Exploring the Emergent Nature of Gravity in the Universe

[WMan]

Good Morning,

What is the universe made of?

To be more specific, i am talking about the framework of the universe, not its contents.

I.e. if you took away all the mass, energy, dark matter, etc... from the universe, then what would be left? What is the universe ITSELF made of? not the contents of the universe.

I suppose another way of looking at this would be, if you moved all the contents of the universe into one corner of it (all squished up), then what would be left in the rest of the universe? Would it exist? or would the size of the universe shrink to where the contents are? I.e. if there is no stuff in the universe (i.e. no contents) then does the universe exist?

Been puzzling me this morning.
Thanks for you help!

Mark

 

[Drakkith]

It is not possible to say what the universe is made of if we take away everything that occupies it. Perhaps there wouldn't even be a universe then.

As for cramming everything into one section of the universe, what would be left would be empty space. And before you ask, we don't know what space is made of, or even if it is made up of anything at all. In science we never talk about space itself without talking about fields, particles, forces, etc. Space is simply the background that everything moves and interacts upon.

 

[WMan]

Thanks Drakkith,
So if we removed all the pre-existing fields and forces as well as the particles, then would this remaining empty frame-work universe perform any forces on itself?
I.e. does an empty universe still create forces/fields? or do you need contents stuff for that? i.e. particles, or pre-existing forces/fields.
Mark

 

[Drakkith]

If you have removed everything, there is nothing to interact. No forces, no nothing. I don't know if you could even claim there was still a "universe" there or not.

 

[WMan]

Given your statement above:-
"Space is simply the background that everything moves and interacts upon"
this implies stuff (particles etc) require a framework to exist in.
the contrary doesn't seem to be well defined by modern physics, i.e.
does the framework require stuff in it, for it to exist?
Is there an official opinion about this in modern physics?
Mark

 

[Drakkith]

Don't take my simple explanation as a comprehensive discussion on the subject lol. I wish I knew a little more so I could explain it better, but I do not. Try this wikipedia article and see if it helps: http://en.wikipedia.org/wiki/Space

 

[WMan]

Thanks Drakkith,
My investigations seem to have branched off into Philosophy.
It seems humans are required for Space to exist...
http://plato.stanford.edu/entries/kant-spacetime/
Mark

 

[Naty1]

"What is the universe ITSELF made of? not the contents of the universe."

That question probably is meaningless, like "What is real?"
even "What is my dog made of ?"...but that doesn't make it a bad question.

In any case there is no comphrehensive theory that can provide a good answer to either. But we kind of understand what you are thinking about.
One answer which some theorists believe is "The universe is made of relationships." Others might say: 'The universe is pruely information based'. more below.

It seems humans are required for Space to exist...

did not read it..silly so I do not need to read it!

A more scientific perspective, but not complete:

[This suggests a bare minimum to get a universe started are an instability followed by degrees of freeom...but how much and what 'constitutents' you could remove might depend on the timing of the removal...]

my comments from a new paper by Padmanabhan:

...One can insert some ’hbar’s’ into the FLRW solution to Einstein’s classical theory of gravity to get equivalent statements in equal partition theory [a form of thermodynamic equilibrium] . “Interpreting gravitational field equations as emergent allows us to obtain the gravitational field equations by maximizing the entropy density of spacetime.” ...

...consider a pure de Sitter universe with a Hubble constant H. Such a universe obeys the holographic principle in the form Nsur = Nbulk The Eq. (29) represents the holographic equipartition and relates the effective degrees of freedom residing in the bulk, determined by the equipartition condition, to the degrees of freedom on the boundary surface. The dynamics of the pure de Sitter universe can thus be obtained directly from the holographic equipartition condition, taken as the starting point.

more in this thread: EMERGENT GRAVITY
https://www.physicsforums.com/showthread.php?p=3984153#post3984153