Heisenberg principle, little question
[tex]\Delta x \Delta p \geq \frac{\hbar}{2}[/tex].
Say I want to measure the best I can the position of an electron, in detriment of its momentum (i.e. velocity since I assume that I know its mass quite well). When [tex]\Delta x \to 0[/tex], [tex]\Delta p[/tex] should tend to [tex]+\infty[/tex] but there's the c limit so that I can't make [tex]\Delta x \to 0[/tex]. Unless I should consider the relativistic mass of the electron and not the rest mass in the [tex]\Delta p =mv[/tex] part of the inequality? So m would tend to [tex]+\infty[/tex] and I'm not really limited by a maximum limit of velocity and I can get a very precise measure for [tex]\Delta x[/tex]. 
Re: Heisenberg principle, little question
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Re: Heisenberg principle, little question
You can't assert [tex]p=mv[/tex], which is the nonrelativistic momentum, and then assert that [tex]v \leq c[/tex] (and hence [tex]p \leq mc[/tex]) because of relativity.
Relativistic momentum is [tex]p = \frac{m_0 v}{\sqrt{1  \frac{v^2}{c^2}}}[/tex], so [tex]v \rightarrow c[/tex] as [tex]p \rightarrow \infty[/tex]. 
Re: Heisenberg principle, little question
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Anyway I get the idea. And the [tex]\Delta p[/tex] is the relativistic momentum, which is what it seems I was doubting on. Thanks guys, question solved. 
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