Skip to main content
15 votes

Why do cosmologists assume that inflation began shortly after the Big Bang, rather than at the exact start?

The universe cannot have begun in an inflationary phase. Note that it is not necessarily the case that there was a phase that preceded inflation. However, if there was no phase preceding inflation, ...
Sten's user avatar
  • 4,764
12 votes
Accepted

Are there ways to estimate size of the "whole universe"?

tl; dr The universe is probably infinite, but if that's the case it's impossible to verify. If the universe is finite, and small enough, and the global curvature is equal to the curvature of our ...
PM 2Ring's user avatar
  • 15k
10 votes
Accepted

BIg Bang Happened everywhere

Okay, I think I know what Max Tegmark is talking about in the video. He is referring to the fact that, when you observe the cosmic microwave background radiation (CMB) — i.e. the radiation that was "...
pela's user avatar
  • 38.9k
9 votes
Accepted

What will the universe be like in a googolplex years time?

That is nearly long enough to reach heat-death, which is estimated as about $10^{10^{120}}$. What that means is rather speculative, since it depends on various events that we have never observed, such ...
James K's user avatar
  • 125k
9 votes
Accepted

Why can't we point the centre of the universe from inflation graph we see?

That diagram does not depict the entire universe. At most, it depicts the history of what is now our observable universe (specifically, a 2D slice through it), with us at the center only because we're ...
Christopher James Huff's user avatar
8 votes
Accepted

What explains the existence of energy/matter if it cannot be created or destroyed?

That's a very complicated question! First, let's remember that Moses didn't bring the Law of Conservation of Energy down from Sinai on stone tablets -- it's something that we've observed to be true ...
Mark Olson's user avatar
  • 7,650
7 votes

How could universe inflate itself out of the very dense and curved early spacetime? Could it happen in a black hole too?

Great question! Sorry for this huge response, and it might not be a satisfying answer, but it'll address your questions. Sadly, as with most of astronomy, the Big Bang is surrounded in mystery. It is ...
Sir Cumference's user avatar
6 votes
Accepted

Could the accelerating expansion of universe inidicate we are surrounded by "denser" space?

It's a pretty clever idea and a solid question that unseen mass might cause gravity outside the observable that tugs on the universe and might be the cause of dark energy as opposed to some unknown ...
userLTK's user avatar
  • 24.1k
6 votes
Accepted

How distant were the furthest currently-observable cosmic events when their currently-observed radiation was emitted?

tl;dr No, it's unfortunately not that simple. Cosmological distances The comoving distance to an object observed to have a redshift $z$ — i.e. the coordinates that expand along with the Universe — is ...
pela's user avatar
  • 38.9k
5 votes

Is the Big Bang inflation caused by Dark Energy

The expansion caused by a cosmological constant (a particularly simple version of dark energy) is not exactly Hooke's law, it is an expansion that maintains a fixed Hubble constant. So this means $\...
Ken G's user avatar
  • 5,336
5 votes
Accepted

Could Dark Energy be a "Cosmic Gravity Background"

There is in fact a cosmic gravitational wave background. These waves are expected to be stochastic, having originated in the early universe (much earlier than the cosmic microwave background). Random ...
HDE 226868's user avatar
  • 37.3k
5 votes
Accepted

Does wavelength affect redshift caused by the metric expansion of space?

Standard cosmological models predicts that the cosmological redshift and the speed of light are wavelength-independent. This result is confirmed observationally e.g. by Ferreras & Trujillo (2016), ...
pela's user avatar
  • 38.9k
5 votes
Accepted

Time dilation due to the expansion of the universe

Hubble's law $$ v=H_0 d,$$ relates the recession velocity $v$ of a distant object to it's physical distance $d$. Today, the physical distance coincides, by definiton, to the comoving distance $\chi \...
pela's user avatar
  • 38.9k
5 votes

Energy density of the inflaton field

I wouldn't say obvious, especially to someone who isn't familiar with quantum field theory, but it's the type of expression that theorists write because it's the only possible thing it could be by ...
ScienceSnake's user avatar
  • 1,048
4 votes
Accepted

How does inflation justify the nonexistence of magnetic monopoles?

Let me start off by stating that scientists have not conclusively proven that magnetic monopoles do or do not exist. There has never had a confirmed detection of one so the jury is still out on if a ...
zephyr's user avatar
  • 15k
4 votes

Does Flat Universe mean even distribution?

No, being flat and being homogeneous is not equivalent$^\dagger\!\!\!$. Flatness refers to the geometry, which depends on the total energy density $\rho$; if it is above or below a certain critical ...
pela's user avatar
  • 38.9k
4 votes

Intuitive explanation for why the universe is flat

The CMB lets us measure how close to flat the universe is right now. On the other hand, inflation tries to explain how we got from whatever the early universe was to right now. The motivation for ...
zibadawa timmy's user avatar
4 votes

Distinction between metric expansion and objects just moving apart from each other?

There's no difference between relative motion and "space expanding" between objects. There is a very common misconception that there is a difference, which has even made it into textbooks, ...
benrg's user avatar
  • 3,870
4 votes
Accepted

What is the acceleration for the expansion of the Universe?

The figure below shows the evolution of the Hubble parameter $H$ from 10 billion years (Gyr) ago, to 10 Gyr into the future: As you can see, the change in $H$ is modest nowadays, compared to the past....
pela's user avatar
  • 38.9k
4 votes

Have astronomers taken into account the fact that red-shifted light from far-away stars is also very old when studying the expansion of the universe?

The bottom line is that "Hubble's law" is a relationship between the (apparent) recession velocity we deduce from an observed spectrum, defined as the speed of light multiplied by the ...
ProfRob's user avatar
  • 156k
3 votes
Accepted

Are there expanding-universe cosmological models that do not include inflation?

Variable speed of light (VSL) theories (for instance Petit (1988) and Moffat (1993)) have been introduced in the past to solve the horizon problem you mentioned, i.e. that the observable universe ...
HDE 226868's user avatar
  • 37.3k
3 votes

Is the Big Bang inflation caused by Dark Energy

The big similarity between inflation and dark energy is that the preferred models for both can be described by scalar fields, however there is a huge difference between the energy scale, with the ...
John Davis's user avatar
  • 1,885
3 votes
Accepted

Standard Big Bang model and space curvature

What exactly did the book say? It all depends on what you mean/define as "curvature". What you describe appears to be a description of the behaviour of $\Omega$. Inflation does indeed drive $\Omega$ ...
ProfRob's user avatar
  • 156k
3 votes

Why is the CMB not simply travelling parallel to us?

Some of your questions seem to be genuine enough, so I'll address those: When the CMB was emitted, it was emitted everywhere in the Universe, in all directions. That means that we see it at all times,...
pela's user avatar
  • 38.9k
3 votes

Was time different before the great inflation?

Food for thought on density and time dilation. Density isn't gravity. We tend to think it is, but it's not. Variation in density gives us gravity. If you have an infinite universe, very young, hot ...
userLTK's user avatar
  • 24.1k
3 votes

Is the Universe really expanding at an increasing rate?

According to this paper I understood that scientists have found that redshift (z) of supernovae depends on relative distance (x) according to formula: ...
Agnius Vasiliauskas's user avatar
3 votes

A black "superhole" possibility?

There exists various theories, some stating that every black hole contains a new universe... In fact as a once very dense object, our universe could also be seen as a black hole itself! About what ...
Jika's user avatar
  • 130
3 votes
Accepted

What's the furthest distance that something could travel and eventually come back to Earth?

There's an easy way to work out the distance to the mirror at the present time, if it moves with the Hubble flow: imagine that instead of being emitted by us, the light is emitted by the mirror image ...
benrg's user avatar
  • 3,870
3 votes

If the energy density during inflation were lower, how would the CMB look in comparison to the observed CMB today?

We don't know the energy density during inflation. This should immediately tell you that it doesn't (directly) impact any of the observables that we are able to measure. Even though the inflation ...
Sten's user avatar
  • 4,764
2 votes

Future of CMB observations: How will our knowledge of the early universe change?

Although this is late, I think an update to this thread would be interesting. As of 2022, satellite-based CMB experiments like PICO, LITEBIRD, and CMB-Bharat are coming up. These experiments would ...
Yami's user avatar
  • 89

Only top scored, non community-wiki answers of a minimum length are eligible