What is Inflation: Definition and 410 Discussions

In economics, inflation (or less frequently, price inflation) is a general rise in the price level of an economy over a period of time.
When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation reflects a reduction in the purchasing power per unit of money – a loss of real value in the medium of exchange and unit of account within the economy. The opposite of inflation is deflation, a sustained decrease in the general price level of goods and services. The common measure of inflation is the inflation rate, the annualised percentage change in a general price index, usually the consumer price index, over time.Economists believe that very high rates of inflation and hyperinflation are harmful, and are caused by excessive growth of the money supply. Views on which factors determine low to moderate rates of inflation are more varied. Low or moderate inflation may be attributed to fluctuations in real demand for goods and services, or changes in available supplies such as during scarcities. However, the consensus view is that a long sustained period of inflation is caused by money supply growing faster than the rate of economic growth.Inflation affects economies in various positive and negative ways. The negative effects of inflation include an increase in the opportunity cost of holding money, uncertainty over future inflation which may discourage investment and savings, and if inflation were rapid enough, shortages of goods as consumers begin hoarding out of concern that prices will increase in the future. Positive effects include reducing unemployment due to nominal wage rigidity, allowing the central bank greater freedom in carrying out monetary policy, encouraging loans and investment instead of money hoarding, and avoiding the inefficiencies associated with deflation.
Today, most economists favour a low and steady rate of inflation. Low (as opposed to zero or negative) inflation reduces the severity of economic recessions by enabling the labor market to adjust more quickly in a downturn, and reduces the risk that a liquidity trap prevents monetary policy from stabilising the economy. The task of keeping the rate of inflation low and stable is usually given to monetary authorities. Generally, these monetary authorities are the central banks that control monetary policy through the setting of interest rates, through open market operations, and through the setting of banking reserve requirements.

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  1. chasrob

    Inflation era energy density

    I need the theoretical energy density of inflation for my story. I seem to recall it as an enormous 1095 ergs per cubic centimeter.

    A Scalar Field Dynamics in Inflation

    I am facing a problem while wanting ##\phi## dynamics in a cubic potential; ##g\phi^{3}##. The equation of motion I get for my case is(this follows from the usual Euler-Lagrange equations for ##\phi## in cosmology--Briefly discussed in Carol's Spacetime Geometry, inflation chapter)...
  3. KingoftheChaosEmpire

    "Rigid airship" using low density hydrogen (LDH) inflation

    I know now that making a full on vacuum airship is unfeasible for it's compressive properties. So why not just make a rigid airship that is evacuated enough that the hydrogen is no longer significantly dangerous to it's surroundings, using say 25-30% density of neutral hydrogen? What's the...
  4. Cody Livengood

    B What if we cut out the Big Bang and inflation?

    Are the Big Bang and inflation really needed to account for the large-scale structure of the universe, nucleosynthesis, baryon acoustic oscillations, and the anisotropies of the CMB? Can the universe not begin in an already expanded state and still have all those things happen just the same...
  5. svenz706

    A Non-minimally coupled inflation — expansion

    Hello, In the Wikipedia article on "Inflaton" there appears the following formula: ##S=\int d^{4}x \sqrt{-g}[ \frac{1}{2}m^2_{P}R-\frac{1}{2}\partial^\mu\Phi\partial_{ \mu }\Phi-V(\Phi)-\frac{ 1 }{ 2}\xi R \Phi^]## with ##\xi## representing the strength of the interaction between R and...

    I Slow-roll Inflation Model

    I have recently studied the slow-roll inflation model. In it, slow-roll inflationary conditions are mentioned in a lot of places(these conditions needed to be satisfied for inflation to happen). I don't really understand the meaning and purpose of slow-roll inflation. I want to know a very...
  7. PainterGuy

    I Some questions about Cosmic Inflation

    Hi, I have some questions about the cosmic inflation. As I tried to find the answers, I got little more confused. I have mentioned all the quotes from relevant articles which I found confusing. I understand that there are quite a few questions but they are all related to each other and I...
  8. L

    B Cosmic Inflation & Censorship: Validation or Corrections?

    Is it just waiting for empirical validation or are there still any corrections to do?
  9. P

    B Explaining Cosmic Inflation using analogies

    An analogy to understand Cosmic Inflation: If the universe grew in size from a subatomic size to the size of a tennis ball (or softball) in a tiny fraction of a second, then a football inflated at the same rate will grow to an approximate size of our solar system. Is this a correct analogy...
  10. S

    I Varying laws of high energy physics in inflation?

    I am have some questions that have arisen while reading an old but interesting article by Andreas Albrecht [1] that cites an article by Andrei Linde in the 90s on cosmic inflation [2]... Albrecht's paper is related to his ideas on "clock ambiguity" in which he proposes that the laws of physics...
  11. K

    I Higgs inflation and primordial black holes

    I've found highly cited papers that explains inflation with the Higgs as the inflaton and primordial black hole as the dark matter, for examples, These papers solve the inflation with the Higgs and Dark matter with PBH without introducing new particles. Primordial Black Hole production in...
  12. Alpha2021

    A Graceful exit of a cosmological inflation model

    How to determine whether a cosmological inflation model (say single-field slow-roll inflation) gracefully exit or not? Is it like showing that inflation is ending at some value of inflaton?
  13. RogerWaters

    B Does dark energy or cosmic inflation explain flatness?

    As I understand, the main theoretical virtue of Guth's inflation hypothesis is that it explains a bunch of otherwise hard-to-account-for phenomena under the standard big bang model without inflation: the Horizon Problem, the Flatness problem, the Monopole problem, and also the problem of how...
  14. RogerWaters

    B Why doesn't cosmic inflation violate conservation of energy?

    Hi all, I'm not a physics student (although I have a PhD in a different field) and so don't have the math, but I'm trying to interpret a key passage from Krauss' book 'A Universe from Nothing' where he is (trying?) to explain, in 'layman's terms', what Alan Guth termed 'the ultimate free lunch'...
  15. B

    I Why aren't Gravitational waves factored in to inflation formulas?

    It seems to me that gravitational waves are ignored when inflationary physics are described. I'm not very well read, and honestly do not know so much about most of the physics going on with inflation. Still, wave mechanics matter, harmonics matter, and it just seems intuitive to me that in order...
  16. Ranku

    I Inflation and size of the Universe

    Among other things, inflation explains the horizon problem, as to why even though the proper distance between two antipodal points on the last scattering surface is greater than the horizon distance, and therefore causally disconnected, yet the two points have the same temperature. So is this...
  17. elcaro

    I How long did inflation last in an eternal inflating universe?

    In so far I know eternal inflation can only constraint the minimum duration that inflation happened to produce the properties of the universe we can experimentally test (a minimum of some 60 e-folds, or in time, at least some 10^-30 seconds), but as eternal inflation is generically eternal to...
  18. kyphysics

    Inflation - Rants & Raves

    I think this topic deserves its own thread after a few mini rants w/ feedback. Unless you've been living in a cave, you probably have noticed the price of goods and services rising in your daily life at a faster than normal pace. Sometimes it's not an inflation of price, but rather...

    I Slow-roll Inflation and Horizon Problem

    I am a bit confused regarding the concept of the horizon problem. I have studied that the background radiation data implies that the radiations were not in causal contact at the beginning of the universe as from the big bang model. I want to know that how inflation is solving that problem? To...
  20. T

    Inflation rate and discount rate?

    I have a payback for a project of 6 years without counting the inflation rate and discount rate. If the Payback is 6 years, how do you add an average yearly inflation rate of 2.10% and a discount rate of 5.75%?
  21. J

    I Rivals for Inflation

    At the footnote of the chapter "Large-Scale Structure of the Universe" in Julian Babour new book The Janus Point is this passage: "Besides a Janus-point origin, there are now several proposals—involving bouncing universes or ones that expand after a long quasi-stable period—in which the...
  22. S

    I Wheeler's Pre-geometry model and multiple universes?

    John A Wheeler proposed that the universe emerged from a primordial chaos (some sort of pre-geometry or pre-space) from where all physics emerged in the universe. I thought this could be interesting in the context of multiple universes. Therefore, has any well renowned physicist considered...
  23. S

    I Is there any inflationary model without a fundamental theory?

    Cosmological inflationary models are general models in the sense that they could be applied to a variety of fundamental theories. Most physicists working in inflation assume that there is only one (but yet unknown) fundamental theory which through inflation would produce multiple regions or...
  24. Buzz Bloom

    I Is there a Friedmann equation form with inflation?

    If it is known that such an equation exists, I would much appreciate seeing a link to a reference. If it is known that such an equation does not exist, I would much appreciate seeing a reference with an explanation of implications regarding the compatibility of general relativity with a...
  25. 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...
  26. W

    B Nearly Scale Invariant Power Spectrum in inflation

    I recall hearing once a very intuitive explanation as to why inflation is thought to lead to a nearly scale invariant power spectrum but i can't recall it. Can anyone offer an explanation that might help me? Why is it nearly scale invariant and not perfectly scale invariant? many thanks
  27. 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...
  28. N

    Inflation and measurement of cosmic bodies

    Hi, Is it true that measurement proves the universe has inflated by 13.8 billion light years, and if so, how do we estimate the age or distance of those measurements? What's giving me pause is my assumption that the oldest light measured (furthest away) is 13.8 billion light years old, but...
  29. S

    A Can Cosmic Inflation and String Theory change fundamental laws?

    Is there any version of string theory or cosmological inflation that allows the most fundamental laws and constants change between universes? String Theory and Cosmological Inflation are two theories or models that allow multiple universes to exist. Laws and constants of physics could change...
  30. S

    A Calculating the Gravitational wave spectrum with Inflation as a source

    I am interested in knowing how to calculate the gravitational wave (GW) spectrum with inflation as a source, I have some background in inflation but I am not so familiar about calculating the GW spectrum. I am reading a paper (https://arxiv.org/abs/0804.3249) about it, however, a big part of it...
  31. C

    I Tom Banks' New Paper - Contra Eternal Inflation

    https://arxiv.org/abs/1910.12817 As a layman I've come to share this paper, mainly to garner the opinions of others to see what you all think, it was fairly insightful and seems interesting at least.
  32. O

    I What does the cosmic inflation theory actually say about flatness?

    I just read an article by Natalie Wolchover (a smart and knowledgeable writer as far as I can tell) in Quanta about the new analysis supporting a closed universe. In the article she makes this comment, "The leading theory of the universe’s birth, known as cosmic inflation, yields pristine...
  33. 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...
  34. QuarkDecay

    I Solving the Horizon Problem: 1 Source or 105?

    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...
  35. W

    I Does Spatial Curvature Falsify Eternal Inflation?

    I have often heard it said that the picture of a multiverse inspired from eternal inflation is not falsifiable. However this paper from 2012 claims that it is: https://arxiv.org/pdf/1202.5037.pdf specifically it says, as I understand it, that if one were to measure sufficient positive spatial...
  36. W

    B Eternal inflation question

    In the eternal inflation scenario described by Guth here: https://arxiv.org/abs/hep-th/0702178 it is usually thought it is impossible to ever travel to one of the other bubble universes as they are separated by inflating space expanding faster than any spacecraft could every travel. However...
  37. 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...
  38. 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?
  39. 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...
  40. 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...
  41. Arman777

    B How exactly inflation solves the Horizon Problem

    I am reading an article, Inflation and CMBR by Charles H. Lineweaver. He explains the inflation period as the shrinking of the event horizon in the comoving coordinate system. Which it makes sense since the inflation was a period of ##\Lambda##. And In this period of time event horizon shrinks...
  42. A

    I Inflation resolves the horizon problem

    Can anyone please explain how inflation removes the horizon. problem of standard cosmology . As much I know inflation is a period of accelerated expansion which can be approximated by ~exp(βt) which can be achieved if the energy density remains constt. throughout (e.g ≠ε(t)),which is the case...
  43. FallenApple

    How to beat inflation?

    Are there any non risky ways of beating the inflation rate( 2% annually I think)? I'm all for saving, but the fact that cash loses value frightens me. Investing is also risky too. Are there any non volatile, surefire way to beat inflation?
  44. 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?
  45. Green dwarf

    I Is inflation needed to explain uniformity?

    Inflation seems to explain why distantly separated parts of the universe are at the same temperature etc. But I've never seen any reason why the different parts should have been at different temperatures in the first place. Is there a simple answer to that?
  46. 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...
  47. 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...
  48. 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: $$...
  49. Safinaz

    I Weyl Transformation of Metric: Cosmological Inflation

    Hello, I’m new to the cosmological inflation so in this paper: https://arxiv.org/abs/1809.09975 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...
  50. ForgeJB

    I How can there be fluctuations in the inflaton field value?

    http://www.counterbalance.org/cq-turok/etern-body.html https://ned.ipac.caltech.edu/level5/Kolb/Kolb3_1.html) http://www.astronomy.ohio-state.edu/~dhw/A873/notes7.pdf) According to QFT, if you make repeated measurements of some property of the field then you will in general measure a...