Read about inflation | 63 Discussions | Page 1

  1. T

    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

    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. Quantum Alchemy

    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. QuarkDecay

    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. M

    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. Ken Lehn

    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. QuarkDecay

    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. newrd

    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. Ranku

    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. Rafid Mahbub

    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. S

    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...
  12. Rafid Mahbub

    A Numerical solution of the Mukhanov-Sasaki equation

    Hi, I am trying to figure out how to solve the Mukhanov equation numerically in Mathematica, but have some problems dealing with it. In terms of the number of efolds, the Fourier modes satisfy the following ODE in terms of the Hubble slow roll parameters: $$...
  13. Safinaz

    I Weyl transformation of the metric

    Hello, I’m new to the cosmological inflation so in this paper: Has some one an idea how to make the Weyl transformation of the metric ## g_{\mu\nu}## Equation (3) , and how to get the potential (4) from the action (3) by this transformation as explained after...
  14. ForgeJB

    I How can there be fluctuations in the inflaton field value? According to QFT, if you make repeated measurements of some property of the field then you will in general measure a...
  15. T

    How is the horizon length related to the power law spectrum

    Homework Statement For a power spectrum density fluctuations ##P(k) \propto k^n##, I need to find the scaling (with respect to ##a##) of the horizon wavenumber ##\frac{2\pi}{\chi_H}## in a matter dominated universe in terms of ##n##. ##\chi_H(a)## is the evolving particle horizon, in a flat...
  16. D

    I Troubles understanding slow-roll conditions in Inflation

    I've been reading up on inflation, and have arrived at the so-called slow roll conditions $$\epsilon =-\frac{\dot{H}}{H^{2}}\ll 1\; ,\qquad\eta =-\frac{\ddot{\phi}}{H\dot{\phi}}\ll 1$$ I have to admit, I'm having trouble understanding a couple of points. First, how does ##\epsilon\ll 1##...
  17. l0st

    I Can gravitational waves cause uniform space expansion?

    I am looking at a couple of very interesting papers, published in MNRAS, that deduce, that the accelerated expansion of the Universe we observe can be attributed to gravitational waves, produced by a very distant merger of two or more universe-mass-scale black holes. The last one is on the...
  18. Ranku

    I False vacuum and matter density

    The false vacuum of the inflationary universe is described as a 'peculiar state of matter'. We know that matter density in the big bang universe dilutes as ρM ∝ a-3. Is it possible to assign a dilution rate to the 'peculiar state of matter' of the false vacuum as well?
  19. Ranku

    I Inflation and density perturbations

    Is it possible to estimate the rate of false vacuum decay in the inflationary universe by looking at the density perturbations in the big bang universe?
  20. J

    I Have we measured the change in the red shift over time?

    Have experiments been done to measure the red shifts of distant objects over time? If inflation is correct, the the speed at which an object is receding relative to us is based on how far away that object is located. Therefore, the most distant objects would also have the highest acceleration...
  21. A

    A Multiverse reduction in the new Hawking/Hertog model?

    Hawking and Hertog's new paper "A Smooth Exit from Eternal Inflation?" does away with the infinite multiverse of Hawking's previous theory and proposes a cosmology that predicts "a simpler and finite universe". But I can't figure out the extent of this reduction to a "simpler and finite"...
  22. nomadreid

    I Bubble universe connections?

    I know this is getting into the highly speculative, but given the mathematics that has been done on versions of these concepts that are not known to be inconsistent: In the inflation concept which leads to a multiverse of the "bubble universes" type, in which the laws governing the space-time...
  23. R

    I Did cosmic inflation happen everywhere in the Universe?

    General Relativity equations tells us that the earliest time of the universe which our physics can tell us had infinite space and infinite density (i.e. matter). Then space started expanding, thus increasing the distance of any 2 points of that infinite dense matter, thus making it less dense...
  24. Ranku

    I Inflation and Omega

    Inflation leads to Ω=1. But we also have Ωmatter+Ωdark matter+Ωdark energy = 1. So if there were no dark energy and dark matter present in the universe, would Ω have eventually deviated away from 1?
  25. T

    Modern Cosmology Dodelson Problem 6.12b (Inflation)

    Homework Statement Show that ##4\pi G(\dot \phi)^2=\epsilon a^2 H^2## Homework Equations Over dots mean derivative with respect to ##\eta##. $$\frac{1}{a}\frac{d}{d\eta}=\frac{d}{dt}$$ $$H=\frac{\dot a}{a^2}$$ $$\epsilon=\frac{-\dot H}{aH^2}$$ $$(\frac{\dot...
  26. T

    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. Arman777

    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?
  28. Posty McPostface

    Your thoughts about excess reserves?

    Chart: Source. So, inflation has been low, which has been troubling economists and the FED over the effectiveness of undertaken Quantitive Easing (QE). What's the cause of this, and are banks holding onto excess reserves the real issue here? What are your thoughts about all this liquidity in...
  29. S

    B Angular momentum, degeneracy pressure, and cosmic inflation

    Considering the angular momentum of a collapsing star preventing it from resulting in a black hole by degeneracy pressure, are there ekpyrotic universe models that include angular momentum and degeneracy pressure as key factors of cosmic inflation?
  30. bapowell

    Insights A Poor Man's CMB Primer. Part 5: Quantum Seeds - Comments

    bapowell submitted a new PF Insights post A Poor Man's CMB Primer. Part 5: Quantum Seeds Continue reading the Original PF Insights Post.