Mittwoch, 11. Februar 2009

Physophy: From Newton's and Mach's Bucket to General Relativity

Newton's bucket is a famous experiment (not a thought experiment) really made by Isaac Newton. If you have a bucket filled with water, and you start to rotate the bucket, what will happen?
  1. Start: The bucket rotates, not the liquid: the water surface is flat
  2. Bucket and water rotate in an equilibrium: The water surface is a parabola (almost)
  3. Stop the bucket: The water continues to rotate and the surface is still parabolic.

The parabolic surface proves that the bucket is rotating: against the environment, against earth, against the next fixstars, against absolute space.

Newton selected absolute space as reference - the "sensorium" for God.
In fact, the experiment states physically just the existence of some (approximate) intertial system as the famous Foucault pendulum!

The Austrian Ernst Mach (born in Moravia as I was) asked:
What if the bucket would be surrounded by thick rotating walls? Thick means really thick, many kilometers of rotating matter while the bucket and the water would be at rest? He predicted that the water surface would also become curved; this means that inertia is the result of the matter in the universe.

General Relativity moved somehow in that direction with the frame-dragging effect (Lense-Thirring effect) ...

The picture from

is a modern version of Newton's bucket in a science museum using two immiscible liquids: The equilibrium interface is a parabola.

Private: Swiss winter impressions

This is just to recall the Swiss situation before the SVP referendum to close the borders against the new European Union members Bulgary and Romania.

Last Sunday, the Swiss people - the Souverain - voted in favor of openness.

PS: The photo shows some concrete tank barriers from the Second World War period crossing a valley. My wife calls them "Toblerone".

Sonntag, 1. Februar 2009

Physophy: Telescopes - almost a Moore's Law

Moore's law - in short, the exponential growth of IT - is mainly driven by the miniaturization of electronics, down to the nanolevel. This implies that all products with IT are driven down in cost or/and performance. But it affects also material-bound products - a nice example are telescopes for astronomy. The figure from a German astronomy blog (German description and legend)

by Leonard Burtscher shows the increase of the resolution of telescopes:
After thousands of years with a natural resolution of human vision of one or two ninutes of arc, the accessible resolution increases dramatically, in particular in the last 3 decades. The reason is that electronics and IT allow to minimize the relative material efforts with tricks as adaptive and active optics, and to economically build larger telescopes than ever! It is great how IT (an almost material-less technology) can help to build large material devices more efficient and therefore assist in the Golden Age of astronomy!

Private: We have a stair-climbing wheel chair

The disease (ALS) of my wife weakens the muscles without mercy: Currently, we manage together to climb and descend the stairs in our house. I have learnt to assist with both hands and symmetrically, but it already takes all my force although my wife has only 50 kg's ...

Our house has 4 levels - this means 3 stairs - , and also stairs outside to the garage. (At 3 of the 4 levels of the house, this gives a wonderful view about the lake and mountain).

In order not to be one day insulated at one house level after a breakdown of my wife, I have bought a stair-climbing wheel-chair. This is nice (expensive) technology with sensors, battery and a strong motor - I have still to learn to master it!