What is the true age of the world?
What is the true age of the world?
We do not know the exact age of the universe, but we believe that it is around 13 billion years — give or take a few billion. Astronomers estimate the age of the universe in two ways: (a) by looking for the oldest stars; and (b) by measuring the rate of expansion of the universe and extrapolating back to the Big Bang.
As Old as the Stars
One way astronomers estimate the age of the universe by studying globular clusters. Globular Clusters are a dense collection of roughly a million stars. Since all of the stars in a globular cluster formed at roughly the same time, they can serve as cosmic clocks. This way of estimating the age of the universe is based on our understanding of the life cycles of stars. The life of a star depends upon its mass. High mass stars are much brighter than low mass stars; they rapidly burn through their supply of hydrogen fuel. A star like the Sun has enough fuel in its core to burn at its current brightness for approximately 9 billion years. A star that is twice as massive as the Sun will burn through its fuel supply in only 800 million years. A 10 solar mass star, a star that is 10 times more massive than the Sun, burns nearly a thousand times brighter and has only a 20 million year fuel supply. Conversely, a star that is half as massive as the Sun burns slowly enough for its fuel to last more than 20 billion years. So if a globular cluster is more than 10 million years old, then all of its hydrogen burning stars will be less massive than 10 solar masses. This implies that no individual hydrogen-burning star will be more than 1, 000 times brighter than the Sun. If a globular cluster is more than 2 billion years old, then there will be no hydrogen-burning stars more massive than 2 solar masses.
|Hubble Space Telescope image of the Globular Cluster M15. The zoom-in shown in the upper right shows that the core of the cluster is composed of many, many stars. |
The oldest globular clusters contain only stars less massive than 0.7 solar masses. These low-mass stars are much dimmer than our Sun. This observation suggests that the oldest globular clusters are between 11 and 18 billion years old. The uncertainty in this estimate is due to the difficulty in determining the exact distance to a globular cluster and in our ignorance of some of the details of how stars evolve.
It Started with a Bang. A Big Bang
An alternative approach to estimate is the age of the universe is to measure the «Hubble constant». The Hubble constant (H0) is a measure of the current expansion rate of the universe. Cosmologists use this measurement to extrapolate back to the Big Bang, the explosion which occurred at the start of the known universe. This extrapolation depends upon the current density of the universe and on the composition of the universe.
If the universe is «flat» and composed mostly of ordinary matter, then the age of the universe is 2/(3 H0). If the universe has a very low density of matter, then its extrapolated age is larger, 1/H0. If the theory of General Relativity is modified to include a cosmological constant, then the inferred age can be even larger.
Many astronomers are working hard to measure the Hubble constant using a variety of different techniques. They sometimes refer to their work as trying to determine the «curvature» or «shape» of the universe. As seen in the graphic below, this «shape» tells us about the age of the universe.
Recent determinations of the value of the Hubble Constant are resulting in an ever-narrowing range of values. An international team of scientists led by Dr. Wendy Freedman of Carnegie Observatories in Pasadena, Calif., used the Hubble Space Telescope to look at several kinds of distant objects. Her team determined a Hubble Constant value of 73, which translates to a universe 9 to 11.5 billion years old. A second team of scientists led by Dr. Allan Sandage, also of Carnegie and also using HST, looked at distant exploding stars and determined an H0 value of about 58 — or a universe 11.5 to 14.5 billion years old.
You Can’t Be Older Than Your Mother
If we compare the various age determinations, there is a potential problem. If the astronomers who estimate that 1/H0 is as small as 10 billion years are correct, then the age of the universe would be less than the age of the oldest stars. This contradiction implies that either the Big Bang theory is incorrect or that we need to modify the theory of General Relativity or that we need to change our beliefs about stellar evolution. Most astronomers believe that this crisis will pass as soon as our measurements improve. Although the numbers are still very uncertain, the different data sets are starting to converge at an age for the universe of about 12 to 13 billion years.
UPDATE! Measurements made by NASA’s WMAP spacecraft have shown that the universe is 13.7 billion years old, plus or minus about 130,000 years. They were able to do this by making detailed observations of the fluctuations in the cosmic microwave background and using that information in Einstein’s Theory of General Relativity to ‘run the clock backwards to time equal zero’.
| || Return to the StarChild Main Page || Go to Imagine the Universe! (A site for ages 14 and up.) || |
StarChild Authors: The StarChild Team
StarChild Graphics & Music: Acknowledgments
StarChild Project Leader: Dr. Laura A. Whitlock
Curator: J.D. Myers
Responsible NASA Official: Phil Newman
The Puzzling Gap Between How Old You Are and How Old You Think You Are
There are good reasons you always feel 20 percent younger than your actual age.
February 23, 2023
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T his past Thanksgiving , I asked my mother how old she was in her head. She didn’t pause, didn’t look up, didn’t even ask me to repeat the question, which would have been natural, given that it was both syntactically awkward and a little odd. We were in my brother’s dining room, setting the table. My mother folded another napkin. “Forty-five,” she said.
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Why do so many people have an immediate, intuitive grasp of this highly abstract concept—“subjective age,” it’s called—when randomly presented with it? It’s bizarre, if you think about it. Certainly most of us don’t believe ourselves to be shorter or taller than we actually are. We don’t think of ourselves as having smaller ears or longer noses or curlier hair. Most of us also know where our bodies are in space, what physiologists call “proprioception.”
Yet we seem to have an awfully rough go of locating ourselves in time. A friend, nearing 60, recently told me that whenever he looks in the mirror, he’s not so much unhappy with his appearance as startled by it—“as if there’s been some sort of error” were his exact words. (High-school reunions can have this same confusing effect. You look around at your lined and thickened classmates, wondering how they could have so violently capitulated to age; then you see photographs of yourself from that same event and realize: Oh.) The gulf between how old we are and how old we believe ourselves to be can often be measured in light-years—or at least a goodly number of old-fashioned Earth ones.
Adults over 40 perceive themselves to be, on average, about 20 percent younger than their actual age.
As one might suspect, there are studies that examine this phenomenon. (There’s a study for everything.) As one might also suspect, most of them are pretty unimaginative. Many have their origins in the field of gerontology, designed primarily with an eye toward health outcomes, which means they ask participants how old they feel, which those participants generally take to mean how old do you feel physically, which then leads to the rather unsurprising conclusion that if you feel older, you probably are, in the sense that you’re aging faster.
But “How old do you feel?” is an altogether different question from “How old are you in your head?” The most inspired paper I read about subjective age, from 2006, asked this of its 1,470 participants—in a Danish population (Denmark being the kind of place where studies like these would happen)—and what the two authors discovered is that adults over 40 perceive themselves to be, on average, about 20 percent younger than their actual age. “We ran this thing, and the data were gorgeous,” says David C. Rubin (75 in real life, 60 in his head), one of the paper’s authors and a psychology and neuroscience professor at Duke University. “It was just all these beautiful, smooth curves.”
Why we’re possessed of this urge to subtract is another matter. Rubin and his co-author, Dorthe Berntsen, didn’t make it the focus of this particular paper, and the researchers who do often propose a crude, predictable answer—namely, that lots of people consider aging a catastrophe, which, while true, seems to tell only a fraction of the story. You could just as well make a different case: that viewing yourself as younger is a form of optimism, rather than denialism. It says that you envision many generative years ahead of you, that you will not be written off, that your future is not one long, dreary corridor of locked doors.
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I think of my own numbers, for instance—which, though a slight departure from the Rubin-Berntsen rule, are still within a reasonable range (or so Rubin assures me). I’m 53 in real life but suspended at 36 in my head, and if I stop my brain from doing its usual Tilt-A-Whirl for long enough, I land on the same explanation: At 36, I knew the broad contours of my life, but hadn’t yet filled them in. I was professionally established, but still brimmed with potential. I was paired off with my husband, but not yet lost in the marshes of a long marriage (and, okay, not yet a tiresome fishwife). I was soon to be pregnant, but not yet a mother fretting about eating habits, screen habits, study habits, the brutal folkways of adolescents, the porn merchants of the internet.
I was not yet on the gray turnpike of middle age, in other words.
“I’m 35,” wrote my friend Richard Primus, 53 in real life and a constitutional-law professor at the University of Michigan Law School. “I think it’s because that’s the age I was when my major life questions/statuses reached the resolutions/conditions in which they’ve since remained.” So: kind of like my answer, but more optimistically rendered. He continued: “Medieval Christian theologians asked the intriguing question ‘How old are people in heaven?’ The dominant answer: 33. Partly bc age of Jesus at crucifixion. But I think partly bc it feels like a kind of peak for the combined vigor-maturity index.”
The combined vigor-maturity index: Yes!
Richard was replying to me on Twitter, where I’d tossed out my query to the crowd: “How old are you in your head?” (Turns out I’m not the only one with this impulse; Sari Botton, the founder of Oldster Magazine, regularly publishes questionnaires she has issued to novelists, artists, and activists of a certain age, and this is the second question.) Ian Leslie, the author of Conflicted and two other social-science books (32 in his head, 51 in “boring old reality”), took a similar view to mine and Richard’s, but added an astute and humbling observation: Internally viewing yourself as substantially younger than you are can make for some serious social weirdness.
“30 year olds should be aware that for better or for worse, the 50 year old they’re talking to thinks they’re roughly the same age!” he wrote. “Was at a party over the summer where average was about 28 and I had to make a conscious effort to remember I wasn’t the same—they can tell of course, so it’s asymmetrical.”
Yes. They can tell. I’ve had this unsettling experience, seeing little difference between the 30-something before me and my 50-something self, when suddenly the 30-something will make a comment that betrays just how aware she is of the age gap between us, that this gap seems enormous, that in her eyes I may as well be Dame Judi Dench.
Although many hewed close to the Rubin-Berntsen rule, the replies I got on Twitter were not always about potential. Many carried with them a whiff of unexpected poignancy. Trauma sometimes played a role: One person was stuck at 32, unable to see themselves as any older than a sibling who’d died; another was stuck for a long time at age 12, the year her father joined a cult. (Rubin has written about this phenomenon too—the centrality of certain events to our memories, especially calamitous ones. Sometimes we freeze at the age of our traumas.)
My friend Alan, who is in his 50s, told me he thinks of himself as 38 because he still thinks of his 98-year-old father as 80. The writer Molly Jong-Fast replied that she’s 19 because that’s the age she got sober. One 36-year-old woman told me she thought the pandemic was a time thief—she simply hadn’t accumulated enough new experiences to justify the addition of more chronological years—which made her younger in her head sometimes, as if she were willing back the clock.
When I mentioned to a colleague that I was writing this piece, he told me he was 12 in his head, not because he thinks of himself as a child, but because his inner self has remained unchanged as he’s aged; it’s “the same consciousness as always since I became conscious.” His words instantly brought to mind a line from the opening pages of Milan Kundera’s Immortality: “There is a certain part of all of us that lives outside of time.”
Of course, not everyone I spoke with viewed themselves as younger. There were a few old souls, something I would have once said about myself. I felt 40 at 10, when the gossip and cliquishness of other little girls seemed not just cruel but dull; I felt 40 at 22, when I barely went to bars; I felt 40 at 25, when I started accumulating noncollege friends and realized I was partial to older people’s company. And when I turned 40, I was genuinely relieved, as if I’d finally achieved some kind of cosmic internal-external temporal alignment.
But over time, I rolled backwards. Other people do this too, just starting at a younger age—25—and Rubin has a theory about why this might be. Adolescence and emerging adulthood are times dense with firsts (first kiss, first time having sex, first love, first foray into the world without your parents’ watchful gaze); they are also times when our brains, for a variety of neurodevelopmental reasons, are inclined to feel things more intensely, especially the devil’s buzz of a good, foolhardy risk. The uniqueness and density of these periods have manifested themselves in other areas of Rubin’s research. Years ago, he and other researchers showed that adults have an outsize number of memories from the ages of about 15 to 25. They called this phenomenon “the reminiscence bump.” (This is generally used to explain why we’re so responsive to the music of our adolescence—which in my case means my iPhone is loaded with a lot more Duran Duran songs than any dignified person should admit.)
Rubin and Berntsen made a second intriguing discovery in their work on subjective age: People younger than 25 mainly said they felt older than they are, not younger—which, again, makes sense if you’ve had even a passing acquaintance with a 10-year-old, a teenager, a 21-year-old. They’re eager for more independence and to be taken more seriously; in their head, they’re ready for both, though their prefrontal cortex is basically a bunch of unripe bananas.
In Rubin and Berntsen’s 2006 study, socioeconomic status, gender, and education did not significantly affect their data. One wonders if this has something to do with the fact that they conducted their research in Denmark, a country with substantially less income inequality and racial heterogeneity than our own.
The picture changes when there’s more variety: A 2021 meta-analysis of 294 papers examining subjective-age data from across the globe found that the discrepancy between chronological age and internal age was greatest in the United States, Western Europe, and Australia/Oceania. Asia had a smaller gap. Africa had the smallest, which could be read as an economic sign (poverty might play a role) but also a cultural one: Elders in collectivist societies are accorded more respect and have more extended-family support.
“Could it be that feeling younger is actually dysfunctional and no longer helping you focus on what’s going on? That’s the more complicated question,” says Hans-Werner Wahl (69 in real life, 55 in his head), a co-author of the meta-analysis. “A lower subjective age may be predictive of better health. But there are other populations around the globe for whom it is not necessary to feel younger. And they’re not less healthy.”
If you mentally view yourself as younger—if you believe you have a few pivots left—you still see yourself as useful.
This seems to be the conclusion of Becca Levy, a professor of epidemiology and psychology at the Yale School of Public Health. As a young graduate student, she went to Japan and couldn’t help noticing not just that people lived longer, but that their attitude toward aging was more positive—and her decades of research since have shown a very persuasive connection between the two. In the introduction to her book, Breaking the Age Code, she describes newsstands in Tokyo lined with manga books filled with story lines about older people falling in love. She reports wandering Tokyo on Keiro No Hi, or “Respect for the Aged Day,” and seeing people in their 70s and 80s lifting weights in the park. She talks about music classes filled with 75-year-olds learning how to play electric slide guitar.
At first blush, Levy’s scholarship may seem to quarrel with the literature of subjective age. But maybe it’s a complement. What underpins them both is an enduring sense of agency: If you mentally view yourself as younger—if you believe you have a few pivots left—you still see yourself as useful; if you believe that aging itself is valuable, an added good, then you also see yourself as useful. In a better world, older people would feel more treasured, certainly. But even now, a good many of us seem capable of combining the two ideas, merging acceptance of our age with a sense of hope. When reading over the many Oldster questionnaires, I was struck by how many people said that their present age was their favorite one. A reassuring number of respondents didn’t want to trade their hard-earned wisdom—or humility, or self-acceptance, whatever they had accrued along the way—for some earlier moment.
Recently, I wrote to Margaret Atwood, asking her how old she is in her head. In the few interactions I’ve had with her, she seems quite sanguine about aging. Her reply:
At 53 you worry about being old compared to younger people. At 83 you enjoy the moment, and time travel here and there in the past 8 decades. You don’t fret about seeming old, because hey, you really are old! You and your friends make Old jokes. You have more fun than at 53, in some ways. Wait, you’ll see! 🙂
This article appears in the April 2023 print edition with the headline “The Age in Your Head.” When you buy a book using a link on this page, we receive a commission. Thank you for supporting The Atlantic.
Ageing and health
People worldwide are living longer. Today most people can expect to live into their sixties and beyond. Every country in the world is experiencing growth in both the size and the proportion of older persons in the population.
By 2030, 1 in 6 people in the world will be aged 60 years or over. At this time the share of the population aged 60 years and over will increase from 1 billion in 2020 to 1.4 billion. By 2050, the world’s population of people aged 60 years and older will double (2.1 billion). The number of persons aged 80 years or older is expected to triple between 2020 and 2050 to reach 426 million.
While this shift in distribution of a country’s population towards older ages – known as population ageing – started in high-income countries (for example in Japan 30% of the population is already over 60 years old), it is now low- and middle-income countries that are experiencing the greatest change. By 2050, two-thirds of the world’s population over 60 years will live in low- and middle-income countries.
At the biological level, ageing results from the impact of the accumulation of a wide variety of molecular and cellular damage over time. This leads to a gradual decrease in physical and mental capacity, a growing risk of disease and ultimately death. These changes are neither linear nor consistent, and they are only loosely associated with a person’s age in years. The diversity seen in older age is not random. Beyond biological changes, ageing is often associated with other life transitions such as retirement, relocation to more appropriate housing and the death of friends and partners.
Common health conditions associated with ageing
Common conditions in older age include hearing loss, cataracts and refractive errors, back and neck pain and osteoarthritis, chronic obstructive pulmonary disease, diabetes, depression and dementia. As people age, they are more likely to experience several conditions at the same time.
Older age is also characterized by the emergence of several complex health states commonly called geriatric syndromes. They are often the consequence of multiple underlying factors and include frailty, urinary incontinence, falls, delirium and pressure ulcers.
Factors influencing healthy ageing
A longer life brings with it opportunities, not only for older people and their families, but also for societies as a whole. Additional years provide the chance to pursue new activities such as further education, a new career or a long-neglected passion. Older people also contribute in many ways to their families and communities. Yet the extent of these opportunities and contributions depends heavily on one factor: health.
Evidence suggests that the proportion of life in good health has remained broadly constant, implying that the additional years are in poor health. If people can experience these extra years of life in good health and if they live in a supportive environment, their ability to do the things they value will be little different from that of a younger person. If these added years are dominated by declines in physical and mental capacity, the implications for older people and for society are more negative.
Although some of the variations in older people’s health are genetic, most is due to people’s physical and social environments – including their homes, neighbourhoods, and communities, as well as their personal characteristics – such as their sex, ethnicity, or socioeconomic status. The environments that people live in as children – or even as developing fetuses – combined with their personal characteristics, have long-term effects on how they age.
Physical and social environments can affect health directly or through barriers or incentives that affect opportunities, decisions and health behaviour. Maintaining healthy behaviours throughout life, particularly eating a balanced diet, engaging in regular physical activity and refraining from tobacco use, all contribute to reducing the risk of non-communicable diseases, improving physical and mental capacity and delaying care dependency.
Supportive physical and social environments also enable people to do what is important to them, despite losses in capacity. The availability of safe and accessible public buildings and transport, and places that are easy to walk around, are examples of supportive environments. In developing a public-health response to ageing, it is important not just to consider individual and environmental approaches that ameliorate the losses associated with older age, but also those that may reinforce recovery, adaptation and psychosocial growth.
Challenges in responding to population ageing
There is no typical older person. Some 80-year-olds have physical and mental capacities similar to many 30-year-olds. Other people experience significant declines in capacities at much younger ages. A comprehensive public health response must address this wide range of older people’s experiences and needs.
The diversity seen in older age is not random. A large part arises from people’s physical and social environments and the impact of these environments on their opportunities and health behaviour. The relationship we have with our environments is skewed by personal characteristics such as the family we were born into, our sex and our ethnicity, leading to inequalities in health.
Older people are often assumed to be frail or dependent and a burden to society. Public health professionals, and society as a whole, need to address these and other ageist attitudes, which can lead to discrimination, affect the way policies are developed and the opportunities older people have to experience healthy aging.
Globalization, technological developments (e.g., in transport and communication), urbanization, migration and changing gender norms are influencing the lives of older people in direct and indirect ways. A public health response must take stock of these current and projected trends and frame policies accordingly.
The United Nations (UN) General Assembly declared 2021–2030 the UN Decade of Healthy Ageing and asked WHO to lead the implementation. The UN Decade of Healthy Ageing is a global collaboration bringing together governments, civil society, international agencies, professionals, academia, the media and the private sector for 10 years of concerted, catalytic and collaborative action to foster longer and healthier lives.
The Decade builds on the WHO Global Strategy and Action Plan and the United Nations Madrid International Plan of Action on Ageing and supports the realization of the United Nations Agenda 2030 on Sustainable Development and the Sustainable Development Goals.
The UN Decade of Healthy Ageing (2021–2030) seeks to reduce health inequities and improve the lives of older people, their families and communities through collective action in four areas: changing how we think, feel and act towards age and ageism; developing communities in ways that foster the abilities of older people; delivering person-centred integrated care and primary health services responsive to older people; and providing older people who need it with access to quality long-term care.
- UN Decade of Healthy Ageing (2021-2030)
- Health topic: ageing
- WHO Ageing and Health Unit
- WHO Demographic Change and Healthy Ageing Unit
- Misconceptions on ageing and health
- Q&A — Ageism