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Frequently Asked Questions

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The Big Bang Theory is widely regarding as the leading explanation for the origin of the universe. Are you telling us that it is completely wrong?

No, the two theories have a lot in common. They both agree that the universe has been expanding and cooling over the last 14 billion years and they agree on how galaxies and stars formed.

Where they disagree is on what happened beforehand. The conventional Big Bang Theory say there was no “beforehand.” Space, time and matter all sprang into existence 14 billion years ago in the event called “the big bang,” and all the events responsible for structure of the universe seen today occurred within the first instant after the big bang.

The Cyclic Theory agrees that there was some violent event 14 billion years ago – we still call it a "big bang" – but this was not the beginning of space and time. The key events causing the creation of matter, radiation, galaxies and stars occurred billions of years before the bang. Furthermore, there was not just one bang. The evolution of the universe is cyclic with big bangs occurring once every trillion or so, each one accompanied by the creation of new matter and radiation that forms new galaxies, stars, planets, and presumably life. Ours is only the most recent cycle.

What led you to consider a new theory?

We were motivated by the fact that, over the last few decades, more and more elements have had to be added to the Big Bang Theory to make it consistent with what we observe. To explain why the universe is so uniform, we had to a new feature called inflation. To explain the formation of structure, we had to add dark matter. The recent discovery that the expansion of the universe has begun to speed up has required the addition of something called dark energy. Each of these elements have been added one by one to make today’s Big Bang Theory a kind of patchwork of disconnected ideas. Furthermore, in the background, there has been the disturbing notion that the big bang is the beginning of everything – something that has never been successfully explained by fundamental physics.

We wanted to see if a completely different history of the universe is possible in which all the elements fit together in a tight and natural way. Furthermore, we saw recent developments in fundamental physics – namely, string theory – offered a radically new view of the big bang itself – not as a beginning but rather as a collision of two parallel worlds along an extra invisible dimension. Much to our surprise, we found we could use this picture to reformulate the history of the universe – recovering all the successful predictions of the conventional Big Bang Theory.

Why should anyone care about which theory is correct?

There are several reasons why everyone should care. First, we are all curious about where the universe came from and where it is headed. Our book shows that there is an exciting and radical alternative worth considering that changes our conception of where we stand in the history of the cosmos.

Second, the answer will determine whether our universe is comprehensible or not. In both theories, the part of the universe we observe is tiny patch of a much larger, perhaps infinite space. In the conventional Big Bang theory, different parts of the universe have widely different physical properties and, some theorists believe, different laws. According to this idea, the properties of the region of the universe we observe are highly atypical of the universe on average and are set by random chance. Hence, our ability to understand the universe as a whole is limited by the fact that we can only see a small part of it.

In the Cyclic Theory, the universe is the same almost everywhere, so the laws and properties we see are typical of the whole. Hence, the Cyclic Theory restores the hope that the universe is simple and comprehensible to us even though we are only able to observe it from a limited vantage point.

How can you test the “Cyclic Theory”?

There are several ways. For example, the Cyclic Theory leaves a distinctive pattern of gravitational waves that is very different from the one expected in the Big Bang Theory, as described in Chapter 9 of our book. A number of experimental groups throughout the world are now starting to search for these waves using detectors on satellites, high altitude balloons and on mountaintop observatories, and may prove or disprove our theory within the next few years.

Why write this book now before the theory has been tested?

Most science books are written after ideas have been around for many years and already well established. We thought it would be interesting to write about a radically new scientific idea with far-reaching implications at a time when it is first emerging and before it is proven. This provides to capture science as it is happening through the eyes of scientists directly involved. We not only describe the ideas, but also the real struggles and risk-taking involved in developing new scientific ideas. In this way, we hope the book not only conveys the new ideas themselves, but also gives the reader an insider’s view on how science really works.

I remember reading once that cosmologists considered the possibility of a cyclic model back in the 1920's, and they eliminated it because it violates the the second law of thermodynamics (the law stating that entropy always increases).

Does the new Cyclic Theory violate the second law of thermodynamics?

No. The second law of thermodynamics says that the total entropy or randomness in the universe always increases. This is true for the new Cyclic Theory. A thorough discussion of this in Chapter 8 of our book, including its relation to Isaac Asimov's famous short story, The Last Question (which is also the title of our Chapter).

There is actually a common misunderstanding regarding this issue. The problem with the oscillatory models of the 1920's was not the entropy, but the entropy density -- that is, not the total amount of randomness but, rather, how concentrate it is. In the oscillatory models of the 1920s, the entropy created during one expansion phase draws together during the periods of contraction and adds to the concentration of entropy at the beginning of the next cycle. If the concentration increases from cycle to cycle, then each cycle ends up being longer than the one before (going forward in time) or the cycles get progressively shorter (extrapolating backward in time). In fact, they converge to zero duration after a short time. So, when the concentration was considered, it became clear that these models failed to give an eternally cycling universe.

In the new cyclic model, the entropy created during one cycle is diluted during the period of accelerated expansion, but is never drawn together again (i.e., it remains dilute) during the contraction period. The total entropy of the universe as a whole increases steadily from bounce to bounce, as demanded by the second law of thermodynamics. However, the entropy from the previous cycle is spread to regions beyond the horizon during the period of dark energy domination and never seen again. So, as far as any local observer is concerned, the entropy density is driven to zero before each bang and the universe appears to begin afresh after each bang.

Does the cyclic model violate the conservation of energy? Is it a perpetual motion machine?

No. The cyclic theory works by constantly converting gravitational energy into new matter and radiation. The peculiar thing about gravity compared to other forms of energy is that you can continue to draw energy from it forever under certain conditions, like those that occur in the cyclic theory as well as eternal inflationary theory. In the cyclic picture, the cycles occur through the regularly repeatring collision of branes. The branes are brought together by a spring-like force between them. But that is not the only factor involved in their collision, or else the "spring" would wind down after a few collisions. Gravitational energy is converted into brane and matter energy during each cycle, ensuring that the cyclies continue at a constant pace. See Chapter 8 for a complete discussion and the cyclic model and perpetual motion.

Will the LHC (the Large Hadron Collider being built at CERN, the European Organization for Nuclear Research) resolve any of these issues the beginning of next year, when it goes online?

The LHC could provide important new indirect information. For example, it could confirm the exist of new particles predicted by string theory and provide evidence of extra dimensions. This would help confirm the overall framework, although not directly the cyclic picture. For that, measurements of gravitational waves are probably the best approach (see Chapter 9 of our book).

If the two branes are currently a quantum length apart [~10^(-28) cm], will the branes really get closer a trillion years hence than they are right now? If so, how much closer?

The branes will collide and actually touch. Then they will bounce and go back to their original positions. Although the distance seems small when measured in centimeters, a better way of thinking about it is to measure it in "Planck lengths" (the characteristic length scale for quantum gravity) -- in those units, the distance today is large, about 10,000 Planck lengths.