New answers tagged

2

The preferred frame of reference is that of the co-moving reference frame that defines the Hubble flow. In practical terms that can be defined by correcting any velocity for the observer's motion with respect to the cosmic microwave background. Individual peculiar velocities for galaxies (including our own) are measured in hundreds to thousands of km/s. This ...


-1

"Why" is a philosophical question in this context, at least as far as the present state of cosmology is concerned. It is a subset of the "Why is there something rather than nothing?". So here is a philosophical answer: "Nothing" would mean no constraints, no laws of physics, no space, no time, no dimensionality etc. In fact, nothing to stop it being ...


1

The answer is that we don't know. Why? Because the theory of gravity which we have and use, GR, has a singularity. Things which should be finite in a physical theory, like the density, become infinite. And theories with a singularity are simply wrong, they need a modification, and this modification is necessary not only at the singularity itself, but already ...


4

A fine tuning problem is only a problem if we require that the considered model is a good or complete model of how we think the universe behaves. In this case, it appears that we require the density of the universe to be as close as 1 part in $10^{64}$ to the exact density that will make it a flat universe that will expand forever, asymptotically coming to ...



Top 50 recent answers are included