Do bubbles in Guinness go down?

Does this only happen in Guinness?

	No, it can happen in any liquid.  There are a number of things about Guinness that make it easier to see though.  Firstly, the bubbles produced are small, making them more easily pushed around by flowing liquid.  The bubbles are small because they have been released at high pressure through fine holes (when poured from the tap or from the "widget").  The gas in the bubbles is also important.  The fizz in most lager-beers (and soda) is carbon dioxide, which is more easily dissolved into the liquid. This is why you can see streamers of bubbles appear to form out of nowhere at the side of a glass of beer or cola: the dissolved carbon dioxide undissolves to form bubbles at tiny defects in the glass surface: they continue to grow, ingesting more dissolved carbon dioxide as they go up (as shown, left, for cola).  In Guinness, the gas is nitrogen (which makes up roughly three quarters of the air we breathe). Nitrogen does not dissolve as well in liquid as carbon dioxide, and so the bubbles do not grow like in lager or cola.  Another factor is the contrast in the colours of the very dark liquid and the light cream bubbles in Guinness, making the waves and bubbles more obvious.
	To prove downflow of bubbles happens in other liquids, we looked at other draught-flow beers (e.g., Boddingtons).  The results are exactly the same as with Guinness.  In this clip (Boddingtons) you see a similar downflow of the bubbles.  A bubble-free wave of liquid can be seen very clearly. Quicktime movie (1.9 MB)   AVI movie (2.2 MB)
	Not being content with beer, we set out to make bubbles go down in other liquids.  To do this we devised a "bubble-maker", as shown in the picture opposite.  This is just a piece of tube with fine holes in the end (at the bottom) through which we can blow gas to make small bubbles.  The liquid in the glass is just plain water.  The bubbles go up the center of the glass, just like in the Guinness, and create a circular flow that causes bubbles at the inside edge near the top to be pushed downwards. You can see the result in the next clip below.
	In this clip you can see the bubbles produced at the top of the glass of water by the bubble-maker.  The bubbles are much larger than are produced in Guinness.  This is because they have not been produced at high pressure as they have in Guinness, a process known as "gas breakout". Quicktime movie (2.8 MB)   AVI movie (1.8 MB)
	Another way of making bubbles go down is to simply add a fizzing tablet to a glass of water.  These are not so easily seen with the eye, but easily seen with the fast camera: as shown in the clip here.  Another way of visualizing the flow is to use a suspension of powder in liquid giving what is known as a rheoscopic fluid.  The particles of the additive powder allow the fluid flows to be visualised.  Bottles of rheoscopic fluids can be purchased at good science or teacher supply stores. Quicktime movie (2.4 MB)   AVI movie (1.9 MB)