Your parallel self is a person born on the same day, in the same city, but exactly 12 hours before or after you. Same Sun sign and Life Path number, but a completely different Ascendant and possibly a different Moon.

Where it comes from

The many-worlds interpretation of quantum mechanics was proposed by Hugh Everett in 1957 and holds that every quantum measurement produces a branching of the universe rather than a collapse. It is a serious position in physics with serious adherents, and it is also the most borrowed idea in contemporary popular metaphysics. The borrowing is loose: nothing in the physics permits communication between branches, and the branching is at the quantum level rather than at the level of life decisions. Used as a metaphor it is old — Robert Frost's two roads are the same device.

How the method works

Used as an exercise rather than a claim, the method takes a decision point and constructs the person you would have become on the other branch: what they do, what they know that you do not, what they gave up that you kept. The value is in the comparison, because the alternative self usually turns out to hold one specific quality you assumed was unavailable to you — and that quality is available now, which is the point of the exercise.

What a reading covers

You get the branch built out in detail from the decision you name, what that version of you has and lacks, and which of those things is actually a function of the choice rather than of circumstance.

Common questions

Is there really a parallel version of me?: The many-worlds interpretation is a position in physics about quantum measurement, not about life choices, and it allows no contact between branches. Treat this as a structured thought experiment.
How is it different from the what-if reading?: What-if follows the consequences of a different decision. This one builds the person rather than the sequence of events, which puts the focus on qualities instead of outcomes.
Does it help or just create regret?: It depends entirely on where it ends. Ending at the comparison produces regret; ending at what is still available produces something usable.