I can see the answer being no for large particles, but what about strings? What stops them from expanding to make up the universe as we know it?
Forget virtual particles, think (and google for) off-shell and on-shell particles. That will help you to fix some of your ideas on it. Something was very wrong about explaining virtual particles in the nglish-speaking world time ago, and a lot of people get it wrong. Perhaps it was some kind of TV program in the nineties, perhaps it is just the semantic meanings of "virtual" in English.
So, if you look at ir with the right angle, virtual particles can create anything, real of virtual, and it only depends of which part of its energy is unaccounted and which part of its energy is real. The point about virtuality is that they incur in an energy debt E over the real energy available, and this phenomena can not be sustained beyond a time t=h/E, and then it can not reach a distance beyond hc/E.
Please do not think of it that way. The idea that the universe maintains a "loan desk" which one can borrow from and later pay back is a very colorful concept but far from the truth.Think of it as borrowing energy and giving it back, but in a really short time.
If a single particle is detected, then the consequences of its existence are prolonged to such a degree that it cannot be virtual...The amplitude that a virtual particle exists interferes with the amplitude for its non-existence; whereas for a real particle the cases of existence and non-existence cease to be coherent with each other and do not interfere any more...In the quantum field theory view, "real particles" are viewed as being detectable excitations of underlying quantum fields...
In the quantum field theory view, "real particles" are viewed as being detectable excitations of underlying quantum fields. As such, virtual particles are also excitations of the underlying fields, but are detectable only as forces but not particles. They are "temporary" in the sense that they appear in calculations, but are not detected as single particles.
Thus, in mathematical terms, they never appear as indices to the scattering matrix, which is to say, they never appear as the observable inputs and outputs of the physical process being modeled. In this sense, virtual particles are an artifact of perturbation theory, and do not appear in a non-perturbative treatment
Do they really mean "physical phenomanea which in theory result from virtual particles"?There are many observable physical phenomena resulting from interactions involving virtual particles.
...quantum jitters can cause momentary virtual string eruptions to occur any number of times producing a sequence of virtual string pairs...The size of the string coupling constant describes how strongly the quantum jitters of the initial loop and the two virtual loops into which it splits are coupled to one another...the larger the string coupling constant the more likely it is that quantum jitters will cause an initial string to split apart...the smaller the constant the less likely it is for such virtual strings to erupt momentarily into existence...
I'll see if I can explain it without resorting to Latin.
Please do not think of it that way. The idea that the universe maintains a "loan desk" which one can borrow from and later pay back is a very colorful concept but far from the truth.
Energy is conserved exactly at all times, even by virtual particles. When arivero mentioned an "energy deficit", what he meant was this: A free particle "on the mass shell" must obey the relativistic equation E2 = p2c2 + m2c4. A virtual particle "off the mass shell" is not so constrained. Its values of E and p may be anything. However the farther it departs from the mass shell relationship, the shorter its existence.
...and that strings abruptly split apart, that they defy the conservation of energy?
Energy is conserved exactly at all times, even by virtual particles.
Why forget virtual particles?
A basic question: Has any virtual particle ever been detected?
I never heard of any virtual particle being 'detected'...that is observed.
This is closer to my limited unerstanding and seems inconsistent with the prior quote:
Is this correct:
Do they really mean "physical phenomanea which in theory result from virtual particles"?
They have not been detected, their existence as anything more real than, say, the GNP, which is nothing more than an ensemble of economic factors, has been ably disputed by skeptics, and the 'evidence' most readily proffered by the big-time boffins (who are afraid of coming on PF and facing the counter-arguments) is the Casimir effect, which has been derived without VPs.
So, to ask if VPs can spawn other VP's is interesting metaphysics at best. Another metaphysics is Hawking radiation, which has been derived by appeal to the conjectured VPs plus 'black holes' for which, once again, there has been no direct evidence as yet.
Quite the hat-trick then: two purported entities responsible for a second-order phenomenon of dubious existence.
That aside, I believe there is very strong evidence for hawking radiation and vacuum energy. This article shows an experiment where particles accelerate around a nanotube. It shows that these particles go from 0.1 Kelvin to thousands of degrees Kelvin in less than a microsecond.” Since the unruh effect (hawking radiation) gives an increase in tempature proportional to acceleration, it seems logical to assume that the tempature increase is due to hawking radiation.
Seems logical? It's certainly not logical.
(All cows are brown. That dog is brown. Therefore that dog is a cow.)
If you don't like the responses to unorthodox posts, maybe you should stop doing that. And take another look at the PF Rules if you want to better understand why.