Questions tagged [universe]

Questions regarding all of time and space and its contents.

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1answer
546 views

Finding equation for energy density of matter

I'm trying to get an equation for the energy density of matter of the universe $\rho(t)$, assuming the number of particles is conserved and rest mass energy is much greater than kinetic energy. $\rho(...
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1answer
2k views

Will we start seeing galaxies disappear due to Universe expansion? [duplicate]

Does the fact that universe is currently expanding at an accelerating rate means that far far away objects (FAO) might start disappearing with time, set aside the "red shift"? I'm saying this ...
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1answer
486 views

How can the observable universe shrink in a Big Rip?

As far as I know, the Big Rip occurs when the scale factor reaches infinity in a finite time. This will only happen in a universe dominated by phantom energy (i.e. a universe with an equation of state ...
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1answer
307 views

What existed before the big bang [closed]

What existed before the big bang? What all thing are there inside big bang object ?.
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1answer
299 views

Who first hypothesized that the universe is accelerating?

I couldn't find this answer anywhere. Before 1998, was there a notable physicist who conjectured that the universe is accelerating and perhaps even submitted some equations to support it (and the ...
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1answer
464 views

What is high redshift?

I'm curious about the difference between low redshift and high redshift universe. Is there any defined limit of redshift beyond which we call things high redshifted?
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11k views

How can 'HD 140283' be older than the universe?

Scientists have known about the star HD 140283, informally nicknamed the Methuselah star, for more than 100 years, since it cruises across the sky at a relatively rapid clip. The star moves at about ...
3
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1answer
656 views

Latest cosmological parameters

I'm looking for the latest values (with uncertainties) of the four main cosmological density parameters $\Omega_i$ : \begin{align}\tag{1} \Omega_{\text{mat}} &={} ?, &\Omega_{\text{rad}} &=...
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1answer
112 views

If a star orbited another star, how would that affect parallax measurements of the other star from the vantage point of the first?

Example: If hypothetically, the vantage point would move 2AU along an orbit around the star being measured, would that make it seem as if the other star moved twice the distance over the back-drop?
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1answer
109 views

How can space expand in accelerating speed when dark energy is constant?

I came to know that dark energy is constant.As mentioned in the Friedmann equations How can a constant energy cause an ...
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2answers
303 views

How is a Galaxy formed?

How is a galaxy formed? I know that the center of our galaxy is considered to be Sagittarius A* and it's surrounded by a lot of stars (also a lot of neutron stars). But what makes this happen? I mean,...
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1answer
154 views

Centerless expansion or a matter of perspective [duplicate]

I get this question a lot: Where is the center of the Universe? I see this question on the internet all of the time: Where is the center of the Universe? Now I have a question regarding all ...
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1answer
3k views

Does the recent news of “ten times more galaxies” imply that there is correspondingly less dark matter?

Nature: Universe has ten times more galaxies than researchers thought NASA feature: Hubble Reveals Observable Universe Contains 10 Times More Galaxies Than Previously Thought Headlines sometimes ...
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1answer
199 views

Why are galaxies distributed as walls and voids, or spider webs?

I have wondered why the "walls and voids" of the cosmological galaxy distribution seem to resemble a "foam", like rising bread that's ready to fall, with "voids" corresponding to empty bubbles in the ...
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2answers
2k views

Does the age of the universe take into account General Relativity / Special Relativity?

It is generally accepted that the age of the universe is approximately 12-15 billion years old based on the speed of the expansion of the universe. Since everything is moving very fast away from us, ...
3
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1answer
411 views

What suggests the cyclic nature of the universe? Proposed by Stephen Hawking

In "A Briefer History of Time" by Stephen Hawking he writes that if we were to travel faster than the universe were expanding and for long enough (in a straight line) we would eventually come back to ...
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2answers
407 views

Why are some universal entities round and others are flat?

I've been wondering for a while now why some objects in the universe (such as stars, planets, etc.) are round, while others are flat (galaxies, planetary rings and protoplanetary disks). I know these ...
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1answer
157 views

How can we use hypervelocity stars to determine the origins of the Universe?

I was reading this article finding evidence of Universe's origin, which describes that in 1 trillion years we may lose the ability to determine how the universe was created. The answer seems to be ...
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2answers
306 views

Is the universe moving through infinite space time as it expands?

What I mean by this, is imagine a person blowing up a balloon. As the balloon expands, the person blowing it up is also walking. At a much grander scale, apply this concept to the universe. As the ...
2
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1answer
315 views

Do some ELF (Extremely low frequency) radio waves pass the atmosphere

...reach Earth surface and then are reflected passing the atmosphere again to reach outer space? And once in outer space can they travel indefinetely in it or the interplabetary plasma would stop them?...
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2answers
133 views

Are there any sounds in space?

Is our universe noisy or silent? Can people hear them? When astronauts are out of the Earth and near an explosion, can they hear its noise.
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1answer
478 views

If the universe is 'flat', what shape is it? [duplicate]

As in the title, If the universe is considered to be 'flat', what shape is it? Is it a disc, elliptical, square, rectangle? Or is this still unknown as we can only study a small segment of the ...
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1answer
612 views

Can information leave the observable Universe?

From what I gather, the observable universe is expanding at the speed of light. In addition, information cannot travel faster than the speed of light. It seems as though these two facts would imply ...
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1answer
164 views

Why can we trust Hubble Time if the rate of expansion is not constant?

The age of the Universe can be estimated from taking the inverse of the Hubble constant: $t_\text{universe} = 1/H_0 =d/v.$ It seems to me this method assumes that any given galaxy has been receding ...
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1answer
83 views

Parts of the Universe Shows Fewer Named Stars [duplicate]

I'm becoming interested in the currently identified stars in the universe. There is a wide swath where much fewer named stars are shown. Why is this? The image below is a mollweide projection of the ...
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1answer
107 views

Can one calculate the size (i.e. the radius) of our universe? [closed]

If one can estimate the mass of our universe, might one also calculate its ultimate size, (after it fully expands), based on the Schwarzschild formula for the radius of a black hole? Please note that ...
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1answer
313 views

If the universe keeps expanding, can we travel to the edge of the universe? [duplicate]

If the universe keeps expanding, is it possible to travel to the edge of the universe?
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1answer
3k views

What is the most dense object in the universe?

Inspired by this answer to the question, Why is the Sun's density less than the inner planets?, what is the most dense object in the universe?
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2answers
150 views

Is there any proof of space being created?

Is there any proof for space being created? Because I guess an explanation for the dark energy (dark = our understanding of it) could be that there is a gigantic amount of matter/dark matter that we ...
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2answers
236 views

In a finite universe, what happens when light reaches the boundary?

If a universe is finite and is not expanding at a speed equal to or greater than c, what happens when light or another form of electromagnetic radiation traveling reaches the boundary?
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1answer
523 views

Birthday of the Universe

With every improvement of measurement we are able to determine the age of the Universe more exactly. I just wondered how much and what means it would need to narrow the range of age so that it would ...
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1answer
216 views

Evidence of CMB redshift

Are there any known spectral lines shifted by ~1100? If not, then how certain is mainstream that the CMB has a redshift of ~1100? All I see is a blackbody radiation curve void of spectral lines.
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4answers
4k views

What is the volume of the universe?

Of course it is not exactly known how big the universe is, but I thougt that the universe is about 100 billion lightyears in diameter. But if that is true can you also make an estimation of the volume ...
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3answers
1k views

Are we center of universe? [duplicate]

So I just learned that CMB redshift is 1100 regardless where we look (up down left right). According to Hubble's Law that makes it around 46 billion light years away, making it the farthest matter ...
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1answer
57 views

Locations of farthest matter

Regarding matter that has the highest redshifts, do we see such matter in every general direction we look (relative to Earth: up down left right front back)?
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1k views

Is the earth bombarded equally in all directions by neutrinos?

Perhaps it is hard to known for sure because neutrinos are very difficult to detect, although they do go through the earth in very large numbers. But are they passing through the earth equally from ...
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1answer
44 views

Are there events in universe which we receive first from their neutrino's instead of their photons?

Neutrino's are very small though they have mass. Because of that it is probably that the don't have a speed faster than photons. But is it in all events, like supernova's or else events, where it is ...
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1answer
2k views

What are the 10 most abundant elements in the universe by number of atomic nuclei?

I've seen websites that show the ratios of the 10 most common elements but they compare them by relative mass. I think it's more interesting to know the relative abundances of atomic nuclei because ...
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2answers
135 views

Regarding the age / size of the Universe [duplicate]

I believe the current estimated age of the Universe is around 14 billion years. I just read in another post on here that the diameter of the Universe is around 90 billion light years. This doesn't ...
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2answers
879 views

What happens outside of the universe? [duplicate]

Since the universe is always expanding, that means there's an edge right? So what are some theories for outside of that growing edge.
3
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1answer
203 views

How could we tell if the Universe is infinite? [duplicate]

I've heard from a number of people that the Universe is infinite, and from my perspective, I can't see how this can actually be known, especially given that the Universe started out a finite size and ...
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2answers
472 views

How does the concept of a universe with no center work?

I understand basically that the universe is homogenous (looks the same from every point) and I was told in my astro class that it's supposed to have no center, but how that works boggles my mind. I ...
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1answer
130 views

Origin of the Universe [closed]

I heard on a you tube video that a new theory came out in 2015 . The theory is that there was no "Big Bang" and that the Universe has no beginning .
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1answer
224 views

Is the flat curvature of the universe in the 5th dimension?

It is hard to imagine that the universe could have a flat curvature while I've read that it is at this moment the most likely. When you look around the universe is expanding in all directions, so it ...
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2answers
129 views

Why can't different regions of the universe be the same as they have the same origin?

The horizon problem states that because of the speed of information can't be faster than light and the distances between far regions are too big there is a problem because they look quite the same. ...
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1answer
3k views

Why is there a difference between the cosmic event horizon and the age of the universe?

According to wiki the cosmic event horizon is 5 Gpc but the age of the universe is about 13,7 billion years. Usually light from far galaxys needed at most 13,7 billion years to reach the earth so the ...
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1answer
629 views

Why when we look through a telescope in space, do the billions of stars not block our view from seeing further?

I know that we are able to "see back into time" by looking very far away through telescopes such as the Hubble telescope, but my question is, wouldn't you run into at least a couple of stars that were ...
5
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1answer
329 views

What is driving the expansion of the Universe?

Is it just the momentum from the Big Bang? If yes, how can it account for the acceleration of the expansion? Why isn't the collective gravitational force slowing it down? What part does dark energy ...
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2answers
159 views

Is parallel universe possible [duplicate]

Does parallel universe really exists or just science fiction which ain't possible? Can we ever know ?
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2answers
102 views

Large hadron collider [closed]

Whether the collision of particle will lead to a massive WORMHOLE or if BLACKHOLE is also possible? How much I know is that it's created for einstien's E=mc^2 ,conservation of energy from mass and ...