In the big bang model, the universe began about 13.8 billion years ago as a hot, dense state. There’s plenty of observational evidence to support this model. One strong bit of evidence is the cosmic microwave background (CMB). It is the thermal remnant of the primordial fireball, cooled now to a temperature of about 2.7 K. What’s amazing about the CMB is how perfectly it light matches that of a blackbody. It is exactly what you would expect to see from a primordial universe of uniform temperature. But that also raises a bit of a mystery, because the CMB is actually more uniform that it should be.
Still in the Dark
Dark matter has an interesting history. It was first proposed to account for the fact that stars in our galaxy move much faster than they should around the galactic core. Evidence of dark matter has been seen in galactic collisions like the Bullet Cluster, as well as through gravitational lensing by galaxies. On the other hand, we have yet to find any direct detection of dark matter particles. In fact, many of the likely candidates for dark matter have been all but eliminated. Then there is the puzzling aspect of dwarf galaxies.
Hot Topic
The structure of the Sun can be divided into three main parts: the interior, which consists of the core, radiative and convective regions; the photosphere, which is basically the surface of the Sun where light comes from; and the atmosphere, of which includes the corona. Since nuclear fusion occurs in the core of the Sun, it’s reasonable to assume that the core is the hottest part of the Sun. In fact we know the core is about 15 million K, and that as you move outward from the center the temperature drops, until you reach a temperature of about 5,800 K at the surface. One would expect that this cooling trend continues, so that the solar atmosphere is cooler than the surface. But what we observe is that the atmosphere, specifically the corona, gets hotter. Much hotter.
Achilles’ Heel
Achilles, so the story goes was a mighty Greek warrior. When he was born, his mother dipped him in the river Styx, rendering him invulnerable except for the heel by which he was held. It was that vulnerable heel that was Achilles’ undoing, when Paris killed Achilles by shooting an arrow through the vulnerable heel. It’s a story of how the mighty can be destroyed by a seemingly minor flaw. A cautionary tale, if you will.
Have You Heard the One About…
This week I’ve gotten a number of questions about various proposed models in astrophysics, such as the one about how anti-gravity could explain dark matter and dark energy. Or the one where dark matter is a result of quantum interference on a cosmic scale. Or the one where the cosmic microwave background is actually due to thermal turbulence rather than the big bang. There are lots of ideas that show up in the literature and in the press, so how do you judge the quality of a particular idea?
Point/Counterpoint
Back in March, a project known as BICEP2 held a press conference where they announced the discovery of inflation in the early universe. This created quite a stir in the press. When the announcement was made, the results had just been made public, and their paper had not been peer reviewed. As everyone started analyzing the work, what initially looked like a pretty strong result started to look less strong. Then there started to be murmurings that perhaps the announcement had been premature.
Evidence That Demands a Verdict
There’s a popular picture that traverses the net now and then that states 97% of climate scientists believe that anthropogenic global warming is true. More specifically, that of peer reviewed climate research papers, of the ones that made a statement on the cause of global warming, 97% agreed that humanity was the cause. You can imagine the lively discussions it induced.
Of Cabbages and Kings
When talking about scientific ideas, you often hear terms such as theories, hypotheses, facts, laws, models, etc. Some of these terms are used in everyday speech, but with meanings other than their scientific ones. Someone might say they have a theory, when they really mean they have an idea. People talk about scientific laws as if they are facts, or use the phrase “just a theory” to distinguish it from some idealized truth. Even scientists will sometimes interchange terms like theory and law. We know what we mean, but we aren’t always precise with our usage. So what do these terms mean in a scientific sense?
Black Swan
Only about half of Americans are confident in the validity of the big bang. That’s a rather surprising number given that the big bang is not only well supported by the evidence, it is now a foundational concept in modern astronomy. There are, of course, several reasons for this lack of acceptance, but one I hear often in interactions with the public is the claim that the big bang (and astrophysics or cosmology in general) is not scientific because it is not falsifiable. After all, there is only one universe, and you can’t run that experiment again.