Questions tagged [universe]

Questions regarding all of time and space and its contents.

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Is the number of galaxies in the observable universe increasing? [duplicate]

Is the number of galaxies in the observable universe increasing? Are more and more galaxies coming into view? Or is the number decreasing? If it's increasing then when will it reach a maximum? If it's ...
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1answer
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Scalar field displacement from the minimum of the potential gives rise to particles/dark matter, why?

The paper Lyman-alpha Constraints on Ultralight Scalar Dark Matter by Kobayashi et al. says, at the beginning of Section 3.1: A light scalar field stays frozen at its initial field value in the early ...
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2answers
611 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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Will there be collision between universes?

I just watched one of those videos that shows the scale of the universe, zooming out from one thing all the way out to the sphere that is thought to be the universe. However, they also showed other ...
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6answers
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Logically, how can the universe be infinite in size?

Many people have told me that the “universe doesn’t care what you think” in my regards to it being infinite in size, and I know something that seems logical doesn’t mean anything when measured by ...
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1answer
102 views

Can magnetic monopoles only exist in a curved universe? [closed]

I’m trying to figure out rules for my Sci-fi universe and I need to know what type of universe, the universe needs to be for the existence of magnetic monopoles to exist. I read somewhere that the ...
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5answers
10k views

Is there a star over my head?

Say I'm standing up straight, and I draw a straight line from my core through the top of my head (perpendicular to the ground). What is the probability that that line intersects with a star? EDIT: I'...
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2answers
374 views

Will the Universe end by time stopping?

I know there are several theories as to how the universe might end, if it does. Is it possible for it to end by time stopping? A friend of mine told me about this theory, but her explanation that it ...
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1answer
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Question re distribution of the baryonic matter in the Universe

In https://phys.org/news/2021-09-universe.html it says:"Scientists thus discovered some of the universe's missing baryons, thereby confirming that 80–90% of normal matter is located outside of ...
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How do scientists know that the distant parts of the universe obey the physical laws exactly as we observe around us?

How do scientists know that distant parts of the universe obey the physical laws exactly as we observe around us? The question might look a bit odd but I am really stuck on my head. We know, ...
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151 views

The energy density of DM (to be fluid,state parameter=-2)increases with time. Does it violate the concept of accelerating universe?

We know that dark energy with value of state parameter $\omega<-1$ is called phantom dark energy model. In this model if we assume dark energy to be a fluid with value of state parameter $\omega=-2$...
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What is the concept of wormholes? [duplicate]

My main queries for now I guess: What is the theory behind wormholes? What is the possibility and likeliness of their existence based on scientific analysis, not conspiracy theories? What is the ...
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1answer
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is there any excuse or reason why our bubble in Hawking's space-time foam theory is retained? [closed]

Hawking said that universes are like bubbles that pop into existence and pop back into the vacuum some form then immediately pop, he calls this space-time foam, our bubble doesn't seem to pop ...
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What is the distance between solar system and a distant galaxy

When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago?
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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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Because the Universe is expanding, what is it taking up?

It is my understanding that the universe is expanding and that matter takes up space. While the universe only contains small percent of matter, wouldn't expansion indicate that the universe is ...
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Why black holes are extremely cold?

"The most massive black holes in the Universe, the supermassive black holes with millions of times the math [sic] of the Sun will have a temperature of 1.4 x $10^{-14}$ Kelvin. That's low. Almost ...
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941 views

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

If the energy/matter that was contained in the singularity before the Big Bang had always existed, and if it’s true that energy/matter cannot be created or destroyed, then what explains its existence?
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Does the mass of the observable universe ever change?

First do we have anyway to even estimate the mass of the entire observable universe? And then is there any data that shows mass being gained or lost? Would we ever know if someone was playing with ...
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1answer
284 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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Are there only $10^{83}$ atoms in the universe?

I'm a high school junior. I assumed there would be an incredibly huge number of atoms in the universe if not infinite. Recently, I've come across a few articles which claim that scientists believe ...
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1answer
48 views

FLWR and curvature

The FLWR metric or model I believe results from Einstein's equations of general relativity if it is assumed the universe is 1. homogeneous and 2. able to expand (or contract). Solutions can have ...
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3answers
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Density of stars on celestial sphere

The pattern of stars on the surface of the celestial sphere seems perceptually to have an universally looking structure. If you pick a region of the sky at random, for instance by using the (excellent)...
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1answer
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Is our universe stable or metastable?

I've been reading and thinking about this subject for some time, but I can't seem to find a clear answer. After reading Q14: Aspects of the Higgs boson suggest that our Universe is only “...
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7answers
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What's the fastest moving object in the universe?

We know that nothing can have proper velocities larger than the speed of light in vacuum. But are there any objects in space that get close to it? Any comets, or other objects thrown by gravity or ...
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Can two neighboring galaxies move apart at steady speed?

While I was trying to understand the three models that obey Friedmann's two assumptions of a non-static universe, I came across a line that says and I quote "It (referring to Big Bang) starts at ...
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Traversing a proton within the Planck time

If I could travel a super small distance (proton) in an even smaller time (Planck time), how long would it take me to cross the observable universe?
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What do falsifiability and verifiability actually mean as a precondition of a scientific hypothesis?

What do falsifiability and verifiability actually mean as a precondition of a scientific hypothesis? I have been hearing from science guys that unlike philosophical hypothesis or theory, to be a ...
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45 views

Is there any theory suggesting the expanding universe may be coupled to another shrinking universe

Our Universe is supposed to be expanding. I was curious if there was any theory suggesting the expanding universe may be coupled to another shrinking universe?
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1answer
267 views

A universal reference point [duplicate]

I would like to use a system of co-ordinates (x,y,z,t) based on a specific well known point. My original choice (the center of the universe in the big bang theory, Bigbang0), was wrong as the universe ...
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1answer
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if the universe is infinite shouldn't it have experienced an infinite number of universe ending events? [closed]

or is it that the definition of infinity used here excludes such events like there are an infinite number of odd numbers but 2 isn't in that set?
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Shouldn't the estimate of the universe's age be higher, not lower, after the attractive strength of gravity is taken into account?

From 'Fundamentals: Ten Keys to Reality', by Frank Wilczek : "Running the movie of cosmic history backward in our minds, we found the galaxies all coming together to meet at a definite time. ...
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Significantly blueshifted Lyman-$\alpha$

Lyman-$\alpha$ line in galaxies is notably known to show a double peaked profile, mainly due to its scattering in a moving medium, see e.g., the very recent Matthee et al. 2021, The X-SHOOTER Lyman-α ...
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Why is the observable Universe larger than its age would suggest?

The age of the Universe is estimated at 13.8 billion years, and current theory states nothing can exceed the speed of light, which can lead to the incorrect conclusion that the universe can't have a ...
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Observable universe equals its Schwarzschild radius (event horizon)?

The estimated age of the universe is 14 billion years. The estimated Schwarzschild radius (event horizon) of the observable universe is 14 billion light-years. What are the ramifications?
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If we lived in a multiverse, what would our universe most likely then be named? [closed]

We live in the Milky Way Galaxy, but we don't just call it "The Galaxy", because we know there are multiple different galaxies. So if we lived in a multiverse, it wouldn't make much sense to ...
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195 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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1answer
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Does the holographic principle contradict eternal inflation?

As it is for example explained here, Andrei Linde's chaotic inflation is among the potential winners or survivors of the spring cleaning induced by the potential detection of primoridal gravitational ...
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Is the Cosmos a super set of the Universe and any hypothetical multiverse(s)? [closed]

I'm quite lost on the definitions of words like omniverse, megaverse, multiverse, meta-universe, universe, and cosmos. I used to think the Universe and the Cosmos were essentially the same things, but ...
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Is there any difference between parallel universes and multiverse?

Nowadays we come across with these two terms - parallel universes and multiverse. I wonder if this is the same thing or its two entirely different principles because the names are a bit confusing to ...
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791 views

On what scale does the universe expand?

According to the theory (or my understanding of it), the universe is not only expanding, but speeding up. If the galaxies are moving apart, are the solar systems within them also moving apart from ...
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87 views

Potential paradox with the Big Rip and the Multiverse?

I came up with this confusing theory a few years ago, but did not ask it on this site. If the Big Rip and the Multiverse theories are true, then when the Big Rip occurs, the universe's size will ...
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41 views

How long does it take for a galaxy (or other object) to disappear behind the cosmic sight horizon?

After looking at this question, I am wondering, how long does it take for a galaxy or other space object, to disappear from our view from the Milky Way due to the expansion of the universe? Assume GN-...
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67 views

How does the universe create more universe ( expand ) out of nothing? [duplicate]

By the law of conversation of energy, mass and matter, how does the universe get the energy to expand itself, and also expand faster than light!! Edit : my main question is that if the matter, energy ...
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What are the stages in the life of a universe?

Geological periods describe varying phases in the last few hundred million years on earth. Are there any names for the periods on a timescale 1-2 orders of magnitude greater, that is, for the stages ...
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3answers
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Why can't this be the simple (and obvious) explanation for the dimming of KIC 8462852?

Couldn't it be just a relatively large object, anywhere in the interstellar space between the star and Earth? I mean, look out the window at a far away car or a tree, then stretch out your hand and ...
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1answer
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How many earths fit in the observable universe?

I was pondering our insignificance, when I wondered - how much smaller is our planet then the (observable) universe? And being as I don't know how to do the math, I'm asking it here. So how many of ...
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487 views

Universe’s Glow Shows There Are Fewer/More Galaxies Than We Thought, Say Scientists

There are several articles like this: Universe’s Glow Shows There Are Fewer Galaxies Than We Thought, Say Scientists NASA’s New Horizons spacecraft beyond Pluto has made a groundbreaking measurement ...
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Can there be planets, stars and galaxies made of dark matter or antimatter?

We know that the universe has more dark and anti matter as compared to normal matter. Can there be dark matter galaxies or antimatter galaxies?
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How can cosmological bubble universes "collide" with each other?

In Eternal Inflation Theory, there exists the idea of multiple "bubble" Universes that grow and according to this theory, can "collide" with each other. The paper suggests that you can search for ...

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