"Change your frequency and the world changes" is an esoteric slogan, but dig past the metaphor and you find an ordinary neurobiological fact. Your inner state really does shift what you see and respond to, because the brain works as a filter with adjustable settings and everything happens inside it.
Here is how it works.
Attentional set: what it is and why it works
At any moment your perceptual field carries thousands of signals: visual, auditory, bodily. You become aware of a tiny fraction of them; the rest is screened out before it ever turns into experience.
Two things decide what gets screened out: biological priority (hunger, danger, motion) and the current task the brain is busy with. Psychologists call this the attentional set, and it works in every direction. Tune yourself to find a familiar face in a crowd and you will find it; tune yourself for grievance and you will find a cause; tune yourself for possibility and you will find that too.
Forty years and thousands of experiments stand behind this. The famous "gorilla in the middle of the basketball game" (Simons & Chabris, 1999) is exactly this effect: you miss a person in a gorilla suit because you were asked to count passes.
Neural correlates
The brain generates different rhythms in different states:
— theta (4–8 Hz): a plastic state, good for learning; — alpha (8–13 Hz): relaxed wakefulness, screening out sensory noise; — beta (13–30 Hz): active problem-solving, narrow focus; — gamma (30–100 Hz): binding perception together, unexpected connections.
When the brain switches between these modes, different neural ensembles come online and go offline, and esoteric "vibrations" have nothing to do with it. Meditation shifts the rhythms toward alpha and theta, anxiety toward high beta, and all of it shows up plainly on an EEG.
The world stays the same throughout. What changes is the filter, and with it what you see in the world.
Three modes, three maps of the world
Anxious mode (high beta, little alpha). You see threats, failures, injustice and reasons to be angry; you make fast, narrow decisions; conversations fall apart, small things grate, the future looks dark. Biologically this is survival mode, useful over minutes and destructive if you stay in it for years.
Calm mode (plenty of alpha, moderate beta). You see the situation whole, notice nuance, hold several options in mind at once; conflicts untangle more easily, and the future looks varied rather than catastrophic. For a healthy nervous system this is the default mode, and it is the one modern environments knock out most often.
Creative mode (theta with short bursts of gamma). You see connections between things you never linked before, find unexpected solutions, write things you later cannot explain how you came up with. Biologically this is the mode of the hippocampus and the default-mode network, and it rarely survives the push for productivity.
Practical takeaway
"Frequency hack" is good marketing and a poor description. Behind it lies a useful truth: you do have levers over your own perceptual filter, and they have been known for a long time.
— Physiology (breathing in for four counts and out for eight, cold, physical exertion) shifts the mode within minutes. — Environment (the people you spend time with, what you read and watch, how much silence you get) shifts it within days. — Meditation, long walks without a phone and keeping a journal shift it within weeks.
Each lever has its own time constant, and confusing them gets you nowhere: one meditation will not give you what a year of practice does, and a change of scene will not replace a breathing exercise.
Where the line is
Everything above is standard neuroscience of attention and brain states, which is to say, work with your own nervous system. There is no "access to parallel realities" and no "quantum shifting" here.
If after a well-spent morning you feel that "the world is different", you are half right: the world stayed the same, and you changed. If you think about it, that is the only version of "reality shifting" with any practical use. The rest is marketing.