Last week we talked about knowledge, what we do and don’t know. This week we talk about questions which are impossible to ask, where the answers don’t actually exist.
What is this thing we keep hearing about – the Higgs Boson, and why is it important?
Continue reading “What is the Higgs Boson?”
In the last few episodes, we’ve been talking about the standard model of physics, explaining what everything is made up of. But the reality is that we probably don’t know a fraction of how everything is put together. This week we’re going to talk about baryons, the particles made up of quarks. The most famous ones are the proton and the neutron, but that’s just the tip of the baryonic iceberg. And then we’re going to talk about where the standard model ends, and what’s next in particle physics.
Continue reading “Astronomy Cast Ep. 395: The Standard Model – Baryons and Beyond”
All fundamental particles are either fermions or bosons. Last week we talked about quarks, which are fermions. This week we’ll talk about bosons, including the famous Higgs boson, recently confirmed by the Large Hadron Collider.
Continue reading “Astronomy Cast Ep. 394: The Standard Model – Bosons”
Physicists are getting a handle on the structure of the Universe, how everything is made of something else. Molecules are made of atoms, atoms are made of protons, neutrons and electrons, etc. Even smaller than that are the quarks and the leptons, which seem to be the basic building blocks of all matter.
Continue reading “Astronomy Cast Ep. 393: The Standard Model – Leptons & Quarks”
Would shooting a black hole into an antimatter black hole destroy them both?
Continue reading “What if a Black Hole Met an Antimatter Black Hole?”
In some of the most extreme objects in the Universe, white dwarfs and neutron stars, matter gets strange, transforming into a material that physicists call “degenerate matter”. Let’s learn what it is, how it forms.
In the world of quantum mechanics, particles behave in discreet ways. One breakthrough experiment was the Stern-Gerlach Experiment, performed in 1922. They passed silver atoms through a magnetic field and watched how the spin of the atoms caused the particles to deflect in a very specific way.
Continue reading “Astronomy Cast Ep. 374: Stern-Gerlach Experiment”
Dark matter can’t be seen or detected by any of our instruments, so how do we know it really exists?
Imagine the Universe was a pie, and you were going to slice it up into tasty portions corresponding to what proportions are what. The largest portion of the pie, 68% would go to dark energy, that mysterious force accelerating the expansion of the Universe. 27% would go to dark matter, the mysterious matter that surrounds galaxies and only interacts through gravity. A mere 5% of this pie would go to regular normal matter, the stuff that stars, planets, gas, dust, and humans are made out of.
Dark matter has been given this name because it doesn’t seem to interact with regular matter in any way. It doesn’t collide with it, or absorb energy from it. We can’t see it or detect it with any of our instruments. We only know it’s there because we can see the effect of its gravity.
Now, you might be saying, if we don’t know what this thing is, and we can’t detect it. How do we know it’s actually there? Isn’t it probably not there, like dragons? How do we know dark matter actually exists, when we have no idea what it actually is?
Oh, it’s there. In fact, pretty much all we know is that it does exist. Dark matter was first theorized back in the 1930s by Fritz Zwicky to account for the movement of galaxy clusters, but the modern calculations were made by Vera Rubin in the 1960s and 70s. She calculated that galaxies were spinning more quickly than they should. So quickly that they should tear themselves apart like a merry-go-round ejecting children.
Rubin imagined that every galaxy was stuck inside a vast halo of dark matter that supplied the gravity to hold the galaxy together. But there was no way to actually detect this stuff, so astronomers proposed other models. Maybe gravity doesn’t work the way we think it does at vast distances.
But in the last few years, astronomers have gotten better and better at detecting dark matter, purely though the effect of its gravity on the path that light takes as it crosses the Universe. As light travels through a region of dark matter, its path gets distorted by gravity. Instead of taking a straight line, the light is bent back and forth depending on how much dark matter is passes through.
And here’s the amazing part. Astronomers can then map out regions of dark matter in the sky just by looking at the distortions in the light, and then working backwards to figure out how much intervening dark matter would need to be there to cause it.
These techniques have become so sophisticated that astronomers have discovered unusual situations where galaxies and their dark matter have gotten stripped away from each other. Or dark matter galaxies which don’t have enough gas to form stars. They’re just giant blobs of dark matter. Astronomers even use dark matter as gravitational lenses to study more distant objects. They have no idea what dark matter is, but they can still use it as a telescope.
They’ve never captured a dark matter particle, and haven’t studied them in the lab. One of the Large Hadron Collider’s next tasks will be to try and generate particles that match the characteristics of dark matter as we understand it. Even if the LHC doesn’t actually create dark matter, it will help narrow down the current theories, hopefully helping physicists focus in on the true nature of this mystery.
This is how science works. Someone notices something unusual, and then people propose theories to explain it. The theory that best matches reality is considered correct. We live in a modern world, where so many scientific theories have already been proven for hundreds of years: germs, gravity, evolution, etc. But with dark matter, you’re alive at a time when this is a mystery. And if we’re lucky, we’ll see it solved within our lifetime. Or maybe there’s no dark matter after all, and we’re about to learn something totally new about our Universe. Science, it’s all up to you.
What do you think dark matter is? Tell us in the comments below.
Waves move through a medium, like water or air. So it seemed logical to search for a medium that light waves move through. The Michelson-Morley Experiment attempted to search for this medium, known as the “luminiferous aether”. The experiment gave a negative result, and helped set the stage for the theory of General Relativity.
Continue reading “Astronomy Cast Ep. 368: Searching for the Aether Wind: the Michelson–Morley Experiment”