# Where will we end?

1. Jan 17, 2014

### Emp-Naval

OK... So I was sitting there minding my own business when my alter ego popped out of no where and started asking me all these weird questions...

One in particular was interesting enough, and I couldn't even imagine what would be the result.

What if we mounted every planet, star, asteroid, and every last bit of matter with thrusters strong enough to move them. Then we simultaneously start them in the same direction (+ve X axis?), where would we end at? For the sake of discussion, let's say that the thrusters will last indefinitely.

2. Jan 17, 2014

### Emp-Naval

After rethinking, this belongs to General Astronomy... If a mod could move it please, and sorry for the inconvenience.

3. Jan 17, 2014

### CWatters

What difference does doing this to "every last bit of matter" make?

4. Jan 17, 2014

### Emp-Naval

so we could move all the matter in the universe...

5. Jan 17, 2014

### davenn

since its impossible to do, its pretty pointless thinking about it.

6. Jan 17, 2014

### Staff: Mentor

We would end up X distance from where we were, where X is an ever increasing amount. Assuming we continue to accelerate, as you've worded your question that way, we would see the CMB blueshift in one direction and redshift in the other. Eventually the blueshift would be so high that the incoming radiation would be in the gamma ray range, and after even more time the gamma rays would be able to disintegrate matter through the photodisintegration effect. http://en.wikipedia.org/wiki/Photodisintegration

7. Jan 17, 2014

### Emp-Naval

I know it's impossible, but why wouldn't you want to use your mind a little?!!!

8. Jan 17, 2014

### Emp-Naval

We will end up an X distance from what... There is nothing to be moving in respect to?

9. Jan 17, 2014

### Staff: Mentor

Sure there is. The cosmic microwave background. We could use that as a reference and devise frames of reference for each object to compare itself to.

10. Jan 17, 2014

### Emp-Naval

Ok, CMB might work as a "temporary" solution, but sooner or later it will just disappear, like in a trillion years from now I reckon...

Besides, If every last bit of matter moved 10 cm to the right, where would it be moving into, the matter is the universe!!! I think the question can be de-dramatized to the classical question, what lies behind the edge of our universe?

11. Jan 17, 2014

### Staff: Mentor

Thrusters work by sending matter in the opposite direction, so you can't move "every bit of matter" in the same direction without sending some of it in the opposite direction. This is momentum conservation 101.

12. Jan 17, 2014

### Emp-Naval

Good point here, and I feel dumb now >.>

13. Jan 17, 2014

### Staff: Mentor

The CMB is only used to give ourselves an initial reference point. We could use any inertial frame and still be okay. For example, if we were to use the frame of a particle that is later annihilated, the frame of reference would still be just fine. You can think of it as putting an imaginary observer right next to the particle that continues on with whatever velocity the particle had before annihilation.

The matter is not the universe, nor is there a known edge to the universe. If everything moved 10 cm to the right, it would be 10 cm to the right from its previous position.

Note that we don't literally need to constantly measure ourselves against a real object. Inertial navigation uses onboard, passive sensors that sense acceleration and direction and then uses that data to calculate a position without ever having to "look" at anything.

14. Jan 17, 2014

Emp-Naval,
Are you thinking that the Universe have a boundary?Like a ball?
When I was a kid,I thought that if I go out of the Universe,I would see white colour all around.

15. Jan 17, 2014

### Staff: Mentor

I always thought it would be pitch black.

16. Jan 17, 2014

### davenn

cuz I have better and more practical, real world, things to think about
than to waste time on the impossible

Dave

17. Jan 17, 2014

### CWatters

Why is that a problem?

18. Jan 17, 2014

### Khashishi

Taking the Machian point of view, if you moved everything, then it's the same as not moving at all, since only relative motions are measurable.