Portable optical atomic clock makes its commercial debut

12 Dec 2023

Simple setup: The iodine vapour cells used in Vector Atomic's portable optical atomic clock. (Courtesy: Vector Atomic)

Atoms are the world’s most precise timekeepers – so much so that the second is defined as exactly 9 192 631 770 ticks of a caesium-based atomic clock. Commercially-available versions of these atomically precise clocks underpin GPS, navigation, data transfer and financial markets, and they run at microwave frequencies, or billions of tick-tocks per second. After a day, their timekeeping is out by less than ten nanoseconds.

 

Quantum simulator visualizes large-scale entanglement in materials

14 Dec 2023

How entangled is it? The researchers obtained temperature profiles of their system showing that particles that interact strongly are “hot” (red) and those that interact little are “cold” (blue). Entanglement is greatest when interactions are strong. (Courtesy: Helene Hainzer)

Physicists in Austria have found a quick and efficient way of extracting information on a quantum material’s large-scale entanglement structure thanks to a 50-year-old theorem from quantum field theory. The new method could open doors in fields such as quantum information, quantum chemistry or even high-energy physics.

 

Charge qubits get a thousand-fold boost

04 Dec 2023

Keeping quantum: Artist's rendering of two charge qubits with a long coherence time and strong coupling. (Courtesy: Dafei Jin/Argonne National Laboratory and the University of Notre Dame)

Researchers in the US have improved the coherence time of charge quantum bits (qubits) by a factor of 1000 thanks to advances in the materials used to construct them. Led by Dafei Jin of the Argonne Center for Nanoscale Materials and David Schuster of Stanford University and the University of Chicago, the multi-institutional team also showed it was possible to read out the state of these qubits with a fidelity of 98.1% – a value Jin says will increase further with the aid of more sophisticated readout technologies.

 

What volcanoes and coffeemaking have in common, the physics of playing the didjeridu

08 Dec 2023 Hamish Johnston

Espresso eruption: static electricity affects your cup of coffee. (Courtesy: iStock/radu984)

What do volcanic eruptions and grinding coffee have in common? According to a team of coffee chemists and geophysicists in the US and the Republic of Korea, they both produce a fair amount of static electricity, so much so that volcanologists are now examining the espresso-making process.

It is well-known that static electricity is created when grinding coffee beans due to the fracturing and friction that occurs. This causes coffee particles to clump together and stick to the grinder. However, not much was known about how this impacts the resulting brewed coffee.

 

Resonant excitation of nuclear clock transition spotted at XFEL

17 Oct 2023

Nuclear timekeeper Illustration of a scandium nucleus with a superimposed clock. (Courtesy: European XFEL/Helmholtz Institute Jena/Tobias Wüstefeld/Ralf Röhlsberger)

An important step towards creating an extremely accurate clock based on a nuclear transition has been taken by an international team of physicists. Yuri Shvyd’ko at Argonne National Laboratory in the US and colleagues have achieved the resonant excitation of a nuclear transition in scandium-45. The transition could be used to create a nuclear clock with the potential to be much more accurate that the best atomic clocks available today.

 

Scandium breaks temperature record for elemental superconductors

07 Dec 2023 Isabelle Dumé

Scandium is the only known elemental superconductor to have a critical temperature in the 30 K range. This phase diagram shows the superconducting transition temperature (Tc) and crystal structure versus pressure for scandium. The measured results on all the five samples studied show consistent trends. (Courtesy: Chinese Phys. Lett. 40 107403)

Scandium remains a superconductor at temperatures above 30 K, making it the first element known to superconduct at such a high temperature. The record-breaking discovery was made by researchers in China, Japan and Canada who subjected the element to pressures of up to 283 GPa – around 2.3 million times atmospheric pressure at sea level.

 

Simultaneous production of a top quark and a photon was observed for the first time

04 Dec 2023

Observational first: physicists have used the ATLAS experiment at CERN to observe the production of top-quark and photon pairs. (Courtesy: CERN)

For the first time, particle physicists have observed the simultaneous production of a photon and a top quark. The milestone was achieved by the ATLAS collaboration, which operates a giant detector at CERN’s Large Hadron Collider (LHC). The discovery could lead to a deeper understanding of the electroweak interaction, and its enigmatic relationship with the Higgs field.

 

Bound antimatter ejects molecular ions from crystals

10 Nov 2023

Antimatter lab: the slow positron beam apparatus used by the Tokyo researchers. (Courtesy: Yasuyuki Nagashima/Tokyo University of Science)

Strong evidence that positrons can exist in short-lived bound states within solid matter has been found by researchers in Japan. By analysing experiments using new theoretical models, Takayuki Tachibana and colleagues at the Tokyo University of Science showed how the exotic states are involved in the emission of molecular ions from ionic crystals that are being bombarded with low-energy positron beams.

 

A surprising link discovered between fast radio bursts and earthquakes

21 Oct 2023

Common trends: researchers at the University of Tokyo have used data taken by telescopes such as the Arecibo observatory in Puerto Rico (pictured here in 2019) to uncover similarities between fast radio bursts and earthquakes (Courtesy: UCF)

Researchers in Japan have found striking similarities between the statistical behaviour of repeating fast radio bursts (FRBs) and earthquakes.

FRBs are brief, intense bursts of radio waves from outside our galaxy. Whilst these bursts typically last a few milliseconds, astronomers have also found bursts a thousand times shorter.

 

Mysterious ultrahigh-energy cosmic ray puzzles astronomers

27 Nov 2023

Sun goddess: illustration of the shower of particles created by Amaterasu as it entered the atmosphere above the Telescope Array in Utah. (Courtesy: Osaka Metropolitan University/L-INSIGHT, Kyoto University/Ryuunosuke Takeshige)

A cosmic-ray particle with an energy about 36 million times greater than the particles accelerated by CERN’s Large Hadron Collider has been detected. At 244 EeV, this is one of the most energetic particles ever observed and was spotted in 2021 by the Telescope Array in Utah. While the ultrahigh-energy cosmic ray (UHECR) was probably created by a violent astrophysical process, researchers were unable to trace it back to its origins.

 

Lots of oxygen existed in the early universe, JWST reveals

06 Dec 2023

Cutting edge: NIRSpec being readied for the launch of the JWST. (Courtesy: Astrium/NIRSpec)

Using a cutting-edge spectrograph on the James Webb Space Telescope (JWST), astronomers have found evidence that interstellar oxygen was far more abundant in many ancient galaxies than previously thought. Led by Kimihiko Nakajima at the National Astronomical Observatory of Japan, the team hopes that their observations could improve our understanding of the early universe.

 

Ion-exchange bead writes underwater

09 Oct 2023 Isabelle Dumé

Water writing: As the bead moves, it trades residual cations in the water for protons, and thus traces out an invisible track of lower pH in the liquid. Linear scales: 250 µm. (Courtesy: ill./©: Thomas Palberg, Benno Liebchen)

Writing requires a substrate, like clay or paper, to fix the written lines and letters in place. Doing the same thing in a liquid such as water is not possible because the movement of the pen creates turbulence that quickly eradicates ink trails. In principle, you could remove this turbulence by using a very tiny pen, since smaller moving objects create fewer vortices, but even a tiny pen would require a substantial reservoir of ink, cancelling out any size advantage.

 

The planet system is perfectly tuned

01 Dec 2023

Planetary harmony: illustration of the orbits of the six exoplanets of HD 110067. (Courtesy:Medienmitteilung/UniBE/UniGE/CHEOPS/TESS/Sextett/Planete/Walzer/Video©UniBE/HughOsborn)

A rare system of six exoplanets, all smaller than Neptune but larger than Earth, has been found with orbits that are all resonant with each other. The system was discovered by astronomers led by Rafael Luque of the University of Chicago, who suggest that the planets have remained undisturbed in this configuration since their formation a billion years ago.

The planetary treasure trove also provides one of the best opportunities for characterizing “mini-Neptunes”, which are a mysterious class of planet that are absent from the Solar System.

 

Terahertz laser induces a room-temperature superconducting phase in a fullerene compound

30 Nov 2023 Isabelle Dumé

The optical setup used to generate the low frequency laser pulses that resonantly excited the sample. Courtesy: J. Witt, MPSD

An organic material in a metastable phase behaves a little like a room-temperature superconductor when excited with laser light. Though this behaviour fades almost as quickly as the laser pulse that induces it, the team behind the discovery say that with the right light source, it might be possible to keep the material in its superconducting-like state continuously.

Scientists have known for a while that shining light at terahertz and mid-infrared frequencies on certain materials is a good way to manipulate their properties. In some cases, this method can even be used to create non-equilibrium material phases that have no analogue under normal conditions.

 

Demon quasiparticle is detected 67 years after it was first proposed

04 Sep 2023

Lurking for decades: researchers have discovered Pines' demon, a collection of electrons in a metal that behaves like a massless wave. It is illustrated here as an artist’s impression. (Courtesy: The Grainger College of Engineering/University of Illinois Urbana-Champaign)

For nearly seven decades, a plasmon known as Pines’ demon has remained a purely hypothetical feature of solid-state systems. Massless, neutral and unable to interact with light, this unusual quasiparticle is reckoned to play a key role in certain superconductors and semimetals. Now scientists in the US and Japan say they have finally detected it while using specialized electron spectroscopy to study the material strontium ruthenate.

 

Earbud biosensors provide continuous monitoring of brain activity and lactate levels

15 Nov 2023

Simultaneous sensing Flexible electrochemical and electrophysiological sensors are attached to in-ear headphones, or earbuds, via a stamp-like surface. Once the earbuds are inserted in the ear canal, the sensors simultaneously monitor brain states and exercise levels. (Courtesy: Erik Jepsen/University of California San Diego)

Earbuds equipped with biosensors can continuously measure the electrical activity of the brain and levels of the sweat secretion lactate. The device represents a potential new wearable sensing technology for detection and monitoring of neurogenerative diseases or long-term health monitoring.

Developed by a multidisciplinary team of engineers at the Center for Wearable Sensors at the UC San Diego Jacobs School of Engineering, the earbud sensors wirelessly transmit the recorded data to a smartphone or laptop computer for visual display and analysis.

 

A nanoscale device produces a stream of chiral single photons

06 Oct 2023 Isabelle Dumé

Formed within wells indented into the stack of two different layered materials (a monolayer semiconductor and an anti-ferromagnetic crystal), the chiral quantum light emissions rise up out of the material and could be used for quantum information and communication applications. (Courtesy: Los Alamos National Laboratory)

A new nanoscale device based on stacks of two-dimensional materials can not only generate a stream of single photons but can also control their chirality, or circular polarization, without the need for an applied magnetic field. Since manipulating a photon’s polarization state is a way to encode information in it, the advance could be important for quantum technologies, according to the researchers at the Los Alamos National Laboratory in the US who developed it.

 

Single-molecule makes a sensitive pressure and force sensor

15 Nov 2023 Isabelle Dumé

Flopping around: A drawing of the bullavene molecule and the rearrangements it undergoes as it changes into its different possible shapes, or isomers. (Courtesy: Wikipedia/public domain image)

Researchers in Australia have detected and controlled changes to the shape of a single molecule in response to an applied mechanical force. The feat could enable the development of miniaturized implantable pressure sensors and accelerometers for the electronics industry.

 

Neutral-atom quantum computers are having a moment

09 Nov 2023

All systems go: A beam of laser light in Jeff Thompson's lab at Princeton University, where he and his colleagues recently demonstrated a new way of erasing errors in a neutral-atom quantum computer. (Courtesy: Frank Wojciechowski)

In the race for the quantum computing platform of the future, neutral atoms have been a bit of an underdog. While quantum bits (qubits) based on neutral atoms have several attractive characteristics, including the ease of scaling up qubit numbers and performing operations on them in parallel, most attention has focused on rival platforms. Many of the largest machines are built with superconducting qubits, including those developed at IBM, Google, Amazon, and Microsoft. Other companies have opted for ions, like Honeywell and IonQ, or photons, like Xanadu.

 

Weak measurement lets quantum physicists have their cake and eat it

20 Nov 2023 Raman Choudhary

Certified entangled In this entanglement certification scheme involving weak certification and reversal measurements, two parties (traditionally known as Alice and Bob) sitting in their respective laboratories share a potentially entangled pair of systems in the shared state |Ψi⟩. In the certification step, they subject their local systems to weak certification measurements to obtain statistics. In each run, they obtain outputs (±1) and the corresponding output state |Ψm⟩ that still has some entanglement. After passing the certification test, the post-measurement state |Ψm⟩ is subjected to reversal measurements in the last step to obtain the original state |Ψf⟩ = |Ψi⟩ probabilistically. (Courtesy: Recovering quantum entanglement after its certification 2003 Science Advances 9 40 doi:10.1126/sciadv.adi5261)

 

Shoot-through proton FLASH: a robust approach to brain tumour treatment

22 Nov 2023 Tami Freeman

Plan comparisons Example dose and LETD distributions for clinical IMPT and shoot-through proton FLASH plans for two patients with brain tumours. (Courtesy: CC BY 4.0/Phys. Med. Biol. 10.1088/1361-6560/ad0280)

Proton therapy is an increasingly popular cancer treatment that offers superior dose shaping to conventional photon radiotherapy. This high-precision dose delivery, however, means that target margins are needed to account for range uncertainties, exposing more healthy tissue to radiation. In addition, uncertainties in linear energy transfer (LET) and relative biological effectiveness (RBE) at the end of the beam range can increase irradiation of healthy tissue behind the target.

 

Flexible X-ray detectors line up for medical imaging and radiotherapy

23 Nov 2023 Tami Freeman

Tissue-equivalent detector Flexible X-ray detectors based on organic semiconductors modified with high-Z heteroatoms could prove ideal for a wide range of medical imaging, radiotherapy and dosimetry applications. (Courtesy: Prabodhi Nanayakkara)

X-ray detectors play a key role in a wide range of medical applications, including diagnostic imaging, radiotherapy dosimetry and personal radiation protection. Many of these applications require large-area detectors that can flexibly conform to curved surfaces. But most commercial X-ray detectors are stiff, power-hungry and expensive to fabricate into large areas.

One alternative is organic semiconductors, which can be used to create large-area optoelectronic devices via environmentally friendly, low-cost manufacturing techniques. Organic materials, however, exhibit low X-ray attenuation, resulting in detectors with low sensitivity. A team headed up at the University of Surrey’s Advanced Technology Institute aims to solve this problem. By adding small amounts of high-Z elements to an organic semiconductor, the researchers created organic X-ray detectors with high sensitivity and high flexibility.

 

New chip architecture offers hope for scaling up superconducting qubit arrays

17 Nov 2023 Avishma Lasrado

Multichip module: A photograph showing the qubit chip (outlined in red) stacked on the single flux quantum (SFQ) chip (outlined in blue). (Courtesy: Adapted from "Single Flux Quantum-Based Digital Control of Superconducting Qubits in a Multichip Module", PRX Quantum 4, 030310 https://doi.org/10.1103/PRXQuantum.4.030310)

Scientists in the US have introduced an ingenious new quantum chip architecture that significantly reduces disturbances caused by the signals used to control superconducting quantum bit (qubit) circuits. Led by Chuan Hong Liu and Robert McDermott of the University of Wisconsin, the team showed that the new multichip module (MCM) reduces gate errors by nearly a factor of 10 compared to earlier designs that used the same control system, making it a viable competitor to standard technologies.

 

Biomedical ethicists call for rules governing human research in commercial spaceflight

23 Nov 2023 Hamish Johnston

Our guest in this episode of the Physics World Weekly podcast is the biomedical ethicist Vasiliki Rahimzadeh, who along with colleagues has called for the commercial space industry to adopt ethical policies and best practices for research done on humans during space flights.

Rahimzadeh, who is at Baylor College of Medicine in the US, explains that as well as minimizing risks to paying astronauts who take part in experiments, an ethical framework should also ensure that private spaceflight – which is still the purview of the elite – benefits society as a whole.

 

New telecoms satellites will degrade our view of the cosmos

16 Nov 2023 Hamish Johnston

Astronomers are becoming increasingly concerned about the growing number of satellites that are lighting up the night sky by reflecting sunlight to Earth. In 2022, the prototype communications satellite BlueWalker 3 was launched and it is now the brightest commercial satellite ever – outshining almost every star in the sky. And to make matters worse, communications satellites like BlueWalker 3 broadcast microwave signals that can interfere with radio astronomy.

 

Top-cited work from North America recognized by IOP Publishing

17 Nov 2023 Michael Banks

This is the first year that IOP has recognised North America, having already published top-cited awards for China and India (courtesy: iStock/Igor-Kutyaev)

Almost 130 articles from researchers in North America have been recognized with a top-cited award for 2023 from IOP Publishing, which publishes Physics World. The papers received over 15400 citations in total and represent the top 1% of the most-cited articles that have been published by IOP Publishing between 2020 and 2022 with corresponding authors from North America.

This is the first year that IOP has recognised North America, having previously published top-cited awards for China and India. The papers were identified using data from Clarivate’s Web of Science database and cover 10 categories including biosciences, machine learning and reviews.

WHEN CHITIN IS CANCEROUS TO HUMAN?

 There is currently no evidence to suggest that chitin itself is carcinogenic to humans. Chitin is a naturally occurring polysaccharide found in the exoskeletons of insects and crustaceans, as well as in the cell walls of fungi. It is widely used in various industries, including food, pharmaceuticals, and cosmetics, without any known carcinogenic effects.

IS CHITIN IN THE FORM OF NANOPARTICLES CANCEROUS FOR HUMANS?

 

IS CHITIN IN THE FORM OF NANOPARTICLES CANCEROUS FOR HUMANS?

Chitin itself is not considered to be carcinogenic for humans. However, it is important to note that the toxicity of chitin nanoparticles can vary depending on their size, shape, and surface characteristics. Some studies have suggested that certain types of nanoparticles, including chitin nanoparticles, may have potential cytotoxic effects. However, more research is needed to fully understand the potential health risks associated with chitin nanoparticles. As with any potential exposure to nanoparticles, it is advisable to follow safety guidelines and take necessary precautions when handling or working with them.

There is currently no evidence to suggest that chitin in the form of nanoparticles is carcinogenic to humans. Chitin is a naturally occurring polysaccharide found in the exoskeletons of insects, crustaceans, and fungi. It is commonly used in various industries, including biomedical applications, due to its biocompatibility and biodegradability. However, like any other material, the safety of chitin nanoparticles will depend on factors such as size, shape, surface charge, and dosage. Further research and studies are always necessary to ensure the safety of any new material.

KONSTANTINOS P. TSIANTIS 20/11/2023

 

The new superconducting nanowire single-photon detector has 400,000 pixels

16 Nov 2023

Cosmic image: illustration of how, with further improvements, the new SNSPD could be used to observe astronomical objects. (Courtesy: S Kelley/NIST/Pixaby)

The highest resolution to date in a superconducting nanowire single-photon detector (SNSPD) camera has been claimed by researchers in the US. Designed by a team at the National Institute of Standards and Technology (NIST) and NASA’s Jet Propulsion Laboratory, the camera offers a pixel count some 400 times higher than other state-of-the-art designs, without sacrificing any of their advantages.

 

New telecoms satellites will degrade our view of the cosmos

16 Nov 2023 Hamish Johnston

Astronomers are becoming increasingly concerned about the growing number of satellites that are lighting up the night sky by reflecting sunlight to Earth. In 2022, the prototype communications satellite BlueWalker 3 was launched and it is now the brightest commercial satellite ever – outshining almost every star in the sky. And to make matters worse, communications satellites like BlueWalker 3 broadcast microwave signals that can interfere with radio astronomy.

 

Evidence emerges for a carbon-rich ocean on Europa

26 Sep 2023

Icy surface: Jupiter's moon Europa, as seen by JWST’s NIRCam. Tara Regio is the white area in the centre. (Courtesy: NASA, ESA, CSA, Gerónimo Villanueva/NASA-GSFC, Samantha K Trumbo/Cornell University).

Planetary scientists in the US have traced carbon on the surface of Jupiter’s moon Europa to the icy ocean beneath it, revealing new information about the ocean’s nature and origin. The discovery raises astrobiologists’ hopes that the carbon, which exists in the form of carbon dioxide, could stem from biological processes taking place under the ice. However, a search for water plumes bursting out of Europa’s surface came up empty, and scientists involved in the observations say that better measurements will be needed to distinguish between biological and geological sources of carbon.

ByDAVID NIELD

(koto_feja/E+/Getty Images)

 

Physicists Discover a New State of Matter Hidden in The Quantum World

PHYSICS24 June 2023

You're familiar with the states of matter we encounter daily – such as solid, liquid, and gas – but in more exotic and extreme conditions, new states can appear, and scientists from the US and China just found one.

They're calling it the chiral bose-liquid state, and as with every new arrangement of particles we discover, it can tell us more about the fabric and the mechanisms of the Universe around us – and in particular, at the super-small quantum scale.

States of matter describe how particles can interact with one another, giving rise to structures and various ways of behaving. Lock atoms in place, and you have a solid. Allow them to flow, you have a liquid or gas. Force charged partnerships apart, you have a plasma.

Cool Copper Collider Most Environmentally Friendly among Higgs Factory Designs Finds study

15 Nov 2023

Cool runnings: an analysis finds that the US-based Cool Copper Collider would, if built, have the lowest overall carbon footprint compared to rival Higgs factory designs. (Courtesy: Emilio Nanni/ SLAC National Accelerator Laboratory)

Changes to the operation of a planned Higgs factory could significantly improve its energy efficiency, but construction will have the biggest impact on the facility’s overall carbon footprint. That is the conclusion of an analysis of the potential environmental impact of the Cool Copper Collider (C3) – a proposed successor to CERN’s Large Hadron Collider (LHC).

 

Electrons accelerated by firing lasers into nanophotonic cavities

25 Oct 2023

Tiny device: photograph of the microchip containing the Friedrich-Alexander University dielectric laser accelerator. A one cent euro coin is shown for comparison. (Image: FAU/Laser Physics, Stefanie Kraus, Julian Litzel)

Laser-driven particle accelerators on silicon chips have been created by two independent research groups. With further improvements, such dielectric laser accelerators could be used in medicine and industry – and could even find application in high-energy particle physics experiments.

 

Organic molecule from trees excels at seeding clouds, CERN study reveals

05 Oct 2023

Cloud expert: Lubna Dada and colleagues have found that sesquiterpenes have the potential to play an important role in cloud formation. (Courtesy: Paul Scherrer Institute/Markus Fischer)

A family of organic compounds released by trees could play a far greater role in cloud formation than previously thought. That is the conclusion of Lubna Dada at Switzerland’s Paul Scherrer Institute and an international team, who say that their insights could play a crucial role in predicting the future of Earth’s climate.

When trees come under stress, they release organic molecules that react with ozone, nitrate radicals and other compounds in the atmosphere. These reactions create tiny solid particles called ultra-low-volatility organic compounds (ULVOCs).

 

The three-qubit computing platform is made from electron spins

28 Oct 2023

Multiple qubit platform: In this diagram, an STM tip coated with iron (top) operates the sensor spin qubit. Also shown are the remote spin qubits, which are aligned by the magnetic fields of nearby iron atoms. (Courtesy: Institute for Basic Science)

A quantum computing platform that is capable of the simultaneous operation of multiple spin-based quantum bits (qubits) has been created by researchers in South Korea. Designed by Yujeong Bae, Soo-Hyon Phark, Andreas Heinrich, and colleagues at the Institute for Basic Science in Seoul, the system is assembled atom-by-atom using a scanning tunneling microscope (STM).

 

NASA’s Mars Sample Return mission slammed by independent review panel

20 Oct 2023

Under fire: the Mars Sample Return mission would bring back Martian samples that had been collected by NASA’s Perseverance Rover (courtesy: NASA/JPL-Caltech)

The future of NASA’s next flagship mission to Mars has been put in doubt following a scathing report from the agency’s Independent Review Board. It concludes that the Mars Sample Return mission, which is set to be launch in 2028, faces a series of technical problems, a runaway budget as well as a dubious launch timetable.

NASA and its collaborator on the project — the European Space Agency – regard the mission as a “critical next step” in plans to explore Mars. Part of that plan involves NASA’s Perseverance Rover, which landed on Mars in 2020. It has already collected a series of Martian samples and deposited them on the surface. They would then be collected by a separate mission – the MSR – and returned to Earth.

 

Aerosol geoengineering will not stop the Antarctic ice sheet from melting, simulations suggest

31 Aug 2023

Running out of time: geoengineering will not prevent the collapse of the West Antarctic Ice Sheet, study suggests. (Courtesy: Shutterstock Bernhard Staehli)

Artificially dimming the Sun by injecting aerosols into Earth’s atmosphere may help to delay a significant consequence of climate change in Antarctica, but not stop it — researchers in Switzerland and the UK have revealed. Through new simulations, a team led by Johannes Sutter at the University of Bern has showed that the collapse of the West Antarctic Ice Sheet (WAIS) can only be avoided if we eliminate global emissions of greenhouse gases as quickly as possible.