## Wednesday, November 02, 2005

### The Cyclic Theory

In 2003 Steinhardt from Princeton and Turok from Cambridge published their landmark paper on what will be the next paradigm: the cyclic theory.

Here are its salient features:
- space and time exist forever
- the big bang is not the beginning of time; rather, it is a bridge to a pre-existing contracting era
- the Universe undergoes an endless sequence of cycles in which it contracts in a big crunch and re-emerges in an expanding big bang, with trillions of years of evolution in between
- the temperature and density of the universe do not become infinite at any point in the cycle; indeed, they never exceed a finite bound (about a trillion trillions degrees)
- no inflation has taken place since the big bang; the current homogeneity and flatness were created by events that occurred before the most recent big bang
- the seeds for galaxy formation were created by instabilities arising as the Universe was collapsing towards a big crunch, prior to our big bang

Why a new theory? For different reasons, but one very important one was the fact that the universe is accelerating.

Now in the Big Bang Theory (BBT), one uses the analogy of sending a rocket into space. To do that, one must calculate the escape velocity of the rocket. What we do is to look at its total energy, its kinetic energy – how fast must it go – and its potential energy – due to the attraction of the Earth on the rocket. To escape the Earth’s gravitational attraction, we calculate that the rocket’s energy at infinity will be zero.

½m(v squared) + - GMm/R = 0

Where: v is the escape velocity of the rocket
m is the rocket’s mass
M is the Earth’s mass
R is the Earth’s radius
G is a universal constant in Newton’s law of universal gravitation

All values are known except for the escape velocity, which can be worked out from the above equation.

v = sqrt(2GM/R) or v = sqrt(2gR) , Where g is acceleration of gravity on the earth's surface.

The value of v is approximately 11100 m/s (40200 km/h or 25000 mi/hr).

Now the BBT uses this notion to look at how the galaxies are moving away from each others. Notice in this calculation that after attaining escape velocity, the rocket will go to infinity with zero velocity. Should we launch the rocket with a velocity less than that, it will fall back to earth. If its velocity is greater than this escape velocity, it will reach infinity with some velocity to spare. But in none of these scenarios, the rocket – after attaining its escape velocity – will it be accelerating. Now in the BBT, the big bang, when all the matter in the universe was launched into space – the mechanism is obscured about how this would be done – that is comparable to the launching of the rocket. So the question was: did the galaxies have enough velocity to escape? If yes, the universe would expand forever and die in a wimp. If not, the universe would eventually reverse course and die in the big crunch. But when it was found out that the galaxies were accelerating that brought major headaches to the theory. One way out was to postulate Dark Energy. But this ad hoc hypothesis was like doing some patch work. Science doesn’t like patch working, it wants a comprehensive theory. The cyclic theory is one such theory that seems to have a lot of wind in its sails.

See: http://wwwphy.princeton.edu/~steinh/