Even if multiverse exists, I doubt it would ever influence your day-to-day life, much less history.
It's too low level. It's all about quantum states, and we're like ten levels above them.
Low level processes tend to either go unnoticed by high level ones (think radio waves) or be harmful to them (think radiation) by messing with their high-level organization.
So please forget about hiding a knife in a parallel universe.
You do realise that this high-level / low-level distinction is all in our minds, right? It's just an intellectual tool we use to understand nature. If Quantum Mechanics is correct, _everything_ is made of quantum states, not just radio waves and radiation. Also, Chaos Theory.
True, but under our current understanding of QM, it is literally impossible for you to interact with parallel worlds. Someone 'outside' the universe may observe[0] that we are in a superposition, but it is theoraticly impossible for our state to be influenced by any of the other states.
Correct. It's only things that are random at a quantum level that might have multiverses.
Most [probably all actually] actions people take are not random at a quantum level.
In fact it's quite hard for something random at that level to have any noticeable [to a human] effect at all. So basically all the multiverses are identical.
> In fact it's quite hard for something random at that level to have any noticeable [to a human] effect at all. So basically all the multiverses are identical.
If and what particular type of tissue damage and/or cancer(s) is caused in someone by exposure to radiation damaging their cells in repairable or unrepairable ways (which depends on the particular times at which particular radioactive atoms decay and the paths of the resulting particles and their interactions with with the small-scale constituents of the person's biology). I would think that whether a person recovers from some radiation exposure or the exposure went just beyond what their cells could handle and thus causes a fatal cancer, that is noticeable to a human. Finding that wasn't altogether hard.
Given a sufficiently long time horizon (some physicists at UC Davies got some press arguing it could be on the scale of months), future weather conditions at individual moments are currently in the realm of quantum uncertainty/randomness. The people who have/don't-have car accidents due to the rain&sleet or not on some winter day a few years hence will easily notice which of the multiple worlds they ended up in.
Also, should anyone so choose, they could easily make world-history-scale decisions based on Geiger counter readings or some other implementation of a quantum-coin-flip. Imagine an assassin setup and ready to take out a large nation's leader(s), and taking the shot or not based on such a random quantum outcome. Scale is no barrier to such things.
It's too low level. It's all about quantum states, and we're like ten levels above them.
Low level processes tend to either go unnoticed by high level ones (think radio waves) or be harmful to them (think radiation) by messing with their high-level organization.
So please forget about hiding a knife in a parallel universe.