For millennia, the question “why are we here?” has intrigued man. It will likely continue to do so for all time.

But science is finally close to answering not the why, which belongs to philosophers and theologians, but the how.

The Big Bang Theory is the most commonly accepted theory of how the universe got to where it is today, but it is not, as it is so often characterized in popular media, a theory of the beginning of time.

What the Big Bang Theory describes is actually what happened immediately after the Big Bang, a cosmological event about which we actually know very little. But that science is willing to admit its limitations doesn’t discredit the theory.

Maybe the most damaging popular misconception about science is the notion that a theory is something like a guess, and that any old “theory” might hold equal weight.

It doesn’t.

For something to become a scientific theory, it must start as a hypothesis. It must make predictions, followed by experiments, observations, peer-reviewed reports and a revised hypothesis. If it’s good, it may reach the status of “theory” — just short of fact.

The Big Bang Theory is no more dismissible than the theory of evolution or the theory of gravity.

Several interesting aspects of our universe make it possible to learn about things happening 13 billion light years out into space — and 13 billion years into the past.

The speed of light is incredibly fast, but finite and measurable. A light year is the distance light travels in one year. So, if we’re looking at a galaxy eight million light years away, we’re actually seeing that galaxy as it was eight million years ago. Light from our own sun takes eight minutes to get here, so what we see is actually what was there eight minutes ago.

Light is the only thing that we can use to gain any knowledge about the universe outside our own immediate solar system (which is too tiny to even consider on a cosmological scale — the scale is even worse than a grain of sand compared to the whole Earth). But light is enough for us to gather several key pieces of evidence for the Big Bang.

The top three are the expansion of the universe, the cosmic microwave background (CMB) and the abundance of helium.

We know the universe is expanding, and as of the last decade or so, we know the rate of the expansion is actually increasing due to a mysterious force, a type of vacuum energy inherent to space itself scientists have dubbed “dark energy.”

Light from all distant galaxies is redshifted, and the further the galaxy, the more dramatic the redshift. This is known as the Doppler Effect, and as an object moves away from you, the space between you increases, stretching out the waves. The faster the receding motion, the greater the redshift. Imagine standing next to a train track, and as the train approaches the pitch gets higher and higher — the waves are being compressed — and as it goes past, the pitch immediately drops as the waves are stretched.

The CMB is a relic of the Big Bang event. Every direction we look, space itself seems to have a temperature of roughly 3 degrees Kelvin, a standardized scientific unit which sets the zero degree at zero molecular motion. It’s what we’d expect if the Big Bang model were correct.

Another thing we’d expect is a particular abundance of atoms. The nearby universe is comprised of roughly 74 percent hydrogen, 23 percent helium and 3 percent heavier elements. Immediately following the Big Bang event, the universe was uniformly hot enough to combine two hydrogen atoms, the simplest element, into a helium. Observational data matches predictions nicely, the hallmark of a solid theory.

But if the Big Bang Theory refers to what happened after the Big Bang event — such as the first formation of atoms, the separation of forces and eventually the creation of primordial stars and galaxies — it remains to be seen what the event itself actually was.

Scientists cannot address what actually happened because of a fundamental block. Time is also finite. It began 10^-43 seconds after the Big Bang — that’s a 1 behind a decimal and 42 zeroes. Before this point, we cannot look. This is where the laws of nature “begin.” This limits our ability to peer back all the way up to the Big Bang.

Several possibilities exist to explain this. One current theory holds that time itself travels at intervals of 10^-43 seconds, a kind of minimum step known as Planck time. Therefore, we can’t look before this time, because there is no time before it.

One theory is that a previous universe collapsed in on itself in a “Big Crunch” and exploded back out in a “Big Bounce.”

Recent calculations make it seem unlikely we live in a cyclic universe of that type. Measurements suggest the universe is just going to continue expanding, faster and faster. Gravity will be overpowered by dark energy, this force of expansion. First galaxies, then stars and planets, then atoms themselves will be separated by vast distances of space in what’s called the “Big Rip.”

Indeed, the expansion will become so incredibly powerful each molecule of your body will tear apart and go flying away from every other molecule of your body.

The good news is, you won’t have to worry about that unless you plan on living another 20 billion years or so.

But far from being mere speculation or mystical voodoo, scientists actually do have a firm understanding of how the universe got where it is today and where it may be headed. Expressions like “just a theory” don’t hold up to the knowledge which actually backs a theory.

If you disagree, feel free to argue against the theory of gravity by floating off into space somewhere.

Respond to Kyle at [email protected]