# Tag Info

5

No, it's not possible. The other galaxies we see are to radically different. Additionally, if we are the surface volume of hyperspace, then the universe should be closed. Our best estimates and observations indicate it's flat. Let me address both of these in more detail. As for the other galaxies. First of all, there's the Andromeda galaxy. That is a galaxy ...

5

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 ...

4

Work is done as long as the force is applied on the body, so in this case, the total work done would be the product of Force applied and the Displacement during the initial push only. If the object moves forever, it would do so with a constant velocity in this scenario, and consequentially its Kinetic Energy would be constant, implying that the work done ...

4

There is an expectation that the redshift of an object will change with time. The details depend on the cosmological parameters (a plot is shown below). This was first explored by Sandage (1962) who predicted that, in a matter-dominated universe (i.e. no consideration of dark energy back then), the redshift should decrease due to the braking action of ...

3

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 ...

3

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 ...

3

Sometimes the word universe is just used colloquially and can just refer to everything on some side of a horizon (an event horizon, a causality horizon, etc.) But when used precisely, I'm sure different definitions are used in different fields. For instance, in mathematical general relativity, you assume that your universe is a connected four dimensional ...

3

If the question is asking whether there is a definition that encapsulates our universe, then I believe the answer is No. This is because encapsulating a "space" into a formal system requires defining bounds. However, we don't know the bounds of our own universe--let alone what bounds might be possible for any universe. We can only describe what we can ...

2

this may or may not be a misunderstanding, but there is no centre of the universe. Imagine the universe as being the surface of an expanding balloon, with all the galaxies and stars on the surface, being stretched away from each other. Just as there is no centre, for example, of the Earth's surface, there is no centre of the universe. If by 'centre' you mean ...

2

Cosmological red-shift depends on the difference in the scale factor between when the light was emitted and when it was received and not directly on recessional velocity, which is of dubious physical significance. The recessional velocity of any given galaxy outside our own (ignoring peculiar velocities) in a LCDM-like cosmology will be arbitrarily large ...

1

It could have been beautiful, and indeed it would have been the case if the Universe consisted of "normal" matter — i.e. baryons and dark matter – above a certain critical density threshold (which you can calculate to $\sim10^{-29}$g/cm$^3$). Unfortunately, as it was realized in 1998, a mysterious "energy" labeled dark energy seems to permeate empty space, ...

1

Singularity. If a big crunch occurs, the entire universe will collapse under it's own gravity until everything is concentrated at one point. What happens after that is really up to speculation. Moreover, in light of recent discoveries, this theory has been dismissed as being a implausible one. There is evidence that the universe is expanding at an ...

1

Things are not difficult if you put yourself in the right perspective. "Curvature" is a mathematical concept. Like many mathematical concepts the word may sound like something a taxi driver in London or Jakarta may have heard, but it is really just a "formula". Likewise: "Work" may evoke ideas of money, strikes, unions, customers..., but in physics it is ...

1

Yes you are correct Sophia. This is a major component of the standard model itself, which concludes the opposite (that space is expanding in an infinite cosmos), but the only reason a conclusion like that comes about, is because what we observe is indistinguishable from being at the centre of a finite universe that races away from precisely us, uniformly in ...

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