"Why does time go forwards, not backwards?" by Martha Henriques for BBC Future

I've been meaning to share this fascinating article from BBC Future for a little while now. I am a bit of armchair physicist so this is really interesting to me. And as we have seen, modern physics also incorporates philosophy and spirituality to varying degrees, areas that I am also interested in.

Why does time go forwards, not backwards?

By Martha Henriques
3rd October 2022

The arrow of time began its journey at the Big Bang, and when the Universe eventually dies there will be no more future and no past. In the meantime, what is it that drives time ever onward?

When Isaac Newton published his famous Principia in 1687, his three elegant laws of motion solved a lot of problems. Without them, we couldn't have landed people on the Moon 282 years later. But these laws brought to physics a new problem, which wasn't fully appreciated until centuries after Newton and still nags at cosmologists today.

The issue is that Newton's laws work about twice as well as we might expect them to. They describe the world we move through every day – the world of people, the hands that move around a clock and even the apocryphal fall of certain apples – but they also account perfectly well for a world in which people walk backwards, clocks tick back afternoon to morning, and fruit soars up from the ground to its tree-branch.

"The interesting feature of Newton's laws, which wasn't appreciated till much later, is that they don't distinguish between the past and the future," says the theoretical physicist and philosopher Sean Carroll, who discusses the nature of time in his latest book The Biggest Ideas in the Universe. "But the directionality to time is its most obvious feature, right? I have photographs of the past, I don't have any photographs of the future."

The problem is not confined to the centuries-old theories of Newton. Virtually all of the cornerstone theories of physics since then have worked just as well going forward in time as they do backwards, says physicist Carlo Rovelli of the Centre for Theoretical Physics in Marseille, France, and the author of books including The Order of Time.

"Starting from Newton, and then Maxwell's theory of electromagnetism, then Einstein's work, and then quantum mechanics, quantum field theory, general relativity, and even quantum gravity – there is no distinction between past and future," Rovelli says. "Which came as a surprise, because the distinction is so evident to all of us. If you make a movie, it's obvious which way is the future and which one is the past."

How does a clear direction of time emerge from these descriptions of the Universe, which all lack their own arrow of time? As Marina Cortês, an astrophysicist at the University of Lisbon, puts it: "There's a lot of implications that start with taking seriously the question, 'Why does time pass?'"

Part of the answer lies at the Big Bang nearly 14 billion years ago. Another insight comes from the opposite extreme, in the Universe's eventual death.

But before embarking on this epic journey back and forth along the timeline of the Universe, it's worth stopping off in 1865, just as the first truly time-directional law of physics came hurtling down the tracks of the Industrial Revolution.

GATHERING STEAM

In the 19th Century, when coal was shovelled into furnaces to generate steam power, scientists and engineers hoping to develop better engines embraced a set of principles that described the relationship between heat, energy and motion. They became known as the laws of thermodynamics.

In Germany, 1865, the physicist Rudolf Clausius stated that heat cannot pass from a cold body to a hot one, if nothing else around them changes. Clausius came up with the concept he called "entropy" to measure this behaviour of heat – another way of saying heat never flows from a cold body to a hot one is to say "entropy only ever increases, never decreases."

As Rovelli stresses in The Order of Time, this is the only basic law of physics that can tell apart the past from the future. A ball can roll down a hill or be kicked back to its summit, but heat can't flow from cold to hot.

To illustrate, Rovelli picks up his pen and drops it from one hand to the other. "The reason this stops in my hand is that it has some energy, and then the energy is turned into heat and it warms up my hand. And the friction stops the bouncing. Otherwise, if there was no heat, this would bounce forever, and I would not distinguish the past from the future."

So far, so straightforward. That is, until you start to consider what heat is on a molecular level. The difference between hot things and cold things is how agitated their molecules are – in a hot steam engine, water molecules are very excited, careening around and colliding into each other rapidly. The very same water molecules are less agitated when they coalesce as condensation on a windowpane.

Here's the problem: when you zoom in to the level of, say, one water molecule colliding and bouncing off another, the arrow of time disappears. If you watched a microscopic video of that collision and then you rewound it, it wouldn’t be obvious which way was forwards and which backwards. At the very smallest scale, the phenomenon that produces heat – collisions of molecules – is time-symmetric.

This means that the arrow of time from past to future only emerges when you take a step back from the microscopic world to the macroscopic – something first appreciated by the Austrian physicist-philosopher Ludwig Boltzmann.

"So the direction of time comes from the fact that we look at big things, we don't look at the details," says Rovelli. "From this step, from the fundamental microscopic vision of the world to the coarse-grained, the approximate description of the macroscopic world – this is where the direction of time comes in.

"It's not that the world is fundamentally oriented in space and time," Rovelli says. It's that when we look around, we see a direction in which medium-sized, everyday things have more entropy – the ripened apple fallen from the tree, the shuffled pack of cards.

While entropy does seem to be inextricably bound up with the arrow of time, it feels a bit surprising – perhaps even disconcerting – that the one law of physics that has a strong directionality of time built into it loses this directionality when you look at very small things.

"What is entropy?" Rovelli says. "Entropy is simply how much we're forgetting about the microphysics, how much we are forgetting about the molecules."

THE BEGINNING AND THE END

If there is an arrow of time, where did it come from in the first place?

"The answer is embedded in the beginning of the Universe," says Carroll. "The answer is because the Big Bang had low entropy. And still, 14 billion years later we are swimming in the aftermath of that tsunami that started near the Big Bang. That's why time has a direction for us."

The extraordinarily low entropy of the Universe at the Big Bang is both an answer and an enormous question. "The thing we understand the least about the nature of time, is why the Big Bang had low entropy, why the early Universe was like that," says Carroll. "And I think honestly, as a working cosmologist, I think that my fellow cosmologists have dropped the ball on this one. They don't really take that problem seriously enough."

Carroll published a paper in 2004 with his colleague Jennifer Chen, in which they aimed to explain why the Universe had such low entropy close to the Big Bang, rather than just assuming or accepting this was the case. "There's plenty of loopholes in the theory, plenty of aspects of it that are not completely baked – but I also think it is by far the best theory on the market," says Carroll. "It doesn't cheat."

Other cosmologists agree that it is indeed time to turn serious thought to this problem of the Universe's low entropy origins. "The likelihood of our current Universe having initial conditions of this kind, and not any other kind, is around one in 10 to the 10 to 124 (1:10^10^124)," says Cortês. (Another way of saying it is that the event had a probability of 0.00…01 – with 10^(10^124) zeroes omitted – a number so large it's awkward to express in conventional maths, Cortês notes.) "I mean I could safely say, this is the largest number in modern physics, outside of philosophy or mathematics."

Simply taking such unlikely low-entropy origins as given is a grand case of "shoving the problem under the rug", Cortês says. "If physicists keep doing this, after a while it's going to be a very big pile under the rug. It's left to us cosmologists to explain why time only moves forward."

Even if we don't yet know why, the Universe's low entropy past is a plausible source of time's arrow. Like most things that have a beginning, the arrow will also have an end. The first person to spot this was, once again, the Austrian physicist Ludwig Boltzmann.

"Boltzmann thought, 'ah, entropy is growing in the Universe and maybe it's going to maximum at some point'," says Rovelli. At that point, heat would be evenly distributed throughout the Universe, no longer flowing from one place to another.

There would be no energy available in a useful form for doing work – in other words, almost nothing interesting would be happening throughout the entire Universe. As astrophysicist Katie Mack describes it, "As that process continues, everything is decaying so much that all that’s left is the waste heat of everything that ever existed in the Universe." This fate is known as the thermal death of the Universe, or heat death.

"Stars will stop burning, nothing will happen anymore. There will be nothing but small thermal fluctuations," says Rovelli. "Suppose this happens – and we don't know for certain if it's going to happen, but suppose it does – should we say that there is no time direction there? Of course there's no time direction, because every phenomenon that happened one way could also go one way or the other. Nothing will distinguish the two directions of time."

This is perhaps the strangest thing about the arrow of time: "It only lasts for a little while," says Carroll.

It's very hard to picture what might happen if the arrow of time eventually vanishes. "When we think we produce heat in our neurons," says Rovelli. "Thinking is a process in which the neuron needs entropy to work. Our sense of time passing is just what entropy does to our brain."

The arrow of time that arises from entropy brings us a long way closer to understanding why time only goes forward. But there may be more arrows of time than this one – in fact there is arguably an entire volley of arrows of time pointing from the past to the future. To understand these, we have to step from physics into philosophy.

HUMAN TIME

The ways that we intuitively understand and experience time shouldn't be taken lightly, says Jenann Ismael, professor of philosophy at Columbia University, New York. If you think about your own experience of time, you may soon be able to recognise several of the psychological arrows that form a core part of human experience. One of these arrows is what Ismael terms "flow".

"If you look out at the world, you don't experience a purely static representation of the instantaneous state of the world," she says, like in a movie made up of a number of static frames every second. "We see directly that the world is changing."

This experience of the flow of time is built into our perception. "Vision isn't like a movie camera at all," says Ismael. "Actually what happens is your brain is collecting information over some temporal period. It's integrating that information so that at any given moment, what you're seeing is a computation that the brain has done. So that you not only see that things are moving, you see how fast they're moving, the direction in which they're moving. So the whole time, your brain is integrating information over temporal intervals and giving you the result. So you see time, in a way."

There's a second feature of time that Ismael distinguishes from flow, which she terms "passage".

The idea of passage is closely bound up with time-oriented experiences such as memory and anticipation. Take the example of a wedding, or any much-anticipated life event. Our experience of these moments has many layers – from the fractious planning stages, to the intensity of the day itself, to recollections that stay with us for years. There is a directionality to these different experiences: the way we anticipate an event in the future is fundamentally different from how we remember it when it's passed.

"All of that is part of what I think of as the experience of passage, this idea that we experience every event as anticipated from the past, experienced in the present, remembered in retrospect," says Ismael. "It's kind of Proustian in its density."

These aspects of the directionality of psychological time – as well as many others, like the sense of openness we have about the future but not the past – could all trace their roots back to the arrow of time born of the Industrial Revolution.

"I think it does all come back to entropy," says Ismael. "I see no reason now to think that the kinds of arrows that are involved in human psychology are anything but ultimately rooted in the entropic arrow. But it's an empirical question. This project to understand human experience in relation to the entropic arrow, I've no reason to think it's going to fail."

That project is what Carroll hopes to do, taking several features of our experience of time and relating them back to entropy. His first target is causality, another element of the arrow of time, as causes happen before their effects.

To say the least, this project is a major undertaking for all physicists and philosophers involved. And still, lurking in the shadows behind all such efforts, there remains that nagging question about why entropy was so low in the earliest Universe.

"I think we understand why we have this sense of flowing," says Rovelli. "We understand why the past seems fixed to us that the future seems open. We understand why there are irreversible phenomena, and we can reduce all that to the second law of thermodynamics, to the rise of entropy.

"It's very much related to the fact that if we trace it back, back, back, to fact that the Universe started very small, in a very peculiar situation. Then somehow, it's falling down from that peculiar situation.

"But of course there's one question open, I mean, why? Why did it start in that particular way?"

Link to original article here:
https://www.bbc.com/future/article/20221003-why-does-time-go-forwards-not-backwards

“Singularity (after Stephen Hawking)” by Marie Howe

http://www.mariehowe.com/
https://www.brainpickings.org/2020/04/23/singularity-marie-howe-animated

Universal Perspective

And now, for some universal perspective...

Proven: Black Holes and Gravitational Waves!

This is fantastic news. Just think: if we could come to an understanding of dark matter, there's no telling what we could accomplish and create.

Gravitational waves from black holes detected
By Pallab Ghosh
Science correspondent, BBC News

Scientists are claiming a stunning discovery in their quest to fully understand gravity.

They have observed the warping of space-time generated by the collision of two black holes more than a billion light-years from Earth.

The international team says the first detection of these gravitational waves will usher in a new era for astronomy.

It is the culmination of decades of searching and could ultimately offer a window on the Big Bang.

Being able to detect gravitational waves enables astronomers finally to probe what they call "dark Universe" - the majority part of the cosmos that is invisible to the light telescopes in use today.

Not only will they be able to investigate black holes and strange objects known as neutron stars (giant suns that have collapsed to the size of cities), they should also be able to "look" much deeper into the Universe - and thus farther back in time. It may even be possible eventually to sense the moment of the Big Bang.


Read the full article here:
http://www.bbc.com/news/science-environment-35524440

Dark Matter: Now Even Stranger Than Before!

Fascinating, important science news from BBC:

Dark matter 'ghosts' through galactic smash-ups
By Jonathan Webb
Science reporter, BBC News

By observing multiple collisions between huge clusters of galaxies, scientists have witnessed dark matter coasting straight through the turmoil.

Dark matter is the mysterious, invisible stuff that makes up 85% of the matter in the cosmos - and these results rule out several theoretical models put forward to explain it.

This is because it barely interacts with anything at all, including the dark matter in the oncoming galaxies.

The work appears in Science magazine.

To conduct their study, astrophysicists looked at 72 smash-ups between galactic clusters, using two space telescopes: visible light was recorded by the Hubble Space Telescope, and X-rays by the Chandra Observatory.

Scouring multiple views of the collisions, the researchers tracked the movement of the three main components of galaxies: stars, clouds of gas, and dark matter.
The violently swirling clouds of gas are hot enough to glow with X-rays, which Chandra detects. And stars can be seen in regular, visible-light images from Hubble.
Dark matter is more difficult to "see" - but not impossible. Although it does not emit or absorb light, it does have gravity, and so it bends the path of light passing nearby. This warps our view of anything on the other side of it, in an effect called "gravitational lensing".

"Looking through dark matter is like looking through a bathroom window," said Dr Richard Massey from Durham University, one of the study's authors. "All the objects that you can see in the distance appear slightly distorted and warped."

Using this distortion allowed Dr Massey, with colleagues from the University of Edinburgh, University College London and Switzerland's Ecole Polytechnique Federale de Lausanne (EPFL), to "map" the dark matter in the clusters as they collided.

Galaxy clusters are vast and contain huge amounts of dark matter, so when they collide - over billions of years - it offers a unique glimpse of how the stuff behaves.
"We like these collisions because it's exactly what we'd do in the lab," Dr Massey told BBC News.

"If you want to figure out what something is made out of, you knock it, or you throw it across the room and see where the bits go."
In this case, the bits went straight through each other.

Unlike the gas clouds, which grind to a turbulent halt, and the stars, which mostly glide past each other, the ubiquitous dark matter passes through everything and emerges unscathed, like a ghost.

"It seems not to interact with anything at all," Dr Massey said.

Earlier observations of the "Bullet Cluster" - a bust-up between two particularly big groups of galaxies, now in its final stages - had already demonstrated dark matter's weird lack of interactions, including with itself.

But this new, major survey was able to deliver much more precision, concluding that there was even less interaction than the previous work allowed for.
"If you bang your head against the wall, the electrostatic force between the molecules in your head and the ones in the wall cause a collision. This is what dark matter doesn't seem to feel," Dr Massey explained.

Dark matter does "feel" gravity; those interactions are the reason we know it is there, and the reason it is bound up in the galactic collisions to begin with. But the lack of almost any other interaction makes it even more mysterious than before.

Link to the original BBC article:
http://www.bbc.com/news/science-environment-32066013

The original article in Science Magazine:
http://www.sciencemag.org/content/347/6229/1462

It Sings

The European Space Agency (ESA) have released audio of the comet upon which us little ol' human beings just landed. And it is not what you would have expected... trilling, gurgling, bubbling...

From the ESA description:
"Rosetta’s Plasma Consortium (RPC) has uncovered a mysterious ‘song’ that Comet 67P/Churyumov-Gerasimenko is singing into space. The comet seems to be emitting a ‘song’ in the form of oscillations in the magnetic field in the comet’s environment. It is being sung at 40-50 millihertz, far below human hearing, which typically picks up sound between 20 Hz and 20 kHz. To make the music audible to the human ear, the frequencies have been increased in this recording. Original data credit: ESA/Rosetta/RPC/RPC-MAG. This sonification of the RPC-Mag data was compiled by German composer Manuel Senfft (www.tagirijus.de). Thumbnail image credit: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0"

http://www.esa.int/ESA

Evolution Really Happened

I am currently watching the new "Cosmos: A Spacetime Odyssey" with astrophysicist Neil de Grasse Tyson on the National Geographic Channel, a follow up to the original "Cosmos: A Personal Voyage" with Carl Sagan. This new version is produced by Seth MacFarlane and Ann Druyan who is Sagan's widow.
Such a worthy show... both of them.

http://channel.nationalgeographic.com/channel/cosmos-a-spacetime-odyssey/
http://www.haydenplanetarium.org/tyson/

Proof of The Big Bang

A huge scientific breakthrough was announced yesterday. The twisting gravity waves from the Big Bang have been detected and seen for the first time! This is being hailed as Nobel worthy and will certainly add to the knowledge base for a Unified Theory of Everything! VERY exciting!


Cosmic inflation: 'Spectacular' discovery hailed
By Jonathan Amos Science correspondent, BBC News

Scientists say they have extraordinary new evidence to support a Big Bang Theory for the origin of the Universe.

Researchers believe they have found the signal left in the sky by the super-rapid expansion of space that must have occurred just fractions of a second after everything came into being.

It takes the form of a distinctive twist in the oldest light detectable with telescopes.

The work will be scrutinised carefully, but already there is talk of a Nobel.

"This is spectacular," commented Prof Marc Kamionkowski, from Johns Hopkins University.

"I've seen the research; the arguments are persuasive, and the scientists involved are among the most careful and conservative people I know," he told BBC News.

The breakthrough was announced by an American team working on a project known as BICEP2.

This has been using a telescope at the South Pole to make detailed observations of a small patch of sky.

The aim has been to try to find a residual marker for "inflation" - the idea that the cosmos experienced an exponential growth spurt in its first trillionth, of a trillionth of a trillionth of a second.

Complete article from BBC News here:
http://www.bbc.com/news/science-environment-26605974
and the BICEP2 findings here:
http://bicepkeck.org/index.html#papers

I See It

The Universal Web

I was very excited to see this story in the news today about how astronomers have, for the first time ever, obtained actual photographic proof of dark matter and have presented their findings in Nature.com, an international weekly journal of science. They have seen, thanks to the intense glow of a quasar, the underlying structure of the universe itself! And that structure is, of course, a web. The photographic evidence looks like neurons in the human brain. We are all part of a web, a net. This could end up explaining a lot, and perhaps proving some ideas that are considered "metaphysical." They even have proof of "dark galaxies!" Th implications are staggering.

Cosmic 'web' seen for first time
By Simon Redfern Reporter, BBC News

The hidden tendrils of dark matter that underlie the visible Universe may have been traced out for the first time.

Cosmology theory predicts that galaxies are embedded in a cosmic web of "stuff", most of which is dark matter.

Astronomers obtained the first direct images of a part of this network, by exploiting the fact that a luminous object called a quasar can act as a natural "cosmic flashlight".

Details of the work appear in the journal Nature.

The quasar illuminates a nearby gas cloud measuring two million light-years across.

And the glowing gas appears to trace out filaments of underlying dark matter.

The quasar, which lies 10 billion light-years away, shines light in just the right direction to reveal the cold gas cloud.

For some years, cosmologists have been running computer simulations of the structure of the universe to build the "standard model of cosmology".

They use the cosmic microwave background, corresponding to observations of the very earliest Universe that can be seen, and recorded by instruments such as the Planck space observatory, as a starting point.

Their calculations suggest that as the Universe grows and forms, matter becomes clustered in filaments and nodes under the force of gravity, like a giant cosmic web.

The new results from the 10-metre Keck telescope in Hawaii, are reported by scientists from the University of California, Santa Cruz and the Max Planck Institute for Astronomy in Heidelberg.

They are the first direct observations of cold gas decorating such cosmic web filaments.

The cosmic web suggested by the standard model is mainly made up of mysterious "dark matter". Invisible in itself, dark matter still exerts gravitational forces on visible light and ordinary matter nearby.

Massive clumps of dark matter bend light that passes close by through a process called gravitational lensing, and this had allowed previous measurements of its distribution.

But it is difficult to use this method to see very distant dark matter, and cold ordinary matter remains tricky to detect as well.

The glowing hydrogen illuminated by the distant quasar in these new observations traces out an underlying filament of dark matter that it is attracted to it by gravity, according to the researchers' analysis.

BBC News/ Science article:
http://www.bbc.co.uk/news/science-environment-25809967

Original article:
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12898.html

Proof Of Dark Matter!

This has been an amazing week for science! A new particle was announced, and now we have proof of dark matter!

Reported by Rachel Bayliss at COSMOS on-line:

LONDON: The fundamental ‘cosmic web’ of dark matter throughout the universe has finally been observed from Earth, confirming theories of how the universe was shaped.

“This result is a resounding confirmation of a key prediction of structure formation in the universe,” said Jörg Dietrich from University Observatory Munich, Germany, and lead author of the study published in Nature today.

“Not only did we for the first time see a dark matter filament directly, we also confirmed that it’s total mass [dark matter plus normal matter] and the amount of hot gas are in agreement with predictions.”

Galaxy clusters Abell 222 and Abell 223 connected by dark matter filament.

Yellow contours and blue shading are indicative of matter density.

Credit: Jörg Dietrich, University of Michigan/University Observatory Munich

DARK MATTER
Large cosmic structures, such as galaxies, exhibit gravitational affects that cannot be justified by the amount of normal matter present in the universe. A principle exists to describe this behavior and is known as the cold-dark-matter model, and it is the foundation of modern cosmology.

Within the model, vast quantities of dark matter, moving much slower than the speed of light (cold), must exist to explain the gravitational affects seen on normal matter.

As the name implies, dark matter cannot be observed in the traditional sense as it does not emit or absorb light at any significant level. However, its presence can be detected.

GRAVITATIONAL LENSING
“The technique we used is gravitational lensing,” said Dietrich. This is where light from, for example, a distant galaxy, is deflected and bent by huge gravitational fields generated by other similarly large objects. “It was widely believed that with current telescopes we would not be able to image dark matter filament with gravitational lensing.”

Dietrich and his team devised a method to boost the lensing signal sufficiently so that the dark matter filament between two clusters of galaxies could be observed with an 8m ground-based telescope.
“The key ingredient that made this result possible, is that we decided to study a very peculiar system of two massive galaxy clusters,” he said. These are called Abell 222 and Abell 223.

“Gravitational lensing is now allowing us to see parts of the universe that were previously invisible,” said astrophysicist Joanna Dunkley, from the University of Oxford, England, who was not involved in the study. “We already have plenty of indirect evidence that galaxy clusters trace a cosmic web of dark matter, but seeing this directly is an important step forward.”

THE COSMIC WEB
She added: “Our standard picture of cosmology tells us that filaments of invisible matter thread through the universe, and this bridge of dark matter connecting two clusters is exactly what we would expect.”

The research confirms that galaxy clusters form at the intersections of these vast filaments of dark matter.

Keen to develop this ground-breaking research further, Dietrich said, “We now want to study the interplay of dark matter density and galaxy population to get a better understanding of the mechanism that transforms galaxies from blue, star-forming spiral galaxies – which are the most common galaxies in filament – to red elliptical galaxies, which are the majority of galaxies in galaxy clusters.”

“The dark matter web makes up about a quarter of the universe,” Dunkley explained. “Being able to measure its morphology should help tell us more about how galaxies and clusters were formed, and may even give us a clue about what the dark matter itself is.” This in itself is a question that has been fascinating scientists for decades.

This research states that the underlying dark matter structure of the universe could comprise over half of all matter in existence. So developing it further is a must if scientists are to understand the elementary nature of the universe.

“We need to observe the lensing signal of more filaments to understand how special the one we found is,” Dietrich said. This will involve both in-depth statistical analysis of thousands of galaxy clusters, and a satellite mission to increase the possibilities of directly observing dark matter filaments.

http://www.cosmosmagazine.com/news/5765/scientists-shine-light-dark-matter

One Step Closer To Infinity

Starry, Starry, Starry Night: Star Count May Triple!

By SETH BORENSTEIN, AP Science Writer Seth Borenstein, Ap Science Writer – Wed Dec 1, 9:32 pm ET

WASHINGTON – The universe may glitter with far more stars than even Carl Sagan imagined when he rhapsodized about billions upon billions. A new study suggests there are a mind-blowing 300 sextillion of them, or three times as many as scientists previously calculated. That is a 3 followed by 23 zeros. Or 3 trillion times 100 billion.

The estimate, contained in a study published online Wednesday in the journal Nature, is based on findings that there are many more red dwarf stars--the most common star in the universe--than once thought.

But the research goes deeper than that. The study by Yale University astronomer Pieter van Dokkum and Harvard astrophysicist Charlie Conroy questions a key assumption that astronomers often use: that most galaxies have the same properties as our Milky Way. And that conclusion is deeply unsettling to astronomers who want a more orderly cosmos.

When scientists previously estimated the total number of stars, they assumed that all galaxies had the same ratio of dwarf stars as the Milky Way, which is spiral-shaped. Much of our understanding of the universe is based on observations made inside our own galaxy and then extrapolated to other galaxies.

But about one-third of the galaxies in the universe are elliptical, not spiral, and van Dokkum found they aren't really made up the same way as ours.

Using the Keck telescope in Hawaii, van Dokkum and a colleague gazed into eight distant, elliptical galaxies and looked at their hard-to-differentiate light signatures. The scientists calculated that elliptical galaxies have more red dwarf stars than predicted. A lot more.

"We're seeing 10 or 20 times more stars than we expected," van Dokkum said.

Generally scientists believe there are 100 billion to a trillion galaxies in the universe. And each galaxy — the Milky Way included — was thought to have 100 billion to a trillion stars. Sagan, the Cornell University scientist and best-selling author who was often impersonated by comedians as saying "billions and billions," usually said there were 100 billion galaxies, each with 100 billion stars.

Van Dokkum's work takes these numbers and adjusts them. That's because some of those galaxies — the elliptical ones, which account for about a third of all galaxies — have as many as 1 trillion to 10 trillion stars, not a measly 100 billion. When van Dokkum and Conroy crunched the incredibly big numbers, they found that it tripled the estimate of stars in the universe from 100 sextillion to 300 sextillion.

That's a huge number to grasp, even for astronomers who are used to dealing in light years and trillions, Conroy said.

"It's fun because it gets you thinking about these large numbers," Conroy said. Conroy looked up how many cells are in the average human body — 50 trillion or so — and multiplied that by the 6 billion people on Earth. And he came up with about 300 sextillion.

So the number of stars in the universe "is equal to all the cells in the humans on Earth — a kind of funny coincidence," Conroy said.

For the past month, astronomers have been buzzing about van Dokkum's findings, and many aren't too happy about them, said astronomer Richard Ellis of the California Institute of Technology.