Category Archives: Physics

The Photon Push-Me Pull-You Update

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Back in June I wrote up a post an the Abraham-Minkowski controversy, which concerns the momentum of a photon when it’s in a medium.

Depending on the assumptions one makes, one can show that the momentum increases or decreases inside the medium, and obviously both solutions can’t be correct. But for a long time it was unclear which assumptions were faulty, because it was such a delicate experiment to do.

I just ran across a post at Everyday Scientist, and the paper (based on the ArXiv preprint I cite in the link) was published last month … and there’s a video.

Light Bends Glass

The researchers performed a second experiment with a longer fiber and continuous–rather than pulsed–laser light and found similar results. The tip of the hanging fiber moved sideways like a pendulum by about 30 microns, which agreed with the tiny force (less than a billionth of a Newton) that they predicted. The team also verified that thermal effects, such as heat expansion, would be too small to influence the fiber’s movement.

You need to a flashplayer enabled browser to view this YouTube video

Just Checking

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Possible Abnormality In Fundamental Building Block Of Einstein’s Theory Of Relativity

Physicists at Indiana University have developed a promising new way to identify a possible abnormality in a fundamental building block of Einstein’s theory of relativity known as “Lorentz invariance.” If confirmed, the abnormality would disprove the basic tenet that the laws of physics remain the same for any two objects traveling at a constant speed or rotated relative to one another.
[…]
The new violations change the gravitational properties of objects depending on their motion and composition. Objects on the Earth are always moving differently in different seasons because the Earth revolves around the Sun, so apples could fall faster in some seasons than others. Also, different objects like apples and oranges may fall differently.

I find it amusing that there are a bunch of relativity cranks who claim that relativity is treated as dogma. The reality is that it isn’t all that hard to find scientists devising tests of relativity of various sorts, whether it’s testing the predictions of GR or checking for anomalies such as this.

Of course, thus far whenever someone has devised a clever test like this, we’ve found that relativity is correct.

Beulah, Peel Me a Grape

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And nuke it.

Things to do in a microwave #2: Create a plasma

It just so happens that grapes are about the size of the wavelength of microwaves, which is important. And grapes also have sugars, which make them into dielectrics. (There are other fun things you can do with grapes because of this). Both of those together make the coupled grape halves into a dielectric dipole antenna, which is just a fancy way of saying that the microwaves that hit one side of the cut grape will pass to the other side, in a very concentrated way. The result is that there is a huge voltage generated between the two sides of the cut grape. That voltage causes electricity to jump from one grape half to the other (”arcing”). This is what happens when you rub your socks on the carpet and touch the doorknob — that spark is electricity jumping from your hand to the doorknob. The difference in this case is that there is a HUGE voltage generated (3000 volts by one website), and that is enough to ignite the steam from the grapes into a plasma state (a glowing ionized gas, where the electrons have been ripped from the gas molecules by the high temperatures). You can capture this plasma in a glass, as in the video above (wow!)

And, of course, this is preceded by Things to do in a microwave #1: Find your microwave hot spots

In addition to the two methods Stephanie lists, you can use marshmallows or chocolate chips, and look for where the melting starts. And then you can eat the experiment. (Stephanie mentions marshmallows; I missed it)

Update: Not done yet! Things to do in a microwave #3: Ivory Soap Monster

Things to do in a microwave #3: Microwave a CD
#3? Should be #4. (I’ve brought the whole “Five is right out!” counting thing to Stephanie’s attention) There’s an image that shows some mini Lichtenberg figures, i.e. the little tree-like patterns the electrons make.

Things to do in a microwave #5: Microwave a lightbulb

Wrong Way! Go Back!

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One-Way Waves

Imagine a string of pearls. You can start a wave by wiggling the first pearl or the last; the waves can travel either way because each pearl is coupled equally to both neighbors. But researchers have lately become interested in “unidirectional” coupling, in which the force between neighbors only allows waves to move in one direction. This can be seen as an extreme example of anisotropic media, in which the wave speed depends on the direction. Computer simulations have shown how waves will propagate through unidirectional arrays, and researchers have built electronic circuits that exhibit unidirectional coupling [1]. But these circuits had only three “pearls” in the array–too small to see all of the wave propagation effects predicted in the simulations.

Milky Way Put On Weight this Holiday Season

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Milky Way 50 Percent Larger, Astronomers Discover

[N]ew measurements of how quickly our galaxy is rotating have led a team of Harvard astrophysicists to conclude that our galaxy is 50 percent more massive than previously thought, and likely does have four arms.

“We should certainly think of the Milky Way no longer as the little sister of the local group,” said Mark Reid of the Harvard-Smithsonian Center for Astrophysics. “We should think of the Milky Way and Andromeda as more like fraternal twins.”