# Theoretical work on how momentum is carried or encoded?

1. Dec 29, 2015

I am not looking for homework help on how to do the math for vectors and momentum. Nor do I expect to understand the answer theoretically, but is/has any work been done that examines what it is that "carries" or encodes or transfers momentum? By this I mean that a particle receives energy from another particle and it moves in a particular direction. How does that particle "know" to continue in a particular direction. I know it's momentum and that the particle has to move, but why always in the same direction? Of course the flip side of that question is "why not?" for which I have no answer.

2. Dec 29, 2015

### davenn

it doesn't "know" anything

Are you familiar with Newton's 3 laws of motion ?
particularly #1

Dave

3. Dec 29, 2015

### ZapperZ

Staff Emeritus
Unfortunately, your question is actually a lot more "fundamental" and deeper than you think. What you are really asking is "why is there conservation of linear momentum?", and via Noether theorem, you are also directly asking "why does the classical empty space have translational symmetry?" (every conservation laws has an underlying symmetry principle).

We have no answers to those right now, the same way we have no answers to the many other "why's" in physics. Some think that physics doesn't address the why's, because the more you dig deeper into those reasons, you came up at the end with a description. But that is delving purely into philosophy.

Zz.

4. Dec 29, 2015

Hi Dave, Thank you for your reply. I'm going to make a wild guess and say that you're referring to his 1st rule:
Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.
Yeah, I've heard of it. The question remains - why? How is that mediated. What makes it not "decide" well, I've got energy, I have to go somewhere. According to quantum mechanics I could be anywhere, why can't I go in another direction for while?

5. Dec 29, 2015

### ZapperZ

Staff Emeritus
First of all, you need to learn how to walk first before attempting to run. Invoking quantum mechanics into this will not help, and as can be seen already, you are confusing yourself unnecessarily (besides, your understanding of QM is flawed here). So stick to classical mechanics for now.

Secondly, you'll notice that the object could actually be stationary in some reference frame, and that YOU are the one moving. So why should that object, just by coincidence, be at rest in your frame of reference? What makes you so special?

So there is nothing to "mediate" that. When there are no external forces involved, it is actually extremely unusual for an object to be stationary with respect to you. Think about it.

And as I expected, my reply to you on the nature of conservation laws and symmetry may have gone over your head. It is actually quite relevant here with your last question.

Zz.

6. Dec 29, 2015

You're absolutely right. about the nature of conservation laws, but your second statement was the winner in that it made the point clear.
"Secondly, you'll notice that the object could actually be stationary in some reference frame, and that YOU are the one moving. So why should that object, just by coincidence, be at rest in your frame of reference? What makes you so special?"

7. Dec 29, 2015