Cool Things You Can Do With a Blue Laser: Reflection vs. Fluorescence
[W]hat is going on here? This isn’t just reflection, this is something else. How do I know? If it were just reflection, the only color would be green (same as the incident light). This is an example of fluorescence. Basically, in fluorescence, the light doesn’t just oscillate the electrons. The light excites the electrons to a higher energy level.
The pressure of living on a spinning planet
This almost seems like a force, doesn’t it, something pushing the air around? In many ways it does act like a force, though it depends on whether you’re looking at it from the ground, rotating with the Earth, or from space, watching the Earth spin beneath you. This whole thing was first figured out in detail by Gaspard Gustave de Coriolis in the 1800s, and we name it after him: the Coriolis effect (or, sometimes, the Coriolis force).
Are we fooling ourselves with faster-than-light neutrinos?
Excellent follow-up to his first post, to which I already linked (under “other commentary”.
What really caught my eye was the “third option” for possible error, where he talks about the possibility of the pulse changing shape and skewing the measurement and we’re fooling ourselves. Because this is nothing new — it has happened in tunneling experiments and with photons in a medium with anomalous dispersion. Those experiments caused the same kind of headlines about relativity being under siege, but turned out to be a confusion between group velocity and phase velocity (which is not limited to c).
The one difference I see here is that the scientists appear to have measured both the leading and trailing edge which would seem to eliminate the errors you get by measuring the peak and having the peak move around relative to the pulse.
What happens if you hold a slinky at the top end, let it extend, and then drop it?
Two videos: set up and solution, but in the second video another question is asked. As with a previous video in this series, you can click on the answer in the second video to load the answer to the question.
Neutrinos Travel Faster Than Light, According to One Experiment
I chose this particular link because of the headline, specifically the addendum According to One Experiment. If it’s not reproducible, then it will go down in the annals of science as a fluke measurement.
[T]he result would be so revolutionary that it’s sure to be met with skepticism all over the world. “I suspect that the bulk of the scientific community will not take this as a definitive result unless it can be reproduced by at least one and preferably several experiments,” says V. Alan Kostelecky, a theorist at Indiana University, Bloomington. He adds, however, “I’d be delighted if it were true.”
It’s important to note that the experimenters are not claiming to have overturned relativity and are calling for independent confirmation. If you read otherwise, that’s the journalists or editors trying to show some scientific cleavage.
Another reason I chose this article was that they mentioned how the timing was done, because that’s a likely candidate for introducing error.
Jung, who is spokesperson for a similar experiment in Japan called T2K, says the tricky part is accurately measuring the time between when the neutrinos are born by slamming a burst of protons into a solid target and when they actually reach the detector. That timing relies on the global positioning system, and the GPS measurements can have uncertainties of tens of nanoseconds. “I would be very interested in how they got a 10-nanosecond uncertainty, because from the systematics of GPS and the electronics, I think that’s a very hard number to get.”
Some other commentary: This Extraordinary Claim Requires Extraordinary Evidence!
Update: Here is the CERN press release
Given the potential far-reaching consequences of such a result, independent measurements are needed before the effect can either be refuted or firmly established. This is why the OPERA collaboration has decided to open the result to broader scrutiny. The collaboration’s result is available on the preprint server arxiv.org: http://arxiv.org/abs/1109.4897
Popcorn pops because the water inside flashes to steam and expands. If you put the system under sufficient pressure it won’t do this … until the pressure is released, and all of the popcorn pops at the same time.
Chad addresses the issue of the greenhouse effect in your car, and whether putting a sunshade inside or outside matters: Greenhouse Physics and Car Shades
In the first comment we find the following question
Does car window glass block IR?
to which Chad answers
I like the idea of testing this with a piece of glass and a heater. You could probably do it with a toaster or an electric stove and a Pyrex baking dish (don’t put the dish directly on the burner, though, because they can explode that way)
Here you go. I had a beaker rather than a baking dish, and I used the IR thermometer I demoed a few months ago
You can see that the filaments are heating up, but when the beaker is put in place, the temperature drops to ambient. So it blocks basically all of the IR in the region of sensitivity of the device.