Next Contents Previous


More important than the precise values of parameters is what we have learned about the general features which describe our observable Universe. Beyond the basic hot Big Bang picture, the CMB has taught us that:

It is very tempting to make an analogy between the status of the cosmological `Standard Model' and that of particle physics. In cosmology there are about 10 free parameters, each of which is becoming well determined, and with a great deal of consistency between different measurements. However, none of these parameters can be calculated from a fundamental theory, and so hints of the bigger picture, `physics beyond the Standard Model' are being searched for with ever more challenging experiments.

Despite this analogy, there are some basic differences. For one thing, many of the cosmological parameters change with cosmic epoch, and so the measured values are simply the ones determined today, and hence they are not `constants', like particle masses for example (although they are deterministic, so that if one knows their values at one epoch, they can be calculated at another). Moreover, the number of parameters is not as fixed as it is in the particle physics Standard Model; different researchers will not necessarily agree on what the free parameters are, and new ones can be added as the quality of the data improves. In addition parameters like tau, which come from astrophysics, are in principle calculable from known physical processes, although this is currently impractical. On top of all this, other parameters might be `stochastic' in that they may be fixed only in our observable patch of the Universe.

In a more general sense the cosmological `Standard Model' is much further from the underlying `fundamental theory' which will provide the values of the parameters from first principles. On the other hand, any genuinely complete `theory of everything' must include an explanation for the values of these cosmological parameters as well as the parameters of the Standard Model.

Next Contents Previous