The annual SciFoo un-conference is always amazing, and 2010 did not disappoint.
Physicist Garrett Lisi, executive editor of Scientific American Mariette DiChristina, and cosmologist Stephon Alexander, pose with Simon Field
We all arrived at about 5:30 Friday afternoon, and as we were waiting for dinner, I found Max Tegmark talking to Paul Davies, and I asked a question that had bothered me on the drive over. How do gravitons get out of a black hole?
Paul Davies jumped right in. “That’s easy,” he said, and launched into a 20 minute description of virtual particles, event horizons, and evaporation of black holes as negative energy fell into them. It turns out he had written the first paper on this subject 20 years ago or more. I think I followed his descriptions pretty well (he is very good at explaining things to non physicists), but I will have to look up that paper before I try to explain it to anyone else. I left him with Lawrence Krauss and went to dinner.
At dinner I found myself across from Saul Perlmutter, the cosmologist who discovered the accelerating expansion of the universe, that led to the realization that dark energy accounts for 74% of everything in the universe. I brought my friend Theo Gray over to meet him, and explained that I had just seen Saul, Max, and Garrett Lisi on television the night before, explaining cosmology to Morgan Freeman.
Me posing next to Saul Perlmutter
On Saturday, the actual talks in conference rooms started. I chose to start with Nat Torkington‘s lightning talks, where speakers get five minutes to describe what they have been working on. These are always fascinating, and a great way to get to know who you absolutely must talk to later. I happened to sit next to physicist Alan Guth, the guy who figured out there was a period of inflation right after the big bang. I told him about my talk with Paul Davies, and he said it was probably best that I talked to Paul first, as Alan might not have had a ready answer for my question. I’m really going to have to read that paper.
The talks were great, everything from getting sued by Facebook for using what they had published on the web, to worm spit used to make biocompatible LED tattoos, to Josh Bailey’s irresponsible behavior with high voltage, to Beth Shapiro‘s wonderfully funny experiences in Beringia digging up fossil DNA and eating mammoth meat.
After the lightning talks, Michael Shermer and Bruce Hood gave a great talk about belief and reason. Then came lunch, where I sat with Jose Gomez-Marquez and talked about using some of the techniques I used to build scientific toys to build medical devices for third world countries. I left him with some of my tiny microscopes to make a laser projection nebulizer analysis tool.
After lunch Paul Davies led a discussion on how to find evidence that life on earth was created more than once from basic chemicals. Finding that life evolved more than once on earth would make it more likely that it evolved elsewhere as well.
Later, Lee Smolin talked about how loop quantum gravity theory got started, Garrett Lisi talked about developing a theory of everything while surfing in Hawaii, Stephon Alexander talked about expanding Alan Guth‘s inflation theory to explain unanswered questions, and all of these stories were told through personal experiences and humor, and you got a real sense of what it is like to live on the cutting edge of theoretical physics.
On Sunday, I taught Connor Gray how to demonstrate science toys while his father Theo and I went to more talks. In return for doing that, I gave him a 405 nanometer laser (purple light). He had spent the day playing at my farm the day before, and had gotten the same 5 hours of sleep that we all had, but he did a stellar job at the demonstrations. Watching Devin and Michael Shermer breath fog out of their noses like dragons after eating whipped cream frozen in liquid nitrogen was a real treat.
Danny Hillis, Simon Field, Paul Fenwick, and Stewart_Brand at SciFoo10
Sometimes a simple piece of technology is so ingenious, it makes you wish you could meet the genius that came up with that idea. Simple twisted pair wiring is just that kind of idea.
Long wires work great as antennas, picking up all kinds of static and noise from their environment. That is bad for communications, where you only want the signal from the source to get to the receiver, without all the environmental noise.
The clever trick is to use something called differential mode transmission. You send your signal on one wire, and you send an inverted copy of the signal on a second wire that is right next to the first one. At the receiver, you invert one of the signals, and then add the two together.
Any noise that is picked up by the pair of wires will be inverted in one of the wires, so that when the signals are added, the noise from one wire will exactly cancel the noise from the other wire, leaving no noise at all. In contrast, adding the two signals will double the strength of the communication you care about.
In one trick, we reduce the noise to zero, and double the signal, giving us the high “signal to noise ratio” that is the holy grail of communications engineers.
Of course, if we have a bundle of wires all carrying different signals, some of them will be closer to one wire in the pair than to another, and we get a form of noise called “crosstalk”. But twisting the pairs eliminates that, because in a short distance, any signal induced by one wire in the pair is cancelled by the second wire, which the twist has brought closer to the other pair.
Just twisting isn’t quite enough, however, since if all the pairs had the same number of twists per inch, there would still be some correlation in the signals, and some crosstalk. But if you look closely at the photo above, you will see that each pair has a different number of twists per inch.
A side benefit from differential mode transmission is that it radiates less energy in the form of radio waves into space. The nearby opposite signals absorb one another, so less power is needed to send a signal the same distance in the cable, and less interference is transmitted to other cables.
So who was the genius who came up with this idea? Did he get fabulously wealthy?
As with many of these stories, the answer is that this stunningly brilliant idea didn’t occur to someone all at once, but took many iterations over many years to take form.
Telegraph lines and early telephone lines used a single wire to send the signal. The earth was used instead of a second wire. The circuit did not actually return to the battery through the earth, there would be far too much resistance. Instead, the earth, being a big object with lots of electrons, can simply absorb or emit as many electrons as are required.
When electric trolley cars were installed next to the telegraph wires, the sparks and current changes from the trolleys acted as strong nearby noise sources, and interfered with the signals. To get around this, telephone companies went to differential mode transmission, using two wires strung a couple feet apart on cross beams at the tops of poles.
This worked pretty well for trolley car interference, but as electrical power lines were installed carrying alternating current, a new source of interference came along. This was especially troublesome because the electrical wires were strung using the same poles as the telephone wires.
To get around this problem, the telephone wires were crossed every few poles. The power line interference was low frequency, so it had very long wavelengths. Crossing the phone wires every few poles had the same effect as a twisted pair for eliminating low frequency noise.
When telephone wires were bundled together, however, the noise was not just the low frequency power line noise, but higher frequency noise from the other phone signals. At this point, it made sense to twist the wires together a few times per inch instead of a few times per mile.
So now we have our familiar computer network cables, handling gigabits of information per second, all thanks to a bunch of telephone engineers solving one little problem after another.
Heterorhabditis bacteriophora is a nematode. A simple roundworm. Colorless, unsegmented, with no appendages, it eats bacteria.
So why do they make great biological insecticides?
They are farmers. They have a symbiotic relationship with the bacteria that they eat. The bacteria like to live inside insect hosts, which they kill and eat. The nematodes eat the bacteria, and then when the insect is eaten up, the nematodes carry some of the bacteria to a new insect. They then regurgitate the bacteria inside the insect, to seed their bacteria farm.
The nematodes are harmless to plants and mammals, but quite deadly to many soil insect pests. They target dozens of harmful pests, yet have no effect on bees and other beneficial pollinators.
Because they are microscopic metazoans, they can be mixed with water and sprayed using common pesticide equipment. They can be grown in standard fermentation tanks up to 40,000 gallons.
The bacterial symbiotes are Photorhabdus luminescens. They kill the host insect quickly, in one to two days. They need the nematode in order to enter the host insect, and the nematode can carry them much longer distances than they could travel alone. In return, the bacteria provide an environment in the host insect that the nematode needs for survival and reproduction. The bacteria produce immune suppressing proteins that prevent the insect from killing off the nematodes, and they produce anti-microbial molecules that prevent other bacteria from colonizing the dead insect.
As biological controls, the nematodes have some advantages over chemical pesticides. They aren’t toxic to mammals, and they don’t pollute the ground water, and they target only specific pests. On the downside, they are living creatures, and are harmed by drying out, ultraviolet light or heat, and they can’t be stored for long periods.
Another plus for the worms is that you can tell if an insect was killed by them. The bacteria glow (hence the name luminescens).
When mutations cause genes to stop functioning, the effect can be caused by damage to the gene, or by damage to the genes that turn on the gene that is no longer expressed.
Take the example of hen’s teeth. Although chickens lost the ability to grow teeth 60 to 100 million years ago, the mechanisms for supporting the growth of teeth are still intact, and can be induced to grow teeth by replacing one lost protein, called BMP4, or reintroducing the production of that protein by the neural crest cells.
There are many genes involved in making teeth, and it appears that in birds, interruption of a single pathway is responsible for the loss of teeth. The rest of the mechanisms are still preserved, 60 million years later.
A similar genetic accident may be responsible for cats being carnivorous. Cats, from domestic cats to tigers and cheetahs, seem to have lost one tiny gene that is responsible for the sweet receptor in taste buds. They can’t taste sugar. They can’t taste the sweetness of plant materials like fruits or sweet sap.
Toying With Science is a series of short essays on scientific topics written by Simon Quellen Field, the author of Gonzo Gizmos, Return of Gonzo Gizmos, and Why There’s Antifreeze In Your Toothpaste. Simon also writes science fiction: A Twisted Garden, A Simple Piece of Mind, and mysteries A Quiet Place to Die. He designs […]more →