The universe refers to the cosmos; all of space-time and that which exists as part of it. Alternatively, it can refer to the observable universe, which only contains the part we can see. Questions tagged with this should ask about physics at scales the size of the universe or specific properties of ...

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Did light already experience death of the universe immediately after the Big Bang?

Let's suppose that I am on Point A with a light-beam launcher. My goal is to launch a beam of light to Point B, which is about 8,000 quadrillion light years away. My friend named Jack is at Point B ...
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3answers
208 views

Is simulating the entire universe possible?

Is it concievable that we may one day simulate the entire universe with every single particle, field and law of physics factored in? Can n number of particles (say the number of particles that make up ...
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2answers
67 views

Expansion of the universe a thermodynamic process or not?

Can the expansion of the universe be thought of as a thermodynamic process? If so, is it a closed system? Is it a reversible system?
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149 views

Question about universe expansion

In general relativity, we cannot determine the global structure of the universe (since it is not flat), therefore all measurements and observations are only meaningful locally. In particular, we can ...
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40 views

Is it possible for the universe to be moving towards something, rather than expanding?

We all know that the universe is flying away from the Big Bang at speeds approaching or exceeding the S.O.L. However, is it physically possible for an object to be pulling the universe away as well?
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56 views

Was there a singularity before the Big Bang or after it? [duplicate]

I am slightly confused. Some say that the initial state of the universe was a singularity, and some say that before the Big Bang; there was a singularity. Can anybody elucidate?
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134 views

Upper limit on the size of the “unobservable” universe based on surface area divided by Planck constant?

There are many kinds of size scale to the universe one can talk of. Much has been discussed with the concept of the upper limit of "bits" contained in the observable universe and therefore the total ...
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701 views

How do scientists calculate the percentage of dark energy in the universe?

I can understand how the percentage of dark matter compared to ordinary matter is calculated, because the amount of dark matter has a clear gravitational effect on the ordinary matter in a Galaxy. ...
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1answer
136 views

What would happen to the universe if dark energy started “disappearing”?

Terribly naive question, I know. Obviously, not simply "disappearing", but if it could, theoretically, be absorbed or "used" somehow, what would happen to the universe? Would it stop expanding, would ...
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4answers
88 views

Effect of expansion on time?

We know that for moving body times moves at a slower rate, but can this happen for Universe itself whose rate of expansion is accelerating?
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2answers
1k views

Was everything in the Universe “created” from light?

Is the following true? The only matter existing directly after the big bang was electromagnetic radiation.
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83 views

Can Parallel Universes exist? [closed]

I saw Stephen Hawking say that there are an infinity of parallel universes. How did he get to that theory, and is it possible?
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1answer
68 views

What are the latest findings on the topology and size of the universe?

The paper G. Aslanyan & A.V. Manohar, The Topology and Size of the Universe from the Cosmic Microwave Background, JCAP 06 (2012) 003, arXiv:1104.0015, uses the 7-year WMAP data. Has any ...
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2answers
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How can we know there is more than just the observable universe

If all we can observe are things inside the observable universe, how do we know that anything even exists outside this boundary? I can see four ways of solving this problem. 1) We wait a while, the ...
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1answer
170 views

What is dimension and how many types of dimensions are there in the universe?

What is dimension and how many types of dimensions are there in the universe? I mean how many total dimensions are there? I have only heard about 2d and 3d. Other than these two, are there any other ...
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1answer
147 views

Angular Power Spectrum of CMB

I was wondering, if anyone could guide me through the different peaks of this spectrum (See below)? I've been reading and reading numerous pages about this, but I can't seem to get my head around ...
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4answers
317 views

Entropy of the whole universe

In "Thermal Physics", Charles Kittel proves that entropy always increases in systems when the degree of freedom are increased (adding particles, adding energy, expanding volume, etc ). I started to ...
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2answers
87 views

Can we solve most of the cosmological questions using the Illustris universe simulation?

The Illustris project (http://illustris-project.org) attempts to simulate the universe in its most accurate form according to their website. With the simulation, they were able to predict the neutral ...
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1answer
87 views

How fast am I moving? [duplicate]

Given the speed of light is 299,792,458 meters per second and that it is constant through out the universe, (i.e a person who measures the speed of light while standing still will get the same result ...
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0answers
41 views

How Do we Know How Old the Universe Is? [duplicate]

It is common knowledge that the universe is 13.8 ± 0.037 billion years - but how was this calculated?
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2answers
1k views

How far away must a galaxy be for its light never to reach us due to the expansion of the universe?

My understanding is that at the present rate of expansion of the universe some galaxies are growing more distant from us at such a rate that light from them will never reach us. My question is how far ...
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6answers
732 views

Is time travel impossible because it implies total energy in the universe is non-constant over time?

I have always argued with my friends regarding Time Travel that it is impossible. My argument has been that it will destroy the theory that all the energy in the universe is constant since when one ...
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3answers
371 views

Entire Universe's Momentum

I was thinking about the definition of the conservation of momentum, which says that momentum is conserved unless outside forces are acting on the system, and I was wondering that if the system is the ...
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2answers
126 views

Infinite Universe and Big Bang

A common view now in the physics community is that the Universe is infinite in extent (which makes Hubble sphere an infinitely small part of the Universe). On the other hand, there is the Big Bang ...
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1answer
166 views

What happens to black holes if/when the universe “ends”

I've heard several ideas about what happens to the universe when it dies, and they range from infinite expansion and heat death, to a "big crunch". In the event that something like a "big crunch" ...
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2answers
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Do things in the universe get farther apart or bigger? (Amateur)

To start off I would like to say I am a complete amateur and have no experience in physics! I am just a sophomore in high school with some questions. Now that that is out of the way. There are many ...
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3answers
146 views

How do you define a “universe” (in the context of multiverse)?

How do you define a universe (in the context of multiverse)? The traditional definition of universe is something like "The Universe is all of spacetime and everything that exists therein". But in ...
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1answer
92 views

Are there more reasons why we can not be part of an $n$ dimensional Game Of Life?

After talking with a colleague about the possible nature of the limitation of information propagation to c, and how everything can be seen relative to it, we wondered if the nature to this could be ...
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2answers
174 views

How can a black hole zap a galaxy into existence?

I am referring to this picture published here. Apparently super massive black holes emit radiation and matter in astrophysical jets. And these jets can form galaxies. I have some questions: Isn't ...
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2answers
148 views

Is the big bang a fact? [duplicate]

I have watched many physics debated and in everyone of them, physicists take big bang for granted. But, is the big bang actually proven, or there are many evidence that indicate that it did happen?
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0answers
38 views

What role did the Higgs boson play in the Big Bang?

Scientists say that inflation stopped when a very peculiar energy was mobilized, did Higgs boson play any role in this? What is it's relation to the Big Bang? Some physicists, such as Michio Kaku, ...
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1answer
84 views

Can the energy of the universe ever be infinite in qunatum physics? [closed]

Suppose that the universe runs under some variants of QFT, with universal wavefunction and Hamiltonian. Then would infinite energy of the universe ever be possible? According to what I am thinking, ...
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0answers
21 views

Space Between Current universe and point of origin [duplicate]

If universe is expanding like a balloon from point zero to current space time. what is there in between the point of origin and current universe. Is there still hot energy in between the current ...
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0answers
61 views

What does it look when we travel at the speed of light? [closed]

Suppose we're in a spaceship or in a car which runs at the speed of light. We are watching the light which is coming towards eyes at the speed of the light. What would it look like when the driver ...
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0answers
99 views

Calculating energy density in the early Universe

I've been told to calculate the energy density in the early Universe. It states that it is completely dominated by neutrinos (3 species), photons, electrons, and positrons. Now, I've found an ...
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0answers
26 views

How is expansion of the Universe consistent with the speed of light? [duplicate]

I have a question that I believe is related to @PetTaxi's question here: How far has a 13.7 billion year old photon travelled, but I didn't want to hi-jack it. My issue is this. I'm assuming the ...
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3answers
99 views

Is the world we are living in discretized? [duplicate]

I do not know how to use professional words to ask my question, so I will try to use a layman language. Please bear with me for a moment. A ROUGH GUESS The world our eyes are seeing every moment is ...
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1answer
99 views

Scalable tool (engine) for simulating the universe

Does there exist a large scale scalable tool (engine) for simulating the universe that incorporates both quantum mechanics and cosmology, i.e. micro & macro scales? (It would be best if this tool ...
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1answer
295 views

What caused the expansion of the universe to slow down after the inflationary epoch?

As everyone knows, when the big bang happened, the universe expanded at an unbelievable rate and this was called the inflationary epoch (or more popularly cosmological inflation) which lasted for ...
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28 views

Converting between cosmological times

David Hogg's 'Distance Measures in Cosmology' is my go-to reference for all things cosmological. It's missing a discussion of time measurements however. How does one convert between different ...
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1answer
119 views

Does dark matter in the universe acts as a pulling force or a pushing force?

Scientists have claimed that in this world there are two kinds of forces which help in keeping everything in its place called dark matter and dark energy. But are these two forces act as a pulling ...
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0answers
21 views

Is it possible for random quantum fluctiations in the Universe to cause a new Big Bang before the death of the Universe? [duplicate]

I have read in some distant future predictions that after some years(numbers like 101500 years) random quantum fluctuations could produce a new Big Bang. Is that possible, and is it possible now, or ...
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0answers
59 views

If the Universe reaches the state of heat death scenario, could it produce a new Big Bang? [duplicate]

So in heat death of the Universe time stops, matter is degraded, only quantum vacuum remains and the universe no longer expands? Aren't those conditions similar to what physicists say about the ...
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3answers
2k views

How many more galaxies are out there in the Universe (beyond the observable radius)?

Let's say that the number of large galaxies in the observable universe is $n$ (approximated to 350 billion). If the universe is homogenous and isotropic, what are the estimations for the total number ...
3
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2answers
200 views

Can hyperbolic space be bounded?

There are many visualisations of hyperbolic geometry using Poincaré disks. What are their purpose? Can hyperbolic space be bounded? Can we endow the disk with the structure described by the FLRW ...
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2answers
274 views

Does “Infinite Universe” Imply Infinite Mass?

In accordance with the FLRW Metric with a curverature of $k=0$ (as observationally supported by several of NASA's experiments including WMAP, Planck satellite, DASI, etc.) the universe is spatially ...
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2answers
165 views

A universe of a finite but increasing number of states of motion?

A limitation of the geometric models of universe is that space locally is considered as a volume, whilst volume is a part of a selected system of inertia. Wouldn't it be more adequate to consider (the ...
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0answers
30 views

Where did the energy of the universe come from? [duplicate]

Last week my Physics teacher asked the class this question: If the internal energy of the universe is constant, then where did all the energy come from originally?
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2answers
123 views

Could these hypothetical very long distance properties of light offer alternatives to an expanding universe or a finite number of galaxies?

Assume that there could be a property of light that it gets very gradually steadily red-shifted by traveling large astronomical distances, in exactly the same way that Doppler shift from receding ...
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37 views

Is There A 'Leading Edge' to the Universe? [duplicate]

Is there a center to the universe? Did the Big Bang happen at a single location, spreading outwards? Or, was the Big Bang more of a state-change, in which the universe went from super-dense and ...