A team of astronomers using the Hubble Space Telescope have found that the current rate of expansion of the Universe could be almost 10 percent faster than previously thought. Image: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)
Just when we think we understand the Universe pretty well, along come some astronomers to upend everything. In this case, something essential to everything we know and see has been turned on its head: the expansion rate of the Universe itself, aka the Hubble Constant.
A team of astronomers using the Hubble telescope has determined that the rate of expansion is between five and nine percent faster than previously measured. The Hubble Constant is not some curiousity that can be shelved until the next advances in measurement. It is part and parcel of the very nature of everything in existence.
“This surprising finding may be an important clue to understanding those mysterious parts of the universe that make up 95 percent of everything and don’t emit light, such as dark energy, dark matter, and dark radiation,” said study leader and Nobel Laureate Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University, both in Baltimore, Maryland.
But before we get into the consequences of this study, let’s back up a bit and look at how the Hubble Constant is measured.
Measuring the expansion rate of the Universe is a tricky business. Using the image at the top, it works like this:
Within the Milky Way, the Hubble telescope is used to measure the distance to Cepheid variables, a type of pulsating star. Parallax is used to do this, and parallax is a basic tool of geometry, which is also used in surveying. Astronomers know what the true brightness of Cepheids are, so comparing that to their apparent brightness from Earth gives an accurate measurement of the distance between the star and us. Their rate of pulsation also fine tunes the distance calculation. Cepheid variables are sometimes called “cosmic yardsticks” for this reason.
Then astronomers turn their sights on other nearby galaxies which contain not only Cepheid variables, but also Type 1a supernova, another well-understood type of star. These supernovae, which are of course exploding stars, are another reliable yardstick for astronomers. The distance to these galaxies is obtained by using the Cepheids to measure the true brightness of the supernovae.
Next, astronomers point the Hubble at galaxies that are even further away. These ones are so distant, that any Cepheids in those galaxies cannot be seen. But Type 1a supernovae are so bright that they can be seen, even at these enormous distances. Then, astronomers compare the true and apparent brightnesses of the supernovae to measure out to the distance where the expansion of the Universe can be seen. The light from the distant supernovae is “red-shifted”, or stretched, by the expansion of space. When the measured distance is compared with the red-shift of the light, it yields a measurement of the rate of the expansion of the Universe.
Take a deep breath and read all that again.
The great part of all of this is that we have an even more accurate measurement of the rate of expansion of the Universe. The uncertainty in the measurement is down to 2.4%. The challenging part is that this rate of expansion of the modern Universe doesn’t jive with the measurement from the early Universe.
The rate of expansion of the early Universe is obtained from the left over radiation from the Big Bang. When that cosmic afterglow is measured by NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and the ESA’s Planck satellite, it yields a smaller rate of expansion. So the two don’t line up. It’s like building a bridge, where construction starts at both ends and should line up by the time you get to the middle. (Caveat: I have no idea if bridges are built like that.)
This Hubble Telescope image shows one of the galaxies used in the study. It contains two types of stars used to measure distances between galaxies. The red circles are pulsing Cepheid variable stars, and the blue X is a Type 1a supernova. Image: NASA, ESA, and A. Riess (STScI/JHU)
“You start at two ends, and you expect to meet in the middle if all of your drawings are right and your measurements are right,” Riess said. “But now the ends are not quite meeting in the middle and we want to know why.”
“If we know the initial amounts of stuff in the universe, such as dark energy and dark matter, and we have the physics correct, then you can go from a measurement at the time shortly after the big bang and use that understanding to predict how fast the universe should be expanding today,” said Riess. “However, if this discrepancy holds up, it appears we may not have the right understanding, and it changes how big the Hubble constant should be today.”
Why it doesn’t all add up is the fun, and maybe maddening, part of this.
What we call Dark Energy is the force that drives the expansion of the Universe. Is Dark Energy growing stronger? Or how about Dark Matter, which comprises most of the mass in the Universe. We know we don’t know much about it. Maybe we know even less than that, and its nature is changing over time.
“We know so little about the dark parts of the universe, it’s important to measure how they push and pull on space over cosmic history,” said Lucas Macri of Texas A&M University in College Station, a key collaborator on the study.
The team is still working with the Hubble to reduce the uncertainty in measurements of the rate of expansion. Instruments like the James Webb Space Telescope and the European Extremely Large Telescope might help to refine the measurement even more, and help address this compelling issue.
The "Canarias Einstein Ring." The green-blue ring is the source galaxy, the red one in the middle is the lens galaxy. The lens galaxy has such strong gravity, that it distorts the light from the source galaxy into a ring. Because the two galaxies are aligned, the source galaxy appears almost circular. Image: This composite image is made up from several images taken with the DECam camera on the Blanco 4m telescope at the Cerro Tololo Observatory in Chile.
A rare object called an Einstein Ring has been discovered by a team in the Stellar Populations group at the Instituto de Astrofísica de Canarias (IAC) in Spain. An Einstein Ring is a specific type of gravitational lensing.
Einstein’s Theory of General Relativity predicted the phenomena of gravitational lensing. Gravitational lensing tells us that instead of travelling in a straight line, light from a source can be bent by a massive object, like a black hole or a galaxy, which itself bends space time.
Einstein’s General Relativity was published in 1915, but a few years before that, in 1912, Einstein predicted the bending of light. Russian physicist Orest Chwolson was the first to mention the ring effect in scientific literature in 1924, which is why the rings are also called Einstein-Chwolson rings.
Gravitational lensing is fairly well-known, and many gravitational lenses have been observed. Einstein rings are rarer, because the observer, source, and lens all have to be aligned. Einstein himself thought that one would never be observed at all. “Of course, there is no hope of observing this phenomenon directly,” Einstein wrote in 1936.
The team behind the recent discovery was led by PhD student Margherita Bettinelli at the University of La Laguna, and Antonio Aparicio and Sebastian Hidalgo of the Stellar Populations group at the Instituto de Astrofísica de Canarias (IAC) in Spain. Because of the rarity of these objects, and the strong scientific interest in them, this one was given a name: The Canarias Einstein Ring.
There are three components to an Einstein Ring. The first is the observer, which in this case means telescopes here on Earth. The second is the lens galaxy, a massive galaxy with enormous gravity. This gravity warps space-time so that not only are objects drawn to it, but light itself is forced to travel along a curved path. The lens lies between Earth and the third component, the source galaxy. The light from the source galaxy is bent into a ring form by the power of the lens galaxy.
When all three components are aligned precisely, which is very rare, the light from the source galaxy is formed into a circle with the lens galaxy right in the centre. The circle won’t be perfect; it will have irregularities that reflect irregularities in the gravitational force of the lens galaxy.
Another Einstein Ring. This one is named LRG 3-757. This one was discovered by the Sloan Digital Sky Survey, but this image was captured by Hubble’s Wide Field Camera 3. Image: NASA/Hubble/ESA
The objects are more than just pretty artifacts of nature. They can tell scientists things about the nature of the lens galaxy. Antonio Aparicio, one of the IAC astrophysicists involved in the research said, “Studying these phenomena gives us especially relevant information about the composition of the source galaxy, and also about the structure of the gravitational field and of the dark matter in the lens galaxy.”
Looking at these objects is like looking back in time, too. The source galaxy is 10 billion light years from Earth. Expansion of the Universe means that the light has taken 8.5 billion light years to reach us. That’s why the ring is blue; that long ago, the source galaxy was young, full of hot blue stars.
The lens itself is much closer to us, but still very distant. It’s 6 billion light years away. Star formation in that galaxy likely came to a halt, and its stellar population is now old.
The discovery of the Canarias Einstein Ring was a happy accident. Bettinelli was pouring over data from what’s known as the Dark Energy Camera (DECam) of the 4m Blanco Telescope at the Cerro Tololo Observatory, in Chile. She was studying the stellar population of the Sculptor dwarf galaxy for her PhD when the Einstein Ring caught her attention. Other members of the Stellar Population Group then used OSIRIS spectrograph on the Gran Telescopio CANARIAS (GTC) to observe and analyze it further.
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
Ever since Lemaitre and Hubble’s first proposed it in the 1920s, scientists and astronomers have been aware that the Universe is expanding. And from these observations, cosmological theories like the Big Bang Theory and the “Arrow of Time” emerged. Whereas the former addresses the origins and evolution of our Universe, the latter argues that the flow of time in one-direction and is linked to the expansion of space.
For many years, scientists have been trying to ascertain why this is. Why does time flow forwards, but not backwards? According to new study produced by a research team from the Yerevan Institute of Physics and Yerevan State University in Armenia, the influence of dark energy may be the reason for the forward-flow of time, which may make one-directional time a permanent feature of our universe.
Today, theories like the Arrow of Time and the expansion of the universe are considered fundamental facts about the Universe. Between measuring time with atomic clocks, observing the red shift of galaxies, and created detailed 3D maps that show the evolution of our Universe over the course of billions of years, one can see how time and the expansion of space are joined at the hip.
Artist’s impression of the influence gravity has on space time. Credit: space.com
The question of why this is the case though is one that has continued to frustrate physicists. Certain fundamental forces, like gravity, are not governed by time. In fact, one could argue without difficulty that Newton’s Laws of Motion and quantum mechanics work the same forwards or backwards. But when it comes to things on the grand scale like the behavior of planets, stars, and entire galaxies, everything seems to come down to the Second Law of Thermodynamics.
This law, which states that the total chaos (aka. entropy) of an isolated system always increases over time, the direction in which time moves is crucial and non-negotiable, has come to be accepted as the basis for the Arrow of Time. In the past, some have ventured that if the Universe began to contract, time itself would begin to flow backwards. However, since the 1990s and the observation that the Universe has been expanding at an accelerating rate, scientists have come to doubt that this.
If, in fact, the Universe is being driven to greater rates of expansion – the predominant explanation is that “Dark Energy” is what is driving it – then the flow of time will never cease being one way. Taking this logic a step further, two Armenian researchers – Armen E. Allahverdyan of the Center for Cosmology and Astrophysics at the Yerevan Institute of Physics and Vahagn G. Gurzadyan of Yerevan State University – argue that dark energy is the reason why time always moves forward.
In their paper, titled “Time Arrow is Influenced by the Dark Energy“, they argue that dark energy accelerating the expansion of the universe supports the asymmetrical nature of time. Often referred to as the “cosmological constant” – referring to Einstein’s original theory about a force which held back gravity to achieve a static universe – dark energy is now seen as a “positive” constant, pushing the Universe forward, rather than holding it back.
Diagram showing the Lambda-CBR universe, from the Big Bang to the the current era. Credit: Alex Mittelmann/Coldcreation
To test their theory, Allahverdyan and Gurzadyan used a large scale scenario involving gravity and mass – a planet with increasing mass orbiting a star. What they found was that if dark energy had a value of 0 (which is what physicists thought before the 1990s), or if gravity were responsible for pulling space together, the planet would simply orbit the star without any indication as to whether it was moving forwards or backwards in time.
But assuming that the value of dark energy is a positive (as all the evidence we’ve seen suggests) then the planet would eventually be thrown clear of the star. Running this scenario forward, the planet is expelled because of its increasing mass; whereas when it is run backwards, the planet closes in on the star and is captured by it’s gravity.
In other words, the presence of dark energy in this scenario was the difference between having an “arrow of time” and not having one. Without dark energy, there is no time, and hence no way to tell the difference between past, present and future, or whether things are running in a forward direction or backwards.
But of course, Allahverdyan and Gurzadyan were also sure to note in their study that this is a limited test and doesn’t answer all of the burning questions. “We also note that the mechanism cannot (and should not) explain all occurrences of the thermodynamic arrow,” they said. “However, note that even when the dark energy (cosmological constant) does not dominate the mean density (early universe or today’s laboratory scale), it still exists.”
Limited or not, this research is representative of some exciting new steps that astrophysicists have been taking of late. This involves not only questioning the origins of dark energy and the expansion force it creates, but also questioning its implication in basic physics. In so doing, researchers may finally be able to answer the age-old question about why time exists, and whether or not it can be manipulated (i.e. time travel!)
A few hundred episodes ago, I answered the question, “What is the Universe Expanding Into?” The gist of the answer is that the Universe as we understand it, isn’t really expanding into anything.
If you go in any one direction long enough, you just return to your starting point. As the Universe expands, that journey takes longer, but there’s still nothing that it’s going into.
Okay, so, I need to put an asterisk on that answer, and then when you read the fine print it’d say something like, “unless we live in a multiverse”.
One of the super interesting and definitely way out there ideas is that our cosmos to actually just one universe in a vast multiverse. Each universe is sort of like a soap bubble embedded in the cosmic void of the multiverse, expanding from its own Big Bang.
Our universe could actually be part of a larger multiverse. Credit: Jim Misti (Misti Mountain Observatory)
And in each one of these universes, the laws of physics are completely different. There are actually a bunch of physical constants in the Universe, like the force of gravity or the binding strength of atoms. For each one of those basic constants, it’s as if the laws of physics randomly rolled the dice, and came up with our Universe – a place that’s almost, but not completely hostile to life.
So imagine all these different bubble universes popping up in this vast cosmic foam of the multiverse, and the laws of physics are different. Maybe in another universe, the force of gravity is repulsive, or green, or spawns unicorns.
In the vast majority of those universes, no life could ever form, but roll the dice an infinite number of times and you’ll eventually get the conditions for life.
Any lifeform capable of perceiving the Universe had to evolve into a universe capable of life.
Of course, this sounds like pseudo scientific mumbo jumbo, and next you’ll expect me to talk about chakras, astrology and channeling the spirit of Big Foot.
However, hang on a second, this might actually be science. If these bubble universes got close enough, there might be a way they could rub together, to interact in ways that were detectable from within the Universe.
In other words, we could look out into space and see a cosmic bruise, and know that’s where our universe is colliding with another one.
Well, have astronomers looked out into space, in search of some sign that our Universe is interacting with other universes? Indeed they have, and they’ve found something really strange.
The cosmic microwave background radiation, enhanced to show the anomalies. Credit: ESA and the Planck Collaboration
When examining the Cosmic Microwave Background Radiation, the afterglow leftover from the Big Bang, astronomers have found a temperature fluctuations. These different temperatures, or anisotropies are regions where different densities of matter in the early Universe were scaled up to enormous scales by the ongoing expansion.
While most of these differences in temperature are explained by the current cosmological theories for the Universe, there’s one region that defies the theories. It’s so strange, the researchers who discovered it hilariously named it the “Axis of Evil” after something some president said.
Anyway, there are lots of ideas for what the Axis of Evil might be. Seriously, every single one of them is more reasonable and more likely than what I’m about to say.
But one really fascinating idea is that we’re seeing a region where our Universe is bumping into another universe, violating each other’s laws of physics.
So if this is the case, and astronomers are witnessing a universal interaction, what does this mean for the poor aliens who might be getting overlapped by the next universe over?
We have no idea, but imagine what might happen as the laws of physics from two completely different universes overlap. What is the average of 7 and green? Or 26 and unicorn dreams? Whatever it is, it can’t be good for the aliens and their continued healthy existence.
But don’t worry, that region is billions of light years away, and it’s probably not another universe anyway, we just need better observations.
We covered this topic in great detail in episode 408 of Astronomy Cast, so if you want hear more from Dr. Pamela Gay, click here and watch the show. You’ll especially enjoy watching me pick up the shattered pieces of my brain as I try to wrap my head around this mind bending concept.
A map of the Cosmic Microwave Background (CMB) as captured by the Wilkinson Microwave Anisotropy Probe. Credit: WMAP team
Something’s up in cosmology that may force us to re-write a few textbooks. It’s all centred around the measurement of the expansion of the Universe, which is, obviously, a pretty key part of our understanding of the cosmos.
The expansion of the Universe is regulated by two things: Dark Energy and Dark Matter. They’re like the yin and yang of the cosmos. One drives expansion, while one puts the brakes on expansion. Dark Energy pushes the universe to continually expand, while Dark Matter provides the gravity that retards that expansion. And up until now, Dark Energy has appeared to be a constant force, never wavering.
How is this known? Well, the Cosmic Microwave Background (CMB) is one way the expansion is measured. The CMB is like an echo from the early days of the Universe. It’s the evidence left behind from the moment about 380,000 years after the Big Bang, when the rate of expansion of the Universe stabilized. The CMB is the source for most of what we know of Dark Energy and Dark Matter. (You can hear the CMB for yourself by turning on a household radio, and tuning into static. A small percentage of that static is from the CMB. It’s like listening to the echo of the Big Bang.)
The CMB has been measured and studied pretty thoroughly, most notably by the ESA’s Planck Observatory, and by the Wilkinson Microwave Anisotropy Probe (WMAP). The Planck, in particular, has given us a snapshot of the early Universe that has allowed cosmologists to predict the expansion of the Universe. But our understanding of the expansion of the Universe doesn’t just come from studying the CMB, but also from the Hubble Constant.
The Hubble Constant is named after Edwin Hubble, an American astronomer who observed that the expansion velocity of galaxies can be confirmed by their redshift. Hubble also observed Cepheid variable stars, a type of standard candle that gives us reliable measurements of distances between galaxies. Combining the two observations, the velocity and the distance, yielded a measurement for the expansion of the Universe.
So we’ve had two ways to measure the expansion of the Universe, and they mostly agree with each other. There’ve been discrepancies between the two of a few percentage points, but that has been within the realm of measurement errors.
But now something’s changed.
In a new paper, Dr. Adam Riess of Johns Hopkins University, and his team, have reported a more stringent measurement of the expansion of the Universe. Riess and his team used the Hubble Space Telescope to observe 18 standard candles in their host galaxies, and have reduced some of the uncertainty inherent in past studies of standard candles.
The result of this more accurate measurement is that the Hubble constant has been refined. And that, in turn, has increased the difference between the two ways the expansion of the Universe is measured. The gap between what the Hubble constant tells us is the rate of expansion, and what the CMB, as measured by the Planck spacecraft, tells us is the rate of expansion, is now 8%. And 8% is too large a discrepancy to be explained away as measurement error.
The fallout from this is that we may need to revise our standard model of cosmology to account for this, somehow. And right now, we can only guess what might need to be changed. There are at least a couple candidates, though.
It might be centred around Dark Matter, and how it behaves. It’s possible that Dark Matter is affected by a force in the Universe that doesn’t act on anything else. Since so little is known about Dark Matter, and the name itself is little more than a placeholder for something we are almost completely ignorant about, that could be it.
Or, it could be something to do with Dark Energy. Its name, too, is really just a placeholder for something we know almost nothing about. Maybe Dark Energy is not constant, as we have thought, but changes over time to become stronger now than in the past. That could account for the discrepancy.
A third possibility is that standard candles are not the reliable indicators of distance that we thought they were. We’ve refined our measurements of standard candles before, maybe we will again.
Where this all leads is open to speculation at this point. The rate of expansion of the Universe has changed before; about 7.5 billion years ago it accelerated. Maybe it’s changing again, right now in our time. Since Dark Energy occupies so-called empty space, maybe more of it is being created as expansion continues. Maybe we’re reaching another tipping or balancing point.
The only thing certain is that it is a mystery. One that we are driven to understand.
We’ve already talked about how you’re living at the center of the Universe. Now, I’m not going to say that the whole Universe revolves around you… but we both know it does. So does this mean that there’s something special about where we live? This is a reasonable line of thinking, and it was how modern science got its start. The first astronomers assumed that the Sun, Moon, planets and stars orbited around the Earth. That the Earth was a very special and unique place, distinct from the rest of the Universe. But as astronomers started puzzling out the nature of the laws of physics, they realized that the Earth wasn’t as special as they thought. In fact, the laws of nature that govern the forces on Earth are the same everywhere in the Universe. As Isaac Newton untangled the laws of gravity here on Earth, he realized it must be the same forces that caused the Moon to go around the Earth, and the planets to go around the Sun. That the light from the Sun is the same phenomenon as the light from other stars.
ESO’s La Silla Observatory in northern Chile. Credit: Iztok Bon?ina / ESO
When astronomers consider the Universe at the largest scales, they assume that it’s homogeneous, and isotropic. Technical words, I know, so here’s what they mean. When astronomers say the Universe is homogeneous, this means that observers in any part of the Universe will see roughly the same view as observers in any other part. There might be local differences, like our mostly harmless planet Earth, orbiting the future course of an interstellar bypass. Or a desert planet with two suns, or a swampy world in the Dagobah system. At the smallest scales, they’ll be different. But as you move to larger and larger scales, it’s all just planets, stars, galaxies, galaxy clusters and black holes. And if you unfocus your eyes, it all looks pretty much the same. Isotropic means that the Universe looks the same in every direction. If you were floating alone in the cosmic void, you could look left, right, up, down out to the edge of the observable Universe and see galaxies, galaxy clusters and eventually the cosmic microwave background radiation in all directions. Every direction looks the same. This is know as the cosmological principle, and it’s one of the foundations of astronomy, because it means that we have a chance at understanding the physical laws of the Universe. If the Universe wasn’t homogeneous and isotropic, then it would mean that the physical laws as we understand them are impossible to comprehend. Just over the cosmological horizon, the force of gravity might act in reverse, the speed of light might be slower than walking speed, and unicorns could be real. That could be true, but we have to assume it’s not. And our current observations, at least to a sphere 13.8 billion light years around us in all directions, confirm this.
The Hubble Telescope’s view of Omega Centauri. Credit: NASA / ESA / The Hubble SM4 ERO Team
While we don’t live in a special place in the Universe, we do live in a special time in the Universe. In the distant future, billions or even trillions of years from now, galaxies will be flying away from us so quickly that their light will never reach us. The cosmic background microwave radiation will be redshifted so far that it’s completely undetectable. Future astronomers will have no idea that there was ever a greater cosmology beyond the Milky Way itself. The evidence of the Big Bang and the ongoing expansion of the Universe will be lost forever. If we didn’t happen to live when we do now, within billions of years of the beginning of the Universe, we’d never know the truth. We can’t feel special about our place in the Universe, it’s probably the same wherever you go. But we can feel special about our time in the Universe. Future astronomers will never understand the cosmology and history of the cosmos the way we do now.
Image from Dark Universe, showing the distribution of dark matter in the universe. Credit: AMNH
The standard model of cosmology tells us that only 4.9% of the Universe is composed of ordinary matter (i.e. that which we can see), while the remainder consists of 26.8% dark matter and 68.3% dark energy. As the names would suggest, we cannot see them, so their existence has had to be inferred based on theoretical models, observations of the large-scale structure of the Universe, and its apparent gravitational effects on visible matter.
Since it was first proposed, there have been no shortages of suggestions as to what Dark Matter particles look like. Not long ago, many scientists proposed that Dark Matter consists of Weakly-Interacting Massive Particles (WIMPs), which are about 100 times the mass of a proton but interact like neutrinos. However, all attempts to find WIMPs using colliders experiments have come up empty. As such, scientists have been exploring the idea lately that dark matter may be composed of something else entirely. Continue reading “Beyond WIMPs: Exploring Alternative Theories Of Dark Matter”
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
How was our Universe created? How did it come to be the seemingly infinite place we know of today? And what will become of it, ages from now? These are the questions that have been puzzling philosophers and scholars since the beginning the time, and led to some pretty wild and interesting theories. Today, the consensus among scientists, astronomers and cosmologists is that the Universe as we know it was created in a massive explosion that not only created the majority of matter, but the physical laws that govern our ever-expanding cosmos. This is known as The Big Bang Theory.
For almost a century, the term has been bandied about by scholars and non-scholars alike. This should come as no surprise, seeing as how it is the most accepted theory of our origins. But what exactly does it mean? How was our Universe conceived in a massive explosion, what proof is there of this, and what does the theory say about the long-term projections for our Universe?
The basics of the Big Bang theory are fairly simple. In short, the Big Bang hypothesis states that all of the current and past matter in the Universe came into existence at the same time, roughly 13.8 billion years ago. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the universe as we know it began.
One of the biggest, most basic questions you can ask is: “why is there something and not nothing?” The reality is that we don’t know the answer, we might never know the answer. Let’s probe to the edge of what we can explain, and what ideas cosmologists have proposed to explain how we all got here.
Democritus, ancient Greek philosopher who is credited with the birth of atomic theory. Credit: phil-fak.uni-duesseldorf.de
As the philosopher Nietzsche famously said “He who would learn to fly one day must first learn to stand and walk and run and climb and dance; one cannot fly into flying.” This is certainly true when it comes to humanity’s understanding of the universe, something which has evolved over many thousands of years and been the subject of ongoing discovery.
And along the way, many names stand out as examples of people who achieved breakthroughs and helped lay the foundations of our modern understanding. One such person is Democritus, an ancient Greek philosopher who is viewed by many as being the “father of modern science”. This is due to his theory of universe that is made up of tiny “atoms”, which bears a striking resemblance to modern atomic theory.
Though he is typically viewed as one of Greece’s many pre-Socratic natural philosopher, many historians have argued that he is more rightly classified as a scientist, at least when compared to his contemporaries. There has also been significant controversy – particularly in Germany during the 19th century – over whether or not Democritus deserves credit for atomic theory.
This argument is based on the relationship Democritus had with contemporary philosopher Leucippus, who is renowned for sharing his theory about atoms with him. However, their theories came down to a different basis, a distinction that allows Democritus to be given credit for a theory that would go on to become a staple of the modern scientific tradition.
Democritus, by Hendrik ter Brugghen – Heraclitus, 1628. Credit: rijksmuseum.nl
Birth and Early Life:
The precise date and location of Democritus birth is the subject the debate. While most sources claim he was born in Abdera, located in the northern Greek province of Thrace, around 460 BCE. However, other sources claim he was born in Miletus, a coastal city of ancient Anatolia and modern-day Turkey, and that he was born in 490 BCE.
It has been said that Democritus’ father was from a noble family and so wealthy that he received the Persian king Xerxes on the latter’s march through Abdera during the Second Persian War (480–479 BC). It is further argued that as a reward for his service, the Persian monarch gave his father and other Abderites gifts, and left several Magi among them. Democritus was apparently instructed by these Magi in astronomy and theology.
After his father had died, Democritus used his inheritance to finance a series of travels to distant countries. Desiring to feed his thirst for knowledge, Democritus traveled extensively across the known world, traveling to Asia, Egypt and (according to some sources) venturing as far as India and Ethiopia. His writings include descriptions of the the cities of Babylon and Meroe (in modern-day Sudan).
Upon returning to his native land, he occupied himself with the study of natural philosophy. He also traveled throughout Greece to acquire a better knowledge of its cultures and learned from many of Greece’s famous philosophers. His wealth allowed him to purchase their writings, and he wrote of them in his own works. In time, he would become one of the most famous of the pre-Socratic philosophers.
The ruins of the ancient Greek city of Abdera, with the west gate shown. Credit: Wikipedia Commons/Marysas
Leucippus of Miletus had the greatest influence on him, becoming his mentor and sharing his theory of atomism with him. Democritus is also said to have known Anaxagoras, Hippocrates and even Socrates himself (though this remains unproven). During his time in Egypt, he learned from Egyptian mathematicians, and is said to have become acquainted with the Chaldean magi in Assyria.
In the tradition of the atomists, Democritus was a thoroughgoing materialists who viewed the world in terms of natural laws and causes. This differentiated him from other Greek philosophers like Plato and Aristotle, for whom philosophy was more teleological in nature – i.e. more concerned with the purpose of events rather than the causes, as well things like essence, the soul, and final causes.
According to the many descriptions and anecdotes about Democritus, he was known for his modesty, simplicity, and commitment to his studies. One story claims he blinded himself on purpose in order to be less distracted by worldly affairs (which is believed to be apocryphal). He was also known for his sense of humor and is commonly referred to as the “Laughing Philosopher” – for his capacity to laugh at human folly. To his fellow citizens, he was also known as “The Mocker”.
Scientific Contributions:
Democritus is renowned for being a pioneer of mathematics and geometry. He was among the first Greek philosophers to observe that a cone or pyramid has one-third the volume of a cylinder or prism with the same base and height. While none of his works on the subject survived the Middle Ages, his mathematical proofs are derived from other works with contain extensive citations to titles like On Numbers, On Geometrics, On Tangencies, On Mapping, and On Irrationals.
Right circular and oblique circular cones. Credit: Dominique Toussaint
Democritus is also known for having spent much of his life experimenting with and examining plants and minerals. Similar to his work in mathematics and geometry, citations from existing works are used to infer the existence of works on the subject. These include On the Nature of Man, the two-volume collection On Flesh, On Mind, On the Senses, On Flavors, On Colors, Causes concerned with Seeds and Plants and Fruits, and to the three-volume collection Causes concerned with Animals.
From his examination of nature, Democritus developed what could be considered some of the first anthropological theories. According to him, human beings lived short lives in archaic times, forced to forage like animals until fear of wild animals then drove them into communities. He theorized that such humans had no language, and only developed it through the need to articulate thoughts and ideas.
Through a process of trial and error, human beings developed not only verbal language, but also symbols with which to communicate (i.e. written language), clothing, fire, the domestication of animals, and agriculture. Each step in this process led to more discoveries, more complex behaviors, and the many things that came to characterize civilized society.
In terms of astronomy and cosmology, Democritus was a proponent of the spherical Earth hypothesis. He believed that in the original chaos from which the universe sprang, the universe was composed of nothing but tiny atoms that came together to form larger units (a theory which bears a striking resemblance to The Big Bang Theory and Nebular Theory). He also believed in the existence of many worlds, which were either in state of growth or decay.
In a similar vein, Democritus advanced a theory of void which challenged the paradoxes raised by his fellow Greek philosophers, Parmenides and Zeno – the founders of metaphysical logic. According to these men, movement cannot exist because such a thing requires there to be a void – which is nothing, and therefore cannot exist. And a void cannot be termed as such if it is in fact a definable, existing thing.
To this, Democritus and other atomists argued that since movement is an observable phenomena, there must be a void. This idea previewed Newton’s theory of absolute space, in which space exists independently of any observer or anything external to it. Einstein’s theory of relativity also provided a resolution to the paradoxes raised by Parmenides and Zeno, where he asserted that space itself is relative and cannot be separated from time.
Democritus’ thoughts on the nature of truth also previewed the development of the modern scientific method. According to Democritus, truth is difficult, because it can only be perceived through senses-impressions which are subjective. Because of this, Aristotle claimed in his Metaphysicsthat Democritus was of the opinion that “either there is no truth or to us at least it is not evident.”
However, as Diogenes Laertius quoted in his 3rd century CE tract, Lives and Opinions of Eminent Philosophers: “By convention hot, by convention cold, but in reality atoms and void, and also in reality we know nothing, since the truth is at bottom.”
Diogenes Laertius, Lives and Opinions of Eminent Philosophers, makes mention of Democritus and his theories. Credit: Public Domain
Ultimately, Democritus’ opinion on truth came down to a distinction between two kinds of knowledge – “legitimate” (or “genuine”) and bastard (or “secret”). The latter is concerned with perception through the senses, which is subjective by nature. This is due to the fact that our sense-perception are influence by the shape and nature of atoms as they flow out from the object in question and make an impression on our senses.
“Legitimate” knowledge, by contrast, is achieved through the intellect, where sense-data is elaborated through reasoning. In this way, one can get from “bastard” impressions to the point where things like connections, patterns and causality can be determined. This is consistent with the inductive reasoning method later elaborated by Renee Descartes, and is a prime example of why Democritus is considered to be an early scientific thinker.
Atomic Theory:
However, Democritus greatest contribution to modern science was arguably the atomic theory he elucidated. According to Democritus’ atomic theory, the universe and all matter obey the following principles:
Everything is composed of “atoms”, which are physically, but not geometrically, indivisible
Between atoms, there lies empty space
Atoms are indestructible
Atoms have always been, and always will be, in motion
There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.
He was not alone in proposing atomic theory, as both his mentor Leucippus and Epicurus are believed to have proposed the earliest views on the shapes and connectivity of atoms. Like Democritus, they believed that the solidity of a material corresponded to the shape of the atoms involved – i.e. iron atoms are hard, water atoms are smooth and slippery, fire atoms are light and sharp, and air atoms are light and whirling.
Democritus’ model of an atom was one of an inert solid that interacted mechanically with other atoms. Credit: .science.edu.sg
However, Democritus is credited with illustrating and popularizing the concept, and for his descriptions of atoms which survived classical antiquity to influence later philosophers. Using analogies from our sense experiences, Democritus gave a picture or an image of an atom that distinguished them from each other by their shape, size, and the arrangement of their parts.
In essence, this model was one of an inert solid that excluded other bodies from its volume, and which interacted with other atoms mechanically. As such, his model included physical links (i.e. hooks and eyes, balls and sockets) that explained how connections occurred between them. While this bears little resemblance to modern atomic theory (where atoms are not inert and interact electromagnetically), it is more closely aligned with that of modern science than any other theory of antiquity.
While there is no clear explanation as to how scholars of classical antiquity came to theorize the existence of atoms, the concept proved to be influential, being picked up by Roman philosopher Lucretius in the 1st century CE and again during the Scientific Revolution. In addition to being indispensable to modern molecular and atomic theory, it also provided an explanation as to why the concept of a void was necessary in nature.
If all matter was composed of tiny, indivisible atoms, then there must also be a great deal of open space between them. This reasoning has also gone on to inform out notions of cosmology and astronomy, where Einstein’s theory of special relativity was able to do away with the concept of a “luminiferous aether” in explaining the behavior of light.
Early atomic theory stated that different materials had differently shaped atoms. Credit: github.com
Diogenes Laertius summarized Democritus atomic theory as follows in Lives and Opinions of Eminent Philosophers:
“That atoms and the vacuum were the beginning of the universe; and that everything else existed only in opinion. That the worlds were infinite, created, and perishable. But that nothing was created out of nothing, and that nothing was destroyed so as to become nothing. That the atoms were infinite both in magnitude and number, and were borne about through the universe in endless revolutions. And that thus they produced all the combinations that exist; fire, water, air, and earth; for that all these things are only combinations of certain atoms; which combinations are incapable of being affected by external circumstances, and are unchangeable by reason of their solidity.”
Death and Legacy:
Democritus died at the age of ninety, which would place his death at around 370 BCE; though some writers disagree, with some claiming he lived to 104 or even 109. According to Marcus Aurelius’ book Meditations, Democritus was eaten by lice or vermin, although in the same passage he writes that “other lice killed Socrates”, implying that this was meant metaphorically. Since Socrates died at the hands of the Athenian government who condemned him, it is possible that Aurelius attributed Democritus death to human folly or politics.
While Democritus was highly esteemed amongst his contemporaries, there were also those who resented him. This included Plato who, according to some accounts, disliked him so much that he wished that all his books would be burned. However, Plato’s pupil Aristotle was familiar with the works of Democritus and mentioned him in both Metaphysics and Physics, where he described him as a “physicist” who did not concern himself with the ideals of form or essence.
Democritus meditating on the seat of the soul, by Léon-Alexandre Delhomme (1868). Credit: Pubic Domain
Ultimately, Democritus is credited as being one of the founders of the modern science because his methods and theories closely resemble those of modern astronomers and physicists. And while his version of the atomic model differs greatly from our modern conceptions, his work was of undoubted value, and was a step in an ongoing process that included such scientists as John Dalton, Neils Bohr and even Albert Einstein.
As always, science is an process of continuing discovery, where new breakthroughs are built upon the foundations of the old and every generations attempts to see a little farther by standing on the shoulders of those who came before.
