Ten yttrium atoms with entangled electron spins, as used to first create a time crystal. Although… [+] these atoms have quantum properties that are not wholly independent of one another, they are not in identically cloned quantum states to one another.
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.
Flipping a coin should result in a 50/50 outcome of getting either heads or tails. If two ‘quantum’… [+] coins are entangled, however, measuring the outcome of one of the coins (heads or tails) can provide you with information to do better than random guessing when it comes to the state of the other coin. However, that information can only be transmitted, from one coin to the other, at light speed or slower.
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.
By creating two entangled photons from a pre-existing system and separating them by great distances,… [+] we can ‘teleport’ information about the state of one by measuring the state of the other, even from extraordinarily different locations. Interpretations of quantum physics that demand both locality and realism cannot account for a myriad of observations, but multiple interpretations all appear to be equally good.
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.
The best possible local realist imitation (red) for the quantum correlation of two spins in the… [+] singlet state (blue), insisting on perfect anti-correlation at zero degrees, perfect correlation at 180 degrees. Many other possibilities exist for the classical correlation subject to these side conditions, but all are characterized by sharp peaks (and valleys) at 0, 180, 360 degrees, and none has more extreme values (+/-0.5) at 45, 135, 225, 315 degrees. These values are marked by stars in the graph, and are the values measured in a standard Bell-CHSH type experiment. The quantum and classical predictions can be clearly discerned.
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.
If two particles are entangled, they have complementary wavefunction properties, and measuring one… [+] determines properties of the other. If you create two entangled particles or systems, however, and measure how one decays before the other decays, you should be able to test for whether time-reversal symmetry is conserved or violated.
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.
The wave pattern for electrons passing through a double slit, one-at-a-time. If you measure “which… [+] slit” the electron goes through, you destroy the quantum interference pattern shown here. Regardless of the interpretation, quantum experiments appear to care whether we make certain observations and measurements (or force certain interactions) or not.
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.
Schematic of the third Aspect experiment testing quantum non-locality. Entangled photons from the… [+] source are sent to two fast switches, that direct them to polarizing detectors. The switches change settings very rapidly, effectively changing the detector settings for the experiment while the photons are in flight. Different settings, puzzlingly enough, result in different experimental outcomes.
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.
A quantum eraser experiment setup, where two entangled particles are separated and measured. No… [+] alterations of one particle at its destination affect the outcome of the other. You can combine principles like the quantum eraser with the double-slit experiment and see what happens if you keep or destroy, or look at or don’t look at, the information you create by measuring what occurs at the slits themselves.
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.
Even by taking advantage of quantum entanglement, it should be impossible to do better than random… [+] guessing when it comes to knowing what the dealer’s hand holds.
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.
If you could somehow take a quantum state and make an identical copy of it, it might be possible to… [+] concoct a faster-than-light communication scheme. However, a valid no-cloning theorem was proven back in the 1970s and 1980s by multiple independent parties, as the act of attempting to even measure a quantum state (to know what it is) fundamentally changes the outcome.
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.
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
