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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Angular Momentum — AP Physics C

Do all of the planets in our solar system have the same angular momentum? If so, why? I'm not sure if the following is correct: If we could drag a planet radially outward from the sun, then no ...
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Is there any possibilities that in multiverse in another situation any civilization may exist and they can live in different conditions than ours [closed]

If this is a possibility,they must have some different quality than ours.Then what can be those qualities.
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Would Wheeler's oscillatory universe model create absolutely different universes in each cycle?

According to physicist John Wheeler, the universe is part of a sequence of cycles of Big Bangs and Big Crunches, called cyclic or oscillatory universe model: https://en.m.wikipedia.org/wiki/Multiverse ...
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109 views

Is Young Earth universe distinguishable from non-creationist one? [closed]

While talking today about some religious beliefs I was struck by the next question: So what if some super-natural being forks our universe 6,000 years ago, i.e. creates the exact same copy of ...
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The limit of the Universe that we'll ever be able to see

After watching Neil Turok's talk at 13:00 - 13:20 he says that the Universe expands and there is a limit beyond which we will never be able to see anything. And that's due to the Dark Matter which (...
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80 views

Expansion of the universe – impossible for future astronauts to make it back

The universe is rapidly expanding. If future astronauts built a spaceship that could travel close to the speed of light and took off, there is a certain point where they could not make it back again ...
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34 views

Big crunch scenario, would black holes form?

Imagine a big crunch scenario in which everything (or almost everything as for I have other doubts, eg about entropy...) rolls back. Shouldn't the contracting universe reach a point of density at ...
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34 views

'My question is about' …the size of the Universe after Inflation [duplicate]

Hitherto, I had assumed, on account of Inflation, "boom" the Universe was "out there" and it has taken light 13.6 BY to get here. However... Quoting the aerospace engineer: In my thinking if the ...
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39 views

Do Holographic Screens eliminate the need of finding holographic dualities?

There are various models in physics based on the famous holographic principle (https://en.wikipedia.org/wiki/Holographic_principle) This does not always work since in these models we must find a ...
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Flat yet finite Universe

I would like to ask you this question: Let's assume that the universe is perfectly flat and big bang happened as described by our theories some 14 billion years ago. Shouldn´t, therefore, the radius ...
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Fine tuning of the cosmological and gravitational constants [closed]

Consider the gravitational constant $G$. According to philosopher Robin Collins, cosmologists have been able to determine a region $W_r\subseteq\mathbb{R}$ for which the universe would have permitted ...
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Why does Penrose expect visible Hawking Points in CMB?

I've only just started reading into Conformal Cyclic Cosmology. My understanding of the hypothesis is that, with some conformal transformation of space, the very end of the universe at $t=\infty$ ...
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Adding up gravitational fields of infinitely many objects?

I'm reading a book introducing gravity and find something I don't understand. Please check the attached image. The sentence in red bracket claims that if one adding up gravitational fields of ...
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86 views

Is it possible that the universe is not expanding faster than the speed of light? [closed]

What if the speed of light increases proportionately to the expansion of space? Is it possible that light traveling in the medium of space gets to travel faster if the medium is expanding? An analogy ...
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Carlo Rovelli: “Is Time’s Arrow Perspectival?”

I came across a paper in which Carlo Rovelli argues that "the entropy we ascribe to the Universe depends on the peculiar coupling between us and the rest of the universe". Rovelli suggests that the ...
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75 views

Why is the measure problem an issue if the universe is always finite?

As a follow-up from this question, I was wondering how the measure problem applies to the idea of eternal inflation. First, why is it even a problem? As time progresses, more universes are created in ...
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How necessary is inflation given the laws of physics?

How deeply is cosmic inflation required for the laws of physics? Is inflation required for a universe remotely like ours, or is it simply a contingent on the starting conditions of the universe? For ...
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Is the speed of light in a vacuum constant?

The news site is titled, “Speed of Light May Not Be Constant, Physicists Say.” It talks about how the speed of light in a vacuum is not constant and that estimates of the size of the universe might be ...
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92 views

Inflation v.s. Big Bang

It is said that that transition or certain quantum rotor field, and “rolling” down into the valley (of some quantum potential), is what causes inflation to come to an end, and create the hot Big Bang. ...
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109 views

COSMIC ACCELERATION

Please forgive a probably naïve question from a lay person. I understand that galaxies are all moving away from us in every direction we look. And for any given distance the speed is the same. And ...
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How will Andromeda collide with Milky Way in spite of Hubble's law? [duplicate]

According to Edwin Hubble our Universe is expanding because he noticed that other galaxies are moving away from us. But then how Andromeda galaxy will collide with Milky Way in ~4.5 billion years, as ...
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Why are we in 3 spatial dimensions? [duplicate]

I am very curious to find if there is any reason that why are we in 3 dimensions not in any other like 1D would be hard almost impossible but 2D could have been possible, or what about 4D or in ...
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Is the expansion of the universe uniform? Are there parts which are expanding faster than others?

Is the expansion of the universe uniform? Are there parts which are expanding faster than others? The very fabric of the universe is expanding..but is it expanding at a constant rate? If it is not ...
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Is it possible that the acceleration of the growth of our universe is driven by the overall gravitational pull of neighboring universes [closed]

I am painfully unequipped when I think about my my knowledge of physics. Still, I am enthralled, as many of us are, by the mysteries and complexity of the universe, both known and unknown. I was ...
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Is the expansion and contraction of the Universe an endless repeating cycle due to Newton's 3rd Law of Motion? [closed]

If the creation & expansion of the Universe was an action, then the reaction to this action is that the Universe will contract and be condensed back into a singularity. If the contraction of the ...
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Can the universe be seen to have an information entropy of about zero?

I recently made some thoughts about fractals and especially how much information they carry. If we consider for example the Mandelbrot set, we can basically "find" an infinite amount of patterns at ...
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If universe is expanding then relative to what? [duplicate]

I am very keen about the fact that universe is expanding.If something expands, it expands relative to something else. If the universe is expanding, then it must expand relative to something else. What ...
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Hubble Parameter in terms of Density Parameters

So I have the equation (derived from the Friedman equations with $a(t_0)=1$ and the powers of $a(t)$ quoted)$$H^2 = H_0^2\left(\frac{\Omega_{R_0}}{a^4(t)}+\frac{\Omega_{M_0}}{a^3(t)}+\Omega_{\Lambda_0}...
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121 views

Question about a mirror Universe

In the article We've seen signs of a mirror-image universe that is touching our own in the popular magazine “New Scientist” (which describes a real scientific theory though, though in a popular form, ...
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What does the Hartle-Hawking state imply?

According to a book I read, the Hartle-Hawking state is a wave function that is meant to explain how the universe started. In the book the author explained that according to Hartle and Hawking’s ...
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64 views

Can we calculate the expansion rate of the Universe at each moment in time?

Do we know the expansion rate of the Universe at each moment of time $t$ of its history? We only measured the expansion rate for a few decades (let's say), which isn't much compared to the age of ...
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91 views

How is observable universe so big if the universe is so young? [duplicate]

The diameter of observable universe is 93 billion light years but the age of universe is only estimated to be 14 billion years. So how does light have 46.5 billion years to travel from the boundary of ...
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What is the proof of constant energy in the universe? [duplicate]

It might sound a bit naive but, How is it that conservation of energy is never broken, how is it that we know that always and for sure the energy in our universe is constant and we cannot create a ...
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Is every object in the universe really expanding? Even small scale objects like humans? [duplicate]

So I was asked a question by someone that "if everything in the universe is expanding, then the lens we use to look at stellar objects is expanding as well, meaning we shouldn't be able to tell the ...
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Update: Does the Planck scale imply that spacetime is discrete? [duplicate]

This question has already been asked Does the Planck scale imply that spacetime is discrete? however I'm wondering if there has been any change in the community since it was asked roughly 8 years ...
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On the death and rebirth of universe in a black hole

Suppose in the end there will remain only one very large black hole, others have died. Now this black hole had absorbed all the matter and energy of the universe due to conservation principle. ...
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Universe simulation

Is it theoretically possible to simulate the universe? I know that some philosophical theories say that our universe is a computer simulation, but is this feasible? Would it ever be possible for a ...
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$c$ slowing down rather than universe expanding?

Can the Friedmann equations be reformulated with taking the universe as being rigid and instead have the vacuum-speed of light in the void decrease over time? So, not changing any equations, just ...
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Universe expanding - Interstellar space, Intergalactic space or Intersupercluster space? [duplicate]

When we say that the universe is expanding, the space between everything is not. The space between atoms, the space between my house and school, and the space between Earth and Sun remains the same, ...
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56 views

Matters Including Resolution of Olbers' Paradox

Is there evidence for galaxies receding from us faster than the speed of light? If so,that might help resolve Olbers' paradox, though other factors must also be taken into consideration. Could such a ...
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Mach's principle and centrifugal force

How does Mach's principle explain the centrifugal force as a result of the relative circular motion of the distant stars? Why does this, in the light of Mach's principle, make a net force although the ...
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49 views

why do quantum fields exist? [closed]

Why did the big bang give rise to the quantum fields it did, could the big bang have created the universe any other way? and why not more elementary particles?
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Speed of at expansion at the start of the big bang [duplicate]

If I understand the basics of the big bang correctly it starts with a very small dense point. At the moment of the big bang, less then microseconds after, the universe is already the size of our solar ...
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In what planetary system can we have arbitrarily long winters?

Unlike on Earth where the length of seasons are almost of the same duration each time, the hypothetical planet on which Game of Thrones took place has seasons of arbitrary length i.e. some winters ...
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Is the location of everything relative? [duplicate]

I have heard that everything in our physical reality is relative. But I wonder: Does the universe have an edge? In an expanding sphere, there would be an edge is it like that? If the above is true ...
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How bright was the universe after Big Bang during photon epoch?

After 10 seconds of Big Bang, most of the leptons and antileptons annihilate each other leading to an outburst of photons. The universe was said to be dominated by photons resembling a glowing fog. ...
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What is the shape of the universe? [duplicate]

If it's flat then how a volume can be flat? And I've read that it's actually not flat .....it's a "Poincaré dodecahedral space". Any suggestions for books posts or articles are highly appreciated.
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Can the shape of our Universe be a Mobius strip? [duplicate]

The Friedmann Equations describe three possibilities for the shape of our using General Relativity, I read in a book that the shape of our Universe is a 3-sphere such that in any direction if you ...
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77 views

How do they know the numbers of the energy pie chart of the universe?

They say that the total energy of the universe consists of 4.9\% ordinary matter, 26.8\% dark matter and 68.3\% dark energy. I hear this pie part in virtually every lecture in cosmology. How do we ...
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Is Hubble's Law Only Valid Nearby?

I am looking this paper by LIGO, and it claims at the very beginning, At nearby distances $(d \lesssim 50 \text{ Mpc})$ [the Hubble constant] is well approximated by the expression $$v_H = H_0d, \...