= Galilean invariance
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= Galilean invariant
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A <law of physics> is Galilean invariant if the same formula works both when you are standing still on land, or when you are on a boat moving at constant velocity.
For example, if we were describing the movement of a <point particle>, the exact same formulas that predict the evolution of $x_{land}(t)$ must also predict $x_{boat}(t)$, even though of course both of those $x(t)$ will have different values.
It would be extremely unsatisfactory if the formulas of the <laws of physics> did not obey <Galilean invariance>. Especially if you remember that <Earth> is travelling extremelly fast relative to the <Sun>. If there was no such invariance, that would mean for example that the <laws of physics> would be different in other <planets> that are moving at different speeds. That would be a strong sign that our laws of physics are not complete.
The consequence/cause of that is that you cannot know if you are moving at a constant speed or not.
<Lorentz invariance> generalizes <Galilean invariance> to also account for <special relativity>, in which a more complicated invariant that also takes into account different times observed in different <inertial frames of reference> is also taken into account. But the fundamental desire for the <Lorentz invariance> of the <laws of physics> remains the same.