Whether he's teaching class, socializing at a cocktail party or talking to visitors at the planetarium where he works, Charles Liu knows that sooner or later he's going to get asked at least one of three questions:
Is there a god? Are there aliens? What would happen if I fell into a black hole?
"I've never been in a public environment where people know what I do where at least one of these questions was not asked," Liu said. He is an astrophysics professor at the City University of New York's College of Staten Island and an associate at the Hayden Planetarium at the American Museum of Natural History.
Over the years, Liu has developed some pretty solid answers, based on scientific evidence and his own opinion, to those three burning questions. Here's what he told us.
Is there a God?
"What I tell people is that science in general and astronomy in particular do not address the question of whether or not there is a God. In science, conclusions are made based on evidence and confirmation of predictions, and that's what differentiates scientific knowledge from unscientific knowledge.
"Recently Pope Benedict said something like this: 'The Big Bang theory is proof that God exists.' Actually it's not. It's only proof that something happened at the beginning of the universe, where there wasn't space or time and then there became space and time. For many people, astronomers' discoveries confirm what they thought was true all along: that God is there. And then for many others, the discoveries of astronomers confirm what they thought all along, and that is that God is unnecessary that God doesn't exist.
"So the Big Bang doesn't really prove whether God or the gods are real or not, or whether the flying spaghetti monster is real or not; it's just really, really cool and what you believe follows from it is just a leap of faith. [Read: Was the Big Bang Really an Explosion? ]
"One last twist to this answer: People ask, 'Well, what do you think?' And what I say is, 'I don't know.' I think that the universe is beautiful, complex and fascinating. And I have not seen any evidence to show that an omniscient or divine being has to exist in order for the universe to be the way it is. But there's nothing to say that it can't exist, either."
Are there aliens?
"Yes. The universe is so vast, and the laws of nature are so consistent throughout that vast universe, that the chances of life developing in only one place in that entire universe is essentially zero. If life appeared in one place, it's got to appear other places. [Read: What Are the Ingredients of Life? ]
"So, do extraterrestrials exist? Yes. But do extraterrestrials land on Earth crash near Roswell, New Mexico? No. None of the so-called evidence of extraterrestrials here on Earth has held any water when it comes to scientific, rigorous, skeptical testing.
"Will we ever make contact with them? Since the advent of broadcast radio, radio signals leaving Earth have traveled about 50 light-years, or 300 trillion miles. But our Milky Way galaxy alone is 600,000 trillion miles across. So those radio signals would have to go for centuries more before they even got a small fraction of the way across our galaxy. So a civilization somewhere else in our galaxy would have almost no chance of picking up our signals unless they were really nearby.
"Similarly we, in all of our efforts, would barely be able to detect radio signals from a nearby star, let alone a faraway one. So are there chances that we will be able to make contact with extraterrestrial life? It's always possible, but the chances are just very, very remote."
What would happen if I fell into a black hole?
"There's a two-stage answer. Here on Earth, we have tides . How that works is basically that the moon pulls on the side of the Earth closer to it a little bit more vigorously than the side away from it, and as a result, Earth elongates ever so slightly depending on where the moon is. Now the land is pretty sturdy, so you don't see it moving that much, but the water on the surface of the Earth is fluid, so it flows along that elongated axis. That's the tidal interaction.
"Now when you get close to a black hole, that tidal interaction is magnified off the scale. So if you were, say, diving head first into a black hole, the top of your head would feel so much more gravitational pull than the tips of your toes that you would be stretched, longer and longer, until really you resembled toothpaste being extruded out of the tube. Sir Martin Rees coined the term 'spaghettification,' which is a perfectly good way to put it. You eventually become a stream of subatomic particles that swirl into the black hole. [Read: What's at the Center of Black Holes? ]
"What might be even more interesting to think about is what happens if you fall into the black hole and somehow can prevent being stretched like that. Turns out that the bigger a black hole is, the less extreme its surface is. If you have a black hole the size of, say, planet Earth, you would certainly turn into spaghetti, no question. But if you had a black hole the size of our solar system, then the tidal forces at the 'event horizon' that is, the point of no return for the black hole are not quite that strong. So you could actually maintain your structural integrity.
"In that case, what happens if you start experiencing the effects of the curvature of space-time, predicted by Einstein's general theory of relativity ? First of all, you approach the speed of light as you fall into the black hole. So the faster you move through space, the slower you move through time.
"Furthermore, as you fall, there are things that have been falling in in front of you that have experienced an even greater 'time dilation' than you have. So if you're able to look forward toward the black hole, you see every object that has fallen into it in the past. And then if you look backwards, you'll be able to see everything that will ever fall into the black hole behind you. So the upshot is, you'll get to see the entire history of that spot in the universe simultaneously, from the Big Bang all the way into the distant future."