A Hubble Space Telescope image of a doubly-imaged quasar. Image Credit: NASA Hubble Space Telescope, Tommaso Treu/UCLA, and Birrer et al
How fast is the Universe expanding? That’s a question that astronomers haven’t been able to answer accurately. They have a name for the expansion rate of the Universe: The Hubble Constant, or Hubble’s Law. But measurements keep coming up with different values, and astronomers have been debating back and forth on this issue for decades.
The basic idea behind measuring the Hubble Constant is to look at distant light sources, usually a type of supernovae or variable stars referred to as ‘standard candles,’ and to measure the red-shift of their light. But no matter how astronomers do it, they can’t come up with an agreed upon value, only a range of values. A new study involving quasars and gravitational lensing might help settle the issue.
The NASA/ESA Hubble Space Telescope offers this delightful view of the crowded stellar encampment called Messier 68, a spherical, star-filled region of space known as a globular cluster. Mutual gravitational attraction amongst a cluster’s hundreds of thousands or even millions of stars keeps stellar members in check, allowing globular clusters to hang together for many billions of years. Astronomers can measure the ages of globular clusters by looking at the light of their constituent stars. The chemical elements leave signatures in this light, and the starlight reveals that globular clusters' stars typically contain fewer heavy elements, such as carbon, oxygen and iron, than stars like the Sun. Since successive generations of stars gradually create these elements through nuclear fusion, stars having fewer of them are relics of earlier epochs in the Universe. Indeed, the stars in globular clusters rank among the oldest on record, dating back more than 10 billion years. More than 150 of these objects surround our Milky Way galaxy. On a galactic scale, globular clusters are indeed not all that big. In Messier 68's case, its constituent stars span a volume of space with a diameter of little more than a hundred light-years. The disc of the Milky Way, on the other hand, extends over some 100 000 light-years or more. Messier 68 is located about 33 000 light-years from Earth in the constellation Hydra (The Female Water Snake). French astronomer Charles Messier notched the object as the sixty-eighth entry in his famous catalogue in 1780. Hubble added Messier 68 to its own impressive list of cosmic targets in this image using the Wide Field Camera of Hubble’s Advanced Camera for Surveys. The image, which combines visible and infrared light, has a field of view of approximately 3.4 by 3.4 arcminutes. Credit: Hubble/NASA/ESA
Imagine yourself in a boat on a great ocean, the water stretching to the distant horizon, with the faintest hints of land just beyond that. It’s morning, just before dawn, and a dense fog has settled along the coast. As the chill grips you on your early watch, you catch out of the corner of your eye a lighthouse, feebly flickering through the fog.
An artist's illustration of the first stars to appear in the universe.
Credit: N.R. Fuller, National Science Foundation
We need to talk about the dark ages. No, not those dark ages after the fall of the western Roman Empire. The cosmological dark ages. The time in our universe, billions of years ago, before the formation of the first stars. And we need to talk about the cosmic dawn: the birth of those first stars, a tumultuous epoch that completely reshaped the face the cosmos into its modern form.
Those first stars may have been completely unlike anything we see in the present universe. And we may, if we’re lucky, be on the cusp of seeing them for the first time.
Radio waves from our galaxy, the Milky Way, reflecting off the surface of the Moon. Image Credit: Dr Ben McKinley, Curtin University/ICRAR/ASTRO 3D. Moon image courtesy of NASA/GSFC/Arizona State University.
The universe wasn’t always such a well-lit place. It had its own Dark Ages, back in the days before stars and galaxies formed. One of the big questions in astronomy concerns how stars and galaxies shaped the very early days of the Universe. The problem is, there’s no visible light travelling through the Universe from this time period.
Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold (Credit: Dana Berry, SkyWorks Digital, Inc.)
Neutron stars scream in waves of spacetime when they die, and astronomers have outlined a plan to use their gravitational agony to trace the history of the universe. Join us as we explore how to turn their pain into our cosmological profit.
One of the greatest challenges of astronomy is locating objects in space that are obscured by the light of nearby, brighter objects. In addition to making extra-solar planets very difficult to directly image, this problem also intrudes on surveys of the local Universe, where astronomers are unable to detect dwarf and isolated galaxies because of all the brighter ones surrounding them.
Because of this, astronomers are unable to do a full inventory of small galaxies in the volume of space surrounding the Milky Way (aka. the Local Volume). However, thanks to the efforts of an amateur astronomer and an international team of scientists, a dwarf spheroidal galaxy was recently discovered lurking behind the Andromeda Galaxy. The discovery of this object, named Donatiello I, could help astronomers learn more about the process of galaxy formation.
The OzGrav supercomputer, which was recently installed at the Swinburne University of Technology, will assist in the hunt for gravitational waves. Credit: OzGrav
Exotic dark matter theories. Gravitational waves. Observatories in space. Giant black holes. Colliding galaxies. Lasers. If you’re a fan of all the awesomest stuff in the universe, then this article is for you.
This single all-sky image, captured by the Planck telescope, simultaneously captured two snapshots that straddle virtually the entire 13.7 billion year history of the universe. Credit: ESA
For thousands of years, human being have been contemplating the Universe and seeking to determine its true extent. And whereas ancient philosophers believed that the world consisted of a disk, a ziggurat or a cube surrounded by celestial oceans or some kind of ether, the development of modern astronomy opened their eyes to new frontiers. By the 20th century, scientists began to understand just how vast (and maybe even unending) the Universe really is.
And in the course of looking farther out into space, and deeper back in time, cosmologists have discovered some truly amazing things. For example, during the 1960s, astronomers became aware of microwave background radiation that was detectable in all directions. Known as the Cosmic Microwave Background (CMB), the existence of this radiation has helped to inform our understanding of how the Universe began. Continue reading “What is the Cosmic Microwave Background?”
Could our Universe be part of a wider Multiverse? And could these other Universes support life? Credit: Jaime Salcido/EAGLE Collaboration
The Multiverse Theory, which states that there may be multiple or even an infinite number of Universes, is a time-honored concept in cosmology and theoretical physics. While the term goes back to the late 19th century, the scientific basis of this theory arose from quantum physics and the study of cosmological forces like black holes, singularities, and problems arising out of the Big Bang Theory.
One of the most burning questions when it comes to this theory is whether or not life could exist in multiple Universes. If indeed the laws of physics change from one Universe to the next, what could this mean for life itself? According to a new series of studies by a team of international researchers, it is possible that life could be common throughout the Multiverse (if it actually exists).
In honor of Dr. Stephen Hawking, the COSMOS center will be creating the most detailed 3D mapping effort of the Universe to date. Credit: BBC, Illus.: T.Reyes
Stephen Hawking is rightly seen as one of the most influential scientists of our time. In his time on this planet, the famed physicist, science communicator, author and luminary became a household name, synonymous with the likes of Einstein, Newton and Galileo. What is even more impressive is the fact that he managed to maintain his commitment to science, education and humanitarian efforts despite suffering from a slow, degenerative disease.
Even though Hawking recently passed away, his influence is still being felt. Shortly before his death, Hawking submitted a paper offering his final theory on the origins of the Universe. The paper, which was published earlier this week (on Wednesday, May 2nd), offers a new take on the Big Bang Theory that could revolutionize the way we think of the Universe, how it was created, and how it evolved.
The paper, titled “A smooth exit from eternal inflation?“, was published in the Journal of High Energy Physics. The theory was first announced at a conference at the University of Cambridge in July of last year, where Professor Thomas Hertog (a Belgian physicist at KU Leuven University) shared Hawking’s paper (which Hertog co-authored) on the occasion of his 75th birthday.
Stephen Hawking’s final theory on the Big Bang, submitted shortly before he passed away, was recently published. Credit: University of Cambridge
According to the current scientific consensus, 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. Suddenly, this ball started to inflate at an exponential rate, and the Universe as we know it began.
However, it is widely believed that since this inflation started, quantum effects will keep it going forever in some regions of the Universe. This means that globally, the Universe’s inflation is eternal. In this respect, the observable part of our Universe (measuring 13.8 billion light-years in any direction) is just a region in which inflation has ended and stars and galaxies formed.
“The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean. The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse. But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can’t be tested. ”
In their new paper, Hawking and Hertog offer a new theory that predicts that the Universe is not an infinite fractal-like multiverse, but is finite and reasonably smooth. In short, they theorize that the eternal inflation, as part of the theory of the Big Bang, is wrong. As Hertog explained:
“The problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein’s theory of general relativity and treats the quantum effects as small fluctuations around this. However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics. As a consequence, Einstein’s theory breaks down in eternal inflation.”
In contrast to this, Hawking and Hertog offer an explanation based on String Theory, a branch of theoretical physics that attempts to unify General Relativity with quantum physics. This theory was proposed to explain how gravity interacts with the three other fundamental forces of the Universe (weak and strong nuclear forces and electromagnetism), thus producing a Theory of Everything (ToE).
To put it simply, this theory describes the fundamental constituents of the Universe as tiny, one-dimensional vibrating strings. Hawking and Hertog’s approach uses the holography concept of string theory, which postulates that the Universe is a large and complex hologram. In this theory, physical reality in certain 3D spaces can be mathematically reduced to 2D projections on a surface.
This illustration shows the evolution of the Universe, from the Big Bang on the left, to modern times on the right. Image: NASA
Together, Hawking and Hertog developed a variation of this concept to project out the dimension of time in eternal inflation. This enabled them to describe eternal inflation without having to rely on General Relativity, thus reducing inflation to a timeless state defined on a spatial surface at the beginning of time. In this respect, the new theory represents a change from Hawking’s earlier work on “no boundary theory”.
Also known as the Hartle and Hawking No Bounary Proposal, this theory viewed the Universe like a quantum particle – assigning it a wave function that described all possible Universes. This theory also predicted that if you go back in time to the beginning of the Universe, it would shrink and close off like a sphere. Lastly, it predicted that the Universe would eventually stop expanding and collapse in on itself.
As Hertog explains, this new theory is a departure from that earlier work:
“When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning. Now we’re saying that there is a boundary in our past.”
Using this theory, Hawking and Hertog were able to derive more reliable predictions about the global structure of the Universe. In addition, a Universe predicted to emerge from eternal inflation on the past boundary is also finite and much simpler. Last, but not least, the theory is more predictive and testable than the infinite Multiverse predicted by the old theory of eternal inflation.
Artist’s impression of merging binary black holes. Credit: LIGO/A. Simonnet.
“We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse, to a much smaller range of possible universes,” said Hawking. In theory, a finite and smooth Universe is one we can observe (at least locally) and will be governed by physical laws that we are already familiar with. Compared to an infinite number of Universes governed by different physical laws, it certainly simplifies the math!
Looking ahead, Hertog plans to study the implications of this theory on smaller scales using data obtained by space telescopes about the local Universe. In addition, he hopes to take advantage of recent studies concerning gravitational waves (GWs) and the many events that have been detected. Essentially, Hertog believes that primordial GWs generated at the exit from eternal inflation are the most promising means to test the model.
Due to the expansion of our Universe since the Big Bang, these GWs would have very long wavelengths, ones which are outside the normal range of the Laser Interferometry Gravitational-Wave Observatory‘s (LIGO) or Virgo‘s detectors. However, the Laser Interferometry Space Antenna (LISA) – an ESA-led plan for a space-based gravitational wave observatory – and other future experiments may be capable of measuring them.
Even though he is longer with us, Hawking’s final theory could be his profound contribution to science. If future research should prove him correct, then Hawking will have resolved one of the most daunting problems in modern astrophysics and cosmology. Just one more achievement from a man who spent his life changing how people think about the Universe!
