So welcome to week three now of our course and the theme for

the week is Etherial Problems and Solutions.

We'll get to the quotes of the week in just a second or two, but

here are the main topics we'll be looking at.

We'll be starting off with Einstein's starting point, the two postulates

that he enunciated in his special theory of relativity, the June 1905 paper.

And essentially, what he said is we're going to just take these two things for

granted.

They actually were two principles that were well-established in a physics, but

that seemed to be somewhat in contradiction with each other.

And what Einstein did is sort of had the intellectual breakthrough, because he saw

that actually, even they seem to be in contradiction with each other.

If you took both of them to be true and then worked out some of the implications,

it gave you some very interesting results.

So he was just basing this on these two postulates, so

we'll figure out what those postulates actually are.

I just want to just give you a heads up, one is the so-called principal of

relativity and the second one is what he called the principal of light constancy.

And because that second principal deals with light and whatever light

constancy means, we need to figure out more this week about how light waves work.

How waves in general work, some of the key principles of light waves and

the phenomenon of light waves, so

that we can understand the background to what Einstein is working with here.

So, we'll spend a little bit of time exploring some light waves more or

less in a qualitative sense not a quantitative sense.

We won't do a full physical review say of how you describe

light waves mathematically and so on, and so forth.

And then well, we're talking about something called the ether.

You see etherial, problems and solution.

That's where it comes from and there's a little problem with the ether.

It was a cutting edge physics of the time, a number of very good and

great physicists had been working on it.

Whenever it happens to be is really the idea of the medium for light waves or

something has called the luminiferous ether, a light bearing ether.

We assume that waves must travel through something.

Water waves travel through waves.

Sound waves travel through air or whatever gas is involved.

And therefore, light waves must travel, have a medium,

which they travel through that the light vibrations.

The electromagnetic vibrations that make up light,

there must be some medium involved.

And so, that was known as the ether.

And yet, there's some key problems with it that Einstein was really

worried about and bothered him greatly.

And not only that, there were certain experiments that bothered everybody,

greatly actually and the classic one is known as the Michelson-Morley experiment.

So we're actually going to spend a fair amount of time looking at this in

a mathematical sense not deep mathematics.

It'll mainly be algebra that we're using here, but

this will be our first foray where we get a little bit more quantity than

we have been up to this point, but don't worry.

We'll take our principle make haste slowly.

So we won't try to rush through it, but make sure we're laying that solid

foundation as we construct our mental models of what this special theory

of relativity is all about and the implications thereof.

So the Michelson-Morley experiment will directly relate to what

the ether is like and give a certain result and then another well-known

experiment result called stellar aberration, also relates to the ether and

we'll find out that these two are actually in contradiction to each other.

So we had two very well-known experimental results and as it related to the ether,

one said one thing, the other said the other thing and

it really puzzled the physicists of the day.

So we're talking about this was in the 1880s, essentially.

Stellar aberration actually went all the way back into the early 1700s around

1725 or so, it was first observed.

So the question was what do you do with something like that,

how do you solve a problem like the ether?

It seemed like they needed the ether.

Otherwise, what is waving in terms of a light wave and the properties

of the ether, the Michelson-Morley experiment was saying one thing and

stellar aberration was saying another thing.

And there are other experiments too sort of on one side or the other and

it was a real problem in the 1890s, and up to 1905.

And so then, we'll look at some of the solutions to this.

How do you solve a problem like the ether?

For those of you who maybe remember the musical,

the sound of music, a sort of comes from how you do you solve a problem like Maria?

So now that I've said that you can probably, for

those of you who remember the musical can't get that out of your head.

So, I apologize for that.

But in this case, it's how do you solve a problem like the ether?

Well, there were certain solutions.

Somewhat ad hoc solutions just sort of pasted in there and

see if we can get our theory to work with it.

Einstein's solution was much more elegant and simple.

And so, we'll certainly want to find out more about that.

So that's where we are going this week and

let's go back to the quotes of the week, have them on your handout.

First one is there is no doubt that the special theory of relativity,

if we look at it's development in retrospect.

Again, this is by Einstein was ripe for discovery in 1905.

And so we will see some of that as we talk about some of these things that

other people working in this area that definitely was a well-known problem.

They had somewhat solved it, but not in a very satisfactory way.

And so Einstein came along and took a very different approach and

came up with a similar solution actually to what others were getting, but

in a more satisfying way.

But even have said that, it still took several years, a number of years before

people really accepted Einstein's approach to the problem versus some of the other

approaches there and the fact Einstein's approach was almost too simple.

It seemed too simplistic that he was just assuming these two postulates and

then taking off from there when some of the other theories that were getting

similar results were much deeper, much more more sophisticated in terms

of their physical and mathematical methods and so on and so forth with that.

But certainly, he said that if he hadn't done what he did in 1905,

somebody else probably would have done it in the next few years.

It was in the air, as it were.

As an aside, actually for his general theory of relativity not the topic of this

course, but ten years later that probably would not have been done as early as it

was if it hadn't been for Einstein working on that.