Artist Mark Rademaker's concept for the IXS Enterprise, a theoretical interstellar spacecraft. Credit: Mark Rademaker/flickr.com
Forty years ago, Canadian physicist Bill Unruh made a surprising prediction regarding quantum field theory. Known as the Unruh effect, his theory predicted that an accelerating observer would be bathed in blackbody radiation, whereas an inertial observer would be exposed to none. What better way to mark the 40th anniversary of this theory than to consider how it could affect human beings attempting relativistic space travel?
Such was the intent behind a new study by a team of researchers from Sao Paulo, Brazil. In essence, they consider how the Unruh effect could be confirmed using a simple experiment that relies on existing technology. Not only would this experiment prove once and for all if the Unruh effect is real, it could also help us plan for the day when interstellar travel becomes a reality.
To put it in layman’s terms, Einstein’s Theory of Relativity states that time and space are dependent upon the inertial reference frame of the observer. Consistent with this is the theory that if an observer is traveling at a constant speed through empty vacuum, they will find that the temperature of said vacuum is absolute zero. But if they were to begin to accelerate, the temperature of the empty space would become hotter.
According to the theory of the Unruh effect, accelerating particles are subject to increased radiation. Credit: NASA/Sonoma State University/Aurore Simonnet
This is what William Unruh – a theorist from the University of British Columbia (UBC), Vancouver – asserted in 1976. According to his theory, an observer accelerating through space would be subject to a “thermal bath” – i.e. photons and other particles – which would intensify the more they accelerated. Unfortunately, no one has ever been able to measure this effect, since no spacecraft exists that can achieve the kind of speeds necessary.
For the sake of their study – which was recently published in the journal Physical Review Letters under the title “Virtual observation of the Unruh effect” – the research team proposed a simple experiment to test for the Unruh effect. Led by Gabriel Cozzella of the Institute of Theoretical Physics (IFT) at Sao Paulo State University, they claim that this experiment would settle the issue by measuring an already-understood electromagnetic phenomenon.
Essentially, they argue that it would be possible to detect the Unruh effect by measuring what is known as Larmor radiation. This refers to the electromagnetic energy that is radiated away from charged particles (such as electrons, protons or ions) when they accelerate. As they state in their study:
“A more promising strategy consists of seeking for fingerprints of the Unruh effect in the radiation emitted by accelerated charges. Accelerated charges should back react due to radiation emission, quivering accordingly. Such a quivering would be naturally interpreted by Rindler observers as a consequence of the charge interaction with the photons of the Unruh thermal bath.”
Diagram of the experiment to test the Unruh effect, where electrons are injected into a magnetic field and subjected to lateral and vertical pulls. Credit: Cozzella, Gabriel (et al.)
As they describe in their paper, this would consist of monitoring the light emitted by electrons within two separate reference frames. In the first, known as the “accelerating frame”, electrons are fired laterally across a magnetic field, which would cause the electrons to move in a circular pattern. In the second, the “laboratory frame”, a vertical field is applied to accelerate the electrons upwards, causing them to follow a corkscrew-like path.
In the accelerating frame, Cozzella and his colleagues assume that the electrons would encounter the “fog of photons”, where they both radiate and emit them. In the laboratory frame, the electrons would heat up once vertical acceleration was applied, causing them to show an excess of long-wavelength photons. However, this would be dependent on the “fog” existing in the accelerated frame to begin with.
In short, this experiment offers a simple test which could determine whether or not the Unruh effect exists, which is something that has been in dispute ever since it was proposed. One of the beauties of the proposed experiment is that it could be conducted using particle accelerators and electromagnets that are currently available.
On the other side of the debate are those who claim that the Unruh effect is due to a mathematical error made by Unruh and his colleagues. For those individuals, this experiment is useful because it would effectively debunk this theory. Regardless, Cozzella and his team are confident their proposed experiment will yield positive results.
Project Starshot, an initiative sponsored by the Breakthrough Foundation, is intended to be humanity’s first interstellar voyage. Credit: breakthroughinitiatives.org
“We have proposed a simple experiment where the presence of the Unruh thermal bath is codified in the Larmor radiation emitted from an accelerated charge,” they state. “Then, we carried out a straightforward classical-electrodynamics calculation (checked by a quantum-field-theory one) to confirm it by ourselves. Unless one challenges classical electrodynamics, our results must be virtually considered as an observation of the Unruh effect.”
If the experiments should prove successful, and the Unruh effect is proven to exist, it would certainly have consequences for any future deep-space missions that rely on advanced propulsion systems. Between Project Starshot, and any proposed mission that would involve sending a crew to another star system, the added effects of a “fog of photons” and a “thermal bath” will need to be factored in.
William Blake's Newton (1795), depicted as a divine geometer. Credit: William Blake Archive/Wikipedia
Four fundamental forces govern all interactions within the Universe. They are weak nuclear forces, strong nuclear forces, electromagnetism, and gravity. Of these, gravity is perhaps the most mysterious. While it has been understood for some time how this law of physics operates on the macro-scale – governing our Solar System, galaxies, and superclusters – how it interacts with the three other fundamental forces remains a mystery.
Naturally, human beings have had a basic understanding of this force since time immemorial. And when it comes to our modern understanding of gravity, credit is owed to one man who deciphered its properties and how it governs all things great and small – Sir Isaac Newton. Thanks to this 17th century English physicist and mathematician, our understanding of the Universe and the laws that govern it would forever be changed.
While we are all familiar with the iconic image of a man sitting beneath an apple tree and having one fall on his head, Newton’s theories on gravity also represented a culmination of years worth of research, which in turn was based on centuries of accumulated knowledge. He would present these theories in his magnum opus, Philosophiae Naturalis Principia Mathematica (“Mathematical Principles of Natural Philosophy”), which was first published in 1687.
In this volume, Newton laid out what would come to be known as his Three Laws of Motion, which were derived from Johannes Kepler’s Laws of Planetary Motion and his own mathematical description of gravity. These laws would lay the foundation of classical mechanics, and would remain unchallenged for centuries – until the 20th century and the emergence of Einstein’s Theory of Relativity.
Newton’s own copy of his Principia, with hand-written corrections for the second edition. Credit: Trinity Cambridge/Andrew Dunn
Physics by 17th Century:
The 17th century was a very auspicious time for the sciences, with major breakthroughs occurring in the fields of mathematics, physics, astronomy, biology and chemistry. Some of the greatest developments in the period include the development of the heliocentric model of the Solar System by Nicolaus Copernicus, the pioneering work with telescopes and observational astronomy by Galileo Galilei, and the development of modern optics.
It was also during this period that Johannes Kepler developed his Laws of Planetary Motion. Formulated between 1609 and 1619, these laws described the motion of the then-known planets (Mercury, Venus, Earth, Mars, Jupiter, and Saturn) around the Sun. They stated that:
Planets move around the Sun in ellipses, with the Sun at one focus
The line connecting the Sun to a planet sweeps equal areas in equal times.
The square of the orbital period of a planet is proportional to the cube (3rd power) of the mean distance from the Sun in (or in other words–of the”semi-major axis” of the ellipse, half the sum of smallest and greatest distance from the Sun).
These laws resolved the remaining mathematical issues raised by Copernicus’ heliocentric model, thus removing all doubt that it was the correct model of the Universe. Working from these, Sir Isaac Newton began considering gravitation and its effect on the orbits of planets.
A comparison of the geocentric and heliocentric models of the universe. Credit: history.ucsb.edu
Newton’s Three Laws:
In 1678, Newton suffered a complete nervous breakdown due to overwork and a feud with fellow astronomer Robert Hooke. For the next few years, he withdrew from correspondence with other scientists, except where they initiated it, and renewed his interest in mechanics and astronomy. In the winter of 1680-81, the appearance of a comet, about which he corresponded with John Flamsteed (England’s Astronomer Royal) also renewed his interest in astronomy.
After reviewing Kepler’s Laws of Motion, Newton developed a mathematical proof that the elliptical form of planetary orbits would result from a centripetal force inversely proportional to the square of the radius vector. Newton communicated these results to Edmond Halley (discoverer of “Haley’s Comet”) and to the Royal Society in his De motu corporum in gyrum.
This tract, published in 1684, contained the seed of what Newton would expand to form his magnum opus, the Philosophiae Naturalis Principia Mathematica. This treatise, which was published in July of 1687, contained Newton’s three laws of motion, which stated that:
When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.
The vector sum of the external forces (F) on an object is equal to the mass (m) of that object multiplied by the acceleration vector (a) of the object. In mathematical form, this is expressed as: F=ma
When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.
Together, these laws described the relationship between any object, the forces acting upon it and the resulting motion, laying the foundation for classical mechanics. The laws also allowed Newton to calculate the mass of each planet, the flattening of the Earth at the poles, and the bulge at the equator, and how the gravitational pull of the Sun and Moon create the Earth’s tides.
In the same work, Newton presented a calculus-like method of geometrical analysis using ‘first and last ratios’, worked out the speed of sound in air (based on Boyle’s Law), accounted for the procession of the equinoxes (which he showed were a result of the Moon’s gravitational attraction to the Earth), initiated the gravitational study of the irregularities in the motion of the moon, provided a theory for the determination of the orbits of comets, and much more.
Newton and the “Apple Incident”:
The story of Newton coming up with his theory of universal gravitation as a result of an apple falling on his head has become a staple of popular culture. And while it has often been argued that the story is apocryphal and Newton did not devise his theory at any one moment, Newton himself told the story many times and claimed that the incident had inspired him.
In addition, the writing’s of William Stukeley – an English clergyman, antiquarian and fellow member of the Royal Society – have confirmed the story. But rather than the comical representation of the apple striking Newton on the head, Stukeley described in his Memoirs of Sir Isaac Newton’s Life (1752) a conversation in which Newton described pondering the nature of gravity while watching an apple fall.
“…we went into the garden, & drank thea under the shade of some appletrees; only he, & my self. amidst other discourse, he told me, he was just in the same situation, as when formerly, the notion of gravitation came into his mind. “why should that apple always descend perpendicularly to the ground,” thought he to himself; occasion’d by the fall of an apple…”
John Conduitt, Newton’s assistant at the Royal Mint (who eventually married his niece), also described hearing the story in his own account of Newton’s life. According to Conduitt, the incident took place in 1666 when Newton was traveling to meet his mother in Lincolnshire. While meandering in the garden, he contemplated how gravity’s influence extended far beyond Earth, responsible for the falling of apple as well as the Moon’s orbit.
Similarly, Voltaire wrote n his Essay on Epic Poetry (1727) that Newton had first thought of the system of gravitation while walking in his garden and watching an apple fall from a tree. This is consistent with Newton’s notes from the 1660s, which show that he was grappling with the idea of how terrestrial gravity extends, in an inverse-square proportion, to the Moon.
Sapling of the reputed original tree that inspired Sir Isaac Newton to consider gravitation. Credit: Wikipedia Commons/Loodog
However, it would take him two more decades to fully develop his theories to the point that he was able to offer mathematical proofs, as demonstrated in the Principia. Once that was complete, he deduced that the same force that makes an object fall to the ground was responsible for other orbital motions. Hence, he named it “universal gravitation”.
Various trees are claimed to be “the” apple tree which Newton describes. The King’s School, Grantham, claims their school purchased the original tree, uprooted it, and transported it to the headmaster’s garden some years later. However, the National Trust, which holds the Woolsthorpe Manor (where Newton grew up) in trust, claims that the tree still resides in their garden. A descendant of the original tree can be seen growing outside the main gate of Trinity College, Cambridge, below the room Newton lived in when he studied there.
Newton’s work would have a profound effect on the sciences, with its principles remaining canon for the following 200 years. It also informed the concept of universal gravitation, which became the mainstay of modern astronomy, and would not be revised until the 20th century – with the discovery of quantum mechanics and Einstein’s theory of General Relativity.
Let us discuss the very nature of the cosmos. What you may find in this discussion is not what you expect. Going into a conversation about the universe as a whole, you would imagine a story full of wondrous events such as stellar collapse, galactic collisions, strange occurrences with particles, and even cataclysmic eruptions of energy. You may be expecting a story stretching the breadth of time as we understand it, starting from the Big Bang and landing you here, your eyes soaking in the photons being emitted from your screen. Of course, the story is grand. But there is an additional side to this amazing assortment of events that oftentimes is overlooked; that is until you truly attempt to understand what is going on. Behind all of those fantastic realizations, there is a mechanism at work that allows for us to discover all that you enjoy learning about. That mechanism is mathematics, and without it the universe would still be shrouded in darkness. In this article, I will attempt to persuade you that math isn’t some arbitrary and sometimes pointless mental task that society makes it out to be, and instead show you that it is a language we use to communicate with the stars.
We are currently bound to our solar system. This statement is actually better than it sounds, as being bound to our solar system is one major step up from being bound simply to our planet, as we were
A defining moment for humanity: Galileo turing his spyglass towards the sky
before some very important minds elected to turn their geniuses toward the heavens. Before those like Galileo, who aimed his spyglass towards the sky, or Kepler discovering that planets move about the sun in ellipses, or Newton discovering a gravitational constant, mathematics was somewhat limited, and our understanding of the universe rather ignorant. At its core, mathematics allows a species bound to its solar system to probe the depths of the cosmos from behind a desk. Now, in order to appreciate the wonder that is mathematics, we must first step back and briefly look at its beginnings and how it is integrally tied into our very existence.
Mathematics almost certainly came about from very early human tribes (predating Babylonian culture which is attributed to some of the first organized mathematics in recorded history), that may have used math as a way of keeping track of lunar or solar cycles, and keeping count of animals, food and/or people by leaders. It is as natural as when you are a young child and you can see that you have
Ancient Babylonian tablet displaying early mathematics
one toy plus one other toy, meaning you have more than one toy. As you get older, you develop the ability to see that 1+1=2, and thus simple arithmetic seems to be interwoven into our very nature. Those that profess that they don’t have a mind for math are sadly mistaken because just as we all have a mind for breathing, or blinking, we all have this innate ability to understand arithmetic. Mathematics is both a natural occurrence and a human designed system. It would appear that nature grants us this ability to recognize patterns in the form of arithmetic, and then we systematically construct more complex mathematical systems that aren’t obvious in nature but let us further communicate with nature.
All this aside, mathematics developed alongside of human development, and carried on similarly with each culture that was developing it simultaneously. It’s a wonderful observation to see that cultures that had no contact with one another were developing similar mathematical constructs without conversing. However, it wasn’t until mankind decidedly turned their mathematical wonder towards the sky that math truly began to develop in an astonishing way. It is by no mere coincidence that our scientific revolution was spurred by the development of more advanced mathematics built not to tally sheep or people, but rather to further our understandings of our place within the universe. Once Galileo began measuring the rates at which objects fell in an attempt to show mathematically that the mass of an object had little to do with the speed in which it fell, mankind’s future would forever be altered.
This is where the cosmic perspective ties in to our want to further our mathematical knowledge. If it were not for math, we would still think we were on one of a few planets orbiting a star amidst the backdrop of seemingly motionless lights. This is a rather bleak outlook today compared to what we now know
Johannes Kepler used mathematics to model his observations of the planets.
about the awesomely large universe we reside in. This idea of the universe motivating us to understand more about mathematics can be inscribed in how Johannes Kepler used what he observed the planets doing, and then applied mathematics to it to develop a fairly accurate model (and method for predicting planetary motion) of the solar system. This is one of many demonstrations that illustrate the importance of mathematics within our history, especially within astronomy and physics.
The story of mathematics becomes even more amazing as we push forward to one of the most advanced thinkers humanity has ever known. Sir Isaac Newton, when pondering the motions of Halley’s Comet, came to the realization that the math that had been used thus far to describe physical motion of massive
Isaac Newton
bodies, simply would not suffice if we were to ever understand anything beyond that of our seemingly limited celestial nook. In a show of pure brilliance that lends validity to my earlier statement about how we can take what we naturally have and then construct a more complex system upon it, Newton developed the Calculus in which this way of approaching moving bodies, he was able to accurately model the motion of not only Halley’s comet, but also any other heavenly body that moved across the sky.
In one instant, our entire universe opened up before us, unlocking almost unlimited abilities for us to converse with the cosmos as never before. Newton also expanded upon what Kepler started. Newton recognized that Kepler’s mathematical equation for planetary motion, Kepler’s 3rd Law ( P2=A3 ), was purely based on empirical observation, and was only meant to measure what we observed within our solar system. Newton’s mathematical brilliance was in realizing that this basic equation could be made universal by applying a gravitational constant to the equation, in which gave birth to perhaps one of the most important equations to ever be derived by mankind; Newton’s Version of Kepler’s Third Law.
You can still see where Kepler’s 3rd Law remains, but with the added values of the gravitational constant G, and M and m representing the masses of the two bodies in question, this equation is no longer restricted to just our solar system
What Newton realized was that when things move in non-linear ways, using basic Algebra would not produce the correct answer. Herein lays one of the main differences between Algebra and Calculus. Algebra allows one to find the slope (rate of change) of straight lines (constant rate of change), whereas Calculus allows one to find the slope of curved lines (variable rate of change). There are obviously many more applications of Calculus than just this, but I am merely illustrating a fundamental difference between the two in order to show you just how revolutionary this new concept was. All at once, the motions of planets and other objects that orbit the sun became more accurately measurable, and thus we gained the ability to understand the universe a little deeper. Referring back to Netwon’s Version of Kepler’s Third Law, we were now able to apply (and still do) this incredible physics equation to almost anything that is orbiting something else. From this equation, we can determine the mass of either of the objects, the distance apart they are from each other, the force of gravity that is exerted between the two, and other physical qualities built from these simple calculations.
With his understanding of mathematics, Newton was able to derive the aforementioned gravitational constant for all objects in the universe ( G = 6.672×10-11 N m2 kg-2 ). This constant allowed him to unify astronomy and physics which then permitted predictions about how things moved in the universe. We could now measure the masses of planets (and the sun) more accurately, simply according to Newtonian physics (aptly named to honor just how important Newton was within physics and mathematics). We could now apply this newfound language to the cosmos, and begin coercing it to divulge its secrets. This was a defining moment for humanity, in that all of those things that prohibited our understandings prior to this new form of math were now at our fingertips, ready to be discovered. This is the brilliance of understanding Calculus, in that you are speaking the language of the stars.
There perhaps is no better illustration of the power that mathematics awarded us then in the discovery of the planet Neptune. Up until its discovery in September of 1846, planets were discovered simply by observing certain “stars” that were moving against the backdrop of all the other stars in odd ways. The term planet is Greek for “wanderer”, in that these peculiar stars wandered across the sky in noticeable patterns at different times of the year. Once the telescope was first turned upwards towards the sky by Galileo, these wanderers resolved into other worlds that appeared to be like ours. If fact, some of these worlds appeared to be little solar systems themselves, as Galileo discovered when he began recording the moons of Jupiter as they orbited around it.
After Newton presented his physics equations to the world, mathematicians were ready and excited to begin applying them to what we had been keeping track of for years. It was as if we were thirsty for the knowledge, and finally someone turned on the faucet. We began measuring the motions of the planets and gaining more accurate models for how they behaved. We used these equations to approximate the mass of the Sun. We were able to make remarkable predictions that were validated time and again simply by observation. What we were doing was unprecedented, as we were using mathematics to make almost impossible to know predictions that you would think we could never make without actually going to these planets, and then using actual observation to prove the math correct. However, what we also did was begin to figure out some odd discrepancies with certain things. Uranus, for instance, was behaving not as it should according to Newton’s laws.
Here you can see that the inner planet is being perturbed by the outer planet. In our situation, that outer planet was Neptune, which had yet to be discovered.
What makes the discovery of Neptune so wonderful was the manner in which it was discovered. What Newton had done was uncover a deeper language of the cosmos, in which the universe was able to reveal more to us. And this is exactly what happened when we applied this language to the orbit of Uranus. The manner in which Uranus orbited was curious and did not fit what it should have if it was the only planet that far out from the sun. Looking at the numbers, there had to be something else out there perturbing its orbit. Now, before Newton’s mathematical insights and laws, we would have had no reason to suspect anything was wrong in what we observed. Uranus orbited in the way Uranus orbited; it was just how it was. But, again revisiting that notion of mathematics being an ever increasing dialogue with the universe, once we asked the question in the right format, we realized that there really must be something else beyond what we couldn’t see. This is the beauty of mathematics writ large; an ongoing conversation with the universe in which more than we may expect is revealed.
It came to a French mathematician Urbain Le Verrier who sat down and painstakingly worked through the mathematical equations of the orbit of Uranus. What he was doing was using Newton’s mathematical equations backwards, realizing that there must be an object out there beyond the orbit of Uranus that was also orbiting the sun,
French mathematician who discovered the planet Neptune by using only mathematics
and then looking to apply the right mass and distance that this unseen object required for perturbing the orbit of Uranus in the way we were observing it was. This was phenomenal, as we were using parchment and ink to find a planet that nobody had ever actually observed. What he found was that an object, soon to be Neptune, had to be orbiting at a specific distance from the sun, with the specific mass that would cause the irregularities in the orbital path of Uranus. Confident of his mathematical calculations, he took his numbers to the New Berlin Observatory, where the astronomer Johann Gottfried Galle looked exactly where Verrier’s calculations told him to look, and there lay the 8th and final planet of our solar system, less than 1 degree off from where Verrier’s calculations said for him to look. What had just happened was an incredible confirmation of Newton’s gravitational theory and proved that his mathematics were correct.
Neptune is more than just the 8th planet in our solar system; it is a celestial reminder of the power that mathematics grants us.
These types of mathematical insights continued on long after Newton. Eventually, we began to learn much more about the universe with the advent of better technology (brought about by advances in mathematics). As we moved into the 20th century, quantum theory began to take shape, and we soon realized that Newtonian physics and mathematics seemed to hold no sway over what we observed on the quantum level. In another momentous event in human history, yet again brought forth by the advancement in mathematics, Albert Einstein unveiled his theories of General and Special Relativity, which was a new way to look not only at gravity, but
Einstein’s equation for the energy-mass equivalency, yet another incredible advancement for humanity brought forth from an ongoing mathematical dialogue. Image via Pixabay.
also on energy and the universe in general. What Einstein’s mathematics did was allow for us to yet again uncover an even deeper dialogue with the universe, in which we began to understand its origins.
Continuing this trend of advancing our understandings, what we have realized is that now there are two sects of physics that do not entirely align. Newtonian or “classical” physics, that works extraordinarily well with the very large (motions of planets, galaxies, etc…) and quantum physics that explains the extremely small (the interactions of sub-atomic particles, light, etc…). Currently, these two areas of physics are not in alignment, much like two different dialects of a language. They are similar and they both work, but they are not easily reconcilable with one another. One of the greatest challenges we face today is attempting to create a mathematical grand “theory of everything” which either unites the laws in the quantum world with that of the macroscopic world, or to work to explain everything solely in terms of quantum mechanics. This is no easy task, but we are striving forward nonetheless.
As you can see, mathematics is more than just a set of vague equations and complex rules that you are required to memorize. Mathematics is the language of the universe, and in learning this language, you are opening yourself up the core mechanisms by which the cosmos operates. It is the same as traveling to a new land, and slowly picking up on the native language so that you may begin to learn from them. This mathematical endeavor is what allows us, a species bound to our solar system, to explore the depths of the universe. As of now, there simply is no way for us to travel to the center of our galaxy and observe the supermassive black hole there to visually confirm its existence. There is no way for us to venture out into a Dark Nebula and watch in real time a star being born. Yet, through mathematics, we are able to understand how these things exist and work. When you set about to learn math, you are not only expanding your mind, but you are connecting with the universe on a fundamental level. You can, from your desk, explore the awesome physics at the event horizon of a black hole, or bear witness to the destructive fury behind a supernova. All of those things that I mentioned at the beginning of this article come into focus through mathematics. The grand story of the universe is written in mathematics, and our ability to translate those numbers into the events that we all love to learn about is nothing short of amazing. So remember, when you are presented with the opportunity to learn math, accept every bit of it because math connects us to the stars.
We are connected to the universe through mathematics…
An artist's conception of a hypervelocity star that has escaped the Milky Way. Credit: NASA
Back in 1988, astronomer Jack Hills predicted a type of “rogue”star might exist that is not bound to any particular galaxy. These stars, he reasoned, were periodically ejected from their host galaxy by some sort of mechanism to begin traveling through interstellar space.
Since that time, astronomers have made numerous discoveries that indicate these rogue, traveling stars indeed do exist, and far from being an occasional phenomenon, they are actually quite common. What’s more, some of these stars were found to be traveling at extremely high speeds, leading to the designation of hypervelocity stars (HVS).
And now, in a series of papers that published in arXiv Astrophysics, two Harvard researchers have argued that some of these stars may be traveling close to the speed of light. Known as semi-relativistic hypervelocity stars (SHS), these fast-movers are apparently caused by galactic mergers, where the gravitational effect is so strong that it fling stars out of a galaxy entirely. These stars, the researchers say, may have the potential to spread life throughout the Universe.
This finding comes on the heels of two other major announcements. The first occurred in early November when a paper published in the Astrophysical Journal reported that as many as 200 billion rogue stars have been detected in a cluster of galaxies some 4 billion light years away. These observations were made by the Hubble Space Telescope’s Frontier Fields program, which made ultra-deep multiwavelength observations of the Abell 2744 galaxy cluster.
This was followed by a study published in Science, where an international team of astronomers claimed that as many as half the stars in the entire universe live outside of galaxies.
Image of a moving star captured by the ESO Very Large Telescope, believed to have been ejected from the Large Magellanic Cloud. Credit: ESO
However, the recent observations made by Abraham Loeb and James Guillochon of Harvard University are arguably the most significant yet concerning these rogue celestial bodies. According to their research papers, these stars may also play a role in spreading life beyond the boundaries of their host galaxies.
In their first paper, the researchers trace these stars to galaxy mergers, which presumably lead to the formation of massive black hole binaries in their centers. According to their calculations, these supermassive black holes (SMBH) will occasionally slingshot stars to semi-relativistic speeds.
“We predict the existence of a new population of stars coasting through the Universe at nearly the speed of light,” Loeb told Universe Today via email. “The stars are ejected by slingshots made of pairs of massive black holes which form during mergers of galaxies.”
These findings have further reinforced that massive compact bodies, widely known as a supermassive black holes (SMBH), exist at the center of galaxies. Here, the fastest known stars exist, orbiting the SMBH and accelerating up to speeds of 10,000 km per second (3 percent the speed of light).
According to Leob and Guillochon, however, those that are ejected as a result of galactic mergers are accelerated to anywhere from one-tenth to one-third the speed of light (roughly 30,000 – 100,000 km per second).
Image of a hypervelocity star found in data from the Sloan Digital Sky Survey. Credit: Vanderbilt University
Observing these semi-relativistic stars could tell us much about the distant cosmos, according to the Harvard researchers. Compared to conventional research, which relied on subatomic particles like photons, neutrinos, and cosmic rays from distant galaxies, studying ejected stars offers numerous advantages.
“Traditionally, cosmologists used light to study the Universe but objects moving less than the speed of light offer new possibilities,” said Loeb. “For example, stars moving at different speeds allow us to probe a distant source galaxy at different look-back times (since they must have been ejected at different times in order to reach us today), in difference from photons that give us just one snapshot of the galaxy.”
In their second paper, the researchers calculate that there are roughly a trillion of these stars out there to be studied. And given that these stars were detected thanks to the Spitzer Space Telescope, it is likely that future generations will be able to study them using more advanced equipment.
All-sky infrared surveys could locate thousands of these stars speeding through the cosmos. And spectrographic analysis could tell us much about the galaxies they came from.
But how could these fast moving stars be capable of spreading life throughout the cosmos?
The Theory of Panspermia argues that life is distributed throughout the universe by celestial objects. Credit: NASA/Jenny Mottar
“Tightly bound planets can join the stars for the ride,” said Loeb. “The fastest stars traverse billions of light years through the universe, offering a thrilling cosmic journey for extra-terrestrial civilizations. In the past, astronomers considered the possibility of transferring life between planets within the solar system and maybe through our Milky Way galaxy. But this newly predicted population of stars can transport life between galaxies across the entire universe.”
The possibility that traveling stars and planets could have been responsible for the spread of life throughout the universe is likely to have implications as a potential addition to the Theory of Panspermia, which states that life exists throughout the universe and is spread by meteorites, comets, asteroids.
But Loeb told Universe Today that a traveling planetary system could have potential uses for our species someday.
“Our descendants might contemplate boarding a related planetary system once the Milky Way will merge with its sister galaxy, Andromeda, in a few billion years,” he said.
Sergei Krikalev gives a thumbs up during suit check before the launch of STS-88 in 1998. Credit: NASA.
Is time travel a fact or is it just science fiction? Thanks to time dilation and Einstein’s theory of relativity, we know that time travel can and actually does happen, albeit only in extremely tiny increments at the speeds and distances we can travel in space. If you add up the accumulated speed cosmonaut Sergei Krivalev has traveled in space – the most of any human with a total time spent in orbit of 803 days 9 hours and 39 minutes – he has actually time-traveled into his own future by 0.02 seconds.
Time dilation is caused by differences in either gravity or relative velocity — each of which affects time in different ways. When astronauts and satellites orbit the Earth, they are slightly further away from the center of the planet –compared to people on the ground – and so they actually experience less gravitational time dilation. This means the astronauts’ time would run slightly faster, and when they return to Earth, they’d have to “come back” to the past compared to when they were in space.
But time dilation due to velocity means that clocks for astronauts in space run slightly slower relative to people who are on the ground. When you come back to Earth, you’d be have to go into the future slightly to catch up with clocks on the ground.
The effect of time dilation due to gravity, however, “is quite small because Earth’s gravity is quite weak,” says educator Colin Stuart in this great instructional video from TedEd, “and so the time dilation due to their speed wins out and astronauts really do travel a tiny amount into their futures.”
But, as stated earlier, with our current technology limiting the velocities of astronauts, these differences are minuscule: after 6 months on the ISS, an astronaut has aged less than those on Earth, but only by about 0.007 seconds. The effects would be greater if we could get the ISS to orbit Earth at near the speed of light (approximately 300,000 km/s), instead of the actual speed of about 7.7 km/s.
This effect has been proven by GPS satellites, which orbit Earth at about 14,000 km/h (9,000 mph) which cuts several microseconds off their clocks daily, relative to clocks on Earth.
Wormhole. Credit: Internet Encyclopedia of Science
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A wormhole is a hypothetical “tunnel” connecting two different points in spacetime, and in theory, at each end of the wormhole there could be two universes. Theoretical physicist Nikodem Poplawski from Indiana University has taken things a step further by proposing that perhaps our universe could be located within the interior of a wormhole which itself is part of a black hole that lies within a much larger universe.
Whoa. I may have just lost my bearings.
As crazy as the concept of wormholes sounds, it does offer solutions to the equations of Einstein’s general theory of relativity. In fact, wormholes – also called an Einstein-Rosen Bridge — offer such a great solution that some theorists think that real wormholes may eventually be found or even created, and perhaps they could even be used for high-speed travel between two areas in space, or maybe even time travel.
However, a known property of wormholes is that they are highly unstable and would probably collapse instantly if even the tiniest amount of matter, such as a single photon, tried to travel though them.
But would it work – and could matter exist — if we were inside a wormhole inside a black hole inside another universe? Poplawski thinks so. He takes advantage of the Euclidean-based coordinate system called isotropic coordinates to describe the gravitational field of a black hole and to model the radial geodesic motion of a massive particle into a black hole.
“This condition would be satisfied if our universe were the interior of a black hole existing in a bigger universe,” Poplawski said. “Because Einstein’s general theory of relativity does not choose a time orientation, if a black hole can form from the gravitational collapse of matter through an event horizon in the future then the reverse process is also possible. Such a process would describe an exploding white hole: matter emerging from an event horizon in the past, like the expanding universe.”
So, a white hole would be connected to a black hole a wormhole, and is hypothetically the time reversal of a black hole. (Oh my, I’m now dizzy…)
Poplawski’s paper suggests that all astrophysical black holes, not just Schwarzschild and Einstein-Rosen black holes, may have Einstein-Rosen bridges, each with a new universe inside that formed simultaneously with the black hole.
“From that it follows that our universe could have itself formed from inside a black hole existing inside another universe,” he said. IU theoretical physicist Nikodem Poplawski. Credit: Indiana University
By continuing to study the gravitational collapse of a sphere of dust in isotropic coordinates, and by applying the current research to other types of black holes, views where the universe is born from the interior of an Einstein-Rosen black hole could avoid problems seen by scientists with the Big Bang theory and the black hole information loss problem which claims all information about matter is lost as it goes over the event horizon (in turn defying the laws of quantum physics).
Poplawski theorizes that this model in isotropic coordinates of the universe as a black hole could explain the origin of cosmic inflation.
Could this be tested? Well, there is the issue that to see if an object could travel through a wormhole, the observer would have to be inside the wormhole as well, since the interior cannot be observed unless an observer enters or resides within.
A possible solution is that exotic matter wouldn’t collapse the wormhole, so we’d have to create – and be made of – exotic matter to keep the it open. But perhaps, as Poplawski proposes, if the wormhole is inside a black hole inside another universe it would work.
