Towards the end of the twentieth century, many distinguished people hailed the arrival of the 'century of biology'. Physics was, in the minds of some, given a pat on the head and sent packing. But now, a hunger for funds, a fashion for multidisciplinary research and genuine intellectual interest are increasingly driving biologists into the welcoming arms of other disciplines.

Experiments on single biomolecules (such as those described on page 984) represent just such a trend. In the 1990s, alert experimental and theoretical physicists noticed that these experiments could provide them with intriguing polymers to explore in relatively cheap bench-top applications. Their involvement offered biologists a new way to scrutinize some of the leading actors in life's haphazard play. Predictive models have been developed on the basis of reproducible, quantifiable experiments. The interplay between life's codes and its physical constraints is being uncovered.

Applying first principles inside the cell remains an enormous challenge, although classic examples of cell physiology provide inspiration. Patch-clamp technology, for example, opened the electrophysiology of neurons to modelling and theory that will continue to chip away at the mysteries of signalling in the brain.

Now, significant multidisciplinary progress can be anticipated in understanding how physical forces shape the inner workings of cells. For example, researchers recently examined glial cells, an enigmatic type of cell found in the brain, and by analysing the mechanical properties of the cells found that they could not act as glue or as support for neurons as had previously been believed (Y. B. Lu et al. Proc. Natl Acad. Sci. USA 103, 17759–17764; 2006).

Marrying measurable physical forces to cellular chemistry in a meaningful way promises to push biology far beyond today's biochemistry.

Other examples have included a predictive model for spindle alignment — a step that tells cells how to divide — based on physical forces inside the cell induced by its adhesion to a surface (M. Théry et al. Nature 447, 493–496; 2007), and an analysis of cytoskeleton behaviour in response to cell stretching (X. Trepat et al. Nature 447, 592–595; 2007).

In such endeavours, efforts must be made to ensure that a collaboration is truly intellectually productive for all disciplines involved. The initial urge may be for biologists to go to physicists or mathematicians for help in developing techniques or building models to answer purely biological questions, creating a one-way relationship. Alternatively, the allure of simple, elegant models may have some theorists working to ends that don't necessarily provide biological insight. But in the best examples of interdisciplinary work, insight and enlightenment are mutual. Biologists get a chance to answer key questions in their field while mathematicians and physicists develop and apply tools that better inform their understanding of the natural world. Otherwise, calling such work 'interdisciplinary' is little more than lip service.

If cell biologists are truly to engage physicists and vice versa, a better sense that both are in this ride together is necessary. The papers mentioned above involve exploring physical forces acting on a cellular scale. Marrying those measurable physical forces to cellular chemistry in a meaningful way promises to push biology far beyond today's biochemistry. It is a challenge that could engage research for decades. And physics, in particular, is needed more than ever.