‪Could the effect of “expanding” gravity (gravitational waves spreading at the speed of light) as it travels through space (and therefore becomes less local) red-shift all EM waves and thus give us the illusion of expanding space? ‬As I understand it, our detection of the expansion of the universe is predicated on the observation of redshifting. The further the light source from us, the more it is redshifted by mass and gravity as it travels to us. As I understand it, in the spacetime framework, this could also be interpreted as slowing time.

This seems like an obvious hypothesis which has surely been debunked but a google search yields no clear answer.


closed as unclear what you're asking by ZeroTheHero, G. Smith, Jon Custer, John Rennie, Kyle Kanos Feb 18 at 12:21

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    $\begingroup$ This seems like an obvious hypothesis It doesn't seem like an obvious hypothesis to me. It seems like random speculation that doesn't make much sense. $\endgroup$ – Ben Crowell Feb 16 at 18:43
  • 1
    $\begingroup$ The further the light source from us, the more it is redshifted by mass and gravity as it travels to us. Why would it do that? When light passes near a massive body it gets blueshifted as it approaches the body, and redshifted by the exact same amount as it climbs back out of the body's gravity well. $\endgroup$ – PM 2Ring Feb 16 at 18:52
  • $\begingroup$ 2Ring, thank you, I was wondering if the universe a whole became a “deeper” gravity well as gravity waves from various matter sources spread over time. Does the overall spacetime curvature become more pronounced as the effect of gravity spreads out. $\endgroup$ – Jerome Gouvernel Feb 16 at 19:10
  • 1
    $\begingroup$ The curvature of the universe is measured to be zero, or very close to it. It is not believed to be increasing. $\endgroup$ – G. Smith Feb 16 at 19:13
  • $\begingroup$ The current cosmological model assumes a homogeneous and isotropic universe on the largest scales. Nothing is “spreading out” into some place it wasn’t already. Space is simply expanding everywhere and galaxies are more or less “sitting still” within this expansion. $\endgroup$ – G. Smith Feb 16 at 19:16

Gravitational waves are very weak and have almost no effect on electromagnetic waves. They go right through each other. The cosmological redshift is caused by the overall expansion of the universe, not by tiny spacetime ripples ”on top of” that expansion.


Not the answer you're looking for? Browse other questions tagged or ask your own question.