Is 'Action at a distance' really a troublesome concept?

Question

I often watch videos where they say that even Newton was bothered by the idea of action at a distance, and that General Relativity solved that problem.
But why is 'Action at distance' a problem in the first place? If universe does it, it does it. We shouldn't presume anything about the universe. What alternative do we even have to 'action at a distance'? Particles touching each other by occupying the exact same position? Action at a distance is certainly better than that. Even intuitve 'touching' is action at a distance.
So can someone explain to me why action at a distance is supposed to be some issue?

niels nielsen · Accepted Answer

The different parts of the universe we inhabit are causally-connected in the sense that one part (a cause) can interact with another part (the effect), by a variety of means at the atomic level. The details of those physical interactions don't matter for the moment.
What does matter here is that none of those interactions are instantaneous; they are all mediated by signals that travel at some speed that we can measure.
If there were some signals that conveyed cause to effect instantaneously, then because of special relativity it would be possible for there to exist circumstances in which we would observe the effects before their causes had occurred (it would look like time was running backwards).
Instantaneous action at a distance thus presents us with very fundamental problems. Fortunately it is ruled out by experiment and a correct accounting of causality in our universe is provided by special and general relativity.

Is 'Action at a distance' really a troublesome concept?

One Answer

Add your own answers!

Ask a Question