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The de Broglie wavelength of any massive particle is $\lambda = \frac{h}{p}$. We know that if a large object (say, a baseball) is at rest, it will have $p=0$ and hence $\lambda$ will be infinite. This should allow us to observe quantum interference of the baseball.

Online sources say something about the uncertainty principle: we can never be certain that $p=0$. There will always be some uncertainty in the value of $p$. If we want to decrease $\Delta p$, we have to increase $\Delta x$, the uncertainty in the position of the baseball. Why doesn't this allow us to observe quantum effects?

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Planck's constant is $6.62607004 × 10^{-34} m^2 kg / s$.

We're unable to know the massive object's momentum to a significantly more refined degree than $10^{-34} kg\space m/s$. (in order to get quotient to be infinite) Moreover, a massive body is just a blob of bunches of particles swimming in all different directions.

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  • $\begingroup$ re: last sentence. Does this mean that the wavefunctions of the bunches of particles comprising the massive body will interfere with each other $\endgroup$ – atenao Jan 28 at 5:41
  • $\begingroup$ @atenao I don't mean to imply anything on that topic (interference of wavefunctions of collections of particles). I just mean to say that - in a practical sense - we must recognize that a massive (really, macroscopic) body cannot be treated as a singular quantum particle with one singular position/momentum because it is instead a collection of quantum particles with many positions and momenta, and the "position" and "momentum" is an average of the collection. $\endgroup$ – jpf Jan 28 at 22:09

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