Unstoppable Or Is It.?

[modeller]

If I was in outer space and I threw an object , say an iron ball , would it travel for ever or could it eventually slow down ? I am assuming it is outer empty space therefore there would not be any gravity effects, or is some gravity everywhere of varying strengths. In which case could that slow it down or speed it up .

[whiskeryron]

Because we do not know if there is an actual end to the cosmos imagine the whole of space being circular, then your iron ball would eventually hit you in the back of the noggin.

WR.

[jim360]

Assuming spacetime is described well by the "Friedmann-Roberston-Walker" spacetime, http://en.wikipedia.org/wiki/Friedmann–Lemaître–Robertson–Walker_metric , then effectively the ball will travel on for ever, following the curves of spacetime smoothly. However this is an idealised model and eventually the ball would slow down, losing energy to whatever else it bumps into along the way.

[ToraToraTora]

Newtons first mate! It'll travel till it hits something!

[Clanad]

You say "...I am assuming it is outer empty space therefore there would not be any gravity effects..." Your assumption is incorrect. Gravit is expressed everywhere in the Universe.

Secondly, If you were in 'outer space' (which you need to define) as you threw the ball, you would move in the opposite direction with equal acceleration making it somewhat difficult to determine if you threw the ball or the ball threw you...

Your ball would eventually begin to orbit something somewhere. Think (meteroites, comets and glalaxies). Nice question though!

[jno]

presumably modeller would also end up orbiting some minor planet?

[ChuckFickens]

"as you threw the ball, you would move in the opposite direction with equal acceleration"

Surely that would only be the case if the ball had equal mass to modeller, if his mass was 100 times that of the ball he'd accelerate the other way 1/100th the acceleration of the ball

[modeller]

I was aware that I would move backwards. I had thought of throwing it from the space station but felt that was too close to earth and space debris
so there was no guarantee that the ball would have a clear run.
I also wondered about sub atomic particles . We know that radiation and gravity has an unequal distribution throughout space so you might expect it to affect the ball. On the other hand if space is fundamentally neutral
then maybe these effects would cancel each other. However the universe is not stable so thats a non starter.

[wildwood]

I wonder if the would eventually travel close enough to some sun/planets/galaxy to be affected by their gravity!

[modeller]

I would think at some time that would happen. Remember what happened
to the space probe that used the planetary gravity to obtain sling shots.

[LazyGun]

Its not specifically relevant to the question, but it does make me laugh every time I see it :)

https://www.youtube.com/watch?v=CwaiXdoEaM8

[bert_h]

It's only in a very very borderline case that your ball could be "captured" by the gravity of some other body. Basically, if it approaches a large body, but not on a collision course, it will be deflected, but not slowed down. You would see it leaving at the same speed that it had been arriving with, but in a different direction. It would only be if it collided with enough fragments of space debris when it was close to a larger body that it could possibly drift into a closed orbit, instead of escaping again. The further out into empty space that it was, the smaller would be the gravity effects of other bodies (but never zero), so the smaller (but never zero) would be the deflections they caused.

[jomifl]

In the space between galaxies it could keep going but it would almost certainly end up in orbit around something.