- #1
yosofun
- 14
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I've been reading Giancoli (Physics for Scientists and
Engineers, 3rd Ed) and Griffiths (Intro to QM). There seems a
contradiction on the applications of the Energy-time uncertainty
principle between the two.
Griffiths claims that energy is always conserved, even though
mathematically, the energy-time uncertainty principle should allow for
energy to be non-conserved for a small period of time. Giancoli
calculates the mass of exchange particles (in the particle physics
chapter, penultimate chapter of the Modern Physics part) by using (or
abusing, as Griffiths would call it) the energy-time uncertainty
principle---that is, Giancoli assumes that energy is non-conserved in the
small time-interval of the lifetime of exchange particle. Who's right?
To quote Griffiths, "It is often said that the uncertainty principle
means that energy is not strictly conserved in QM--that you're allowed
to 'borrow' energy as long as you 'pay it back' in time [in a quantity
in accords to the uncertainty principle]... There are many legitimate
readings of the energy-time uncertainty principle, but this is not one
of them. Nowhere does QM license violation of energy conservation, and
certainly no such authorization entered in the derivation of
[Energy-time uncertainty principle]."
(Griffiths limits his book to nonrelativistic QM. And, the first part
of it covers time-independent SE. I am wondering if exchange particles
are beyond the scope of the first part and if his statement is limited
by the section, not to be taken as a general reference. Or, if the
calculation of the mass of exchange particles is subjective, as
whether one believes in the orthodox view or the realist view. Or, if
it's just a mistake on one of the author's part..)
Engineers, 3rd Ed) and Griffiths (Intro to QM). There seems a
contradiction on the applications of the Energy-time uncertainty
principle between the two.
Griffiths claims that energy is always conserved, even though
mathematically, the energy-time uncertainty principle should allow for
energy to be non-conserved for a small period of time. Giancoli
calculates the mass of exchange particles (in the particle physics
chapter, penultimate chapter of the Modern Physics part) by using (or
abusing, as Griffiths would call it) the energy-time uncertainty
principle---that is, Giancoli assumes that energy is non-conserved in the
small time-interval of the lifetime of exchange particle. Who's right?
To quote Griffiths, "It is often said that the uncertainty principle
means that energy is not strictly conserved in QM--that you're allowed
to 'borrow' energy as long as you 'pay it back' in time [in a quantity
in accords to the uncertainty principle]... There are many legitimate
readings of the energy-time uncertainty principle, but this is not one
of them. Nowhere does QM license violation of energy conservation, and
certainly no such authorization entered in the derivation of
[Energy-time uncertainty principle]."
(Griffiths limits his book to nonrelativistic QM. And, the first part
of it covers time-independent SE. I am wondering if exchange particles
are beyond the scope of the first part and if his statement is limited
by the section, not to be taken as a general reference. Or, if the
calculation of the mass of exchange particles is subjective, as
whether one believes in the orthodox view or the realist view. Or, if
it's just a mistake on one of the author's part..)