September 08, 2002
Bemusement and Relativity

John Quiggin believes that I shouldn't be bemused at how Einstein's special theory of relativity replaces the absolute ideas of 'past', 'present', and 'future' with the ideas of 'past light cone', 'future light cone', and 'outside the light cone' that are different for each observer at each different point and moving at each possible velocity. (It is a theory of relativity, after all.) John Quiggin: ...It's only surprising in the 'isn't science amazing' way that a microwave oven is surprising the first time you see it. I wouldn't have thought you could boil water while not heating the cup containing the water, but now I don't give it a second thought. Well, let me put it on the record right now that I find my microwave oven pretty damn amazing every single time I turn it on. Hell, I even find a spinning bicycle wheel suspended from a rope attached to one end of its axle amazing......

Posted by DeLong at 09:23 AM

September 04, 2002
Messrs. Lorentz and FitzGerald

Uncertain Principles if you start to get close to light speed, you need Special Relativity to describe what really happens... *Sigh.* This is what happens when you read weblogs by real physicists--especially those who have been part of a team making Bose-Einstein condensates in their laboratory. (Kids! Don't try this at home!) My spreadsheet on the effects of product and income-side estimates of total output on our conception of the economic boom of the 1990s is now filled with Lorentz-FitzGerald contraction formulas... Consider a person standing on the surface of the earth, and consider an event--the birth of a child, say--at that exact same time (in his frame of reference) on the other side of the galaxy--100,000 light years, or 9 x 10^20 meters away. Now consider a second person walking past that first person at that exact same moment (when in the first person's reference frame the child is born), in the direction of the point 100,000 light years away. If you asked that second person whether the child on the other side of the galaxy had been born yet, and if so how old was she, you would get a different answer. According to my calculations, the...

Posted by DeLong at 05:04 PM

May 11, 2002
Determining the Speed of Light with Marshmallows

Students in physics always seem to be fascinated by the properties of light. However, speed-of-light demonstrations often require extensive preparation or expensive equipment. I have prepared a simple classroom demonstration that the students can also use as a take-home lab...

Posted by DeLong at 03:01 PM