On Monday, August 26, 2019 at 11:55:47 PM UTC-6, Jason wrote: > > > > On Tue, Aug 27, 2019 at 12:02 AM Alan Grayson <[email protected] > <javascript:>> 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 >
But if virtual particles don't exist, if they're based on conceptual errors, what's the basis for claiming the vacuum is not a vacuum of nothingness? AG -- 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/4c286016-c1b5-45df-a23a-d31c8d0a445f%40googlegroups.com.
