Status Updates From Physical Foundations of Cos...

The frequency (energy) of a photon measured by an observer is equal to the time component of the photon's 4-momentum in the comoving local inertial frame of the observer. Therefore in a coordinate system where the has 4-velocity uᶦ and photon 4-momentum is pᵢ, this frequency can be expressed as ω = pᵢuᶦ.

I am sure the Rev. Paley would have seen cold dark matter as yet another proof of the existence of God. Exactly the right amount to get the galaxies forming! It's such a shame that he can't release an updated edition of Natural Theology.

In a Newtonian universe, initial mass concentrations collapse exponentially. But in an expanding Einsteinian universe, the collapse is only polynomial. So much larger inhomogeneities are needed in the early universe to explain what we currently see - galaxies, galactic clusters, etc.

It is fascinating to see how people construct detailed models for what was happening during the first 10⁻³⁴ seconds of the universe's existence, despite having no real knowledge of how physics works at the relevant energy scales. That magical borderland between godlike intuition and complete bullshit. But if you look at Classical Greek models of the Solar System, they weren't actually that bad.

"Is there any point to which you would wish to draw my attention?"

"To the curious incident of the number of magnetic monopoles so far discovered."

"But no magnetic monopoles have ever been discovered."

"That was the curious incident," remarked Holmes.

OMG! The phase transition related to the Higgs field must have been responsible for the creation of the whole... uh...

Sorry. False alarm. Nothing. Nothing.

As we will see, CP violation plays a very important role in baryogenesis, ensuring the possibility of different decay rates for particles and their antiparticles in different decay channels. If this were not the case, generation of baryon asymmetry would be impossible.

(One of the more technical answers to the old question "Why is there something rather than nothing?)

It is always rather startling to see what detailed, evidence-based models people can now make of what was going on when the universe was less than a second old. There must be a moral here.

As Mukhanov says, it's extraordinary that dark energy has become the dominant force in the universe at this exact moment! A staggering coincidence that absolutely requires an explanation.

Note: when he says "at this exact moment", he actually means a few billion years ago. But when you're a theoretical cosmologist, you don't nitpick these petty details.

Problem 2.1 Estimate the total amount of energy received by all optical telescopes over the last century, and compare this energy with that required to return the present book to your bookshelf.

For most of the twentieth century, the homogeneity and isotropy of the universe had to be taken as an assumption, known as the "Cosmological Principle". Physicists often tend to use the word "principle" to designate what are at the time wild, intuitive guesses, in contrast to "laws", which refer to experimentally established facts.

Having miserably failed to understand Laura Mersini-Houghton's arXiv papers, I decided I would try and get more familiar with the background.