Yeah, wasn't making myself clear. It's easier to do the maths for SR, not GR. GR maths is a nightmare, and we had to derive the field equations for my astronomy degree. Glad I did it but never again.

I will, just been a tad busy. I'll post tomorrow.

You’ve just proved that reverse time travel is real as I’ve just gone back in time about 40 years to my school days!

What does "made of maths" mean tho? I find it hard to conceive of a universe that couldn't have its laws described mathematically, so inferring things from that apparent fact always seems weird to me.

We use Pythagoras all the time in layout our gardens and buildings, always amazes me somehow.

But what would the opposite of "made of maths" be?

acemuzzy wrote:

But what would the opposite of "made of maths" be?

A place where there are no rules. Sounds silly but it's no sillier than a place where the rules never change. What if pi was suddenly 10? Or Pythagoras didn't hold?

So I'll ask you, why are the universal constants constant?

What about the vowels?

Isn't it weird how F = m x a mirrors E = m x c^2?
It suggests mass at lightspeed becomes a photon? Or some kind of energy.

Is it the same m tho, eh?

acemuzzy wrote:

Is it the same m tho, eh?

The mass changes as the energy changes, because they're the same thing. Pick a ball off the ground and it gains mass because it gains potential energy. Wind a watch up and it gains mass for the same reason.

This is good vid and it'll come in handy later.

I have a question after watching that video. If you shone a beam of light into a perfectly mirrored cube or sphere (that reflected all energy), and then turned off the light source, would the inside of the object go dark or remain bright? My thinking is that light would continue to bounce around indefinitely as there is nothing to absorb or dissipate it?

GooberTheHat wrote:

I have a question after watching that video. If you shone a beam of light into a perfectly mirrored cube or sphere (that reflected all energy), and then turned off the light source, would the inside of the object go dark or remain bright? My thinking is that light would continue to bounce around indefinitely as there is nothing to absorb or dissipate it?

If the mirrors were perfect then yeah. This actually happens all the time with atoms. They absorb light, the electrons get punted up an energy 'orbit' and when they fall back down the light is emitted, so in a way they are perfect. They will absorb a frequency of light and if it's really high the electrons get kicked out of the atom for good and go flying off maybe to find a new partner.

There is no reason btw that electrons and protons make such stable bedfellows. They're independent things that have found each other and dance so beautifully with each other in this stable way. It's easy to be astonished how this crazy coincidence could've happened but we'd be getting philosophical again. If there are loads of universes with different laws then fortunate coincidences are going to happen in some of them! Or maybe life in universes without atoms could still happen and we'd be talking about something else being fortunate.

Ok. So we've bounced around a bit and must now get into it again, but it's important to consider the absurdly mathematical universe because it's going to make what we're about to discover a little more easier to get to grips with - that it's not just a mathematical trick. If the maths says so then it's true, however bizarre it might seem to us. Physical laws, planets, black holes existing etc are discovered by maths these days and experimentally verified later. Mental but true, and so it is with relativity.

So far we still only have this concept of inertia (and something about Maxwell's equations). The law of inertia is really the explanation of this business of coins dropping at your feet on a smooth boat ride - that the laws of physics are the same in all non-accelerating frames. There is no difference between moving at constant speed and being 'still'.

There are only two frames in physics and we'll give them their formal names so everyone understands the lingo.


INERTIAL FRAMES

This is a non-accelerating frame and all inertial frames are EQUAL. That is, there are no science experiments that distinguish one inertial frame from another, It doesn't matter what relative speed you're moving at, the coin still drops at your feet.

NON-INERTIAL FRAMES

This is an accelerating frame and they aren't all the same. Your science equipment is sliding all over the place and the faster you accelerate the faster sliding you see.


We'll only need Inertial frames right now. Now the idea that all inertial frames are the same hasn't been proved yet. Inertia hints they are but Newton thinks that god can tell you have an absolute position and velocity according to some divine coordinate scheme. But Einstein is convinced this is unnecessary but there's a problem, and that's Maxwell's equations and the discovery of electromagnetism (light). Now he has to incorporate this phenomena into his view of motion.

It's a very strange thing (as discussed) that new truths come from manipulating equations, but this is exactly what happened when Maxwell decided to combine the equations of magnetism with the equations of electricity. They are so similar they share similar terms and you can combine them with a bit of algebra using the equals sign. This was done by Maxwell just for fun but the extraordinary thing is that when you do, this unexpected constant just pops out, and it's a speed. This has never happened before in physics. There are other universal constants like pi but you have to measure them. What does it mean?

Maxwell knew it meant something, and that something was to obvs to do with electricity and magnetism. Not only that but he had a value for this constant because he knew (by experiment) all the values of the other terms in the equation.

The equation btw looks like this:



Uo and Eo are to do electricity and magnetism respectively and we needn't get into it ( U is the electrical permittivity and E is the magnetic permeability of a vacuum if you want to look it up) but they are constants that can be measured by experiment. They have a certain value and therefore c can be calculated even if nobody was quite sure what c was - but it was a constant because the other two terms are!

Maxwell suspected it was to do with light. Partly because everyone had wondered about light's nature for centuries and also that they knew c was very fast. You see lightning before thunder and back then the speed of sound was considered very fast! They actually knew light must be really really fast and the speed of c that was calculated by Maxwell was 300,000 km per second, so it seemed it might be a plausible candidate.

So how do you deal with a constant that pops up like this that has a value? A speed relative to what? The obvious answer was that it's the speed relative to the light source. So if I'm driving towards you with a torch pointed at you, I see the light as going at c, but you see the light going at c plus the velocity of the car. We are so used to speeds stacking that this makes sense to us.

But there's a problem. Maths people have all sorts of tools in the box, calculus being one of them -  a thing that Newton co-discovered btw. They looked at these U and E terms and played around with the equation and discovered (again by only using maths) that the speed c was independent of the speed of the source of the light! 

This seemed odd but the speed of sound is the same. If you fly past mach one then you overtake the shock wave because you're going faster than it. The shock wave is actually caused because the air particles can't get out of the way fast enough as the plane pushes on them. And if light is a wave (that Maxwell's equations hinted that it was), then it needs a medium to travel in doesn't it? Water and sound do, so why not this?

Maybe absolute space is this medium? And maybe it's not quite so invisible after all! So the idea is that light travels through this absolute space stuff at c, just like sound moves at a constant speed through air.

This could prove Einstein wrong, because just like the jet pilot and air, a person moving at a speed relative to absolute space need only measure the speed of the beam coming from their torch. If it's less than c they're truly moving like Newton said - and you can measure your true speed according to this constant. If they measure it at c they can be said to be at rest with respect to this absolute space stuff.

We'll see how Einstein proved this wrong next time. I was hoping to get to this is in this post but I never really know what I'm going to say when I sit in front of the laptop, It always takes longer.