## Tuesday, October 29, 2013

### Gravity (2013)

I finally went to see Gravity, the new blockbuster with Sandra Bullock and George Clooney (I won't use their codenames Ryan Stone and Matt Kowalski: isn't it a good idea to simply use real actors' names in the movies?).

It's a visually impressive movie that can and should make you cry, be terrified, as well as think about the empty space, the human courage, the orbits, the angular momentum, and the hard job of astronauts on spacecrafts that experience problems. (But it isn't such a bad job to be a Hollywood star in a movie where astronauts experience problems.) Buzz Aldrin has said that the movie should re-energize the people's interest in space research. The box office results are highly encouraging but I am still afraid that most people in 2013 are distinguishing Hollywood and Houston and they prefer the former.

Tommaso Dorigo suggests that a more accurate name for the movie would be "Inertia" rather than "Gravity" because it's the inertia that played a fundamental role, not gravity.

I partly agree with that but I would have two comments. First, according to the equivalence principle of Albert Einstein, the cornerstone of the general theory of relativity, inertia and gravity are really the same thing. The motion that the astronauts exhibit – the motion under the influence of inertia – is really a special kind of motion in a gravitational field. This is how the motion in a gravitational field looks like in a freely falling frame.

Second, the gravitational field as quantified by some invariants such as the Riemann curvature tensor isn't really zero over there. Gravity is actually needed for those things to be kept in the orbit.

Well, I don't really believe that the people behind the movie think about the phenomena in terms of the equivalence principle and general relativity. Because I admitted this much, I also have to offer you a much simpler explanation why the movie is called "Gravity": it's a shortened version of "Zero Gravity" which describes all the key phenomena in the movie rather well. Or a shortened version of "Bullock is looking forward to experiencing gravity at the end of the movie again." It makes sense, doesn't it?

Tommaso also doesn't know any movies with just two actors. Well, cultural people in my nation know many, for example realizations of Václav Havel's "Audience".

Now the plot.

Bullock and Clooney are repairing the Hubble telescope or something when the Russians "fix" a broken satellite by a brute force, igniting some chain reaction or something, and creating lots of debris that just happens to shoot straight at the Hubble telescope. The "Explorer" spacecraft with Bullock and Clooney is irreversibly damaged and all the other crew members are killed. The communication with Houston is also breaking down.

There are just several minor inaccuracies in the movie – like a wrong motion of Bullock's hair in zero gravity; absence of surface tension between her tears and her skin, and a few others – but there's one recurring theme in the errors that is rather serious. The filmmakers are clearly assuming that the space around the Earth is much smaller than it is.

So in their view, it's possible to see dozens of larger pieces and thousands of smaller pieces of the Russian debris in a ball of radius 10 meters around Bullock. (A real explosion, a Russian one or otherwise, makes it much more likely for the pieces of debris to fly almost isotropically and this high density of debris is simply impossible at such a high distance from the epicenter of the Russian screw-up.) They also think that the International Space Station just keeps on sitting 60 miles from the Hubble telescope so the only thing you need to do is to walk there.

After some shocks caused by the rotating bodies that can't be stopped (without an external object, you just can't invent a maneuver or an exercise that stops your rotation, give it up: this much is guaranteed by the angular momentum conservation law and the movie is very realistic about all similar points) and after some reunion and elementary plans, Bullock and Clooney decide to relax and "walk" to a nearby International Space Station. It's a sunny day – no clouds at this height ;-) – so they may regain some composure on this trip.

Now, this is another example of the "too small space around Earth" idea that the filmmakers have. The Hubble and the ISS actually flew along different trajectories. The difference between their heights is just of order 100 kilometers but there is also a horizontal distance that oscillates between zero and thousands of kilometers each half-orbit (i.e. each 45 minutes). So it's highly unrealistic to think that the ISS is a "fixed destination" where you can just walk. In minutes, it's hundreds of kilometers away from the original place. You either need enough fuel that may "drive" you thousands of kilometers in less than an hour – something you can't achieve with the small jetpacks they have – or a precise planning of the point where the orbits "nearly" intersect.

If you have never seen the bright dot above your head indicating the ISS, you should click at this link and find the nearest time when it will be visible from your place. You may repeat the same with the Hubble telescope to see that it's much closer to the equator i.e. much less tilted/inclined than the ISS' orbit (and you won't see it for other reasons, too: it's too small).

But fine, they get to the ISS. It has been damaged, too. The ISS crew left and even though it could have saved some parachutes, it has wasted all of them, so there's nothing useful. Moreover, due to a complication involving ropes, Clooney has to disconnect himself from Bullock to sacrifice his life and save at least her life. Once he is floating towards his death, he's still using the radio to send her instructions and to encourage her. A true American hero and Gentleman. A touching scene.

She's almost out of oxygen but makes it to the module where she can create a nice atmosphere and undress her spacesuit. Once she exposes her skin, legs, and so on, she regains a good mood and surely improves the mood of many viewers, too. These astronauts were heroes, of course, but their psychological reactions in the movie seemed very realistic to me, too. Bullock, the woman, was more hysterical at the beginning while Clooney was acting totally professionally and heroically. Once she earned a good enough environment for her, she was doing fine and became a professional, too. However, at the same moment, she's getting used to the fact that Clooney is gone and will never be recovered. Sad.

Her plan designed by Clooney was to use the Soyuz module from the ISS to fly to a Chinese space station (again, pretty much a fixed target, another doable 100-kilometer trip, we're told).

She is realizing the plan very well – using some handy instruction manuals to perform some of the steps – but once she gets there, she finds out that there's no fuel in the space station. A radio conversation with a fisherman in the Greenland who is apparently playing with his baby doesn't provide her with a sensible survival plan, either (he wouldn't be close enough to send the signals for so many minutes, either). The most peaceful way for her to commit suicide is gradual decompression of the cabin – another realistic detail, I think. However, before she dies, Clooney returns to her place and offers her some friendly criticism and good mood. She agrees it's unprofessional to give up. Instead, she should try something she has never succeeded in before. Clooney managed to have saved her life again, despite the fact that he's already dead and what appeared in the space station was just a hallucination, of course.

At the beginning of the movie, we learned from a Bullock-Clooney conversation that just recently, she lost a 4-year-old daughter. During the tense space operations, she was praying for the first time in her life, right before the Clooney mirage visited her. But how did she make a breakthrough? She just ejected herself via explosive decompression and used a fire extinguisher as a jetpack in the final stages of the transfer. Simply clever. But we must admit it was a (virtual) man's idea (why can't women discover ingenious things in physics and engineering by imagining what ingenious men would advise them?). She arrives to the Chinese space station and gets in.

After the conventional realistic 90 minutes, the debris returns again "to the region" and kicks the Chinese space station out of the orbit. After some vibrations and surrounding fires in the atmosphere, you see a working parachute and feel quite some relief: Bullock finally lands, confined in a Chinese module, drops to the seawater, and manages to escape another down-to-earth trap (more precisely, a down-to-the-bottom-of-the-ocean hassle) over here: she has to open the spacesuit to stop an electrical fire which allows the water to get in which would mean that the spacesuit wouldn't float. She throws the spacesuit away, unmasks her optimistic skin again in front of a nice ocean-mountains scenery, swims to the beach, and she's waiting for the rescue workers over there, while getting used to nonzero gravity again.

A powerful movie with more solid physics foundations than what we're used to from other catastrophic thrillers and with extreme accuracy when it comes to the laymen-comprehensible details such as "which wirecutter was used during the most similar space missions".

1. It's an engaging movie. (Not polar) Satellites are launched eastward, with the Earth's rotation, picking up free ~1000 mph tangential speed. Looks to me that everything is orbiting westward. Confiscate Mt. Chimborazo for the planetary weal. Sending an MD to do engineering is like boarding your dog at a taxidermist. Sure, you'll get it back.

Serious space travel requires large /_\(mv) without paying large /_\(mv^2)/2. Noether's theorems are inert to absolutely discontinuous symmetries - external symmetry parity. Physics must exploit a footnote to get us from here to there.

2. Many have remarked on the seeming implausibility of having to cut Clooney loose - there is no obvious force pulling them apart.

3. I completely agree with this, too. This Clooney maneuver looked like a silly suicide to me. At least, he could have tried to redirect himself towards some part of the spaceship before he disconnected himself.

4. Dear Lubos

I have been reading your blog for some years now. I am a lurker but today you have made smile my soul again. I would like to let you know that I very much enjoy your posts, in spite of the fact that I do not concur with your, sometimes, male chauvinist position or harsh comments to some people you do not agree with. Your cutting edge knowledge of specialized subjects and the sharp analysis of simple situations have convinced me that your purported (and well promoted) high IQ is real. Reading your posts and listening to a fair interpretation of Marais' "Sonnerie de Ste Genevieve du Mont de Paris", have made my night.

5. For Lumo with gratitude:
I ignored the warning; have largely let go of Gravity; and am with stingy satisfaction subtracting from the probability of a prospective outlay on a ticket to it.

Am also slightly less unlikely to never recover from some surges in an overspending lifestyle.

(Maybe I should apply for Greek citizenship. ;>)

6. Thanks for your opinion and inacurracy in the movie Lubos. Can't wait to go and see it.
Hopefully they'll make a parody of the movie too... with some space toilet issues ;-D

7. I saw it last week. I thought the simulation of weightlessness was amazing (how did they do it!?), but the movie didn't make me cry or feel terrified, even though I'm one who tends to cry (begins to cry) at some movies. As for terror, I come nearer to being terrified at some other movies, e.g., movies about the supernatural, sad movies, and patriotic movies. Gravity, for me, was "just a movie," however wonderful the special effects.

Have you seen the story that a Mexican journalist asked the director, Alfonso Cuaron (himself Mexican), what it was like filming in space? Cuaron replied something like: Difficult, incredibly difficult. We were up there for three months, and believe me, it's not something you'd ever want to do. Later the journalist claimed he had been joking.

8. Well I actually didn't cry and wasn't terrified, either, although they're frequent phenomena with similar movies. It was more the novelty of the technological things in the movie that impressed me. So we are completely on the same frequency.

9. You may have replied while I was editing. I had senilely :-) said that some sad movies and patriotic movies made me begin to cry.

10. No, wait. Senility compounds. I had senilely said that some sad movies and patriotic movies made me feel terrified.

11. Yes, some of it could have been done in parabolic shooters, but some of that would have to be computer-merged with scenes of environment, and it seemed to me that computer processing of imagery must have come a long way in a few years.

12. I liked it as a straightforward adventure thriller. To the point, no clumsy leftish social message, just human spirit vs chaos and danger.
No "parabolic shooters." (I prefer the more evocative term "vomit comet.") Instead, underwater filming, wires and harnesses (digitally removed), large turn tables, and the "Light Box." http://www.nbcnews.com/science/how-gravity-threw-sandra-bullock-zero-gravity-big-screen-8C11326787

Quote from one of their science advisors:

"There are places where they went against the science input that they got, because it blows up their story," Kevin Grazier, a planetary scientist who served as an adviser for "Gravity," told NBC News. "You have a choice. You can either say 'You can get to the ISS from here,' or you have a movie like 'Open Water' in space. That's a different movie, and that's not what they were shooting for."

13. In the scene immediately preceding the (unphysical) separation, we see Bullock falling past the ISS towards the earth. At the last moment, she snags one of the drifting parachute lines left over from the defective Soyuz. It's a short sequence, only a few seconds long. Somehow, even though she is wrapped in a bulky spacesuit, Bullock conveys a sense of poignancy and desperation, only through the movements of her arms and legs, that is astounding to behold. You want to reach out and hug her.

I don't know how the actress does it. I saw an interview with her where she explained that "weightless" scenes where shot underwater and/or with wires holding and moving the actors. However, because this was not a real weightless environment motions would be different from what they would be in space, so that they had to laboriously train themselves to use "unnatural" body movements to mimic the movements that would occur "naturally" in space.

But that only tells us about the attention to detail that the film makers applied, it doesn't explain how Bullock conveyed so much of her character through the physical action of flailing wildly while wearing a suit that makes her look like the Michelin man.

14. I saw Gravity last night! I rented the video. I loved it and that is why I wanted to read Luboš' comments again, and give my opinion. Do astronauts really fly in space with these jet packs ? I'd like to know more about these, they're really cool, although not so accurate on the landing :-). To me my favorite scene is when she talks to some random Chinese on the radio on Earth -who can't speak English-, then she hears a dog and she barks with it and the Chinese :-) :'-(... Funny but moving. Grasping her last opportunity to communicate while she can... Bullock plays that part so well! To me only for that scene she deserves an Oscar.