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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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
38 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
46 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
90 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
62 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
51 views

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

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
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1answer
234 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
86 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
20 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
30 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
196 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
49 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
62 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
385 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
50 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
242 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
76 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?
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1answer
128 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 ...
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4answers
491 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
76 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
90 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
92 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
46 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 ...
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2answers
102 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
37 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
490 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 ...
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0answers
48 views

Confusion on entropy in the universe [closed]

I was researching about the heat-death of the universe, and I was wondering if my understanding of it so far is factual to the theory? However, the 3rd Law of Thermodynamics prevents the universe’s ...
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1answer
57 views

How has the age of the Universe been derived from the observations made by the Planck mission?

The parameters of $\rm\Lambda CDM$ model have been determined to an amazing high precision from the measurements made by the Planck mission. In particular, the Hubble "constant" (the value of Hubble ...
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1answer
88 views

Why is an electric and magnetic field present in all universe?

the Earth has its fields due to the motion of molten metals in the core but how does this whole universe has its fields without any discontinuity? And we can say for sure that fields are present in ...
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1answer
80 views

Is the universe infinite? [duplicate]

Is the universe infinite? Or is it finite? If it is infinite,it's very difficult to imagine an endless space(though not impossible). But if it's finite, the idea that we can't go beyond a certain ...
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2answers
64 views

How fast to travel to end up where i started from?

I've heard that if one travels far enough in one direction through the universe, one ends up at the starting point, due to the "geometry" of the universe. What rate is space expanding at? Is it in ...
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2answers
111 views

When was the cosmic background radiation in the visible spectrum?

From what I understand about the Cosmic Microwave Background Radiation is that it was from the big bang, and since space has streched and become bigger since then the wavelength of the CMBR has ...
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1answer
78 views

Estimating age of the universe by Hubble's law?

Hubble's law states that $v=Hx$ Age of the universe is calculated by $T= \frac{x}{v} = \frac{1}{H}$ but the velocity is not constant; it changes with distance, so I think that this equation cannot ...
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1answer
176 views

Does everything orbit around some universal “center of mass”?

I have read many questions about the center of the Universe. I even have some favorite ones. I understand the fact that every point in the universe experiences inflation the same way. Also that it ...
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4answers
3k views

Why does a flat universe imply an infinite universe?

This article claims that because the universe appears to be flat, it must be infinite. I've heard this idea mentioned in a few other places, but they never explain the reasoning at all.
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3answers
86 views

Did “big bang” radiate light?

According to present day physics nothing existed before the "big bang", even space and time. But often in documentaries, the "big bang" is shown as a ball of light that exploded at some point. If this ...
3
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4answers
108 views

Accelerating expansion of the universe: so?

Please help me out, I’m missing something. We know that, right now, space is expanding at roughly 73km/s/Mpc. This means: two points in space 1Mpc away from each other “move” 73 km farther away ...
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1answer
28 views

What is the current rate of change of the volume of the Universe?

Is it possible to know the current rate of change of the volume of the Universe? If we can't see past the cosmic horizon, can we still get a value for this rate of change, and if so, how would it be ...
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1answer
84 views

Why and how the Universe has (at least) 3 spatial dimensions [closed]

We are conscious to live in a 3 dimension universe. Maybe it has more than 3 spatial dimensions (like the 10 mentioned in the string/M-theory) but that is not my concern here. My question is the ...
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2answers
197 views

What is space made of?

General Relativity posits that matter curves spacetime, such that geodesics point towards the object in question, hence, gravity. Now, how does matter do this? What is spacetime "made of", anyway, ...
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7answers
1k views

Mathematically possible vs physically probable outcomes

A good buddy of mine and I have had a friendly debate about the origins of the current state of our universe (namely; Earth and life on Earth) and have fundamentally disagreed in our stances with ...
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1answer
86 views

Reconciling “The Big Crunch” with the 2nd Law of Thermodynamics

Assume "The Big Crunch" scenario (the universe will collapse to a singularity). In this case, I think of the entire universe as an isolated system; in the "Big Crunch" scenario, it seems to me gravity ...
3
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3answers
112 views

If we say the universe is expanding, shouldn't it be expanding relative to something?

I don't understand, if everything in this world is relative to something else, then cannot we essentially say that nothing exists independently? We say that the universe is considered to be the ...
0
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1answer
95 views

Aside from Noether's theorem, what other concepts would explain energy conservation?

Energy is defined more in the mathematical sense, and tends to show true with observations in the physical world. But why is energy conserved aside from "Noether's theorem"? In a closed system that ...
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5answers
194 views

Is the universe expanding at a speed of almost $2c$?

I've been told nothing can travel faster than the speed of light. Therefore, from my vantage point the diameter of the universe is increasing at a rate of $2c$. Are there any flaws in my thinking?
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1answer
103 views

Is this how a Universe could be created from nothing? [closed]

So this is a rather simplistic understanding but I want to know if it's fundamentally correct: We have nothing which we'll represent as $0$. Then we need a Universe which we can represent as any ...
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3answers
604 views

Dark Energy / Accelerating universe: naive question

Folks, I have a naive question regarding the subject of dark energy and an accelerating universe: From what I understand/read, it seems that the further we look out into deep space, the faster the ...
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2answers
137 views

Does gravity actually contract space-time?

In the Big Crunch Theory it says that gravity (curvature in space-time) will stop the universe's expansion and gravity will cause the universe to contract on itself. My question is if gravity is a ...