13 votes
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Is the Universe really expanding at an increasing rate?

I don't take this at face value because we should expect more distant objects to have higher observed speeds and therefore higher observed red-shifts. That's true. That was the original Hubble ...
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  • 22.9k
12 votes
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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 ...
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  • 10.4k
10 votes
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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 "...
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  • 33.8k
8 votes

Did cosmological inflation occur at speeds greater than $c$?

The simple answer to your question is "yes" - the universe expanded at much greater speeds than $c$ during the inflationary epoch. This period of time was very quick but very dramatic, lasting from ...
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  • 34.1k
8 votes
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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 ...
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  • 7,390
8 votes
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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 ...
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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 ...
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6 votes
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Does the universe expand at the same rate everywhere in the universe?

What's outside the observable Universe, we can't say anything about, but averaged over large enough scales ($\gtrsim$ a billion lightyears), it does indeed seem to be expanding uniformly. However, ...
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  • 33.8k
6 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 ...
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  • 33.8k
6 votes
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Dark Energy Expansion

Is Cosmos seriously using that exact number? Egads... if they are, don't take it too seriously, but otherwise they're probably conceptually correct. How do we know it was dark energy? In cosmology,...
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  • 7,684
6 votes
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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,...
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  • 118k
6 votes
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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 ...
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6 votes
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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 ...
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  • 91.4k
6 votes
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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 \...
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  • 33.8k
6 votes
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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 ...
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  • 33.8k
5 votes

What is our universe expanding into?

It's a rather difficult concept to grab but, in short, the image of expansion you have in your mind is wrong. It's not your fault, it's everywhere out there, the inflatable balloon etc. And it's ...
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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 $\...
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  • 5,170
5 votes
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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 ...
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  • 34.1k
5 votes
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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), ...
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  • 33.8k
4 votes

Is the expansion of the universe greater than the speed of light?

After inflation, the expansion of the universe did indeed slow down. During the inflationary epoch (lasting roughly $1 \times 10^{-33}$ seconds), the universe expanded by a factor of $10^{26}$. That's ...
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  • 34.1k
4 votes

What is the explanation for rapid inflation just after the big bang?

With normal matter, the strength of gravity depends on the stress-energy tensor, which, in an isotropic homogeneous universe, has trace of $\rho + 3p$. The positive pressure from relativistic ...
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4 votes
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How long was the hyper inflation phase?

Googling "hyperinflation" mostly returns articles about Zimbabwe and the Weimar Republic, so I'm going to assume that you are referring to what is usually just called (cosmological) inflation. We are ...
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  • 33.8k
4 votes
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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 ...
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  • 33.8k
4 votes
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The universe is dying vs the universe is ever expanding

Both are true. The universe is "dying" in the sense that stars eventually run out of hydrogen, and there aren't infinite amounts of hydrogen in galaxies to replace old stars. This will take a very ...
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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'/\...
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  • 7,684
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 ...
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4 votes
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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....
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  • 33.8k
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 ...
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  • 33.8k
4 votes
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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 ...
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  • 14.5k
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 ...
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