Black Holes
Black holes may be heard but not seen. As the death state of a star, black holes emit no light. They are dark against the dark sky. But like mallets on a drum, black holes can ring out a song on space itself in the form of gravitational waves. Monumental Earth-based detectors such as LIGO and the planned space-based mission LISA aim to record the songs from space for the first time thereby turning up the volume on the soundtrack to the Universe.
There is no sound in empty space. But when the gravitational waves hit the Earth, detectors in the next few years will measure the stretching and shrinking of space and will be able to amplify the result as sound. To hear the sounds of two black holes ringing space, play the movie at the left.
Finite Universe
Our universe appears to stretch nearly thirty billion light years across. As far as the eye can see, there is no visible bound to spacetime. Still the universe may not be infinite. There was once a cultural prejudice that the earth was flat and unconnected, so much so that explorers were feared to have fallen off the edge. The assumption that space must be infinite may represent a similar bias. A tenable possibility is that space itself is not only curved, as Einstein suggested, but that it is also finite. A finite universe, and indeed a finite universe with several extra dimensions, may be a prediction of a theory beyond Einstein’s – the long coveted Theory of Everything. Even as we struggle to understand the universe as drawn by a TOE, recent Astronomical observations may be on the cusp of resolving this age old question: Is the universe infinite?
Theories of Everything
A physical Theory of Everything is the greatest ambition consuming theoretical physics. Yet last century we were forced to concede that there will never be a mathematical theory of everything. Kurt Gödel, Alan Turing, and Gregory Chaitin proved that our knowledge of numbers themselves is fundamentally incomplete. Most numbers are random, a toss of the coin. There are true relations among the numbers about which we can only prove that we can never prove them.
Many times in the history of physics, theories have been shaped by such profound limits. Einstein proposed a fundamental limit in the speed of light and thereby discovered Relativity. Heisenberg invoked an uncertainty principle in measurements of quantum phenomena and thereby laid a cornerstone for Quantum Mechanics. Alongside these should be listed the profound incompleteness in our knowledge of numbers – there can never be a mathematical theory of everything. The proposal is to define the limits mathematical incompleteness might set on a physical theory of everything. Just as Relativity emerged from the limit of light’s speed and Quantum Theory emerged from the limits of measurement, deep insight into the universe and its origins could emerge by confronting the limit of mathematical incompleteness.
