The wife asked, what if we jump and there's no gravity? You are the science dude. Extrapolate.
Well, that's a great question (and you are very pretty, of course). A small correction to the question. There is no place where there's zero gravity. If there is such a place it is infinitely far away and we'll never get there. The place with no gravity is infinitely far away because the force of gravity - although it weakens as we get far away from its source - never becomes zero. However, there are places with very very weak gravity.
So, what if we jump where there's very very weak gravity?
If we rate earth's gravity as one, then the force is six times weaker on moon (gravity is proportional to mass). If you jump one feet on earth, you can jump six feet on the moon. Suppose, you land on an Asteriod and it looks desolate that you get suicidal and jump off. How far would you (or your dead body) go? Quite far. That's because the asteroid has a very weak gravitational field. If you are near a planet when jumping off the asteroid, you'll probably fall into the planet as it would slowly but surely pull you in. If you are lucky, the asteroid may be near the Sun, in which case you can go blazing into the Sun like Marvin, the paranoid android in Douglas Adams novel.
A more visual example would be spacewalking astronauts. They are in orbit around earth along with the craft when they do their spacewalk (spacewalk is a charmingly earth-centric misnomer, it's mostly free-floating and firing tiny rockets on their backpack). If they jump by kicking the spacecraft, and if their rotten luck has it that they are untethered, they'll jump all the way into earth (and burn up as they enter). They could get away from the spacecraft because it has very weak gravity and since it is near earth (which has more gravity), they eventually fall into earth.
After all I have told you, if you really want to experience zero-gravity, you would have to rig the laws of our universe.
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None of the above will make any sense to your wife.
Just say "You go up and you don't come down again."
Right?
I want to nitpick...
I am going to venture a wild guess (without even attempting any math) and say that there are probably plenty of points in the universe with zero gravity. The key word being "points".
All you have to do is pick any location, figure out the net graviational vector at that point, then place a rock of the right size the right distance opposite you, so that the net gravity becomes zero.
And I'm also guessing this happens naturally (maybe unavoidably too, based on some kind of max/min theorem?).
I suppose I also guess that there can be no volumes with zero gravity throughout.
Having equal and opposite gravitational fields is not the same as having no gravity.
In engineering we intelligently talk about zeroing out a bias voltage. Only a purist would argue that there is no such thing in a circuit as zero voltage, since there will be random fluctuations even in the absence of an applied potential.
When we say 'zero gravity', we mean 'negligible gravity' -- gravitational attraction that is imperceptible on whatever time scale applies to the particular problem and can be ignored in calculations.
Bringing my nitpickerplucker to bear, saying there's no place without gravity is much like rooting for the centripetal force in favour of the centrifugal. You say tomato, I say tomato. It all depends on ones perspective. In any case, Einstein argued in his famous theory that effects of gravity are independent to those caused by acceleration. It follows that the difference between free fall and zero gravity is physically irrelevant.
Also, I quite doubt that jumping off an asteroid could take you to the Sun or onto a planet, unless the asteroid is also on a collision course with the same body. In any case, I'd guess that a large enough asteroid to be solid enough to jump off of would have enough gravity to pull you back. (Unless the asteroid is passing close by a black hole or some other body with a very steep gradient of gravity.)
Furthermore, I'm quite sceptical of an astronaut being able to jump off the shuttle and fall into Earths atmosphere in any reasonable circumstances. No matter how hard the astronaut would jump, he'd likely just slightly adjust his orbit around Earth, because orbital velocities are measured in kilometers per second and the astronaut just can't jump so hard as to make a significant difference. (Of course the shuttle might be low enough to for the astronaut to be dragged into the thicker atmosphere eventually.)
doh. Now the wife will know I was bluffing.
Lagrangian points (points in space near earth and moon, or other such bodies where gravity cancels out): I missed it completely when I wrote the post. Equivalence principle may not have much bearing on the question.