When Johannes Kepler proposed a new model of the solar system in the early 1600s, it was a revolutionary idea. The model addressed many of the problems with earlier circular-orbit models, and greatly simplified the calculation of planetary motions. Still, the model was so radical that it wasn’t fully accepted until Newton was able to derive the model from his law of universal gravitation. What made Kepler’s model so powerful is that is required only three simple rules, which we now call Kepler’s laws.
And Then There’s Maude
In modern physics, matter in the universe is made up of quanta or “particles” such as electrons, protons and neutrons. These particles can be said to interact through various forces or fields (strong, weak, electromagnetic, gravitational) for which there are corresponding “field quanta” such as photons and gluons. These quanta can are often seen as the particles that make up these fields, and while things are a bit more complicated it is the right basic idea. We have a lot of experimental evidence for these quanta, but there is one that’s often mentioned for which we have no experimental evidence. That’s the graviton.
The Emperor’s New Clothes
Often when talking about gravity and general relativity the “fabric of spacetime” will be mentioned. This fabric is often visualized as a kind of rubbery sheet that can be bent and stretched by the presence of masses. We use this kind of imagery so often that one might imagine that’s actually what spacetime is. But if spacetime is a fabric, it is the same type of fabric used to make the Emperor’s new clothes.
Weight For It
In an earlier post I wrote about how light moves at a single universal speed. Not only has this been well observed experimentally, it forms the foundation for the theories of special and general relativity, which are also well supported by experiment. Often, relativity is summarized as “nothing can travel faster than light.” Which raises the interesting question, what about gravity?
Time in a Bottle
In an earlier post I talked about how certain kinds of dark matter might be detectable by the global positioning system (GPS). Part of the reason for that is due to the fact that GPS satellites have extremely precise clocks in them. So precise that the relativistic effects of gravity and relative motion have a measurable effect on the rate at which their clocks tick. This led some readers to ask just how gravity can affect the flow of time. It all has to due with Einstein’s theory of relativity.
Delta-V
Of all the inner planets, only Mercury hasn’t had a probe land on it. It likely won’t for quite some time. The reason isn’t because of lack of desire, or worthy science to be done, but because of a simple thing known as delta-v.
Wonder Falls
There’s a new video from Human Universe where Brian Cox shows how, in a vacuum, a bowling ball and feathers fall at the same rate. The idea that all objects fall at the same rate regardless of their mass is often attributed to Galileo. It’s commonly said that Galileo proved this fact to be true by dropping masses off the leaning tower of Pisa. But in fact it’s quite likely that Galileo never performed the experiment. Given the experimental apparatus at the time, it’s unlikely that such an experiment would be conclusive anyway. So why was Galileo convinced that objects fall at the same rate?
Radion Days
We usually think of efforts to unify Einstein’s theory of gravity with other forces as a more modern trend. Models such as string theory and loop quantum gravity are seen as modern ideas. But in fact, as soon as Einstein presented his model there were efforts to unify it with the other known force at the time, electromagnetism.
Problematic
Newton’s law of gravity takes a bit of calculus to really wrap your head around it, but the basic relation is very simple. Every pair of masses in the universe experiences a mutual gravitational attraction, each feeling the pull of the other’s gravitational field. The force of attraction is mutual, which leads to some interesting consequences. For example, when you …