In 1671, Isaac Newton submitted a letter to the the Royal Society outlining a new theory of light and color. While Newton is probably most famous for his theory of gravity—and the mythical apple—he was also deeply interested in the nature of light, and made one of the first detailed studies of the properties of light. The work he describes in this 1671 paper is so brilliantly simple you can do it at home. All you need is some sunlight and a couple of prisms.
What You Get is What You See
These images look very different from each other because they were observed by different instruments, that each detect different ranges of wavelengths of light. Just as our eyes are capable of observing a particular range of wavelengths, each instrument can only observe a particular range of wavelengths.
Time After Time
Part 3 in the equations series. How a beam of light overturned 300 years of physics, and changed our view of the universe.
I’m Tired…
Yesterday I wrote about the Alcock-Paczynski cosmological test (http://goo.gl/uouVEh), and how it narrowed the field of cosmological models down to two broad choices: an expanding universe with dark matter and dark energy, or a static universe that exhibits what is known as “tired light”. Now you might think that adding “tiredness” to light is no worse than inventing “dark matter” and “dark energy” to fit observational data. From a theoretical standpoint you’d be right. So why do astronomers accept dark matter and dark energy rather than tired light?
Taking the Quantum Leap
The common view of the atom is that of a compact nucleus with electrons swirling around it like little planets. But this “mini solar system” idea leads to a serious problem.
Light Meter
It is impossible to measure the speed of light, and it has been impossible since 1983. No, the behavior of light didn’t suddenly change in 1983. What changed was the way we define the length of a meter.
The Color of Speed
In our everyday lives, we’re familiar with the Doppler effect as it applies to sound. You might notice when a car or train passes you, its sound shifts downward as it passes. This is because the sound waves from an object are bunched together as it moves toward you, and stretched apart as it moves away from you. For light a similar thing occurs.
Matters of Gravity
By the principle of general relativity, free fall under gravity and the absence of gravity feel the same because they are the same. The idea seems ridiculous because we can see the space station orbit the Earth, so something must be pulling it. But remember that space and time are not absolute.
So What About Light?
From the photon’s perspective, the instant it is emitted in the Andromeda galaxy, it strikes your eye.