# Can the gravitational force be described just with virtual particles of its own field? [closed]

Similarly to steady electric or magnetic fields for example?

## closed as unclear what you're asking by John Rennie, ZeroTheHero, Yashas, David Hammen, honeste_vivereJul 15 '17 at 19:31

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• The QFT description of the electromagnetic field also needs real particles (i.e. photons), not just virtual particles. – probably_someone Jul 14 '17 at 6:51
• I mean specifically for the gravitational field of large mass objects. – Georgi Pavlov Jul 14 '17 at 6:57
• Why would the mass of the object make a difference? – probably_someone Jul 14 '17 at 6:57
• Similarly to the way more charges create a stronger electric field around themselves. – Georgi Pavlov Jul 14 '17 at 7:01
• Again, I don't see how the presence of more mass obviates the need for real particles. Do you have a reason for thinking that you only need virtual particles? – probably_someone Jul 14 '17 at 7:02

Lets clear up terminology:

Virtual particles are mathematical entities in Feynman diagrams, used in quantum field theory in order to calculate measurable quantities, crossections, lifetimes etc. The wavy line represents the virtual particle , in this case the photon,and it is a mathematical propagator where the mass of the virtual particle is in the denominator and the line carries the quantum numbers of the named particle, except that its four vector is off mass shell, it is not unique, it varies under the integral limits.

A steady electric or magnetic field is a classical measure. One can connect it with QFT since classically an electric field is measured by a test charge, so that one can write a feynman diagram between the particles of the source of the field ( in the above case the electron on the left) and the test particle ( the electron on the right). There is an isomorphism which when cumbersomly carried through the QFT mathematics gives the same answer for the value of the electric field. So in a sense the electric field can be associated with the mathematical virtual particles.

Now these electrons have a gravitational field. The expectation of physicists is that an equavalent diagram can be written for the gravitational exchange of a graviton, BUT there is no definitive quantum field theory of gravitation. There do exist effective field theories, which presume that the infinities from higher order diagrams will be someday resolved, and who do use Feynman diagrams for gravitational interactions.

In this framework the classical gravitational field will emerge from the quantum mechanical mathematical exchanges of virtual gravitons, similar to the way electric fields emerge from the quantum mechanical mathematical exchanges of virtual photons. It remains to be seen whether expectations will be fulfilled. String theories have no infinity problems with gravity, so maybe in the future the hypothesis will be justified, if they lead to the theory of everything.

• I see, so this may have been a too obvious question then, but I'm very new in quantum mechanics. Can the gravity field exert exert 'real' or non-virtual particles? – Georgi Pavlov Jul 14 '17 at 21:21
• Sure, if quantization of gravity is successful, the gravitational waves recently detected by LIGO will be emerging from zillions of gravitons, the way the light ( electromagnetic wave) emerges from zillions of photons. We can detect single photons , but single gravitons are 10^-36 less likely to interact with atoms, so they will probably never be seen in the lab. – anna v Jul 15 '17 at 6:15

Virtual particles are used as a tool in Feynmann diagrams for describing phenomena which happens between real "physical" objects (e.g. particles). So you can not describe a theory in physics without having as ingredients the physical objects = real particles.

• I see. I'm not talking about the particles of the field. Just about zones of steady components of the field, caused by the field interacting with the Higgs, quark, electron etc. fields. – Georgi Pavlov Jul 14 '17 at 7:07
• The components of the field that you mentioned, are all real particles. In QFT of course that you can consider them as fields, but they are not virtual. – Robert Poenaru Jul 14 '17 at 7:10
• Actually, I don't think I know what you want to say with that comment :)) – Robert Poenaru Jul 14 '17 at 7:10
• In quantum field theories the attraction and repulsion between electric charges IS described by the exchange of virtual photons! – Georgi Pavlov Jul 14 '17 at 7:27
• So you say, that maybe there is no need for particles (like the "yet to be found" graviton) when you describe the grav. force? – Robert Poenaru Jul 14 '17 at 7:27