This story is from The Pulse, a weekly health and science podcast.
Radio astronomer Scott Ransom essentially listens to outer space. Mostly, it makes a hissing sound.
Ransom works at the National Radio Astronomy Observatory in Charlottesville, Virginia, where they use radio telescopes. They’re these enormous dishes in the neighborhood of a football field wide and designed to pick up super faint radio waves from thousands of light years away.
“What we’re measuring basically at the front of the telescope is just oscillations in the electric and magnetic fields that are coming from space,” he said. “And those oscillations are pure noise, like 99.999999% noise throughout all frequencies, and that sounds like a hiss.”
Computers convert these radio signals into audio — you end up with the sound of everything, all mixed together. The radio telescopes are so sensitive their receivers need to be super-cooled to near absolute zero. Otherwise, their own temperatures drown out whatever distant celestial body astronomers are trying to listen for.
“It’s because everything that has any kind of temperature — temperatures is jiggling, a jiggling electron — when you jiggle any kind of electron, you generate electromagnetic signals, noise,” he said.
Ransom is listening for specific celestial bodies called pulsars.
“Pulsars were discovered just over 50 years ago,” Ransom said. “They’re basically like cosmic lighthouses. It’s basically a giant nucleus that’s the size of a city.”
They occur after supermassive stars start burning out. Their own gravity collapses them in on themselves, into so-called neutron stars. They get smaller and smaller, denser and denser.
“Conservation of angular momentum causes that star to spin really fast, just like a figure skater when her arms come in, she spins much, much faster,” Ransom said. “So we have a really, really rapidly rotating, incredibly dense object with really strong magnetic fields.”
As it spins, its stream of electromagnetic radiation sweeps over our planet like the sweeping rays of a lighthouse on a ship.
Advanced computers can hear these things buried in the endless hiss of the universe.
“There’s a dunk dunk dunk from the rotating pulsar signal. The type I specialize in are so-called millisecond pulsars, which spin hundreds of times per second, which is just mind-blowing by themselves,” Ransom said. “Since they’re spinning hundreds of times a second, they’ll actually sound like a pure tone.”
The fastest pulsar spins so fast, it’s converted signal produces a musical note you can get close to on the piano, between F and F sharp above middle C.
Ransom has been listening for these things for decades. In that time, radio telescopes have gotten more and more sophisticated, but so has the rest of the world. The result: Whole chunks of the universe have essentially disappeared from view. They’ve been drowned out by radio interference from our everyday consumer tech.
“So to give you an example, the digital TV transmitters, which happen in like the 500 megahertz to 600 megahertz regime, that part of the spectrum is basically completely useless,” Ransom said.
It’s constantly in use carrying sitcoms and sports over the air.
“You can do almost no science whatsoever in that band. Another example is in the middle of the Wi-Fi band,” Ransom said. “There’s a whole chunk around 2 gigahertz, which is the standard Wi-Fi band, that’s extremely hard to do anything with. And we basically just blank out those channels in our data.”
Wi-Fi may seem somewhat modern. But like Bluetooth, GPS, and your smart fridge that talks to your even-smarter watch, it’s all over good, old-fashioned radio waves.
“You know, everyone nowadays carries around one or two or three things with them all the time that transmit and receive in the radio. Your laptop, your cellphone, any kind of tablet, you have your Bluetooth headset, your little clicker that opens your car door,” Ransom said. “All of these things are sending and receiving radio signals.”
It used to be easier to get away from these things, to find secluded enough areas or, as is the case with the National Radio Quiet Zone in West Virginia, to engineer them.
“So knowing that you’re in one, that the best way is that you basically lose your cellphone signal,” Ransom said.
Greenbank, West Virginia, is home to the largest movable radio telescope in the world. What is not there is Wi-Fi. Like certain cellphone signals, it’s prohibited within the zone — microwave ovens are even banned in some parts of it, while landlines and pay phones live on.
But even there, it’s still not completely quiet, not all the time. Newer cars for instance, produce their own Wi-Fi signals.
“If someone’s using Wi-Fi in their cars, that’s going to directly impact my observation because we can’t regulate everyone in a car driving past a radio telescope,” Ransom said.
There’s always something new on the horizon. What has Ransom especially worried now is Starlink, Elon Musk’s proposed system of low-Earth-orbit satellites that will provide internet to rural areas.
“That’s why I’ve mentioned satellite radio and GPS multiple times, because those two signals are two of the biggest problems for my type of science, because they are always there,” Ransom said.
At the heart of this problem is the fact that the radio spectrum is finite — it runs from 30 kilohertz to 300 gigahertz. We’re using pretty much all of it.
“I mean … you can just look and we’ve gone over the last couple of decades into a relentless use of the spectrum,” Ransom said. “We’re basically using every little open megahertz of it.”
It’s actually big money. Any time a broadcaster doesn’t need its particular frequency anymore, it goes to auction.
“They get sold for many, many millions of dollars. I mean, this is incredibly valuable territory, and that’s the way people can think of it. You can think of the radio spectrum as something that can be bought and sold as property,” Ransom said. “It’s like land because it really does have value, and it’s only going to get worse because we’re going to be using all of it someday.”
Though radio interference frustrates Ransom’s ability to peer into space, it’s also messing up Priscilla Mohammed‘s efforts to peer back down at Earth. She’s a researcher at NASA’s Goddard Earth Sciences Technology and Research.
“We’re looking down, so we have imagers that looked down on the earth and what are they looking at is faint signals that come from the earth,” Mohammed said. “The earth actually radiates heat off the planet.”
Scientists like Mohammed use satellites with very sensitive instruments to measure heat. Every patch of Earth is giving off some kind of energy — it’s just much too weak for us to notice it.
“It’s much too small. So just to give you an idea, your cellphone emits 1 watt of energy and the amount of energy we’re trying to measure is … 10 to the minus 15 watt,” Mohammed said. “So it’s like trying to discern like a whisper, like somebody’s whispering across the room and there’s like, you know, football and conversation with a lot of people going around.”
The whispers can be translated into, say, how much water vapor is in the air, or how much salt is in ocean surface water. Those bits of data add up to help with weather forecasts and studies of climate change.
But it’s incredibly easy to drown these signals out. Remember, scientists are listening for these whispers from space, hundreds of miles straight up.
“A few months after the SMAP launched, we actually noticed a source in, Kerrville, Texas,” Mohammed said.
SMAP, which stands for Soil Moisture Active Passive, is a NASA satellite launched in 2015 that measures soil moisture. All its data from this corner of Texas was unusable because something was blowing out all the readings.
“We notified the FCC and they sent somebody out there to actually look at the location that we gave to them,” Mohammed said. “And it was actually a woman using a wireless camera on a farm ’cause she wanted to monitor her horses foaling.”
The nice men from the government told the woman her particular camera was messing with a $912 million satellite streaking some 400 miles above them. Could she please consider using a different one?
“And it was probably a camera that was operating at the frequency it was supposed to, but it was also spewing out frequencies in our band,” Mohammed said. “So it was faulty.”
Unintended frequencies leak out of gadgets all the time. Regulators tell widget makers their products must operate in certain bands, but it’s imperfect. Little things go wrong all the time.
“The whole of Japan is just shrouded by this radio frequency interference,” Mohammed said. Apparently because of a super popular cable box a lot Japanese households had.
“Your satellite dish, like DirecTV, collects these signals. And then what it does is it has electronics that down-convert that signal to a lower frequency and it can now travel over like a co-ax [coaxial] cable and go to your set-up box into your house,” Mohammed said.
That’s where the leak was. When the signal from these two channels passed through the co-ax, it just spewed radio interference.
Mohammed said there are certain algorithms she and others have developed that try to clean up otherwise unusable data. They essentially look for artificial noise and delete it from datasets automatically. But the problem is that when things get too crowded, good data starts getting cut out with the bad.
The real solution to this, Mohammed thinks, is conservation. International treaties preserve certain bands. Just as we have nature preserves that governments fiercely guard, so too do we need radio spectrum preserves kept pristine.
“I think it’s really important for us to kind of manage what we have,” Mohammed said. “So there are slivers of the spectrum that [are] dedicated just for passive sensing, just for radio astronomy.
Ransom, the radio astronomer, described a bit of protected territory in his field — the so-called hydrogen 21 centimeter line.
Hydrogen is the most common atom in the universe, he said. “And when you have a hydrogen atom sitting out in space, it has an electron going around it. And once every few million years, that electron, the spin of that electron, switches, it flips upside down basically,” Ransom said. “When that happens, a photon shoots out with a wavelength of 21 centimeters. That corresponds with a certain frequency.”
Which is about 1.4 gigahertz. So if you want to study galaxies with hydrogen, you can dial that in, and it should be clear.
The problem is the universe is expanding. Signals from the farthest galaxies red shift, toward longer wavelengths, as they move away from us. It’s similar to the way the wail of an ambulance siren goes from high to low in pitch as it zooms toward you, and then past you.
Suddenly, from Earth’s perspective, a galaxy’s signal isn’t 1.4 gigahertz anymore, it’s down to like 600 or 700 megahertz.
“And that means that’s right in the middle of the digital TV stations,” Ransom said.
So, it’s gone essentially.
There are types of science that just can’t happen in our crowded radio spectrum. And conservation efforts are always going to clash against commercial needs and wants.
The Spectrum Collaboration Challenge
Another possible solution is more efficient use of the limited spectrum we have.
Right now, different broadcasters all have their own bandwidths. It’s a bit like a highway where each traveler has a lane. One rental car agency, one lane. Its competitor, one whole lane just for its customers. Police cars, one lane. Could broadcasters share these lanes in an efficient manner?
The Defense Advanced Research Projects Agency, or DARPA, held a competition that pit teams of engineers against one another to try and figure this out.
It was called the Spectrum Collaboration Challenge and went on for three years before wrapping up in 2019. Team GatorWings, out of the University of Florida, took first prize in this incredibly nerdy Super Bowl.
“Originally, Wings was the Wireless Information and Networking Group,” said John Shea of Team GatorWings. “We put wings together with Gator for GatorWings.”
“Sometimes, you’ve got to explain to our family or our friends exactly what we are doing,” said Tan Wong, team leader. “The cool thing is it’s kind of like the ultimate esport for us communication engineers.”
The teams had to engineer an artificial intelligence switchboard that made decisions in real time about how to use which parts of the spectrum to get a message through all kinds of competing noise.
“So we actually have to build our system robust enough so that our system actually can work well in all the crazy cases that DARPA dreams up,” Wong said.
There were all kinds of simulated scenarios. For instance, the teams had to find a way for soldiers to message one another in a city and cut across the crowded spectrum. The actual competition took place in front of giant monitors in an auditorium. The late Grant Imahara of the TV show “MythBusters” hosted it.
One thing all the events had in common was that the winning team has to get its message through without completely drowning out everyone else. It had to be just aggressive enough.
“We had a real shock, the very first preliminary round they had in the final competition we were almost eliminated according to the scores,” Team GatorWings’ Shea said. “We dropped into this elimination competition and then came back out of that.”
The team’s intelligent radio robot was too aggressive at first, not so much sharing the road as it was ramming others off it. A message for the pizza delivery guy can’t drown out the 911 dispatch call.
But in the end, the team struck the right balance. Team GatorWings came out of the elimination bracket and fought its way to the final — and won.
“It was elation. We worked really, really hard for three years, day and night, literally weekends all the time in the last two years. You can see when people add updates, and it just updates at 2 or 4 or 5 in the morning, all the time,” Shea said.
The victory came and went without much fanfare from the rest of us. Like much of the radio spectrum that the modern world relies on, few people really understand how it all works. But if it’s going to keep working, it’s going to be thanks in no small part to engineers like the GatorWings crew.