Why do people insist on the graviton

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In summary, there is no contradiction between the existence of gravitons and the theory of general relativity. Gravitons, if they exist, would be a quantized version of gravitational waves, which are allowed by general relativity. However, the concept of virtual particles mediating gravitational forces may not be useful, as quantum gravity is still a speculative and incomplete theory. Additionally, general relativity itself is not a quantum theory, and may need to be replaced by a theory that incorporates quantum mechanics.
  • #1
Denton
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When Einstein specifically showed there was no gravitational 'force', rather a repulsion of curved space. Is there something wrong with his theory that we must throw it all out the window and replace it with another meaningless hypothetical particle scenario?
 
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  • #2
A graviton is a quantized gravitational wave, it needn't necessarily contradict general relativity's claim that gravity is a consequence of curved spacetime (not curved space as you said). This is discussed on Some Frequently Asked Questions About Virtual Particles:
I hear physicists saying that the "quantum of the gravitational force" is something called a graviton. Doesn't general relativity say that gravity isn't a force at all?

You don't have to accept that gravity is a "force" in order to believe that gravitons might exist. According to QM, anything that behaves like a harmonic oscillator has discrete energy levels, as I said in part 1. General relativity allows gravitational waves, ripples in the geometry of spacetime which travel at the speed of light. Under a certain definition of gravitational energy (a tricky subject), the wave can be said to carry energy. If QM is ever successfully applied to GR, it seems sensible to expect that these oscillations will also possesses discrete "gravitational energies," corresponding to different numbers of gravitons.

Quantum gravity is not yet a complete, established theory, so gravitons are still speculative. It is also unlikely that individual gravitons will be detected any time in the near future.

Furthermore, it is not at all clear that it will be useful to think of gravitational "forces," such as the one that sticks you to the Earth's surface, as mediated by virtual gravitons. The notion of virtual particles mediating static forces comes from perturbation theory, and if there is one thing we know about quantum gravity, it's that the usual way of doing perturbation theory doesn't work.

Quantum field theory is plagued with infinities, which show up in diagrams in which virtual particles go in closed loops. Normally these infinities can be gotten rid of by "renormalization," in which infinite "counterterms" cancel the infinite parts of the diagrams, leaving finite results for experimentally observable quantities. Renormalization works for QED and the other field theories used to describe particle interactions, but it fails when applied to gravity. Graviton loops generate an infinite family of counterterms. The theory ends up with an infinite number of free parameters, and it's no theory at all. Other approaches to quantum gravity are needed, and they might not describe static fields with virtual gravitons.
 
  • #3
Denton said:
Is there something wrong with his theory...
Yes, it's not a quantum theory. General relativity is a classical theory about an equation called Einstein's equation that describes the relationship between the geometry of space-time and its content of matter. "Matter" is the key word here, because it's been known for a long time that matter can't be described by classical theories. If you just look closely enough, you need quantum mechanics to describe what you see. So the right-hand side of Einstein's equation is a classical description of something that definitely should be described by quantum mechanics.
 

Related to Why do people insist on the graviton

Question 1: What evidence supports the existence of gravitons?

Currently, there is no direct experimental evidence for the existence of gravitons. However, the concept of gravitons is supported by the success of the Standard Model in explaining the behavior of other fundamental particles, and by the fact that other fundamental forces, such as electromagnetism, have been successfully described by a particle (photon) as well.

Question 2: How does the existence of gravitons explain the force of gravity?

Gravitons are hypothesized to be the fundamental particles that mediate the force of gravity. Similar to how photons mediate the electromagnetic force, it is believed that gravitons are responsible for the attraction between masses. This theory is known as quantum gravity.

Question 3: Can gravitons be detected or observed?

Due to their hypothetical nature and extremely small size, gravitons are incredibly difficult to detect or observe directly. However, scientists are currently working on experiments and technologies that may be able to indirectly detect the presence of gravitons.

Question 4: Why do some scientists doubt the existence of gravitons?

Some scientists doubt the existence of gravitons because they are not directly observed or detected, and the concept of quantum gravity is still a theoretical framework that has not yet been fully proven. Additionally, the effects of gravity can also be explained by the theory of general relativity, without the need for gravitons.

Question 5: How does the existence of gravitons relate to the search for a theory of everything?

The existence of gravitons is closely tied to the search for a theory of everything, which is a unified theory that can explain all fundamental forces and particles in the universe. Gravitons are a crucial component of the theory of quantum gravity, which aims to unify the theories of general relativity and quantum mechanics. If gravitons are proven to exist, it would provide strong support for the theory of quantum gravity and bring us closer to a potential theory of everything.

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