Why do we say gravity is a long range force? Does Earth's gravity field rely on real or virtual
Submitted : 20180614 06:53:07 Popularity:
Tags: force Earth field gravity long
Wow, you have managed to ask 3 very difficult questions .... I hope you are serious about this ...
First, let’s talk gravitons. They come from the idea (
Wow, you have managed to ask 3 very difficult questions .... I hope you are serious about this ...
First, let’s talk gravitons. They come from the idea (more like hope) that we can treat gravity like the other three known forces, each of which has one or more mediator particles that the force acts through. We do not know whether gravitons exist or not. If they do exist, we expect the graviton to behave as the other force mediators  virtual particles for static fields and real particles for propagating fields. So, the answer to one of your questions is that if gravitons exist, a static gravitational field (an idealized earth) would be mediated by virtual gravitons. The recently discovered gravitational waves, which propagate, would be mediated by real gravitons.
The range of a force depends on the mass of the force mediator, and this is a rather strange consequence of quantum mechanics. Virtual particles exist because of the energy timeversion of the uncertainty principle. This allows a virtual particle with energy to exist for a time inversely proportional to it’s energy (mass in this case). The greater the energy, the less time that it can exist. So, if a virtual particle’s action is limited by the speed of light, it’s energy will determine how far it can travel before its ‘lifetime’ is over. A massless virtual particle then can in principle have infinite range. For example, a photon has zero rest mass, can have an arbitrarily low frequency, and so has infinite range. Based on observations and general relativity, It is assumed that the gravitons have zero mass and thus can have infinite range also.
Now for the hardest thing of all, curvature. Since we have not successfully quantized gravity into gravitons, it’s very difficult. There are simplifications of general relativity that linearize gravity so that gravitons don’t create gravitons in a never ending nonconverging (infinite) series. These linearized gravities actually work but don’t represent the theory of general relativity except for weak fields. So, curvature doesn’t really exist as spacetime curvature, but as an effect of gravitons acting like force mediators in a manner similar to other fields.
Curvature in general relativity which has passed all of its tests, is pretty nasty. There is a type of curvature (Ricci curvature) that appears in the field equations as a constraint that basically says that gravitational curvature has to conform to one of two scenarios. The first scenario involves a geodesic ‘ball’ of space with matter/energy present inside it. The field equations define the rate of change in volume reduction of the ball. The second scenario involves the geodesic ball with no matter/energy within it, but influenced by an external source of gravity (this is called th vacuum solution). The field equations describe how the ball is distorted into an ellipse, but the volume is preserved (unlike the the first scenario).
Full spacetime curvature is given by a nasty object called the Riemann curvature tensor. This describes how a vector will change direction when transported around a closed path in spacetime.
A short range force is one which diminishes with distance alone.
A long range force is one where the only diminution of the force is due to the area that it spreads over. Distance does not reduce the total gravitational flux.
At least no distance that we have any way of measuring or knowing anything about.
As far as what it relies upon don't ask a scientist because we are only hypothesizing and looking for answers.
As your local Guru instead. Perhaps he will tell you what you want to hear.
Now curvature? The physical curvature of an object has no bearing on its gravity.
The general theory of relativity assigns the term curvature to a variation in space time that can also represent the acceleration of gravity in a non accelerating space.
because, like the electostatic force, gravitational force goes on forever. Both are inverse square forces, ie, they decrease as the square of the distance.
Earth's gravitational field is real, not virtual.
We say that gravity is a long range force because it actually IS a long range force. At least out to 80 million light years, and seems to explain a lot of what we see way beyond that. The word "curvature" gets used because gravity affects space in a nonlinear way .. but the difference from straight space is very very tiny.
Gravitons exist only the imagination of a few scientists.


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