# Tag Info

## Hot answers tagged universe

9

There's a very common misconception that the Big Bang happened at a point like a bomb going off. It doesn't help that almost ever TV documentary on the subject represents the Big Bang in this way. Explaining what actually happened is hard without going into the Maths, but here's an explanation I gave taken from (of all places) the Science Fiction Stack ...

7

This is a rather lengthy answer as I tried to go a bit in depth; there is a short summary at the end. Will we see more or fewer stars with time? The short answer to this is: We see less stars with time, due to the fact that cosmic expansion is accelerating. Although what we really see at the relevant distances are galaxies; single stars are far too far ...

5

From the Friedmann equations, you can derive that $$\dot{R}^2 - \frac{8\pi}{3}G\rho R^2 = -k c^2,$$ where $\rho$ is the total density of the universe and $k$ is a constant that determines the shape of the universe: $k=-1,0,1$ for an open, flat and closed universe, respectively. If the universe is a hypersphere ($k=1$), then $R$ can be thought of as its ...

5

The question you are asking yourself is ill defined. The universe has no center, thus you cannot ask what is there. The important thing to realize is that a singularity (presented in the Big Bang Theory) is not a physical thing, you can't say "oh look at that singularity over there"(from that point the universe started). In fact a singularity is merely a ...

4

The uncertainty principle is a mathematical consequence of wave behaviour. It is true for sound waves, electrical signals, radio waves, etc. Anywhere you might want to work with Fourier transforms. Let's say you want to send a pulse via a radio wave. Furthermore, lets say you make the amplitude of the pulse a Gaussian function with time: \$f(t) \sim ...

3

You are right that we do not know if the universe is finite or infinite in space. Cosmologists do now think that it has an infinite future because of the accelerated expansion rate due to dark energy but this does not tell us anything about the question of infinite space. To answer the question for space we first have to assume spacial homogeniety, i.e. ...

3

The temperature 2.73 K is not calculated, it is measured. The cosmic microwave background (CMB) has the properties of a blackbody radiation at the temperature 2.73 K. It is based just on the measurement of CMB, no calculation of dark matter or dark energy is involved. Temperature does not simply depend on mass or gravity. Temperature is a quantity which in ...

2

This is a really interesting question. I think the easy answer has already been given: Stars require lighter elements (Hydrogen, Helium) in order to generate energy (and hence light) from fusion. There is a finite (but thankfully enormous) amount of these lighter elements in our universe, all (in a "black boxed" sense) of which is gradually heading down ...

1

Light itself has temperature. If you let it fall upon a cold black body long enough, the body would warm up to that temperature and emit light of that temperature itself. What's the temperature of sunlight on the earth? About 5000K. It's the temperature that the surface of the sun had about 8 minutes ago. The sun could have extinguished 8 minutes ago, but ...

1

Mass in and of itself will not generate heat. Heat comes about when two objects interact with each other i.e. when they change from one state with a given energy to another. More specifically, if an object has more energy after an event than it did before, the net gain in heat would be negative for the surroundings (the environment becomes colder), and vice ...

1

The answer depends on the interpretation of quantum mechanics you like the most. As they are mathematically equivalent, the question is metaphysical rather than scientific. Some of the ways to explain: There is no uncertainty in the system. The uncertainty is in the observer. By making the measurement the observer introduces the uncertainty because he ...

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