Questions tagged [universe]

Questions regarding all of time and space and its contents.

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How did we measure the mass of the universe?

In an wiki article, observable universe, it was mentioned that, Mass (ordinary matter) 1.5×10^53 kg I wonder how did we measure the mass of our observable universe?
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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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Is it possible to be 'still' in space?

So I was reading this answer about how galaxies are the fastest moving objects in the universe because space is expanding faster than the speed of light. This got me wondering, would it be possible to ...
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Picking two random points in space and drawing a line between them, what is the chance the line intersects anything?

I thought of this question after pondering how most of the observable universe is observable. If we can observe it, then the space between us and that object must have been unoccupied to allow the ...
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How can something infinitely big have expanded from an infinitely small?

Please help me reconcile what I see as contradicting theories: The universe began with the Big Bang and expanded from an infinitesimally small point. The universe is infinite. How can something ...
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1answer
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What was the the value of the Hubble constant at the time of the CMB's 'release' (i.e., 379,000 years after Big Bang)?

What about its value roughly 9 billion years after the Big Bang, when dark energy started to 'take over' and accelerate the expansion of the universe? Is there a timeline or chart somewhere that shows ...
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How to calculate the mass of a galaxy?

How to calculate the mass of a galaxy? I have its apparent angular diameter and its distance. A H2 cloud at the galaxy's disc has a velocity of 410 km/s. How to calculate the mass of the galaxy?
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Bounded Observable Universe and General Relativity

The book General Relativity for Mathematicians by Sachs and Wu defines a "spacetime" as a connected 4-dimensional, oriented and time oriented Lorentzian manifold. I emphasize the word "connected." ...
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Bounded Observable Universe; is there an object we once could see but can no longer? [duplicate]

If the universe is expanding faster than the speed of light, then there will be objects (matter or energy or whatever) that previously could be seen, but no longer can be seen, precisely because the ...
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1answer
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What is the composition of the Universe in terms of Types Of Stars?

There are Main Sequence Stars Red Giants White Dwarfs Red Dwarfs Neutron Stars and other types of Stars. How many % of stars are Main Sequence? How many are Red Giants? and so on. I searched ...
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Will the “fabric of space time” rip from expansion?

I'm quite familiar with the fabric of space time theory and as I've been quite lonely these past few weeks, I started thinking that since the universe is expanding and since the "fabric" is the ...
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Is it be correct to say that we live in a young (only 14 billion years old) universe?

From what I have read, it seems that our universe is expected to function more or less as it does now for some $10^{12}$ years, possibly more. If that is correct, our universe's current age of $14$ ...
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what is the acceleration parameter in a universe?

Obtain the value of the acceleration parameter in a universe, including cosmological radiation and constant. what is the exactly acceleration parameter in a universe means ?
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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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How do we measure the age of the universe?

As mentioned in wiki/Age_of_the_universe, The current measurement of the age of the universe is around 13.8 billion years (as of 2015) – 13.799±0.021 billion years When my friend who is not from ...
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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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Will the Heat Death scenario ever occur or just the Big Freeze?

According to the Wikipedia page regarding the ultimate fate of the universe, heat death is a different scenario than the big freeze. It states that in the big freeze, temperature will asymptotically ...
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Why is rotational motion absolute, is the universe spinning? [duplicate]

When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say ...
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1answer
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If a black hole pulls every object in the universe, why there is a light around it?

I've seen some black hole images and I've seen some movies about it e.g(interstellar). I wonder why it has a light around it. Even if I know that light can't escape through it. Can someone enlighten ...
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Based off of the study that found the universe has a positive curvature, how big would the whole universe be?

This study found that the universe has a positive curvature https://www.nature.com/articles/s41550-019-0906-9. I didn't really want to buy it and see if it says how big the universe might be. I know ...
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The Matter Anti Matter Asymmetry

The matter anti matter asymmetry is still a mystery that still can't be explained. But what if there wasn't an asymmetry? Isn't it possible that there was exactly equal amounts of matter and anti ...
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Anecdote of an astronomer looking for correlations in antipodal pairings of stars; what am I remembering?

The question Are the stars distributed in uniform distribution, on the celestial dome, with respect to brightness? brings to mind a different study that I vaguely remember hearing about a while ago, ...
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Is the Big Bounce Theory valid? If so does that mean all this have happened before?

IF the universe is just an infinite loop of events from expanding to contracting does that mean all this has happened before? The initial conditions for the next big bang would (or rather could) be ...
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What book(s) should I read to get started learning about astronomy? [duplicate]

I'm an undergrad software engineer but I also love physics and math. I'm starting to get going in AI/Machine Learning techniques and I'm going to use NASA data-sets to conduct analysis. However, I am ...
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Does the universe have an edge?

I've heard the universe is just an empty cavity. Does the universe have any edge or stop or is it just an infinite empty cavity?
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Does the Milky Way move through space?

Does our galaxy moves through space? Or does it stay in a single location? If it does move, what causes it to move?
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Why does the star formation rate correlate with the total stellar mass in star forming galaxies?

The so-called "Main Sequence" of star-forming galaxies (e.g., Brinchmann et al. 2004; Noeske et al. 2007) clearly points to a linear relation between the stellar mass of galaxies and their star ...
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As the Universe expands, do things like planets expand also, or just the space in between?

Just what the question says. As the universe expands, and space expands, do objects like planets ever expand? Does the space INSIDE of those objects expand?
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How do astrophysicists handle the topic 'boundaries'?

The naive perception, at least mine, is that in astrophysics the objects of investigation evolve in an infinitely large environment. Since the scenery is so much larger than the events unfolding in it,...
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How is the Dating of Samples of Cosmic Objects Performed, Including Pre-Solar Dust?

In the new Space.com article 7 billion-year-old stardust is oldest material found on Earth I had read about some pre-solar grains dating back to 7 billion years. What techniques are used in ...
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Does a flat universe mean not finite and circular?

I am trying to wrap my head around what a flat universe means; Trying to imagine why angles of triangles in spherical volumes are different. Because my brain can't do that well and I became a bit ...
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Any theories about universal expansion due to action at the universal event horizon?

I'm curious if there are any theories about the increasing rate of the expansion of the universe that are centered around gravitational pull from matter outside the event horizon of either the ...
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Fate of the Universe

Which scenario will be worse for the ultimate fate of the Universe, forever expanding or the "Big Crunch"? Will the Universe be destroyed in both scenarios? At the present time does it appear that it ...
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Why the space is so dark even there are billions of stars and many quasars emitting light [duplicate]

In our galaxy itself, there are millions of stars, and there are many more other galaxies in our local group and billions in the observable universes. For sure they all emit a lot of light, still why ...
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24th Nov 2019.0515 hrs.GMT +1.saw a line of stars moving in a staright line.straight.what could it be? [duplicate]

While doing our morning navigation watch.. we saw stars moving in line.. it continued for atleast 10 mins.. not a airplane or shooting stars.. Can it be satellites orbiting??
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What makes the planets to be symmetric [closed]

I have seen, in my text books, and on nasa sites, the all the planets are symmetrical. And universe also love symmetry. What cause this symmetry, why the symmetry is important. As we know that ...
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Is the eventual heat death of the universe due to the expansion of the universe?

I am reading about the accelerating expansion of the universe and something struck me. The observation that things further away were accelerating away faster and that early observations made it look ...
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1answer
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What will the universe be like in a googolplex years time?

It will be cold and dark in 10^(10^100) years. What else can be said of the state of things in the far distant future? Will everything have fallen into supermassive black holes and then radiated ...
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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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Does time slow down because the universe is expanding at an accelerating rate?

If the universe is expanding at an accelerating rate, such that the galaxies' moving away from each other is accelerated, then time should also slow down. And when universe will accelerate to the ...
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How do we know so many details about Big Bang, but we do not know if Universe is finite/infinite?

I understand that this question may be too vague, but I am confused about the following: On one hand we know a lot of "details" about Big Bang, like really precise details, evolution of universe, age ...
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What is the largest cluster of merging galaxies?

Reading about the Andromeda–Milky Way collision, a galactic collision predicted to occur in about 4.5 billion years between the two galaxies, I went to the galaxy merger page and Wikipedia states that ...
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how are the celestial objects measured? [closed]

So I am guessing that chemical composition of the starts is measured using the spectrum analysis of waves emitted by them. But what if the spectrum is super packed by different wave lengths? How do ...
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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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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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Do we know what happens at the boundary of the universe, what are some theories about it? [duplicate]

Do we know what happens at the boundary of the universe, what are some theories about it? Does space time differ at the boundary? Do things become larger at the boundary? Do the trajectories curve and ...
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3answers
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Does the universe curve in on itself?

I've read a little bit about the universe, but its not clear to me if there is a place in the universe beyond which there are no stars. For example, is there anywhere in the universe that one could ...
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Probability of collision of another bubble universe with our universe

This is rephrased from a previous question and expanding on it. Considering the model of an "inflating" universe which extends infinitely in past (and possibly future) time, constantly creating new ...
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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 ...
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Energy to expand

I do have a small question, which may seem a bit stupid but we are all here to learn. Anyways my question is: Is the universe expanding using the energy it had from the Big Bang? if so what would ...

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