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.
Dying Light
Photons are massless. We know they are massless because particles with mass can’t move at the speed of light. We know that special relativity works, and the speed of light is the same in all frames of reference, and special relativity only works if photons are massless. Except…
Ten Billionths of a Gee
Pioneer 10 was launched in 1972. The next year Pioneer 11 was launched. Their mission was to fly past Jupiter and then Saturn, making the first detailed studies of the planets. Afterwards, they continued their journey to the outer reaches of the solar system. At this point they entered a second phase of their mission, to study the diffuse gases in the solar system on their way to interstellar space. Their observations indicated that something rather strange was going on.
The Great Unknown
Last time I talked about how things like photons and electrons have a strange wave-particle duality. Related to this is the fact that there are limits to what you can know about quantum particles. To see how this works, let’s return to our baseball analogy. Suppose you were watching a game, and just after the ball was hit you wanted to determine where the ball will land. In principle you could measure the ball’s position and speed. Knowing its position and speed at a particular time you could then use Newton’s laws to predict where the ball will land. That’s because Newtonian mechanics is deterministic. If you know an object’s position and momentum (velocity and mass) and the forces acting on the object, then you know where it will be at any point in the future.
As You Like It
Suppose you lose your baseball in the woods, and you and your friend decide to look for it. You know that either you will find it, or your friend will (or it will remain lost). Assuming the ball hasn’t been damaged, it won’t be the case that you and your friend each find half of the ball, or that you both find the ball in different locations. There is only one ball, and it has an exact location, even if you don’t know where it is. It can only be found once, and only by one of you.
Accentuate the Negative
There’s news on the web that cosmologists have proven the existence of negative mass. The news is based upon an article that recently appeared on the preprint arxiv, and has not yet been peer reviewed. The article in no way proves the existence of negative mass, but rather demonstrates the theoretical possibility of a form of negative mass within general relativity. In other words, it is an interesting “what if” paper rather than applied astrophysics.
Accepting a Compliment
If you shine ultraviolet light on a negatively charged metal such as zinc, it will begin to release electrons. This is known as the photoelectric effect, and it has some unusual properties. For example, if you change the frequency (color) of the light, then the energy of the released electrons will change. At higher frequencies the electrons have more energy, and at lower frequencies less energy. On the other hand, if you keep the frequency of light the same and vary the brightness, then the number of electrons released will vary. Brighter light causes more electrons to be released, while dimmer light releases less electrons.
Infinity and Beyond
Objects around us come in a variety of colors. The reason for this is that most objects will absorb certain wavelengths of light, while other wavelengths reflect off the object. So if you are wearing a red shirt for example, the colors such as green and blue are absorbed by the shirt, but red reflects off the shirt, so you only see red.
Step by Step
In the 1860s James Clerk Maxwell published a set of elegant and beautifully subtle equations now known as Maxwell’s equations. Maxwell’s equations describe charges and magnets not by the forces between them, but by their fields of electricity and magnetism. Thus, a charge is surrounded by a field of electricity, a field that other charges can detect. Charges possess electric fields, and charges interact with the electric fields of other charges. Likewise, magnets possess magnetic fields, and interact with magnetic fields.