it? You are not alone in this, but before we delve into the film and analyse the events, we need to better understand Einstein’s theories of Special and General Relativity.

In 1905 Einstein proposed a theory that explains how space and time are linked to objects that are moving at a constant speed in a straight line. In a nutshell, this is what it comes down to: the laws of physics are the same in all inertial systems (non-accelerating frames of reference) and that the speed of light in a vacuum is the same for all observers, regardless of the motion of the light source. Special Relativity also tells us that times runs slower as someone approaches the speed of light. For example, think of how your GPS works. Each of our satellites orbits the Earth at about 20, 000km from the ground and has an orbital speed of 14, 000 km/h. The satellites carry an atomic clock that ticks with a nominal accuracy of 1 nanosecond. Because the observers on Earth see the satellites in motion relative to them, Special Relativity predicts that we should see the atomic clocks tick slower than the ones on Earth. To be exact, time on the satellites runs 7,200 nanoseconds slower relative to us on Earth.

In 1915, Einstein published his Theory of General Relativity. In layman’s terms, General Relativity says that the closer you are to a heavy mass, such as Earth, the slower time will pass for you. In other words, massive objects cause a distortion in the space-time continuum, which is felt as gravity. Again, we can take GPS as an example and prove that GR exists and it affects our lives on a daily basis. Due to the satellites being 20, 000 km from the Earth and therefore in weaker gravity, time runs slower. This is why GPS systems need to correct for the time difference and send the correct signals to your device. The point is, we can prove Einstein’s Theory of General Relativity.

 “We can test general relativity, and general relativity has passed the test,”

one scientist says after LIGO confirmed the existence of gravitational waves.

Confused yet? Here is a list of things to remember:


  • Special Relativity applies only to special cases: frames of reference in constant, unchanging motion.
  • General Relativity applies to frames that are accelerating with regard to each other.
  • Times Dilation – time does not pass at the same rate for everyone. A fast moving observes measures time passing more slowly than a stationary observer would.
  • Mass and energy are different manifestations of the same thing.  E = mc^2 – a quantity of energy is equivalent to a quantity of mass times the speed of light squared.
  • As a result of this, fast moving objects appear to have increased mass, relative to a slow moving one.
  • Relativity explains where gravity comes from.
  • Gravity bends light – this is called gravitational lensing.

Movie time.

In the science-fiction film Interstellar, a number of environmental catastrophes reduce the population of the world and society starts to produce and maintain crops in order to survive. Because the Earth is dying, scientists come up with two plans to save it: Plan A consists of saving the people and transporting them to another planet, Plan B’s objective is to colonise a new planet with test-tube humans. In order for Plan A to work, Professor Brand needs to solve the gravity equation. What’s the gravity equation, I hear you ask? In short, the scientists at NASA are trying to control gravity. However, the problem is the equation couldn’t reconcile quantum mechanics with relativity. The data needed is found in a black hole and since no one has even been into one and survived to tell the story, Professor Brand comes up with Plan B.

Early in the film Cooper questions how NASA intends to find a habitable planet and Professor Brand reveals that an unknown civilization, called “They” throughtout the film has created a wormhole near Saturn – essentially a bridge connecting two points in space. Einstein’s Theory of Relativity predicts the existence of wormholes, but it is important to note, that none have been discovered to date. It is believed that a wormhole may not only connect two regions of the Universe, but also connect two different universes. Pretty cool, right?

Three of the astronauts that were sent through the wormhole to search for habitable planets, ping back positive information and Cooper, together with Dr. Brand and Dr. Romily is sent to discover the best possible option. The three planets are named after the scientists that went there – Mann, Edmunds, and Miller.

The Miller planet is the first location, the crew of Endurance visits, and this where people often get confused. The planet is orbiting the massive black hole, called Gargantua. Due to the gravitational pull of the black hole, every hour on the Miller planet is seven years back on Earth. According to Einstein’s Theory of Relativity, the bigger the object is, the more spacetime is warped and twisted around it. This is why when Coop and Dr. Brand are back on the ship (conveniently stationed outside of gravitational pull of the black hole, and therefore unaffected), 23 years have passed. Time on the Miller planet ran slower and for each hour there, seven years passed on the ship. That’s relativity folks.

Moving on. Enter evil Matt Damon.


Matt Damon’s involvement was deliberately kept a secret and shocked a huge number of people. In the film, he represents humanity’s selfish nature, as he manipulates his data and pretends his planet is habitable. Dr. Mann tries to sabotage Coop’s crew in order to steal the ship and escape. Sounds like he is deranged, don’t you think?

After discovering the first two planets could not sustain life, the crew decides to implement Plan B and go to the Edmunds planet and to send a robot into the black hole, with the hopes that it will solve the gravity equation and send information back to Earth. However, Cooper realises the ship is too heavy and won’t make it out of the black hole’s gravity and sacrifices himself. He is sucked into the Gargantua with Tars and end up on a strange construct of bookshelves after passing the event horizon. I believe this is the part that confuses people most.

The tesseract was built by them for the sole purpose of Coop going back to one precise moment to pass on the information to Murph. Here, time is nonlinear. Here, time is represented as a physical dimension. Everything happens all the time and every moment is represented by physical lines, through which Coop can travel.  As TARS is unable to transmit the information from the black hole outside of the tesseract, Coop tries to pinpoint the best moment when Murph will be able to understand the data.

When Cooper’s job is done, the tesseract starts dismantling and he is thrown out of it and exists near the wormhole, where he gets picked up by a NASA station. Because he has been in the Black Hole and traveled through time and space with speed close to that of light, more time has passed on Earth than for Cooper. You can thank Special Relativity for that.


The power of Love

It is believed by some that the theme of the film is Love. Others fiercely dispute this and think that love across dimensions is a bit of a stretch. Here is why. When Dr. Brand insists on visiting Edmunds Planet because it is orbiting a neutron star, and it is more likely to sustain life, compared to the Miller planet, which orbits a black hole, the other astronauts are skeptical. Eventually, Amelia’s relationship to Edmunds is revealed and she justifies her decision with love.

“Love is the one thing that we’re capable of perceiving that transcends dimensions of time and space”.  

Coop is doubtful at the beginning but later he says that love is quantifiable as it gives him hope that Murph will go back to her room and look at the watch, he gave her as a present. It is because of their shared love that he knew she would go back to the library, where he would send readings of singularity, which ultimately helps her solve the gravity equation and save humanity.

Is love a dimension we can’t perceive but only feel? It is for you to decide, but Christopher Nolan would like you to accept that Love plays an important part in the film and it is Love that saves mankind in the end.

The poem featured in the film – Do not go gentle into that good night, by Dylan Thomas

Do not go gentle into that good night,
Old age should burn and rave at close of day;
Rage, rage against the dying of the light.

Though wise men at their end know dark is right,
Because their words had forked no lightning they
Do not go gentle into that good night.

Good men, the last wave by, crying how bright
Their frail deeds might have danced in a green bay,
Rage, rage against the dying of the light.

Wild men who caught and sang the sun in flight,
And learn, too late, they grieved it on its way,
Do not go gentle into that good night.

Grave men, near death, who see with blinding sight
Blind eyes could blaze like meteors and be gay,
Rage, rage against the dying of the light.

And you, my father, there on the sad height,
Curse, bless, me now with your fierce tears, I pray.
Do not go gentle into that good night.
Rage, rage against the dying of the light.

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