If wave packets spread, why don't objects disappear?If you have an electron moving in empty space, it will be represented by a wave packet. But packets can spread over time, that is, their width increases, with it's uncertainty in position increasing. Now, if I throw a basketball, why doesn't the basketball's packet spread as well? Wouldn't that cause its uncertainty in position to increase so much to the point it disappears?EDIT: I realize I wasn't clear what I meant by disappear. Basically, suppose the wave packet is spread over the entire Solar System. Your field of vision covers only an extremely tiny part of the Solar System. Therefore, the probability that you will find the basketball that you threw in your field of vision is very small.

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If wave packets spread, why don&#039;t objects disappear?If you have an electron moving in empty space, it will be represented by a wave packet. But packets can spread over time, that is, their width increases, with it&#039;s uncertainty in position increasing. Now, if I throw a basketball, why doesn&#039;t the basketball&#039;s packet spread as well? Wouldn&#039;t that cause its uncertainty in position to increase so much to the point it disappears?EDIT: I realize I wasn&#039;t clear what I meant by disappear. Basically, suppose the wave packet is spread over the entire Solar System. Your field of vision covers only an extremely tiny part of the Solar System. Therefore, the probability that you will find the basketball that you threw in your field of vision is very small.

stormiinazlhdd · Accepted Answer

Short answer is it won&#039;t disappear because the integral of the probability density is still 1 even for a highly spread wavepacket, i.e. the object will still be found somewhere.Slightly longer answer is that, if I start with a Gaussian wavepacket with width   a, then after time   t, the width will have spread to                              a          2                +                  ℏ          2                          t          2                          /                          m          2                    a      The incredible smallness of   ℏ makes the spread negligble for something as massive as a basketball.

Alexis Meyer · Accepted Answer

It is true that the spreading depends on the mass as @twistor59 has already noticed, but the more important fact is that the basketball is an open system and interaction with its surrounds makes that (due to decoherence) the state of the basketball is not described by quantum wavefunction theory [*]. Using the Wigner-Moyal formulation of quantum mechanics it is possible to show that the basketball always have a well-define position   x  (  t  ) at each instant.[*] Wavefunction theory only applies to isolated quantum systems.

If wave packets spread, why don't objects disappear? If you have an electron moving in empty space

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