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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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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2answers
84 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
66 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 ...
2
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1answer
58 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
44 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
76 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
42 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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0answers
59 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
73 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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29 views

Could we predict everything in the universe from the beginning to the end of it, if we could measure every factor of the “big bang”? [duplicate]

Like throwing dice, if we know every factor we can predict the final numbers everytime because we know the laws of physics. Does this mean we could predict everything in the universe from the ...
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3answers
61 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 ...
2
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1answer
63 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
937 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
301 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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1answer
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 ...
2
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1answer
60 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
98 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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1answer
57 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 ...
2
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2answers
243 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
70 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
93 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 ...
2
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1answer
56 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 ...
1
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1answer
39 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 ...
2
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1answer
49 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
52 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
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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
104 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
64 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
77 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
12
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1answer
250 views

As the universe expands, the wavelengths of photons are stretched, and energy is lost. What about electrons?

Will electrons, and other particles, also loose energy as they travel through the cosmos? They have wavelengths. Do they get "stretched"? My guess is that the EM force, somehow, counteracts this ...
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2answers
107 views

Are the implications of an infinite universe necessarily so unsettling

I have often heard it said (by professional cosmologists) that if the universe is infinite, then there necessarily exist infinitely many copies of me repeated throughout. The reasoning seems to be ...
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0answers
25 views

How did the gravity of the particles/objects behave at the edge of the expanding universe moments after big bang?

During a very short time after the big bang, the universe must have had an edge of space-time which is very close to all the matter in the universe. The particles which are close to or on the edge ...
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0answers
39 views

Does the zero energy universe hold true on some mathematical grounds besides observations?

I was reading Stephen Hawking's 'The theory of everything' when I came across a very interesting type of universe, the 'zero energy universe' since then, I've read some websites but all they used to ...
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2answers
227 views

Lattice QCD and attempt to prove that the universe is a simulation [closed]

Assume that we have access to a computer with unlimited computing power. As with the Lattice QCD can try to prove that we live in a simulated universe? Apparently, one may use the issue of cosmic ...
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1answer
58 views

Is there an absolute center of mass exist in the universe? [duplicate]

By the "absolute center of mass" I mean the center of all the matter that exists in a given moment. My friend asserted that today and it intrigued us very much but since we only have a CS degree and ...
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2answers
65 views

What is entropy of the universe? [duplicate]

What is entropy of the universe? What is the change in entropy of our universe? Is this change increases or decreases? If the entropy of universe keeps on increasing then what are the consequences? Is ...
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2answers
394 views

Wouldn't the presence of dark matter slow the expansion of the universe?

If there is a huge element of dark matter in the universe, wouldn't this extra gravity prevent the accelerated expansion of the universe?
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2answers
59 views

Will the Universe eventually stop expanding

Sorry if this is a naive question, not being even a part qualified physicist in any way shape or form. I've read that the universe is expanding and the rate of expansion is increasing. The assumption ...
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4answers
254 views

Is our universe an emulation?

I was watching one of Neil Degrasse Tyson talks and there was a scientist (can't recall his name sorry) who was talking about a recent discovery: "Doubly-even self-dual linear binary ...
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1answer
83 views

The universe appears to have a lower bound in the time dimension, why not an upper bound?

The Big Bang looks like a lower bound to the "size" of the universe in the time dimension. Could it also have an upper bound, some furthest point in time from the Big Bang?
3
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1answer
142 views

How far can something travel in a straight line?

Suppose you have an object some distance from you and moving at a velocity different to the Hubble velocity you'd expect at that point. How does the motion of this object change with time? Does it ...
6
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4answers
515 views

Expansion of the Universe, will light from some galaxies never reach us?

Is it true that the light from some galaxies will never reach us? The explanation for that is that the Universe expanding faster than the speed of light. But, if the speed of light is constant in ...
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1answer
82 views

Leonard Susskind said that the small value of the cosmological constant could mean that the universe is much bigger than we thought. Why?

He said that near the beginning of this Youtube video that it could mean that the universe is much bigger than he had thought that it was, and that the cosmological constant wasn't even a constant. I ...
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1answer
96 views

How did the universe get so big so fast? [duplicate]

The universe started at the big bang around 15 billion years ago. The universe is now at least 92 billion light-years in diameter. Together, don't these mean that the universe, at some time in the ...
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2answers
95 views

Does expanding space cost energy?

Does the cosmic inflation reduce the energy density (inversely) proportional to the volume, or does the inflation "cost" energy? Is space itself "something" created at the expense of energy?
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1answer
49 views

Number of Stars vs Value of Omega (Crtitical Density of the Universe)

I may be badly mixing things up here. If I am, please kindly correct me. As I understand it, if the universe was too dense at the start of the big bang, it would have collapsed back in on itself. Too ...
0
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2answers
241 views

Does the universe have an edge/boundary/barrier? If yes, what is at the edge? [duplicate]

My question related kind of to asking what the shape of the universe is. Say a hypothetical alien civilization built an faster-than-light spaceship. If they keep flying would they end up where they ...
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0answers
38 views

Cosmic Expansion - Why aren't we ripped off yet? [duplicate]

According to Hubble's law, the universe expands exponentially ever since the big bang. If the space-time expands, what effects does it have upon us, (1.Earth, 2.solar system and 3. Milky Way). ...
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2answers
499 views

What is “Energy” of a vacuum in the context of quantum theory?

I'm not a physicist or cosmologist, so I hope I am asking the right question with the right words here. My question regards the word "energy" as it pertains to quantum vacuum states, and to concepts ...