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Can’t Use Quantum Entanglement To Communicate Faster Than Light

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Chris Monroe, University of Maryland

One of the most fundamental rules of physics, undisputed since Einstein first laid it out in 1905, is that no information-carrying signal of any type can travel through the Universe faster than the speed of light. Particles, either massive or massless, are required for transmitting information from one location to another, and those particles are mandated to travel either below (for massive) or at (for massless) the speed of light, as governed by the rules of relativity.

Since the development of quantum mechanics, however, many have sought to leverage the power of quantum entanglement to subvert this rule, devising clever schemes to attempt to transmit information to “cheat” relativity and communicate faster-than-light after all. Although it’s an admirable attempt to work around the rules of our Universe, faster-than-light communication is still an impossibility. Here’s the science of why.

Nicu Buculei / flickr

Conceptually, quantum entanglement is a simple idea. You can start by imagining the classical Universe and one of the simplest “random” experiments you could perform: conducting a coin flip. If you and I each have a fair coin and flip it, we’d each expect that there’s a 50/50 chance of each of us getting heads and a 50/50 chance that each of us would get tails. Your results and my results should not only be random, they should be independent and uncorrelated: whether I get heads or tails should still have 50/50 odds irrespective of what you get with your flip.

But if this isn’t a classical system after all, and a quantum one instead, it’s possible that your coin and my coin will be entangled. We might each still have a 50/50 chance of getting heads or tails, but if you flip your coin and measure heads, you’ll instantly be able to statistically predict to better than 50/50 accuracy whether my coin was likely to land on either heads or tails.

Melissa Meister, of laser photons through a beam splitter

How is this possible? In quantum physics, there exists a phenomenon known as quantum entanglement, which is where you create more than one quantum particle — each with their own individual quantum state — where you know something important about the sum of both states together. It’s as though there’s an invisible thread connecting your coin and my coin, and when one of us makes a measurement about the coin we have, we instantly know something about the state of the other coin that goes beyond the familiar classical randomness.

This isn’t mere theoretical work, either. We’ve created pairs of entangled quanta (photons, to be specific) that are then carried away from one another until they’re separated by large distances, then we have two independent measurement apparatuses that tell us what the quantum state of each particle is. We make those measurements as close to simultaneously as possible, and then get together to compare our results.

Richard Gill, 22 December 2013, drawn with R

What we find, perhaps surprisingly, is that your results and my results are correlated! We’ve separated two photons by distances of hundreds of kilometers before making those measurements, and then measuring their quantum states within nanoseconds of one another. If one of those photons has spin +1, the other one’s state can be predicted to about a 75% accuracy, rather than the standard 50%.

Moreover, we can “know” that information instantaneously, rather than waiting for the other measurement apparatus to send us the results of that signal, which would take about a millisecond. It seems, on the surface, that we can know some information about what’s going on at the other end of the entangled experiment not only faster than light, but tens of thousands of times faster than the speed of light could ever transmit information.

Wikimedia Commons user David Koryagin

Does that mean, though, that we can use quantum entanglement to communicate information at faster-than-light speeds?

It might seem so. For example, you might attempt to concoct an experiment as follows:

  • You prepare a large number of entangled quantum particles at one (source) location.
  • You transport one set of the entangled pairs a long distance away (to the destination) while keeping the other set at the source.
  • You have an observer at the destination look for some sort of signal, and force their entangled particles into either the +1 state (for a positive signal) or a -1 state (for a negative signal).
  • Then, you make your measurements of the entangled pairs at the source, and determine with better than 50/50 likelihood what state was chosen by the observer at the destination.

Dr. Tonomura and Belsazar of Wikimedia Commons

This seems like a great setup for enabling faster-than-light communication. All you need is a sufficiently prepared system of entangled quantum particles, an agreed-upon system for what the various signals will mean when you make your measurements, and a pre-determined time at which you’ll make those critical measurements. From even light-years away, you can instantly learn about what was measured at a destination by observing the particles you’ve had with you all along.

Right?

It’s an extremely clever scheme, but one that won’t pay off at all. When you, at the original source, go to make these critical measurements, you’ll discover something extremely disappointing: your results simply show 50/50 odds of being in the +1 or -1 state. It’s as though there’s never been any entanglement at all.

Chad Orzel

Where did our plan fall apart? It was at the step where we had the observer at the destination make an observation and try to encode that information into their quantum state.

When you take that step — forcing one member of an entangled pair of particles into a particular quantum state — you break the entanglement between the two particles. That is to say, the other member of the entangled pair is completely unaffected by this “forcing” action, and its quantum state remains random, as a superposition of +1 and -1 quantum states. But what you’ve done is completely break the correlation between the measurement results. The state you’ve “forced” the destination particle into is now 100% unrelated to the quantum state of the source particle.

Wikimedia Commons user Patrick Edwin Moran

The only way that this problem could be circumvented is if there were some way of making a quantum measurement to force a particular outcome. (Note: this is not something permitted by the laws of physics.)

If you could do this, then someone at the destination could conduct observations — for example, learning whether a planet they were visiting were inhabited or not — and then use some unknown process to:

  • measure their quantum particle’s state,
  • where the outcome will turn out to be +1 if the planet is inhabited,
  • or -1 if the planet is uninhabited,
  • and thereby enable the source observer with the entangled pairs to instantaneously figure out whether this distant planet is inhabited or not.

Unfortunately, the results of a quantum measurement are unavoidably random; you cannot encode a preferred outcome into a quantum measurement.

Maksim / CSTAR of Wikimedia Commons

As quantum physicist Chad Orzel has written, there is a big difference between making a measurement (where the entanglement between pairs is maintained) and forcing a particular result — which itself is a change of state — followed by a measurement (where the entanglement is not maintained). If you want to control, rather than simply measure, the state of a quantum particle, you’ll lose your knowledge of the full state of the combined system as soon as you make that change-of-state operation happen.

Quantum entanglement can only be used to gain information about one component of a quantum system by measuring the other component so long as the entanglement remains intact. What you cannot do is create information at one end of an entangled system and somehow send it over to the other end. If you could somehow make identical copies of your quantum state, faster-than-light communication would be possible after all, but this, too, is forbidden by the laws of physics.

MinutePhysics / YouTube

There’s an awful lot that you can do by leveraging the bizarre physics of quantum entanglement, such as by creating a quantum lock-and-key system that’s virtually unbreakable with purely classical computations. But the fact that you cannot copy or clone a quantum state — as the act of merely reading the state fundamentally changes it — is the nail-in-the-coffin of any workable scheme to achieve faster-than-light communication with quantum entanglement.

There are a lot of subtleties associated with how quantum entanglement actually works in practice, but the key takeaway is this: there is no measurement procedure you can undertake to force a particular outcome while maintaining the entanglement between particles. The result of any quantum measurement is unavoidably random, negating this possibility. As it turns out, God really does play dice with the Universe, and that’s a good thing. No information can be sent faster-than-light, allowing causality to still be maintained for our Universe.

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Las Vegas Aces Rookie Kate Martin Suffers Ankle Injury in Game Against Chicago Sky

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Las Vegas Aces rookie Kate Martin had to be helped off the floor and taken to the locker room after suffering an apparent ankle injury in the first quarter of Tuesday night’s game against the Chicago Sky.

Late in the first quarter, Martin was pushing the ball up the court when she appeared to twist her ankle and lost her balance. The rookie was in serious pain, lying on the floor before eventually being helped off. Her entire team came out in support, and although she managed to put some pressure on the leg, she was taken to the locker room for further evaluation.

Martin returned to the team’s bench late in the second quarter but was ruled out for the remainder of the game.

“Kate Martin is awesome. Kate Martin picks up things so quickly, she’s an amazing sponge,” Aces guard Kelsey Plum said of the rookie during the preseason. “I think (coach) Becky (Hammon) nicknamed her Kate ‘Money’ Martin. I think that’s gonna stick. And when I say ‘money,’ it’s not just about scoring and stuff, she’s just in the right place at the right time. She just makes people better. And that’s what Becky values, that’s what our coaching staff values and that’s why she’s gonna be a great asset to our team.”

Las Vegas selected Martin in the second round of the 2024 WNBA Draft. She was coming off the best season of her collegiate career at Iowa, where she averaged 13.1 points, 6.8 rebounds, and 2.3 assists per game during the 2023-24 campaign. Martin’s integration into the Aces organization has been seamless, with her quickly earning the respect and admiration of her teammates and coaches.

The team and fans alike are hoping for a speedy recovery for Martin, whose contributions have been vital to the Aces’ performance this season.

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Asteroid Apophis will visit Earth in 2029, and this European satellite will be along for the ride

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The European Space Agency is fast-tracking a new mission called Ramses, which will fly to near-Earth asteroid 99942 Apophis and join the space rock in 2029 when it comes very close to our planet — closer even than the region where geosynchronous satellites sit.

Ramses is short for Rapid Apophis Mission for Space Safety and, as its name suggests, is the next phase in humanity’s efforts to learn more about near-Earth asteroids (NEOs) and how we might deflect them should one ever be discovered on a collision course with planet Earth.

In order to launch in time to rendezvous with Apophis in February 2029, scientists at the European Space Agency have been given permission to start planning Ramses even before the multinational space agency officially adopts the mission. The sanctioning and appropriation of funding for the Ramses mission will hopefully take place at ESA’s Ministerial Council meeting (involving representatives from each of ESA’s member states) in November of 2025. To arrive at Apophis in February 2029, launch would have to take place in April 2028, the agency says.

This is a big deal because large asteroids don’t come this close to Earth very often. It is thus scientifically precious that, on April 13, 2029, Apophis will pass within 19,794 miles (31,860 kilometers) of Earth. For comparison, geosynchronous orbit is 22,236 miles (35,786 km) above Earth’s surface. Such close fly-bys by asteroids hundreds of meters across (Apophis is about 1,230 feet, or 375 meters, across) only occur on average once every 5,000 to 10,000 years. Miss this one, and we’ve got a long time to wait for the next.

When Apophis was discovered in 2004, it was for a short time the most dangerous asteroid known, being classified as having the potential to impact with Earth possibly in 2029, 2036, or 2068. Should an asteroid of its size strike Earth, it could gouge out a crater several kilometers across and devastate a country with shock waves, flash heating and earth tremors. If it crashed down in the ocean, it could send a towering tsunami to devastate coastlines in multiple countries.

Over time, as our knowledge of Apophis’ orbit became more refined, however, the risk of impact  greatly went down. Radar observations of the asteroid in March of 2021 reduced the uncertainty in Apophis’ orbit from hundreds of kilometers to just a few kilometers, finally removing any lingering worries about an impact — at least for the next 100 years. (Beyond 100 years, asteroid orbits can become too unpredictable to plot with any accuracy, but there’s currently no suggestion that an impact will occur after 100 years.) So, Earth is expected to be perfectly safe in 2029 when Apophis comes through. Still, scientists want to see how Apophis responds by coming so close to Earth and entering our planet’s gravitational field.

“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surface,” said Patrick Michel, who is the Director of Research at CNRS at Observatoire de la Côte d’Azur in Nice, France, in a statement. “Nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”

The Goldstone radar’s imagery of asteroid 99942 Apophis as it made its closest approach to Earth, in March 2021. (Image credit: NASA/JPL–Caltech/NSF/AUI/GBO)

By arriving at Apophis before the asteroid’s close encounter with Earth, and sticking with it throughout the flyby and beyond, Ramses will be in prime position to conduct before-and-after surveys to see how Apophis reacts to Earth. By looking for disturbances Earth’s gravitational tidal forces trigger on the asteroid’s surface, Ramses will be able to learn about Apophis’ internal structure, density, porosity and composition, all of which are characteristics that we would need to first understand before considering how best to deflect a similar asteroid were one ever found to be on a collision course with our world.

Besides assisting in protecting Earth, learning about Apophis will give scientists further insights into how similar asteroids formed in the early solar system, and, in the process, how  planets (including Earth) formed out of the same material.

One way we already know Earth will affect Apophis is by changing its orbit. Currently, Apophis is categorized as an Aten-type asteroid, which is what we call the class of near-Earth objects that have a shorter orbit around the sun than Earth does. Apophis currently gets as far as 0.92 astronomical units (137.6 million km, or 85.5 million miles) from the sun. However, our planet will give Apophis a gravitational nudge that will enlarge its orbit to 1.1 astronomical units (164.6 million km, or 102 million miles), such that its orbital period becomes longer than Earth’s.

It will then be classed as an Apollo-type asteroid.

Ramses won’t be alone in tracking Apophis. NASA has repurposed their OSIRIS-REx mission, which returned a sample from another near-Earth asteroid, 101955 Bennu, in 2023. However, the spacecraft, renamed OSIRIS-APEX (Apophis Explorer), won’t arrive at the asteroid until April 23, 2029, ten days after the close encounter with Earth. OSIRIS-APEX will initially perform a flyby of Apophis at a distance of about 2,500 miles (4,000 km) from the object, then return in June that year to settle into orbit around Apophis for an 18-month mission.

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Furthermore, the European Space Agency still plans on launching its Hera spacecraft in October 2024 to follow-up on the DART mission to the double asteroid Didymos and Dimorphos. DART impacted the latter in a test of kinetic impactor capabilities for potentially changing a hazardous asteroid’s orbit around our planet. Hera will survey the binary asteroid system and observe the crater made by DART’s sacrifice to gain a better understanding of Dimorphos’ structure and composition post-impact, so that we can place the results in context.

The more near-Earth asteroids like Dimorphos and Apophis that we study, the greater that context becomes. Perhaps, one day, the understanding that we have gained from these missions will indeed save our planet.

 

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McMaster Astronomy grad student takes a star turn in Killarney Provincial Park

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Astronomy PhD candidate Veronika Dornan served as the astronomer in residence at Killarney Provincial Park. She’ll be back again in October when the nights are longer (and bug free). Dornan has delivered dozens of talks and shows at the W.J. McCallion Planetarium and in the community. (Photos by Veronika Dornan)

Veronika Dornan followed up the April 8 total solar eclipse with another awe-inspiring celestial moment.

This time, the astronomy PhD candidate wasn’t cheering alongside thousands of people at McMaster — she was alone with a telescope in the heart of Killarney Provincial Park just before midnight.

Dornan had the park’s telescope pointed at one of the hundreds of globular star clusters that make up the Milky Way. She was seeing light from thousands of stars that had travelled more than 10,000 years to reach the Earth.

This time there was no cheering: All she could say was a quiet “wow”.

Dornan drove five hours north to spend a week at Killarney Park as the astronomer in residence. part of an outreach program run by the park in collaboration with the Allan I. Carswell Observatory at York University.

Dornan applied because the program combines her two favourite things — astronomy and the great outdoors. While she’s a lifelong camper, hiker and canoeist, it was her first trip to Killarney.

Bruce Waters, who’s taught astronomy to the public since 1981 and co-founded Stars over Killarney, warned Dornan that once she went to the park, she wouldn’t want to go anywhere else.

The park lived up to the hype. Everywhere she looked was like a painting, something “a certain Group of Seven had already thought many times over.”

The dome telescopes at Killarney Provincial Park.

She spent her days hiking the Granite Ridge, Crack and Chikanishing trails and kayaking on George Lake.  At night, she went stargazing with campers — or at least tried to. The weather didn’t cooperate most evenings — instead of looking through the park’s two domed telescopes, Dornan improvised and gave talks in the amphitheatre beneath cloudy skies.

Dornan has delivered dozens of talks over the years in McMaster’s W.J. McCallion Planetarium and out in the community, but “it’s a bit more complicated when you’re talking about the stars while at the same time fighting for your life against swarms of bugs.”

When the campers called it a night and the clouds parted, Dornan spent hours observing the stars. “I seriously messed up my sleep schedule.”

She also gave astrophotography a try during her residency, capturing images of the Ring Nebula and the Great Hercules Cluster.

A star cluster image by Veronika Dornan

“People assume astronomers take their own photos. I needed quite a lot of guidance for how to take the images. It took a while to fiddle with the image properties, but I got my images.”

Dornan’s been invited back for another week-long residency in bug-free October, when longer nights offer more opportunities to explore and photograph the final frontier.

She’s aiming to defend her PhD thesis early next summer, then build a career that continues to combine research and outreach.

“Research leads to new discoveries which gives you exciting things to talk about. And if you’re not connecting with the public then what’s the point of doing research?”

 

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