Why does the Universe expand the way it does? Why does it accelerate? Einstein’s equations offer an explanation of gravity that works on the scale we know, but do they work on the grandest scales of space and time? Humanity now has a way to find out. The General Theory of Relativity predicts the behaviour of gravity, and includes a term known as the cosmological constant. Einstein added this term to make the universe static and unchanging, as he believed it was. But when the expansion of the universe was discovered by Edwin Hubble, Einstein regarded it as ‘the greatest blunder...
When you start to think about the most massive and extreme ‘stuff’ in the universe, you inevitably go to Dark Matter and Dark Energy. They exist as opposites, one with incredible gravity holding the universe together, and the other a mysterious vacuum energy tearing it apart. Studying this cosmic tug of war gives astronomers a chance to determine the past and future of the entire universe. To study the immense scale of these two quantities, the Baryon Oscillation Spectroscopic Survey (BOSS) program of the Sloan Digital Sky Survey-III (SDSS) constructed a 3D map of the sky, amounting to a volume...
Baryonic matter, which is everything we are made of and everything we can see in the universe, is not a lot of stuff. I mean to a tiny Earthling, it’s a heck of a lot, but if you put it all together it only makes up about 5% of the total Mass-Energy in the Universe. If you’ve ever seen the Millennium simulation, it highlights the fact that both baryonic and dark matter are organized into filaments of mass, with the baryonic matter at the densest points, ie the galaxies. What lies between these dense nodes and filaments are vast empty...
Beyond the atmosphere, past the stars we see, farther than the Milky Way, and continuing past Andromeda, we reach the real cosmic ocean. So called because like an ocean on Earth, it is vast, homogeneous, and impossible to navigate by common sense alone. In the cosmic ocean, an impossibly huge amount of space separates island galaxies, whose strong gravity binds them across incredible distances, dictating their course, and forming the largest and most massive structures in the universe: galaxy clusters. Because these immense structures are so vast and so distant, it requires the work of several telescopes to map out...
Dark matter is everywhere. There is way more of it in the universe than the matter we are made of and interact with. Yet for the sheer amount of it, we have no way of determining what exactly it is. It’s as if we didn’t know what air was, and even though we could see it and breathe it, we couldn’t measure it. The most tantalizing part about dark matter is that we can see the gravitational effect it has, and so we can determine how much of it there has to be. Some places in the universe have more dark matter than...
Type 1a supernova explosions are used by Astronomers as a standard candle for measuring distances in Astronomy. They all explode with the same intrinsic brightness, and so depending on their apparent magnitude, ie how bright they look, we can determine the distance to them. It’s like a 40 watt light bulb. No matter how far away I move it, it’s still 40 watts, even though it looks dimmer if it’s further away. However, a few months ago some research came forward about type 1a supernova explosions, hinting that there may actually be two or more distinct types with slightly different...
One of the big questions in astrophysics is about variation of the laws of Physics. The laws we know and are familiar with; angular momentum, gravity, energy, are the same everywhere on Earth. But what about beyond Earth? The universe is so large and so vast, we may be in a local region where the laws of Physics are set, and our laws may be different from a distinct region somewhere else in the universe. The good news is that we can make predictions based on our understanding of physics. And with our powerful telescopes that allow us to view a variety of...
After yesterday’s post about some data that has caused us to rethink a theory, I wanted to follow it up today with an even bigger bit of data that could substantially change an even bigger theory. Dark energy was discovered as a large-scale repulsive force in the universe that is responsible for the acceleration of its expansion. It was discovered by looking at type 1a supernovae in distant galaxies. since the supernovae all explode with the same mass limit, they appear to all have the same intrinsic luminosity. If we know how bright they actually are, we can compare them...
The biggest problem in theoretical physics today is the marriage between Quantum Mechanics and Gravity. Throw in the fact that whatever theory comes out of it has to additionally be able to explain Dark Matter and Dark Energy, and we have ourselves a massive problem to solve. How do we reconcile the seemingly random probabilistic nature of quantum mechanics with the smooth, pliable space-time of General Relativity. We have two incredible theories that explain the Universe, make predictions accurately, and have led to amazing advances in technology and understanding, yet they completely disagree with each other at common scales. So...
Dark Matter; Dark Energy; We basically use the term ‘dark’ as a cool sounding version of ‘We have no clue what this is.’ But Dark Matter is a better name than ‘We haven’t a clue’ Matter. Over the years, Astronomers have been trying to pinpoint what the stuff actually is that seems to permeate the universe and makes up 26.8% of the entire total energy-mass (Compare this to a paltry 4.9% of ordinary matter, ie the stuff we can see). But now, as per usual, theorists have come up with another possibility for the source of dark matter: moderately sized,...
