What is Spacetime?

The full context has already been given.
At one time I knew that stuff and used it, therefore I know it's true.
Now, however, after many years of doing something else I am no longer up to speed, therefore I couldn't explain it completely to a beginner.
But that does not mean that I am making claims about something I have no knowledge of.
As per my comment about angles in a triangle.

 

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oh I get it

so if you get it
you referred to a post you don't understand

end of story

 

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Still wrong.
Bye.

 

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ah... no

bye

 

to reiterate

 

"The mathematical four dimensional representation" part is correct, however spacetime is about more than an object and its changing position in space. It is about an interaction between mass or matter and space and time, that results in a curvature of space (or spacetime) that we experience as gravity.

And where it does involve the change in position or changing position of an object in space it also involves a dynamic change in the shape of space associated with that object. From that perspective, spacetime is more about the dynamics of space and time than the dynamics of an object.

On the other hand neither spacetime or an object could be represented as changing in position or shape without the other.......

_________________​

Spacetime is a 4-D mathematical representation of how "we" have come to describe the dynamics of what we can observe of the universe within which we exist.

 

hmmm

you are implying that both space and time have substance , true ?

 

You are asking for my personal view?

Space has some undefined substance through which it interacts with mass/matter.

(and I just know this could open a whole can of worms, which I dread)

Change is real and time is a conceptual construct we use to describe change. Time is our measuring stick for change.

 

So what you're effectively claiming is that, for example, unless someone can describe a car mathematically, off the top of their head, they don't understand what a car is?
Unless someone can give you the chemical composition of a nail, they don't understand what a nail is?

And still wrong.

 

well you implied this in your last post

hmm.. perhaps but it has to be adressed

agreed

 

Would you agree that our conclusions are made up from our memories, and lists of physics in our head, and rules?

You have to calculate the rules that Einstein used to come up with space time.

He used his previous rules of physics, and his previous memories of historic experiments.

From this list of results in Einstein's head, what rules did he apply to come up with space time?

What did Einstein call Relativity?...

"Aether, and the theory of Relativity"

That's what he called it. That was his thinking. That's what it is supposed to be. He backed down... why did he back down? Because every time anyone mentions the Aether the ideas are thrown in the rubbish bin, and you get flamed.

Einstein spent years working on the Aether, do you really think that he could just erase those years from his memory?

 

This thread has degenerated a lot, but if you don't know what a pseudoriemannian manifold is then let me give you the important property: A manifold is a set of points in, for concreteness lets say 4 dimensions. That means a coordinate system on the manifold will have 4 independent components. Now, the important property of a (pseudo)riemannian manifold is that when you zoom in to a very small region it looks flat, that is it looks like Minkowski space (or Euclidean space if you are considering a Riemannian manifold without the pseudo). This rules out creases, pinches and the like. This fact, that a pseudoriemannian manifold is smooth, means physically that at any point in spacetime, I can choose a coordinate system for some observer where there is no gravitational force felt, like close to earth an object in freefall experiences no gravitational forces (objects are "weightless").

Hopefully that makes things a bit clearer.

 

Aether theories get rubbished because it has been shown in many ways that a theory with an aether simply cannot work. This has been shown mathematically and also experimentally, so if you're arguing there is an aether you're not arguing with physicists you're arguing with nature and we all know who the winner of that particular argument will be.

 

It works with its new name space time. What's in a name? What's the big difference between...

"Aether and the Theory Of Relativity"
"Space time and the Theory Of Relativity"

Can we find the Aether... no.
Can we find space time... no.

But if someone asks "What is space time?" It evolved from Einstein's previous works, and it was a paper which changed the way to describe the Aether. And that is important, because it still needs describing more clearly, and so you will have to use the same principles that Einstein used, the same rules, which is a knowledge of the Aether.

 

Spacetime is not in any way like an aether.

 

70% of the Universe is Dark Energy, the other 25% is Dark Matter. So these are the materials of space time. So the curvature of these materials is Gravity. You can play with the English Language all day, but Einstein had no knowledge of these materials when he wrote relativity, so he used other materials that he did know about, and he only knew of one material at that time. Now people sit in caves looking for Dark Matter instead of Aether. Which looks like full circle to me, so the name also goes full circle.

 

If 75% of the universe is dark energy, could that much dark energy directly red shift energy to create an illusion of space-time expansion, since this expansion is based on inference from the red shift.

In the above, we cut off the middleman and have dark energy red shift energy, but without the need for space-time expansion. Once we collect dark energy we will know. Has anyone ever expanded spar-time in the lab to make sure we are not adding an assumed middleman.

 

Firstly, dark matter and dark energy are very far from the same thing. Dark matter is some gravitationally interacting matter that doesn't emit light and is responsible for the altered galaxy rotation curves we observe. Dark energy is responsible for the accelerating expansion of the universe. Secondly, I don't really know how people arrive at the 70% dark energy figure. If you could explain it I'd be grateful.

Neither of these things are anything like an aether (which is a fluid that exists throughout space and time) The aether has been proven not to exist by experiment. Einstein included a dark energy term in the gravitational field equations of GR because he didn't like the idea of an expanding universe. He called this term the cosmological constant, and it has been shown recently that it is very close to zero but it seems to be not exactly zero. When the universe was shown to be expanding he manned up and admitted he was wrong about the steady state universe, which is a lesson I suggest you learn from him.

Dark matter is probably some massive particle that doesn't interact strongly (or at all) with the other forces so we can't see it. This is categorically not an aether, which is a fluid. Dark matter does not behave like a fluid.

 

You call the Aether a fluid, it was never discovered. Why give it properties? Basically, it could be anything, so long as it propagates photon waves. A fluid is close, but space time also looks like a fluid in those bendy images. And you can't prove something to not exist, it is impossible. The point is that the answer to the thread question is Einstein's theory.. and he was keen to use the Aether.. but backed down to replace the Aether with space time. The thread asks a question, and that is historically where space time came from.

 

The expansion of the universe is inferred by the red shift. A red shift of energy implies the energy is lowering it energy value in joules as wavelenght stretch. If dark energy is very subtle does the potential between regular energy and subtle dark energy suck the joules out of energy, red shifting it. If it did, the observed red shift could occur even with a static universe. We do not know enough about dark energy to know either way. But the burden of proof is on the traditions to show this concern is not valid. Unless there is a dual standard.

Dark energy, by being at lower potential that regular energy draws energy value from regular energy causing a red shift and a cooling of the universe. The absorbed energy changes the state of dark energy into dark matter. Since the most energy is near galaxies this is where there is the most dark matter from the energy transference.

Since we have never seem space-time expand in the lab and nobody seem so care or notice, we can assume space-time is expanding. This worked fine until we needed dark energy to explain the expansion energy. But this lead to the middleman concern that why does dark energy need a middleman to red shift energy when it is different and at lower potential? But traditions do get grandfathered in and don't have to address this if they want. Thee are too many jobs at stake to deal with reality at this time.