In our February cover story, “Before the Big Bang,” author and Time magazine senior writer Michael D. Lemonick explores the idea that the Big Bang was triggered when our three-dimensional universe collided into another three-dimensional universe hidden in higher dimensions. Rather than being the beginning of everything, the Big Bang was but one cataclysm in a long, perhaps infinite cycle of collisions and cosmic rebirths.
Needless to say, we got a large number of amazed and curious letters. Through our new Web-exclusive feature, the Expert Forum, readers had a chance to pose their questions directly to Lemonick, whose answers to about two dozen of these queries appear below. “I'm impressed with how Discover readers absorbed a mind-bending concept and came back with so many thoughtful and challenging questions,” he says.
Full name: Donna Frisoli
Question: Were you saying that the universes are flat? I’m a little confused about that because if that is the case, I would find that hard to believe, as this universe is made up of spheres. Am I way off base?
Lemonick: It’s not surprising that you’re confused—I get that way too when the dimensions start to multiply. When astrophysicists say the universe is flat, they’re talking about a three-dimensional version of flatness. It’s analogous to the flatness we see in a two-dimensional sheet of paper, say, but it’s not something you can easily visualize. But just as you can draw a circle on a flat piece of paper, you can put spherical planets, stars, and such into a three-dimensional flat universe.
Full name: Raymond Ellis
Location: Brisbane, Australia
Question: My question is essentially psychological. Why do we prefer a Big Bang theory? Is our preference for a Big Bang theory based on logic or on an emotional liking? Why did we choose a spectacular event like the Big Bang for the beginning of the universe? Is it merely because we worship power as a society—the powerful motor car, the intense grand finale, the spectacular music concert?
Lemonick: No, it’s because the observed evidence—an expanding universe, a remnant bath of microwaves, and a precise ratio of hydrogen to helium—all point to a Big Bang. We didn’t “choose” the Big Bang any more than we “chose” gravity.
Full name: Charles R. Turley
Location: Hurricane, West Virginia
Question: If our universe is destined to “bump” into our unseen universe again, have the minds of physics come up with a timetable? And if there are 10 dimensions (seven more than we currently perceive), what are the other seven?
Lemonick: The timetable is pretty reassuring: The next bump wouldn’t happen for at least 10100 years from now (that’s 1 followed by 100 zeros). As for the extra dimensions, they’re . . . dimensions, that’s what. The reason we don’t perceive them is that they’re “compactified”—that is, they’re so small they don’t impinge on our lives.
Full name: David G. Karustis
Location: Sacramento, California
Question: You say in the article: “Trillions of years from now, matter will be so widely spread out that its average density will be much less than a single electron per quadrillion cubic light-years of space. That’s so close to zero density that there’s no meaningful difference.” Where then does the matter come into existence to create the countless galaxies and stars when the branes collide? It appears a universe is created ex nihilo. This is a point I am really trying to understand.
Lemonick: The matter condenses out of the energy generated by the collision, much as the matter in the conventional Big Bang theory condensed out of the energy of the bang. The energy already exists, but it exists outside of our universe prior to the collision.
Full name: Tony Johnson
Question: Would it be possible for matter to be left over from a previous universe?
Lemonick: In the Big Bang scenario, no. In the ekpyrotic universe, the matter would be so sparsely distributed that the answer is still no, in a practical but not an absolute sense.
Full name: Rick Freeman
Question: As I understand it, the ever-faster acceleration of the universe’s expansion began about 5 billion years ago, when the cosmos was about 8.7 billion years old. Why? What happened? And is there any connection to the creation of our solar system and/or planet?
Lemonick: No, no connection. What happened was that there’s the same amount of dark energy in every cubic meter of space. As the universe expands, that means more cubic meters and thus more force. It took several billion years for the universe to get big enough to contain enough dark energy to overcome the force of gravity, which until then had tended to slow the expansion down.
Full name: Kyle Foster
Location: Portland, Oregon
Question: If there is a second universe a proton’s width away from the current universe, wouldn’t particle accelerators be able to test this theory of universe interaction and energy release?
Lemonick: No. According to the current theory, the second universe would be completely inaccessible to us, even though it would be incredibly close.
Full name: Roberto C. Chavez
Location: Chino Valley, Arizona
Question: Was the possibility considered that matter from the higher dimension “brane” invaded our universe at the time of inflation and is that which we now call dark matter? If it was, why was it not mentioned?
Lemonick: It wasn’t considered because that’s a wildly elaborate extra hypothesis for which there is no evidence.
Full name: Clarence Hall
Location: Baltimore, Maryland
Question: If the Big Bang actually happened, then what existed before the Big Bang, assuming that some form of existence did exist? Math proves that something cannot simply appear from nothing! E = mc2.
Lemonick: Math proves nothing of the sort; there are ways in which matter and energy can balance each other out. As for what existed before, modern physics is simply incapable of answering that question, or even speculating intelligently on it.
Full name: Terry Ward
Location: Denver, Colorado
Question: As we look at more distant stars, it doesn’t make sense that they are moving faster. We are seeing them as they existed billions of years ago. It does not follow that they are accelerating away today. Your comments, please.
Lemonick: This is a subtle point and a good question. Actually, they’re not “moving” as you would ordinarily think of it. The space between us and them has stretched, and the light traversing that space has also stretched, making it look redder. So, it’s the stretching over all that time, from then until now, that makes the images of stars look as though they’re moving away faster than nearby stars—a direct consequence of the expanding universe.
Full name: Graham Robertson
Location: Sarnia, Ontario
Question: If the universe is expanding, how can galaxies collide?
Lemonick: The universe is expanding overall, but locally, gravity can overcome the expansion. It’s the same reason you aren’t expanding away from the surface of Earth.
Full name: Graham Robertson
Location: Sarnia, Ontario
Question: Given the abundance of stars everywhere in the universe, it seems that all radiation from all stars is ultimately reabsorbed into other stars. What effect does this recycling of energy have on judging the age of the universe?
Lemonick: Actually, there’s a lot more empty space than there are stars. The light we see from ancient galaxies has come directly to us in most cases.