September 29, 2003
Global Warming

Berkeley physics professor Richard Muller has well-informed and nuanced views on global warming, and other topics: "I am terrified of human-activity-generated CO2 causing global warming. I think it is the biggest environmental challenge humanity faces. I think strict conservation is the key, induced by high taxes on carbon emissions. I am not sure that we can see human-caused global warming in the climate data. I am opposed to the Kyoto Treaty." CO2 shouldn't be causing as much temperature change as we are seeing, at least not unless there are stronger positive-feedback amplifiers in the climate system than I think likely. We could have ten cold years. Then where would we be? In the ****, because there is no doubt that global warming is a big threat, and that the politicians really need to listen to us--if not in this generation, in the next one. "After 2 1/2 years of painstaking work I've disproved my theory of the [recent, 100,000-year] ice age cycle. But I've disproved their theory too. Which leaves us nowhere." "Physics is that part of science in which friction plays no role. If friction does play a role, you give it to the engineers." "Our experiment found that...

Posted by DeLong at 05:45 PM

March 17, 2003
Planck Scale Reality

It's sad to think that I will never understand quantum gravity or particle physics in the way I understand special relativity or basic electromagnetism. (Leave to one side the subjects--like angular momentum--where I could do the calculations correctly, but simply could not make myself believe that the results made any sense.) On the other hand, the parts of the universe I do understand are really quite amazing. A gallon jug of a strange liquid can be used to propel that one-ton automobile over a distance of twenty miles (or that SUV over five miles). And could anything be spookier than the rainbow diffraction pattern on the back of a CD, with what it tells us about the manyfold splitting and recombination of our world line (or, alternatively, about the mystical "reduction of the wave packet")? | Planck-scale physics" ...The energy that would be needed to probe the granularity of space is known as the Planck energy. Unfortunately, even the biggest particle accelerators in existence probe energies which are only about a millionth of that. The lack of a reality check which this causes has led theorists so far into the deep end of mathematical speculation that many have started...

Posted by DeLong at 07:46 AM

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

April 09, 2002
Personal Physics Trainer

One of the nice things about the internet is that there are people out there prepared to act as my personal physics trainer...

Posted by DeLong at 04:00 PM