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.
Donna Frisoli, age 47, Maine
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, age 45, 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.
Charles R. Turley, age 70, 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 10^100 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.
David G. Karustis, age 35, 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.
Tony Johnson, age 32, Utah
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.
Rick Freeman, age 50
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, age 24, 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.
Roberto C. Chavez, age 73, 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, age 52, 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 = mc^2.
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.
Terry Ward, age 65, 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.
Graham Robertson, age 63, 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.
Graham Robertson, age 63, 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.
Nathaniel, age 16, Pennsylvania
Question: I just want to know when the government is going to release information on life-forms other than ours. I know for a fact that we are not alone in this universe if it’s expanding more and more every day. I also want to know what is beyond the ends of the universe. If you can answer those questions, I will be absolutely amazed. Thank you very much.
Lemonick: I think the government will release such information if and when they ever get it. As for the ends of the universe, there’s no evidence that such a thing as the end or boundary of the universe exists. There is a visible edge to the universe, but it is in no way a physical boundary.
Ronald Garrett, age 50, New Jersey
Question: I too agree with the theory that there are some infinite origins to the beginning of all things. I don’t believe that it all started with the Big Bang. But isn’t it probable that sometime way back in an unimaginable past, the one first “thing” that started it all had to come into existence from nothingness? Otherwise, isn’t the universe that includes the known and unknown an impossibility? And so I think, therefore I am! What else could this all be but divine intervention from God? I know, I know—so where did God come from? Hopefully, that’s part of the reward we get when we pass on from this universe.
Lemonick: Declaring anything to be an “impossibility” based on our current understanding would be foolish, in my opinion. God may well exist, but I don’t consider the above a very strong argument.
Jessica Cowles, age 19, Michigan
Question: You said in the article that Pope Pius XII declared approval for the Big Bang theory in 1951. Does this mean that the Catholic Church agrees with the theory?
Lemonick: That’s my understanding, yes.
Seana K. Niederpruem, age 42, Illinois
Question: Is dark matter part of our brane or the neighboring brane? Is the gravitational force from dark matter the result of the presence of the neighboring brane?
Lemonick: It’s all part of ours. If the dark matter were not in this universe, it would not be able to affect us.
Michael J. Sexton, age 35, Manheim, Pennsylvania
Question: Infinite space, which ultimately has to be, pretty much dictates that there could not possibly have been only one Big Bang. Is there any decent speculation on what lies beyond all possible measurement? Our Big Bang eventually must hit another big bang. Or is it assumed we’ve seen the biggest omni-collective of the known forms of light and matter?
Lemonick: Infinite space does not have to be. But even if it is, the Big Bang happened everywhere in our universe at once, so there wouldn’t be any “meeting” involved.
Nicholas P. Dunbar, age 21, Omaha, Nebraska
Question: If the zero point of the Big Bang event began with zero, the physical existence of nothing, and expanded dichotomously in equal and opposite infinities, what is the opposite of zero?
Lemonick: This sounds like a Zen koan, not a question involving any science I recognize.
Paul Smith, age 56, Michigan
Question: Has this work been peer-reviewed? If so, where? With the basis for this theory being the quantum side of physics, are there any new predictions involving where and how to find gravitons that might resolve their persistent absence?
Lemonick: Yes, it’s been peer-reviewed in the Astrophysical Journal, I believe. You can find relevant papers through the online preprint resource arXiv (http://arXiv.org/archive/astro-ph). On the second question, no. This new idea relies on quantum theory, but it doesn’t refine it in any way that would help the search for gravitons.
Terry Choncoff, age 35, Merrillville, Indiana
Question: Max Tegmark has also stated that there are multiple universes existing as explained in this article—only he predicted a very large number of them. Did you describe only two in this article just to keep things simple? If your research has shown that there would be a great many, wouldn’t that imply more frequent interactions that could result in a Big Bang?
Lemonick: Tegmark’s multiple universes are based on plain old general relativity and are of a very different type than the ones Paul Steinhardt is discussing, which are based on M-theory. I’m not sure anyone has gone as far as exploring the scenario you mention, which is certainly a provocative one.
John E. Quick III, 25, York, Pennsylvania
Question: I’ve been wondering about this for quite some time now: They say that the universe is expanding, but what is it expanding into? What space is it taking up?
Lemonick: This is a good question, but you won’t like the answer. It’s not expanding into anything. All of space itself started tiny and is expanding. As an analogy, imagine the two-dimensional surface of a sphere. (In the analogy, there is no interior to the sphere and no exterior—just the surface itself. It’s a “universe” unto itself.) OK, now the surface expands. There’s more and more “space,” but it’s not expanding into anything. It’s just getting bigger.
If this doesn’t give you a headache, you’re not trying hard enough.
John Harris, age 40, Maryland
Question: Whether the Big Bang was a single event, or multiple events over billions of years, still does not answer the question of why something exists at all. Multiple and/or parallel worlds simply beg the question at another level: Where did those parallel worlds come from?
Lemonick: True—unless they’ve been here forever, and thus never had a beginning. The ekpyrotic theory still does not explain why there is something rather than nothing.