# Tag Info

## Hot answers tagged universe

4

This is a commonly considered idea, of which one variant is the "Hubble bubble". Anything that happens outside of the visible universe, is, after all, in principle unknowable to us.

4

I'll answer your question with an analogy. Imagine a really small balloon, so small that it occupies a point. Now, imagine that the balloon is expanding uniformly outward from that point. Note that that central point is not part of the balloon. It's the same idea as to what happened with the BB. In this analogy, the universe is the surface of the balloon. ...

3

If by fire you mean flames as seen at room temperature by the combustion with oxygen of various materials the answer is, we do not know in the solar system of a planet with an oxygen atmosphere at a level that given combustibles flames will appear given the trigger. Hydrogen vents for example would need an atmosphere with oxygen to start flames. In ...

2

Firstly we should note that the universe as a whole is not described by the Schwarzschild metric, so the Schwarzschild radius of the universe is a meaningless concept. However if you take the mass of the observable universe you could ask what the Schwarzschild radius of a black hole of this mass is. For a mass $M$ the Schwarzschild radius is: $$r_s = ... 2 The latest data is from the Planck satellite, and you can find the results in this 15MB PDF. The matter and dark energy densities are;$$\begin{align} \Omega_M &= 0.315 \pm 0.017 \\ \Omega\Lambda &= 0.686 \pm 0.020 \end{align} So we get a total density of $\Omega = 1.001 \pm 0.026$. So within the 2.6% experimental error spacetime is flat.

1

The premise of your question is flawed. It is not possible to know everything with perfect accuracy, even in a non-quantum fully deterministic system. (In a quantum system, even if you do know its state with perfect accuracy, you can't predict it accurately.) Ever hear of chaos? the butterfly effect? the three-body problem? No matter how well you know the ...

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You need to be careful about comparing the curvature of spacetime to the deformation of a block of jelly. In particular, in general relativity time is curved as well as space, and this is impossible to represent with the jelly model. In fact it's just about impossible to give a really good description of spacetime curvature to anyone who doesn't have at ...

1

Must every point in spacetime remain attached to its current neighbours? Basically yes, this captures the spirit of allowable deformations. Some background: If you want to measure distances between points, this is very much in the realm of mathematical analysis. However, it is sometimes useful to be able to discuss "closeness" in a looser (but still ...

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The balloon analogy imagines the universe as a 2D surface expanding around a central point as it moves through a 3rd dimension of time. This may be the origin of confusion as in reality there is no 2D surface of expansion, like a wave front, but rather an expansion of 3D spacetime, wherein every point in space quite literally is its own central point from ...

1

The universe does not "calculate". The universe just exists as it is and evolves. We calculate things like how far a particle with a given speed goes in a given time because we don't actually have the particle or the time. The universe just has everything in a state, has the laws of nature in place, and everything works itself out. In the universe an actual ...

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it must have started from a single point This is a common misconception popularized buy the media. Imagine this grid: Imagine each square getting larger. If you think about it, you will see that each point on the grid is expanding. The grid is the universe. Each point on the universe is its own "singularity".

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