Will Inflation be confirmed by discovering cosmological gravitational waves?

Steven Weinberg forecasts the future

• 18 November 2006

The most important development in physics that I can imagine in the next 50 years would be the discovery of a final theory that dictates all properties of particles and fields. That may be too much to hope for. A major step in this direction would be the discovery of particles like gauginos or squarks that are required by supersymmetry. Alas, we don't know what the masses of these particles would be, and they may be beyond the reach of any particle accelerator.

On the other hand, we can confidently predict breakthroughs in cosmology. We will know whether the density of dark energy varies with time at a rate comparable to the cosmic expansion rate, or is essentially constant - a crucial clue to the nature of dark energy. We will either have confirmed the general idea of inflation by discovering signs of cosmological gravitational waves (which I expect), or we will have ruled out inflation by showing that these gravitational waves are weaker than predicted. We may be using laser interferometers in space to detect cosmological gravitational waves that bear clues about the behaviour of the matter of the universe at energies higher than we can reach in accelerators. But the origin of the universe will remain obscure until we make more progress toward a final theory.