- #1
mrspeedybob
- 869
- 65
For th sake of simplicity I will state the question in terms of magnetism but the same problem would arise from any of the 4 forces.
Suppose you have a self-contained electromagnet and piece of iron 300,000 kilometers apart. Each is at rest relative to the other and to the observer.
Switch the magnet on. 1 second later the magnetic field reaches the iron and applies a force to it. An observer can see it begin to accelerate toward the magnet. The magnet must begin to accelerate at the same instant or the center of mass of the two body system will move and violate the law of conservation of momentum. What causes the magnet to move when it's field reaches the iron? If the Iron were not there then the magnet would not move so it seems like the minimum reaction time of the magnet would be 1 second for the field to reach the iron and another 1 second for the irons effect on the field to be transmitted back to the magnet for a total of 2 seconds. As stated above though, this time lag would cause a violation of the law of conservation of momentum.
Suppose you have a self-contained electromagnet and piece of iron 300,000 kilometers apart. Each is at rest relative to the other and to the observer.
Switch the magnet on. 1 second later the magnetic field reaches the iron and applies a force to it. An observer can see it begin to accelerate toward the magnet. The magnet must begin to accelerate at the same instant or the center of mass of the two body system will move and violate the law of conservation of momentum. What causes the magnet to move when it's field reaches the iron? If the Iron were not there then the magnet would not move so it seems like the minimum reaction time of the magnet would be 1 second for the field to reach the iron and another 1 second for the irons effect on the field to be transmitted back to the magnet for a total of 2 seconds. As stated above though, this time lag would cause a violation of the law of conservation of momentum.