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Old 03-11-2017, 12:13 AM
 
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Quote:
Originally Posted by Bitey View Post
If that bullet were the only object or matter or energy source in space besides the gun that fired it, then yes it would continue on its course and velocity in perpetuity, as would the gun in the opposite direction.
You mean it will continue accelerating, or just stay at muzzle velocity?
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Old 03-11-2017, 01:03 AM
 
Location: Brackenwood
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Even space isn't completely frictionless as there is debris, dust particles, gases, etc. that will slow it down, albeit negligibly so. Provided the bullet doesn't come close enough to a celestial body with enough mass and gravitational pull to alter the bullet's trajectory, it will travel through space on its present course in perpetuity, probably decelerating ever so slightly as it does. And if the gun is out in the middle of space well away from any celestial bodies, it won't reach any unless the bullet is traveling faster than the universe is expanding, which is unlikely.
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Old 03-11-2017, 09:37 PM
 
6,851 posts, read 6,740,930 times
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Quote:
Originally Posted by Bitey View Post
Even space isn't completely frictionless as there is debris, dust particles, gases, etc. that will slow it down, albeit negligibly so. Provided the bullet doesn't come close enough to a celestial body with enough mass and gravitational pull to alter the bullet's trajectory, it will travel through space on its present course in perpetuity, probably decelerating ever so slightly as it does. And if the gun is out in the middle of space well away from any celestial bodies, it won't reach any unless the bullet is traveling faster than the universe is expanding, which is unlikely.
What exactly is moving away from each other? Is it just galaxies or galaxy cluster? Why not the celestial bodies within, like star system moving away from star system, or even within the star system, like planets moving away from each other?
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Old 03-12-2017, 12:03 AM
 
Location: Somewhere in northern Alabama
18,514 posts, read 55,435,808 times
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Quote:
Originally Posted by NJ Brazen_3133 View Post
What exactly is moving away from each other? Is it just galaxies or galaxy cluster? Why not the celestial bodies within, like star system moving away from star system, or even within the star system, like planets moving away from each other?
That is one of the harder concepts to grasp. Imagine a sphere with the visible universe in it. Now increase the size of the sphere, but at the same time, keep the particles of universe in their same positions relative to each other and the exterior of the sphere. That is the basics of expansion.

Now... remove the sphere but imagine the same action.

Then... allow that the force of gravity in planetary systems and galaxies is enough greater than the force causing expansion that the distances between planets and the sun don't change, and the galaxies remain as galaxies.

That is a crude model, but shows the basics. A key that it is true is the red shift of light from stars. That red shift occurs equally in all directions, which can only happen if the stars are moving away at more or less equal speeds.
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