For centuries humankind has been fixated on the sky. We’ve created mythology around the constellations, built the Hubble telescope, and ventured into the uncharted terrain of space, all to answer life’s great question: Are we alone in the universe?
The universe is scary. After all, it’s a black, anti-gravity abyss that contains gigantic balls of fire, black holes that shrink mass to oblivion and meteors streaming through the galaxy. What in the world is going on with the universe?
It started with a bang
The “Big Bang” is what we call space being rapidly added amongst the parts that make up our universe.
Imagine the galaxies as little spots on a rubber sheet, and then stretch it. This is what it looks like to add space by a fractional increase ever so slowly over a very large distance.
In order for something deep in the universe to communicate with us, it essentially has to run along that stretching rubber sheet.
Jeffrey Hutchinson, a physics professor at FGCU, explains that since the Big Bang happened 13.8 billion years ago, a long yet finite amount of time, there is a set amount of objects that could even in principle communicate with us.
It could be that other life forms have been trying to send us a signal that has never been able to reach us. There has never been enough time. A galaxy that’s billions of miles away could be sending us a signal, but it would take billions of years for the light to reach us.
We gaze along a cosmic horizon
If you’re on the ground looking out at the horizon, there’s only so far that you can see. Similarly if you look into space, there’s only so far that humans have been able to observe.
This is what’s referred to as our cosmic horizon, the space that contains our observable universe.
“The observable universe is the edge to what we know,” Hutchinson said. “But that doesn’t mean that space ends there. To all of our ability to measure it looks like space could be to no end. It could truly be infinite.”
A pencil that stands upright forever
According to Hutchinson, space appears to us to be flat, or regular, like an infinitely large plane. However in theory, the shape could change over time and unless you have exactly the right density and it’s very flat it tends to curve in one or two directions.
Hutchinson compares the perfect coincidence of matter that makes up space to a pencil that miraculously stands upright.
“It’s like a pencil that’s standing head on,” Hutchinson said. “If it’s done just right it will stand up forever but you have to be really precise in making sure that it’s straight upwards otherwise it’s going fall one way or another. The same thing happens with space.”
It’s been almost 14 billion years and the pencil is still standing upright. How could this be?
The answer to this is the theory of inflation.
The universe is like a balloon
Inflation flattens out space, ironing it super broad and giving it the appearance that it goes on infinitely.
“The idea is to imagine a balloon,” Hutchinson said. “A balloon that’s not blown up is wrinkly and curvy, but if you blow it up, it gets to be nice and smooth. Even if it wanted to crinkle on itself naturally if you very very quickly blew it up you would smooth it out and would take a really long time to crinkle back up.”
This rapid expansion that started our universe is problematic in nature. It expands but it doesn’t dilute. Once it begins, it’s hard to stop.
An army of rabbits barrel into the sky
In order to imagine how space grows imagine a generation of rabbits reproducing.
Hutchinson suggests imagining a generation of rabbits that keeps exponentially doubling. Two rabbits become four rabbits become eight rabbits become 16 rabbits and so forth. In this army of rabbits, they don’t die of old age and they don’t run out of food, but in every generation you kill one.
“If you keep doubling and only kill 1 percent average each generation, you’re not going to run out of rabbits,” Hutchinson said.
According to Hutchinson, what happens is that some little region, like the one we live in, suddenly becomes stabilized. However there are other places out there where this inflation is still going on.
“Way out there you still have an infinite sea of this funny stuff making more of itself and making more space that has it” Hutchinson said.
Hutchinson says that given how vast the universe is, and how much space is being generated, it’s very likely that our universe has a large number of sibling universes.
The String Theory is born
“Scientists have been hoping that one could come up with some idea to say ‘this is the right one’ that explains all that we see with one idea,” Hutchinson said. “But it looks like that’s not the case. Something that looks very simple at high energies could look very different and complex at low energies.”
Water vapor is easy to describe. As you cool it down, molecules stick together and form the pattern of snowflakes which form in a tremendous variety of ways. Even though you can describe vapor you can’t predict the snowflake.
Not unlike snowflakes, the phenomenal forces in the string theory are easy to describe at high energies but those forces sort of “freeze” like snowflakes. The idea is that the forces we see now are just the one way that they have frozen.
Take for example the size of the electron. We have no idea why it’s the size that it is, but it effects every aspect of the matter around us that makes up our lives. In a different universe, when things became stabilized, the atom might have been formed in an entirely different way, which would dramatically alter life on those far away planets.
The idea that there are multiple sections of the universe like ours is highly probable, but each “bubble is it’s own snowflake.” If we were able to peek into another universe, it might look very different than ours.
It might be that human beings are only able to survive in our patch of the universe, but that other beings are thriving in galaxies far far away. For now, all we can do is stare at the sky and speculate.