Australian scientists have recreated a famous experiment and confirmed quantum physics’s bizarre predictions about the nature of reality, by proving that reality doesn’t actually exist until we measure it – at least, not on the very small scale.
That all sounds a little mind-meltingly complex, but the experiment poses a pretty simple question: if you have an object that can either act like a particle or a wave, at what point does that object ‘decide’?
Our general logic would assume that the object is either wave-like or particle-like by its very nature, and our measurements will have nothing to do with the answer. But quantum theory predicts that the result all depends on how the object is measured at the end of its journey. And that’s exactly what a team from the Australian National University has now found.
“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” lead researcher and physicist Andrew Truscott said in a press release.
Known as John Wheeler’s delayed-choice thought experiment, the experiment was first proposed back in 1978 using light beams bounced by mirrors, but back then, the technology needed was pretty much impossible. Now, almost 40 years later, the Australian team has managed to recreate the experiment using helium atoms scattered by laser light.
“Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, a PhD student who worked on the experiment.
To successfully recreate the experiment, the team trapped a bunch of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them all until there was only a single atom left.
This chosen atom was then dropped through a pair of laser beams, which made a grating pattern that acted as a crossroads that would scatter the path of the atom, much like a solid grating would scatter light.
They then randomly added a second grating that recombined the paths, but only after the atom had already passed the first grating.
When this second grating was added, it led to constructive or destructive interference, which is what you’d expect if the atom had travelled both paths, like a wave would. But when the second grating was not added, no interference was observed, as if the atom chose only one path.
The fact that this second grating was only added after the atom passed through the first crossroads suggests that the atom hadn’t yet determined its nature before being measured a second time.
So if you believe that the atom did take a particular path or paths at the first crossroad, this means that a future measurement was affecting the atom’s path, explained Truscott. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,” he said.
Although this all sounds incredibly weird, it’s actually just a validation for the quantum theory that already governs the world of the very small. Using this theory, we’ve managed to develop things like LEDs, lasers and computer chips, but up until now, it’s been hard to confirm that it actually works with a lovely, pure demonstration such as this one.
The basic concept of quantum spin provides an understanding of a vast range of physical phenomena.
Otto Stern.
The moment I meet Horst Schmidt-Böcking outside the Bockenheimer Warte subway stop just north of the downtown area of Frankfurt, Germany, I know I have come to the right place. After my “Hi, thank you for meeting me,” his very first words are “I love Otto Stern.”
My trip on this prepandemic morning in November 2018 is to visit the place that, precisely a century before February 8, 2022, saw one of the most pivotal events for the nascent quantum physics. Without quite realizing what they were seeing, Stern and his fellow physicist and collaborator Walther Gerlach discovered quantum spin: an eternal rotational motion that is intrinsic to elementary particles and that, when measured, only comes in two possible versions—“up” or “down,” say, or “left” or “right”—with no other options in between.
Before the Roaring Twenties were over, physicists would reveal spin to be the key to understanding an endless range of everyday phenomena, from the structure of the periodic table to the fact that matter is stable—in other words, the fact that we don’t fall through our chair.ADVERTISEMENT
But the reason why I have a personal obsession with the Stern-Gerlach experiment—and why I am here in Frankfurt—is that it provided nothing less than a portal for accessing a hidden layer of reality. As physicist Wolfgang Pauli would explain in 1927, spin is quite unlike other physical concepts such as velocities or electric fields. Like those quantities, the spin of an electron is often portrayed as an arrow, but it is an arrow that does not exist in our three dimensions of space. Instead it is found in a 4-D mathematical entity called a Hilbert space.
Schmidt-Böcking—a semi-retired experimentalist at Goethe University Frankfurt and arguably the world’s foremost expert on Stern’s life and work—is the best guide I could have hoped for. We walk around the block from the station, past the Senckenberg Natural History Museum Frankfurt, to the Physikalischer Verein, the local physicists’ society, which predates Goethe University Frankfurt’s 1914 founding. In this building, in the wee hours of February 8, 1922, Stern and Gerlach shot a beam of silver atoms through a magnetic field and saw that the beam neatly split into two.
Once we are upstairs in the actual room of the experiment, Schmidt-Böcking explains that the whole experimental setup would have fit on a small desk. A vacuum system, made of custom blown-glass parts and sealed with Ramsay grease, enclosed the contraption. I find it hard to picture that in my mind, though, because the room, now windowless, is taken up by some of the nearby museum’s collections—specifically, cabinets with tiny specimens of bryozoans, invertebrates that form coral-like colonies.
Stern and Gerlach expected the silver atoms in their beam to act like tiny bar magnets and therefore to react to a magnetic field. As the beam shot horizontally, it squeezed through a narrow gap, with one pole of an electromagnet bracketed above and the other below. It exited the magnet and then hit a screen. When the magnetic field was turned off, the beam would just go straight and deposit a faint dot of silver on the screen, directly in line with the exit path of the beam from the magnet. But when the magnet was switched on, each passing atom experienced a vertical force that depended on the angle of its north-south axis. The force would be strongest upward if north pointed straight up, and it would be strongest downward if north pointed down. But the force could also take any value in between, including zero if the atom’s north-south axis was horizontal.
In these circumstances, a magnetic atom that came in at a random angle should have its trajectory deflected by a corresponding random amount, varying along a continuum. As a result, the silver arriving at the screen should have painted a vertical line. At least, that was Stern and Gerlach’s “classical” expectation. But that’s not what happened.ADVERTISEMENT
Unlike classical magnets, the atoms were all deflected by the same amount, either upward or downward, thus splitting the beam into two discrete beams rather than spreading it across a vertical line. “When they did the experiment, they must have been shocked,” says Michael Peskin, a theoretical physicist at Stanford University. Like many physicists, Peskin practiced doing the Stern-Gerlach experiment with modern equipment in an undergraduate lab class. “It’s really the most amazing thing,” he recalls. “You turn on the magnet, and you see these two spots appearing.”
Later that day in 2018, I get to see some of the original paraphernalia with my own eyes. Schmidt-Böcking drives me north in Frankfurt to one of the university’s campuses, where he keeps the artifacts inside well-padded boxes in his office. The most impressive piece is a high-vacuum pump—a type invented only a few years before the experiment—that removed stray air molecules using a supersonic jet of heated mercury.
It all looks tremendously fragile, and it is: According to witnesses, when the pieces were used, some glass part or other broke virtually every day. Restarting the experiment then required making repairs and pumping the air out again, which took several days. Unlike in modern experiments, the displacement of the beams was tiny—about 0.2 millimeter—and had to be spotted with a microscope.
At the time, Stern was shocked at the outcome. He had conceived the experiment in 1919 as a challenge to what was then the leading hypothesis for the structure of the atom. Formulated by physicist Niels Bohr and others starting in 1913, it pictured electrons like little planets orbiting the atomic nucleus. Only certain orbits were allowed, and jumping between them seemed to provide an accurate explanation for the quanta of light seen in spectroscopic emissions, at least for the simple case of hydrogen. Stern disliked quanta, and together with his friend Max von Laue, he had pledged that “if this nonsense of Bohr should in the end prove to be right, we will quit physics.”
To test Bohr’s theory, Stern had set about exploring one of its most bizarre predictions, which Bohr himself did not quite believe: that in a magnetic field, atomic orbits can only lie at particular angles. To pursue this experiment, Stern realized that he could look for a magnetic effect of the electron’s orbit. He reasoned that the outermost electron of a silver atom, which according to Bohr is orbiting the nucleus in a circle, is an electric charge in motion, and it should therefore produce magnetism.ADVERTISEMENT
In Stern and Gerlach’s experiment, the physicists detected the splitting of the beam, which they saw as confirmation of Bohr’s odd prediction: The atoms got deflected—implying that they were magnetic themselves—and they did so not over a continuum, as in the classical model, but into two separate beams.
It was only after modern quantum mechanics was founded, beginning in 1925, that physicists realized that the silver atom’s magnetism is produced not by the orbit of its outermost electron but by that electron’s intrinsic spin, which makes it act like a tiny bar magnet.Soon after he heard about of Stern and Gerlach’s results, Albert Einstein wrote to the Nobel Foundation to nominate them for a Nobel Prize. But the letter, which Schmidt-Böcking discovered in 2011, was apparently ignored because it nominated other researchers as well, against the foundation’s rules. Stern did not quit the field. Eventually he was one of the most Nobel-nominated physicists in history, and he did get his prize in 1943, while World War II was raging.
Stern’s prize did not honor his work with Gerlach, however. Instead it was awarded for another tour de force experiment in which Stern and a collaborator measured the magnetism of the proton in 1933—shortly before the Nazi regime drove Stern out of Germany because of his Jewish background. That result was the earliest indication that the proton is not an elementary particle: we now know that it is made of three building blocks called quarks. Gerlach never won a Nobel Prize, perhaps because of his participation in the Nazi regime’s attempt to build an atomic bomb.
Today the concept of quantum spin as a 4-D entity is the foundation for all quantum computers. The quantum version of a computer bit, called the qubit, has the same mathematical form as the spin of an electron—whether or not it is in fact encoded in any spinning object. It often is not.
Even so, to this day, physicists continue to argue about how to interpret the experiment. According to now textbook quantum theory, initially, the silver atom’s outer electron does not know which way it is spinning. Instead it starts out in a “quantum superposition” of both states—as if its spin were up and down at the same time. The electron does not decide which way it is spinning—and therefore which of the two beams its atom travels in—even after it has skimmed through the magnet. When it has left the magnet and is hurtling toward the screen, the atom splits into two different, coexisting personas, as if it were in two places at the same time: one moves in an upward trajectory, and the other heads downward. The electron only picks one state when its atom arrives at the screen: the atom’s position can only be measured when it hits the screen toward the top or bottom—in one of the two spots but not both. Others take what they call a more “realist” approach: the electron knew all along where it was going, and the act of measurement is simply a sorting of the two states that happens at the magnet.ADVERTISEMENT
A recent prominent experiment seems to lend added credence to the former interpretation. It suggests that the two personas do coexist when the two spin states are separated. Physicist Ron Folman of Ben-Gurion University of the Negev in Israel and his colleagues re-created the Stern-Gerlach experiment using not individual atoms but a cloud of rubidium atoms. This was cooled to close to absolute zero, which made it act like a single quantum object with its own spin.
The researchers suspended the cloud in a vacuum with a device that can trap atoms and move them around using electric and magnetic fields. Initially, the cloud was in a superposition of spin up and spin down. The team then released it and let it fall by gravity. During its descent, they first applied a magnetic field to separate the atoms into two separate trajectories, according to their spin, just as in the Stern-Gerlach experiment. But unlike in the original experiment, Folman’s team then reversed the process and made the two clouds recombine into one. Their measurements showed that the cloud returned into its initial state. The experiment suggests that the separation was reversible and that quantum superposition persisted after being subject to a magnetic field that separated the two spin orientations.
The experiment goes to the heart of what constitutes a measurement in quantum mechanics. Were the spins in the Stern-Gerlach experiment “measured” by the initial sorting done by the magnet? Or did the measurement occur when the atoms hit the screen—or perhaps when the physicists looked at it? Folman’s work suggests that wherever a measurement happened, the separation was not at the first stage.
The results are unlikely to quell the philosophical diatribes around the meaning of quantum measurement, says David Kaiser, a physicist and historian of science at the Massachusetts Institute of Technology. But the impact of the Stern-Gerlach experiment remains immense. It led physicists to realize “that there was some internal characteristic of a quantum particle that really doesn’t map on to analogies to things like planets and stars,” Kaiser says.
Australian scientists have recreated a famous experiment and confirmed quantum physics’s bizarre predictions about the nature of reality, by proving that reality doesn’t actually exist until we measure it – at least, not on the very small scale.
That all sounds a little mind-meltingly complex, but the experiment poses a pretty simple question: if you have an object that can either act like a particle or a wave, at what point does that object ‘decide’?
Our general logic would assume that the object is either wave-like or particle-like by its very nature, and our measurements will have nothing to do with the answer. But quantum theory predicts that the result all depends on how the object is measured at the end of its journey. And that’s exactly what a team from the Australian National University has now found.
“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” lead researcher and physicist Andrew Truscott said in a press release.
Known as John Wheeler’s delayed-choice thought experiment, the experiment was first proposed back in 1978 using light beams bounced by mirrors, but back then, the technology needed was pretty much impossible. Now, almost 40 years later, the Australian team has managed to recreate the experiment using helium atoms scattered by laser light.
“Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, a PhD student who worked on the experiment.
To successfully recreate the experiment, the team trapped a bunch of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them all until there was only a single atom left.
This chosen atom was then dropped through a pair of laser beams, which made a grating pattern that acted as a crossroads that would scatter the path of the atom, much like a solid grating would scatter light.
They then randomly added a second grating that recombined the paths, but only after the atom had already passed the first grating.
When this second grating was added, it led to constructive or destructive interference, which is what you’d expect if the atom had travelled both paths, like a wave would. But when the second grating was not added, no interference was observed, as if the atom chose only one path.
The fact that this second grating was only added after the atom passed through the first crossroads suggests that the atom hadn’t yet determined its nature before being measured a second time.
So if you believe that the atom did take a particular path or paths at the first crossroad, this means that a future measurement was affecting the atom’s path, explained Truscott. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,” he said.
Although this all sounds incredibly weird, it’s actually just a validation for the quantum theory that already governs the world of the very small. Using this theory, we’ve managed to develop things like LEDs, lasers and computer chips, but up until now, it’s been hard to confirm that it actually works with a lovely, pure demonstration such as this one.
Experimental results that seem to defy known physics might be explained by positing a parallel world..
From many-worlds to multiverses, physicists have had to come up with some pretty bizarre theories to explain the strange world of quantum mechanics, many of which sound less like science and more like science fiction. Now you can add parallel worlds to that list, according to Physorg.com.
A reanalysis of experimental data, originally obtained by the research group of Anatoly Serebrov at the Institut Laue-Langevin in France, has shown that when some free neutrons are ‘lost’ during experiments where they are subjected to a magnetic field, those neutrons might have disappeared from our world and ‘traveled’ to a mirror world, or a parallel reality.
The explanation might sound outlandish, but so were some of Serebrov’s original experimental data. Italian physicists Zurab Berezhiani and Fabrizio Nesti, who performed the reanalysis, posited this hypothetical mirror world because the potential loss rate of free neutrons in Serebrov’s data could not be accounted for by known physics.
Basically, the loss rate of free neutrons– unstable neutrons that have broken free of a nucleus– is usually expected to occur within the timescale of their rate of decay. Neutron decay operates under a half-life of about 10 minutes. But the reanalysis of Serebrov’s data showed that some neutrons could be lost within a timeframe of just a few seconds depending on the strength of the magnetic field applied.
One way of explaining this anomaly is to posit a hypothetical parallel world consisting of mirror particles. In such a scenario, each neutron would have the ability to transition into its mirror twin, essentially having the ability to oscillate from one world to the other.
The theory amounts to more than just a fanciful mind trip, too. Because this hypothetical oscillation can be effected by the presence of magnetic fields of varying strengths, it could even be detected experimentally.
So what might this hypothetical parallel world look like if we could travel there too? No doubt that depiction remains strictly the fodder for science fiction authors everywhere.
“We choose to examine a phenomenon which is impossible, absolutely impossible, to explain in any classical way, and which has in it the heart of quantum mechanics. In reality, it contains the only mystery.” Richard Feynman, a Nobel laureate of the twentieth century (Radin, Dean. Entangled Minds: Extrasensory Experiences.
The concept of “time” is a weird one, and the world of quantum physics is even weirder. There is no shortage of observed phenomena which defy our understanding of logic, bringing into play thoughts, feelings, emotions – consciousness itself, and a post-materialist view of the universe. This fact is no better illustrated than by the classic double slit experiment, which has been used by physicists (repeatedly) to explore the role of consciousness and its role in shaping/affecting physical reality. (source) The dominant role of a physical material (Newtonian) universe was dropped the second quantum mechanics entered into the equation and shook up the very foundation of science, as it continues to do today.
“I regard consciousness as fundamental. I regard matter as derivative from consciousness. We cannot get behind consciousness. Everything that we talk about, everything that we regard as existing, postulating consciousness.” – Max Planck, theoretical physicist who originated quantum theory, which won him the Nobel Prize in Physics in 1918
There is another groundbreaking, weird experiment that also has tremendous implications for understanding the nature of our reality, more specifically, the nature of what we call “time.”
It’s known as the “delayed-choice” experiment, or “quantum eraser,” and it can be considered a modified version of the double slit experiment.
To understand the delayed choice experiment, you have to understand the quantum double slit experiment.
In this experiment, tiny bits of matter (photons, electrons, or any atomic-sized object) are shot towards a screen that has two slits in it. On the other side of the screen, a high tech video camera records where each photon lands. When scientists close one slit, the camera will show us an expected pattern, as seen in the video below. But when both slits are opened, an “interference pattern” emerges – they begin to act like waves. This doesn’t mean that atomic objects are observed as a wave (even though it recently has been observed as a wave), they just act that way. It means that each photon individually goes through both slits at the same time and interferes with itself, but it also goes through one slit, and it goes through the other. Furthermore, it goes through neither of them. The single piece of matter becomes a “wave” of potentials, expressing itself in the form of multiple possibilities, and this is why we get the interference pattern.
How can a single piece of matter exist and express itself in multiple states, without any physical properties, until it is “measured” or “observed?” Furthermore, how does it choose which path, out of multiple possibilities, it will take?
Then, when an “observer” decides to measure and look at which slit the piece of matter goes through, the “wave” of potential paths collapses into one single path. The particle goes from becoming, again, a “wave” of potentials into one particle taking a single route. It’s as if the particle knows it’s being watched. The observer has some sort of effect on the behavior of the particle.
This quantum uncertainty is defined as the ability, “according to the quantum mechanic laws that govern subatomic affairs, of a particle like an electron to exist in a murky state of possibility — to be anywhere, everywhere or nowhere at all — until clicked into substantiality by a laboratory detector or an eyeball.”
According to physicist Andrew Truscott, lead researcher from a study published by the Australian National University, the experiment suggests that “reality does not exist unless we are looking atit.” It suggests that we are living in a holographic-type of universe.
Delayed Choice/Quantum Eraser/Time
So, how is all of this information relevant to the concept of time? Just as the double slit experiment illustrates how factors associated with consciousness collapse the quantum wave function (a piece of matter existing in multiple potential states) into a single piece of matter with defined physical properties (no longer a wave, all those potential states collapsed into one), the delayed choice experiment illustrates how what happens in the present can change what happens(ed) in the past. It also shows how time can go backwards, how cause and effect can be reversed, and how the future caused the past.
Like the quantum double slit experiment, the delayed choice/quantum eraser has been demonstrated and repeated time and time again. For example, Physicists at The Australian National University (ANU) have conducted John Wheeler’s delayed-choice thought experiment, the findings were recently published in the journal Nature Physics. (source)
In 2007 (Science315, 966, 2007), scientists in France shot photons into an apparatus and showed that their actions could retroactively change something which had already happened.
“If we attempt to attribute an objective meaning to the quantum state of a single system, curious paradoxes appear: quantum effects mimic not only instantaneous action-at-a-distance, but also, as seen here, influence of future actions on past events, even after these events have been irrevocably recorded.” – Asher Peres, pioneer in quantum information theory
The list literally goes on and on, and was first brought to the forefront by John Wheeler, in 1978, which is why I am going to end this article with his explanation of the delayed choice experiment. He believed that this experiment was best explained on a cosmic scale.
Cosmic Scale Explanation
He asks us to imagine a star emitting a photon billions of years ago, heading in the direction of planet Earth. In between, there is a galaxy. As a result of what’s known as “gravitational lensing,” the light will have to bend around the galaxy in order to reach Earth, so it has to take one of two paths, go left or go right. Billions of years later, if one decides to set up an apparatus to “catch” the photon, the resulting pattern would be (as explained above in the double slit experiment) an interference pattern. This demonstrates that the photon took one way, and it took the other way.
One could also choose to “peek” at the incoming photon, setting up a telescope on each side of the galaxy to determine which side the photon took to reach Earth. The very act of measuring or “watching” which way the photon comes in means it can only come in from one side. The pattern will no longer be an interference pattern representing multiple possiblities, but a single clump pattern showing “one” way.
What does this mean? It means how we choose to measure “now” affects what direction the photon took billions of years ago. Our choice in the present moment affected what had already happened in the past….
This makes absolutely no sense, which is a common phenomenon when it comes to quantum physics. Regardless of our ability make sense of it, it’s real.
This experiment also suggests that quantum entanglement (which has also been verified, read more about that here) exists regardless of time. Meaning two bits of matter can actually be entangled, again, in time.
Time as we measure it and know it, doesn’t really exist.
Australian scientists have recreated a famous experiment and confirmed quantum physics’s bizarre predictions about the nature of reality, by proving that reality doesn’t actually exist until we measure it – at least, not on the very small scale.
That all sounds a little mind-meltingly complex, but the experiment poses a pretty simple question: if you have an object that can either act like a particle or a wave, at what point does that object ‘decide’?
Our general logic would assume that the object is either wave-like or particle-like by its very nature, and our measurements will have nothing to do with the answer. But quantum theory predicts that the result all depends on how the object is measured at the end of its journey. And that’s exactly what a team from the Australian National University has now found.
“It proves that measurement is everything. At the quantum level, reality does not exist if you are not looking at it,” lead researcher and physicist Andrew Truscott said in a press release.
Known as John Wheeler’s delayed-choice thought experiment, the experiment was first proposed back in 1978 using light beams bounced by mirrors, but back then, the technology needed was pretty much impossible. Now, almost 40 years later, the Australian team has managed to recreate the experiment using helium atoms scattered by laser light.
“Quantum physics predictions about interference seem odd enough when applied to light, which seems more like a wave, but to have done the experiment with atoms, which are complicated things that have mass and interact with electric fields and so on, adds to the weirdness,” said Roman Khakimov, a PhD student who worked on the experiment.
To successfully recreate the experiment, the team trapped a bunch of helium atoms in a suspended state known as a Bose-Einstein condensate, and then ejected them all until there was only a single atom left.
This chosen atom was then dropped through a pair of laser beams, which made a grating pattern that acted as a crossroads that would scatter the path of the atom, much like a solid grating would scatter light.
They then randomly added a second grating that recombined the paths, but only after the atom had already passed the first grating.
When this second grating was added, it led to constructive or destructive interference, which is what you’d expect if the atom had travelled both paths, like a wave would. But when the second grating was not added, no interference was observed, as if the atom chose only one path.
The fact that this second grating was only added after the atom passed through the first crossroads suggests that the atom hadn’t yet determined its nature before being measured a second time.
So if you believe that the atom did take a particular path or paths at the first crossroad, this means that a future measurement was affecting the atom’s path,explained Truscott. “The atoms did not travel from A to B. It was only when they were measured at the end of the journey that their wave-like or particle-like behaviour was brought into existence,” he said.
Although this all sounds incredibly weird, it’s actually just a validation for the quantum theory that already governs the world of the very small. Using this theory, we’ve managed to develop things like LEDs, lasers and computer chips, but up until now, it’s been hard to confirm that it actually works with a lovely, pure demonstration such as this one.
Building a quantum computer can sometimes yield unexpected benefits — like providing the right environment to demonstrate that Albert Einstein’s theory of special relativity is, in fact, correct.
Using atoms in certain quantum states, researchers at the University of California, Berkeley, were able to show that space does not appear squeezed in one direction compared to another, as it would if relativity were not correct. Rather, space looks the same from any direction, as relativity predicts. The experiment used partially entangled atoms that were a byproduct of an attempt to build quantum computers.
Special relativity is a cornerstone of modern physics, and was formulated by Einstein in 1905. The theory states two things: the laws of physics are the same everywhere, and the speed of light is a constant, provided that you’re not accelerating when you’re measuring such phenomena. It can be used to explain the behavior of objects in space and time. (It’s companion, the general relativity includes the effects of gravity and acceleration). [Twisted Physics: 7 Mind-Blowing Findings]
Since relativity says the speed of light in a vacuum is constant, space should look the same in every direction, no matter what. For instance, if you move at half the speed of light toward or away from a flashlight, you will see the beam always move at about 186,000 miles per second, no more or less. The concept of time dilation, in which time slows down the faster you go (for example, if you are in a speeding spaceship), is a direct consequence of this phenomenon — it’s something that has to happen in order for the speed of light to look the same to everyone in the universe.
Early experiments measuring the speed of light used perpendicular light beams to generate interference patterns — alternating bands of light and dark. Most famous is the Michelson-Morely experiment in 1887, which bounced two light beams between mirrors and showed the speed of light was constant – there was no change in the interference pattern no matter how the apparatus was oriented, which showed there is no “ether” for light waves to pass through, and thus no preferred direction in space. Light speed in a vacuum has one value and one only.
The new study, researchers led by Hartmut Häffner, an assistant professor of physics at UC Berkeley, used atoms. The scientists put two calcium atoms in a vacuum chamber and applied an alternating voltage, which trapped the atoms in place.
Each of the atoms had two electrons, whose energies could be measured. The electrons moved perpendicularly to each other. One in an up-and-down motion, tracing out a volume that looked like a bowling pin around the nucleus, while the other revolved around the nucleus in a toruslike region. In the experiment, the team measured the kinetic energy of the electrons 10 times every second, for a day. If the theory of relativity is correct, then the difference between the electrons’ energies should be a constant. [Images: The World’s Most Beautiful Equations]
This may seem like a strange way to test a well-established theory, but Häffner said experiments like this have been done with other particles. Electrons, however, give more precise results, he said.
The findings are also important for other areas of physics, including the Standard Model, the reigning theory of particle physics, which describes how particles behave and why the universe appears the way that it does. “The Standard Model depends heavily on special relativity to be correct,” Häffner said.
The study also demonstrates how different areas of science are connected, since the experiment started with quantum computing. To make a quantum computer, you need to trap atoms and put them in a special quantum state called superposition. This means that you haven’t measured what state the atoms are in, so they can be in two states at once. According to quantum mechanics, until an atom’s state is measured, it has no definite value. This is what gives quantum computers their power to solve complex problems much faster than traditional computers can.
It was quantum computing that inspired Häffner to use atoms in such a dual state to test the theory of relativity, he said.
Researchers can use this type of experiment to probe other mysteries in physics and cosmology, the researchers said. For instance, “we can use it to look for dark matter,” Häffner said. If there is a lot of dark matter surrounding Earth, the relative energies of the electrons would change, because the presence of the dark matter’s mass would alter the surrounding space, he said.
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