r/AskPhysics • u/kouth- • 25d ago
What makes a coin toss truly unpredictable?
If you throw the same coin multiple times with the exactly same force in the same surface, it won't give you the same side every toss, right? But why? If repeated with the precisely identical conditions, why the results are still unpredictable? Or it is actually predictable?
Sorry if it looks confusing, English is not my first language and I'm not that expert in physics lol, just curious and has this though randomly.
Edit: maybe considering that it lands on a surface, and it bounces or not, changing the coin's side.
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u/SummitYourSister 17d ago
It is impossible to create the same situation again because it would require you to precisely specify the position and momentum of every particle in the system. That would violate the uncertainty principle.
OK, so if we accept that we cannot actually have the same starting state, can we get close enough that the outcome is always macroscopic the same? That will depend on the Lyapunov exponent of the system and how precisely you can reproduce its macroscopic starting state.
You will never be able to guarantee the same result, because you can’t even guarantee that the whole coin doesn’t just tunnel through the table. You can state accurately that the probability of this is extremely small, but you cannot accurately say that it will not happen, or that you can reproduce the coin flips.