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]
<javascript:>> wrote:
On Mon, Aug 26, 2019 at 9:25 PM Bruce Kellett
<[email protected] <javascript:>> wrote:
On Tue, Aug 27, 2019 at 10:35 AM Jason Resch
<[email protected] <javascript:>> wrote:
On Mon, Aug 26, 2019 at 7:32 PM Bruce Kellett
<[email protected] <javascript:>> wrote:
On Tue, Aug 27, 2019 at 10:27 AM Jason Resch
<[email protected] <javascript:>> wrote:
These videos provide a good introduction:
https://www.youtube.com/watch?v=X5rAGfjPSWE
<https://www.youtube.com/watch?v=X5rAGfjPSWE>
https://www.youtube.com/watch?v=fG52mXN-uWI
<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
<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
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