Researchers from Washington State University (USA) have achieved the behavior of rubidium atoms as a substance with a negative effective mass. This means that these atoms, under external influence, did not fly towards the vector of this influence. In the experimental conditions, they behaved as if they were running into an invisible wall every time they approached the boundaries of an area with a very small volume. The corresponding one was published in Physical Review Letters. The experiment was misinterpreted by the media as "the creation of matter with negative mass" (in theory, this allows the creation of wormholes for long-distance space travel). In fact, obtaining a substance with a negative mass, if possible, is far beyond what is achievable by modern science and technology.
The rubidium atoms were forced to move in the direction opposite to the vector of force applied to them. The media misinterpreted this as the creation of a substance with "negative mass"
The authors of the work slowed down rubidium atoms with a laser (decreasing the particle's speed means cooling it). At the second stage of cooling, the most energetic atoms were allowed to leave the cooled volume. This cooled it even further, just as the evaporation of refrigerant atoms cools the contents of a household refrigerator. At the third stage, another set of lasers was used, the pulses of which changed the spin (in simplified terms - the direction of rotation around its own axis) of parts of the atoms.
Since some atoms in the cooled volume continued to have normal spin, while others received the opposite spin, their interaction with each other acquired an unusual character. Under normal behavior, rubidium atoms would collide and fly apart in different directions. The central atoms would push the outer atoms outward, accelerating them in the direction of the force applied (the motion vector of the first atom). Due to the discrepancy in spins, in practice, rubidium atoms, cooled to small fractions of a kelvin, did not fly apart after collisions, remaining in their original volume, equal to approximately a thousandth of a cubic millimeter. From the outside it looked as if they were running into an invisible wall.
A very distant analogy for a group of atoms with different spins is the collision of two or more soccer balls, which were previously twisted with a side impact until they rotate around their axis in different directions. It is clear that the directions and speeds of their movement after the collision will differ significantly from the same results for ordinary balls. But this does not mean that the balls have changed their physical mass. Only the nature of their interaction with each other has changed. Also in the experiment, the mass of atoms did not become negative. In a gravitational field they would still fall down. The only thing that really changed was where they moved after collisions with other similar atoms, but “rotating” around their axis in the other direction.
The way rubidium atoms behaved in experiment corresponds to the definition of negative effective mass in physics. It is used, for example, when describing the behavior of an electron in a crystal lattice. For him, the formal mass depends on the direction of movement relative to the crystal axes. Moving in one direction, it will show one dispersion (scattering), in the other - another. The concept of effective mass was introduced for them because otherwise, when describing their dispersion by formulas, the mass would begin to depend on energy, which is not very convenient for calculations. An example of a negative effective mass is the behavior of holes in semiconductors, which every user of modern electronics deals with.
Most media, including Russian ones, interpreted the experiment as the creation of a substance with negative mass. In theory, matter with similar properties can be used to keep wormholes in working order, allowing long-distance travel in space and time in near-zero time. The practical possibility of creating such a substance, as well as the wormholes themselves, has not yet been proven. Even if it is possible, obtaining it with the modern technical capabilities of mankind is unrealistic.
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Scanned by Igor StepikinTribune of bold hypotheses
Ponkrat BORISOV, engineer
Negative mass: a free ride to infinity
Physicists at the University of Washington have created a liquid with negative mass. Push it, and unlike every physical object we know in the world, it will not accelerate in the direction of the push. It will accelerate in the opposite direction. The phenomenon is rarely created in a laboratory setting and could be used to study some of the more complex concepts about space, says Michael Forbes, an assistant professor of physics and astronomy at the University of Washington. The study appears in Physical Review Letters.
Hypothetically, a substance could have negative mass in the same sense that an electric charge could be either negative or positive. People rarely think about this, and our everyday world demonstrates only the positive aspects of Isaac Newton's Second Law of Motion, which states that the force acting on a body is equal to the product of the mass of the body and the acceleration imparted by that force, or F = ma.
In other words, if you push an object, it will accelerate in the direction of your push. The mass will accelerate it in the direction of the force.
“We are used to this state of affairs,” says Forbes, anticipating a surprise. “With negative mass, if you push something, it will accelerate towards you.”
Conditions for negative mass
Together with his colleagues, he created the conditions for negative mass by cooling rubidium atoms to near absolute zero, thereby creating a Bose-Einstein condensate. In this state, predicted by Shatyendranath Bose and Albert Einstein, particles move very slowly and, following the principles of quantum mechanics, behave like waves. They also synchronize and move in unison as a superfluid fluid that flows without loss of energy.
Led by Peter Engels, a professor of physics and astronomy at the University of Washington, scientists on the sixth floor of Webster Hall created these conditions by using lasers to slow down particles, making them cooler and allowing hot, high-energy particles to escape like steam, further cooling the material.
The lasers captured the atoms as if they were in a bowl less than a hundred microns in size. At this stage, superfluid rubidium had normal mass. The rupture of the bowl allowed the rubidium to escape, expanding as the rubidium in the center was pushed outward.
To create negative mass, the scientists used a second set of lasers that pushed the atoms back and forth, changing their spin. Now, when rubidium runs out fast enough, it behaves as if it has negative mass. "Push it and it will accelerate in the opposite direction," says Forbes. “It’s like the rubidium is hitting an invisible wall.”
Elimination of major defects
The method used by the University of Washington scientists avoided some of the major flaws found in previous attempts to understand negative mass.
"The first thing we realized was that we had careful control over the nature of this negative mass without any other complications," says Forbes. Their research explains, already from the perspective of negative mass, similar behavior in other systems. The increased control gives researchers a new tool to design experiments to study similar physics in astrophysics, such as neutron stars, and cosmological phenomena such as black holes and dark energy, where experiments are simply not possible.
British astrophysicist Jamie Farnes has proposed a cosmological model in which negative mass is produced at a constant rate throughout the evolution of the Universe. This model contradicts the generally accepted view of the nature of matter, but it explains well most of the effects that are usually attributed to dark matter and dark energy, in particular, the expansion of the Universe, the formation of the large-scale structure of the Universe and the galactic halo, the rotation curves of galaxies and the observed spectrum of the cosmic microwave background radiation. Article published in Astronomy & Astrophysics, a preprint of the work is posted on arXiv.org.
Currently, most cosmologists believe that the evolution of the Universe is described by the ΛCDM model. According to this model, about 70 percent of the mass of the Universe comes from dark energy, 25 percent from cold dark matter (that is, matter whose particles move slowly), and only the remaining 5 percent from the familiar baryonic matter. Scientists determined these relationships by analyzing the harmonics in the cosmic microwave background radiation pattern. You can read more about measuring the “composition” of the Universe in articles by Boris Stern about the WMAP and Planck satellites, which made the main contribution to this work.
Unfortunately, scientists have a poor understanding of dark matter and dark energy. None of the ultra-precise experiments to search for dark matter particles, predicted by a number of theoretical models (for example, SUSY), has received a positive result. Currently, the scattering cross section for ordinary particles and “dark” particles with masses from 6 to 200 megaelectronvolts is on the order of 10 −47 square centimeters, which practically excludes particles in this mass range and forces physicists to develop alternative theories. However, dark matter still manifests itself through gravitational interaction, modifying the rotation curves of galaxies and the picture, and therefore scientists reject this hypothesis.
With dark energy it's even worse. The only observation that directly confirms its existence, regardless of the analysis of the cosmic microwave background radiation, is the accelerated expansion of the Universe, measured by (indirectly, dark energy is confirmed by the ratio of chemical elements in the observable Universe). Moreover, physicists have little understanding of what dark energy is fundamental level . Certainly, qualitatively it can be described using the cosmological constant (lambda term) in , but this method does not provide new knowledge and does not allow us to establish what does it consist of dark energy. Einstein explained such additions using particles with negative mass - in this approach, the equations of motion become symmetrical, like the equations of electrodynamics, and the lambda term appears as a constant of integration, which does not contain any physical meaning.
Matter with negative mass is matter that accelerates in the direction opposite to a force. A particle with negative mass repels particles with positive and negative mass, while "positive" particles attract "negative" particles. Unfortunately, within the framework of the ΛCDM model, this method of describing dark energy is obviously doomed to failure. The fact is that during the expansion of the Universe, the density of various components changes according to different laws: the density of cold matter falls, and the density of dark energy remains constant. Therefore, it is impossible to identify matter with negative mass and dark energy.
Interaction of particles with negative mass: black arrows indicate forces, red arrows indicate accelerations
Jamie Farnes / Astronomy & Astrophysics
Interaction of particles with positive and negative mass: black arrows indicate forces, red arrows indicate accelerations
Jamie Farnes / Astronomy & Astrophysics
Interaction of particles with positive mass: black arrows indicate forces, red arrows indicate accelerations
Jamie Farnes / Astronomy & Astrophysics
However, astrophysicist Jamie Farnes claims that he was able to connect Einstein's idea with observational data. To do this, he combined the idea of negative mass with another counterintuitive idea of the continuous and uniform production of mass throughout the volume of the Universe. This idea is also far from new; it was first proposed back in the 40s of the last century.
Theoretically, such processes can indeed occur against the background of a strong gravitational field (for example, due to ). Considering similar additions to the standard energy-momentum tensor for positive masses, the physicist wrote out and solved the Friedmann equation, and then calculated the law by which the Universe expands in this model. Scientists did not take into account the contributions of the usual dark matter and dark energy. As a result, it turned out that the known laws are reproduced if the negative mass is produced at a constant rate Γ = −3 H, Where H is the Hubble constant. In this case, the negative mass density will remain constant during the expansion, and it will effectively simulate the cosmological constant. In this case, the expansion rate and lifetime of the Universe are the same as in the ΛCDM model.
The astrophysicist then calculated how negative mass would manifest itself on smaller scales. To do this, he simulated within the framework of his model the interaction of a large number of particles of positive and negative mass. Since all existing astrophysics packages do not take into account such unusual modifications, Farnes had to develop his own program. To avoid any approximations during the calculations, the researcher calculated the coordinates and velocities of each particle at each moment of time - this made it possible to increase the reliability of predictions, although the program's demands on computing resources grew as the square of the number of particles. In particular, because of this, the scientist had to limit himself to modeling 50 thousand particles.
Using the developed program, Farnes saw several effects that are traditionally attributed to dark matter. First, he modeled the evolution of a dense group of positive-mass particles immersed in a “sea” of negative-mass particles. Such a system should qualitatively describe the evolution of galaxies in the late stages of the expansion of the Universe, when “negative” particles significantly predominate over “positive” ones. In this problem, the scientist chose the number of “positive” particles N+ = 5000, number of negative N− = 45000. As a result, he obtained a density distribution that agrees well with observational data - the particle density increases slowly as one approaches the center of the galaxy and coincides with the Burkert profile. This solves the cuspy halo problem that occurs in the ΛCDM model.
Evolution of a “galaxy” of positive matter immersed in a “sea” of negative matter
Jamie Farnes / Astronomy & Astrophysics
Galaxy mass profile calculated by Farnes (blue) and observed in practice (pink dotted line)
Jamie Farnes / Astronomy & Astrophysics
Secondly, with the same initial data, the scientist calculated the rotation curve of the galaxy and found that it also coincides well with observational data. While in a model with purely “positive” particles the matter at the edge of the galaxy moves slower than in the center, in a model with a predominance of “negative” particles the speed is approximately constant.
Rotation curve of a galaxy immersed in a “sea” of negative matter (red) and a “free” galaxy (black)
Jamie Farnes / Astronomy & Astrophysics
Thirdly, Farnes showed that in his model the filamentary large-scale structure of the Universe naturally arises: galaxies unite into clusters, clusters into superclusters, and superclusters into chains and walls. To do this, he calculated the evolution of a system that contains the same number of “positive” and “negative” particles. Due to limitations on available computing power, the scientist put the number of both types of particles N + = N− = 25000. As in the previous case, “negative” particles surrounded particles of ordinary matter and formed a halo, but this time the researcher was able to discern patterns on larger scales that resembled the structure of the observable Universe.
Homogeneous structure of the Universe at the beginning of the simulation
Jamie Farnes / Astronomy & Astrophysics
Registered in practice. Unfortunately, he was unable to see this effect in simulations with 50,000 particles. However, the scientist hopes that in larger-scale simulations with a million particles such processes will be visible, and also suggests that they will confirm or refute the new theory.
Finally, the scientist checked how strongly the proposed modification of the ΛCDM model would distort the actually observed effects - the expansion of the Universe measured by standard candles, the cosmic microwave background and observations of mergers of galaxy clusters. In all these cases, the astrophysicist found that his hypothesis was consistent with the observed data. However, quite a lot of questions still remain open - in particular, it is not clear how to connect such a hypothesis with the Standard Model (can the Higgs mechanism generate negative masses?), how to experimentally detect particles with a negative mass, and how to explain the contradictions between the repulsion of “negative” ones. particles and theory. However, the scientist believes that all these problems can be solved within the framework of the new model.
Thus, the model with constant production of negative mass explains not only the observed expansion of the Universe, but also the formation of its large-scale structure, dark matter halos around galaxies and rotation curves - most of the effects that are usually attributed to dark energy and dark matter. Oddly enough, such intuitively unnatural a hypothesis that contradicts the generally accepted view of matter is completely agrees with observational data. Moreover, she proposes to explain them in a simpler way, involving fewer entities. As the author himself writes in the conclusion, “Although this proposal is apostate and heretical, [the paper] suggested that negative values of these parameters could in principle explain cosmological observational data, which have always been interpreted within the reasonable assumption of positive mass.”
Sometimes physicists come up with rather unusual ideas to explain observed discrepancies between theory and experiment. For example, last November, American theoretical physicist Hooman Davoudiasl introduced a new force that is carried by an ultra-light scalar particle and pushes dark matter away from the Earth. This assumption well explains the failures of all terrestrial experiments to search for dark matter - if such a force really exists, the detectors, in principle, could not register anything. Unfortunately, it is impossible to verify this statement at the current level of technology development.
Dmitry Trunin
Hypothetical wormhole in spacetime
In theoretical physics, this is the concept of a hypothetical substance, the mass of which has the opposite value to the mass of a normal substance (just as an electric charge can be positive and negative). For example, −2 kg. Such a substance, if it existed, would violate one or more and exhibit some strange properties. According to some speculative theories, matter with negative mass can be used to create (wormholes) in space-time.
It sounds like absolute science fiction, but now a group of physicists from Washington State University, University of Washington, OIST University (Okinawa, Japan) and Shanghai University is showing some of the properties of a hypothetical negative mass material. For example, if you push this substance, it will accelerate not in the direction of the force applied, but in the opposite direction. That is, it accelerates in the opposite direction.
To create a substance with negative mass properties, scientists prepared a Bose-Einstein condensate by cooling rubidium atoms to almost absolute zero. In this state, particles move extremely slowly, and quantum effects begin to appear at the macroscopic level. That is, in accordance with the principles of quantum mechanics, particles begin to behave like waves. For example, they synchronize with each other and flow through capillaries without friction, that is, without losing energy - the effect of so-called superfluidity.
In the laboratory of the University of Washington, conditions were created for the formation of a Bose-Einstein condensate in a volume of less than 0.001 mm³. The particles were slowed down by a laser and waited until the most energetic of them left the volume, which further cooled the material. At this stage, the supercritical fluid still had a positive mass. If the seal of the vessel was broken, the rubidium atoms would fly apart in different directions, since the central atoms would push the outermost atoms out, and they would accelerate in the direction of the applied force.
To create a negative effective mass, physicists used another set of lasers that changed the spin of some of the atoms. As the simulation predicts, in certain areas of the vessel the particles should acquire negative mass. This can be clearly seen by the sharp increase in the density of matter as a function of time in the simulations (in the bottom diagram).
Figure 1. Anisotropic expansion of a Bose-Einstein condensate with different cohesion force coefficients. Real experimental results are shown in red, simulation prediction results are shown in black.
The bottom diagram is a close-up of the middle frame in the bottom row of Figure 1.
The bottom diagram shows a one-dimensional simulation of total density as a function of time in the region where dynamic instability first appeared. Dotted lines separate three groups of atoms with velocities
at a quasi-moment
Where is the effective mass
begins to become negative (top line). Shown is the point of minimum negative effective mass (middle) and the point where mass returns to positive values (bottom line). The red dots indicate places where the local quasi-moment lies in the region of negative effective mass.
The very first row of graphs shows that during the physical experiment, the substance behaved in exact accordance with the results of the simulation, which predicts the appearance of particles with a negative effective mass.
In a Bose-Einstein condensate, the particles behave like waves and therefore do not propagate in the direction in which normal particles of positive effective mass should propagate.
In fairness, it must be said that physicists have repeatedly recorded during experiments, but those experiments could be interpreted in different ways. Now the uncertainty has been largely eliminated.
Scientific article April 10, 2017 in the journal Physical Review Letters(doi:10.1103/PhysRevLett.118.155301, available by subscription). A copy of the article before submission to the journal on December 13, 2016 is freely available on the website arXiv.org (arXiv:1612.04055).
