Trade.Information

Computational Physicist Neil Turok Says Big Bang Wasn't the Beginning

For decades, physicists have accepted the notion that the universe started with the Big Bang, an explosive event at the literal beginning of time. Now, computational physicist Neil Turok is challenging that model -- and some scientists are taking him seriously.

According to Turok, who teaches at Cambridge University, the Big Bang represents just one stage in an infinitely repeated cycle of universal expansion and contraction. Turok theorizes that neither time nor the universe has a beginning or end.

It's a strange idea, though Turok would say it's no stranger than the standard explanation of the Big Bang: a singular point that defies our laws of physics, where all equations go to infinity and "all the properties we normally use to describe the universe and its contents just fail." That inconsistency led Turok to see if the Big Bang could be explained within the framework of string theory, a controversial and so-far untested explanation of the universe as existing in at least 10 dimensions and being formed from one-dimensional building blocks called strings. Within a school of string theory known as m-theory, Turok said, "the seventh extra dimension of space is the gap between two parallel objects called branes. It's like the gap between two parallel mirrors. We thought, What happens if these two mirrors collide? Maybe that was the Big Bang."

Turok's proposition has drawn condemnation from string theory's many critics and even opposition from the Catholic Church. But it's provoked acclaim and wonder, too: He and Princeton University physicist Paul Steinhardt published Endless Universe: Beyond the Big Bang last year, and Turok -- also the founder of the South Africa-based African Institute for Mathematical Sciences -- won 2008's first annual TED Prize, awarded to the world's most innovative thinkers.

Turok spoke with about the Big Bang, the intellectual benefits of cosmology and his bet with Stephen Hawking.

Q: In a nutshell, what are you proposing?

Neil Turok: In our picture, there was a universe before the Big Bang, very much like our universe today: a low density of matter and some stuff called dark energy. If you postulate a universe like this, but the dark energy within is actually unstable, then the decay of this dark energy drives the two branes together. These two branes clash and then, having filled with radiation, separate and expand to form galaxies and stars.

Then the dark energy takes over again. It's the energy of attraction between the two branes: It pulls them back together. You have bang followed by bang followed by bang. You have no beginning of time. It's always been there.

Q: But isn't there still a beginning?

Turok: Imagine you have a room full of air, with all these molecules banging around. The vast majority of time, these molecules spread uniformly -- but once in a trillion trillion years, they all end up in the corner of the room. If you look at the room and run the clock forward, they'll eventually make themselves uniform: But it would reverse, and you'd watch them flying into the corner. Then they'd fly out again.

If this is right, it means that time runs forward for a while. Then there's a random state without an arrow of time, then time runs backwards, and then time runs forward again. That's the bigger picture: We're still very far away from understanding it, but that would be my bet.

But my main interest is the problem of the singularity. If we can't understand what happened at the singularity we came out of, then we don't seem to have any understanding of the laws of particle physics. I'd be very happy just to understand the last singularity and leave the other ones to future generations.

Q: How do you test this theory?

Turok: If the universe sprung into existence and then expanded exponentially, you get gravitational waves traveling through space-time. These would fill the universe, a pattern of echoes of the inflation itself. In our model, the collision of these two branes doesn't make waves at all. So if we could measure the waves, we could see which theory is right.

Stephen Hawking bet me that we'll see the signal from inflation. I said that we won't, and he can take it for any amount of money at even odds. So far he hasn't named an amount. He's richer than me, so he's being nice.

Note for Big Bang
The Big Bang is a cosmological model of the universe which has the primary assertion that the universe has expanded into its current state from an initial state of infinite density and temperature. The term is also used in a narrower sense to describe the rapid expansion of spacetime that started at or close to an initial event in the history of our observed spacetime. The term 'Big Bang' was first coined by Fred Hoyle, ironically, in a derisory statement seeking to belittle the credibility of the theory which he did not believe to be true.

Theoretical support for the Big Bang comes from mathematical models, called Friedmann models. These models are framed in the context of general relativity and are based on the cosmological principle, which states that the properties of the universe is everywhere similar, and that there is no preferred orientation or in other words the universe is homogeneous and isotropic when viewed over sufficiently large spatial scales.

Analysis of the spectrum of light from galaxies reveals a shift towards longer wavelengths proportional to each galaxy's distance in a relationship described by Hubble's law indicating that space-time is undergoing a continuous and uniform expansion. Furthermore the accidental discovery of cosmic microwave background radiation in 1964 suggests that the universe had cooled from an initial hot dense state via the expansion of space-time. The discovery of the cosmic microwave background led to general acceptance among physicists that the Big Bang describes the evolution of the universe reasonably well. Further evidence comes from the relative proportion of light elements in the universe, which is a close match to predictions for the formation of light elements in the first minutes of the universe, according to Big Bang nucleosynthesis. However there are features of the universe which are not well explained by the Big Bang model such as the similarity of regions of the universe which, within the scope of the model, have never been causally connected. Augmenting the Big Bang model with an early rapid inflationary phase can explain many of the features unaccounted for by the standard Big Bang model.

Note for String Theory
String theory is an as-yet incomplete mathematical approach to theoretical physics, whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point particles that form the basis for the standard model of particle physics. By replacing the point-like particles with strings, an apparently consistent quantum theory of gravity emerges, which has not been achievable under the standard model. Usually, the term string theory includes a group of related superstring theories and a few related frameworks such as M-theory, which seeks to unite them all.

String theorists have not yet completely described these theories, or determined if or how these theories relate to the physical universe. The elegance and flexibility of the approach, however, and a number of qualitative similarities with more traditional physical models, have led many physicists to suspect that such a connection is possible. In particular, string theory may be a way to "unify" the known natural forces (gravitational, electromagnetic, weak nuclear and strong nuclear) by describing them with the same set of equations, as described in the theory of everything. On the other hand, the models have been criticized for their inability, thus far, to provide any testable predictions.

Work on string theory is made difficult by the very complex mathematics involved, and the large number of forms that the theories can take depending on the arrangement of space and energy. Thus far, string theory strongly suggests the existence of ten or eleven (in M-theory) spacetime dimensions, as opposed to the usual four (three spatial and one temporal) used in relativity theory; however, the theory can describe universes with four effective (observable) spacetime dimensions by a variety of methods. The theories also appear to describe higher-dimensional objects than strings, called branes. Certain types of string theory have also been shown to be equivalent to certain types of more traditional gauge theory, and it is hoped that research in this direction will lead to new insights on quantum chromodynamics, the fundamental theory of the strong nuclear force.

Note for Dark Energy
In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. Assuming the existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total mass-energy of the universe.

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously, and scalar fields such as quintessence or moduli, dynamic quantities whose energy density can vary in time and space. In fact, contributions from scalar fields, which are constant in space, are usually also included in the cosmological constant. The cosmological constant is thought to arise from the vacuum energy. Scalar fields which do change in space are hard to distinguish from a cosmological constant, because the change may be extremely slow.

High-precision measurements of the expansion of the universe are required to understand how the speed of the expansion changes over time. The rate of expansion is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today.

Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. Dark energy has been used as a crucial ingredient in a recent attempt to formulate a cyclic model for the universe.