New (age?) Scientist

pH

Here's the story (Link via slashdot)
http://www.newscientisttech.com/article/mg19125681.400;jsessionid=NMGHKBGMCGMM

And here's my attempt at a coral cache (in case that top link breaks)
http://www.newscientisttech.com/article/mg19125681.400?DCMP=ILC-OpenHouse&nsref=mg19125681.400INT.nyud.net:8080

Bonus points if you can explain to New Scientist what's wrong with this :
http://www.newscientisttech.com/data/images/archive/2568/25681401.jpg

A Plea to save New Scientist (from a SF writer, oh the shame!)

Son Goku

The magazine has been a very poor one for years now. Every issue features something which violates Noether's Theorem for as long as I remember.
The dreadful thing is that it usually how the general public comes in contact with the theoretical physics and leads to speculative (and often outright false) ideas being seen as an established field.
It is a very good magazine for biology. (At least that's what a few biologists have told me)
Although I think it is symptomatic of the whole "Golly, gee wizz!!" view of science in the media.

pH

Can you provide a simple explanation of why a container with stuff bouncing around inside it can't produce a force in one direction regardless of which end is bigger or how the container is shaped?

Son Goku

pH wrote:

Can you provide a simple explanation of why a container with stuff bouncing around inside it can't produce a force in one direction regardless of which end is bigger or how the container is shaped?

Essentially the thing would violate conservation of momentum.

However here is my attempt.
Now of course light has momentum and can cause pressure. Lets assume that light is reflected perfectly, going from momentum p to momentum -p.

This means that the walls of the container will be kicked with a force of 2p. This would result in a thrust on the wall.

However in the case where the frustum is a cylinder both ends get hit an equal amount and provide no net thrust.
When it is a frustum in general, more force will be exerted on one end, the larger end, but since the walls are slanted they will no longer exert a purely tangental force, but also a force favoured in the direction of the smaller end. Again resulting in no net thrust.

Son Goku

That is obviously for a constant amount of light. All that will happen is that there will be a pressure on the walls, which very quickly be cancelled out.

There is a load of other stuff wrong with it, but I hope that does for now.