The physics of “Interstellar” explained

Photo courtesy of Paramount Pictures

Photo courtesy of Paramount Pictures

“Interstellar” is a movie about humanity trying to save themselves by understanding the physics of space and time, giving them the ability to leave the planet. In the process there was time travel, wormholes, black holes and other troubles that sci-fi fans would gawk at. The plot of the movie, therefore, heavily relied on understanding how these concepts work. Here is an explanation of some theoretical physics in the movie that may have gone over the non-physicist’s head.

The entire movie’s plot is kick-started on the idea of wormholes being possible. They first use this wormhole to travel to another galaxy where potentially habitable planets are. The real name used in theoretical physics for this wormhole is an Einstein-Rosen bridge. This theoretical hole in space was found to be possible in, you guessed it, the mathematics of Albert Einstein’s theory of relativity with help from his colleague Nathan Rosen.

The concept is that a wormhole is a shortcut between two points in the universe. It is explained very well in the movie as having a piece of paper and folding it, then poking a hole in it with a pencil, creating a shortcut from one side of the paper to the other.

Cooper, the pilot, was expecting a physical 2-dimensional hole in space but is corrected by Romilly. He explains by saying that on a 2-D plane, in this case the paper, a hole is flat. In a 3-dimensional plane which we live in, a flat circle is a sphere, therefore we would see a hole in space as a sphere.

An Einstein-Rosen bridge, or a wormhole, has never been observed in space before. It is completely theoretical and has many problems. Most theories say that a wormhole would be too unstable to actually be used for travel—it would need another theoretical substance called exotic matter or negative energy to stabilize it. Wormholes are as theoretical as a time-traveling DeLorean.

Speaking of time-travelling DeLoreans, there was an interesting kind of time travel in the beginning of the movie. Cooper acquired the coordinates for the secret government bunker that ended up being NASA by reading the binary gravity slits made by his future self in the fifth dimension. Fun sentence to try to explain out of context. Cooper did not physically time-travel though, he affected his past by interacting with its gravity, which his past self noticed.

The reason that he succeeded in this kind of time travel is because he fulfilled his own past by doing what he remembered happening to his past self.

Another big idea in the movie was time dilation. One of the planets with the scientists on it is closer to the black hole than the others, therefore the time spent on the surface would be dramatically longer in the perspective of the ship or Earth. Time goes slower, from an outsider’s perspective, wherever there is gravity. Romilly was on the ship while Cooper and Brand went onto the surface of the planet and only experienced half an hour, but when they got back Romilly had experienced 23 years.

This is a graph of time dilation. The left is seconds per second while the bottom is the speed you are going based of the speed of light. 0.1 is 10% the speed of light etc. Photo courtesy of Wikipedia.

This is a graph of time dilation. The left is seconds per second while the bottom is the speed you are going based of the speed of light. 0.1 is 10% the speed of light etc. This means that, going 70% the speed of light, for every 1 second you experience, everyone else would experience 1.5 seconds.
Photo courtesy of Wikipedia.

The reason this happens is because gravity is simply time and space curving from the the mass of an object. I explain this thoroughly here, but here’s a quick example. Imagine a bowling ball (Earth) on a mattress (space), the indent from the mass of the bowling ball on the mattress is the same idea as the curve of space because of the Earth’s mass. This curvature doesn’t just warp space though, it warps time, and this is the concept that works against Cooper and the others, since the human race is experiencing time on a much faster rate compared to the ship.

What may be the most confusing concept for a person not knowledgeable in theoretical physics and cosmology might be what is so special about the inside of a black hole. A black hole is called this because you cannot see it. The black hole warps space and time so strongly that light cannot escape its grasp, hence the black in black hole. Theoretically, since we have never actually experimented on a black hole, there is a point of no return where neither light nor anything else can escape called the event horizon. Because of this property we cannot see inside it and therefore can’t find out what happens at this singularity.

This is the drive of the supposed plan A in the movie, to find out how the inside of a black hole works and why, so that we may be able to manipulate space like a black hole does. In the movie, this is why the NASA station was built sideways—they had intended to be able to manipulate gravity to have the station drift off of the Earth and into space.

This stretching has been nick-named spaghettification. Ouch. Photo courtesy of Wikipedia.

This stretching has been nick-named spaghettification. Ouch.
Photo courtesy of Wikipedia.

In reality, as compared to what happens in the movie, there are other factors that play into falling into a black hole. There is a special kind of radiation called Hawking radiation, the only evidence of something escaping a black hole, which would kill you if you got close enough. There are also tidal forces that would stretch and squeeze you as you got closer to the black hole. These are the same type of forces that cause the oceans to have high tide and low tide on Earth from the moon’s gravity, but instead stretching and squeezing the ocean, they stretch and squeeze you.

The movie was based on Kip S. Thorne’s equations and research into black holes. He was part of the writing process for the script as an adviser to make sure the science was accurate. There are a lot of theoretical physics concepts in the movie, all based off of real science. Evidence of this is the representation of Gargantua, the black hole in the movie. It is the first completely accurate representation of a black hole in a movie, based completely off of physics equations.

Hopefully explaining some of the concepts in the movie helps you to appreciate how amazing science is and how beautiful the universe around us is.

Science of the Seasons

This is a panel from from Jeff Smith's graphic novel "Bone" that illustrates this funny idea.

This is a panel from from Jeff Smith’s graphic novel “Bone” that illustrates this funny idea.

You’re walking down the street, bright orange and red leaves crunching under your feet, when suddenly the sun is blotted out by a 2-foot thick layer of snow falling from the sky. It lands with a WHUMP, and now it is winter. Winter doesn’t actually happen like that, it would be cool if it did, but it also might a hurt a bit. So why doesn’t it? The shift in the seasons is gradual and it happens this way because of the Earth’s spin on its axis.

As the Earth goes around the sun, it spins in place but at an angle, its axis. This angle is what gives our planet the seasons — one of the two halves of the Earth, the northern and southern hemisphere, gets hit more directly by the sun at different times throughout the year, depending on the Earth’s position around the the sun. Summer occurs when a hemisphere is almost directly facing the sun and winter occurs in the other hemisphere that’s angled away from the sun. So, if it’s winter in Europe, than it will be summer in southern Africa because they are in opposite hemispheres.

Fall and spring are the transition times between these two seasons. You may have noticed, though, that the intensity of the seasons varies greatly in different places. Areas near the equator are less affected by the tilt of the Earth, causing them to see almost no temperature change throughout the year. The only climatal thing that changes are the two wet seasons and two dry seasons that occur on lands on the equator.

Diagram showing the axis (purple) and how it's tilted to give the seasons Coutesy of Wikipedia

Diagram showing the axis (purple) and how it’s tilted to give the seasons
Coutesy of Wikipedia

The equator is an imaginary line that cuts through the halfway point of the northern and southern hemisphere — the only land it crosses is mid-Africa, the northern part of South America and Indonesia. It is also the point where the radius of Earth is a bit larger than the rest of the planet itself. As the Earth spins at 1,000 mph, the spinning force causes the Earth’s middle to bulge and creates an imperfect sphere. These areas are not as affected by the tilt of the Earth due to the fact that they are bulging. The closer you get to the equator, the warmer it will be (and the longer that warmth will be) throughout the year, which is why the equator is home to all the rainforests.

This is a satillite view of the seasons. Notice how the green across the center, this is the equator and the rainforests.  Courtesy of Wikipedia

This is a satillite view of the seasons. Notice how the green across the center, this is the equator and the rainforests.
Courtesy of Wikipedia

It is because of the equator that there is a distinct temperature difference between the northern and southern U.S. Winter in the north means snow and 10 degree weather (maybe even qworse), whereas winter in the south means 60-70 degree weather and snow is just a dream. If it did snow in the south, people might have a heart attack and think it’s the ice age again.

The seasons have been surrounded by folk lore and tradition all throughout history, but now we know how simply they work and just how predictable they are. No matter what, spring will come after winter, and eventually the leaves will fall off the trees. Despite knowing how this part of nature works now, it’s still just as beautiful without the mystery.

What Lies Beyond The Black of a Black Hole?

Black holes are funky things. They have a lot of science to them and it seems like something you’d find in a science-fiction book to fix a plot-hole but they do exist and get even weirder the more you learn about them.

This is an example of lighting being bent around a black hole because of it's mass. I think it looks cool.

This is an example of gravitational lensing. It is when a massive object, like a  black hole, is between you and a far off object,like a galaxy, and distorts the light coming from it.

I’ve already explained how to time travel with black holes, the huge amount of mass the black hole has warps space and time around it causing time to go slower closer to it compared to something farther away. Orbiting the black hole would more or less fast forward you in time, pushing you into the future faster than something not being affected by this black hole. This is just one of the weird things about black holes, it gets worse.

I’ve also explained how black holes are formed and how they need to be spinning to allow the point in the center, the singularity, to be a ring instead of point. This allows the possibility of moving through the ring and potentially moving through time and space but at that point it’s complete speculation.

The outside of the black hole is the weirdest part of it that can be observed without actually being inside the black hole. If you cross the event horizon, the point where you cannot escape being pulled towards the black hole, then you would not see that thing enter it. You would see them stop where they crossed it and that’s it. At that point the indestructible person, that can somehow not die from all the forces and radiation of the black hole, wouldn’t even notice that they passed through the event horizon. they would continue towards the singularity while the person on the outside watching would just see the person frozen there in time. Eventually the image of the person would just fade away.

The Earth, like any object with mass would, bends the 2-D version of space and time around it represented as a grid

The Earth, like any object with mass would, bends the 2-D version of space and time around it represented as a grid

Now begins the fun part. The reason you cannot escape the inside of a black hole is not because it’s gravity is too strong. This is what is always assumed because of the way gravity is taught as two objects being attracted to each other, but this is also wrong according to Einstein’s theory of relativity. His theory says that what we see as gravity is really an object distorting space and time around itself proportional to its mass. If you pretended all of space was a grid you could imagine a bowling ball on a mattress, it sinks a lot doesn’t it? Now imagine a baseball on a mattress, it doesn’t sink as much. This is what a black hole, and anything else with mass like Earth, does to space around it, it warps it. The picture to the right illustrates this example.

The real reason you cannot escape a black hole is because, if time was the y-axis and space was the x-axis on a graph, once you cross the event horizon time and space switch. Yes you read that correctly, THEY SWITCH. This is practically impossible to actually comprehend but the easiest way to think about it is this, once you you cross the event horizon you cannot move out of the black hole because you would have to move backwards in time to move away from the black hole’s center since space and time switched. Time naturally moves forward so since time and space switched, time is bringing you towards the center. To physically move away from the center you would have to essentially travel backwards in time which, for intents and purposes, is impossible in those circumstances. A funny byproduct of this situation is that you wouldn’t be able to see anything in front of you since, with time and space switched, it literally hasn’t happened yet for you to see.

An interesting thing about a Kerr black hole, or a black hole that is spinning, is that it has TWO event horizons. One is the normal outside one but then there is a second one closer inside, a drawing below shows this. The best part about this is that the second event horizon switches time and space back to normal so you could actually move around in the inner section of the black hole, you still can’t get out since you’d have to travel through the first section of the black hole, but then again this whole scenario is ignoring a lot of other things that would have killed a person by now.

An illustration representing the layers of a Kerr black hole

An illustration representing the layers of a Kerr black hole with the two rings being the inner and outer event horizons

In this section of the black hole you would, theoretically, be able to see the ring singularity in the center. At this point we don’t know what could happen. Maybe you can travel through the ring over and over and go backwards in time and meet yourself, maybe the ring is a gateway to a different universe, no one knows. The sad part is that no one will probably ever know unless they are the one who go into the black hole since once you go in you can never escape. Would your curiosity be strong enough to get you to enter a black hole given the chance?

Science Can Make A Hoverboard! (Sort-of…)

Some die-hard sci-fi fans may think science has failed us because we don’t have hoverboards like in Back To The Future II yet and it’s getting close to the “future” that was in the movie (2015), but science is getting pretty damn close. There is an interesting phenomenon called superconductivity that may help us to get that hoverboard and do even crazier things like, according to the recent game Bioshock Infinite, build flying cities.

The majestic hoverboard from Back To The Future

The majestic hoverboard from Back To The Future

There are certain materials, like ceramics, that when cooled to a low temperature (some can be cooled to a low enough temperature with liquid nitrogen) they gain zero electrical resistance. This means that if you put a charge into this superconducting wire, took away the energy source and then made a circle out of the wire, the charge would never dissipate. What about in 10 years? Nope 100% of the energy still there. 100 years? Nope. HOW ABOUT WHEN THE SUN GOES RED GIANT AND EATS THE EARTH? Nope, there will still be the same amount of charge going through that wire, until the sun melts it by engulfing the Earth that is.


The top wires carry the same amount of energy as the bottom wire, the bottom one is superconducting.

Tons of energy gets lost from the simple process of moving it from place to place, this is caused by resistance in the wire heating it up and therefore releasing energy. This is the same concept that an electric stove takes advantage of to heat its coils, the coils are highly resistant and therefore expel a lot of heat in-turn cooking your food. This idea of no energy being lost in transport is so powerful (pun completely intended) that the most prominent science research facility in the world, CERN, uses superconducting wires in the machine that they used to find the higgs boson not too long ago, the Large Hadron Collider or LHC. The picture to the right shows just how powerful these superconducting wires can be.

The field bends around the material mostly except for some places where it pierces it in tiny distances

The field bends around the material mostly except for some places where it pierces it in tiny distances

The more entertaining part, and what I like the most about the phenomenon, is that while the superconductive material is in a state of superconductivity it ejects most magnetic fields, but some of it squeezes through. The diagram to the left shows it very well. This may seem like just some random science trivia but it is the key to that hoverboard. What this really means is that the material will be locked in its position wherever you put it as long as there is a powerful enough magnetic field surrounding it. Whatever position you move the material in, whether it is left, right, forward, back, or UP AND DOWN, it will stay where you put it. LITERALLY. LOCKED. IN. SPACE.

The implications of this concept is amazing, huge floating cities, millions of sci-fi fans (including myself) screaming out in joy at having a hoverboard and subsequently screaming in pain as we fall off our hoverboards, but there is one small problem. Remember how they have to be cooled using liquid nitrogen? Well liquid nitrogen only costs about the same as milk but it still puts a huge hold on being able to mass produce anything using this concept. To be able to actually use anything taking advantage of superconductivity the object would have to be constantly cooled with liquid nitrogen which, as you can imagine, would be a pain. Currently scientists are trying to find a material that shows this phenomenon of superconductivity at room-temperature allowing all of these amazing inventions to become real-life. Unfortunately and funny enough, the science for a time-travelling DeLorean is still much farther behind, when it actually took time-travelling to the future to GET the hoverboard.

How to Find The Next Earth (if you have a giant telescope in the desert)

Good example of telescopes in the desert looking into deep space Courtesy of European Southern Observatory

Good example of telescopes in the desert looking into deep space
Photo courtesy of European Southern Observatory

People have been finding planets in distant space since Galileo first looked up at the stars with a telescope. By now though we can look much farther than just our solar system, we’ve even been able to see into the distant past. Astronomers find planets all the time as they look out into space with giant telescopes. The telescopes are usually in the middle of nowhere so other light does not interfere with them. XKCD describes well in one of his comic strips how amazing this is and also how much some people don’t care. Since finding planets is so common now it may seem easy to find one, like looking for a giant sphere of rock hurtling through space but it’s actually not as obvious as it seems.

There are many tactics to finding planets orbiting stars, most aren’t exactly for people in their backyards with a little telescope. One tactic called the transit method is to measure the light coming off of a star (the term is lumens). By keeping a consistent log of the light coming from a star, scientists can tell if there are planets orbiting it by noticing small variations in the brightness when the planet passes in front of our telescope. Another method came about by accident: scientists were studying the motion of a distant star and noticed, again, slight variations in their data. It was caused by something big pulling on the star, maybe a planet in orbit per-say.

Finding Earth-like planets is even more difficult though since the planet needs to be a certain distance from the star and even that is determined by the size and heat of it. Our planet Earth is in a place called the goldilocks zone around our sun. We aren’t too far where the planet will freeze to death and we aren’t too close where we will slowly burn and melt. The biggest reason this is the goldilocks zone is because it allows for liquid water. This is the biggest sign astronomers look for to find “Earth-like” or habitable planets. Also if there is little green men walking around on the surface it’s safe to assume the planet is habitable, that’s a bit of a larger hint.

Looking for other habitable planets like Earth may seem like a waste of time since our planet isn’t going anywhere anytime soon, but in a couple billion years when our sun turns into a red giant and engulfs our home in fiery radioactive fire, maybe everyone will be thankful that we did the research to find somewhere else to live and that the human race wasn’t born and then snuffed out but had the ability to expand and spread beyond our own home…or maybe we didn’t explore and instead burned to death on our own measly planet, who knows.