EFE -for beginners!

A short post again, sorry.

Looking for info into old posts, youtube has pointed out a nice video from user DrPhysicsA which seems... shiny!

Old fashinated english accent (I think it's English, pretty sure not American nor Australian, nor Irish... what else could it be?) for 2 hours of EFE fun!

Frequency in general relativity.

Ok. It's clear what's the role of frequency in special relativity. Frequency does not change essentially from its origin in classical mechanics. Frequency has units of inverse of time, which means it's something with no dimensions that is measured per unit of time. In case of frequency that 'something with no dimension' is a repetition.

Quite clear, right? Better explanations here, and don't forget to donate. I will when I get paid for what I do, which has not come yet.

Back to the subject, in special relativity time changes and so does frequency. If there's a time dilation according to velocity value, frequency changes as time does. With an inverse proportionality relation, of course. 

In general relativity, all references I've found so far point out frequency is the same. They talk about red-shifting and the same time dilation issues special relativity does.

But, how come?

We have said before time is just another dimension in general relativity (a special one because our perception, but just another dimension). Several questions arise, then:

1. Are there spatial frequencies the same as a temporal one? If so, what's their use?
2. What does it make time so special? Why are we so used to talk about temporal frequency as frequency?

Easy answer for a physicist, but you have to remember I'm not one them.

In any case, what's the point of this? Well, that picture of the response to a step input in a second order system has made me think about frequency and an old friend/foe concept known as resonance. Which I'll go deeper later. Not now.

The Cavendish experiment

Disappointed with this blog? Yeah, sorry again. Too much time between posts and I'm not getting very deep in any subject I deal with. That's because it requires time, and that's a thing I didn't nor I have at the moment.

So, let's talk about a funny experiment finally I've found in the internets. It's called Cavendish experiment and you can get good historical explanations of it here and here.

The experiment seems easy to follow. In Newtonian terms, two masses attract each other.

Proportionally to the masses, inverse proportionality to distance squared. But proportional doesn't mean equal. There's a constant in somewhere you have to add to make things right. Unit conversion stuff. Kinky stuff. If you want to measure how much does it weight Earth (is there anything British-er than asking yourself that kind of questions? ) you need to get that constant first.

But, how can you measure the gravitational constant without knowing Earth mass? And harder still, you are living on Earth. In case you figure out a way of measuring without taking into account Earth gravitational pull, doesn't it still f*ck with your measurements?

Before explaining something you probably already know I need to make clear why am I interested in Cavendish experiment:

1. It's an "easy" experiment which allows us to understand gravity in human size scales.
2. What is its relationship with space-time? Before you say human scales are Newtonian, which is almost truth for every almost example you can find, just keep on reading.