### Review: Death from the skies

#SciDoom
The universe is trying to kill you.
Philip Plait, Death from the skies
The Universe is the most dangerous place that you can imagine. There are a lot of perils: asteroids and comets, supernavae, gamma ray bursts and finally our star, the Sun. Every source of danger is examined in nine chapters introduced by a fictional short story, that is scientifically correct. In these introductory stories, Plait describes a possible scenario in which Earth is shotted by, for example, a comet o a great asteroid, like the one that leaves the Meteor Crater in Arizona
or the ones that probably caused the dinosaurs extintion.
In order to prevent a bad encounter with a great object, physicists describe a lot of possible solutions: in the list there are a nuclear bomb, an impact against an artificial object (like Deep Impact with Tempel 1) or try to change the bullet's trajectory using the gravitational force of an ather astetoids. This last solution is proposed by B612 Foundation and, like the others, present a lot of difficulties, but is technically realizable now!
Some possible problems are, for example with shot solutions, that the object is broken into too big pieces, while for the gravitational solution we must demonstrate a very precise control of the gravity. These are the only enemies we can prevent, but against the others we could realize some particular protection, like radiations from Sun or from supernovae explosions. In this last case, the probability to be shot is 1/10000000, against 1/700000 of an asteroid shot, that is a probability actually higher than terrorism!
Another danger from outer space is an... alien attack! Don't worry! I don't mean the little green men from Mars, but simply eventually microscopic life present in asteroids or comets. An attach like this has a very low probability, first of all because the aliens must survive at Earth atmosphere, and after because they have a low probability to interact with DNA developed in our environment: following our knowledge, we must remeber that in the Universe our planet is unique!
I don't know if we are alone or not, but in this moment it is so...
In the last part of the post I spend some words about Sun:

The Sun is the star of our planetary system. Solar System was composed by 7 planets, 1 dwarf planet, and some other objects like asteroids, comets, and so on. Using Newton's gravitation law and Kepler's laws we can mathematical explain orbits around the Sun.
Our star has a mass equals to $1.9891 \cdot 10^{30} Kg$, $333000 \, ME$, where $ME = 5.97 \cdot 10^{24} Kg$ is Earth's mass. Its density is less:
$d_S = 01.408 \cdot 10^3 \frac{Kg}{m^3}, \; d_E = 5.5153 \cdot 10^3 \frac{Kg}{m^3}$
where density is defined like ratio between mass and volume:
$d = \frac{m}{V}$
Photosphere's temperature is 5778 K, where K is absolute temperature: name and symbol come from Lord Kelvin. Absolute temperature is related to usual temperature by the following relation:
$T (K) = T (°C) + 273.15$
For example, 0°C equals to 273.15 K.
Absolute temperature is used in termodynamics' laws. In kinetic theory of gasses, we can relate temperature with the energy of the particles that constitute the gas:
$E_k = \frac{3}{2} k_B T$
where $k_B$ is Boltzman's constant.
The Sun will became dangerous for us in 1.1 to 3.5 billion of years: it emits a lot of energy and Earth surface became more heath than today, so in future Sun cookies Earth (if we don't cook us before!). But it's not finished here: the Sun will eat Earth!
But there's a solution: change the place of the Earth, but this is a very complicated solution: probably in future we will have the techonology in order to move our planet, but I think that is more simple colonize the Solar System or other planetary systems.
But the last enemy for our culture is... the Universe!
In the most probable scenario, described following Einstein's theory, Universe will death after all matters will be reduced in radiation and elementary particles like leptons (also baryons will decade, but in leptons and radiation because quarks cannot exist free at the temperature of the dying Universe).
So to the question "Are we doomed?" the answer is "Yes, we are doomed" but, after reading Plait's book, I think that our only hope is science and knowledge: they could be give us the possibility to escape in another universe, or to recreate another little big bang nearly some black hole, or simply the confirmation that the life in Universe will return in another start, because nothing is forever, also the death of the Universe!