'Interstellar': A Sci-Fi Film with Plenty of 'Ifs'
This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun.
Credit: NASA/JPL-Caltech

Kelen Tuttle, writer and editor for The Kavli Foundation, contributed this article to Space.com's Expert Voices: Op-Ed & Insights.

From spinning black holes to the morphing of time, characters in the blockbuster film 'Interstellar' step right into cosmic phenomena usually only covered in textbooks and scientific papers. But just how much of the movie is true to what we know about the universe? And how much of it is creative license?

During a recent Google Hangout, three Curious Stardust bloggers — Mandeep Gill, Eric Miller and Hardip Sanghera — separated 'Interstellar' science fact from science fiction, revealing a story steeped in real scientific knowledge but not afraid to delve into the unknown. The conversation below features three astrophysicists:

Mandeep Gill is an observational cosmologist at the Kavli Institute for Particle Astrophysics and Cosmology, located at Stanford University and SLAC National Accelerator Laboratory. His research focuses on gravity's bending of light and the mysteries of dark matter and dark energy.

Eric Miller is a research scientist at the MIT Kavli Institute for Astrophysics and Space Research, where he studies diffuse gas to understand the structure of mass and how galaxies interact with their surroundings. He is a member of science and instrument teams for the Chandra and Suzaku X-ray Observatories, with active collaborations in the U.S. and Japan.

Hardip Sanghera is a member of the Cambridge Planck Analysis Centre, based in the Kavli Institute for Cosmology Cambridge. He supports the European Space Agency's space-based Planck observatory, which recently completed mapping the universe's earliest light.

Below is a modified transcript of their discussion. Edits and changes have been made by the participants to clarify spoken comments recorded during the live webcast. To view and listen to the discussion with unmodified remarks, you can watch the original video.

The Kavli Foundation: Before we talk about the movie itself, let's begin by explaining some of the phenomena in 'Interstellar.' To help us out, Eric, will you give us a simple explanation of a black hole? And to make more challenging for you — and because it's nearly the Thanksgiving holiday here in the U.S. — I'm hoping you'll explain it to us using only objects you might find in a kitchen.

Eric Miller: That might be a little challenging but I'll give it a go. A black hole is essentially a very dense concentration of matter — or food that you could find in the kitchen. A black hole is that it's so dense that there's a region around it outside which light can't escape. This is why it's called a black hole. The radius inside of which light can't escape is called the event horizon.

Eric Miller is a research scientist at the MIT Kavli Institute for Astrophysics and Space Research.
Eric Miller is a research scientist at the MIT Kavli Institute for Astrophysics and Space Research.
Credit: MIT

But the key to a black hole is not that it's massive but that it's very dense. In fact, a black hole can be made of very little mass — maybe like a green pea. But they can also be supermassive — which I guess would be like the turkey on the Thanksgiving table. The green pea black holes have about 10 times the mass of the sun and an event horizon maybe 20 to 30 kilometers across. In contrast, the turkey ones — like the one in this movie — are more like a million to a billion suns worth of mass concentrated in a very small amount of space with an event horizon about the size of our solar system.

Another thing about black holes is that matter is sucked into them kind of like matter travels down a funnel. As it travels down, it often spins around — much as we see in the movie. I think we'll talk more about that later.

TKF: You mentioned one term, the event horizon. Is that the point at which gravity is so strong that nothing, even light, can escape?

E.M.: That's right. It's called the event horizon because you have no knowledge of events that happen inside. Instead, it looks black because light is not escaping the event horizon. That's why we call it a black hole.

TKF: Moving on from black holes, Hardip, I'm hoping you can tell us a bit about far away planets. What do we know about planets in other solar systems? Are there likely to be habitable ones out there?

Hardip Sanghera: We discovered the first extrasolar planet in about 1992. Now we're up to about nearly 2,000 discovered extrasolar planets, thanks in great part to the NASA Kepler Mission. If we extrapolate from that number, we can estimate that there's probably anywhere between 100 billion and 1 trillion planets just within our galaxy. One of the things that we've learnt is that our solar system actually isn't the typical scenario for a solar system; most other solar systems are nothing like ours. What we tend to find is a lot of big gas giant planets clustered close to their stars. That would make it far too hot for life or habitability as we understand it. Plus, there's no real surface to talk of on these planets.

Hardip Sanghera is a member of the Cambridge Planck Analysis Centre, based in the Kavli Institute for Cosmology Cambridge.
Hardip Sanghera is a member of the Cambridge Planck Analysis Centre, based in the Kavli Institute for Cosmology Cambridge.
Credit: Cambridge Planck Analysis Centre

There's actually a catalog of habitable exoplanets that lists about 21 planets we've found so far that have the best chance of life. These planets seem to be in habitable zone, where the planet could harbor liquid water, not frozen or evaporated. What we really want to find are planets that are not too big — so that they have a surface — and not too small — so that they can hold onto an atmosphere.

The 21 planets we've found match these criteria. But these are, as I said, only the ones we can see: we can view light from a sun coming through the planet's atmosphere or we can isolate the light from the sun off the planet. What's even more amazing is that in this way we can actually learn, to some degree, the weather conditions on these planets. In perhaps a few years time we'll actually be able to look for signatures of life. Maybe we'll see traces of the oxygen in the atmosphere. You never know what's to come. [The Science of 'Interstellar': Black Holes, Wormholes and Space Travel ]

TKF: Mandeep, will you explain the general concept of a wormhole? Maybe you have a piece of paper there with you and can demonstrate using a couple of origami moves.

Mandeep Gill: First let me brush the popcorn off so we can talk. Now, wormholes are pretty speculative. We are very clear that exoplanets exist; we've seen them. Likewise, we know there are black holes because we see very clear evidence, as Eric mentioned, at the center of our galaxy and in other places. Wormholes are different. They are a potential solution to what are called Einstein's equations — our best theory of gravity. Albert Einstein and Nathan Rosen wrote papers on them originally, and then John Wheeler coined this term wormhole. He showed that wormholes would be unstable, that the ends would "pinch" off. Later it was Kip Thorne, who was actually an executive producer on the movie 'Interstellar,' along with his student Mark Morris who showed that in some way you might be able to stabilize the two ends.

Mandeep Gill is an observational cosmologist at the Kavli Institute for Particle Astrophysics and Cosmology, located at Stanford University and SLAC National Accelerator Laboratory.
Mandeep Gill is an observational cosmologist at the Kavli Institute for Particle Astrophysics and Cosmology, located at Stanford University and SLAC National Accelerator Laboratory.
Credit: Stanford University

So what are these things? As you see in the movie, there's an area that's kind of a portal, an extra dimension, between two points in the universe. I'm going to use this two-dimensional analogy, a sheet of tissue paper, to demonstrate. If you lived in two dimensions on this plane, you would never see the third dimension — if one existed around you. But if you could somehow fold space, and go through that third dimension, you could move between two points on the tissue paper, traveling through the portal.

As I mentioned before, Thorne and Morris sought to find a way to stabilize the mouths of these wormholes to keep them in place. They thought of some weird, negative energies — things that we don't normally see. But we do now have this concept called dark energy — people may have heard of it, it's something that was discovered about 15 years ago when we found that the universe's expansion is accelerating. That type of a strange "substance" — which involves high but constant energy density and negative pressure — could possibly allow for wormholes. But to implement it to stabilize wormholes is still very theoretical — the stuff of science fiction buffs' dreams. And I think that's great.

TKF: With that little bit of background, let's jump into the movie. But let's not worry about how the destruction of the earth is portrayedit's just too depressing. Let's instead start in space with the trip to Saturn. In the film it takes the astronauts 2 years to get from Earth to Saturn. How realistic is this? If we still had a space shuttle, could we point it towards Saturn and be there in a couple years?

M.G.: I don't think the space shuttle would make it because that's made for landing back to Earth.

E.M.: That's right, the space shuttle wouldn't have the necessary propulsion system to make the journey. Even with the right equipment, a mission to Mars would take about 18 months to 2 years, and Saturn is quite a bit farther than that. So I think with our current technology the answer is no, it wouldn't be possible to get there in 2 years. But that doesn't preclude future technologies and a future propulsion system that would allow us to get there.

I also want to mention that in the movie, they slingshot around Mars. This is a technique we often use for unmanned interplanetary missions. It's a way of stealing a little bit of valuable momentum from a huge body and giving it to this comparatively tiny spacecraft. That's a great way to accelerate very quickly.

H.S.: I read somewhere that the fastest missions take about 2.5 years to get to Saturn. But if you actually want to land on Saturn, you would have to decelerate when you got there. Taking that into account, you would be talking about timescales closer to 4 years. So they were a bit short in the film.

TKF: Now our astronauts are approaching Saturn and they see the wormhole entrance. Just how likely it is that wormholes actually exist somewhere in the universe? Let's rate the likelihood on a Thanksgiving scale from, say, a low end of Jell-O salad to a high-end of a perfectly cooked turkey.

H.S.: Well, I would say Jell-O salad. Sorry to be a pessimist.

E.M.: I would sort of give it a cranberry sauce, somewhere in the middle around a 50 percent chance. I like to be skeptical about these things.

M.G.: I don't know, maybe stuffing? We've never come across any evidence for one and they would be very strange objects. I do want to point out that even black holes are very strange objects, though. When they were first theorized, people said they were impossible. But there are strange things that are true in gravity and in quantum mechanics, so we can't rule it out. I doubt we'll find one nearby real soon though.

H.S.: Wormholes are tiny objects , much smaller than the dimensions of an atomic nucleus, and they only last for the tiniest fraction of a second. So to travel through one, not only do you need to find one of these tiny objects, but you've got to enlarge it and then you've got to maintain it so it doesn't collapse on itself. So it unfortunately sounds very unfeasible to me. General relativity doesn't preclude wormholes but it doesn't need them in any sense either.

TKF: For now, let's suspend our disbelief and continue following the astronauts through the wormhole. They emerge to find a dozen planets orbiting a black hole. Now, in our solar system the planets orbit a star, the sun. Have we ever seen planets orbiting a black hole?

H.S.: No, nobody has. We have seen planets around dense, compact objects like neutron stars. In fact, the very first exoplanet discovered orbits a neutron star. But as for black holes, no we haven't.

M.G.: I'm going to step up and defend the movie in this case. I had a discussion with a friend about supermassive black holes like the one in 'Interstellar.' We wouldn't be able to easily see if planets were orbiting around a large black hole because, oddly enough, black holes are usually very bright — their accretion disks give off a lot of X-rays. Another idea is that there could be other stars that are orbiting the black hole, and that the planets are orbiting around those stars. So it might be possible. Also, I don't think they went into this in the movie, but one of the coolest things about spinning black holes is the orbits of objects that get close to them. These objects, drawn in by the black hole's gravity, don't stay in a plane but actually travel in three-dimensional orbits.

H.S.: That's right. We can't see planets around black holes because we currently detect a planet by the wobble the planet induces on its host star — or the parent object that it's orbiting — or we see it by a dimming of the light as the planet passes in front of the star. We can't use either of those methods with a black hole; you wouldn't see a wobble induced by a planet on a black hole and also black holes don't emit conventional light or radiation. So we wouldn't be able to find them either way.

TKF: So they could be out there were just not seeing them quite yet.

H.S.: Correct. But then you get into questions of whether you would have stable orbits around a black hole, which is another thing all together.

TKF: One of our viewers would like to know if a black hole at the center of the solar system could actually provide the light that's needed to support life?

E.M.: With a supermassive black hole like the one in the movie, you get an accretion disk: essentially material that's being collected by the gravitational field of the black hole and is spiraling into the black hole. As this material falls in, there's a lot of gravitational energy that's released. Also, bits matter falling in will often collide with other bits of matter, heating things up. That's why you can typically see black holes shining in X-rays.

In fact, we think that there's a supermassive black hole at the center of essentially every galaxy . And a lot of them are very bright in X-rays. We see them shining steadily but with these occasional outbursts. Now, I don't think that a planet inhabitable by humans would survive if bombarded with this amount of X-rays. For comparison, the supermassive black hole in the center of our galaxy is sort of anemic, putting out in X-rays about the same amount of light as the sun puts out. In that way, you do have the same amount of energy released from a black hole — but it's in X-rays and also, as I said, fairly anemic. So I think the answer is probably not. Any life would probably be fried.

H.S.: Yes, the energetic radiation mostly in the X-rays would probably sterilize the planet, unfortunately.

M.G.: That's right. But if the stars were orbiting the black hole at a distant enough radius, then they could have planets around them. So it all depends on how realistic you want to be.

E.M.: That's true; it does depend on the distance. Although there are some other things in the movie that suggest that these planets are closer than you would want to be.

TKF: That's a great segue in to the next question. On the first planet the astronauts visit, time goes completely wonky and for every hour they spend on the surface of that planet seven years pass back home. We've had several viewers write in to ask for a rundown on how this works. Why would clocks run differently in two different parts of the universe?

M.G.: This is probably the biggest thing that really hasn't been displayed before in movies, and that physicists are excited about. The concept is called "time dilation by strong gravity." There are actually two forms of time dilation. One happens when things move very fast, and the other happens when things get very close to a very massive object. Most people have seen the equation E=mc^2. That tells us that light in a gravitational field feels the effect of gravity and falls downward. Yet, at the same time, somebody seeing it from far away sees it travel on a longer path than someone seeing it from close up. But light always travels at the same speed, and the discrepancy between how it looks from near and far eventually translates to time dilation.

E.M.: I think that was a good explanation. It's actually very hard to describe. As Mandeep said, it comes out of Einstein's equations and the fact the speed of light is a constant from all frames of reference. And that's essentially what controls how time passes for you. The same thing happens when you're in a gravitational field and when you're moving quickly with respect to some other person.

H.S.: I'd like to add that clocks actually run slower the stronger the gravitational field. In the 1970s, scientists took atomic clocks up in planes, and when they brought them down those clocks were running a little faster than the clocks on the ground. Another way we use this in daily life has to do with GPS satellites. Because they're in orbit above the Earth, their clocks run slightly faster than clocks on Earth. So the software in them has to take that into account to give us a proper clock signal. It's nice to see this concept of time dilation portrayed properly in the movie.

M.G.: It's true. Lots of times there are these esoteric-sounding physics concepts, but there are actually a good number of applications that come out of them. People thought at some point that you would never make use of general relativity but, like Hardip said, you would be off by many meters if the GPS satellite didn't account for it. It's pretty amazing.

TKF: One of our viewers has an interesting thought experiment that relates to this concept. He says: Let's say that the folks on the surface of this planet decided to radio their friend back on the ship to sing him happy birthday. Would the friend back on the ship perceive them singing excruciatingly slowly?

M.G.: We actually see something similar to this in astrophysics, where the wavelength of photons coming from a star are shifted a little bit toward the red end of the spectrum as they escape the star's gravity and come toward us. So yes, you would see weird effects like that, especially if they're in a very strong gravitational field. But in terms of singing? I'm not sure.

E.M.: This gravitational redshift means that whatever frequency they're using to send this radio broadcast — in other words, the frequency at which it leaves – is going to be different when it arrives at the ship. It's going to be redshifted, so the frequencies are going to be much lower at ship. The astronaut on the ship would need to tune to that frequency, with its longer wavelength. But I don't know what the decoded signal would sound like. Maybe it would depend on whether they're using FM or AM or something like that. But if they recorded a message on a thumb drive or cassette tape and brought it back with them to the ship, it would sound normal because all the mechanical stuff in there would be working in its local time-dilated framework. With a radio message, I'm not exactly sure because you have to think about how the information is actually modulated in the particular radio transmission. We do have a radio astronomer here. Maybe he knows. Hardip?

H.S.: I wish I knew how to answer the question myself actually.

E.M.: I think it's something that we need to think about. But if it's FM, if its frequency is modulated, I think you would just have to tune into a different frequency. I bet it will sound the same as long as you modulated it properly.

TKF: On that same planet, everything is covered in water. Suddenly a huge wave starts to approach. Viewers are asking why there is no discernible movement in the water as the wave moves closer, just a huge bulge approaching?

E.M.: The way the tide works on Earth involves the sun and the moon. Essentially, each of them gravitationally pull out a bulge of water, and the Earth rotates under that bulge. And so the tide would work the same way on this planet. You'd have a bulge pointing toward the supermassive black hole and the world would turn under it. That means that if you had one of these waves every hour, the planet would have to be spinning once every two hours. That's very fast, about 10 times the speed of the Earth. But I think what if you were a boat on that planet, you would just go up and down quickly — but I don't think you would even notice, especially since there isn't any land mass to compare your height to. So I think these very sharp waves is Hollywood fiction.

TKF: One more question about this planet: A viewer asks if astronauts needed to use a rocket to get off Earth, how could they possibly use a single Ranger to take off from this planet, where the gravity was 130% the gravity on the Earth?

H.S.: This is one of those holes in the film. To get off these planets, they would need exactly the same mechanism as they needed to get off Earth: a three-stage rocket. It's a common issue in stories; in Star Trek they used transporters to get on and off the planet. This is one of those holes, like the fact that there were no obvious fuel tanks onboard their spaceship. You wonder how they could have gotten from Earth to Saturn without a vast amount of fuel to carry them there and also to slow them down.

E.M.: Fuel tanks aren't photogenic.

M.G.: I think you guys are just a bit of spoilsports! I really liked the adventure aspect of the movie. I've been trying to solve these problems in my mind. Perhaps they invented antimatter drives, which would take very little room. If you could use antimatter as fuel, you'd need very little of it. The total amount of antimatter we've created on the Earth is less than a microgram, so it's pretty expensive stuff. But it would work. So there are ways to get around this, even if on the face of it things might not make total sense.

Neptune-size planets like this one, drawn orbiting the star Gliese 436, may be able to form around stars that contain far less metal than previously thought.
Neptune-size planets like this one, drawn orbiting the star Gliese 436, may be able to form around stars that contain far less metal than previously thought.
Credit: NASA

TKF: Let's skip ahead in the film a bit. After the astronauts visit another planet – which isn't as scientifically interesting as the first – the astronauts don't have enough fuel to make it to the third planet. So they slingshot themselves around the black hole and one of the astronauts, Cooper, ejects himself from the main spacecraft to help his colleague gain enough momentum reach that third planet. How would this help?

E.M.: That is a good question. As I mentioned when we were talking early on, you can slingshot around an object to gain momentum. That works around a spinning black hole too. The original models of black holes, theorized by Karl Schwarzschild had no spin and no charge, just mass. Later, Roy Kerr came up with another version of black hole that spins. And as it spins, it actually drags space-time around with it outside the event horizon. So there's a region outside the event horizon that the spinning affects. And if you enter that region — which, as I said, is outside the event horizon, so you can still escape — you can steal some of the spin of the black hole. But the way this works with a spinning black hole is that you actually have to leave some of your mass behind. That's how you exchange the energy; you give some of your rest mass energy to the black hole. So that's exactly what they showed in the movie. Cooper stayed behind and Brand was able to get to the planet.

M.G.: Can I mention a science aside? We're not going to be slingshotting around black holes anytime soon. But one of the coolest things Eric mentioned is how spinning black holes do this dragging of space-time. The faster anything in the universe spins, the more it does this frame-dragging. There's actually a very cool experiment called Gravity Probe B that checks for that around the Earth.

Also, a neat thing about spinning black holes is that we think you should actually be able to see their shadow deform. It would look something like a lima bean because the spinning is different on one side than the other. And we think we're going to be able to see that reasonably soon using radio telescopes, looking at the black hole at the center of the Milky Way and another that's much bigger but also much farther away from us in the galaxy called M87 in the Virgo constellation. It's going to be incredibly cool if we can get "real" pictures of the black hole.

TKF: As part of this whole interaction Cooper ends up propelling himself toward the black hole. I'm hoping you can tell us a little bit about what science tells us it might be like to approach the edge of a black hole and how it compares to the film.

M.G.: We simply don't know. Lots and lots of people have thought about this. It's going to be hot if you're coming along the accretion disk, and there's going to be X-rays coming out along that disc. You probably wouldn't want to be there. If you were to enter along the pole, avoiding the accretion disk, as long as there wasn't a jet of energetic particles shooting out, it might be okay. But Cooper skims right along the disc because he's a brave guy. There's also this idea that if the black hole is a small one you would be stretched because tidal forces — the same forces that cause the tide — are much stronger than gravitational force and could pull you apart.

TKF: There's a term for that, isn't there? Spaghettification.

M.G.: That's right. You get spaghettified. If the black hole is big enough, you wouldn't feel those tidal forces as much and you might be able to go in. We have a nice post on the KIPAC blogabout that from a couple months ago. It's a really cool thing.

H.S.: I've read that for small black holes, the tidal effects would be so strong you would get torn apart. We actually saw that happening to the spaceship but not to the astronaut in the film. As Mandeep said, if this were a supermassive black hole with the mass of a hundred million suns, the tidal effects would be very gradual and so you could theoretically survive the trip into the black hole. In the process, you would also cross the event horizon. Cooper didn't know he was crossing the event horizon when that happened, and that's exactly what we would expect. Only an external observer would see anything happening. For Cooper, he would just pass through it and go in the black hole. Once he's in the black hole, it's anybody's guess what goes on there.

TKF: We're running out of time, but I want to make sure that we talk about this at least a bit. Inside the black hole, Cooper enters a strange realm where time is a spatial dimension. Do we have any idea if such things exist?

E.M.: No. I think this is all speculation and a lot of it is science fiction. Clearly there's room for it — you can put a lot of things inside of Einstein's equations. If you start going into higher dimensions, certainly you can do almost anything. I think that's exactly what they did here.

How they showed him entering the black hole was interesting though. I think what Hardip said was right. When you're crossing the event horizon, you wouldn't actually know it — and in fact you wouldn't really see anything different. But I think the way they showed it is not exactly how it would look. If you were falling in, you would constantly see an event horizon below you, rather than blackness all around you. So I didn't think that made a lot of sense in the movie. As far as we know, you would just go straight to the singularity of the center. In all, though, there could be lots of things going on with the black hole that we don't know about. But I think everything that was shown inside the black hole was probably science fiction.

If you're a topical expert — researcher, business leader, author or innovator — and would like to contribute an op-ed piece, <a href="mailto:expertvoices@techmedianetwork.com">email us here</a>.
If you're a topical expert — researcher, business leader, author or innovator — and would like to contribute an op-ed piece, email us here.
Credit: SPACE.com

TKF: One of the things that happens in that black hole is that Cooper manages to communicate with his daughter using gravity. Let's consider the idea of communicating with gravity. Is that possible?

M.G.: Well, we do know about gravitational waves. We've indirectly seen them far away, coming out of two pulsars orbiting each other, but haven't yet seen in them on Earth. We're looking for them on the Earth right now in Louisiana, in Washington State, and in Europe, with the U.S. observatories being funded by the NSF. We're looking for them passing through the Earth, after being created in big supermassive black hole collisions and things like that. So yes, in theory you could communicate with them. But since we haven't been able to detect them and since they're huge — their deviation over a two-kilometer range would be about a hundred thousandth of the diameter of a proton — they would be hard to see or to communicate with. But in theory many things are possible. Hardip is actually writing a blog post about this right now.

H.S.: From what I understand, these gravitational waves are very, very weak — at least the ones we hope to detect from these instruments. There's Advanced LIGO, which I think goes live in about two years' time, and then there are space missions like eLISA. But because gravitational waves are so weak, the only signals we are going to pick up with these instruments are the massive ones, like the ones created in the merger of two black holes or in collisions between two stars. But I'm not quite sure I understood what they were doing in the film, trying to communicate with gravity. I just accepted the story and switched my science brain off at that point.

TKF: One last question about black hole: One of our viewers asks if not even light can escape the clutches of the black hole's gravity, how could flesh and bone? How did Cooper escape? Is that possible in any possible way?

H.S.: We have to assume that this more advanced civilization — the one that presented him with all the views of Earth laid out in front of him inside the black hole — must have the capability to take him out and put him elsewhere. That's one possibility. Another idea is that if you go into a supermassive black hole with the right trajectory, supposedly you can pass through and potentially come out somewhere else in the universe. So maybe he fell in in the correct way.

M.G.: I would say we really don't know what goes on inside black holes, as Eric mentioned. Our physics only goes up to a certain point. The thought that black holes even exist was a crazy idea in the last century and now we know they're there. So any question you're going to ask about what's happening inside is going to be hard to answer.

Pulsars like the one shown here emit a lighthouse-like beam of light (magenta) as they rotate.
Pulsars like the one shown here emit a lighthouse-like beam of light (magenta) as they rotate.
Credit: NASA's Goddard Space Flight Center/Cruz deWilde

TKF: Let's look beyond the black hole to the movie as a whole. Physicist Kip Thorne, who was an executive producer on the film, has said that he had the job of keeping the moviemakers from violating any known laws of physics, with his criterion for acceptance being "something serious physicists would at least discuss over beer." Would you say he succeeded?

M.G.: Yes. There are a lot of things like the time dilation that we haven't seen in the movies before, and that were really great to see. Kip actually wrote to us before this hangout, and it was great to hear that he's published a book on the science of 'Interstellar,' which I think will probably answer these questions better than us. But overall, there's a lot of physics in the movie, from just how the black hole looks to how light bends as it interacts with gravity.

H.S.: I think Kip did keep them honest about the gravitational lensing, what you would see around a black hole, and time dilation. There I think it lived up to the hype; the science was accurate. But many other science concepts in the film had holes. So parts were accurate, the rest… well, it was a story.

E.M.: There were things that were kind of taken to a science fiction extreme, but overall I was actually very happy with the science and very happy to see something where these science concepts were put up on the big screen.

H.S.: But you have to say there were lots of "ifs": if a black hole could capture a planet, if there's such a thing as a stable orbit for a planet orbiting a black hole, if a planet could survive a tidal effect. There's also a big if about what the radiation would be like on that planet. Yes, possibly these things could happen, but they're probably extremely unlikely.

TKF: One last question: If the three of you were science advisors on a science fiction movie, what concepts would you want to include?

H.S.: I'd like to see pulsars. You could imagine a film in which we're zipping through the galaxy in our interstellar spaceship. We're going to need some sort of navigational markers or we're going to get lost in the galaxy. In that situation, you could imagine using pulsars as a framework for navigation. A pulsar is basically a neutron star, a stellar remnant in which the electrons and neutrons are forced together to create this very dense compact object that is rapidly spinning and has an intense magnetic field. These pulsars spin a thousand times a second, and like a lighthouse they pulse at that rate. But these objects also flash in the visible. What I'd love to see is an interstellar pilot going past one of these basically interstellar lighthouses. And because these pulsars are embedded in supernova remnants, we would have a really nice backdrop.

E.M.: I think this movie was great. I'm excited to see general relativity treated this way. I was also excited to see a wormhole reproduced in realistically. It's this hyper-dimension projected onto three dimensions, so you wouldn't see a tornado vortex that you see in a lot of movies, like Star Trek. Instead you see a sphere, which was great.

I'd also like to see a realistic treatment of exoplanets. We're starting to discover a lot of these things. It would be interesting to see in a movie setting the wide range of planets that we've discovered. It's more exciting than what Star Wars is showing. It's not like you just have frozen planets and desert planets; you've got hot Jupiters and you've got dwarf planets and things like that. That would be really cool to see in the movie.

M.G.: For me, there's the stuff that we know about in the universe, like magnetars and pulsars and extreme black holes. But then there's stuff like dark matter and dark energy; these are very different and we don't know too much about them. It would be neat to see that portrayed in some way. Will the universe expand forever? Is there a multiverse? There's an amazing amount of stuff that we're still discovering. It would be neat to see things like that — everything from the things we expect to see soon, like gravitational waves, to the further out stuff. We humans are a good, creative species.

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