By Andrew Hendricks
Astronomy enthusiasts are torn when they encounter people who know little-to-nothing about astronomy basics. On the one hand, it's positive to have anyone interested in hearing and learning some amazing, cool stuff that goes on in space, and on the other it can be really disheartening for us to encounter full-grown adults who don’t know anything about the really big questions that have been answered.
Take a moment to consider the Earth, and where you live in relation to the universe. Try to make sense of where you are, and close your eyes, imagining it. Do you feel like you have a real grasp of where you are? Or were you just happily dreaming up the pretty astronomical images of nebulae and moons and stars?
It's a big bad universe, and just like you should know your home address, city, and state, you should know your relative location in this universe, and a little bit about our stellar neighborhood.
It's called a Super-Massive Black Hole
If a nerdy ten year old knows anything about astronomy, he knows about black holes: infinitely condensed points of space and time crushing matter to a singularity. Raw power distorting the natural world in a way our brains did not evolve to process. Cool, huh? But old news to most.
I found it shocking how many people have seen images of our galaxy, think black holes are nifty, and don't know that at the very center of our universe, there is what is known as a Super-massive Black Hole around which our galaxy is revolving, not too dissimilar from the way our earth revolves around the sun.
We are certain that our Milky Way Galaxy has one at its center, and we're pretty sure it's a common feature among galaxies across the universe. Making them even more enticing, famous astrophysicist Stephen Hawking once mentioned that were he given the option, before he died he would like to go into a super-massive black hole. His reason being that because the tidal forces of a SMBH are much less at the event horizon than a regular black hole, you could potentially make it into the super-massive black whole (where you will still probably die, being crushed down to a density not advisable for human life) without going through a horrifying process known as spaghettification.
While I don't know if I'd prefer dying a normal death in lieu of being plunged into our galaxies trash compactor, it's good to know not to fall into a regular black hole if I want to avoid the astronomical equivalent of being put on “the rack”: lengthened, stretched, and tortured for a distorted amount of time approaching infinity.
But super-massive black holes—those are cool.
We won’t always be able to prove the Big Bang
The universe began with an infinitely dense and incredibly hot point of space from which matter expanded in all directions, cooled, and became the universe we now know and love. It seems like for every meaningful fact we discover about the universe, there is an oppositional force motivated by philosophy rather than science. Also, it doesn't help that the scientific use of the word theory and the colloquial usage of the word are quite different. Electromagnetism is a theory. It still works. A hypothesis is something conjectured that may or may not be true, and needs to be tested. A theory is a quantified way of looking at existing, tested knowledge.
The big bang isn't just an assumption about how the universe began based on models—we can directly measure its effects. Roughly 1% of the static you see when turning on older televisions is actually background radiation from the big bang. In 1965, two astronomers were awarded the Nobel Prize for detecting this Cosmic Microwave Background Radiation that pervades our observable universe. Measurements of hydrogen and helium distribution back up what we would expect them to be from the big bang. To put it quite simply, it happened, and we know it happened.
What is most fascinating about the firm proof on which the Big Bang theory of the universe is that we are lucky we got it when we did. We are actually losing our ability to measure the concrete evidence that is the cosmic microwave background radiation. This is because we are in an expanding universe, and one that is expanding at an accelerating rate. Brian Greene put it most eloquently in a recent TED oriented towards astrophysics. He says:
“Because the expansion is speeding up, in the very far future, those galaxies will rush away so far and so fast that we won't be able to see them—not because of technological limitations, but because of the laws of physics. The light those galaxies emit, even traveling at the fast speed, the speed of light, will not be able to overcome the ever-widening gulf between us.
"So astronomers in the far future looking out into deep space will see nothing but an endless stretch of static, inky, black stillness. And they will conclude that the universe is static and unchanging, populated by a single central oasis of matter that they inhabit—a picture of the cosmos that we definitively know to be wrong.”
It's kind of sad and interesting to imagine a future in which the most intelligent scientists may look at our accurate models of a vast and enormous the universe with literally hundreds of billions of galaxies—and think it is merely error-riddled data from a primitive people who didn't understand how empty the universe really is.
Our galaxy is colliding Andromeda (oh, and the Heat Death of the Universe)
Because evidence of the big bang has proved conclusively that the universe is expanding at an accelerating rate, this has led some to have the image of a universe where everything is moving away from each other. And this notion of the universe is not quite true—yet. This misunderstanding is partly due to lack of knowledge about what we currently know about gravity and dark energy, which is the placeholder term for whatever is the reason behind the acceleration of the expansion (as opposed to what had previously been thought to be a steady-state expansion).
Gravity works by what is known as an inverse-square law. This means it is a lot weaker the further away it is. You step one foot away from an astronomical body, and its gravitational pull on you is four times weaker than it was where you were previously standing.
So currently, clusters or super-clusters of galaxies are still either held or attracted towards each other, however the clusters themselves are moving apart with the expansion of the universe. In fact, our galaxy, the Milky Way, is currently on a collision course with Andromeda as we are still gravitationally bound inside our larger galaxy cluster. This collision (which isn't so much a smashing of matters and stars so much as two galaxies merging their materials into new orbits) won't be happening for another four billion years, scientists estimate.
However, even though gravity is still able to hold on in pockets of galaxies, the reason for the mistaken belief that everything is moving away from everything else, is that this is the theorized endgame of the universe. Complete Heat Death, is a term some scientists use to describe it. As entropy increases and clusters of galaxies are undetectably far away from each other, the galaxies themselves will begin to separate from each other—dark energy finally winning a battle with gravity hundreds of billions of years in the making. As galaxies are pulled apart, eventually individual solar systems will be too, with planets being pulled apart from their star. Stars being pulled apart at the seems, and even atoms stretched and diffused to the point of absolute zero. Our universe began with a fiery bang, but it will die with a whimper. At least, this is the current best guess.
Do aliens believe in you?
But don't be too bummed. You'll be dead long before our universe falls apart at the seems. We're still here now, and you might find it important to know that you're already in the process of saying hello to the neighbors.
Plenty of you may have seen the movie Contact and know we're currently beaming radio waves, advertising our presence in an ever-expanding sphere in all directions outward from Earth. While this could give some intel about humans to other beings listening in, information about us gained solely from our emissions would be a schizophrenic picture of human beings to say the least.
But have no fear! As originally advocated by Carl Sagan (interestingly the author of the novel Contact) at least four current probes are rocketing away from our solar system into the interstellar medium with some very sensitive information about our species. Pioneer 1 and 2, some of the first missions to explore Saturn and Jupiter, had in their payload what has since been dubbed the Pioneer Plaque. Launched in the late 60s, the Pioneer missions were to continue out of the solar system after their flyby studies of planets on the way. Sagan and others thought it would be a good idea to give a message of sorts, to beings that could potentially intercept Pioneer.
Sagan said of the Pioneer Mission and its plaque that "The spacecraft will be encountered and the record played only if there are advanced space faring civilizations in interstellar space. But the launching of this bottle into the cosmic ocean says something very hopeful about life on this planet."
The Pioneer Plaque displayed two naked humans, male and female, silhouetted in front of an image of the probe to give a scale of who we are. It also included a diagram map of where we are, relative to 14 different pulsars and the center of our Galaxy along with a symbolic representation of the lowest state of hydrogen—the most common element in the universe.
Not content at merely giving away our GPS coordinates and revealing our naked vulnerable bodies, when it came time to launch the Voyager mission during the Carter administration, these probes were packed with a golden record, that was a slightly more ambitious reveal of human life to other beings. It is an audio-visual phonograph and has instructions for how a being can play it. On this record is a huge collection of images and sounds. Greetings in fifty-five languages, sounds of birds chirping and thunderclaps, and images many of us would all agree are uniquely human. Voyager, which was launched just years after Pioneer and significantly faster, has actually surpassed the Pioneer probe, and is now the furthest man-made object from Earth, and the first to ever leave the solar system. Discussing the Voyager mission, Jimmy Carter gave his famous message:
“This Voyager spacecraft was constructed by the United States of America. We are a community of 240 million human beings among the more than 4 billion who inhabit the planet Earth. We human beings are still divided into nation states, but these states are rapidly becoming a single global civilization.
"We cast this message into the cosmos. It is likely to survive a billion years into our future, when our civilization is profoundly altered and the surface of the Earth may be vastly changed. Of the 200 billion stars in the Milky Way galaxy, some--perhaps many--may have inhabited planets and space faring civilizations. If one such civilization intercepts Voyager and can understand these recorded contents, here is our message:
"This is a present from a small distant world, a token of our sounds, our science, our images, our music, our thoughts, and our feelings. We are attempting to survive our time so we may live into yours. We hope someday, having solved the problems we face, to join a community of galactic civilizations. This record represents our hope and our determination, and our good will in a vast and awesome universe.”
It's hard not to get a little choked up at the sentiment contained in this message. But, geeze Jimmy, I can't help but still be a little disconcerted at the detailed information we've been purposely sending out. Living peacefully in a galactic society is great and all, but the heartwarming greeting is essentially an admission of how useless we are when it comes to space travel. I have to wonder if there were National Security Advisers standing beside Carter when he was drafting his message, urging him to slip in a little disinformation. It wouldn't hurt for other civilizations to believe we have the ability to blow things up with our minds rather than knowing what sitting ducks we really are.
In reality, debates about whether we should or shouldn't broadcast our location and existence don't really matter any more. We've already done it. We're currently still doing it. The cat's out of the bag, and we have to just hope that any intelligence that stumbles our way is benign, if curious, or wimpy, if malevolent.
At least now you know a little bit more about your stellar neighborhood if they do come knocking.