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, ...
- 4,260
13
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 ...
- 13.1k
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 "...
- 37.1k
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 ...
- 7,580
8
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 ...
- 1,158
7
votes
Does time slow down because the universe is expanding at an accelerating rate?
Yes, time does run slower for far-away objects, as observed from our point of view; this is a prediction of general relativity. And yes, because expansion accelerates, this time dilation slowly, very ...
- 37.1k
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 ...
- 8,119
6
votes
Accepted
How can cosmic inflation make an infinite universe homogeneous?
Inflation is used to explain why the observable universe is extremely homogeneous.
Without inflation, we can do the following crude calculation. The cosmic microwave background was formed about 300,...
- 146k
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 ...
- 23.9k
6
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 ...
- 116k
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 ...
- 37.1k
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 $\...
- 5,300
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 ...
- 36k
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), ...
- 37.1k
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 \...
- 37.1k
4
votes
Does the accelerating expansion of spacetime mean that the pace of time is changing?
To talk about 'the rate of time', we essentially need at least two different time coordinates. For example, this happens in special-relativistic time dilation, which is equivalent to $\mathrm{d}t'/\...
- 7,874
4
votes
Accepted
Problem with denoising the BICEP2 data?
B-modes in the raw CMB data can be caused by primordial gravitational waves, as well as by cosmic dust. After subtracting the cosmic dust polarization from the BCEP2 data, the residual signal is too ...
- 11.5k
4
votes
Accepted
Looking back in time by looking further away
Before the advent of telescopes, we could only look back in time from a few years (for nearby stars) to a few thousand years (for the most distant stars visible to the unaided eye). In addition to ...
- 37.1k
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 ...
- 3,260
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....
- 37.1k
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 ...
- 37.1k
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 ...
- 15k
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 ...
- 146k
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 ...
- 36k
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 ...
- 1,855
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 $\Omega$ ...
- 146k
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,...
- 37.1k
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 ...
- 23.9k
3
votes
Does time slow down because the universe is expanding at an accelerating rate?
In general, better refrain from using 'inflation' unless you're talking about the early Universe-inflation. Rather, the Universe is expanding at an accelerated rate.
The crux of this question seems ...
- 834
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:
...
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