A thought experiment.
Take a sealed system, a container.
Inside the container, against one wall, eject an electron. It will have momentum mv and will have imparted an equal and opposite momentum into the wall of the container. Left to its own devices, the electron will fly across the container and impact the opposite wall, when the two momenta will cancel one another out. If we had been able to look carefully enough, we would have seen the container jiffle slightly as it momentarily held the created momenta component.
But what if... part way across the container, the electron met a wanton positron and together they fused in the perfect dance of energy creation. Energy does not have momentum, so where did the electrons momentum go ??
More to the point, the container is now left with unresolved momentum and will continue to move under its influence until some external force steps in and stops it.
Action begat reaction, but action got itself totalled leaving only reaction.
Keep this up and the container will start to wiz along without any interaction on the outside world - reaction without action (granted, the formation of all that energy within the container is going to make it one smokin hot pot), but it is a pot that is breaking the law of conservation of Momentum - or is it ??
Take a sealed system, a container.
Inside the container, against one wall, eject an electron. It will have momentum mv and will have imparted an equal and opposite momentum into the wall of the container. Left to its own devices, the electron will fly across the container and impact the opposite wall, when the two momenta will cancel one another out. If we had been able to look carefully enough, we would have seen the container jiffle slightly as it momentarily held the created momenta component.
But what if... part way across the container, the electron met a wanton positron and together they fused in the perfect dance of energy creation. Energy does not have momentum, so where did the electrons momentum go ??
More to the point, the container is now left with unresolved momentum and will continue to move under its influence until some external force steps in and stops it.
Action begat reaction, but action got itself totalled leaving only reaction.
Keep this up and the container will start to wiz along without any interaction on the outside world - reaction without action (granted, the formation of all that energy within the container is going to make it one smokin hot pot), but it is a pot that is breaking the law of conservation of Momentum - or is it ??
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