Is this a good metaphor?

[TheManicMonocle]

So I was thinking, most people are familiar with the theory of parallel dimensions. Do you think it's a fitting metaphor to say alternate dimensions are like different saves on Civ 5?

[Khedrac]

To be honest, no.

Parallel universes are usually envisaged as different branches from key decision points in history (where key points could be things like who wins a battle or which way a particle decays) and these can be thought of a like different game saves.

However, these are not the only possible parallel universes; so a parallel universe might be more like a saved game for Mario when you are playing Civ 5.

Parallel dimensions are something different (even if the term gets abused a lot) - I am not sure what they really are, I think they woudl be the same 3+1 dimensions we have, just offset somehow.

As such, it is a good metaphor for the conventional view of parallel universes, but this is a small subset of such things, and parallel dimensions opens the door even wider.

[Lvl 2 Expert]

That depends on what you mean by alternate dimensions and which theory you go by.

Dimensions in the usual sense of the word are the things that make up space and time. An alternate dimension in that context would be like having glorp and sip instead of up and down. If you assume our universe has more than the usually observed four dimensions there could at least theoretically be whole worlds full of aliens occupying the same three dimensions as we do except slightly shifted glorpwards, and we have no way of interacting with them. They would follow the same or nearly the same natural laws, but there's no reason for them to be similar enough to us that they look human and know what a fidget spinner is. So in that case the answer is not really. I think most physicists who calculate using multiple dimensions assume that numbers five and above are all rolled up tightly some way, and that's why we don't see them rather than a complete inability to interact with those dimensions.

The words alternate dimension as a combination are often used to mean a different universe inside the multiverse. The multiverse is a theoretical concept, but at its most basic it just means there is a space-like sort of something where big bangs happen every now and then. A big bang creates time and space for itself, or at least all the useful stuff that fills it. We can't really get outside of our own universe or even take a peak, because the universe is bigger than the observable universe, the collection of things we can see because they started emitting light long enough ago close enough by. In its most basic form, no, the multiverse is not like alternate save games, and there's no telling if most other universes even have recognizable forms of matter, as things like the universal constants could be different. With a near infinite number of universes there would be some that are more like ours than others, but just going over into the next one is not going to result in you meeting your evil twin.

So the thing you're probably thinking of is the branching worlds interpretation of quantum mechanics: Every "choice" made on a quantum level creates two new universes: one where the radioactive atom did split of a gamma radiation photon this Planck time and one where it didn't. In this theory there are bazillions of worlds which are just like ours except a second ago a quark in your head went spinning the other way. In science fiction people stumble upon these all the time, usually ones where exactly one big thing went the other way. Some subatomic interaction snowballed into Hitler winning ww2, smoking never going out of style or your father never being born. (That one is actually kind of plausible because of how many sperm cells are involved. The slightest change in circumstances gives a different winner.) Plus there are loads and loads of worlds where Earth is exactly the same, the only differences are found in particles floating around in a far off star. These worlds are like different save games, except uncountable amounts of them are created at every second of every day. If you end up in one of these chances of finding your way back are super slim, as it's hard to have stable superspatial coordinates in a multiverse full of rapidly multiplying universes. This theory is also, in my humble opinion, the biggest nonsense of them all. Nobody has even a start of an explanation of how these worlds/universes branch. There is a tiny quantum choice in a particle somewhere, fine, how does that make all of the mass in the universe double instantly, and how does that teleport half of this mass to some newly created location to become its own universe? Conservation of anything goes out the window. If this idea is true I propose we build a reactor that has a subatomic particle inside and every time it makes a choice the reactor consumes one of the two branching universes to convert it into energy. Just burn it or something, efficiency doesn't matter. We're getting a whole universe per Planck time, that's a lot of energy any way you do it. I'm sure this theory is theoretically possible, it was proposed by physicists after all, but that's more a case of "you can't prove it's not true" than of anything that resembles evidence in favor of it.