Questions tagged [universe]
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 the universe
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Could the Universe be Toroidal with a Black Hole at the Centre?
Thought experiment that occurred to me. Rather than a Big Bang, the Universe Cycles through a black hole at the centre. It looks like a big bang upon exit when it goes through an expansion phase, ...
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Can increase in entropy increases the probability of finding something specific [closed]
See if we take a bookshelf with 10 books in it and drop all of them in a room and repeat this process infinite times. So we can say that entropy of room increases and now we have to find a specific ...
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What if everything doubled linearly? [duplicate]
There is a question that goes:
Suppose you are told that the linear size of everything in the universe has been doubled overnight. Can you test it by using the fact that the speed of light is a ...
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If we copy-paste the universe, would it follow the same trajectory? [closed]
If we would copy-paste the universe in a single instant, would they follow the same trajectory? If yes. would this mean that the trajectory of our universe (and our self) is set in stone? If no. What ...
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Why is Big Bang so misunderstood?
I was reading this answer where it's explained that the Big Bang is not a theory but a model and that it doesn't say anything about the origins of the Universe.
I was taught in school instead that ...
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What if the universe was not uniform...?
In this popular science article, they say that if our universe resulted to be non-uniform (that is highly anisotropic and inhomogeneous) then the fundamental laws of physics could change from place to ...
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What is meant by: "each particle in the observable universe contains 1.509 bits?"
What do physicists generally mean by particles "storing" bits and the idea that information is neither created nor destroyed?
Example:
"We determined that each particle in the ...
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Is there anything truly "stationary" in the universe? [closed]
Ok, so I read this question and it got me thinking about something. Is there anything genuinely stationary in our universe? What does it mean to be stationary or devoid of any motion? If there isn't ...
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Is there a natural coordinate system in general relativity?
After reviewing some different coordinates systems that describe Schwarzschild spacetime (such as Gullstrand–Painlevé coordinates) it seems like we can always make a coordinates transformation very ...
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Can the history of an indeterministic universe be precisely inferred given full knowledge of its current state?
In a deterministic universe, there is only one later state that necessarily follows from the current state and only one earlier state that necessarily precedes the current state. However, in an ...
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What portion of the universe is black holes?
What portion of the universe is black holes? Is it possible to estimate the percent of all mass that is in the black holes?
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Why does Americium-241 not exist naturally?
A few searches says that it's because "the half life is too short with respect to the age of the universe." I don't understand what that means.
Note that the half life of Americium-241 is ...
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If all the black holes in the Universe were combined into one supermassive black hole, what would its diameter be?
I am curious to know if anyone has ever sat down and calculated what the diameter of a black hole would be, in kilometers, if it were to contain all the mass of all the black holes that are currently ...
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Why didnt early universe collapse into black hole? [duplicate]
Given the early universe was infinitely small, why didnt it immediately collapse into a blackhole before it had time to expand?
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Can a physical object escape the universe? [duplicate]
Can a particle, like an electronic or photon, leave the universe? If the photon for instance travels out toward the edges of the universe, assuming it is flat, will it encounter an invisible wall, or ...
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Can some regions of space (independent of size), be completely devoid of matter?
Before answering the question, keep in mind that I am a second year Biology student, with no experience in studying Physics and a very basic understanding of Mathematics. However, I have some ...
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How would the universe look like without matter?
I was wondering how the universe would look like if it would have been perfectly symmetrical in terms of matter and antimatter. If I understand correctly, there would be no "particle" but ...
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Is the universe getting hotter? Brighter?
Due to their fusion processes every star is radiating massive amounts of photons and (to a lesser extent) neutrinos. Are all of these getting absorbed in matter over time, warming it, or is the total ...
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Any non-speculative situation or event where the fundamental symmetries and laws of physics could change? [closed]
Is there any situation or event that could radically change the fundamental symmetries or laws of physics that is not speculative (like, for example, if the universe underwent through a really high ...
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Why is all matter in the universe, not found at its lowest state of potential energy?
Preface: it may be of interest that I am a second year Biology student, with no experience in studying Physics and a very basic understanding of Mathematics. ...
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Does the holographic principle allow realistically-sized universe simulation?
I was reading about the holographic principle and a question came up to my mind which I can't find an answer to. My understanding is that the holographic principle states that the description volume ...
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Non-mathematical formalizations of physics?
The deeper I carve into physics, the more clear it becomes to me that there might be a better way to analyze the universe than our mathematical frameworks. Not like defining new algebras or thinking ...
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Doesn't the increase in redshift of galaxies over larger distances mean that the expansion of the universe is slowing down? [duplicate]
This question seems too simple to not have been asked, but I cannot seem to find an explanation. So apologies if this is a duplicate.
The current explanation for the expansion of the universe as I ...
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The General form of the Friedmann equation written in another way
Using the general form of the Friedmann equation:
$$H^2 =H_0^2(Ω_{m0}(1+z)^3+Ω_{r0}(1+z)^4+Ω_{k0}(1+z)^2+Ω_Λ)$$
and taking $a_0=1$, How can I derive that the Friedmann can be writing in the following ...
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What will happen to the the various fields of the universe after heat death?
What will happen to the various fields like the electromagnetic field, gravitational field etc that make up the universe after heat death? Will they continue existing even after a heat death?
Sorry if ...
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Thermodynamical argument in cosmology
I'm interested in the following question: What could we say about the thermodynamical properties of the Universe, using thermodynamics alone (without using general relativity), assuming that the ...
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What is the estimated velocity of expansion at the beginning of the Dark Energy era?
Approximately 7.5 billion year ago Dark energy began to accelerate the expansion of the universe. Data has shown us that up until that time the universe was decelerating in its expansion velocity. ...
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Reheating in the Ekpyrotic / Cyclic Universe
As it’s known, an important part of inflationary cosmology is reheating, the process of conversion of the inflaton energy into conventional matter after inflation. It occurs through coupling of the ...
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Formal definitions of the Universe
I'm looking for formal, i.e. citable, definitions of the Universe. To my surprise, I couldn't find any in textbooks at my disposal. All I found were definitions in online dictionaries and Wikipedia ...
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What have been the biggest factors for the increase in entropy in the universe?
Entropy has been increasing since the Big Bang. But how? It seems relatively intuitive, but the universe is cooling down. Often when things cool down, entropy decreases. So why, in the case of the ...
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Isn't the universe older than 13.8 billion years? [duplicate]
To preface this, I'm not an expert, I'm just an avid astronomer with little mathematical knowledge.
I was watching a video that was explaining the cosmic scale and how the observable universe is only ...
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Can we say that for everything in our universe to exhibit a behaviour, it should have the capability to process information?v(details below) [closed]
Take the simple case of water molecules.. you freeze them, it turns into ice.. at around 100° it vaporizes.
For each and every reaction in this example, the molecule needs to react to heat, for it to ...
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How deep can a 'deep field' image be?
Hubble's famous deep field image was created by pointing the telescope at the same spot for 10 days continously. This aggregates photons and creates a coherent image - If I understand what's going on ...
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How can the universe die if all energy is conserved?
So according to physics, because of the expansion of the universe, there will be a time in the future, where all that exists (maybe...quantum fields) will be so far away from each other that it will ...
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Are Scientists (& Astronomers) able to see the Same Distance away from Earth (or Solar System) in all Directions?
Thinking about the Universe being shaped like a huge ball , & given that we are not in the center because there is no center : When Scientists (& Astronomers) look out in various Directions , ...
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What is the average prevalence/density of stars in space?
By average density $D$, I mean that, if you look at a huge volume $V$, you would expect to see $V\cdot D$ stars in that volume.
Just a rough answer is fine. I'm sure the prevalence of stars changes ...
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At what average rate do supernovas happen?
By average rate $R$, I mean I want an answer with units $$[R]=\frac{\text{supernovas}}{\text{length}^3 \cdot \text{time}}$$. That is to say, if I consider a huge volume $V$ and a long timeframe $T$, I ...
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Could black hole be one way exit out of the universe? [duplicate]
As by definition of "a black hole" - it is a place in space where gravity pulls so much that even light can not get out. But could that be a one way exit to outside of matrix of our universe?...
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Age of the universe and density parameter
As you can find in all the literature, the age of the universe can be computed easily $$t_0= (H_0)^{-1} = 14Gy$$
For the accepted values of Hubble constant $H_0$, but recently I read that this result ...
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The gravitational field of all the distant mass exactly cancels the positive mass-energy in the universe. Why do they think so? [duplicate]
It is often said that the gravitational field has negative energy, and that this negative gravitational energy of all the distant mass exactly cancels the positive mass-energy in the universe.
Why do ...
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If the universe is infinite, would it be homogenous?
I know, that we can't really know the answer to that, but what is the current state of understanding?
We seem to assume that on very large scales, the universe is homogenous. As I understand it, this ...
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Is it possible for the universe to return to the exact current state if information cannot be lost?
My understanding is that, if information in the universe cannot be lost, it will always be possible (in principle) to tell which prior state of the universe has led to the current state. Is this true ...
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Heat death of universe, are there any interactions
As far as I understand, in the so called "Heat death of universe" universe is still expanding, but in that case, average distance among particles is gradually increasing to infinity, and ...
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So is it possible to enter a black hole or will the time dialation make it so that you can never get inside of it becuase it will decay faster? [duplicate]
So is it possible to enter a black hole or will the time dialation make it so that i can never get inside of it? Becuase it will decay faster? I know it sounds wrong but i have not done the math or ...
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Consequence of entropy increasing with time [duplicate]
Our bodies are a highly ordered collection of atoms. Entropy is a measure of disorder. Since the entropy of the universe increases with time, does that imply that humans will necessarily become ...
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Are the claims about repeating states and space in Netflix's "A Trip to Infinity"'s based on real research?
I just watched Netflix's documentary on infinity "A trip to infinity". They have an example where you put an apple in a perfectly sealed box. They make a claim that seems odd to me.
The ...
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The scale of extra dimensions
I wonder how in this Paper (page : 6) the scale of extra dimensions have been assumed or calculated
The authors study a Generalized (n+1)-d Randall-Sundrum Model, in the beginning of page 6 they ...
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The size of the universe and the scale factor of $\Lambda$CDM model
I wonder is there a relation between the size of the universe and the scale factor calculated by solving Friedmann equations.
I mean if the volume of the universe nowadays is a round $V= 10^{78} m^3$, ...
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How to know the scale of an extra dimension in units of length?
I’m studying a model with an extra fifth dimension with
a scale factor $b(t)$ . The modified Friedmann-like equations are:
$$
\left[ {\left( {\frac{{\dot a}}{a}} \right)^2 + \left( {\frac{{\dot a}}{a}...
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Particle horizon in an empty universe
So in this thread,
Can space expand with unlimited speed?,
the author Pulsar made amazing diagrams of different horizons and paths for a benchmark model that describes our current universe, and gave a ...
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