Thinking About Time Travel Helps Solve Problems in Physics

Physicists have shown that simulating models of hypothetical time travel can solve experimental problems that appear impossible to solve using standard physics. Credit: Yaroslav Kushta via Getty Images

Time travel. We’ve all thought about it at one time or another, and the subject has been explored extensively in science fiction. Once in a while, it is even the subject of scientific research, typically involving quantum mechanics and how the Universe’s four fundamental forces (electromagnetism, weak and strong nuclear forces, and gravity) fit together. In a recent experiment, researchers at the University of Cambridge showed that by manipulating quantum entanglements, they could simulate what could happen if the flow of time were reversed.

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New Muon g-2 Result Improves the Measurement by a Factor of 2

First results from the Muon g-2 experiment at Fermilab have strengthened evidence of new physics. Credit: Reidar Hahn/Fermilab

At the Fermi National Accelerator Laboratory (aka. Fermilab), an international team of scientists is conducting some of the most sensitive tests of the Standard Model of Particle Physics. The experiment, known as Muon g-2, measures the anomalous magnetic dipole moment of muons, a fundamental particle that is negatively charged (like electrons) but over 200 times as massive. In a recent breakthrough, scientists at Fermilab made the world’s most precise measurement of the muon’s anomalous magnetic moment, improving the precision of their previous measurements by a factor of 2.

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Are We Entering the Era of Quantum Telescopes?

Beyond James Webb and LUVOIR, the future of astronomy could come down to telescopes that rely on quantum mechanics. Credit: Anton Pozdnyakov

For astronomers, one of the greatest challenges is capturing images of objects and phenomena that are difficult to see using optical (or visible light) telescopes. This problem has been largely addressed by interferometry, a technique where multiple telescopes gather signals, which is then combined to create a more complete picture. Examples include the Event Horizon Telescope, which relies on observatories from around the world to capture the first images of the supermassive black hole (SMBH) at the center of the M87 galaxy, and of Sagittarius A* at the center of the Milky Way.

That being said, classic interferometry requires that optical links be maintained between observatories, which imposes limitations and can lead to drastically increased costs. In a recent study, a team of astrophysicists and theoretical physicists proposed how these limitations could be overcome by relying on quantum mechanics. Rather than relying on optical links, they propose how the principle of quantum entanglements could be used to share photons between observatories. This technique is part of a growing field of research that could lead to “quantum telescopes” someday.

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Do Advanced Civilizations use Black Holes as Giant Quantum Computers?

Artist view of an active supermassive black hole. Credit: ESO/L. Calçada

If life is common in our Universe, and we have every reason to suspect it is, why do we not see evidence of it everywhere? This is the essence of the Fermi Paradox, a question that has plagued astronomers and cosmologists almost since the birth of modern astronomy. It is also the reasoning behind the Hart-TIpler Conjecture, one of the many (many!) proposed resolutions, which asserts that if advanced life had emerged in our galaxy sometime in the past, we would see signs of their activity everywhere we looked. Possible indications include self-replicating probes, megastructures, and other Type III-like activity.

On the other hand, several proposed resolutions challenge the notion that advanced life would operate on such massive scales. Others suggest that advanced extraterrestrial civilizations would be engaged in activities and locales that would make them less noticeable. In a recent study, a German-Georgian team of researchers proposed that advanced extraterrestrial civilizations (ETCs) could use black holes as quantum computers. This makes sense from a computing standpoint and offers an explanation for the apparent lack of activity we see when we look at the cosmos.

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Fermilab’s Muon g-2 Experiment Finally Gives Particle Physicists a Hint of What Lies Beyond the Standard Model

The Muon g-2 experiment at the Fermi National Accelerator Laboratory (Fermilab). Credit: Reidar Hahn/Fermilab

Since the long-awaited detection of the Higgs Boson in 2012, particle physicists have been probing deeper into the subatomic realm in the hope of investigating beyond the Standard Model of Particle Physics. In so doing, they hope to confirm the existence of previously unknown particles and the existence of exotic physics, as well as learning more about how the Universe began.

At the Fermi National Accelerator Laboratory (aka. Fermilab), researchers have been conducting the Muon g-2 experiment, which recently announced the results of their first run. Thanks to the unprecedented precision of their instruments, the Fermilab team found that muons in their experiment did not behave in a way that is consistent with the Standard Model, resolving a discrepancy that has existed for decades.

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Quantum Theory Proposes That Cause and Effect Can Go In Loops

Causality is one of those difficult scientific topics that can easily stray into the realm of philosophy.  Science’s relationship with the concept started out simply enough: an event causes another event later in time.  That had been the standard understanding of the scientific community up until quantum mechanics was introduced.  Then, with the introduction of the famous “spooky action at a distance” that is a side effect of the concept of quantum entanglement, scientists began to question that simple interpretation of causality.

Now, researchers at the Université Libre de Bruxelles (ULB) and the University of Oxford have come up with a theory that further challenges that standard view of causality as a linear progress from cause to effect.  In their new theoretical structure, cause and effect can sometimes take place in cycles, with the effect actually causing the cause.

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LIGO Will Squeeze Light To Overcome The Quantum Noise Of Empty Space

The LIGO Hanford Observatory in Washington State. Credit: LIGO Observatory
The LIGO Hanford Observatory in Washington State. Credit: LIGO Observatory

When two black holes merge, they release a tremendous amount of energy. When LIGO detected the first black hole merger in 2015, we found that three solar masses worth of energy was released as gravitational waves. But gravitational waves don’t interact strongly with matter. The effects of gravitational waves are so small that you’d need to be extremely close to a merger to feel them. So how can we possibly observe the gravitational waves of merging black holes across millions of light-years?

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French Scientists Claim to Have Created Metallic Hydrogen

Using two diamonds, scientists squeezed hydrogen to pressures above those in Earth's core. Credit: Sang-Heon Shim, Arizona State University

Scientists have long speculated that at the heart of a gas giant, the laws of material physics undergo some radical changes. In these kinds of extreme pressure environments, hydrogen gas is compressed to the point that it actually becomes a metal. For years, scientists have been looking for a way to create metallic hydrogen synthetically because of the endless applications it would offer.

At present, the only known way to do this is to compress hydrogen atoms using a diamond anvil until they change their state. And after decades of attempts (and 80 years since it was first theorized), a team of French scientists may have finally created metallic hydrogen in a laboratory setting. While there is plenty of skepticism, there are many in scientific community who believe this latest claim could be true.

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Antimatter Behaves Exactly the Same as Regular Matter in Double Slit Experiments

Credit: University of Bern

In 1924, French physicist Louis de Broglie proposed that photons – the subatomic particle that constitutes light – behave as both a particle and a wave. Known as “particle-wave duality”, this property has been tested and shown to apply with other subatomic particles (electrons and neutrons) as well as larger, more complex molecules.

Recently, an experiment conducted by researchers with the QUantum Interferometry and Gravitation with Positrons and LAsers (QUPLAS) collaboration demonstrated that this same property applies to antimatter. This was done using the same kind of interference test (aka. double-slit experiment) that helped scientists to propose particle-wave duality in the first place.

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The Coldest Place in Space Has Been Created. Next Challenge, Coldest Place in the Universe

This series of graphs show the changing density of a cloud of atoms as it is cooled to lower and lower temperatures (going from left to right) approaching absolute zero. Credit: NASA/JPL-Caltech

Despite decades of ongoing research, scientists are trying to understand how the four fundamental forces of the Universe fit together. Whereas quantum mechanics can explain how three of these forces things work together on the smallest of scales (electromagnetism, weak and strong nuclear forces), General Relativity explains how things behaves on the largest of scales (i.e. gravity). In this respect, gravity remains the holdout.

To understand how gravity interacts with matter on the tiniest of scales, scientists have developed some truly cutting-edge experiments. One of these is NASA’s Cold Atom Laboratory (CAL), located aboard the ISS, which recently achieved a milestone by creating clouds of atoms known as Bose-Einstein condensates (BECs). This was the first time that BECs have been created in orbit, and offers new opportunities to probe the laws of physics.

Originally predicted by Satyendra Nath Bose and Albert Einstein 71 years ago, BECs are essentially ultracold atoms that reach temperatures just above absolute zero, the point at which atoms should stop moving entirely (in theory). These particles are long-lived and precisely controlled, which makes them the ideal platform for studying quantum phenomena.

The Cold Atom Laboratory (CAL), which consists of two standardized containers that will be installed on the International Space Station. Credit: NASA/JPL-Caltech/Tyler Winn

This is the purpose of the CAL facility, which is to study ultracold quantum gases in a microgravity environment. The laboratory was installed in the US Science Lab aboard the ISS in late May and is the first of its kind in space. It is designed to advance scientists’ ability to make precision measurements of gravity and study how it interacts with matter at the smallest of scales.

As Robert Thompson, the CAL project scientist and a physicist at NASA’s Jet Propulsion Laboratory, explained in a recent press release:

“Having a BEC experiment operating on the space station is a dream come true. It’s been a long, hard road to get here, but completely worth the struggle, because there’s so much we’re going to be able to do with this facility.”

About two weeks ago, CAL scientists confirmed that the facility had produced BECs from atoms of rubidium – a soft, silvery-white metallic element in the alkali group. According to their report, they had reached temperatures as low as 100 nanoKelvin, one-ten million of one Kelvin above absolute zero (-273 °C; -459 °F). This is roughly 3 K (-270 °C; -454 °F) colder than the average temperature of space.

Because of their unique behavior, BECs are characterized as a fifth state of matter, distinct from gases, liquids, solids and plasma. In BECs, atoms act more like waves than particles on the macroscopic scale, whereas this behavior is usually only observable on the microscopic scale. In addition, the atoms all assume their lowest energy state and take on the same wave identity, making them indistinguishable from one another.

The”physics package” inside the Cold Atom Lab, where ultracold clouds of atoms called Bose-Einstein condensates are produced. Credit: NASA/JPL-Caltech/Tyler Winn

In short, the atom clouds begin to behave like a single “super atom” rather than individual atoms, which makes them easier to study. The first BECs were produced in a lab in 1995 by a science team consisting of Eric Cornell, Carl Wieman and Wolfgang Ketterle, who shared the 2001 Nobel Prize in Physics for their accomplishment. Since that time, hundreds of BEC experiments have been conducted on Earth and some have even been sent into space aboard sounding rockets.

But the CAL facility is unique in that it is the first of its kind on the ISS, where scientists can conduct daily studies over long periods. The facility consists of two standardized containers, which consist of the larger “quad locker” and the smaller “single locker”. The quad locker contains CAL’s physics package, the compartment where CAL will produce clouds of ultra-cold atoms.

This is done by using magnetic fields or focused lasers to create frictionless containers known as “atom traps”. As the atom cloud decompresses inside the atom trap, its temperature naturally drops, getting colder the longer it remains in the trap. On Earth, when these traps are turned off, gravity causes the atoms to begin moving again, which means they can only be studied for fractions of a second.

Aboard the ISS, which is a microgravity environment, BECs can decompress to colder temperatures than with any instrument on Earth and scientists are able to observe individual BECs for five to ten seconds at a time and repeat these measurements for up to six hours per day. And since the facility is controlled remotely from the Earth Orbiting Missions Operation Center at JPL, day-to-day operations require no intervention from astronauts aboard the station.

JPL scientists and members of the Cold Atom Lab’s atomic physics team (left to right) David Aveline, Ethan Elliott and Jason Williams. Credit: NASA/JPL-Caltech

Robert Shotwell, the chief engineer of JPL’s astronomy and physics directorate, has overseen the project since February 2017. As he indicated in a recent NASA press release:

“CAL is an extremely complicated instrument. Typically, BEC experiments involve enough equipment to fill a room and require near-constant monitoring by scientists, whereas CAL is about the size of a small refrigerator and can be operated remotely from Earth. It was a struggle and required significant effort to overcome all the hurdles necessary to produce the sophisticated facility that’s operating on the space station today.”

Looking ahead, the CAL scientists want to go even further and achieve temperatures that are lower than anything achieved on Earth. In addition to rubidium, the CAL team is also working towards making BECSs using two different isotopes of potassium atoms. At the moment, CAL is still in a commissioning phase, which consists of the operations team conducting a long series of tests see how the CAL facility will operate in microgravity.

However, once it is up and running, five science groups – including groups led by Cornell and Ketterle – will conduct experiments at the facility during its first year. The science phase is expected to begin in early September and will last three years. As Kamal Oudrhiri, JPL’s mission manager for CAL, put it:

“There is a globe-spanning team of scientists ready and excited to use this facility. The diverse range of experiments they plan to perform means there are many techniques for manipulating and cooling the atoms that we need to adapt for microgravity, before we turn the instrument over to the principal investigators to begin science operations.”

Given time, the Cold Atom Lab (CAL) may help scientists to understand how gravity works on the tiniest of scales. Combined with high-energy experiments conducted by CERN and other particle physics laboratories around the world, this could eventually lead to a Theory of Everything (ToE) and a complete understanding of how the Universe works.

And be sure to check out this cool video (no pun!) of the CAL facility as well, courtesy of NASA:

Further Reading: NASA