Quantum setback for warp drives
Bad news I’m afraid — it looks as if faster-than-light travel isn’t possible after all. That’s the conclusion of a new study into how warp drives would behave when quantum mechanics is taken into account. “Warp drives would become rapidly unstable once superluminal speeds are reached,” say Stefano Finazzi at the International School for Advanced Studies in Trieste, Italy, and a couple of friends.
When two objects collide, the coefficient of restitution, or COR, is the ratio of the speed of separation after the collision to the initial speed of approach. A perfectly elastic collision will have a restitution coefficient of one, but almost all macroscopic collisions are inelastic, with coefficients less than one. A golf ball dropped on a concrete floor, for example, will bounce with a COR of around 0.8, and it can never be greater than one–despite golfers’ dreams–because some of the kinetic energy always goes into heating the ball.
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[B]elow a certain threshold of cohesiveness some of the simulated events displayed a COR greater than one and as high as 1.05. The fraction of these anomalous rebounds increased with the cluster temperature. “When the temperature increases, more and more vibrating modes are excited,” Kuninaka says. These vibrations can sometimes give an extra kick to the collision, like a gymnast pushing off the pummel horse to get a greater lift.
IOW, when the particles are really small, you are more likely to see when they are expanding or contracting, a behavior that will get averaged out for larger particles. If you have a collision when the expansion happens, that internal vibration energy gets transferred to translational energy, and a COR > 1.
I don’t like how they say that the second law of thermodynamics doesn’t necessarily hold, because later on they explain how it actually does. There will an increase in entropy for the system, but you have to look at this stochastically rather than for an individual particle. It’s like a compressed spring which is at maximum compression just as it hits the ground, and snaps open on the impact (you can sometimes do this with a retractable pen) — it will rebound higher than the point from which it was dropped, because you convert the potential energy of the spring into kinetic energy, and this doesn’t violate any physical laws. But for an ensemble of springs for which the spring motion is random, the average rebound will be lower than the release point.
For the (statistically speaking) fraction of a reader within commuting distance of Washington, DC. Tomorrow (Saturday) is the Naval Observatory Open House
Though it is raining today, the weather looks like it’s going to be great tomorrow. Which means that no meteorologists will need to be strangled.
Hamster in a Wok
Energized now?
probably needs to be Benny Hillified, though, to cover up the breathing.
Movie Trivia: The Wizard of Oz
This one sounds like a total urban legend, but Snopes says it’s true. The costume designers were looking for a very fancy coat for Professor Marvel – the Wizard’s Kansas counterpart – but one that had gotten quite shabby. Some of the crew went to a secondhand shop and bought a bunch of coats to go through; Frank Morgan (the actor who played the Wizard), the director and the wardrobe people selected one out of the bunch that seemed perfect. It had a velvet collar but the nap was worn off of the velvet and it was looking a little worse for the wear. It even fit Morgan just right. Morgan was wearing the coat one afternoon and discovered a label that said “L. Frank Baum.” The coat had originally been made for Baum in Chicago – the tailor verified it, and Baum’s widow did as well. She was given the coat after the movie wrapped.
When someone makes a prediction, people post it to the site along with a brief description and a URL. We monitor it and change its status to true or false when appropriate.
They want significant, empirically testable predictions made by public figures, that have no more than a five-year horizon. Topics (thus far) are politics, technology, and finance.
Research has shown that experts make predictions at a rate worse than chance. This site exists in order to hold people and media outlets accountable for pretending to see into an unpredictable future.
And despite being often-wrong, they keep at it. And people still listen to them and cite them as authorities.
I remember about 75% of those things. Not quite old enough for the iceman or not having indoor plumbing, but I remember having four channels of black & white TV (6, 10 and 13, plus PBS on 17) and adjusting rabbit ears to get better reception.
Other things I remember
Church keys for opening cans, and there was no such thing as a twist-off bottle cap
– later, pop-top tabs that weren’t attached to the can
78 RPM (though I never bought one) and 45 and 33 records, and putting a coin on the tonearm
Reel-to-reel tapes
Green stamps at the grocery store
Single-use flash bulb (blue) on a camera
Adding water to a car battery
Using a typewriter with a ribbon on a spool
Vacuum-tube electronics
Using a card catalog in the library
Dr Bunsen Honeydew- Gorilla Detector
I know, scientifically, that I am not being eaten by a gorilla!
Reviews by kids for kids
40 reviews of Charlotte’s Web. No Kafka, though. Strange omission, that.