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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0answers
29 views

Looping fractal paradox

Is it popular belief in the scientific community that all matter is infinitely fractal in a looping manner, if so where does this loop wrap? Particle equals universe? Would all particles contain a ...
2
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1answer
330 views

Is the Universe Past-Eternal?

Does the Borde-Guth-Vilenkin theorem definitively demonstrate that the Universe cannot be past-eternal, whatsoever? Does it not assume a classical space-time while the real world requires Quantum ...
10
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7answers
5k views

Does anything exist in the intergalactic space?

I am a part time physics enthusiast and I seldom wonder about the intergalactic space. First, it is my perception that all(almost all) the objects in the universe are organized in the forms of ...
3
votes
1answer
1k views

Obtaining a copy of Hawking's Ph.D thesis - Properties of Expanding Universes

Due to its popularity, I am interested to know the 4 chapter titles and topics covered in S.W. Hawking Ph.D, Properties of Expanding Universes. I also ask this because that thesis is hardly available. ...
13
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5answers
7k views

Is the total energy of the universe constant?

If total energy is conserved just transformed and never newly created, is there a sum of all energies that is constant? Why is it probably not that easy?
3
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1answer
59 views

Universe vs Multiverse. Time and Space

Wikipedia defines a multiverse as a hypothetical set of finite and infinite possible universes. Similarly, it defines the Universe is as "all of time and space and its contents". On the surface, ...
2
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2answers
323 views

How can the Schwarzschild radius of the universe be 13.7 billion light years?

So i was reading about Schwarzschild radius on Wiki and I found a interesting thing written there link. It says that the S. radius of the universe is as big as the size of the universe? How is ...
4
votes
3answers
953 views

What is meant by positive and negative gravity/energy/spacetime-curvature?

I have recently come across some cosmological assertions (based on empirical data) about the universe being self contained in the sense that it is entirely capable of coming into existence from a ...
2
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0answers
53 views

Where does all the energy in the universe come from? [duplicate]

The principle of conservation of energy says that all energy in a system will remain the same. It can just be transformed. The universe contains a huge amount of energy, but where did it come from? ...
3
votes
2answers
113 views

Gravitational waves, tides and the end of universe

Is tides proof of gravitational waves with low frequency? According to Wikipedia, In physics, gravitational waves are ripples in the curvature of space-time which propagate as waves, travelling ...
20
votes
8answers
4k views

Entropy is…disorder?

As I read somewhere, it said that the universe is heading toward disorder a.k.a entropy increasing. Now as far as I know from the second law of thermodynamics it states that entropy is indeed ...
1
vote
0answers
61 views

Intuitions for the simplest model in which the evolution of the laws of nature arises from the natural selection of structures [closed]

The problem I’m trying to solve can be described as To create the simplest model possible in which the evolution of the laws of nature arises from the natural selection of structures. This approach ...
0
votes
3answers
218 views

Why is universe expanding?

Okay, this question may sound silly: base on the observation Besides an expanding universe, would there be other possibilities? Would it be possible, say, there exists a fundamental repelling ...
0
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2answers
80 views

Expansion of the Universe [duplicate]

At what speed is our solar system expanding, and if it is, why don't the positions of the sun and planets change, or grow farther apart? Why is the Big Dipper still where it is?
0
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0answers
25 views

Chaotic inflationary model - bubble inside bubble

I was reading a bit about Prof. Linde's chaotic inflationary model of expansion of universe. He has mentioned about 'bubbles' of space time expansion. But no one has spoke about bubbles inside ...
3
votes
6answers
248 views

Could the universe be accurately simulated with an infinitely powerful computer? [duplicate]

This would mean that every event happens because of what has hapened before it and there is no randomness factor. At a microscopic level, the motion of atoms is a result of the motion of other atoms ...
1
vote
0answers
44 views

What would be the implications of a Penrose Universe?

A Penrose tiling of a plane (note this not the same as a Penrose diagram) is a tiling that is "non-periodic", without "translational symmetry", meaning that you can't simply slide the pattern one ...
0
votes
1answer
187 views

How fast are we moving when standing still? [duplicate]

The Earth rotates around itself and revolves around the Sun. Our solar system revolves around the center of our galaxy and our galaxy is moving in some way throughout the universe. If you took into ...
0
votes
1answer
108 views

Is it impossible to practically predict the future?

For the sake of curiosity, let us postulate a universe that can be completely described by mathematics. Let us further postulate, that humankind has fully discovered all the fundamental laws of ...
2
votes
0answers
21 views

is the expansion of the universe observable at a smaller scale? [duplicate]

I have searched the network for a possible duplicate to this question but I have not found one particulary answering my question so recommendations are welcome. I understand that distances of ...
1
vote
0answers
17 views

Dust mass-loss rate from a massive star given a set of parameters?

I've been looking for examples at how mass-loss rates are determined. I'm studying a circumstellar dust shell ejected from a Wolf-Rayet star. I have some parameters like, expansion velocity of the ...
1
vote
1answer
309 views

Does matter shrink uniformly without restriction in freefall to central region of black hole?

It is often stated that a distant observer will observe a freefalling object as experiencing an infinite journey to the event horizon, but that a traveler in the local frame will experience a ...
3
votes
1answer
90 views

Hawking in A Brief History of Time: No beginning or end of the Universe

I am reading Stephen Hawking's book - A Brief History of Time. I haven't studied cosmology and the related sciences. Nevertheless, I am interested to know few things regarding the extract taken from ...
3
votes
1answer
338 views

Can universal continuity be experimentally falsified?

It is an unresolved question whether the universe is discrete or continuous in its intricate quantum level structure. See for example: Is the universe finite and discrete? How could spacetime become ...
1
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1answer
84 views

Will physics ever be able to answer the question: “What caused the universe to come into existance”? [closed]

Or is this just the flip side of a metaphysical question "why does the universe not exist", if the opposite was the case and nothing existed i.e. a universe devoid of all energy, matter forces, ...
0
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1answer
25 views

Is there any possible evidence that can give us insight into what happened exactly at the Big Bang/why it happened?

It's mostly well accepted today that the Big Bang was the reason for today's universe, mostly due to the expansion, the cosmic microwave background etc. and mathematically the FLRW metric supports it. ...
19
votes
5answers
5k views

Does red shift evidence necessarily imply that the universe started from a singularity?

We are taught that the universe began as a singularity - an infinitely small and infinitely dense point. At the beginning of time there was a 'Big Bang' or, more accurately, 'Inflation'. The main ...
1
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1answer
67 views

Could our universe be destroyed within seconds? [closed]

I'm not that deep in physics. But some days ago I read, there could be different coexisting universes, which could even share "space" (or what ever it is) where each of them could have absolutely ...
1
vote
1answer
57 views

​Universe as a projection of something

Who has proposed this and is there an experimental proof? Where can I start to learn about this?
3
votes
4answers
321 views

Is simulating the entire universe possible?

Is it physically possible 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 ...
0
votes
0answers
28 views

Is there any reason (other than convenience) to assume the universe is paracompact?

In this discussion on MathOverflow, it is mentioned that the universe, being a Riemannian manifold, must be paracompact. But is there any reason to assume the universe is globally 'small enough'? In ...
0
votes
2answers
49 views

Double the mass in the universe, double the inertia

If I double (halve) the mass in the visible universe, will my inertia double (halve)? I think it should, at least as soon ''I have received the news of this doubling''. But what does the General ...
7
votes
2answers
635 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 ...
5
votes
1answer
81 views

Why quantum fluctuation existed before big bang?

I read somewhere that quantum fluctuation can give rise to a big bang and thus the creation of a universe which we know today, where do these quantum fluctuations come from if space is only created ...
0
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0answers
20 views

Possible fate of our universe? A point in the future where the expansion remains a constant and the universe is just energy dominated.

What if The universe is ever expanding, but slows down at a continuous exponential rate, let's say (e), but continues as an asymptote. Is that liable? Would you say that, when it reached to an ...
0
votes
2answers
185 views

Many-world interpretation: simple physics explanation? [closed]

We went a little off topic in physics class today and my teacher was explaining how quantum physics explains the idea of parallel universes. She believes in a idea called many world interpretation ...
0
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1answer
34 views

Is it possible for the universe to be already developed when the dark energy appeared and expansion started?

The main piece of evidence that supports Big Bang Theory is basically evidence that the expansion of the universe started long time ago (not necessarily from the begining of the universe). Is it ...
0
votes
0answers
49 views

Size of the universe from CMB?

The CMB is almost 13.8 billion light years away in every direction so the diameter of the visible universe as we actually observe it is 27.6 billion light years, twice the distance light traveled over ...
0
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0answers
23 views

Curved light cones converge at big bang

Space has expanded manyfold since the big bang, presumably even 1090x since the CMB. Thus our light cones which start out straight must curve inward to theoretically meet at the single point of the ...
-2
votes
1answer
51 views

If there were infinite many stars [duplicate]

If there were infinite many stars, is the sky then always full of light so is there than even night?
2
votes
1answer
52 views

Does the universe emit Hawking radiation?

Would there be any experimental validation from cosmological observation?
70
votes
10answers
11k views

Is time continuous or discrete?

While working on physical system simulation software, I noticed that I had implemented discrete time, which means that there was an update mechanism advancing the simulation for a fixed amount of time ...
0
votes
0answers
33 views

“How” infinite is the Universe? [duplicate]

They say the Universe may be infinite. Is it about matter (energy) or space? If it's about space, then would the "spatial infinity" likely imply that the amount of energy is also infinite? If ...
0
votes
0answers
32 views

Charged Universe and charge-dependent inertia/anti-inertia

I posted this same question as a follow up for the main question here. I expected to get a quick answer but since none have come up I raise it as a topic in its own right. So the question is: Suppose ...
0
votes
1answer
50 views

What's the bubble's wall made up of in false vacuum decay? [closed]

It is well known that for some kind of double well potentials, there are two minima with one is unstable called the false vacuum while the other stable one called the true vacuum. The tunneling is ...
4
votes
0answers
50 views

How to understand particle decoupling in the early universe?

We often say that when the rate of some interactions, say the beta decay and electron capture, are slower that the rate of universe's expansion, then the corresponding particles, say neutrinos, ...
0
votes
0answers
65 views

Matter and dark energy

So dark energy is the biggest thing in the universe, it keeps accelerating the expansion. But it's a constant so at some point there was a matter - dark energy equivalence. My question is how can you ...
0
votes
1answer
39 views

How long was the universe radiation dominated?

Using the Friedmann metric I've been trying to calculate how long the universe was radiation energy dominated. I've reduced the metric to: $c.dt$ = $a(t).dr$ where a is the scale factor. I can work ...
1
vote
0answers
67 views

Experiments to resolve dillema between continuity and discrete

Which experiments/experimental methods are suggested to resolve an alternative about the structure of our universe space and time - is it continuous or is it discrete in a very small scale, especially ...
1
vote
1answer
86 views

Why did the big bang happen when it did?

Was there time before the big bang? I assume there wasn't, so is it even logical to ask if there was anything before the big bang? If there was time before the beginning of the universe, what happened ...