Recent content by kimbyd

Perhaps in terms of the overall structure, but I don't believe it is able to reproduce the CMB in detail. Similar to the above theory which sorta works, but gets the parameters way off.

This one uses a TeVeS theory where the scalar component is contrived to mimic dark matter (that is, its energy density scales close to ##1/a^3##). I guess I'm not terribly surprised this could replicate the CMB data, as it's basically an alternative form of dark matter theory. This one isn't a...

I haven't seen any modified gravity theory which comes close to reproducing the CMBR power spectrum without dark matter. It seems quite unlikely to me to be possible given the nature of the physics involved.

The basic reason is because before the CMB was emitted, the universe was a plasma. While the universe was a plasma, baryonic matter experienced pressure. This meant that on large scales, when normal matter fell into a gravitational potential well, the pressure would cause it to bounce back...

I'm unsure about the original paper. I looked up the papers which cite it on INSPIRE HEP (linked from the arxiv page), and found this paper: https://arxiv.org/abs/2004.13554 They do a more detailed analysis which includes some inhomogeneities, and find that the gravitational waves decay with...

The 93 billion light year across portion is the observable universe. Given how smooth and regular the observable universe is, it's reasonable to expect that the universe is much larger than this, but we can't know how much larger. The relationship between curvature and size isn't likely to be...

Short answer: no, for many reasons. First, there isn't enough of it. We can see this matter quite clearly in galaxy clusters through x-rays, and it only amounts to a small fraction of what is required to hold the galaxy clusters together. There's lots of other reasons why this can't work, but...

General Relativity conserves the stress-energy tensor. This is a quantity that contains energy, momentum, pressure, and shear forces. This conservation law can be reduced to energy conservation in specific circumstances. In this case they're implicitly considering a fixed coordinate system...

Fictional universes generally violate the laws of physics in one way or another. Often in very mundane ways. Mythbusters has a bunch of episodes where they debunk various Hollywood tropes and shows that the real world doesn't work that way, for instance. A simple example is gunfire. Gunfire...

My reading of it is that they're saying there are two reservoirs of energy: the input energy of the quasar, and the kinetic energy of the matter that makes up the Hubble flow. To do this, they're operating in a coordinate system that is not moving with the expansion (the amount of energy...

This is a good blog post that talks about the lack of conservation of energy in General Relativity: https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/

I don't think this follows. There are basically three possibilities: 1) There is some kind of physical process that drives the universe towards flatness to an extreme degree. Cosmic inflation is an example of one such process. 2) Most universes are actually close to flat and we're just not...

That's potentially a stretch. The universe being actually flat requires infinite fine tuning. Specifically, it requires an exact balance between the rate of expansion and the average density.

There's also two other facts that are important here: 1) Galaxies very far away were too dim or too redshifted to be observed when that 100 billion number was coined (If I remember correctly, this came from the Hubble Ultra Deep Field). We only saw either the very bright ones or the more nearby...

That analogy doesn't follow, because the curvature of the Earth is spatial curvature, and the curvature of space-time which causes our universe's horizon is in space-time. The analogy only really works locally. Now, it is possible, as others have noted, that the universe wraps back on itself...