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In my textbook about atomic structure we have a brief part about Heisenberg uncertainty principle. While the derivation was not given in the book which simply stated Heisenberg as $\Delta x\, \Delta p\geq\frac{\hbar}{2}.$ also in the book momentum was expanded as $\Delta mv\ $. And the next step removed the mass from $\Delta mv\ $ and wrote it as $m\Delta v\ $ (Not a typing mistake checked my friends copy for that)

What I am confused about is that according to Einstein's principle of relativity mass must change with change in velocity but the book seems to look over that while explaining the Heisenberg Uncertainty principle. Can Somebody explain me this because the book contradicting itself is becoming very confusing for me and my mind

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    $\begingroup$ Quantum mechanics is non-relativistic. $\endgroup$ – lemon Jun 24 '16 at 13:35
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    $\begingroup$ I do find it a tad disrespectful to tag something as a textbook-erratum just because you do not understand it $\endgroup$ – Sanya Jun 24 '16 at 13:36
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    $\begingroup$ One of the most frequently encountered ideas on this site is the concept of "relativistic mass". That mass increases with speed. This concept was generally abandoned half a century ago, but refuses to die. In 1948 Einstein himself warned against it in a letter to Lincoln Barnett. If you can read German and Einstein's handwriting you can read it for yourself on page 32 of this June 1989 Physics Today Article by Lev Okun But this fact is just a side-bar to your question, and doesn't address your concerns. $\endgroup$ – garyp Jun 24 '16 at 14:19
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The basics of atomic structure are studied in the non-relativistic limit (mass not changing with velocity). Relativistic corrections are then added as perturbations to the non-relativistic states & energies (this gives you the fine structure https://en.wikipedia.org/wiki/Fine_structure). For a full quantum treatment of relativistic effects you need to go to Quantum Field Theory, where you no longer have position and momentum observables (see: Uncertainty principle in quantum field theory).

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