TVs, radar guns and other technologies linked to Einstein’s theories of relativity
If you’ve ever received a speeding ticket or enjoyed a night watching TGIF in the 1990s, then you can thank Albert Einstein. This week marks a century since the patent clerk-turned-physicist presented his Field Equations for Gravitation at the Prussian Academy of Sciences in Berlin, establishing the framework for the theory of general relativity.
These lectures represented a sequel to work that Einstein had introduced a decade earlier on the photoelectric effect, which ultimately won the Nobel prize, and special relativity, which has been popularized by the equation E = mc2.
Despite the abstract nature of relativity, both theories permeate through society inside everyday technology. The concepts don’t only explain the fabric of the universe, but are carried in most purses and pockets. Einstein’s ideas send text messages, but also form the basis for the single most destructive weapon ever constructed.
It’s hard to say if society would have missed out on the following gadgets without Albert Einstein. Einstein had many academic competitors, some of which published aspects of special and general relativity theory before he did. However, Einstein was more than just a titan of theoretical physics. Writer Walter Isaacson describes Einstein as the reinventor of reality, but the German-born physicist was also thought of as a wantaway father, a civil rights advocate, an antifeminist, a pacifist, an iconoclast and a rock star.
— C&EN (@cenmag) November 25, 2015
That’s the thing. By hunting for a unified theory of everything, Einstein united our fascinations in theoretical physics, the universe and him.
Television would be blurry without special relativity
Here’s how special relativity kept that original episode of “Friends” from being out of focus, at least from a visual perspective.
Einstein’s theory of special relativity describes the speed of light as the only constant in the universe, while also saying that the laws of motion are always the same, regardless of how fast an object is traveling. But if light stands alone as an immutable champion, then everything else in the universe must be flexible, including distances between things (space) or even time. That’s been proven experimentally and leads to some wacky trends in our existence.
For instance, if you’re standing by the road and a car zooms past, that vehicle is physically shorter, time passes slower for the driver relative to you and the motorist’s mass increases — albeit all at minuscule levels.
Those changes become more apparent as one moves faster, which factors into the clarity of box television sets.
“Special relativity becomes relevant if objects move with speeds close to the speed of light. We don’t see this happening to large objects, but particles can easily do this. For example, electrons,” said Robbert Dijkgraaf, who heads the Institute for Advanced Study where Einstein served as a professor from 1933 until his death in 1955.
Old-fashioned TVs use cathode rays tubes to shoot electron beams at a screen. The screen is internally coated with compounds called phosphors, which glow as energy passes in the beams cause the phosphors to glow, creating color and an image, but to do so, the electrons must be moving fast. Real fast.
“In an old-fashioned TV set, electrons can be easily accelerated to 20-30 percent of the speed of light,” Dijkgraaf said. “At these speeds, things become really crazy.”
That’s because of special relativity. The super-speeds cause the electrons to grow in mass in relationship to the rest of the TV set.
“From the perspective of the electron, the TV has shrunken,” Dijkgraaf said.
Magnets inside the TV guide the electrons to different parts of the screen to produce a picture, but Dijkgraaf said that the design of the magnets has to take account of special relativity. Otherwise everything would be out of focus by as much as millimeters.
Dijkgraaf said a much more spectacular example of this phenomenon happens inside particle accelerators, where fast speeds cause the internal time of particles slows down by a remarkable degree, through a process known as time dilation. As a result, these particles live much longer than normal.
These principles don’t apply to LCD or plasma TVs because those devices don’t rely on electron beams.
If you’ve ever received a speeding ticket from a traffic trap, you can thank Einstein.
Light moves in waves. That’s true if you’re dealing with visible light, ultraviolet light, X-rays or other types of light, which are collectively classified as electromagnetic radiation.
All waves exhibit the Doppler effect. You’ve witnessed this happen while standing on a curb while an ambulance raced toward a hospital. The siren has a higher pitch as it approaches you, a regular pitch when it’s right beside you and a lower pitch as the car speeds away. That’s because the frequency of sound waves changes if their being emitted from a moving object.
The Doppler effect doesn’t only apply to emitted waves, but those reflecting off an object, which explains how radar guns work. Police scanners emit infrared waves that rebound off cars and then detect the frequency of the reflections as they return, giving a calculation of speed.
Thanks to Einstein’s special theory of relativity and light’s immutable pace, a radar gun can make precise, almost instantaneous predictions of a vehicle’s speed, even if the cop car is moving too.
Nuclear power and Einstein’s aversion to the A-Bomb
Particle accelerators and special relativity factor into a legacy often misattributed to Einstein: The creation of the atomic bomb.
The “E” in E = mc2 refers to energy, so on a basic level, Einstein’s equation says mass and energy are interchangeable. As Alok Jha explained masterfully for the Guardian:
In Einstein’s new world, mass became a way to measure the total energy present in an object, even when it was not being heated, moved or irradiated or whatever else. Mass is just a super-concentrated form of energy and, moreover, these things can turn from one form to the other and back again.
Nuclear reactions rely on this principle to create energy. When a neutron — a subatomic particle — is smashed into unstable uranium atoms, the latter splits into smaller atoms. This atom splitting releases energy in the form of heat and more neutrons, which repeat the cycle, causing a chain reaction. The process repeats millions of times in a second, releasing tremendous energy. One gram of uranium or plutonium (0.035 ounces) can release the energy equivalent to three tons of coal or 600 gallons of petroleum oil in a single day, according to the Lawrence Berkeley National Laboratory. This energy can power cities, but as the Manhattan Project proved, it can also be harnessed for a weapon.
Einstein didn’t contribute to the Manhattan Project and came to regret his one association with the war effort. In August 1939, he wrote a letter warning Franklin Roosevelt about Germany’s quest for a nuclear weapon. But as Walter Isaacson described in 2008 for Discover Magazine, Einstein “knew little about the nuclear particle physics underlying the bomb” and was once quoted in Newsweek saying, “Had I known that the Germans would not succeed in producing an atomic bomb, I never would have lifted a finger.”
GPS, Jell-O and the heart of your cellphone
Ok, special relativity is great, but what about technology inspired by the theory of general relativity?
The most pervasive example is the Global Positioning System (GPS), and it results from Einstein’s general theory of relativity clarifying the origins of gravity.
Three hundred years ago, Isaac Newton observed that small objects in the universe are drawn toward larger objects, and he discerned that strength of this attraction depended on their mass. More massive objects — like Jupiter — have a stronger pull than smaller bodies like Mercury. This concept was a fine and dandy foundation for gravity, but it didn’t explain how two objects become attracted in the first place? Enter Einstein and general relativity.
His theory proposed that massive objects can physically bend space. To get a sense of what that means, imagine that you’ve dropped a big marble onto a big ol’ bowl of Jell-O. When the marble lands, the Jell-O will press downwards and the adjacent areas will slant like a ramp toward the marble. If a smaller marble sits on the edge of that ramp, it’ll be drawn toward the first one.
Using his field equations, Einstein explained that gravity is actually the curving of this Jell-O, which in the real universe is made from space and time. As California Institute of Technology theoretical physicist Sean Carroll wrote for the NewsHour earlier this week:
In Einstein’s universe, space and time are absorbed into a single, four-dimensional “spacetime,” and spacetime is not solid. It twists and turns and bends in response to the motion of matter and energy. We perceive that stretching and distortion of the fabric of spacetime as the force of gravity.
This means that large sources of gravity — for instance, the Earth — can alter time. As a result, a clock on the planet’s surface runs slower than one onboard a GPS satellite plopped 12,000 miles into free space. (This is also considered time dilation.)
Relativity was a roadblock during the early days of GPS. GPS satellites must be in sync with your phone or car receiver in order to pinpoint your location. When engineers initially blasted GPS satellites into outer space, they assumed that the effects of relativity would be too small to alter the highly precise atomic clocks onboard.
They were wrong. The satellite’s clocks ran 38 millionths of a second faster than clocks on Earth per day. That sounds marginal, but it would have thrown off your location by as much as seven miles.
Dijkgraaf said ignoring relativity wouldn’t only cripple GPS, but telecommunications as a whole.
“Our communication network is a configuration of transmitters, receivers, satellites — both earthbound and in outer space. And in some sense, all of our technology is operating at the speed of light,” Dijkgraaf said. “These devices are interacting with each other through space and time with precision, so we need atomic clocks for all of our communications.”
Experiments with atomic clocks have measured gravity-based shifts in spacetime over extraordinarily short distances, such as a 2010 study from the National Institute of Standards and Technology that measured the effect over the length of a foot. The difference is small — 90 billionths of a second over 79 years — but this subtle shift in relativity means you age faster than a friend if she is standing a couple of stairs below you on a staircase.
Also, if space can bend, then general relativity argues that gigantic collisions between stellar objects can send shockwaves through outer space.
“If you have a collision of two black holes, it basically creates a tsunami in space that can propagate from a very distant star or galaxy all the way to Planet Earth,” Dijkgraaf said. The same thing happens if you wave your hand through the air, though on a much smaller scale.
These gravity waves haven’t been detected on Earth yet, but scientists know the phenomena exists
“We’ve indirectly seen them with a pair of stars that are rotating around each other. We don’t see the waves themselves but we see the stars losing energy by radiating the gravitation away,” Dijkgraaf said.
Next week, the European Space Agency will launch the LISA Pathfinder, a space satellite on a mission to detect gravitational waves. If it spots these waves, the event could be illuminating, Dijkgraaf said
“What does the universe look like in the ‘light of gravity’ so to speak? We might detect gravitational waves all the way from the Big Bang, but it’s like waiting for the clouds to part and having no idea what’s behind them,” Dijkgraaf said.
Einstein and how to send a text message to deceased relatives
Astronauts are arguably the world’s first time bandits. People who spend lengthy spells on space stations have actually moved forward in time relative to folks stuck on Earth.
That’s because space stations travel fast — 17,000 miles per hour — to remain in orbit, and the clocks along for the ride start to suffer from special relativity. Orbital speed slows time, so when astronauts return to Earth, they land in the future.
Russian cosmonaut Gennady Padalka, who earlier this year set the record for the longest collective time spent in space at 879 days, has traveled 22 thousandths of a second into the future. If American astronaut Scott Kelly landed today, he would have jumped six thousandths of a second into the future.
As recent history can attest, when people picture time travel, they think of Michael J. Fox, a puffy red vest and a tricked-out Delorean. But this perception doesn’t vibe with relativity, said University of Connecticut theoretical physicist Ronald Mallett.
“As far as taking a time machine with you, no. That’s not really an option,” Mallett said.
He should know, since he is building a time machine. That’s right. A time machine … and because of Einstein’s theories, the idea isn’t as far-fetched as you might expect.
To understand, let’s start with E = mc2. As we mentioned before, this equation states that mass and energy are interchangeable. Light has energy, so it also carries mass. If you remember our journeys with the marble and Jell-O, then you know that mass can bend space and time, giving off the perception of gravity.
Mallett’s time machine would harness this relationship: “If gravity can affect time, and light can create gravity, then light can affect time.”
To tweak space and time, the project will need lasers … about 10,000 of them organized into rings. Next, Mallet and his colleague — UConn experimental physicist Chandra Roychoudhuri — plan to stack these ring lasers like pancakes. The collective vortex created by the lasers might twist space, based on a theoretical equation published by Mallett 15 years ago.
If it works, Mallett would have, in a sense, satisfied a childhood dream of reconnecting with his deceased father, Boyd.
“He was only 33, and I was 10 years old. He looked like a very healthy man, but we didn’t know he had a weak heart. He died of a massive heart attack. It completely devastated me,” Mallett said.
A year later, the younger Mallett stumbled upon the H.G. Wells book The Time Machine. “It was like a lightbulb for me. If I could build a time machine then I can go back and see him again,” Mallett said.
Mallett and Roychoudhuri would judge the twisting of space by shooting a stream of neutrons into the vortex. Neutrons spin in a certain direction, so if their rotations changed by the time that they exited the vortex, the researchers could conclude space had been twisted.
It’s a bold idea with a heartwarming backstory, but as Mallett learned on his road to becoming a physicist, the rules of spacetime would likely prevent a trip to the 1950s.
Construction of the prototype would be simple on a practical level. A diode laser is about a thousandth of an inch high, so if you have a tower of 10,000 laser, that’s only about 5 feet, Mallett said. It’s the date that’s a problem.
“The machine is responsible for the twisting of space and time, so you can’t go earlier than that. Once the first time machine is turned on, our descendants would be able to communicate with us, but we won’t be able to communicate with our ancestors,” Mallet said. The same thinking applies to wormholes, which are theoretical tunnels between sections of spacetime. A time traveler could visit as far back as the creation of the wormhole but no earlier. (For more, here are Sean Carroll’s 10+1 rules for time travel).
Another barrier to time twisting is energy. The juice required for prototype’s ability to twist space would be 23.9 Joules — about as much power as 24 mile per hour baseball pitch. But the energy for twisting time would be off the charts.
“That on the surface appears to require an enormous amount of energy. I mean a huge amount of energy, like stellar quantities,” Mallett said. However, twisting space may serve as the foundation for a warp drive.
Yet humanity might one day figure out how to produce the necessary power to bend time or maybe we’ll find an extraterrestrial civilization that has planted megastructures around a star to harvest energy. If so, Mallett believes his time machine would be a great way to exchange information between the present and future. These text messages could be encoded in the spins of the neutrons, akin to what’s planned with quantum cryptography and could carry warnings about natural disasters.
“Imagine the thousands of lives that we could save by having an early warning,” Mallett said.
Or perhaps we’ll stumble upon aliens that built a time machine centuries ago, so Mallett or anyone else could visit cherished moments from their past?
Dijkgraaf is certainly open to the prospect.
“Our current technology is certainly not there, and if you took a poll of physicists, you’d see a lot of skepticism,” Dijkgraaf said. “But if you take a broad point of view and say, ‘we don’t know what kind of civilizations are out there and how far they have developed technology’ … who knows?”