ZERO Gravity

[Kaito]

Astronauts in the ISS only feel like they are in zero-g because they are falling at the same speed as the ISS is. But they are still feeling the effects of gravity.

Would the same happen if suddenly there was NO gravity? Like, they were put in some region of space between two galaxies? (I know there will always be some gravity, but it is so small that it wouldn't matter)

 

[Artlav]

Not much effects, unless you got very good measures.
On ISS it's more orbital motion effects than gravity ones.

In your scenario, local things will still be pushed together, but once they reach equilibrium, they should remain with the same orientation.
On ISS, they will rotate due to orbital motion, and in lesser extent - due to tides.

Technically, you can make a gravity gradient meter - accelerometers on booms, but the precision required for it to sense a distant galaxy might be beyond even theoretical limits, and the local items will likely override it anyway.

If you have a precise enough clock (and not ridiculously precise this time), then after getting home you'll find some difference in passed time (wormhole or something-travel assumed, or it will be screwed by relativity).

 

[the.punk]

Between two galaxies there is much gravity. The two gravity sourses are only balanced. Not zero. But the astronauts would feel the same as on ISS I think.

---------- Post added at 07:22 PM ---------- Previous post was at 07:19 PM ----------

In your scenario you could also say that the two galaxies are rotating around you!

 

[Quick_Nick]

Gravity specifically isn't too important here. It's general acceleration. (or lack of) If the ISS moved at a constant velocity, there would be real zero-g. However, any Ecc over 0 means that the velocity is changing, thus there is accelaration. If you were in empty space with 'no' gravity, then you wouldn't feel or see any acceleration unless you caused it.

 

[Calsir]

Between two galaxies there is much gravity. The two gravity sourses are only balanced. Not zero.

Not really. The gravity field of LEO (450km altitude) is about 8.5m/s^2. The gravity field of the milky way (~5.8e11 Solar masses or ~1.46e42 kg) at 35e3 light years (half the distance of the Sagittarius Dwarf Galaxy) is just about 7e(-10) m/s^2 or 1/10000000000 of Earth Gravity field in LEO.

My source is wikipedia, but I don't think their data is controversial .

Edit: it is likely that the milky way at 75k light years may not be a gravitation point source, but the comparison still stands.

In your scenario you could also say that the two galaxies are rotating around you!

This is a truism in any case , it just depends on your reference system.

 

[Linguofreak]

Astronauts in the ISS only feel like they are in zero-g because they are falling at the same speed as the ISS is. But they are still feeling the effects of gravity.

Would the same happen if suddenly there was NO gravity? Like, they were put in some region of space between two galaxies? (I know there will always be some gravity, but it is so small that it wouldn't matter)

Well, in Newtonian Physics and Special Relativity, Gravity is a force (although special relativity doesn't really deal much with gravity at all, it basically makes the same assumptions about it as Newtonian physics does, and it's the fact that those assumptions don't work well in special relativity that lead Einstein to go one step further and develop General Relativity).

In General Relativity, gravity and the law of inertia are exactly the same thing. An object at rest will remain at rest unless acted upon by an outside force, and an object in motion will remain in motion unless acted upon by an outside force, but space itself moves inwards towards massive objects, so that "remaining at rest" or "in motion" becomes "falling". Black holes are unescapable because space at the event horizon is moving inwards at the speed of light (and faster inside), so that an object would have to move faster than the speed of light just to be able to move outwards. (This explanation is a bit rough, but is probably the best I can do without an in-depth course on what exactly "spacetime" means, and what it means for it to be curved, and how exactly special relativity works, etc, etc).

In any case, General relativity states that, with regards to the forces you feel, there is no difference at all* between being in freefall in a gravitational field and sitting still (or maintaining a constant velocity) outside of one. It also states that there is no difference at all between the forces you feel when standing on a planet with a one-gee surface gravity, and those you feel when accelerating in a rocket at one g.

(* This is not completely true. In the vicinity of a planet, you will feel tidal forces due to the difference between the effects of gravity at different points, and the fact that you yourself are not just one point, but if you're really small, or the planet is really far away, you won't feel them as strongly. If you were so small that you were just one point, then the statement in question would be completely true.