Universe

UNIVERSE

Where did the Universe come from?

Assuming the Big Bang is a valid theory of the creation of Earth and the Universe, then where did the original mass come from, that formed everything that we see today?

First of all, note that mass and energy are equivalent. So, the total mass of the Universe need not be conserved even though the total energy (taking into account the energy that is equivalent of the mass in the Universe) is conserved. Mass and energy are related by the famous equation E=mc2. Hence if there is enough energy, photons can create matter-antimatter pairs. This is called pair production and is responsible for the mass in the Universe.

As to where everything came from, there is no conclusive opinion. One idea was that the Universe was created from vacuum. This is because according to quantum theory, the apparently quiescent vacuum is not really empty at all. For example, it is possible for an electron and a positron (a matter antimatter pair) to materialize from the vacuum, exist for a brief flash of time and then disappear into nothingness. Such vacuum fluctuations cannot be observed directly as they typically last for only about 10-21 seconds and the separation between the electron and positron is typically no longer than 10-10 cm. However, through indirect measurements, physicists are convinced that these fluctuations are real.

Hence, any object in principle might materialize briefly in the vacuum. The probability for an object to materialize decreases dramatically with the mass and complexity of the object. In 1973, Edward Tyron proposed that the Universe is a result of a vacuum fluctuation. The main difficulty of this proposal is that the probability that a 13.7 billion year old Universe could arise from this mechanism is extremely small. In addition, physicists would question Tyron's starting point: if the Universe was born from empty space, then where did the empty space come from?

In 1982, Alexander Vilenkin proposed an extension of Tyron's idea and suggested that the Universe was created by quantum processes starting from "literally nothing", meaning not only the absence of matter, but the absence of space and time as well. Vilenkin took the idea of quantum tunneling and proposed that the Universe started in the totally empty geometry and then made a quantum tunneling transition to a non-empty state (subatomic in size), which through inflation (the Universe expands exponentially fast for a brief period of time which causes its size to increase dramatically) came to its current size.

Another idea is from Stephen Hawking and James Hartle. Hawking proposed a description of the Universe in its entirety, viewed as a self-contained entity, with no reference to anything that might have come before it. The description is timeless, in the sense that one set of equations delineates the Universe for all time. As one looks to earlier and earlier times, one finds that the model Universe is not eternal, but there is no creation event either. Instead, at times of the order of 10-43 seconds, the approximation of a classical description of space and time breaks down completely, with the whole picture dissolving into quantum ambiguity. In Hawking's words, the Universe "would neither be created nor destroyed. It would just BE."

So, the origin of mass in the Universe and the Universe itself is quite speculative at this point. If you are interested, you can read Alan Guth's book "The Inflationary Universe", page 271-276. You can also read Hawking's "A brief history of time: From the Big Bang to black holes" page 136.

Big Bang

What was there before the Big Bang and what is there outside of our universe?

We can define the universe as everything there is, so in that case there is nothing outside of it. We also say that space and time both started at the Big Bang and therefore there was nothing before it.

Another definition for the universe is the observable universe - which is the part of it that we can technically see. We cannot know what is outside of that (since we can't observe it), but we think that physics works the same everywhere and so we think that it should be very similar to the observable universe. We actually think that the universe might be infinite in extent, and so goes on forever, even though we can only see a finite part of it.
We can speculate in meta-physics or in religion about what was before the Big Bang, but again, we cannot use science to tell anything about it as physics as we understand it breaks down at that point.

About the Universe

What makes up most of the Universe?

For a long time, astronomers thought that almost all of the Universe was made of regular matter (called "baryonic matter". It is the same kind of matter that makes up everything on earth and all the stars (protons, neutrons and electrons)). However, they have now found out that this baryonic matter was only a small fraction of the matter in the Universe.

By measuring the motion of galaxies, and of stars inside galaxies, astronomers have been able to determine that there exists also some matter that we cannot see. They know that because even though they cannot see it, they measure the effects of their gravity on these stars and planets. This is what we called "dark matter".

There is also something that makes up most of the Universe and that we refer to as "dark energy". The nature of this dark energy is completely unknown, but we know it behaves quite differently from regular matter. It is believed it has an opposite effect to gravity pushing everything apart and thus contributing to the expansion of the Universe.

Very recent observations of the Cosmic Microwave Background have revealed the relative fractions of each of these components. The best estimates now say that the Universe is made of 4% regular baryonic matter, 23% dark matter and 73% dark energy.

Water in the Universe

Where did all the water in the universe come from?

Hi, water water everywhere--but where did it come from?
Our solar system is made of star stuff, did our water form during a super nova? Can H2O exist in stars?

No, H20 cannot exist in stars, but H and O separately can. Hydrogen is the basic building material of the universe, created in the Big Bang. Oxygen is created by nuclear reactions in stars. If you put H and O together in the cold of space, you get H2O. There are enourmous amounts of water in space. In fact, nearly all of the oxygen in space is in the form of water or carbon monoxide. Similarly, most the carbon and nitrogen in space are also in their most hydorgenated forms: methane (CH4) and ammonia (NH3).

Mass of the Universe

Mass of the Universe

What is the mass of the Universe?

Also how can you prove that this is the true mass of the Universe?

As nobody knows the size of the universe, one cannot really talk about the mass of the universe, though one can talk about the mass of the observable universe. What is normally sought after is the density of matter in the universe (which is the mass per unit volume). This is what is important in determining the fate of the universe: whether it will collapse one day or whether it will continue expanding forever.

The density of matter in the universe can be measured by various means, which are too technical to go into at this point: people measure the density by studying the fluctuations in the Cosmic Microwave Background, superclusters, Big Bang nucleosynthesis, etc.

According to these studies, the density of matter in the universe is about 3 x 10-30 g/cm3, which means that it is 300 billion billion billion times less dense than water. Note that this includes the contribution of dark matter and so the density of luminous matter (that we see as stars and galaxies) is only about one-tenth of the figure given above.

Now, the size of the observable universe is about 14 billion light years, and using the above value of density gives you a mass (dark and luminous matter) of about 3 x 1055 g, which is roughly 25 billion galaxies the size of the Milky Way.