Tagged Questions

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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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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18 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
60 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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57 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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95 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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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
34 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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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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55 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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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 ...
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146 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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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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155 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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29 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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50 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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33 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 ...
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2answers
77 views

If the universe is spatially infinite, and if something (A) is possible, does that mean the thing (A) happens?

Assuming that the universe is spatially infinite, extending outwards in all directions without end, and is consistent with what we have thus far observed, and predict to find (and predict to be out ...
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45 views

My idea on parallel universes [closed]

I have a question I've long wanted to ask somebody and I see no place better than here to do it! I am not a physicist in any way, Im just a big fan :) So, I have an idea of parallel universes in my ...
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115 views

Is the Universe still believed to be flat?

I have read a handful of old articles from mid 2013 expressing that the Universe may, in fact, be curved. http://www.nature.com/news/universe-may-be-curved-not-flat-1.13776 ...
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2answers
96 views

Where's all the light going in the universe?

According to my knowledge, matter can not go faster than light, and light is emitted constantly in the universe from many types of reactions. If this is so, then isn't light constantly getting past ...
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3answers
639 views

Failure of the Steady State Theory

I was reading a journal of astronomy and came to the most famous opponent of Big Bang theory: The Steady State Theory: The 20th - century theory was proposed by Hoyle,Gold and Bondie. The ...
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1answer
101 views

Infinite space, nothingness, and the concept of infinity [closed]

These two questions are a follow-up to my previous Phys.SE question on finite space. The first question challenges the concept of infinite space. Space is something: it is ruled by laws, and ...
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1answer
75 views

Infinite space or finite space?

I have been reading about the nature of space (Brian Greene's and Max Tegmark's recent books) and have a question on the size of space. Both references acknowledge that general relativity equations ...
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1answer
69 views

What does the “size of the universe” mean if the Universe is infinite?

There are questions that may seem to be similar to this one, but I've yet to find an answer. I have come to understand that a flat universe, that is to say a curverature of $k=0$ which means that ...
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1answer
50 views

Determining zero energy from $k=0$?

I'm curious as to the equations necessary for finding a total energy of 0 (or, I suppose, the energy density of empty space due to quantum fluctuations) in a flat Friedmann universe such as ours. The ...
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1answer
102 views

The 3rd derivative of the size of the universe?

We know the size of observable universe, that it is expanding, that expansion is accelerating. Does sufficiently precise data exist to determine at least the SIGN of the next (the 3rd) derivative? ...
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1answer
43 views

Size of the Hubble volume in 4 billion years

What will the size of the observable universe be in 4 billion years? At present day, light would only reach us if it came from a galaxy within 13.5 billion1 light years, with anything outside that ...
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69 views

Center of mass & Big Bang Theory

I have read in my text books about the Big Bang theory and quote "the entire matter in the universe was once concentrated in a single very dense and hot fire ball; it exploded some 20 billion years ...
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1answer
91 views

If the universe is infinite, should there be a duplicate of me with probability 1? [duplicate]

I was just wondering: if the universe is really infinite, and there is a certain probability to find a life form just like me on another planet (for example $1.0 \cdot 10^{-150}$), is it therefore ...
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3answers
64 views

source of energy for expansion of the universe

I know in order for something to expand or grow it has to be fueled by something? So, if the universe is expanding their must be something that's keeping the universe at a temperature high enough for ...
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1answer
67 views

Is there, and if there is, what is the name of the concept that matter is made out of void/space?

I can't recall where I heard about this, but it was rather intriguing. I recall the notion that matter is compressed void/space, where I remember an example of a bedsheet representing space, and the ...
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1answer
972 views

What happens when a photon reaches the “edge” of the universe? [duplicate]

As I understand it, there are several models for what the universe could look like from the “outside”. I don’t know if any of these are outdated, so if they are please tell me if they are. Expanding ...
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3answers
305 views

Will an un-scattered photon go to the edge of the universe? [duplicate]

Will an unhindered (un-scattered) photon go to the edge of the universe?
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51 views

TEO: raise of a System [closed]

I think this question is settled somewhere betweeen physics and philosophy and we surely can not find a answer that fits 100%, but lets talk about it. While thinking about how the universe and its ...
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1answer
82 views

How can the Big Bang singularity exist in spacetime if it has zero volume? [closed]

How can the Big Bang singularity exist if it has zero volume? I tried googling to find the answer - no help. Can someone give a general idea how can the big bang singularity exist even if it has zero ...
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1answer
108 views

Existence of a physics-god [closed]

In your opinion, what is the most cosmological or physics argument that may favor the existence of something like a god to produce a universe like ours and what is the most counter argument for that. ...
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2answers
111 views

How do we estimate $10^{23}$ stars in the observable universe?

Now, I read somewhere, that there are $10^{23}$ stars in the observable universe. How did scientists estimate this?
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72 views

A model that predicts the universe is finite in space and time

A physics professor talked in a YouTube video about a paper he and his colleagues published. The paper presents a model that ties the mass of particles to the size of the universe. He summarizes their ...
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2answers
255 views

How do we know that space expanded with speed faster that a speed of light during big-bang inflation?

How do we know that space expanded faster than a speed of light in inflation? I have read this Phys.SE question, and it says that limit for faster than a speed of light is for matter and waves only. I ...
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1answer
75 views

A universe from nothing [duplicate]

The more time you spending in measuring your experiment (thus standard deviation will become smaller) the more precisely you will measure energy of this system.... energy time uncertainly principle ...
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3answers
120 views

Has the universe we live in started as a black hole that is imploding?

As discussed in this question, as far back as the 1960s it was suggested that the Schwarzschild metric can be smoothly joined to a de Sitter metric. For example the idea has been used by Lee Smolin in ...
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1answer
64 views

Can a lone black hole in a closed Universe evaporate?

If there is a closed Universe which only has a black hole in it, can that black hole evaporate? As the black hole evaporates, it gives off energy, which will eventually come back and be re-absorbed ...
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1answer
43 views

Is the universe expanding on a preferred axis, or asymmetrically?

I remember back in 2011 i found this paper on the research a team of Chinese physicist completed about the universe may having a prefered axis when expanding. On ARXIV I haven't seen any other ...
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1answer
55 views

Could false vacuums potentially describe, in part, the Big Bang?

I've just read about something I had never of before, false vacuums. After reading a couple descriptions of what a drop (or rather, a vacuum metastability event) would imply, I thought of the Big ...
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1answer
61 views

Expanding universe space through matter or matter through space? [duplicate]

So the universe is expanding, rather space is expanding. By expanding we mean space is coming into existence at all points.  Is that an equal rate of expansion everywhere? Now the expansion does not ...
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5answers
1k views

If everything is relative to each other in this universe, why do we keep the Sun to be the reference point?

and study the solar system and universe relative to it and why not relative to the Earth?
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3answers
4k views

How can interstellar space have a temperature of 2-3K?

Several different sources online state that the average temperature of interstellar space (or the universe in general) is around 2-3K. I learned that temperature is basically the wiggling of matter, ...
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3answers
109 views

The Universe as a four-dimensional sphere?

I was chatting with my 12yo cousin yesterday and we got to the Universe, its size and stuff like that. Then he came up with the idea (I'll rephrase it), that the Universe could basically be a 4d ...
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2answers
66 views

How do we observe the expansion of the universe?

This is my first question. So I was reading about expansion of the universe and from what I've seen, the only way that we know that universe is expanding is by measuring redshift. Also, here it says ...
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2answers
87 views

Why did the big bang need to produce equal amounts of matter and antimatter? [duplicate]

I've tried to find an answer for this but couldn't find one. Whats the problem with matter being created with little or no antimatter