Composition. The Universe is composed almost completely of dark energy, dark matter, and ordinary matter. Other contents are electromagnetic radiation (estimated to constitute from 0.005% to close to 0.01% of the total mass-energy of the Universe) and antimatter.Read more
We live in the Milky Way Galaxy, which is a collection of stars, gas, dust, and a supermassive black hole at it’s very center. Our Galaxy is a spiral galaxy, which are rotating structures that are flat (disk-like) like a DVD when looked upon edge-on. There is also a bulge in the middle that consists of mostly old stars. When you look at a spiral galaxy face-on, you can see beautiful spiral arms where stars are being born. Our solar system is in the Orion arm, and we are about 25,000 light years (2.5 X 10^17 miles) from the very center of the Galaxy.Read more
The very first stars likely formed when the Universe was about 100 million years old, prior to the formation of the first galaxies. … This started the cosmic chemical enrichment that led to the formation of the stars that we see in the Milky Way today, to rocky planets and eventually humans.Read more
Our Milky Way Galaxy was once thought to comprise the entire known universe. Today our universe encompasses many billions of galaxies, and its history can be recounted back to its earliest moments.
Our universe began with an explosion of space itself – the Big Bang. Starting from extremely high density and temperature, space expanded, the universe cooled, and the simplest elements formed. Gravity gradually drew matter together to form the first stars and the first galaxies. Galaxies collected into groups, clusters, and superclusters. Some stars died in supernova explosions, whose chemical remnants seeded new generations of stars and enabled the formation of rocky planets. On at least one such planet, life evolved to consciousness. And it wonders, “Where did I come from?”Read more
Space-time is a mathematical model that joins space and time into a single idea called a continuum. This four-dimensional continuum is known as Minkowski space. Combining these two ideas helped cosmology to understand how the universe works on the big level (e.g. galaxies) and small level (e.g. atoms).Read more
A black hole cosmology is a cosmological model in which the observable universe is the interior of a black hole. Such models were originally proposed by theoretical physicist Raj Pathria, and concurrently by mathematician I. J. Good.
Any such model requires that the Hubble radius of the observable universe be equal to its Schwarzschild radius, that is, the product of its mass and the Schwarzschild proportionality constant. This is indeed known to be nearly the case; however, most cosmologists consider this close match a coincidence.
In the version as originally proposed by Pathria and Good, and studied more recently by, among others, Nikodem Popławski, the observable universe is the interior of a black hole existing as one of possibly many inside a larger parent universe, or multiverse.Read more
In physics, space-time is any mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Space-time diagrams are useful in visualizing and understanding relativistic effects such as how different observers perceive where and when events occur.
Until the turn of the 20th century, the assumption had been that the three-dimensional geometry of the universe (its description in terms of locations, shapes, distances, and directions) was distinct from time (the measurement of when events occur within the universe). However, Albert Einstein’s 1905 special theory of relativity postulated that the speed of light through empty space has one definite value, a constant, that is independent of the motion of the light source. Einstein’s equations described important consequences of this fact. The distances and times between pairs of events vary when measured in different inertial frames of reference (separate vantage points that aren’t being subjected to g‑forces but have different velocities).
Einstein’s theory was framed in terms of kinematics (the study of moving bodies), and showed how quantification of distances and times varied for measurements made in different reference frames. His theory was a breakthrough advance over Lorentz’s 1904 theory of electromagnetic phenomena and Poincaré’s electrodinamic theory. Although these theories included equations identical to those that Einstein introduced, they were essentially ad hoc models proposed to explain the results of various experiments—including the famous Michelson–Morley interferometre experiment—that were extremely difficult to fit into existing paradigms.Read more
What is the Universe? That is one immensely loaded question! No matter what angle one took to answer that question, one could spend years answering that question and still barely scratch the surface. In terms of time and space, it is unfathomably large (and possibly even infinite) and incredibly old by human standards. Describing it in detail is therefore a monumental task. But we here at Universe Today are determined to try!
So what is the Universe? Well, the short answer is that it is the sum total of all existence. It is the entirety of time, space, matter and energy that began expanding some 13.8 billion years ago and has continued to expand ever since. No one is entirely certain how extensive the Universe truly is, and no one is entirely sure how it will all end. But ongoing research and study has taught us a great deal in the course of human history.Read more
Planets in the hundreds of billions are likely caught up in the vast whirlpool of the Milky Way galaxy. From Earth, a lonely outpost on one of its spiral arms, we’ve begun to peer across the void. We can already make out, dimly, the light from planets orbiting distant stars. We’ve even tasted a few of their atmospheres by dissecting those faint traces of light.
But the ultimate goal of NASA’s exoplanet program is to find unmistakable signs of current life. How soon that can happen depends on two unknowns: the prevalence of life in the galaxy and how lucky we get as we take those first, tentative, exploratory steps.
The Big Bang that gave birth to our Universe sounds like a spectacular event, an explosion that was unbelievably loud and bright. But the birth of our Universe was probably very subtle.
For a long stretch of time after its birth, our Universe was totally dark, silent and empty. The first stars didn’t spark into existence until the Universe was perhaps 100 million years old. At this time nothing existed in the Universe but gases.
The first stars to exist in our Universe have never been seen because they went extinct a long time ago. But many astronomers have discussed their existence. These stars would have been born out of material created by the Big Bang.
The only chemicals that existed before stars were hydrogen, helium and lithium. This means that the first stars must have been made only out of these chemicals, unlike the Sun and all the other stars in our galaxy.Read more