“Nearly 60 percent of all college students today are women. That’s an all-time high… U.S. colleges and universities have lost about 1.5 million students in the past several years. Men accounted for 71 percent of that loss.”
This is a quote from a Freakanomics podcast episode I listened to this week called “What is the future of college—and does it have room for men?”
In the 1950s, men outnumbered women 2:1 in college.
By the 1990s, the ratio was 1:1.
Today the ratio is 4:6 with fewer men than women attending college.
The question on everyone’s mind is why? Why aren’t men going to college anymore?
Scholars, journalists, college presidents and reddit thread philosophers have all come to the table to add their particular offering to the buffet of reasons why fewer boys are going to college.
The Pew Research Center has found that boys are more likely to think they don’t need a degree for the jobs they want, and when they do enroll in college, work opportunities lure them away.
Ruth Simmons, president of A&M University thinks “the problem is the way we treat our boys in k-12. They turn away from school because of the negative messages they get at school… Behavior that is rewarded for boys doesn’t fit well with good student behavior.”
Another college president, Donald Ruff believes it boils down to money. “Honestly I think it’s the sticker shock. To see $100,000 that’s daunting.”
Author Richard Reeves thinks, “The main reason is that girls are outperforming boys in school."
Young men are less likely than young women to attend college in every racial group. Source: AIBM
Other reasons I came across while researching for this article include:
Men can make more money without a college degree than women can, so women need college more.
Higher rates of alcohol, drug use, gangs and prison for boys negate college as a viable option.
Colleges are usually left-leaning, so right-leaning students increasingly don’t feel comfortable there. And more men than women lean right.
Men join the military more than women.
A man will sometimes have to provide for wife/kids before he can finish college.
While many of these reasons address why college is less appealing to boys, almost none of them address what has actually CHANGED in recent decades to cause the drop.
Many people cite the lure of trade schools and blue collar jobs as more appealing to men, but when you consider that blue collar jobs have gone down from 31.2% of total employment in 1970 to 13.6% today- why would men suddenly be more attracted to blue collar work compared to an era when these jobs were more plentiful?
As I listened to the Freakanomics podcast, I was confused why they kept skirting around the thing that has actually changed—
What has changed is an increase in girls.
When you look at other areas where this exact same thing has happened, it is not such a head scratcher why fewer men are going to college.
We’re just not talking about it.
Male Flight
White flight is a term that describes how white people move out of neighborhoods when more people of color move in. White flight is especially common when minority populations become the majority. That neighborhood then declines in value.
Male flight describes a similar phenomenon when large numbers of females enter a profession, group, hobby or industry—the men leave. That industry is then devalued.
Take veterinary school for example:
History of the College - Veterinary Medicine at Illinois
University of Illinois’s College of Veterinary Medicine 1948
In 1969 almost all veterinary students were male at 89%.
By 1987, male enrollment was equal to female at 50%.1
By 2009, male enrollment in veterinary schools had plummeted to 22.4%
A sociologist studying gender in veterinary schools, Dr. Anne Lincoln says that in an attempt to describe this drastic drop in male enrollment, many keep pointing to financial reasons like the debt-to-income ratio or the high cost of schooling.
But Lincoln’s research found that “men and women are equally affected by tuition and salaries.”
Her research shows that the reason fewer men are enrolling in veterinary school boils down to one factor: the number of women in the classroom.
“There was really only one variable where I found an effect, and that was the proportion of women already enrolled in vet med schools… So a young male student says he’s going to visit a school and when he sees a classroom with a lot of women he changes his choice of graduate school. That’s what the findings indicate…. what's really driving feminization of the field is ‘preemptive flight’—men not applying because of women’s increasing enrollment.” - Dr. Anne Lincoln
For every 1% increase in the proportion of women in the student body, 1.7 fewer men applied. One more woman applying was a greater deterrent than $1000 in extra tuition!
Education - Veterinary Medicine at Illinois
Other disciplines that have experienced male flight include:
Biology. While most STEM professions remain male dominated, 10 years ago biology became a 50/50 male/female split. By 2022, 62% of biology majors were women. Biology is now often considered the “easiest” of the STEM majors.
Interior Design. William Morris is considered the father of interior design. After finishing his education at Oxford, he began an architectural design school called “the Firm”— just for men. Many universities had interior design programs. Until women began to enter the design space, at which point it was relegated to a mere “hobby.” Since the influx of women, interior design programs have been pulled from almost all universities.
Teaching. In the 18th century, schooling in colonial America was reserved for the white and the wealthy. Most tutors were men who taught boys. By the middle of the 19th century, girls started becoming students and women became teachers. Consequently, men swiftly left the profession, the pay dropped and teaching was no longer considered a prestigious occupation.
Similar patterns of male flight have occurred in nursing, cheerleading, social work, architecture, gymnastics, library sciences and psychology.
The tipping point
Since males had dominated these professions for centuries, you would think they would leave slowly, hesitantly or maybe linger at 40%, 35%, 30%, but that’s not what happens. Once the tipping point reaches majority female- the men flee. And boy do they flee!
It’s a slippery slope. When the number of women hits 60% the men who are there make a swift exit and other men stop joining.
Morty Schapiro, economist and former president of Northwestern University has noticed this trend when studying college enrollment numbers across universities:
“There’s a cliff you fall off once you become 60/40 female/male. It then becomes exponentially more difficult to recruit men.”
Now we’ve reached that 60% point of no return for colleges.
From aspirational to unimportant: the devaluing of college
As we’ve seen with teachers, nurses and interior design, once an institution is majority female, the public perception of its value plummets.
Scanning through Reddit and Quora threads, many men seem to be in agreement- college is stupid and unnecessary. A waste of time and money. You’re much better off going into the trades, a tech boot camp or becoming an entrepreneur. No need for college.
Compare that sentiment with these quotes about college from years past when more men than women went to college:
“The advantage of education is to better fit a man for life’s work. I would advise young men to take a college course as a rule.” - John D Rockefeller
“The best means of forming a manly, virtuous and happy people will be found in the right education of youth. Without this foundation, every other means, in my opinion, must fail.” - George Washington
“A college degree is the key to realizing the American dream, well worth the financial sacrifice because it is opens the door to a world of opportunity.” - Dan Rather
When mostly men went to college? Prestigious. Aspirational. Important.
Now that mostly women go to college? Unnecessary. De-valued. A bad choice.
Discrimination or Masculinity Norms?
Disturbingly, many men point to women outnumbering men in college enrollment as evidence that feminism is ruining the world and unfairly penalizing men. Discriminating against men.
But men are not structurally or legally prohibited from attending college as women were decades ago. Men are choosing not to go to college.
"Among adults, men are more likely than women to cite factors that reflect personal choices to not attend college or complete their degrees. According to the Pew Research Center, about a third (34%) of men without a bachelor’s degree say a major reason they didn’t finish college is that they just didn’t want to. Only one-in-four women said the same." - Forbes
They just don’t want to. And why don’t they want to?
Chris Bren offers this explanation on Quora:
School is now feminine. College is feminine. And rule #1 if you want to safely navigate this world as a man? Avoid the feminine.
Read why it’s harder to be a man than a woman here.
But we don’t seem to want to talk about that.
Why would we rather look at everything else before looking at traditional masculinity?
Remember that Freakanomics podcast I listened to? Amazingly, astonishingly, against all odds, they managed to talk for 53 minutes and 32 seconds, interview nine experts on the topic and not once- NOT ONCE -mention male flight or masculinity as a reason men aren’t going to college.
I’m almost impressed witnessing the back-bending they did to gymnastics away from the topic of masculinity.
They came so close many times.
They mentioned that there is one subset of men who out-enroll women. Which subset might that be?
Gay men.
While only 36 percent of US adults have bachelor’s degrees, 52% of gay men do.
‘If America's gay men formed their own country, it would be the world's most highly educated by far.’” - Joel Mittleman
At the Joel Mittleman quote in the podcast, I leaned forward…yes… surely now we will wonder why only straight men aren’t attending college… yes?
No. They cartwheeled right back to talking about money.
At one point they mentioned that while male enrollment is down for four year colleges, for two year institutions, the male-to-female ratio has not changed.
But they pretzeled around pointing to masculinity as a reason that the only programs not dropping in male enrollment are those where masculinity is not threatened (HVAC, manufacturing, construction and construction management, welding, etc).
The podcast’s concluding remarks as to why boys aren’t going to college were: “College has become too expensive, too inaccessible and too divorced from its original goals.”
Freakanomics is far from the only one avoiding the topic of masculinity.
Of the 16 articles I read on men not going to college, only two mentioned masculinity or male flight.
Elise Loehnen in her recent article “What’s Happening to Our Boys” noticed this very same omission.
The book “Of Boys and Men: Why the Modern Male is Struggling, Why it Matters and What to do about it” by Richard Reeves has become a go-to resource where men and college attendance is discussed.
Reeves was interviewed on that Freakanomics podcast and is quoted in many of the articles I read. Here is what Loehnen says about what his book leaves out:
“While Reeves presents oodles of data about how many boys are falling behind academically… many men are failing economically, and men are the subject of too many deaths of despair, he skates over the question of why. He lands somewhere in the space of “it’s biology,” and that absent the need to protect and provide…
“He offers some practical solutions like redshirting boys in school for a year and incentivizing men to go into HEAL career trajectories (health, education, administration, literacy), but doesn’t address why boys and men are loathe to pick up this thread in the first place. (Hint: It has to do with a collective aversion toward the ‘feminine.’)” - Elise Loehnen
Loehnen references another book touching on why boys don’t go to college where the author interviews boys and men extensively. Masculinity norms are discussed there. That book is called “Rebels Without a Cause: Reimagining Boys, Ourselves and Our Culture” By Niobe Way.
“According to boys and young men, however, the fault lies entirely with a culture that has gendered and sexualized human capacities, interests, and careers and thus made academic achievement, including going to college, a ‘girlie and gay’ thing. We now think in our modern version of ‘boy’ culture that wanting to follow a career in which one takes care of others or teaches people, are part of a pink-collar economy (i.e., girlie and gay). ‘Be a man and get a real job,’ one that is blue-collar, is the message directed at many young men..” - Niobe Way
Way’s book that cites masculinity norms as a main cause of boys not going to college has five reviews on Amazon, while Reeves’s book that does not touch on masculinity norms, has 1047 reviews and is frequently referenced as the authority on the issue.
It’s frustrating to listen to proposed solutions like “teach boys college is important” or “encourage men to go into HEAL professions” without addressing the reason boys don’t want to go to college or into HEAL professions in the first place.2
Male flight and masculinity norms aren’t the only reasons men aren’t going to college, but they make a sizable contribution.
One we seem loathe to look at.
Until we’re actually able to dig up the root of these issues, we’ll just keep weed whacking the behaviors.
INDIA IPPON DESU
Friday, October 11, 2024
Thursday, October 10, 2024
Wimbledon to replace all human judges
Wimbledon will replace all 300 line judges with artificial intelligence and an electronic system from next year, removing human officials for the first time in the championship's 147-year history.
The All England Club has confirmed all 18 match courts will be installed with automated electronic line calling (ELC).
The system will be the same as the one used at the US Open since 2020, where automated voice calls are played out within a tenth of a second of the ball landing.
As a result of the change, it is expected that Wimbledon's Hawk-Eye challenge system - brought into use in 2007 - where players could review calls made by the line judges will be removed.
In recent years, 300 line judges aged between 18 and 80 have been used at Wimbledon to cover 650 matches over a two-week period.
"The decision to introduce Live Electronic Line Calling at The Championships was made following a significant period of consideration and consultation," said Sally Bolton, chief executive at the All England Lawn Tennis Club.
"Having reviewed the results of the testing undertaken at The Championships this year, we consider the technology to be sufficiently robust and the time is right to take this important step in seeking maximum accuracy in our officiating. For the players, it will offer them the same conditions they have played under at a number of other events on tour
"We take our responsibility to balance tradition and innovation at Wimbledon very seriously. Line umpires have played a central role in our officiating set-up at The Championships for many decades and we recognise their valuable contribution and thank them for their commitment and service."
The French Open, which has relied solely on human officials, is now the outlier, although it may well follow suit, with all ATP Tour events to feature the technology from next year.
'Line judge change inevitable'
"It is sad, it's quite quaint having the line judges there in their regalia at the side of the court and with the calls going on we'd never have had the John McEnroe 'You cannot be serious' if the robots had guarded the line 40 years ago.
"But it is inevitable because what's happening on the tennis tours next year is automatic line calling is coming in as a matter of course, so the robots will be guarding the lines.
"It's been a success in the tournaments this year, it really does work. People thought it wouldn't work as well as it has done but it undoubtedly works so the grand slams can't be left behind.
"It's already in place at the Australian Open and the US Open so the big question was what were Wimbledon going to do. It will be a huge change and it will mean that the battalion of line judges will have to find something else to do for a fortnight which is a shame because for so many of them that has been their dream moment of the year for decades in some cases."
Wimbledon also announce change to final weekend schedule
Wimbledon have also announced they are adjusting the schedule to their final weekend.
For 2025, the men's and women's doubles finals will start at 1pm, followed by the women's and men's singles finals at 4pm on the second Saturday and Sunday respectively.
The singles semi-finals schedules will remain the same, while the slot for the mixed doubles final will also remain as the third match on the second Thursday.
Bolton said: "We have adjusted the provisional schedule for the final weekend of The Championships with the ambition of improving the experience for all involved.
"The doubles players competing in the finals will have increased certainty over their schedule and fans will enjoy each day's play as it builds towards the crescendo of the ladies' and gentlemen's singles finals, with our champions being crowned in front of the largest possible worldwide audience."
The All England Club has confirmed all 18 match courts will be installed with automated electronic line calling (ELC).
The system will be the same as the one used at the US Open since 2020, where automated voice calls are played out within a tenth of a second of the ball landing.
As a result of the change, it is expected that Wimbledon's Hawk-Eye challenge system - brought into use in 2007 - where players could review calls made by the line judges will be removed.
In recent years, 300 line judges aged between 18 and 80 have been used at Wimbledon to cover 650 matches over a two-week period.
"The decision to introduce Live Electronic Line Calling at The Championships was made following a significant period of consideration and consultation," said Sally Bolton, chief executive at the All England Lawn Tennis Club.
"Having reviewed the results of the testing undertaken at The Championships this year, we consider the technology to be sufficiently robust and the time is right to take this important step in seeking maximum accuracy in our officiating. For the players, it will offer them the same conditions they have played under at a number of other events on tour
"We take our responsibility to balance tradition and innovation at Wimbledon very seriously. Line umpires have played a central role in our officiating set-up at The Championships for many decades and we recognise their valuable contribution and thank them for their commitment and service."
The French Open, which has relied solely on human officials, is now the outlier, although it may well follow suit, with all ATP Tour events to feature the technology from next year.
'Line judge change inevitable'
"It is sad, it's quite quaint having the line judges there in their regalia at the side of the court and with the calls going on we'd never have had the John McEnroe 'You cannot be serious' if the robots had guarded the line 40 years ago.
"But it is inevitable because what's happening on the tennis tours next year is automatic line calling is coming in as a matter of course, so the robots will be guarding the lines.
"It's been a success in the tournaments this year, it really does work. People thought it wouldn't work as well as it has done but it undoubtedly works so the grand slams can't be left behind.
"It's already in place at the Australian Open and the US Open so the big question was what were Wimbledon going to do. It will be a huge change and it will mean that the battalion of line judges will have to find something else to do for a fortnight which is a shame because for so many of them that has been their dream moment of the year for decades in some cases."
Wimbledon also announce change to final weekend schedule
Wimbledon have also announced they are adjusting the schedule to their final weekend.
For 2025, the men's and women's doubles finals will start at 1pm, followed by the women's and men's singles finals at 4pm on the second Saturday and Sunday respectively.
The singles semi-finals schedules will remain the same, while the slot for the mixed doubles final will also remain as the third match on the second Thursday.
Bolton said: "We have adjusted the provisional schedule for the final weekend of The Championships with the ambition of improving the experience for all involved.
"The doubles players competing in the finals will have increased certainty over their schedule and fans will enjoy each day's play as it builds towards the crescendo of the ladies' and gentlemen's singles finals, with our champions being crowned in front of the largest possible worldwide audience."
Saturday, October 05, 2024
Thursday, October 03, 2024
Evidence of ‘Negative Time’ Found in Quantum Physics Experiment
Physicists showed that photons can seem to exit a material before entering it, revealing observational evidence of negative time
By Manon Bischoff & Jeanna Bryner
Quantum physicists are familiar with wonky, seemingly nonsensical phenomena: atoms and molecules sometimes act as particles, sometimes as waves; particles can be connected to one another by a “spooky action at a distance,” even over great distances; and quantum objects can detach themselves from their properties like the Cheshire Cat from Alice’s Adventures in Wonderland detaches itself from its grin. Now researchers led by Daniela Angulo of the University of Toronto have revealed another oddball quantum outcome: photons, wave-particles of light, can spend a negative amount of time zipping through a cloud of chilled atoms. In other words, photons can seem to exit a material before entering it.
“It took a positive amount of time, but our experiment observing that photons can make atoms seem to spend a *negative* amount of time in the excited state is up!” wrote Aephraim Steinberg, a physicist at the University of Toronto, in a post on X (formerly Twitter) about the new study, which was uploaded to the preprint server arXiv.org on September 5 and has not yet been peer-reviewed.
The idea for this work emerged in 2017. At the time, Steinberg and a lab colleague, then doctoral student Josiah Sinclair, were interested in the interaction of light and matter, specifically a phenomenon called atomic excitation: when photons pass through a medium and get absorbed, electrons swirling around atoms in that medium jump to higher energy levels. When these excited electrons lapse to their original state, they release that absorbed energy as reemitted photons, introducing a time delay in the light’s observed transit time through the medium.
Sinclair’s team wanted to measure that time delay (which is sometimes technically called a “group delay”) and learn whether it depends on the fate of that photon: Was it scattered and absorbed inside the atomic cloud, or was it transmitted with no interaction whatsoever? “At the time, we weren’t sure what the answer was, and we felt like such a basic question about something so fundamental should be easy to answer,” Sinclair says. “But the more people we talked to, the more we realized that while everyone had their own intuition or guess, there was no expert consensus on what the right answer would be.” Because the nature of these delays can be so strange and counterintuitive, some researchers had written the phenomenon off as effectively meaningless for describing any physical property associated with light.
After three years of planning, his team developed an apparatus to test this question in the lab. Their experiments involved shooting photons through a cloud of ultracold rubidium atoms and measuring the resulting degree of atomic excitation. Two surprises emerged from the experiment: Sometimes photons would pass through unscathed, yet the rubidium atoms would still become excited—and for just as long as if they had absorbed those photons. Stranger still, when photons were absorbed, they would seem to be reemitted almost instantly, well before the rubidium atoms returned to their ground state—as if the photons, on average, were leaving the atoms quicker than expected.
The team then collaborated with Howard Wiseman, a theoretical and quantum physicist at Griffith University in Australia, to devise an explanation. The theoretical framework that emerged showed that the time these transmitted photons spent as an atomic excitation matched perfectly with the expected group delay acquired by the light—even for cases where it seemed as though the photons were reemitted before the atomic excitation had ebbed.
To understand the nonsensical finding, you can think of photons as the fuzzy quantum objects they are, in which any given photon’s absorption and reemission through an atomic excitation is not guaranteed to occur over a certain fixed amount of time; rather, it takes place across a smeared-out, probabilistic range of temporal values. As demonstrated by the team’s experiments, these values can encompass instances when an individual photon’s transit time is instantaneous—or, bizarrely, when it concludes before the atomic excitation has ceased, which gives a negative value.
“I can promise you that we were completely surprised by this prediction,” Sinclair says, referring to the matchup between the group delay and the time that the transmitted photons spent as atomic excitations. “And as soon as we were confident we hadn’t made a mistake, Steinberg and the rest of the team—I had moved on to do a postdoc at [the Massachusetts Institute of Technology] by this point—began planning to do a follow-up experiment to test this crazy prediction of negative dwell time and see if the theory would hold up.”
That follow-up experiment, the one led by Angulo that Steinberg touted on X, can be understood by considering the two ways a photon can be transmitted. In one, the photon wears blinders of sorts and ignores the atom entirely, leaving without even a nod. In the other, it interacts with the atom, boosting it to a higher energy level, before getting reemitted.
“When you see a transmitted photon, you can’t know which of these occurred,” Steinberg says, adding that because photons are quantum particles in the quantum realm, the two outcomes can be in superposition—both things can happen at the same time. “The measuring device ends up in a superposition of measuring zero and measuring some small positive value.” But correspondingly, Steinberg notes, that also means that sometimes “the measuring device ends up in a state that looks not like ‘zero’ plus ‘something positive’ but like ‘zero’ minus ‘something positive,’ resulting in what looks like the wrong sign, a negative value, for this excitation time.”
The measurement results in Angulo and her colleagues’ experiment suggest that the photons moved through the medium faster when they excited the atoms than when the atoms remained in their ground state. (The photons aren’t communicating any information, so the outcome does not contradict the “nothing can travel faster than light” speed limit set by Einstein’s special theory of relativity.)
“A negative time delay may seem paradoxical, but what it means is that if you built a ‘quantum’ clock to measure how much time atoms are spending in the excited state, the clock hand would, under certain circumstances, move backward rather than forward,” Sinclair says. In other words, the time in which the photons were absorbed by atoms is negative.
Even though the phenomenon is astonishing, it has no impact on our understanding of time itself—but it does illustrate once again that the quantum world still has surprises in store.
“[Angulo] and the rest of the team have accomplished something really impressive and produced a beautiful set of measurements. Their results raise interesting questions about the history of photons traveling through absorptive media and necessitate a reinterpretation of the physical meaning of the group delay in optics,” Sinclair says.
A version of this article originally appeared in Spektrum der Wissenschaft and was reproduced with permission.
By Manon Bischoff & Jeanna Bryner
Quantum physicists are familiar with wonky, seemingly nonsensical phenomena: atoms and molecules sometimes act as particles, sometimes as waves; particles can be connected to one another by a “spooky action at a distance,” even over great distances; and quantum objects can detach themselves from their properties like the Cheshire Cat from Alice’s Adventures in Wonderland detaches itself from its grin. Now researchers led by Daniela Angulo of the University of Toronto have revealed another oddball quantum outcome: photons, wave-particles of light, can spend a negative amount of time zipping through a cloud of chilled atoms. In other words, photons can seem to exit a material before entering it.
“It took a positive amount of time, but our experiment observing that photons can make atoms seem to spend a *negative* amount of time in the excited state is up!” wrote Aephraim Steinberg, a physicist at the University of Toronto, in a post on X (formerly Twitter) about the new study, which was uploaded to the preprint server arXiv.org on September 5 and has not yet been peer-reviewed.
The idea for this work emerged in 2017. At the time, Steinberg and a lab colleague, then doctoral student Josiah Sinclair, were interested in the interaction of light and matter, specifically a phenomenon called atomic excitation: when photons pass through a medium and get absorbed, electrons swirling around atoms in that medium jump to higher energy levels. When these excited electrons lapse to their original state, they release that absorbed energy as reemitted photons, introducing a time delay in the light’s observed transit time through the medium.
Sinclair’s team wanted to measure that time delay (which is sometimes technically called a “group delay”) and learn whether it depends on the fate of that photon: Was it scattered and absorbed inside the atomic cloud, or was it transmitted with no interaction whatsoever? “At the time, we weren’t sure what the answer was, and we felt like such a basic question about something so fundamental should be easy to answer,” Sinclair says. “But the more people we talked to, the more we realized that while everyone had their own intuition or guess, there was no expert consensus on what the right answer would be.” Because the nature of these delays can be so strange and counterintuitive, some researchers had written the phenomenon off as effectively meaningless for describing any physical property associated with light.
After three years of planning, his team developed an apparatus to test this question in the lab. Their experiments involved shooting photons through a cloud of ultracold rubidium atoms and measuring the resulting degree of atomic excitation. Two surprises emerged from the experiment: Sometimes photons would pass through unscathed, yet the rubidium atoms would still become excited—and for just as long as if they had absorbed those photons. Stranger still, when photons were absorbed, they would seem to be reemitted almost instantly, well before the rubidium atoms returned to their ground state—as if the photons, on average, were leaving the atoms quicker than expected.
The team then collaborated with Howard Wiseman, a theoretical and quantum physicist at Griffith University in Australia, to devise an explanation. The theoretical framework that emerged showed that the time these transmitted photons spent as an atomic excitation matched perfectly with the expected group delay acquired by the light—even for cases where it seemed as though the photons were reemitted before the atomic excitation had ebbed.
To understand the nonsensical finding, you can think of photons as the fuzzy quantum objects they are, in which any given photon’s absorption and reemission through an atomic excitation is not guaranteed to occur over a certain fixed amount of time; rather, it takes place across a smeared-out, probabilistic range of temporal values. As demonstrated by the team’s experiments, these values can encompass instances when an individual photon’s transit time is instantaneous—or, bizarrely, when it concludes before the atomic excitation has ceased, which gives a negative value.
“I can promise you that we were completely surprised by this prediction,” Sinclair says, referring to the matchup between the group delay and the time that the transmitted photons spent as atomic excitations. “And as soon as we were confident we hadn’t made a mistake, Steinberg and the rest of the team—I had moved on to do a postdoc at [the Massachusetts Institute of Technology] by this point—began planning to do a follow-up experiment to test this crazy prediction of negative dwell time and see if the theory would hold up.”
That follow-up experiment, the one led by Angulo that Steinberg touted on X, can be understood by considering the two ways a photon can be transmitted. In one, the photon wears blinders of sorts and ignores the atom entirely, leaving without even a nod. In the other, it interacts with the atom, boosting it to a higher energy level, before getting reemitted.
“When you see a transmitted photon, you can’t know which of these occurred,” Steinberg says, adding that because photons are quantum particles in the quantum realm, the two outcomes can be in superposition—both things can happen at the same time. “The measuring device ends up in a superposition of measuring zero and measuring some small positive value.” But correspondingly, Steinberg notes, that also means that sometimes “the measuring device ends up in a state that looks not like ‘zero’ plus ‘something positive’ but like ‘zero’ minus ‘something positive,’ resulting in what looks like the wrong sign, a negative value, for this excitation time.”
The measurement results in Angulo and her colleagues’ experiment suggest that the photons moved through the medium faster when they excited the atoms than when the atoms remained in their ground state. (The photons aren’t communicating any information, so the outcome does not contradict the “nothing can travel faster than light” speed limit set by Einstein’s special theory of relativity.)
“A negative time delay may seem paradoxical, but what it means is that if you built a ‘quantum’ clock to measure how much time atoms are spending in the excited state, the clock hand would, under certain circumstances, move backward rather than forward,” Sinclair says. In other words, the time in which the photons were absorbed by atoms is negative.
Even though the phenomenon is astonishing, it has no impact on our understanding of time itself—but it does illustrate once again that the quantum world still has surprises in store.
“[Angulo] and the rest of the team have accomplished something really impressive and produced a beautiful set of measurements. Their results raise interesting questions about the history of photons traveling through absorptive media and necessitate a reinterpretation of the physical meaning of the group delay in optics,” Sinclair says.
A version of this article originally appeared in Spektrum der Wissenschaft and was reproduced with permission.
Wednesday, October 02, 2024
Tuesday, October 01, 2024
Subscribe to:
Posts (Atom)