Tbf to Newton he did live in the 17th century so we shouldn't treat him too harshly.

Are you getting it so far unc?

Wookienopants wrote:

This thread is great, loving your explanations.

This. The SG twist is legit.

Gazelle is doing a great job with this stuff.

This is just going to be a short one as I'm a tad busy but it's an important one.

I hope you're starting to see that the theory of space and time is really the theory of motion. Speed after all is just distance divided by time, and if motion is only a relative thing then maybe distance and time are too?

We've still only got The Law of Inertia, the law that states you don't have to have the engines firing the entire journey to get to the Moon. But we've looked at this idea of absolute space that Newton had, which is wrong. but it's hard for us humans to understand why it's wrong, and it took nearly 300 yrs before physicists could finally accept it was a mistake. You don't need a sciencey brain to understand this stuff, you just need a bit of courage. If we can free ourselves of this notion that absolute space is not a thing then we're pretty much home and dry as far as special relativity is concerned and the rest will fall into place.

So what is space exactly anyway? Or to put it more simply, what is distance?

Einstein said the the notion of distance only exists if you have two points apart. Se we'll imagine a universe and all that exists in this universe is a ruler. This ruler has no volume, so it's just a straight line between two points essentially. Einstein argued that such a universe was purely one dimentional and the size of that universe is just the size of the ruler, the distance between the ends. We've only got the ruler, and the most it can measure is the length of the ruler. The ruler IS the universe.

But Newton wouldn't like this one bit. For Newton absolute space is a thing, and although he knew the only thing that the ruler could measure was some 1D space, he imagined the ruler was free to float and around in this absolute space stuff, this invisible coordinate system God created and was forever there. It wasn't God's problem we only had a ruler. He thought such a universe was bigger than the ruler and could have a speed, even though us puny humans could never measure it

So Newton actually over complicates the picture. He invents stuff that isn't there and that can never be measured.

Sounds like this Newton chap was a proper grade-A moran

OOPS. I rushed it a bit today and didn't have time to proof read my own post. A universe with just a line in it is 1D, not 2D. 

You can add another dot that's not on the line and get a triangle. Then it's 2D and only 2D. You can then add a dot above or below the plane of this triangle and then you get a 3D universe. Then you can add as many dots as you like and it remains at 3D.

I'm sure if you ask newton now he'd make similar excuses

Weird i wrote a few extra lines to complete the joke but it hasn't posted

This is ace.

Using the realm of physics can you confirm if the clitoris is indeed real or, as we all know already, if its a myth

Oh I forgot to do a summary.

Summary:

Space (distance) is a thing you can measure, and if you can't measure it then it doesn't exist. If we think of a universe that only has 3 points in it that form a triangle, then by definition this universe is 2D. Each point can see the other two points and the universe only exists within this triangle because that's all you can measure, and it makes no sense to say the universe is bigger than the confines of the triangle.

But what if each point saw that the other two points were drifting away from it? That the triangle was getting bigger?

AHA Newton would say, I told you there was all this other space behind the points all along! Einstein realised this wasn't the right way to think about it because each point could only measure what the other two points are doing. He realised if space was just a measurement of distance, the only sensible way to think about it was that the space between the points was expanding.

That's all you can measure and there is still no stuff outside the confines of the triangle. We can only say the universe (this triangle) is expanding and it's still true that nothing exists outside the confines of this growing triangle.

It isn't expanding into anything, it's just expanding.

Surely a timeline is 2D?

Yeah love that show and that episode was great.

Also if talking about 1d to 2D to 3d etc this video by Carl
Sagan is a great visualiser (sorry if some of this is jumping around SG)

So, we've still only got the theory of inertia so far! And this idea that Newton has of absolute space. I touched on some heavy ideas perhaps a tad early but the important thing is that Newton believed in an invisible coordinate system that only god could see. In a universe where everything in it could be regarded as moving relative to something else, god still knew the 'real' position of everything. And that comforted him.

So back to History.

This is the age of telescopes. Kepler has discovered these laws of planetary motion - that they could move in ellipses and still be in a stable orbit, and rich people around Europe were looking though telescopes and seeing all kinds of wonderful things. Saturn had moons too! Galileo had already looked at The Milky Way and discovered it was actually a huge cloud of stars. Once we accept the Earth isn't at the centre of everything we can start to imagine all crazy kind of things might be happening out there. Maybe the stars are just suns really far away?

Because of Copernicus and Kepler all the planets are finally behaving (except Mercury but we'll get to that much later), the comets can be explained by being on really long ellipses and everything is going swimmingly.

So we can finally introduce Newton. We don't need his theory of gravitation at all for Special Relativity and we can safely ignore it for now, except to say he unified Kepler's planetary motion with phenomena we see on Earth, like things falling to the floor. We'll come back to it when we look at Einstein's theory of gravitation - General Relativity.

For now we're concerned about motion without gravity, and despite all the wonderful discoveries Newton made we only really care about the three laws of motion that he published in 1687.

And Newton's Three Laws of Motion are these:

1. If a body is at rest or moving at constant speed in a straight line, it shall remain so unless acted on by a force.

This is just Galileo's law of inertia.

2. F = ma

We'll examine this closely in the next post.

3. When one body exerts a force on another body, the second body will exert an equal and opposite force on the first.

This is the law that states if you punch a brick wall it will hurt, and it's really just the law that sates motion is relative. As far as your fist is concerned the wall is the aggressor.

So law 1 is inertia and law 3 is the idea motion is relative. But law 2 is altogether more puzzling and this acceleration business is weird when looked at more closely. If all motion is relative then we have a problem. If two astronauts are moving toward each other at a faster and faster speed, who's doing the accelerating? Is it valid for each astronaut to say they're at rest and the other is accelerating towards them?

The answer is no. Unlike motion, acceleration is not relative. It's absolute. If you're accelerating then it's definitely happening to you and not the other astronaut and we'll look at the second law properly next time.