We all know where we come from, why the universe is the way it is, and what the laws of physics that govern it are. However, even with a thorough knowledge of those laws, we're at a loss to explain what else is out there and how that came to be.
We know almost all there is to know about the fundamentals; what we lack is knowledge of how they combine to give rise to new phenomena. The universe isn't magnanimous enough to let the laws and effects operate in isolation. In fact, in some parts of the universe, things are so crammed that hundreds of thousands of laws collapse into what we call a black hole, the aptly named singularity: a oneness.
[caption id="attachment_22790" align="aligncenter" width="338" caption="Where all our laws go to die"]
[/caption]There are many such incidents of apparently inexplicable behaviour, which is what makes astronomy and cosmology fascinating: people think that the only way out of this mess of human unawareness is to delve deeper into the atom, but at the other end of the physical spectrum, there's a host of things happening that we might not be able to understand at all even if we found all the particles there are to be found.
This post doesn't discuss the unknowns and the unknowables but some examples of the cohabitation of events born of separate evolutionary processes. In fact, that's where the definitive characteristics of the unknowables reside, within the little loopholes which are widened over time by repetition and preservation.
[caption id="attachment_22802" align="aligncenter" width="494" caption="Pi is a natural mathematical constant, describing the ratio between the circumference and the diameter of all circles. To know why it stands close to 3.14, we must known how it came to be. And to figure out how it came to be, we must understand all about how it works. Just like how we learn about the universe."]
[/caption]For example, the reason it's so hard to find the Higgs boson is linked intricately to why the universe contains galaxies that are millions of times denser than its mean density. The value of the mean density was measured using the Wilkinson Microwave Anisotropy Probe (WMAP), which studied the coupling radiation emitted when protons and electrons combined to form the first hydrogen atoms.
And why did that happen? It happened because of something called baryon acoustic oscillations (BAO), which were the cause for large empty spaces in this universe called voids.
[caption id="attachment_22794" align="aligncenter" width="593" caption="An artist's depiction of the WMAP in space. The spacecraft was launched in 2001 as a joint project by NASA and Princeton University."]
[/caption]Let's start with the density thing. When the universe was born, there were particles called quarks, gluons, leptons, and bosons. Bosons (photons) were force mediators, leptons were light particles (electrons and neutrinos), gluons were sticky things that held quarks together, and when quarks were held together in twos and threes, they were called baryons and mesons.
At some point, because of the extreme heat, these particles coalesced into a plasma while the universe expanded around them. When things expand, the amount of energy they contain is distributed across a larger and larger volume. As a result, the temperature at each point inside the system drops. Similarly, when the universe had expanded enough to bring the temperature of the plasma to 3,000 K, protons and electrons had lost enough energy to combine and form the first hydrogen atoms.
Now, the plasma also contained photons, which do not engage with neutrally charged entities. When the electrons and protons were floating around uncoupled, photons were being scattered around by them as they increased and decreased the frequency of their vibration. Once coupling occurred, the photons were let loose throughout the universe, having no particles to engage with.
[caption id="" align="aligncenter" width="384" caption="The Standard Model of Elementary Particles shows the quarks (in purple), leptons (in green) and the bosons (in orange)."]
[/caption]This release led to the universe acquiring a colour. Better known as colour-temperature, it arose because the fleeing photons had a certain amount of energy attached to them, energy that is even today being lost as heat and light. This radiation was called the cosmic microwave background (CMB) radiation.
At present, because of the CMB, the temperature of the universe is around 2.7 K. As the universe expands further, so will its temperature drop as the photons chart larger and larger territories.
This is what scientists map when they operate the WMAP, and the resulting spectacular image shows the concentration of this radiation in the entire universe: some regions can be seen to be hotter than the rest (note that radiation-hoarding is a reflection of matter-concentration).
[caption id="attachment_22783" align="aligncenter" width="480" caption="Behold! The WMAP data!"]
[/caption]Looking at the WMAP map, there are regions visible that seem to be colder than others. Given how much the universe has been scaled down to in the above image, it becomes obvious that these cold volumes are actually HUGE voids - a vast space within which there is (or can be) close to nothing.
Since the amount of CMB radiation within them is minimal, it's safe to assume that these voids' innards have been graced with bare minima of light, leaving them dark and effectively dead.
The Big Bang model argues that such voids could have come into existence only if the original distribution of particles at the beginning of time had a directional-dependency, a feature called anisotropy. The existence of an anisotropy predicates that any event occurring involving just that set of particles will be obliged to proceed more along one direction than in any other direction.
[caption id="attachment_22800" align="aligncenter" width="450" caption="Voids are CMB cold-spots whereas clusters are CMB hot-spots."]
[/caption]The Big Bang was one such procession, and the directional dependency showed up as matter being concentrated in a few directions and diluted in the rest. The directions of dilution are now occupied by voids. The directions of concentration, on the other hand, are occupied by the largest structures observable by humankind in this universe: galactic filaments.
A galactic filament is a cluster of galaxies held together by the weak gravitational force between them, essentially aligning a star-beaded string tens of megaparsecs long (1 megaparsec is 3.26 million light-years) in space. Broadly speaking, filaments form the boundaries between which voids and supervoids exist. Ever since astronomers began looking for them in 1980, three really massive megastructures have been discovered:
- Pisces-Cetus Supercluster Complex (PCSC) - Discovered in 1987 by Brent Tully, an astronomer at the University of Hawaii, the PCSC contains the Virgo Supercluster, a part of which is the Local Group that contains the Milky Way.
- Sloan Great Wall - Richard Gott III and Mario Juric of the University of Pennsylvania spotted the Sloan Great Wall when working on the Sloan Digital Sky Survey. It is a gigantic wall of galaxies that forms part of a filament that spans ~1.37 billion light-years in length. The Great Wall is located 1.0 billion light-years from Earth and is the largest structure known to humankind.
- The Lyman-alpha blobs - These blobs are essentially extremely large concentrations of gas that stretch for 400,000 light-years at a time, making them the largest individual entities known to humans. They are called so because they emit ultraviolet radiation corresponding to the Lyman-alpha line in the electromagnetic spectrum.
[caption id="attachment_22801" align="aligncenter" width="474" caption="An image of the Sloan Great Wall (left) and the PCSC (right) reconstructed using the Delaunay tessellation field estimator (DTFE)."]
[/caption]Let's forget these things making humankind look insignificant: marvel at how a tiny species of beings has pieced together a large-scale picture of the universe that made life possible. We started off by asking what is out there. By now, there is possibly only lesson worth learning: that no matter how far and wide anything is scattered, the laws of physics will be there. Of course, we might not be able to explain some things, but receiving constant affirmation that nothing anywhere has ever fallen outside the laws' ambit is reassuring and, most importantly, promises that persistence will be rewarded.
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