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 ...

learn more… | top users | synonyms

1
vote
1answer
321 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
103 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 ...
1
vote
1answer
94 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
votes
1answer
28 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
vote
1answer
82 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
59 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
392 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
57 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
649 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
99 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
votes
0answers
21 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
211 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
votes
1answer
48 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
62 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
votes
0answers
26 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
54 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
53 views

Does the universe emit Hawking radiation?

Would there be any experimental validation from cosmological observation?
72
votes
10answers
12k 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
34 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 ...
1
vote
1answer
63 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
63 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
84 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
67 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
72 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
112 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 ...
0
votes
3answers
107 views

Why is the universe expanding while its components actually attract each other?

First of all, what's the difference between gravity & gravitation? Anyway that's not the actual question. If every matter attracts each other toward itself, then wasn't the universe supposed to be ...
-4
votes
0answers
96 views

Is Salah A. Mabkhout's hyperbolic universe theory convincing? [closed]

Did Salah A. Mabkhout develop a formula accounting for the flat rotation curve without a need for dark matter? Is his theory of the hyperbolic universe paradigm convenient? Did his theory connect both ...
0
votes
3answers
171 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 ...
1
vote
0answers
63 views

Is there a model of the universe with the transfinite (space)time?

In mathematics there is a concept of ordinal numbers where one can count to infinity and beyond. For example the least number that is greater than all the finite numbers is denoted by $\omega$. Such ...
2
votes
2answers
322 views

How accurately could we theoretically see into far space?

Travels to different galaxies are strongly limited by the speed of light. Unless we find a way to travel through space with some wormholes, we will never reach planets in another galaxy. But what ...
0
votes
0answers
41 views

Is a terminal gravitational center to the universe possible?

The current consensus is that there is no evidence of, or no way to tell whether or not there is a center to the universe. Considering our observable universe is only a small portion of what we know ...
16
votes
6answers
2k views

How many times has the “stuff” in our solar system been recycled from previous stars?

Is there a cosmologist in the house? I've got a basic understanding (with some degree of error) of some simple facts: The Universe is a little over 13 billion years old. Our galaxy is almost that ...
2
votes
0answers
253 views

What would happen if all dark matter disappeared?

This is related to this question which provided evidence about dark matter, and this question which asked what would happen if dark energy started disappearing. This question assumes that dark matter ...
0
votes
0answers
54 views

Outer Space & Universe Expansion: [duplicate]

Experts agree that the stuff within the universe is moving farther apart from all the other stuff in the universe--much like the dots marked on the outside of a balloon that is being inflated. We ...
3
votes
3answers
356 views

Is there an exact formal definition of the Universe?

I've read several articles about Observable universe, Universe and Hubble volume, including Wikipedia articles and other references. After this I wondered: Is there a formal, rigorous definition in ...
0
votes
1answer
66 views

Do sound waves travel before Big Bang?

So I was reading a Scientific American article about how the universe is spreading apart and how it is getting faster. But in the article there was something that baffled be and it was this "Sound ...
-1
votes
1answer
60 views

Why is the expansion of universe continuously increasing? [closed]

If our universe is expanding and the concept of the multiverse is true, then why is the rate of the expansion of the universe increasing? Surely it must decrease?
0
votes
2answers
2k views

Atoms pop out of nothing/vacuum/pre-big-bang?

I saw a great documentary last night about 'nothing'. It's about vacuums, and how if you have a total vacuum atoms will pop out of nowhere! Pretty crazy stuff. Atoms literally coming out of ...
1
vote
3answers
105 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 ...
6
votes
3answers
786 views

If the universe were a fractal

Inflation seems to solve many of the problems of cosmology like horizon problem, flatness problem etc. Now suppose, I am a devil's advocate and tries to find holes in this beautiful theory. I argue ...
0
votes
2answers
88 views

If the Universe is going to last infinitely long, what is the type of this infinity?

Let's say we've built a machine, that prints a sequence of all natural numbers from 0 to $\infty$. We "could" do this in a Universe with an infinite amount time (if we also make many other assumptions ...
0
votes
1answer
53 views

How can a finite amount of matter be uniformly distributed in a flat, infinite space?

There are some properties of the Universe I find in the (mostly popular) literature which are often described as "the most probable in case of our Universe". I can't put them together in a way that ...
-1
votes
2answers
91 views

How many dimensions our universe consists of?

Omnibus science convinces us in that we live within three-dimensional space. The coordinate measuring units XYZ. Quite controversial, but there are some legitimate theories clarifying why we live in ...
0
votes
1answer
85 views

Could this be a valid reason for why the universe could be infinite?

So, special relativity says that every frame is as good as any other frame, and there is no absolute frame of reference. All good. Suppose there is a finite universe (let's just assume the universe ...
1
vote
0answers
92 views

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

A physics professor talked in the YouTube video Cosmological Constant & The End of the Universe - Sixty Symbols about a paper he and his colleagues published. The paper presents a model that ties ...
2
votes
1answer
296 views

Since the universe is expanding, does anything ever occupy the same point in space?

Let's say we can observe expansion in a supercluster. We define origin of our frame of reference at the center of the supercluster. We observe an object/atom at point A at time T. The object is ...
2
votes
2answers
129 views

How fast does space/time travel?

It is said that before the big bang there was no before, as space/time was created in the big bang. The big bang creates a rapid expansion of space/time... so how fast is rapid?