1. ### I Is the Universe bigger than we think?

As inflation happens, effectively, faster than the speed of light (between any given two points) and we can only see 14 billion years back, is it possible the data we need, to judge the age of the universe, is actually beyond our detection abilities. Could the age of the universe be greater...
2. ### I Big Bang singularity: can we say anything about its size?

The Big Bang is sometimes described as started from a singularity, which I have interpreted as meaning that its characteristics are undefineḍ. If that is the case, can we not even say that the Universe as a singularity was still infinite? Otherwise we are implying that the singularity was...
3. ### B How constrained are the initial conditions of the universe?

Do we know? Do we have any idea? There seems to be 2 schools of thought. 1. The initial conditions can be almost any value with universes inflating with different laws of physics. This is the multiverse and string theory 10^500 false vacua view. 2. The initial conditions are more restrained...
4. ### I Horizon Problem

It says that since there is homogeneity in the Universe's temperature, all these points must have come from one source (or a source close to each other?) at a certain time. Then it also calculates the number of these sources and it's ~105. But isn't that very dense mass right before the Big...
5. ### A Observables when the symmetry is not broken?

Hi, Let be a scalar field φ that permeates all space. The quantum of the field has a mass m. The field is at the minimum of its potential. When this minimum is for φ≠0 (a broken symmetry), the quantum may be observed by exciting the field, as with the Higgs boson. But if the symmetry is not...
6. ### B Question concerning dark energy

Was all dark energy "born" at the moment of the Big Bang? Or does it "spring" into existence continually?
7. ### Prove that a~t^(8pπ) (inflation)

Problem gives these for a chaotic model; V(Φ)=Voexp(-√(2/p)* Φ/Μp) Φ(t)=√(2p)*Mpln[√(Vo/24πp2) *t/Mp] There's a standard method to follow and find the a(t) by using Friedmann's and inflaton equations. I think my mistake is most likely on the math part, because in the physics aspect we always...
8. ### B Andromeda Collision VS Expansion

Hi Folks, I've read that by the time mankind is ready for intergalactic travel, our nearest galactic neighbour will be too far to even travel to. But I've also read that Andromeda is on a collision course with the Milky Way. Which is correct? And if the universe is expanding and everything is...
9. ### I Inflation and the size of the Universe

By how many times is the size of the observable universe larger than expected because of inflation?
10. ### A Exploring parameter space of inflation models

I have been studying primordial black hole formation through inflation for a while and I was curious to know how the parameters in an inflation model are determined such that they are consistent with CMB constraints. In my literature reviews, there are quite a few models that exhibit an...
11. ### Dodelson Cosmology 6.8 Inflation Klein Gordon Equation

Homework Statement Show that Eq. (6.33) follows from Eq. (6.32) by changing variables from t to ##\eta##. Homework Equations (6.32) $$\frac{d^2\phi^{(0)}}{dt^2}+3H\frac{d\phi^{(0)}}{dt}+V'=0$$ (6.33) $$\ddot{\phi^{(0)}}+2aH\dot{\phi}^{(0)}+a^2V'=0$$ The Attempt at a Solution So...

26. ### Modern Cosmology by Dodelson: Problem 6.12 a

Homework Statement The general goal of the problem is to derive some useful identities involving the slow-roll parameters during inflation. For part a show that: $$\frac {d} {d\eta} (\frac {1} {aH})= \epsilon - 1$$ Homework Equations \epsilon \equiv \frac {d} {dt} (\frac {1} {H})= \frac...
27. ### B The Universe without Cosmic Inflation?

I don't know this question makes sense or not but; Respect to the two possible size universe models (finite and infinite) how would be the evolution of the universe without the cosmic inflation?