| The first age of the universe is what we call the Primordial Era, which is really the Big Bang Theory. In the beginning, there was no real space or time, because space and time had not yet separated. Also, in this Primordial Age, quantum theory and general relativity have to be incorporated in a theory ofquantum gravity to describe the universe. At this moment, the universe is roughly 10 to-the-minus 43 (10-43) seconds old, and out of this quantum gravity epoch, some type of nucleation event leads to the production of our universe. What this means in practice is that some small region of space-time bursts into existence, and "into existence"means, in this context, that space and time became defined in that tiny region. From that moment onward, our universe, as a universe, exists, and it is the goal and job of cosmologists to how that evolves. Here’s the story. The first thing that happens in the universe's existence is that it starts inflating incredibly rapidly. This early phase of extremely fast expansion explains many of the properties that we see in our universe today, such as why it’s homogeneous and isotropic (in other words, why the universe is the same everywhere in space and why it looks the same in all directions that we look in the sky). This early burst of rapid expansion also explains why the universe is as old and as flat as it is. This inflationary stage occurs when the universe is about 10-37 seconds old. In the early stages of the universe, everything is in the form of radiation. Particles and anti-particles come in and out of existence on a regular basis. Between that time and the one-microsecond mark, perhaps the most important event in the early universe happens. Matter is created. Now, most of the laws of physics are symmetric with respect to matter and anti-matter. And the physics experiments that we've done so far support the theory that when you create matter, you also create an equal amount of anti-matter (that can annihilate with matter). But we don't live in an anti-matter world. If you touch the person next to you, you don't explode. When we landed people on the moon, the astronauts didn't explode in a matter-anti-matter reaction. What that means is that everything in this room or on the moon is made of matter and not anti-matter. Through more indirect methods, astronomers have successfully done this experiment across the universe, almost all the way to our cosmological horizon today. In that whole volume, as best we know, all material is made of regular matter and not anti-matter. This is very important. What this means is that during the first microsecond of cosmic history, some process set up an asymmetry between matter and anti-matter, producing a little bit of extra matter. The amount of excess matter that was produced in the earliest existence of the universe was tiny. If you had 30 million anti-matter quarks, it would annihilate 30 million matter quarks, with one quark left over made of regular matter. That one extra matter quark in 30 million is just like a contaminated residue, but that’s the only thing that survives the early universe to become everything that you would call ordinary matter in our universe today. After the microsecond mark, those excess quarks condense and make protons and neutrons for the first time. This event has profound implications for the future of the universe. Namely, if there is a process that can prefer matter over anti-matter, or the other way around, such a physical process is still around. If we know that there's a process that can be asymmetric with respect to matter and anti-matter, then every proton in the universe is eventually doomed. We think that protons live longer than 1033 years, but somehow, some way, in the far future all of the protons will decay. So matter is not forever. It lives from the microsecond mark in the universe, and it only lives until protons decay, sometime later in our story. By the time the universe is one second old, it has cooled enough that protons and neutrons can get together and form large nuclei like helium. The amount of helium that is produced in this early burst of nucleosynthesis--that starts when the universe is a second old and ends when the universe is about three minutes old--is the vast majority of all the helium in our universe. Stars produce helium today, but this early burst of nucleosynthesis generated more helium than all the stars that have ever lived anywhere in our universe. Similarly, this early interaction produced more energy than has been generated by all the stars in the universe today. This is an enormously energetic event. It is the smoking gun of Big Bang Theory. Without this theory, there's no other way to account for the helium that we see today in our universe. We also feel that the Big Bang Theory is on solid footing because if the universe did go through such an early hot dense phase, there should be some residual radiation left over, which can be called the afterglow of the "Big Bang." And we can see this radiation in the sky. The whole universe is filled with a pervasive sea of microwaves. In fact, the universe is similar to a really low-power microwave oven. What's more, if the universe were hot and dense in its earliest phases, then the distribution of the energy in this background should have a certain blackbody shape. This shape indicates that there's almost no way that this radiation could come from anything other than an early, hot, dense "big bang." What's more, although the universe is very homogeneous in that the temperature in this microwave background is the same everywhere in the sky, it's not quite the same. It's only the same to one part in a hundred thousand. And this departure of one part in a hundred thousand is very significant. First of all, it's a heroic effort to measure; it wasn't measured until the very early 1990s. Most importantly, these small fluctuations eventually form the galaxies. They condense through gravitational contraction, and eventually condense into galaxies, clusters of galaxies and larger-scale structures. 
NASA and The Hubble Heritage Team (STScI/AURA)
Acknowledgment: N. Scoville (Caltech) and T. Rector (NOAO) | Images from NASA's Hubble Space Telescope are helping researchers view in unprecedented detail the spiral arms and dust clouds of a nearby galaxy, which are the birth sites of massive and luminous stars. The Whirlpool galaxy, M51, has been one of the most photogenic galaxies in amateur and professional astronomy. Easily photographed and viewed by smaller telescopes, this celestial beauty is studied extensively in a range of wavelengths by large ground- and space-based observatories. This Hubble composite image shows visible starlight as well as light from the emission of glowing hydrogen, which is associated with the most luminous young stars in the spiral arms. Intricate structure is also seen for the first time in the dust clouds. Along the spiral arms, dust "spurs" are seen branching out almost perpendicular to the main spiral arms. The regularity and large number of these features suggests to astronomers that previous models of "two-arm" spiral galaxies may need to be revisited. The new images also reveal a dust disk in the nucleus, which may provide fuel for a nuclear black hole.
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