Paper Mario!

Also, what if space-time loops into intself?
Like how the earth's surface is not actually flat but a sphere....
Imagine going straight in one direction only to eventually end up in the exact same place where you started?

Also, if lightspeed is a constant and space and time are variable, what actually is space time? Does it always follow the lines (field?) of gravity? Why? Could space time even exist without gravity?

Thought I'd add to this after all while we're on the subject and I have a bit of time because it can seem confusing, mainly because it is.

So is spacetime a tangible thing? The answer is no, but why? As hunk points out and as we'll see, we all measure space and time differently because we're all moving independently through space (and therefore time). If two people aren't moving relative to each other they'll agree on distance and time but that's about it.

But if all inertial frames are equal then what do we exactly agree on? Well we agree on the equation that describes it because the equation holds in any inertial frame. But we disagree on the values of the terms in the equation, like distance and time. This applies to curved and flat space and the equations that describe them. So we all agree that the equations hold, that the LHS = RHS, but some might measure 6 = 6 or 1234 = 1234 or whatever they measure in their inertial frame. The equations hold but the values do not.

The thing that unites the inertial frames are the equations - the laws of physics. So spacetime is the equation, which is true for everyone in their inertial frame, and that's all that can really be said about it. You can't prove spacetime exists exactly, because it probably doesn't in any real sense in that it's a different measurement for everyone.

So what is spacetime? The question probably has no meaning. It's just an abstract mathematical object that everyone agrees is true, in their frame. This may seem weird but it's no different to anything else in physics. It's equations all the way down. The equations are the only truth everyone agrees on. The equals sign is quite a thing.

It's a complicated question. The aether is the idea that space and time are the same for everyone - a hidden truth, but spacetime isn't a tangible thing. 

Roger Penrose is working on a rather lovely idea about cyclic big bangs, and the idea is this:

The universe is going to experience a heat death. What this means is that all the particles are eventually going to decay into photons. This happens because once all the stars stop shining black holes dominate until everything is part of some black hole. They then decay via Hawking radiation into photons.

Once the last black hole has evaporated it's all just photons. The moment that happens spacetime stops exisiting because photons don't experience time and distance has no meaning. Photons do cause mini gravitational fields because all energy does but without the concept of measurement within that universe it can't be said to exist, curved or no. And no spacetime is the same condition as pre-big bang, so the ideal condition to have another big bang!



It's hard to imagine spacetime as being just an abstract concept. Imagine playing Mario Bros. Does the space between the platforms really exist? You could say it does and measure the length on your tv. People have different sized monitors and so people measure the space differently but everyone agrees the same physics model applies in the game. But turn the tv off and keep the NES running. Does the gap between the platforms still exist? If it does then what exactly is this Mario space stuff? 

It's a mistake to think spaetime is somehow real because it can curve like a fabric. The curvature is just a mathematical equation but that's fine for the physicist. They're only trying to figure out the equations after all. If spacetime was a real thing we'd all measure distance and time the same. The only truth is the equation that describes it which is true in all reference frames, just like it is for Mario on all tv sizes.

Yeah I love it.

They can adjust like Christians did with the New Testament, or as I call it - What God Meant to Say. Plenty of religious people believe in evolution. They're very adaptable because they need to be.

cyclical Big Bang is far more comforting than infinite heat death, that's for sure.

Not convinced "comforting" is the right word. Infinity troubles me because if it does end up that way then any finite existence placed against an infinity of nothing pretty much means you didn't exist at all.

Well - yeah - that's the rub, isn't it?

The biggest problem with science is the same as it's always been, it makes humans seem insignificant. Tough shit but that's the way it is. Just because we can't cope with infinity doesn't mean it doesn't exist. It might or it might not. Either way nature is not concerned with how we think.

I'm proudly insignificant.
It's good knowing I can't do too much lasting damage when I fuck up.

I don't hold with the infinite variation theory since if true then at least one of those infinite variations would have communicated with us somehow.

an infinite number of universes is nonsense, no one can count that high. there's maybe a few hundred

davyK wrote:

The other mad thing about infinity is that if our universe is infinite then everything that can possibly happen in it will

Confusingly, we don't need an infinite universe for that but we might need infinite universes.

https://thereader.mitpress.mit.edu/the-many-worlds-theory/

Been crazy busy lately but I'll get back to the relativity posts soon.

I was today years old when I learnt that the sun also moves through space, and is not a stationary or near-stationary object.

But lots of things are stationery.

Don't want to get penned in by rules.