- #1
Weston
- 3
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Hi all, this is my first post to the forum.
I've been thinking about a mechanism that can't work, but I can't figure out why not. Here is the idea:
1) If I have two wires parallel to each other on a table and I run a current through them, they will be attracted to each other. I believe this will happen even if the current in the two wires is the same (same speed and direction).
2) Now imagine putting the wires on a train. If I run the train at the drift velocity of the current, then I could imagine the charge in the wires standing still (from the reference point of the train) while the wires zip by. That is, my train keeps pace with the electrons so that they are standing still in the "train frame".
3) Now, as long as the electrons aren't moving in the train's reference frame, let's replace them with statically charged marbles. Two negatively charged marbles sitting on the train should look a lot like a little piece of the current in the wires.
Here's the problem. From the "ground" reference frame, the marbles have a velocity and a charge, so they represent a current and the marbles should be attracted to each other. But from the reference frame of the train, the marbles are not moving, so they should not be attracted to each other.
Shouldn't I be able to measure the attraction between the marbles (or just watch whether they roll towards each other), and deduce some kind of "absolute velocity"? I know that isn't possible, but I'm not sure where my reasoning breaks down.
Thanks in advance for any thoughts.
Weston
I've been thinking about a mechanism that can't work, but I can't figure out why not. Here is the idea:
1) If I have two wires parallel to each other on a table and I run a current through them, they will be attracted to each other. I believe this will happen even if the current in the two wires is the same (same speed and direction).
2) Now imagine putting the wires on a train. If I run the train at the drift velocity of the current, then I could imagine the charge in the wires standing still (from the reference point of the train) while the wires zip by. That is, my train keeps pace with the electrons so that they are standing still in the "train frame".
3) Now, as long as the electrons aren't moving in the train's reference frame, let's replace them with statically charged marbles. Two negatively charged marbles sitting on the train should look a lot like a little piece of the current in the wires.
Here's the problem. From the "ground" reference frame, the marbles have a velocity and a charge, so they represent a current and the marbles should be attracted to each other. But from the reference frame of the train, the marbles are not moving, so they should not be attracted to each other.
Shouldn't I be able to measure the attraction between the marbles (or just watch whether they roll towards each other), and deduce some kind of "absolute velocity"? I know that isn't possible, but I'm not sure where my reasoning breaks down.
Thanks in advance for any thoughts.
Weston