Tagged: Quantum vacuum Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 11:08 am on July 20, 2019 Permalink | Reply
    Tags: "Yes Virtual Particles Can Have Real Observable Effects", A neutron star despite being mostly made of neutral particles produces the strongest magnetic fields in the Universe., As particle-antiparticle pairs pop in-and-out of existence they can interact with real particles, , , , , In 2016 scientists were able to locate a neutron star that was close enough and possessed a strong enough magnetic field to make these observations possible., On scales of both the very large and the very small we do far better by applying our best scientific theories extracting physical predictions and then observing and measuring the critical phenomena., Quantum vacuum, Real particles like electrons or photons leaving signatures imprinted on the real particles that are potentially observable., The light around RX J1856.5–3754 is just perfect., The nature of our quantum Universe is puzzling counterintuitive and testable. The results don’t lie., Vacuum birefringence, When you apply a strong magnetic field particles and antiparticles have opposite charges from one another., When you have particle/antiparticle pairs present in empty space you might think they simply pop into existence live for a little while and then re-annihilate and go back into nothingness.   

    From Ethan Siegel: “Yes, Virtual Particles Can Have Real, Observable Effects” 

    From Ethan Siegel
    July 19, 2019

    1
    As electromagnetic waves propagate away from a source that’s surrounded by a strong magnetic field, the polarization direction will be affected due to the magnetic field’s effect on the vacuum of empty space: vacuum birefringence. By measuring the wavelength-dependent effects of polarization around neutron stars with the right properties, we can confirm the predictions of virtual particles in the quantum vacuum. (N. J. SHAVIV / SCIENCEBITS)

    The nature of our quantum Universe is puzzling, counterintuitive, and testable. The results don’t lie.

    Although our intuition is an incredibly useful tool for navigating daily life, developed from a lifetime of experience in our own bodies on Earth, it’s often horrid for providing guidance outside of that realm. On scales of both the very large and the very small, we do far better by applying our best scientific theories, extracting physical predictions, and then observing and measuring the critical phenomena.

    Without this approach, we never would have come to understood the basic building blocks of matter, the relativistic behavior of matter and energy, or the fundamental nature of space and time themselves. But nothing matches the counterintuitive nature of quantum vacuum. Empty space isn’t completely empty, but consists of an indeterminate state of fluctuating fields and particles. It’s not science fiction; it’s a theoretical framework with testable, observable predictions. 80 years after Heisenberg first postulated an observational test, humanity has confirmed it. Here’s what we’ve learned.

    2
    An illustration between the inherent uncertainty between position and momentum at the quantum level. There is a limit to how well you can measure these two quantities simultaneously, and uncertainty shows up in places where people often least expect it. (E. SIEGEL / WIKIMEDIA COMMONS USER MASCHEN)

    Discovering that our Universe was quantum in nature brought with it a lot of unintuitive consequences. The better you measured a particle’s position, the more fundamentally indeterminate its momentum was. The shorter an unstable particle lived, the less well-known its mass fundamentally was. Material objects that appear to be solid on macroscopic scales can exhibit wave-like properties under the right experimental conditions.

    But empty space holds perhaps the top spot when it comes to a phenomenon that defies our intuition. Even if you remove all the particles and radiation from a region of space — i.e., all the sources of quantum fields — space still won’t be empty. It will consist of virtual pairs of particles and antiparticles, whose existence and energy spectra can be calculated. Sending the right physical signal through that empty space should have consequences that are observable.

    3
    An illustration of the early Universe as consisting of quantum foam, where quantum fluctuations are large, varied, and important on the smallest of scales. (NASA/CXC/M.WEISS)

    The particles that temporarily exist in the quantum vacuum themselves might be virtual, but their effect on matter or radiation is very real. When you have a region of space that particles pass through, the properties of that space can very much have real, physical effects that be predicted and tested.

    One of those effects is this: when light propagates through a vacuum, if space is perfectly empty, it should move through that space unimpeded: without bending, slowing, or breaking into multiple wavelengths. Applying an external magnetic field doesn’t change this, as photons, with their oscillatory electric and magnetic fields, don’t bend in a magnetic field. Even when your space is filled with particle/antiparticle pairs, this effect doesn’t change. But if you apply a strong magnetic field to a space filled with particle/antiparticle pairs, suddenly a real, observable effect arises.

    4
    Visualization of a quantum field theory calculation showing virtual particles in the quantum vacuum. (Specifically, for the strong interactions.) Even in empty space, this vacuum energy is non-zero. As particle-antiparticle pairs pop in-and-out of existence, they can interact with real particles like electrons or photons, leaving signatures imprinted on the real particles that are potentially observable. (DEREK LEINWEBER)

    When you have particle/antiparticle pairs present in empty space, you might think they simply pop into existence, live for a little while, and then re-annihilate and go back into nothingness. In empty space with no external fields, this is true: Heisenberg’s energy-time uncertainty principle applies, and so long as all the relevant conservation laws are still obeyed, this is all that happens.

    But when you apply a strong magnetic field, particles and antiparticles have opposite charges from one another. Particles with the same velocities but opposite charges will bend in opposite directions in the presence of a magnetic field, and light that passes through a region of space with charged particles that move in this particular fashion should exhibit an effect: it should get polarized. If the magnetic field is strong enough, this should lead to an observably large polarization, by an amount that’s dependent on the strength of the magnetic field.

    5
    There have been many attempts to measure the effect of vacuum birefringence in a laboratory setting, such as with a direct laser pulse setup as shown here. However, they have been unsuccessful so far, as the effects have been too small to be seen with terrestrial magnetic fields, even with gamma rays at the GeV scale.(YOSHIHIDE NAKAMIYA, KENSUKE HOMMA, TOSEO MORITAKA, AND KEITA SETO, VIA ARXIV.ORG/ABS/1512.00636)

    This effect is known as vacuum birefringence, occurring when charged particles get yanked in opposite directions by strong magnetic field lines. Even in the absence of particles, the magnetic field will induce this effect on the quantum vacuum (i.e., empty space) alone. The effect of this vacuum birefringence gets stronger very quickly as the magnetic field strength increases: as the square of the field strength. Even though the effect is small, we have places in the Universe where the magnetic field strengths get large enough to make these effects relevant.

    Earth’s natural magnetic field might only be ~100 microtesla, and the strongest human-made fields are still only about 100 T. But neutron stars give us the opportunity for particularly extreme conditions, giving us large volumes of space where the field strength exceeds 10⁸ (100 million) T, ideal conditions for measuring vacuum birefringence.

    6
    A neutron star, despite being mostly made of neutral particles, produces the strongest magnetic fields in the Universe, a quadrillion times stronger than the fields at the surface of Earth. When neutron stars merge, they should produce both gravitational waves and also electromagnetic signatures, and when they cross a threshold of about 2.5 to 3 solar masses (depending on spin), they can become black holes in under a second. (NASA / CASEY REED — PENN STATE UNIVERSITY)

    How do neutron stars make such large magnetic fields? The answer may not be what you think. Although it might be tempting to take the name ‘neutron star’ quite literally, it isn’t made exclusively out of neutrons. The outer 10% of a neutron star consists mostly of protons, light nuclei, and electrons, which can stably exist without being crushed at the neutron star’s surface.

    Neutron stars rotate extremely rapidly, frequently in excess of 10% the speed of light, meaning that these charged particles on the outskirts of the neutron star are always in motion, which necessitated the production of both electric currents and induced magnetic fields. These are the fields we should be looking for if we want to observe vacuum birefringence, and its effect on the polarization of light.

    7
    Light coming from the surface of a neutron star can be polarized by the strong magnetic field it passes through, thanks to the phenomenon of vacuum birefringence. Detectors here on Earth can measure the effective rotation of the polarized light. (ESO/L. CALÇADA)

    It’s a challenge to measure the light from neutron stars: although they’re quite hot, hotter even than normal stars, they’re tiny, with diameters of just a few dozen kilometers. A neutron star is like a glowing Sun-like star, at perhaps two or three times the temperature of the Sun, compressed into a volume the size of Washington, D.C.

    Neutron stars are very faint, but they do emit light from all across the spectrum, including all the way down into the radio part of the spectrum. Depending on where we choose to look, we can observe the wavelength-dependent effects that the effect of vacuum birefringence has on the light’s polarization.

    8
    VLT image of the area around the very faint neutron star RX J1856.5–3754. The blue circle, added by E. Siegel, shows the location of the neutron star. Note that despite appearing very faint and red in this image, there is enough light reaching our detectors for us, with the proper instrumentation, to search for this vacuum birefringence effect. (ESO)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo,


    Glistening against the awesome backdrop of the night sky above ESO_s Paranal Observatory, four laser beams project out into the darkness from Unit Telescope 4 UT4 of the VLT, a major asset of the Adaptive Optics system

    All of the light that’s emitted must pass through the strong magnetic field around the neutron star on its way to our eyes, telescopes, and detectors. If the magnetized space that it passes through exhibits the expected vacuum birefringence effect, that light should all be polarized, with a common direction of polarization for all the photons.

    In 2016, scientists were able to locate a neutron star that was close enough and possessed a strong enough magnetic field to make these observations possible. Working with the Very Large Telescope (VLT) in Chile, which can take fantastic optical and infrared observations, including polarization, a team led by Roberto Mignani was able to measure the polarization effect from the neutron star RX J1856.5–3754.

    8
    A contour plot of the phase-averaged linear polarization degree in two models (left and right): for an isotropic blackbody and for a model with a gaseous atmosphere. At top, you can see the observational data, while at the bottom, you can see what you get if you subtract out the theoretical effect of vacuum birefringence from the data. The effects match partically perfectly. (R.P. MIGNANI ET AL., MNRAS 465, 492 (2016))

    The authors were able to extract, from the data, a large effect: a polarization degree of around 15%. They also calculated what the theoretical effect from vacuum birefringence ought to be, and subtracted it out from the actual, measured data. What they found was spectacular: the theoretical effect of vacuum birefringence accounted for practically all of the observed polarization. In other words, the data and the predictions matched almost perfectly.

    You might think that a closer, younger pulsar (like the one in the Crab Nebula) might be better suited to making such a measurement, but there’s a reason that RX J1856.5–3754 is special: its surface is not obscured by a dense, plasma-filled magnetosphere.

    If you watch a pulsar like the one in the Crab Nebula, you can see the effects of opacity in the region surrounding it; it’s simply not transparent to the light we’d want to measure.

    Supernova remnant Crab nebula. NASA/ESA Hubble

    But the light around RX J1856.5–3754 is just perfect. With the polarization measurements in this portion of the electromagnetic spectrum from this pulsar, we have confirmation that light is, in fact, polarized in the same direction as the predictions arising from vacuum birefringence in quantum electrodynamics. This is the confirmation of an effect predicted so long ago — in 1936 — by Werner Heisenberg and Hans Euler that, decades after the death of both men, we can now add “theoretical astrophysicist” to each of their resumes.

    9
    The future X-ray observatory by the ESA, Athena, will include the capability of measuring the polarization of X-ray light from space, something that none of our leading observatories today, such as Chandra and XMM-Newton, can do. (ESA / ATHENA COLLABORATION)

    NASA/Chandra X-ray Telescope

    ESA/XMM Newton

    Now that the effect of vacuum birefringence has been observed — and by association, the physical impact of the virtual particles in the quantum vacuum — we can attempt to confirm it even further with more precise quantitative measurements. The way to do that is to measure RX J1856.5–3754 in the X-rays, and measuring the polarization of X-ray light.

    While we don’t have a space telescope capable of measuring X-ray polarization right now, one of them is in the works: the ESA’s Athena mission. Unlike the ~15% polarization observed by the VLT in the wavelengths it probes, X-rays should be fully polarized, displaying right around an 100% effect. Athena is currently slated for launch in 2028, and could deliver this confirmation for not just one but many neutron stars. It’s another victory for the unintuitive, but undeniably fascinating, quantum Universe.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    “Starts With A Bang! is a blog/video blog about cosmology, physics, astronomy, and anything else I find interesting enough to write about. I am a firm believer that the highest good in life is learning, and the greatest evil is willful ignorance. The goal of everything on this site is to help inform you about our world, how we came to be here, and to understand how it all works. As I write these pages for you, I hope to not only explain to you what we know, think, and believe, but how we know it, and why we draw the conclusions we do. It is my hope that you find this interesting, informative, and accessible,” says Ethan

     
  • richardmitnick 6:03 pm on July 3, 2017 Permalink | Reply
    Tags: Delbrück scattering, , , , Polarized gamma rays, Quantum vacuum, The Casimir effect, The future Extreme Light Infrastructure in Măgurele Romania, Vacuum studies, Werner Heisenberg's Uncertainty Principle   

    From Inside Science via Don Lincoln at FNAL: “A Study About Nothing” 

    Inside Science

    June 29, 2017
    Yuen Yiu

    1
    Image credits: Abigail Malate

    Scientists find new ways to measure the infinitesimally small fluctuations that exist in a vacuum.

    A vacuum is a space absolutely devoid of matter, at least according to the Merriam-Webster dictionary. But if you talk to a physicist you may get a different answer. According to quantum physics, even vacuums are not completely empty. Constant fluctuations in energy can spontaneously create mass not just out of thin air, but out of absolutely nothing at all.

    “It’s like a boiling sea of appearing and disappearing particle pairs,” said James Koga, a theoretical physicist from the National Institutes for Quantum and Radiological Science and Technology in Kyoto, Japan. The pairs, made up of one particle and one antiparticle, exist for only moments. Koga is investigating the subtle effects caused by these fluctuations.

    This peculiar nature of vacuum, sometimes referred to as “quantum vacuum,” is not just theoretical speculation. It has real, measurable effects on our physical reality. Although these effects are usually far too small to impact even the most sensitive instruments of today, scientists think the picture will change for the miniaturized technologies of tomorrow.

    “In the macroscopic world, we don’t care about these forces at all. You wouldn’t care about it when you are driving a car for instance. It’s totally negligible,” said Alejandro Manjavacas, a physicist specializing in photonics at the University of New Mexico in Albuquerque. “But in the context of nanotechnology or nanophotonics — at a super small scale, these effects will start playing a role.”

    Although the concept of a fluctuating vacuum was theorized and proven during the first half of the last century, scientists are still grappling with the implications. Two recently published papers explore two separate aspects of the same mystery — what happens when there is nothing at all?

    A glistening ocean

    The energy fluctuation in vacuum can be explained by the uncertainty principle of quantum physics. The principle, first introduced by German physicist Werner Heisenberg, states that at any definite point in space, there must exist temporary changes in energy over time. Sometimes this energy is converted into mass, generating particle-antiparticle pairs.

    Most of the time these newly born pairs recombine and vanish before interacting with anything. Because of this, physicists like to refer to these pairs as “virtual particles,” but this doesn’t mean they aren’t real — they just need something to interact with to make their presence felt.

    For this, Koga and his team envision a way to observe this boiling sea of vacuum the same way we see glistening waves in the ocean — with light. In their latest paper, published in Physical Review Letters, they lay down the theoretical groundwork needed for the experiment. Specifically, they want to study photons that bounce off an atomic nucleus in a distinctive way that wouldn’t happen without the “boiling” vacuum acting as the middleman. This peculiar light phenomenon is known as Delbrück scattering, predicted by German-American physicist Max Delbrück in 1933. The effect was later observed experimentally in 1975 — but just barely.

    “[Scientists] could kind of guess that the Delbrück scattering was there, but it was like if you include this effect in your calculation then it agrees more with the data,” said Koga.

    Koga and his team hope to take Delbrück scattering to another level by characterizing the phenomenon’s effect. It is as if scientists knew about air resistance, but still needed to study it further so that engineers could use the knowledge to build an airplane.

    The task is tricky. To measure Delbrück scattering, one must shine light onto trillions of atomic nuclei, which creates a problem. Photons bounce off nuclei, electrons and even each other in all directions, via all kinds of different interactions. How can one distinguish which photon is scattered from what?

    Koga’s team suggests that we use polarized gamma rays. Just like polarized sunglasses can help you see better by filtering out unwanted solar glares, polarized gamma rays can help scientists sift through the gazillions of photons based on their polarization, in addition to energy and scattered angle. As long as one knows where to look for the specific photons that are the results of Delbrück scattering, one should be able to pick them out from the lineup.

    “The point that we are trying to make in our paper is by using a new polarized source, you can almost see the signal isolated,” said Koga.

    But there is just one problem — such an instrument doesn’t exist. At least not yet.

    Enter the future Extreme Light Infrastructure in Măgurele, Romania. This facility will not only provide the polarized gamma rays Koga proposed, but will make some of the brightest gamma rays in the world. This is important because just like a brighter ambient light can shorten the exposure time for taking a photo, a brighter gamma ray can shorten the run time for Koga’s proposed experiment.


    Credit: ELI-NP Romania

    Kazuo Tanaka, the scientific director of the Nuclear Physics division of the future facility, is pleased with Koga’s team’s proposal.

    “I think their proposal is very crystal clear. They calculated how many days of shooting they need for the experiment, and came up with 76 days,” he said. “I think if they do the experiment we can have a very definitive measurement for Delbrück scattering.”

    While the facility is still under construction, and will not be ready for the experiment at least until 2019, a different group of physicists are studying the same nothingness of vacuum, but with a different set of eyes. Instead of beaming light into the vacuum and looking for a glint, physicist Alejandro Manjavacas and his group at the University of New Mexico want to know if the fluctuations of vacuum can actually exert an invisible force on physical objects — as if they were being moved by Jedis.


    The video shows two plates moving towards each other in a vibrating pool of water, an analogy to the Casimir effect that exist in a fluctuating vacuum. Credit: Denysbondar

    The Casimir effect, named after Dutch physicist Henrik Casimir, describes the force that pushes two objects together due to surrounding waves. The effect exists for two beads on a vibrating string, or two boats in a wavy ocean, as well as two particles in a fluctuating vacuum. Much like Delbrück scattering, the Casimir effect was theorized in 1948 and has already been confirmed, in 1996. So, what is left to be discovered?

    “Most of the work that was done on Casimir effect was for systems that weren’t moving, or if they were moving, they were moving in a uniform motion,” said Manjavacas.

    In a paper published in Physical Review Letters, Manjavacas and his colleagues calculated how the Casimir effect can nudge objects that are already spinning and moving. Through calculations, they discovered that when a tiny sphere spins near a flat surface, it will move as if it is rolling down the surface, despite never making contact with it.

    “If you try to make a nanostructure that involves moving parts that are very close together, it is crucial to know what is going to be the effect from these type of forces. You’ll need to know whether it is going to cause the moving parts to get stuck,” said Manjavacas. “Or we can use these forces to our advantage, such as using them to move objects or to force them to do the things that we want.”

    In their study, the researchers evaluated the effect for spheres with diameters ranging from 50 to 500 nanometers, much less than one hundredth the width of a human hair. As expected, the relationship between the spinning and the lateral movement isn’t straightforward — it depends on the speed that the sphere is spinning, as well as the size of the sphere and the distance between the sphere and the surface. These minute effects may soon be relevant on the frontier of technology, for example when engineers design medical nanobots.

    2
    Virtual Particles and Black Holes
    The sidebar image shows a simulated animation of a black hole moving across a galaxy in the background. Credit: Wikicommons/CC BY-SA 3.0
    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?
    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it

    Beyond its impact on nanotechnologies and particle accelerators here on earth, the fluctuating vacuum extends its effects into space. In 1968, British astrophysicist Stephen Hawking predicted that when a particle-antiparticle pair is created on the edge of a black hole’s event horizon, the pair can be pried apart by gravity — one particle falling into the black hole and the other escaping. The escape of one of the particles then contributes to an infinitesimally small, and so far purely theoretical, radiation known as Hawking radiation.
    Hawking radiation, if proven, will play a crucial role in determining the lifetime of black holes. However, even if the radiation is real, it will still be far too faint for us to detect it. There have been a few analogous models that can successfully reproduce the phenomenon in a laboratory setting, but they use light waves or sound waves instead of gravitational waves of black holes. There is hope that the Large Hadron Collider near Geneva, Switzerland, with a higher energy output, can create a super tiny black hole that lasts but a split second, and offer a more definitive answer on Hawking radiation. But for now, no direct observation for Hawking radiation has been possible, leading to some saying that the “jury is still out.”
    “This is a pity, because if they had, I would have got a Nobel prize,” said Hawking during a 2008 lecture.

    A real virtuality

    Even though the quantum interpretation of vacuum — complete with strange particles popping into and out of existence — accurately describes our reality, how can we tell that this isn’t just another placeholder theory? Will the theory eventually fail just like the geocentric model, or the flat earth model, or perhaps most relevantly, the famous failed theory of ether from the 19th century?

    The theory of ether was proposed by physicists to explain how light waves can propagate through the vacuum of space. Based on intuition, scientists back then believed that a medium was necessary for light waves to travel, just like the waves in the ocean travel through the medium of water. This hypothesis was disproved in 1887 by Albert Michelson and Edward Morley, in a famous experiment, in which they measured the speed of light in perpendicular directions and found no difference. Albert Michelson was later awarded a Nobel Prize in 1907 for his achievements, and became the first Nobel laureate from the United States.

    So, will the quantum model of vacuum also be proved wrong? Most physicists today do not think so. In fact, Nobel laureate Robert Laughlin from Stanford University has written in his book “A Different Universe: Reinventing Physics from the Bottom Down” specifically about this comparison: “The word [ether] has extremely negative connotations in theoretical physics because of its past association with opposition to relativity. This is unfortunate because, stripped of these connotations, it rather nicely captures the way most physicists actually think about the vacuum.”

    Because unlike the ether theory, the quantum model of vacuum, with all its fluctuations and peculiar features, has since been thoroughly tested and proven.

    “We see pair creation all the time actually, like in particle accelerators,” said Koga. In fact, it happens so often that for certain experiments scientists actually have to consider the phenomenon as “noise” that could obscure the signal they are looking for, according to Koga.

    “We now have experimental evidence of all kinds of particles coming in and out [of the vacuum],” said Toshiki Tajima, a physicist from the University of California, Irvine. “Muons and anti-muons, protons and anti-protons, and even quarks and anti-quarks.”

    In 1665, Robert Hooke and Antoni van Leeuwenhoek discovered microbes when they pointed their microscopes at “nothing.” In 1964, Arno Penzias and Robert Woodrow Wilson discovered the cosmic microwave background when they pointed their telescopes at “nothing.” Vacuum is perhaps the ultimate “nothing,” so if history is any indication, “nothing” is an interesting place, especially if you want to look for something.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Inside Science is brought to you in part through the generous support of The American Physical Society and The Acoustical Society of America and a coalition of underwriters.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: