Gravity - a force created by the presence of mass.

Any two pieces of mass attract each other with a force more or less inversely proportional to the square of their separation and directly proportional to the product of their masses. This is Isaac Newton's famous law of gravity, F = Gm1m2/r2 where G is the gravitational constant.

Of course, this has been proven wrong by Albert Einstein's theory of general relativity, which treats gravity as the result of the warping of space-time by mass. In most cases, the answers given by relativity match those of Newton's law. Gravity is always attractive. Two pieces of mass are never repulsed from each other due to gravity.

Black holes are one prediction of general relativity, as are gravity waves and various other phenomena.

General relativity isn't the final word on gravity, either. Attempts at combining GR with quantum mechanics and the unification of the four forces (electromagnetism, gravity, the strong nuclear force, and the weak nuclear force) under one unified theory have lead to things such as superstring theory and M-theory which describe the universe in ways different from both QM and GR.

Gravity is the Earth's excuse for keeping us down.
One reason the Earth has continuously kept humanity down through the so-called scientific explanation of gravity - loneliness. Mother Earth is afraid of being alone and keeps man close to her. Examples of the Earth's use of gravity to keep humans from soaring into their rightful place in the heavens include the tragic flight of Icarus and the Russian space program.

That warp in Space and Time that all known matter creates; this warp causes any other piece of matter that enters it to curve towards the generating (usually larger or greater-mass) piece of matter although it is still for all intents and purposes moving in a straight line. Earth is moving AWAY from the sun, but the curvature in space-time that the sun creates causes the earth to move AROUND the sun. The farther you get away from the gravitational event, the slower time moves. Gravity does not only effect matter but time as well.

Einstein spoke of gravity but he never wrote the equation which unlocked it. Gravity is the last " frontier" for physics, well at least as far as we know. Einstein did start the train rolling on the understanding of its effects in space as well as time, see the satellite orbiting around the sun and the delay of its signal returning to Earth because of the Sun's gravity experiment. If and when gravity is "conquered" space travel as we now know it will more closely resemble the hollywood version aka Star Trek.

< Back to How Far To Turn | Up to MIT Guide to Lockpicking | Forward to Pins Not Setting >

#### Gravity

Picking a lock that has the springs at the top is different than picking one with the springs at the bottom. It should be obvious how to tell the two apart. The nice feature of a lock with the springs at the bottom is that gravity holds the key pins down once they set. With the set pins out of the way, it is easy to find and manipulate the remaining unset pins. It is also straightforward to test for the slight give of a correctly set pin. When the springs are on top, gravity will pull the key pins down after the driver pin catches at the sheer line. In this case, you can identify the set pins by noticing that the key pin is easy to lift and that it does not feel springy. Set pins also rattle as you draw the pick over them because they are not being pushed down by the driver pin.

In the spirit of "things could be very different than you imagine" (mentioned by Noung), there's an idea that springs to mind when one considers that not only are we in an expanding universe, but that the expansion is accelerating.

Those of you who have watched popular television science shows have seen the rubber sheet demonstration. I have seen these shows, and while I am impressed with them, there is always one aspect that has nagged me immensely. The balls only create dents in the rubber sheet because they are being pulled by Earth's gravity. A two-dimensional illustration of gravity, but it depends on a three-dimensional gravity to be effective.

The lastest scientific thinking that I've heard about rumors that the universe is expanding at an accelerating rate. If that is so, this acceleration can take the place of the Earth's gravity in the rubber sheet experiment. Balls will cause a dent in the rubber sheet, not by being gravitationally attracted to something, but by simply having inertia to work against the motion of the accelerating rubber sheet. The experiment will show the same results if the sheet is accelerating upwards as if it's stationary within a gravitational field.

Another demonstration that's shown in popular science magazines is the idea that our universe may be like a balloon that's expanding - thus, things in the universe are mutually moving away from one another without all moving away from a particular point in the universe. These two ideas can now be linked - the rubber balloon is expanding at an accelerating rate, with masses denting spacetime simply by the inertia they have. Locally the rubber-sheet model holds, and this links the inertial property of mass with the gravitational property. In that case, all the dents are pointing inwards, and massive objects are in fact closer to the centre of the universe than less massive objects or empty space.

Taking this idea to outlandish extremes... what if the acceleration of the universe were to change? Gravity would be affected. What if it has been changing? Gravity isn't what it used to be. If there is a big crunch, then there will be a point where spacetime is shrinking but the massive objects will still be moving outward. Will there be oscillation? Will it be damped? Will it be underdamped, overdamped, or critically damped?

Yes, I've probably been thinking far too much about this fanciful idea. For one thing, I've heard it said that gravitational fields cannot be expressed as scalar fields (which would probably be the case if this idea were true), they can only be expressed as tensor fields (of higher rank). But, the idea tickles the imagination.

Gravity is the 5th album by the Canadian rock group Our Lady Peace. The much-anticipated (by me, anyway) album lives up to my every expectation, even if it's absolutely nothing like I thought it would be. Yay surprises!

Track Listing:
1. All For You   4:14
2. Do You Like It?   3:58
3. Somewhere Out There   4:11
4. Innocent   3:42
6. Not Enough   4:33
7. Sell My Soul   4:20
8. Sorry   3:18
9. Bring Back the Sun   5:11
10. A Story About a Girl   4:18

Total Run Time: 41:26

Overview:
This is a very good album, although I feel it's a little too short. Then again, I'm a big Our Lady Peace fan--it could have been three hours long and I'd still want more. YMMV.

Gravity has a much different feel from their other albums. I'm not sure if this is because of the addition of Steve Mazur, Our Lady Peace's new guitarist, or if this was just something they had to do, but it sounds great. The album as a whole is much heavier than their previous releases--they've always been reasonably hard rock, but Gravity takes it to a new level. A friend commented, "They sound like a Canadian Staind!"

Track Analysis:
Listening to the intro of the first song, All For You, it's easy to tell where one could draw that comparison. A slowish, dreamy, very soothing synthesizer melody takes up the first :23. It sounds like the making for a slower, Are You Sad?-esque song... and then the guitars crash in. And then the double-bass rolls on the drum kit start up. Now it sounds almost like nü-metal, and if it wasn't for Raine Maida's familar voice you wouldn't have any idea who was playing. Our Lady Peace definitely chose the right song to begin their album with: All For You lets the listener know that the days of Clumsy and Thief are over and shows just how versatile a band they can be.

Do You Like It? follows up All For You very nicely. Although there has always been a hint (or perhaps a bit more than that, in some cases) of angst and self-hatred in Maida's lyrics, Do You Like It? shows this much clearer than I've ever seen from him in any of his other songs. The words

```   //~...I hate myself for begging
I hate myself for staying
I hate myself for listening to you...~\\
```
leave very little to the imagination. All in all a very good angry song.

The third track is also the first single from the album, Somewhere Out There. A slower, somewhat lighter song (although still nothing like Life, the first single from Spiritual Machines), "Somewhere Out There" was a good choice for the radio. It's a song about an ex-lover who has gone away and Maida wants her back (//~...I miss your purple hair/I miss the way you taste...~\\). Orchestral strings (I believe I hear a violin and a viola, but I play trombone, what the hell do I know?) are mixed in with the guitar parts to create a very beautiful and melodic piece of music. Another keeper.

One of my favorite songs on Gravity is Innocent. It tells the story of two people who could really be anyone in the world--Johnny and Tina--as well as Maida himself, and how they all wish things were better in the world. It again tells about people who seem to hate themselves, as is apparent in Tina's verse:

```   //~...Every calorie is a war
While she wishes she was a dancer
And that she'd never heard of cancer
She wishes God would giver her some answers
And make her feel beautiful...~\\
```
The chorus is what really makes the song, though. It's very simple, but brings everything together. If you hear just one song off of this album, make it Innocent.

The first song I'm not a huge fan of is Made of Steel. It's not a bad song by any stretch of the imagination, surely, and lyrically it's very good, but musically... again, it's not horrible, but certainly no where near as good as the first four tracks, in my humble opinion. Three stars our of five, in other words.

Track six, Not Enough, is a slower, pretty depressing song. Comparisons can be made between it and 4AM, but that's probably a bad idea because 4AM is awesome and it makes Not Enough seem much worse than it actually is. It would be one of the poorer tracks on the album if not for the very heavy bridge (//~...it's not enough...~\\ with a ostinato distorted guitar line underneath it), but it still ranks about as high as Made of Steel.

Sell My Soul is much like the previous two songs, unfortunately, as far as quality is concerned. Maybe it's just that the first four songs were so mindbogglingly awesome that it's hard to follow up on, but I think this is one of my least favorite songs on Gravity. Others may tell you differently, but it comes down to my node, my editorial.

Luckily, Sorry kicks ass. Yay! I'm beginning to realize that I like Our Lady Peace's upbeat stuff better than their slower songs as a general rule. There are exceptions, of course, but Sorry is an upbeat song with, while not a totally upbeat lyric, not a thoroughly depressing one either. A very nice song that's refreshing to hear after a rather disappointing stretch of mediocrity.

Bring Back the Sun is kinda dreamy: it almost makes me wish I knew how to dance so I could softshoe around my basement. Although not a terrific song either, for some reason I like this better than tracks five through seven. Probably about a 3.5 out of 5.

The album closes out with A Story About a Girl. This song starts off sounding uninteresting but winds up being very good towards the end. All I really have to say her is stick with it. It's a very good choice to close out the album with; if nothing else, Gravity is organized very well.

Concluding Thoughts:
Fans of Our Lady Peace should definitely appreciate the new sound the Canadians bring to the table with their latest release. Definitely go out and buy this one.

Oh, and I'll node the lyrics to the tracks later, assuming no one beats me to it. In the meantime, if you just can't wait, they are listed in the liner notes and most likely can be found at www.ourladypeace.com

This is quite a helpful way to memorise the history of theories of gravity, and is astonishingly accurate for a limerick.

A Brief History of Gravity

It filled Gallileo with mirth
To watch his two rocks fall to Earth.
"Their rates are the same,
And quite independent of girth!"

Then Newton announced in due course
His own law of gravity's force:
"It goes, I declare,
As the inverted square
Of the distance from object to source."

But remarkably, Einstein's equation
Succeeds to describe gravitation
As spacetime that's curved,
And it's this that will serve
As the planets' unique motivation.

Yet the end of the story's not written;
By a new way of thinking we're smitten.
We twist and we turn,
Attempting to learn
The Superstring Theory of Witten!

(Written by Bruce Elliott, published by The American Physical Society, reproduced with permission)

g r a v i t y

Newton once said, "gravity explains the motions of the planets, but it cannot explain who set the planets in motion." He understood that for every action there is an equal and opposite reaction. For all of his restrained brilliance Newton was incapable of offering even a twinkle of vision into the chaotic realm of the human heart. Isaac wasn’t alone in his revelation; the frosty realm of hard science systematically ignores the mayhem of feelings that classify our being. I find it interesting that we can characterize the guiding theorems of the very cosmos but be short of understanding the world within. I may subsist in the corporeal world, but I exist in the territory of the self. And that hallowed world appears to be far more intangible then the stellar fireballs that smolder quietly in the coastal sky.

I can’t help but think that maybe Newton’s theory has some equivalent in the uneven landscape of my heart. Gravity has no power in that noiseless province, but there are other forces laboring to bend all motion and events. The recollection of a sun lit sky where a girl in love fights back tears as her plane takes flight carries the raw power of a thousand suns - its tidal strength tethering a ribbon of my being to that sun-drenched day.

When slumber conceals consciousness, time expands according to the desires of the heart. And for a golden moment I am back there speeding under a translucent sun, sea spray gently falling upon my face.

I am with much respect

Your most humble and most obedient Servant

E. Haulfield.

# Oh, Gravity!

What attractive force is this that pulled down

The same that grabs on ev’ry other noun?

Oh gravity! Without you we’d be dead:

Yet you’re such a weak fundamental force;

O’er come by less than holy messiah

A balloon’s static is sufficient source.

Fantastic finding that all things plummet

Downward acceleration, nothing sparèd

From deep ocean to valley to summit

Nine point eight meters per second squarèd.

Expansion slowed at constant rate of G.

Gravity is one of the four known fundamental forces of the universe. It is the one that determines which way is down - in some ways it is the most obvious and familiar of the forces, but it is only since Isaac Newton that people have really thought of it as being a force at all. Before that people just figured that stuff has a natural tendency to fall downwards, which is not quite the same thing; Newton's great insight was to realise that the observed universe starts making a lot more sense if we suppose that everything is attracted to everything else, and that the motions of the moon and the planets and our own Earth around the Sun can be explained by the exact same force that drops an apple to the ground.

Gravity is by far the weakest of the forces. To get an idea of just how weak it is compared to electromagnetism, consider how easy it is to pick up pieces of paper using the static electric charge on a comb that has just been through clean, dry hair: all it takes to overcome the entire gravitational pull of the planet Earth is those few electrons that have jumped from your hair to the comb. Yet gravity dominates at large scales, because electromagnetism has an in-built tendency to cancel itself out - positive charges are so strongly attracted to negative charges that they almost always appear together, and from a distance, the conflicting positive and negative pulls almost always balance each other out.

Gravity is strongly self-reinforcing, since it attracts everything to everything. This gives bulk matter a tendency to congregate and to collapse in on itself, which is one of the main reasons the cosmos orders itself into galaxies, stars, planets and clouds, with vast areas of mostly-empty space between them. Things tend to collapse into balls, on a big enough scale, or spin into discs. When a dust cloud collapses in on itself, its gravitational potential energy is converted into other forms of energy, much of it ending up as heat. This is why the centre of the earth is hot, and how stars get hot and dense enough to initiate nuclear fusion.

Every object in the universe is attracted to every other object in proportion to the mass of each object, and in inverse proportion to the square of the distance between them. That is, an object twice as far away will be attracted one quarter as strongly. This inverse square law is the result of the gravitational field spreading out in all directions from any body. It happens for exactly the same reason that when you look at something from twice the distance, it looks a quarter of the size, in the sense that it is half as wide and half as tall. The area of a sphere (or cube) is therefore in proportion to the square of the distance, and gravity spreads out in a sphere from its source.

At any point in space, the total strength of the gravitational field tells you how strongly it pulls on any unit of mass - the force applied per kilogram of mass, or equivalently the rate at which things accelerate. Right here on the surface of the Earth, everything is pulled downwards at the rate of about 9.8ms-2 (or equivalently, 9.8N/kg) - that is, ignoring drag, any falling object will fall 9.8 metres per second faster (or 22 miles per hour) for every second it falls. We can't ignore drag in the real world, of course, and in practice any given object will eventually reach a terminal velocity where the drag matches the force of gravity. This depends on the weight and shape of the object. For an adult human it is around 55 metres per second - that's more than 120 miles per hour. For a mouse it is less than a tenth of that, so it is probably true that mice can survive a fall from any height - depending on how they land. Cats appear to be slightly more likely to survive after they reach their terminal velocity (which is around about 7 floors down), presumably because they find their feet, stop panicking and very quickly get the hang of being their own feline parachute.

The fact that gravitational field strength can be measured as a rate of acceleration was one of the threads that led Einstein towards the General Theory of Relativity. He started considering what it might mean if gravity is in fact identical to acceleration, in the light of what the Special Theory of Relativity tells us about velocities - in particular, Minkowski's formulation of relativity in terms of spacetime. If velocity can be seen as a rotation in spacetime, and gravity can be seen as a rate of change of velocity, maybe gravity arises from a change in spacetime? Einstein figured out that if he supposed that spacetime is curved by the presence of any mass, he could use the equations of four-dimensional geometry that Riemann had worked out sixty years before, to produce something that looked very much like Newton's equations of gravity... until you looked at what happens near extremely massive bodies, or at subtleties like the way light curves around stars.

Einstein's conception of gravity has a number of very interesting consequences. One is that the distortion of spacetime around every massive body means that the closer you get to it, the more time slows down - so time passes measurably slower for us than it does for a satellite in orbit. The effect is small here, but around much more massive bodies, it would become far more noticeable.

Another rather odd consequence of General Relativity is that from a certain point of view, gravity is not a force at all - it is just what happens when things follow their natural trajectory along the most direct path through spacetime. Indeed, someone in freefall does not feel anything like a force of gravity - which is why astronauts in orbit feel weightless, although they have by no means escaped the pull of the Earth's gravity entirely. From the more familiar frame of reference of someone standing on the surface of a planet, of course, gravity looks very much like a real force - just as it makes sense for someone on a fast-spinning roundabout to treat centrifugal force as a real thing. Indeed, there are two ways of viewing the weightlessness of orbit. One is that being in orbit is like being in freefall, while moving sideways so quickly that you never touch down. The other perspective is that since you are moving around in an ellipse at just the right speed, you feel a centrifugal force that exactly matches the pull of gravity, cancelling it out. The distinction between 'fictitious' and 'real' forces is not clear-cut, and string theory suggests that all forces may in fact depend on one's frame of reference - which would make them, in some sense, fictitious.

Black holes and wormholes might also be fictitious, and they certainly sound unlikely when you first hear about them. In fact, though, black holes are almost certainly quite real, and wormholes are at the very least plausible. There is no apparent limit to the amount of spacetime curvature that general relativity allows, you see, and no known force in the universe which can resist a strong enough gravitational pull. That makes it seemingly inevitable that when sufficient mass collects in one place, it will eventually collapse into a gravitational singularity - a point, or ring, of infinite spacetime curvature, from which almost nothing can escape. Although we cannot observe it directly - conclusively proving the existence of an actual black hole is extremely difficult, even in principle - the signs are very strong that there is a black hole at the centre of our own galaxy, with the mass of more than four million suns. There is less reason to think that our universe contains actual wormholes, which is to say hyper-dimensional tunnels connecting two regions arbitrarily far apart in space and in time. However, they are at the very least a tantalising possibility suggested by the mutability of spacetime - nobody has been able to rule out that it might be possible to build one.

In daily life, of course, we usually don't have to think about relativistic gravity - in fact, as long as we stay close to the surface of the Earth, even Newton's universal gravitation is barely relevant. The main thing to know on Earth is that the gravity around here accelerates things downwards at about 9.8ms-2, which means that a 1kg weight gains 9.8J of kinetic energy for every metre it falls (or gains the same amount of potential energy for every metre you raise it up). Having said that, the effective strength of gravity on Earth actually varies from about 9.832ms-2 at the poles to about 9.780ms-2 at the Equator, so a 1000lb pumpkin at the North Pole would only be a 994.7lb pumpkin by the time you got it to the Equator. Even for interplanetary space missions, good old-fashioned Newtonian physics is generally enough to plan your trajectories around the solar system. It is true, though, that as soon as you are in orbit you will start gaining 38 microseconds on us every day. Granted, that is only one full second every 73 years - but 38 microseconds of time is also the equivalent of seven miles' worth of space, and sometimes that is important.

I was so extravagantly impressed by the portrayal of the reality of zero gravity.... The spinning is going to happen — maybe not quite that vigorous — but certainly we've been fortunate that people haven't been in those situations yet. I think it reminds us that there really are hazards in the space business, especially in activities outside the spacecraft.
Buzz Aldrin, on Gravity

An accident in space sets an engineer and a medical specialist adrift. Against the views of space, billions and billions of stars and the blue expanse of earth and the brilliance of sunrise, they must try to survive.

Options are limited.

All too often in Hollywood, SF gets limited to space opera. Gravity gives us scientifically plausible (if not scientifically perfect) SF, depicting events in space that could happen next Tuesday. Its premise reminds us of just how hazardous real space travel remains; simple mistakes and minor accidents are likely to prove fatal. Hollywood thrillers, meanwhile, all too often involve uninteresting characters and shock-a-moment pacing that numb the viewer. Gravity's plot puts likeable people in a grave situation, and lets the story unfold over ninety minutes of something like real time. The movie observes the classical unities, and these prove more immersive than the 3-D effects. We feel the passing of limited time.

Written SF has handled similar scenarios many times before. One of my first real SF reads was Ray Bradbury's 1949 tale, "Kaliedoscope," which has a superficially similar premise. Motion pictures, however, have avoided hard, near-future SF and the mundane disasters that might befall space travelers. Gravity may not be original for the genre, but it's remarkable for a film, and it finds its own direction, distinct from similar tales.

Two Hollywood heavyweights, Sandra Bullock and George Clooney, must carry most of the story's drama. Overall, they prove equal to the task. Bullock, in particular, successfully transforms herself into her atypical character. She trained for six months to get in shape for this demanding role, and it shows. George Clooney remains a little more like, well, George Clooney, though the part requires a certain affable charisma. Perhaps their characters could be further delineated, but the few actors carry ninety minutes admirably. I must say, though, I wonder how this film would have worked with the director's alleged first choices, Angelina Jolie and Robert Downey, Jr.

The backdrops against which the astronauts maneuver prove that digital effects, well done, can serve a story without overwhelming it. No trip to Middle Earth or Pandora has ever looked this spectacular, and the sights Gravity recreates really exist. Although this film differs dramatically from 2001: A Space Odyssey, it occupies a similar place; it establishes a standard for off-world visuals. This film looks like it has been shot in space.

Gravity is not perfect. With everything else the script throws at its protagonists, I found the fire aboard the space station unnecessary and the scene's execution of it a tad far-fetched. And, given the movie's overall scientific accuracy, I'm surprised they had a certain character drift away so rapidly, as though earthbound rules applied at that moment. The filmmakers could have handled this differently and had a similar result. The ending, too, may stretch some viewers' tolerance. The score, meanwhile, ranges from effective to intrusive.

These points do not significantly diminish the effect of the film. We rarely see real SF1 on the big screen, much less SF that borders on real-world, mimetic drama. I hope Gravity takes next year's Hugo, along with its mainstream accolades. The studios need to know that quality films that stray from the summer blockbuster format can repay their investment-- and that science fiction extends far beyond power fantasies and interstellar lens flare.

Directed by Alfonso Cuarón
Written by Alfonso Cuarón and Jonás Cuarón

Cast
Sandra Bullock as Ryan Stone
George Clooney as Matt Kowalski
Ed Harris as Mission Control
Marvin the Martian as Special Cameo

1. A few readers have asked whether this film should be classified as SF. It's a fine line. It's fiction based on science, and Clooney's character uses a space-walk device that's a little ahead of current tech. YMMV.

"I hate space!"

Gravity is a spectacular, awe-inspiring and thrilling film which retrospectively really ticks me off.

It never ceases to astonish me how good special effects are right now. We're spoilt! Ron "Apollo 13" Howard would have killed for this technology. I saw Gravity on a screen which claimed to be IMAX (but realistically, probably wasn't quite there), and what I saw was crystal clear and so lush as to be almost edible. We are finally, finally in an era in which 2001: A Space Odyssey - the high water mark of space technology FX for what, four decades? - has been definitively surpassed. We have perfect clarity of picture in an environment entirely without atmospheric effects. More importantly, we're finally in an era which can do that environment justice. It really looks like that!

We have impressively accurate reproduction of real-world space hardware from the Space Shuttle (called Explorer in the film, but for some reason still referred to as Atlantis on the soundtrack?) to individual one-of-a-kind wirecutters. And laudably accurate and effective use of sound, and that booming bass score by Steven Price, clearly taking cues from Jaws. In case the rest of this thing persuades you otherwise, I think this is a film you should see. It is a spectacle. It is one of the films which justify the existence of cinemas.

And, if you're meaning to, you should probably watch it before reading the rest of this.

I disagree very strongly with the message of Gravity.

"Space is terrible," says the film. "Do not go there. You're only a real human being if you're on the ground." Space is a place where the protagonist undergoes a profound transformation - and this is arguably one of the more technically accurate aspects of the film, as this is a real, observed phenomenon in space travellers, going back as far as Yuri Gagarin. But the transformation doesn't mean anything until the lady is walking on solid ground again. In fact it barely takes hold until she's well on her way home! Sandra Bullock's character is too much of a figurative baby to understand how amazing it is, and how privileged she is, to be working in space. She blows up, by my estimation, some two hundred billion dollars' worth of space hardware in the process of trying to get back into her comfort zone.

"If you do go there," says the film, "get what you need and come back as soon as possible." The scientific justifications for space exploration receive no acknowledgement in dialogue, even though the Hubble's right there in shot. "Half of North America just lost their Facebook," says a character, as if that's the greatest loss that would arise from a real Kessler outbreak.

Gravity has strong spiritual themes, including an event whose most embarrassingly unscientific interpretation would be a visit from the afterlife. Are astronauts spiritual? I have no doubt of this. Is space an environment where survival has nothing to do with faith and everything to do with rigid adherence to procedure and respect for cold, implacable equations? Yes. Is this a film where the character who does everything absolutely by the book dies for it, and the spunky rookie relying on inner strength lives? Yes.

(And another thing. What's the point of having incredibly long single continuous shots be your directorial trademark, and then making a space film which doesn't have a long real-time continuous shot stretching from orbit all the way through re-entry to climbing out of the capsule at ground level? I mean, what the hell?)

The film opens with some fixed text explaining how hostile space is. The final line of this text is "LIFE IN SPACE IS IMPOSSIBLE". Meanwhile, the ISS has been continuously inhabited for more than fifteen years. Cuarón even blows it up, just to make sure it doesn't contradict his point.

Gravity is disrespectful to the accomplishments of space explorers. It reduces space travel to a purely selfish emotional journey. Astronauts have important and dangerous work to do up there, and the emotionally immature are not admitted.

Grav"i*ty (?), n.; pl. Gravities (#). [L. gravitas, fr. gravis heavy; cf. F. gravit'e. See Grave, a., Grief.]

1.

The state of having weight; heaviness; as, the gravity of lead.

2.

Sobriety of character or demeanor.

"Men of gravity and learning."

Shak.

<-- p. 648 needs proofing ##proof - especially italicized words (aso in etymologies) are not properly marked-->

3.

Importance, significance, dignity, etc; hence, seriousness; enormity; as, the gravity of an offense.

They derive an importance from . . . the gravity of the place where they were uttered. Burke.

4. Physics

The tendency of a mass of matter toward a center of attraction; esp., the tendency of a body toward the center of the earth; terrestrial gravitation.

5. Mus.

Lowness of tone; -- opposed to acuteness.

Center of gravity See under Center. -- Gravity battery, See Battery, n., 4. -- Specific gravity, the ratio of the weight of a body to the weight of an equal volume of some other body taken as the standard or unit. This standard is usually water for solids and liquids, and air for gases. Thus, 19, the specific gravity of gold, expresses the fact that, bulk for bulk, gold is nineteen times as heavy as water.

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