If you’ve ever watched a sunrise or sunset, you’ve seen how the Sun appears deep orange, or even red when low in the sky. In the middle of the day the Sun appears merely yellow. So why does it appear different colors at different times of the day? The answer lies in how light interacts with our atmosphere.
The Lithium Experiment
One of the big successes of the big bang model is its prediction of elemental abundances. The first elements were produced in the early moments of the universe through a process known as baryogenesis. This process is very complex, and it is highly dependent upon the temperature and density of the universe at that time. Change the temperature a bit one way or the other, and the initial ratio of primordial elements would be different. Knowing the temperature of the early universe, we can predict the amount of hydrogen vs. helium produced by the big bang, and this agrees fairly well with observation.
The Hologram Cosmos
There has been a flurry of news articles about a new experiment that could prove we live in a two-dimensional hologram. Needless to say, we do not live in a 2-D hologram, and even if successful this new experiment would prove nothing of the sort. Unfortunately the “universe is a hologram” headlines always make great link-bait, and it doesn’t help that the press release for this experiment uses a similar link-bait headline. That said, the experiment is is very real, and if it succeeds it could revolutionize our understanding of the cosmos, so it is worth talking about.
If It Ain’t Got That Swing
A pendulum is a remarkably simple device that can be used in a range of scientific experiments. It can be used to measure the Earth’s rotation, for example. It can also be used as a timing mechanism. The period at which a pendulum swings depends upon the distribution of mass throughout the pendulum (known as the moment of inertia) and the distance of the swing point from its balance point (center of mass). The period also depends upon the acceleration of gravity, known as g. Because of that you can also use a pendulum to measure Earth’s gravity.
Flat Stanley
One of the things we often say about the universe is that it is “flat.” Of course this usually raises the question about what that actually means. How can space be flat? Sure, a surface such as a table can be flat, but space?
Not So Fast
One of the fundamental principles of modern physics is that nothing can travel faster than light. Of course when this is mentioned, someone usually suggests a way to get around that limit. What about warp drive, for example. Or what about tachyons? These are hypothetical particles that can never go slower than the speed of light. What I like about tachyons is that it’s a good example of how what seems like a simple and obvious solution turns out to be deeply complex when you take it seriously.
Spherical Cow
There’s an old joke in physics where a farmer wants to increase milk production, and asks his physicist neighbor for advice. She agrees to think about the problem, and after a week comes back declaring she’s found a brilliant solution. “The first step is to get some spherical cows that can breed in a vacuum.” The point of the joke is physicists often make wildly unphysical assumptions when creating physical models, such as assuming cows are spherical. While that might seem like a poor way to do science, it is actually a powerful tool.
The Rules
I’ve been on the road the past two days, hence the lack of a morning post. But as I was driving for countless hours I noticed lots of signs detailing the Law. Don’t drive drowsy; Wear your seatbelt; Don’t text while driving; Speed limits, etc. I also noticed that pretty much all of these laws being violated by drivers along the way. Apparently laws are really more like guidelines, at least until you get caught. It’s interesting, then, that we describe the behavior of the universe in terms of laws. Law of gravity, law of relativity, etc. Unlike traffic laws they aren’t violated, at least as far as we know.
Bend It Like Newton
Yesterday’s post on testing the assumption that photons are massless raised a few questions for readers. One of the most common was the idea that the gravitational lensing of light must mean that photons have mass. After all, if a star or galaxy can deflect light gravitationally, doesn’t that mean the light is gravitationally attracted to it? If that is the case, doesn’t that mean that light has mass?