Bubble in a drop of water on the ISS that shows two images of André Kuipers.
A better shot than the one of Clayton Anderson on STS-131 that I linked to way back when but the physics is the same, of course.
via Bad Astronomy
Category Archives: Physics
Putting the Right Spin on It
Infinite-capacity wireless vortex beams carry 2.5 terabits per second
Actually, it’s not spin. It’s the other angular momentum, pork the orbital variety.
These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream. In current state-of-the-art transmission protocols (WiFi, LTE, COFDM), we only modulate the spin angular momentum (SAM) of radio waves, not the OAM. If you picture the Earth, SAM is our planet spinning on its axis, while OAM is our movement around the Sun. Basically, the breakthrough here is that researchers have created a wireless network protocol that uses both OAM and SAM.
I couldn’t get a mental image of how you’d do this, but I think that’s because I was thinking about individual photons, and I don’t see how to get a photonic orbital angular momentum state. But this is data transmission, which can be analog, or even of it’s digital a “one” is made up of a bunch of photons, i.e. it’s classical.
So I grabbed the paper I could (an earlier one that demonstrated the effect, and to which I had access). Here’s what the antenna looks like
The light being sent will have a different phase depending on what part of the antenna is transmitting it, which gives you the vortex. 3 GHz signals have a wavelength of 10 cm, so that’s probably gives you the scale of the depth of the slice in the parabolic dish.
This technique is likely to be used in the next few years to vastly increase the throughput of both wireless and fiber-optic networks.
I think this is overly optimistic. It’s going to take time to make this robust for data transmission and then you have to deploy the technology. And fiber-optics? I don’t see how this would work in a fiber (a less forgiving environment to good polarization, which is likely to cause problems here), but I also don’t see it as being necessary. I don’t think fiber is as clogged as the RF spectrum is, and you can always add more fiber if you need to.
Don't Worry, It's not Contagious
I'm Also A Drachma Short
June 19, 240 B.C.: The Earth Is Round, and It’s This Big
Eratosthenes knew that at noon on the day of the summer solstice, the sun was observed to be directly overhead at Syene (modern-day Aswan): You could see it from the bottom of a deep well, and a sundial cast no shadow. Yet, to the north at Alexandria, a sundial cast a shadow even at the solstice midday, because the sun was not directly overhead there. Therefore, the Earth must be round — already conventionally believed by the astronomers of his day.
What’s more, if one assumed the sun to be sufficiently far away to be casting parallel rays at Syene and Alexandria, it would be possible to figure out the Earth’s circumference.
The Hippocratic Oath Does Not Apply Here
Did the OPERA affair harm or benefit science?
I think there was a benefit, because the actual process of science was displayed. But your mileage varied, as always, depending on your source. There were a lot of good stories, in which you would find explanations of what was going on. Unfortunately, there were a lot of stories that sensationalized the events, and gave us Einstein Overturned/Relativity is Dead – type headlines and stories, despite the fact that nobody associated with the experiment made such claims (of which I am aware, at least). But that’s par for the course. You have good reporting, you have bad reporting, and you have headline editors. They care about circulation, not whether they are doing harm to physics.
There were also instances of people stepping beyond their expertise in trying to explain the results. People were awfully quick to blame GPS (but not one of the critiques I read came from within the timing community; we know how well you can do time transfer) and with that came some “problem solved” stories. That, too is probably par for the course.
I think the only real damage to any credibility was the discovery that an internal calibration/check of the local timing system hadn’t been done in a couple of years. That seemed sloppy. People at the top resigned. They took responsibility for the oversight.
Overall I’m much happier showing off science, warts and all, than allow a stereotype to perpetuate — the mistaken notion that every announced result is the final word and that scientists see themselves as infallible. We got to have a discussion about uncertainty and statistical significance that wasn’t framed by someone equating uncertainty with failed science. The effect on public perception? I don’t know. I suspect that this just reinforced their biases — if they didn’t trust science before, this is just one more reason not to. But, as the adage goes, there is no bad publicity. If it raised anyone’s interest in science, that’s got to be good.
Walking Into a Cloud
One of my favourite bits about being a dad is, every now and then, just casually blowing my little boy’s mind – with science. Last weekend, we were out for a stroll when he came out with “I wish I had a rocket so I could go and stand on a cloud”. Sensing an opening, I explained that clouds were made of tiny drops of water that hang in the air, so you wouldn’t ever be able to stand on one. But that, when it’s misty, that’s just a cloud that’s really low down on the ground, so it’s actually very easy to stand inside a cloud. That pleased him, as he acknowledged his chances of owning a rocket any time soon were sadly marginal.
"Granular Jamming" is not a Music Phrase
More Than You Probably Wanted to Know About Dominos
A domino can knock over another domino about 50% larger than itself. A chain of dominos of increasing size makes a kind of mechanical chain reaction that starts with a tiny push and knocks down an impressively large domino.
Original idea by Lorne Whitehead, American Journal of Physics, Vol. 51, page 182 (1983).
See http://arxiv.org/abs/physics/0401018 for a sophisticated discussion of the physics.
One thing not discussed in the video (but the paper treats in gory detail) is that it’s not just an energy argument — you also must consider the collision between the dominos. It should be pretty obvious that the dominos can’t be separated by more than their height, else they won’t collide, but that they also need to hit the next high enough in order to exert a sufficient torque to topple it. Which contributes to this limit on the size of the next one.
Peek a Boo
How well can the government spy on us via satellite?
[I]f [the donated satellites] had actually been used as spy satellites, what would these super telescopes have been able to see on the ground? It’s a fascinating question, and leads into a nice basic discussion of the optical resolution of imaging systems. In other words, what is the smallest detail that could be picked up by one of these telescopes in orbit?
I'm Your Fire, at Your Desire
OK, look, I know I’ve posted a lot of Venus Transit pix, and it’s been a week now, so you have to know I wouldn’t post one this late unless it was really awesome.