0

I just read that the Lambda CDM model assumes that General Relativity holds on a cosmological scale.

Could someone please explain to me why that assumption would be needed?
General relativity is the best theory of gravity we have right now.

What would be the reasons to call this an assumption and not a fact?
In what cases could GR actually fail on cosmological scales.

  • 1
    In science a theory is considered as "valid" until it gets falsified. So even if we think that GR is best theory at all, the day may come and the theory gets falsified and in a second step replaced by another, even better theory. Therefore, it is always good to remember that scientific conclusions are based on the Assumption of the validity of some theory. Because the conclusion might not be valid anymore, if the theory it is based upon gets one day falsified. I am sure we still have to learn a lot about gravitation as we still not be able to renormalize it in a satisfactory way. – Frederic Thomas Sep 18 '17 at 14:18

1 Answers1

0

Three main reasons. One is that the universe is so large that thinking that anything happening here can affect anything on "the other side" of the universe is most definitely not a fact no matter what theory of gravity we use. The second reason is that the whole is more than a collection of its parts. For example, in Special Relativity, all inertial frames are equal. However the whole universe breaks this symmetry twice, by CMB and by distant stars. Finally, the inverse square law is not sufficient to hold stars in galaxies without a substantial amount of dark matter, which has not been observed. It will take more research to reveal the details of how the universe works.

safesphere
  • 12,640