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Imagine an electron as a spherical cloud of negative charge. If that ball were ever so slightly less round, it could help explain fundamental gaps in our understanding of physics, including why the universe contains something rather than nothing.
Given the stakes, a small community of physicists has been doggedly hunting for any asymmetry in the shape of the electron for the past few decades. The experiments are now so sensitive that if an electron were the size of Earth, they could detect a bump on the North Pole the height of a single sugar molecule.
The latest results are in: The electron is rounder than that.
The updated measurement disappoints anyone hoping for signs of new physics. But it still helps theorists to constrain their models for what unknown particles and forces may be missing from the current picture.
“I’m sure it’s hard to be the experimentalist measuring zero all the time, [but] even a null result in this experiment is really valuable and really teaches us something,” saidPeter Graham, a theoretical physicist at Stanford University. The new study is “a technological tour de force and also very important for new physics.”
Poaching Elephants
TheStandard Model of Particle Physicsis our best roster of all the particles that exist in the universe’s zoo. The theory has held up exceptionally well in experimental tests over the past few decades, but it leaves some serious “elephants in the room,” saidDmitry Budker, a physicist at the University of California, Berkeley.
For one thing, our mere existence is proof that the Standard Model is incomplete, since according to the theory, the Big Bang should have produced equal parts matter and antimatter that would have annihilated each other.
In 1967, the Soviet physicist Andrei Sakharov proposed apossible solutionto this particular conundrum. He conjectured that there must be some microscopic process in nature that looks different in reverse; that way, matter could grow to dominate over antimatter. A few years before, physicists haddiscoveredsuch a scenario in the decay of the kaon particle. But that alone wasn’t enough to explain the asymmetry.
Ever since then, physicists have been on a hunt to find hints of new particles that could further tip the scale. Some do so directly, using the Large Hadron Collider—often touted as the most complicated machine ever built. But over the past several decades, a comparatively low-budget alternative has emerged: looking at how hypothetical particles would alter properties of known particles. “You see footprints [of new physics], but you don’t actually see the thing that made them,” saidMichael Ramsey-Musolf, a theoretical physicist at the University of Massachusetts, Amherst.
Our mere existence is proof that the Standard Model is incomplete.
One such potential footprint could appear in the roundness of the electron. Quantum mechanics dictates that inside the electron’s cloud of negative charge, other particles are constantly flickering in and out of existence. The presence of certain “virtual” particles beyond the Standard Model—the kind that could help explain the primordial supremacy of matter—would make the electron’s cloud look slightly more egg-shaped. One tip would have a bit more positive charge, the other a bit more negative, like the ends of a bar magnet. This charge separation is referred to as the electric dipole moment (EDM).
The Standard Model predicts a vanishingly tiny EDM for the electron—nearly a million times smaller than what current techniques can probe. So if researchers were to detect an oblong shape using today’s experiments, that would reveal definitive traces of new physics and point toward what the Standard Model might be missing.
To search for the electron’s EDM, scientists look for a change in the particle’s spin, an intrinsic property that defines its orientation. The electron’s spin can be readily rotated by magnetic fields, with its magnetic moment serving as a sort of handle. The goal of these tabletop experiments is to try to rotate the spin using electric fields instead, with the EDM as an electric handle.
“If the electron’s perfectly spherical, it’s got no handles to grab onto to exert a torque,” saidAmar Vutha, a physicist at the University of Toronto. But if there’s a sizable EDM, the electric field will use it to tug on the electron’s spin.
The dream is that these EDM experiments will be the first to detect signs of new physics.
In 2011, researchers at Imperial College Londonshowedthat they could amplify this handle effect by anchoring the electron to a heavy molecule. Since then, two main teams have been leapfrogging one another every few years with increasingly precise measurements.
One experiment, now at Northwestern University, goes by the name of Advanced Cold Molecule Electron EDM, or ACME (a backronym inspired by the oldRoad Runnercartoons). Another is based at the University of Colorado’s JILA institute. The competing teams’ measurements have jumped in sensitivity by a factor of 200 in the last decade—still with no EDM to be seen.
“It is sort of a race, except we have no idea where the finish line is, or whether there is a finish line, even,” saidDavid DeMille, a physicist at the University of Chicago and one of the leaders of the ACME group.
A Race to the Unknown
To keep trekking ahead, researchers want two things: more measurements and a longer measurement time. The two teams take opposite approaches.
The ACME group, which set theprevious recordin 2018, prioritizes quantity of measurements. They shoot a beam of neutral molecules across the lab, probing tens of millions of them every second, but only for a few milliseconds each. The JILA group measures fewer molecules, but for longer: They trap a few hundred molecules at a time, then measure them for up to three seconds.
The ion-trapping technique, first developed byEric Cornell, a physicist at the University of Colorado, Boulder who directs the JILA group, was “a big conceptual breakthrough,” DeMille said. “Many people in the field thought this was nuts. Seeing it come to fruition is really exciting.”
Having two distinct experimental setups that can cross-check one another is “absolutely crucial,” Budker said. “I don’t have words to express my admiration of this cleverness and persistence. It’s just the best science there is.”
Cornell’s technique was firstshowcasedin 2017 with hafnium fluoride molecules. Since then, technical improvements have allowed the group to surpass ACME’s record by a factor of 2.4, as described in arecent preprintled by Cornell’s former graduate student Tanya Roussy. The team declined to comment while their paper is under review atScience.
Probing the electron’s roundness with increased precision equates to looking for new physics at higher energy scales,or looking for signs of heavier particles. This new bound is sensitive to energies above roughly 1013electron-volts—more than an order of magnitude beyond what the LHC can currently test. A few decades ago, most theorists expected that hints of new particles would be discovered significantly below this scale. Each time the bar rises, some ideas are discredited.
“We have to keep wrestling with what these limits imply,” Ramsey-Musolf said. “Nothing’s killed yet, but it’s turning up the heat.”
Meanwhile, the electron EDM community forges ahead. In future experimental iterations, the dueling groups aim to meet somewhere in the middle: The JILA team plans to make a beam full of ions to increase their count, and the ACME team wants to extend the length of their beam to increase their measurement time. Vutha is even working on “some totally crazy” approaches, like freezing molecules in blocks of ice, in the hope of jumping several orders of magnitude in sensitivity.
The dream is that these EDM experiments will be the first to detect signs of new physics, prompting a wave of follow-up investigations from other precision measurement experiments and larger particle colliders.
The shape of the electron is “something that teaches us about totally new and different pieces of the fundamental laws of nature,” Graham said. “There’s a huge discovery waiting to happen. I’m optimistic that we’ll get there.”
This article wasoriginally publishedon theQuanta Abstractionsblog.
Lead image: If an electron were the size of Earth, the experiment could detect a bump the size of a sugar molecule. Credit: Kristina Armitage/Quanta Magazine.
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Zack Savitsky
Posted on April 14, 2023
Zack Savitsky is a science journalist who has written for Science, The Mercury News and other publications. He earned a master’s degree in science communication from the University of California, Santa Cruz. Before that, he studied in the journalism college with a physics minor at the University of Florida. You can find him on his website zacksavitsky.com and on Twitter @savagitsky.
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FAQs
The Electron Is So Round That It’s Ruling Out Potential New Particles? ›
The Electron Is So Round That It's Ruling Out Potential New Particles. If the electron's charge wasn't perfectly round, it could reveal the existence of hidden particles. A new measurement approaches perfection. If an electron were the size of Earth, the experiment could detect a bump the size of a sugar molecule.
How round is the electron? ›Electrons are extremely round, and some physicists are not pleased about it. The symmetrical roundness of the electrons suggested that unseen particles aren't big enough to skew electrons into squashed oblong shapes, or ovals.
What is the wave theory of the electron? ›The electron is a point particle. When an electron is behaving more like a wave, it can have all sorts of shapes, as long as its shape obeys the electron wave equation. An electron's wave equation, and therefore its shape, is a function of its energy and the shape of the potential well trapping it.
Are electrons spherical? ›Physicists from the Advanced Cold Molecule Electron Electric Dipole Moment (ACME) Collaboration have examined the shape of an electron's charge with unprecedented precision to confirm that it is extremely round.
Why do electrons pop in and out of existence? ›Thanks to the uncertainty principle, the vacuum buzzes with particle-antiparticle pairs popping in and out of existence. They include, among many others, electron-positron pairs and pairs of photons, which are their own antiparticles. Ordinarily, those "virtual" particles cannot be directly captured.
Is an electron a circle? ›The most accurate measurement yet of the shape of the electron has shown it to be almost perfectly spherical.
How many times does the electron go round? ›The answer is 6.59 ×10^15.
What is the particle wave theory? ›The Wave-Particle Duality theory states that waves can exhibit particle-like properties while particles can exhibit wave-like properties. This definition opposes classical mechanics or Newtonian Physics.
How does electron theory work? ›Electron Flow theory states that the flow of electrons is from negative to positive. Electric current creates its own magnetic field around the wire. Magnetic lines have direction and change direction when the current flow changes in the wire from one direction to another. As current increases the field strengthens.
What is electron in quantum theory? ›Quantum theory states that there are only certain allowed energy states for an electron and that these are quantized. Further, it tells us that no two electrons, in the same system, can occupy the same energy state, and that all the energy states are filled from the lowest levels to the highest levels.
Do electrons go in circles? ›
Though a useful visual tool, electrons in an atom don't actually orbit the nucleus in concentric circles. Quantum mechanics (see Basics of Quantum Theory) tells us that electrons are quantum particles, and therefore we cannot precisely determine their position around an atom.
Why is an electron a sphere? ›These are called virtual particles. They cloud around an electron in a specific shape determined by how some forces of the electron might push them out, and it is this shape that has been found to be very spherical.
Are electrons actually particles? ›) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure. The electron's mass is approximately 1/1836 that of the proton.
Could the universe exist without God? ›Our universe could have popped into existence 13.7 billion years ago without any divine help whatsoever, researchers say. Our universe could have popped into existence 13.7 billion years ago without any divine help whatsoever, researchers say.
What is the quantum theory something from nothing? ›In the quantum realm, something really can emerge from nothing. In theory, the Schwinger effect states that in the presence of strong enough electric fields, (charged) particles and their antiparticle counterparts will be ripped from the quantum vacuum, empty space itself, to become real.
Why are electrons always moving? ›All atoms have the same number of electrons as protons. Negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving around the nucleus. The region where an electron is most likely to be found is called an orbital.
Why do electrons follow a circular path? ›If an electron towards in an area with the constant magnetic field (B), it experiences a force that is perpendicular to the direction of the magnetic field and its velocity. This force is like a centripetal force, so the path force of the electron tends to curve and form a circular trajectory.
Why do electrons circle atoms? ›All it needs is the electrostatic attraction between the positively-charged protons in the atom's nucleus and the negatively-charged electron. In short, electrical attraction to the nucleus is what keeps the electron in orbit, and this attraction doesn't cost energy.
Do electrons actually circle the nucleus? ›"Early on, we thought that electrons were revolving around the nucleus like planets," Cooley said. "We no longer think of it that way because of experiments that came later on." Now we know that electrons do not orbit around the nucleus like planets around the sun.
Do electrons spin all the time? ›But many physicists will tell you that electrons are not really spinning—they merely act like it. For example, electrons have angular momentum, which is the tendency of something to keep rotating—like a moving bicycle wheel or a spinning skater—and because they have this property, one might conclude they are spinning.
Do electrons ever run into each other? ›
No. Like rmhleo said, the Pauli exclusion principle prevents this. For an analogy, think of whirlpools. They don't overlap, and they don't crash into each other like billiard balls.
Do electrons move through time? ›A calculation shows that the electron is traveling at about 2,200 kilometers per second. That's less than 1% of the speed of light, but it's fast enough to get it around the Earth in just over 18 seconds.
Are we a wave or a particle? ›In fact, if we can define it, we can quantify just how “wave-like” a particle or set of particles is. Even an entire human being, under the right conditions, can act like a quantum wave.
What is quantum theory of particles? ›Quantum particles are described by a complex, square-integrable wave function Ψ(x1,… xN) with |Ψ|2 representing the probability density of finding N particles at positions x1,x2,… xN, which will be assumed to be in a d-dimensional square box V with side L and periodic boundary conditions.
Is light a particle or a wave? ›Light can be described both as a wave and as a particle. There are two experiments in particular that have revealed the dual nature of light. When we're thinking of light as being made of of particles, these particles are called “photons”. Photons have no mass, and each one carries a specific amount of energy.
What is electron theory in simple terms? ›The basis of our understanding of electricity is the electron theory. This theory states that all matter, that is, everything that occupies space and has weight, is composed of tiny invisible units called atoms. Atoms in turn are subdivided into still smaller particles called protons, neutrons, and electrons.
How do you explain an electron? ›An electron is a negatively charged subatomic particle that can be either bound to an atom or free (not bound). An electron that is bound to an atom is one of the three primary types of particles within the atom -- the other two are protons and neutrons. Together, electrons, protons and neutrons form an atom's nucleus.
What is the theory behind the discovery of electrons? ›Summary. J.J. Thomson's experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup."
Is the quantum of energy an electron? ›Quantized energy means that the electrons can possess only certain discrete energy values; values between those quantized values are not permitted. 2.
Does energy travel in circles? ›Electricity flows in a closed circle, called a circuit. To reach our homes, electricity travels from power stations, through transmission lines and distribution lines, until it flows into the wires that power our devices.
Do electrons flow or vibrate? ›
We know that electrons are free to move about in a conductor ..they have a drift velocity of 1cm/s , yet when we see any conductor (antenna for eg.), the electron actually does not move along the whole length of the conductor,it just vibrates about its mean position and its enery moves ahead.
Who said electrons move in circles? ›In Bohr's model, electrons moved around the atomic nucleus in circular orbits, but those orbits had set discrete energies, and electrons could gain or lose energy only by moving from one orbit to another, absorbing or emitting radiation as necessary.
What is an electron made of? ›Protons and neutrons are made of quarks, but electrons aren't. As far as we can tell, quarks and electrons are fundamental particles, not built out of anything smaller.
Can electrons be seen? ›An electron is a sub-atomic particle which is negatively charged. Electrons lie in orbits present around the nucleus in an atom. The sub-atomic particles of an atom are not visible. Hence, we cannot see an electron.
Do electrons have mass? ›Electrons are extremely small. The mass of an electron is only about 1/2000 the mass of a proton or neutron, so electrons contribute virtually nothing to the total mass of an atom. Electrons have an electric charge of −1, which is equal but opposite to the charge of a proton, which is +1.
Is an electron a cloud? ›The electron has assumed a form that can only be described as a cloud of probability. The electron possesses both kinetic energy and momentum, yet there is no motion. The cloud is perfectly static. The electron does not "orbit" the proton at all – it surrounds it like a fog.
Do quantum particles exist? ›A quantum particle can exist in two mutually exclusive conditions at once. For example, a photon can be polarized so that the electric field in it wriggles vertically, horizontally, or both ways at the same time—at least until it's measured. The two-way state then collapses randomly to either vertical or horizontal.
Can electrons behave like waves? ›Students will know that electrons carry energy and momentum when they are moving. Yet these moving electrons seem to be guided to an interference pattern just like waves of light; or just like photons of light in the micro-physical world.
What are the 5 arguments against the existence of God? ›- Evil: Because evil exists, God cannot be all-powerful. ...
- Pain: ...
- Injustice: ...
- Multiplicity: ...
- Simplicity:
Without God, even if human life could be meaningful within the frame of the universe, it would be ultimately meaningless because the universe itself would be pointless. It would be like playing a part in a pointless play. Problem: It is true that without God there is no point to the universe.
How did the universe begin from nothing? ›
The Big Bang was the moment 13.8 billion years ago when the universe began as a tiny, dense, fireball that exploded. Most astronomers use the Big Bang theory to explain how the universe began.
Can energy be created from nothing? ›The short answer is no. Energy didn't come "from nothing". Since the big bang is an observational event horizon, we cannot talk about any events earlier, so one assumes that all the energy and matter has always been contained in your universe. So now, we cannot create energy.
Can something exist without a cause? ›Perhaps the principle of causality applies within the universe, but not to the universe. This might allow the universe as a whole to be uncaused. An event doesn't have a cause if it doesn't actually happen and there was never anything that stopped it happening. Coincidence!
What is the smallest thing in our universe? ›As far as we can tell, quarks can't be broken down into smaller components, making them the smallest things we know of. In fact, they're so small that scientists aren't sure they even have a size: they could be immeasurably small! We do know that they're at least 1018 (or one quintillion) times smaller than Alice.
Can an electron have any energy? ›There is also a maximum energy that each electron can have and still be part of its atom. Beyond that energy, the electron is no longer bound to the nucleus of the atom and it is considered to be ionized. When an electron temporarily occupies an energy state greater than its ground state, it is in an excited state.
Why don't we feel electrons moving when we touch something? ›Electrons that exist in every atom of our bodies push other electrons in every atom of other bodies or things. This electron repulsion ensures that we never touch anything, unless it punctures our body.
Can you stop an electron from moving? ›No, it's not possible to stop an electron. because of the simple fact, it has to obey the Heisenberg uncertainty relation with respect to place and momentum. In the extreme case (theoretically) we can measure the electron's momentum with absolute certainty.
What is the shape of the electron? ›As far as we know, electrons don't actually have a 'shape' per se - rather, they are either point particles or they are behaving like a wave, which changes shape depending on its energy.
Do electrons have a radius? ›Using the best available values for the wave-length and the scattering by matter of hard X-rays and γ-rays, the radius of the electron is estimated as about 2 × 10−10 cm.
Can you pinpoint an electron? ›The Heisenberg uncertainty principle states that the exact position and momentum of an electron cannot be simultaneously determined. This is because electrons simply don't have a definite position, and direction of motion, at the same time!
What shape do electrons travel in? ›
The electrons can be found at any point in their orbital. The orbitals can be shaped as a sphere, as lobes — which kind of look like two squashes put together at the small ends — or in the shape of a doughnut around the nucleus.
Is electron really a particle or wave? ›In 1924, a French scientist, Louis De Broglie, suggested that an electron shows dual nature, that is, an electron has both wave nature and particle nature. The energy an electron holds can be deposited at a point. Thus, it behaves as a particle.
What shape do electrons orbit in? ›Each orbital type has a unique shape based on the energy of its electrons. The s orbital is a spherical shape. The p orbital is a dumbbell shape. There are three p orbitals that differ in orientation along a three-dimensional axis.
How does electron radius work? ›The gain of an electron adds more electrons to the outermost shell which increases the radius because there are now more electrons further away from the nucleus and there are more electrons to pull towards the nucleus so the pull becomes slightly weaker than of the neutral atom and causes an increase in atomic radius.
What is the radius of electron particle? ›The electron is a subatomic particle whose electric charge is negative in nature. It carries a negative charge of 1.602 × 10-19 C. The radius of an electron is 2.81 × 10-15 meters. The mass of an electron is 9.0 × 10-31 kg.
What determines electron radius? ›A higher effective nuclear charge causes greater attractions to the electrons, pulling the electron cloud closer to the nucleus which results in a smaller atomic radius. Down a group, the number of energy levels (n) increases, so there is a greater distance between the nucleus and the outermost orbital.
What keeps an electron moving in a circle? ›Electrostatic force provides necessary centripetal force for circular motion of electron.
What keeps electrons moving? ›The answer is electricity and magnetism. The atom's center, or nucleus, is positively charged and the electrons that whirl around this nucleus are negatively charged, so they attract each other. The reason the force is strong is because the atom is so small.
Do electrons flow through humans? ›Yes, they can. Your tissue conducts electricity which is why you can be electrocuted.
Is there a magnetic field around an electron? ›All the electrons do produce a magnetic field as they spin and orbit the nucleus; however, in some atoms, two electrons spinning and orbiting in opposite directions pair up and the net magnetic moment of the atom is zero. The direction of spin and orbit of the electron determines the direction of the magnetic field.
Has a human ever seen an electron? ›
Yet, all physicists believe in the existence of electrons. An intelligent but superstitious man advances this analogy to argue that 'ghosts' exist even though no one has 'seen' one.