During the latter half of the 20th century, cosmologists determined that there were three possible scenarios for the end of the universe, and they all depend on its density. If the density were high enough, then gravity would eventually slow…
The age of the universe is approximately 13.77 billion years. This age is calculated by measuring the distances and radial velocities of other galaxies, most of which are flying away from our own at speeds proportional to their distances. Using…
We know that the universe is expanding because, with some nearby exceptions, almost every galaxy in the universe is moving away from us and from one another. Not only that, but very distant galaxies appear to be receding even more…
Vesto Slipher’s observations of spiral nebulae in the early 20th century led him to conclude that most spirals, with the exception of a few (such as Andromeda), were receding from Earth. Edwin Hubble confirmed that the spiral nebulae were actually separate…
At the end of the 20th century, the universe seemed to face two possible fates: either it contained enough matter that gravity would ultimately force a re-collapse, or at the very least, its expansion would slow. But Hubble Space Telescope’s observations…
Dark matter is a mysterious type of matter that doesn’t interact with any form of electromagnetic radiation, i.e., light. It doesn’t radiate light, and light doesn’t bounce off it. Although we’ve never detected dark matter directly, a large amount of…
When we say a galaxy is 300 million light-years away, is that its distance now or 300 million years ago? Oftentimes, neither! In most cases astronomers try to get a handle on a galaxy’s distance by measuring its redshift: the…
LOCAL CURVATURE OF SPACE According to Einstein’s theory of general relativity, massive objects warp the spacetime around them, and the effect a warp has on objects is what we call gravity. So, locally, spacetime is curved around every object with…
In a word, no. The universe began as a singularity (an infinitely tiny point with infinite density) that started expanding at the moment of the Big Bang. However, the Big Bang wasn’t a normal explosion starting from a single point in space.…
Where was the Big Bang located? In which constellation? Should we observe more young galaxies in that direction and more old ones in the opposite direction? You’ve got the commonest misconception about the Big Bang: that it happened at some…