Theory FAQs (Theory)

1. Universe 2. Cosmology

3. Life

1. Universe

Where are We in the Universe?
Most objects in the Universe are located inside galaxies. We are just in one of them too. Galaxies are these vast, large clusters of stars, some of them spiral-shaped, some ellipticals. Our Sun is one of the hundreds of billion stars contained in our Milky Way Galaxy. Our Earth is one of the nine planets orbiting around the Sun. The Earth is the third planet from the Sun

How Many Planets are There Around the Sun?
Nine. Venus, Mercury, the Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, in this order, starting at the Sun

What's the Difference Between a Planet and a Moon?
A moon is a minor celestial object orbiting a planet, as a planet is a celestial object orbiting a star

What's our Sun?
Our Sun is a star. This means that, like any star, the Sun formed down from a dust and gas cloud, and that it's a thermonuclear factory where hydrogen is transformed into helium. CAUTION! Observing the Sun is dangerous and requires dedicated safe techniques!

What are NEOs?
Near-Earth Objets (NEOs) are asteroids or comets orbit of which may represent a hazard to the Earth. Such objects might one day hit Earth in the same way that some already hit, bringing e.g. to the extinction of the dinosaurs 65 million years ago, or on a lesser scale, to the Tunguska event, at the beginning of the 20th century, when 1200 square miles forest were destroyed in Siberia, Russia. Research program are underway to catalog all such hazardous objects. None until now have been found to be directly threatening although some are forecasted to come very close to Earth

What's the Asteroid Belt?
The asteroid belt is a swarm of minor planets -or "asteroids"- which is found between the orbit of Mars and the one of Jupiter. Such objects were created when planetesimals -those blocks of materials which accrete to form planets- were prevented from accreting further by Jupiter gravitational influence. Further collisions between them eventually produced this number of asteroids which are populating the asteroid belt nowaday

What are Supernovae?
Supernovae are one way stars are ending their lives. After having burned down to the heaviest elements all the fuel they had got to burn, some stars are just ending in a fiery explosion. Another type of supernovae event is the one resulting from a binary system where one star is accreting material from another one. The star is exploding when enough infalling material has accumulated

What Are these Black Holes Found at Galaxies' Center?
Such black holes are now thought to exist at the center of most galaxies. They are about the orbit of Mercury in size and in the range of multimillion solar masses, as they are the most gravitation-featured object in the Universe. Matter there have become condensed to the point that not even light may escape, as spacetime is definitively warped on itself! Such black holes likely formed when smaller galaxies merged together to form the galaxies we know today. Why the black holes formed in the early galaxies is probably due to the fact that the first objects to form in the Universe were stars which quickly turned supernovae and then black holes

What are Quasars?
Quasars are highly active galaxies located faraway in the early Universe. This hyperactivity is thought to be due to the supermassive black hole located at the center of these galaxies. The quasar phase might well be an usual period of the life of the early galaxies in the early Universe

2. Cosmology

How Did the Universe Originate?
The definitive view now of how the Universe has been born is the Big Bang theory. The Universe appeared 13.7 billion years from a quantum singularity, that is from an event related to the world of elementary particles. From there, in a swift period of time, all the known Universe and particles were created, expanding in all directions. The present Universe is the Universe 13.7 billion years after this primordial event. We and all the other galaxies are still hurtling through space

What Are the Theories of Everything (TOEs)?
Theories of Everything (TOEs) are a quest to unify the understanding of the Universe from the particles world to the large-scale structures. Until now the large-scale structures of the Universe are explained by Einstein's relativity which is a theory of gravity and energy as the particle world is best explained by the quantum physics which is a description of the building-block particles and of the forces which are at the origin of the atoms. TOEs are building upon Grand Unified Theories (GUTs) which, as far as they are concerned, are trying to push quantum physics further, unifying together all forces of the subatomic world. A first hint that TOEs are true will be observations that some constants linked to Relativity are violated. Up to now experiments brought evidence that even at a high accuracy Einstein's relativity is correct. Would Relativity be outshined, a new theory for the Universe would surely continue to include it somehow in the same way Relativity itself continues to include Newtonian vision of the world

What is Dark Matter?
Dark Matter is a part of what is composing the Universe but nature of which is still unknown. Dark Matter was theorized as what was visible of the Universe was not enough to account for the mass budget of it. Dark matter is accounting for 25 percent of the Universe. Dark matter halos are thought to exist around galaxies

What is Dark Energy?
Dark Energy was found lately as a force which began to accelerate the Universe's expansion 7 billion years ago. Its nature is still unknown but it might that such a force be an anti-gravitational force. It is still badly known weather this force is constant, leading to an ever expanding Universe or whether it is increasing, leading everything in the Universe to be eventually torn down, down to the atoms, 30 billion years from now. Dark Energy accounts for 75 percent of the energy-mass budget of the Universe

What Is the Inflation?
Inflation theory is a recent addition to the Big Bang theory. It states that the Universe endured a dramatic expansion shortly after its beginnings. Such a view allows to better understand some characteristics of the observable Universe. Inflation theory is mostly demonstrated by recent experiments and space missions as the cosmic microwave background radiation (CMB) is showing inprints related to the inflation moment

3. Life

What are Exoplanets?
Exoplanets is a neologism used to term planets found around stars other than the Sun. Solar system formation around stars seems now an usual phenomenon resulting from the coalescence of dust disks found when a star forms. Although until now the findings of exoplanets have been biased due to the field of research being limited to about 50 light-years from the Earth -most exoplanets found until now are of the Jupiter class- hopes are neat that Earth-sized planets exist too. Such search will be performed by most recent tools, methods, and coming space missions

Is There Any Other Life in the Universe?
Life processes like they have been studied until now let think that the Universe is life-friendly and that life may work based on processes different from the oxygen-friendly photosynthesis. As soon as in the giant gas clouds were stars are forming, life building blocks are available and such building blocks may easily turn into life in a planetary environment. It can begin there to work upon hydrogen, sulfates, or methane deep into terrestrial crust or inside primordial oceans. It would be no surprise that a lot of exoplanets might be found with a teaming life, although mostly lying at the microbian level only. On the other hand some studies think that there might be 1 million advanced intelligent civilizations just in our Milky Way Galaxy, that is one every 150 light-years! Life is now aggressively searched by space missions in our solar system and beyond

What is the Fermi Paradox?
It's a kind of joke, in 1950, about aliens by Enrico Fermi, the famed nuclear scientist. As other civilizations would have had plenty of time to travel in the Galaxy and expand there, Earth had not yet been invaded by little green men. Fermi asked: "Where is everybody?"

What is the Drake Equation?
It's an attempt to quantify the probability of alien worlds. It was deviced in 1961 by Frank Drake, a radio astronomer who, the previous year (Project Ozma), had been the first to listen to alien radio signals, with the 25-meter dish of the National Radio Astronomy Observatory in Green Bank, West Virginia. In preparation of a meeting where young Carl Sagan was, Drake came up with this famous equation:
N=R x f_p x n_e x f_l x f_i x f_c x L,
with N the possible number of civilizations existing in the Milky Way Galaxy; R the yearly rate of birth of stars in the Milky Way; f_p the fraction of such stars having a solar system; f_e the average number of Earth-like planets; f_l the number of such planets where life actually appeared; f_i the number of the latters where intelligence evolved; f_c the fraction of intelligent species which produce interstellar radio communications; and L is the average lifetime of a communicating civilization (in years)

Is There Anything Special About our Solar System and Earth?
Yes. It seems that our solar system is orderly compared to the more chaotic ones which have been seen until now around other stars. We are protected, for example, against tidal disruption by two or more Jupiter-like giants, as, on the other hand, our Earth is stabilized on its axis of rotation by the influence of our Moon. Without it, Earth would experience axis tilt variations of as much as between 20 and 60°. Hence it seems that our solar system and our Earth would be some privileged locations