the reach of forces

[gib65]

Suppose the universe was a trillion light years across, and suppose the only things in the universe were a proton and an electron. If the electron was at one end of the universe and the proton at the other (i.e. they were 1 trillion light years apart), and given enough time for photons to travel, would they still 'feel' each other's electromagnetic attraction? If they did, the force would have to be incredibly weak at that distance, but would it still happen? In other words, what I'm asking is, is there a critical distance such that any two particles that are separated by distance greater than this, the influence one can have on the other in virtue of their forces (whatever that force may be) actually reaches zero - as opposed to perpetually approaching zero but never reaching it?

[Klaynos]

If there was nothing else other than the two particles in the universe then they would feel each others EM force. We see the photons from stars many many many light years away.

[CanadaAotS]

The thing is the magnetic attraction between the two propagates at the speed of light. So it'd take a trillion years for either to feel the attractive pull anyways lol.

[[Tycho?]]

The two particles would move together at an incredibly tiny rate. Electromagnitism and gravity both work over arbitrarly large distances. I'm not sure about the nuclear forces. I dont see why they would be different, but I've read they do drop to zero, so I'm not sure.

[bascule]

gib65, it seems like you're trying to ask "Does every particle in the universe transfer some small bit of force, however incomprehensibly small, to every other particle in the entire universe?"

 

Or, to put it another way, is the state of any given particle for a particular timeframe truly dependent on the state of the entire universe? Is everything causally interconnected?

 

I'm afraid the answer is just going to be "models are just models and can't answer those kinds of questions"

 

I presupposed the answer to this question to be "Yes" in my crazy theory of the universe.

[Severian]

To answer the original question, yes - they would, but you would need 1 trillion years to pass a signal between them (which is rather a long time considering the univers is about 13.7 billion years old).

 

In other words the electromagnetic force has infinite range. the same is true for gravity.

 

The strong force, on the other hand does not have infinite range, and will be cut off at distances of order 1/GeV (with appropriate factors of c which I can't remember off-hand).

[gib65]

gib65' date=' it seems like you're trying to ask "Does every particle in the universe transfer some small bit of force, however incomprehensibly small, to every other particle in the entire universe?"

 

Or, to put it another way, is the state of any given particle for a particular timeframe truly dependent on the state of the entire universe? Is everything causally interconnected?

 

I'm afraid the answer is just going to be "models are just models and can't answer those kinds of questions"

 

I presupposed the answer to this question to be "Yes" in my crazy theory of the universe.

 

Yes, I remember this post. I'll have to reread it.