On Tue, Aug 27, 2019 at 12:02 AM Alan Grayson <[email protected]> wrote:
> > > On Monday, August 26, 2019 at 10:55:23 PM UTC-6, Brent wrote: >> >> >> >> On 8/26/2019 8:48 PM, Alan Grayson wrote: >> >> >> >> On Monday, August 26, 2019 at 9:18:50 PM UTC-6, Bruce wrote: >>> >>> On Tue, Aug 27, 2019 at 12:40 PM Jason Resch <[email protected]> wrote: >>> >>>> On Mon, Aug 26, 2019 at 9:25 PM Bruce Kellett <[email protected]> >>>> wrote: >>>> >>>>> On Tue, Aug 27, 2019 at 10:35 AM Jason Resch <[email protected]> >>>>> wrote: >>>>> >>>>>> On Mon, Aug 26, 2019 at 7:32 PM Bruce Kellett <[email protected]> >>>>>> wrote: >>>>>> >>>>>>> On Tue, Aug 27, 2019 at 10:27 AM Jason Resch <[email protected]> >>>>>>> wrote: >>>>>>> >>>>>>>> These videos provide a good introduction: >>>>>>>> >>>>>>>> https://www.youtube.com/watch?v=X5rAGfjPSWE >>>>>>>> https://www.youtube.com/watch?v=fG52mXN-uWI >>>>>>>> >>>>>>>> Virtual particles are the basis of all particle interactions in >>>>>>>> QED, called the jewel of physics for having made the most accurate >>>>>>>> predictions of any physical theory. >>>>>>>> >>>>>>> >>>>>>> The trouble is that virtual particles are internal lines in Feynman >>>>>>> diagrams, and the Feynman diagrams are formed as a perturbation >>>>>>> expansion. >>>>>>> They have to be summed to make contact with physical processes. This >>>>>>> puts >>>>>>> the status of virtual particles, as ontological entities, into >>>>>>> considerable >>>>>>> doubt. Ultimately, they are nothing but a calculational device, and >>>>>>> quantum >>>>>>> amplitudes can be evaluated without ever using Feynman diagrams, so >>>>>>> virtual >>>>>>> particles need never appear anywhere. >>>>>>> >>>>>>> >>>>>> But this "calculational device" (funny how many things are mere >>>>>> devices) predicts the lamb shift as well as the Casimir effect, to great >>>>>> accuracy. >>>>>> >>>>> >>>>> No, virtual particles do not predict the Lamb shift -- they are just >>>>> an aid to calculating terms in the perturbation expansion of the QED >>>>> vertex >>>>> function. >>>>> >>>>> >>>> Is this answer in error? >>>> https://physics.stackexchange.com/questions/443186/lamb-shift-and-virtual-particles >>>> >>>> >>> >>> No, that seems to give the standard Feynman diagrams for radiative >>> corrections to the photon propagator. (I misremembered previously. >>> Radiative corrections to the vertex function are important for the >>> calculation of g-2 for the electron, not for the Lamb shift, which is a >>> photon propagator correction.) But the standard calculation says nothing >>> about reifying the internal lines in the diagrams. In fact, a good >>> approximation to the Lamb shift can be obtained from a simple >>> non-relativistic calculation that never mentions quantum fields, vacuum >>> polarisation, or virtual particles. >>> >>> Aren't virtual particles necessary for explaining the limited range of >>>> the strong force? >>>> >>> >>> No. The uncertainty principle can do that. >>> >>> >>>> And solving the blackhole information paradox? >>>> >>> >>> No. There is no BH information paradox, and virtual particles are not >>> necessary in order to understand Hawking radiation (despite what Hawking >>> says in his popular accounts. His original paper on the matter does not use >>> virtual loops. Not that these exist in the way described, anyway.) >>> >>> Bruce >>> >> >> Your objections to reifying virtual particles seems very well founded. >> Despite that, in your opinion is there a consensus in the physics community >> that they exist? Remember, the existence of the quantum foam is the >> necessary condition for the conjecture that the Cosmos arose as a quantum >> perturbation or eruption from that foam. AG >> >> Quantum foam is just an idea J. A. Wheeler had, that down at the Planck >> scale, the topology of spacetime was foam-like, a maze of connecting >> wormholes. It was never worked out as a theory, although string-theory >> might be thought of as foam in more dimensions. It's not an assumed basis >> for cosmogony in any theory I know of. >> >> Brent >> > > Doesn't the theory or conjecture that the Cosmos emerged from a quantum > fluctuation assumes the existence of a quantum foam? AG > It assumes the pre-existence of the quantum vacuum. But the vacuum is far from the philosopher's nothing: "The Universe had to have a way to come into being out of nothingness. ...When we say “out of nothingness” we do not mean out of the vacuum of physics. The vacuum of physics is loaded with geometrical structure and vacuum fluctuations and virtual pairs of particles. The Universe is already in existence when we have such a vacuum. No, when we speak of nothingness we mean nothingness: neither structure, nor law, nor plan. ...For producing everything out of nothing one principle is enough. Of all principles that might meet this requirement of Leibniz nothing stands out more strikingly in this era of the quantum than the necessity to draw a line between the observer-participator and the system under view. ...We take that demarcation as being, if not the central principle, the clue to the central principle in constructing out of nothing everything." — John A. Wheeler "Cosmologists sometimes claim that the universe can arise 'from nothing'. But they should watch their language, especially when addressing philosophers. We've realized ever since Einstein that empty space can have a structure such that it can be warped and distorted. Even if shrunk to a 'point', it is latent with particles and forces -- still a far richer construct than the philosopher's 'nothing'. Theorists may, some day, be able to write down fundamental equations governing physical reality. But physicists can never explain what 'breathes fire' into the equations, and actualizes them in a real cosmos. The fundamental question of 'Why is there something rather than nothing? remains the province of philosophers. And even they may be wiser to respond, with Ludwig Wittgenstein, that 'whereof one cannot speak, one must be silent'." -- Martin Rees Jason -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/CA%2BBCJUjwJkFqWKFc4sLBWvpLqy3u6_vaV%3D_nS4FgBB6p5ijf3A%40mail.gmail.com.
