Relativity

We have to talk about LIGO

I’ve mentioned LIGO a couple of times in passing. You know, LIGO, the Laser Interferometer Gravitational Wave Observatory. Rainer Weiss of MIT had a lot to do with the idea back in the 1960s, as did Kip Thorne of Caltech. Things got serious in 1980 when the US National Science Foundation funded prototypes at Caltech and MIT, and funded Weiss to lead a study into a full size interferometer. Construction eventually started in 1994 and was finished in 1997. Observations eventually started in 2002 and stopped…

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Most laymen completely misunderstand what a black hole is

I saw Luboš Motl’s blog post Most laymen completely misunderstand what a black hole is. When I read the title my irony meter skipped a beat, so I thought I’d take a closer look. Especially since he said this in his opening paragraph: One of those invalid memes that I want to discuss… is the idea that the point of the black hole is the singularity. That is what makes a black hole a black hole and that's also where the mysteries of black holes hide.…

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Misconceptions in gravitational physics

I think it’s safe to say that there are some misconceptions in physics. The issue of course, is how many. That’s where I part company with your average physicist. He’ll tell you that whilst we don’t understand everything, we do understand some things, such as black holes. Only he doesn’t. Take a look at the Wikipedia black hole article. It says this: “a black hole is a region of spacetime exhibiting gravitational acceleration so strong that nothing - no particles or even electromagnetic radiation such as…

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A compressed prehistory of dark energy

In the Wikipedia dark energy article you can read how the term "dark energy" was coined by Michael Turner in 1998. This was in a paper co-authored with Dragan Huterer called prospects for probing the dark energy via supernova distance measurements. It referred to the type 1a supernovae observations made by the Supernova Cosmology Project and by the High-Z Supernova Search Team. Their observations indicated that the expansion of the universe is accelerating, which was contrary to expectations and led to Nobel prizes in 2011: Expanding…

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The principle of equivalence and other myths

Once you know that an optical clock goes slower when it’s lower because light goes slower when it’s lower, you soon understand why light curves. Not because it follows the curvature of spacetime. Because the speed of light is spatially variable, like Einstein said. Then once you know about the wave nature of matter and electron spin, you soon understand why matter falls down, and why the Newtonian deflection of matter is only half the deflection of light. Then once you know how gravity works, you…

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How gravity works

Once you understand that there is no time flowing inside an optical clock, then you understand that an optical clock goes slower when it’s lower because light goes slower when it’s lower. Because the speed of light varies in the room you’re in. After that you understand that light waves curve downwards in a gravitational field for the same reason that sonar waves curve downwards in an ocean. Search the ES310 sonar propagation webpage and you find where the US Navy said it: “Recall how differences…

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The speed of light is not constant

The speed of sound in air is sometimes said to be 343.2 metres per second or 768 miles per hour. But actually, it varies. It usually decreases with altitude up to about 11 kilometres above sea level. That’s about 36,000 feet, which is typical for a passenger jet. At that altitude the speed of sound is circa 295 m/s or 660 mph, which is one reason why passenger jets don’t fly as fast as you might like. Interestingly enough, the speed of sound typically decreases with…

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A detective story

So why isn't the future what it used to be? I think it’s something of a detective story, one where you have to look back at the history. In 1831 Michael Faraday was doing his ground-breaking experiments, showing how electricity and magnetism were interrelated. Then in 1865 James Clerk Maxwell developed the theory, and in 1880 we had light bulbs courtesy of Joseph Swan and Thomas Edison. In 1905 Einstein gave us E=mc², saying there was an awful lot of energy in matter. Then in 1934…

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