Point of View: Are theoretical results ‘Results’?
Figures
![](https://iiif.elifesciences.org/lax/40018%2Felife-40018-fig1-v1.tif/full/617,/0/default.jpg)
Experimental setup to study diffusion of the green alga Chlamydomonas.
(a) A light sheet is used to gather the algae, which are swimming in a petri dish, into a narrow strip of cells along the -axis. (b) After the light is turned off, the cells swim randomly and spread out. The concentration profile, , is then measured along a thin strip parallel to the -axis; is time.
![](https://iiif.elifesciences.org/lax/40018%2Felife-40018-fig2-v1.tif/full/617,/0/default.jpg)
Experimental results on diffusion in a population of the green alga Chlamydomonas.
(a) Concentration profiles, , normalized to unity, at the following times: 1 second (red), 3 seconds (green), 7 seconds (blue) and 30 seconds (black). (b) The variance, , of the data shown in (a) as a function of time; the dashed magenta line is a linear fit to the data. (c) The peak height, , of the data shown in (a) as a function of time.
![](https://iiif.elifesciences.org/lax/40018%2Felife-40018-fig3-v1.tif/full/617,/0/default.jpg)
A random walk in one dimension.
(a) A cell at site moves with probability to the left or right. (b) Diagram illustrating the counting that underlies the evolution equation (Equation 1).
![](https://iiif.elifesciences.org/lax/40018%2Felife-40018-fig4-v1.tif/full/617,/0/default.jpg)
Flux and the diffusion equation.
(a) Concentration profiles, , at times s and s
. (b) The flux of cells past a given point, (black; left axis), and the concentration gradient, (yellow; right axis), versus position, . (c) Flux, , versus concentration gradient, , for all the values of and shown in Figure 2a. The dashed magenta line has a slope mm2/s.
![](https://iiif.elifesciences.org/lax/40018%2Felife-40018-fig5-v1.tif/full/617,/0/default.jpg)
Rescaling the data.
(a) The peak amplitude, , from Figure 2c plotted as a function time, , on a log-log scale; the dashed magenta line has a slope of , which shows that . (b) When the data in Figure 2a are rescaled (see main text) and replotted, they collapse to a universal curve; the dashed magenta curve is the function .