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Since photon wavelengths are stretched by our expanding universe, appearing to us as a redshift, would graviton wavelengths similarly be stretched? For that matter, do gravitons even have a wavelength like photons?

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  • $\begingroup$ Gravitational waves are essentially classical waves. It makes very little sense to talk about them in terms of gravitons that would be completely unmeasurable by any imaginable means. Think about both as classical wave phenomena in this context and you have captured the essential physics. The answer is positive. Gravitational waves will undergo the same cosmological redshift as light. $\endgroup$ – CuriousOne Mar 25 '16 at 17:09
  • $\begingroup$ There is a big "IF." Experimentally there is no hope to detect gravitons with modern technologies. It is still a mathematical construct. However, it does seem to explain some of the most important characteristics of Gravity as a fundamental interaction. Otherwise I don't know what will be the relation between gravitons and gravitational waves but I would like to agree with CuriousOne that their wave feature will undergo a stretch. $\endgroup$ – Benjamin Mar 25 '16 at 18:07
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    $\begingroup$ Related: physics.stackexchange.com/q/245413/2451 $\endgroup$ – Qmechanic Mar 25 '16 at 23:01
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What has just been proven is the existence of gravitational waves, not gravitons. Beside, if graviton exists, they are likely to be a "pseudo particle" like the photon, i.e., mostly a quantized emission of wave packet.

As a wave, by construction the downstream part is late compared to the upstream part, and because of expansion, it will have slightly more length to cross than the uptream part at anytime, which accumulates with distance, resulting into the increase of the wavelenght. All kinds of waves thus "red"shift.

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  • $\begingroup$ It is interesting to note that if BICEP3 manages to detect gravitational waves the existence of gravitons will be becoming much more "real", as real as photons $\endgroup$ – anna v Mar 26 '16 at 5:07
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Suppose, there are gravitons, and space is expanding.

Gravitons stretching with stretching space, would loose strength in same way as lower frequency (red shifted) light has lesser energy. That would change laws of gravity constantly. At the least, it would keep changing gravitational constant. That does not seem to be the case. There are no colors in gravity.

Gravity appears to be apart from all other stuff. It is property of space that becomes evident in presence of mass/energy. The space has this property everywhere but it becomes intense (curved inward) due to presence of mass/energy. It seems to be a property, and not any particle. Most fundamental property (gravity) of most fundamental entity (empty space).

We keep going smaller and smaller, the particles must end at some level and we will have to deal with emptiness in any case. It is just a matter of - at what level.

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  • $\begingroup$ It seems you and Fabrice disagree. I also read the similar question (physics.stackexchange.com/q/245413/2451 from above) where others agree that gravity waves would indeed stretch. I still gave you a +1 for responding since I cannot be a good judge of who is right. I'll let others who have a better theoretical grasp of the subject bubble the right answer to the top. $\endgroup$ – CramerTV Mar 26 '16 at 4:49
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    $\begingroup$ This is wrong. Gravitons are a quantum mechanical, hypothetical particle , because quantization of gravity is only effective. As QM particles they will participate in a redshift as all waves. BUT the gravitational interaction when viewed quantum mechanically will involve virtual gravitons . These will not be "stretching" as the virtual photons tying up matter are not "stretching" with the expansion of the universe. Virtual just means a mathematical tool, both for photons and gravitons, and there is no stretching on virtuals. $\endgroup$ – anna v Mar 26 '16 at 5:05
  • $\begingroup$ @cramerTV: I have also said in one of the answers recently that gravitational waves will stretch with stretching space. But that is when gravitational wave is a ripple in space and the ripple will stretch with stretching of space. What I am saying here is - it is unlikely that gravitons carry gravity. I am saying it is property of space. Virtual particles are mathematical convenience, not a reality. Even in case of real particles - the particles are not continuous, there is empty space in between them and that empty space, ultimately has to play a role. $\endgroup$ – kpv Mar 26 '16 at 5:55
  • $\begingroup$ Continued - And I am also saying that assuming there are gravitons, they will not stretch. The stretching will change the gravitational constant. GW can stretch as a ripple in space. But stretching of gravitons (gravity) will cause inconsistency with gravitational constant value. $\endgroup$ – kpv Mar 26 '16 at 6:01

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