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25 votes
Accepted

If the universe has no true center, could it have antipodes?

Yes, it's conceivable. If the universe is spatially hyperspherical, then there would be a most distant location from every location in the universe, much like there is on the surface of a sphere. ...
benrg's user avatar
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21 votes
Accepted

If the universe were infinite, how would it look through a telescope?

If the universe were infinite in space, but finite in time, we could see back no further than a light-travel time of the age of the universe. — This is very possibly reality. We can see back to ...
James K's user avatar
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15 votes
Accepted

Why speed of light is considered to be the fastest?

The recession rates relevant to Hubble's law are not relative velocities, so there's no reason to compare them to the speed of light. They can be defined as follows. Conceptually, imagine a chain of ...
Sten's user avatar
  • 4,694
14 votes

Are there some (simple) mathematical models which can simulate the cellular/web structure of the universe?

I suppose it depends on your definition of "simple", but I would say "No". Kepler simulations A solar system is simple because you have one dominating mass with orbiting masses ...
pela's user avatar
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12 votes

Is the gravitational constant really constant over our Universe?

See also Do the laws of physics work everywhere in the universe? on the Physics SE. If the gravitational constant were not constant, then the laws of physics work differently elsewhere in the universe....
Allure's user avatar
  • 4,554
10 votes
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Are there some (simple) mathematical models which can simulate the cellular/web structure of the universe?

In order to make a cosmic web pattern one can run a physics-based simulation approximating the flow of mass, as in Pela's answer. However, it is also possible to make "phenomenological models&...
Anders Sandberg's user avatar
9 votes
Accepted

Why does Helix Nebula look like an eye?

Look at Helix Nebula NGC 7293 (Aquarius) on the left and Ring Nebula M57 (Lyra) on the right. Both are of the planetary nebula type, and very similar. This NASA video, based on Hubble Space Telescope ...
Albert's user avatar
  • 2,102
9 votes
Accepted

Size of the Unobservable Universe

The article Applications of Bayesian model averaging to the curvature and size of the Universe cited in the question is from 2011. It is now 2023 and we have much better data, in particular from the ...
Albert's user avatar
  • 2,102
8 votes

Does space expand?

Space is not uniquely defined. Spacetime, not space, is the physical domain in general relativity. Space is just a 3-dimensional surface within the 4-dimensional spacetime. The definition of a spatial ...
Sten's user avatar
  • 4,694
7 votes

Why speed of light is considered to be the fastest?

I'm standing next to Usain Bolt, he runs off in the opposite direction to the Earth's rotation, why is he consider the fastest human when I'm moving faster than him? Also there are people in planes or ...
Alex Dawn's user avatar
  • 151
6 votes

Was the Big Bang an event within a preexisting Universe, or did it mark the beginning of the entire Universe, beyond just the observable Universe?

Could it be that the Universe is truly infinite It looks like it is infinite in space in all directions, and infinite in time in one direction. Going back in time one reaches a singularity. It is ...
James K's user avatar
  • 123k
5 votes

Size of the Unobservable Universe

Yes, you are right. It refers to the Hubble volume rather than the Hubble radius, specifically it is 251 times the Hubble volume, but based on the volume, we can calculate the radius of the whole ...
Arjun's user avatar
  • 1,464
4 votes

Is the gravitational constant really constant over our Universe?

Within General Relativity (GR), the gravitational constant $G$ is postulated to be a fundamental constant having the same value over our Universe. Within the Brans-Dicke theory, which is a competitor ...
Michael_1812's user avatar
  • 1,456
3 votes

How can $\Omega_m<1$ indicate an infinitely expanding universe?

I studied that if $\Omega=\frac{\rho}{\rho_c}$, which is the sum of the three is greater than one, the universe eventually collapses, if exactly one, its flat and if less than 1, it keeps expanding. ...
Sten's user avatar
  • 4,694
3 votes

Why does Helix Nebula look like an eye?

Prior to the formation of the Helix Nebula, there was a star similar to our own Sun in its post-main sequence stage. Eventually, this star consumed its entire fuel supply, which caused fusion to cease ...
4NT4R3S's user avatar
  • 1,015
3 votes

Size of the whole universe if it were spherical

The Planck (2018) results combined with BAO constraints give a curvature density $\Omega_k = 0.0007 \pm 0.0019$, where the error bar is a 68% confidence limit. That means a reasonable 3-sigma upper ...
ProfRob's user avatar
  • 153k
3 votes

Amount of black holes over time

Black holes are produced from the core collapse of massive stars. As such stars are short-lived, the rate of production of black holes follows the rate of production of such massive stars. This rate ...
James K's user avatar
  • 123k
3 votes

Are there some (simple) mathematical models which can simulate the cellular/web structure of the universe?

Here's a relatively simple way to make fake cosmic web patterns. Unfortunately, it takes a lot of points to make diagrams that resemble the one from Wikipedia, and with relatively small numbers of ...
PM 2Ring's user avatar
  • 14.8k
3 votes

Was the Big Bang an event within a preexisting Universe, or did it mark the beginning of the entire Universe, beyond just the observable Universe?

You're asking about something that's beyond the realm of well-understood physics, so a lot of it is speculation. However, people work on the idea, so it's not impossible. The key words you want to ...
Allure's user avatar
  • 4,554
2 votes

If the universe has no true center, could it have antipodes?

Given a point $p_0$ and a metric $d$, we can define the antipode $p_1$ as the argmax of $d(p_0,p)$ as $p$ varies across all points. There are things that could happen that would make this definition ...
Acccumulation's user avatar
2 votes
Accepted

What natural astronomical object is rare on a Hubble volume scale?

The space density of ultraluminous quasars (those with luminosities greater than $5\times 10^{13}L_\odot$) in the local universe is $\sim 10^{-9}$ (Mpc)$^{-3}$ (see for example Caplar et al. (2015) ...
ProfRob's user avatar
  • 153k
2 votes

How can 'HD 140283' be older than the universe?

The most recent age estimates for this stars using improved interferometric estimations of angular diameter (to better estimate the effective temperature) and more sophisticated stellar models are: $...
ProfRob's user avatar
  • 153k
2 votes

Light/Dark energy/Dark matter

Light is a form of energy, and like other forms of energy (such as "mass") it has a gravitational effect. Two photons travelling in space will be attracted to each other by gravity. Of ...
James K's user avatar
  • 123k
1 vote

Is there evidence against a Universe Black Hole?

The Hubble length $c/H$ is indeed the same as the Schwarzschild radius of the energy enclosed within a radius $c/H$. This is because the same physics set both. It does not imply that the Universe is a ...
Sten's user avatar
  • 4,694
1 vote
Accepted

Does space expand?

The short answer is that spacetime is changing in such a way that, to put it clumsily, the amount of space between objects is increasing at a rate proportional to the distance between them. One can't ...
RLWatkins's user avatar
  • 150
1 vote

What's the name of outside the cosmic horizon?

The view of the philosopher physicist: The nature of science is empirical. Because "outside" the cosmic horizon is outside the realm of experience, we can make no well-founded claims about ...
Stephen Anastasi's user avatar

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